&EFA
Office of Transportation EPA420-R-06-006
United States and Air Quality March 2006
Environmental Protection
Agency
EPA Technical Study on the
Safety of Emission Controls
for Nonroad Spark-Ignition
Engines < 50 Horsepower
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EPA420-R-06-006
March 2006
EPA Technical Study on the Safety of
Emission Controls for
Nonroad Spark-Ignition Engines < 50 Horsepower
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
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Executive Summary
The purpose of this technical study is to assess the incremental impact on safety of applying the advanced emission
control technology expected to meet the new emission standards under consideration for particular subcategories of
nonroad engines and equipment, focusing on the risk of fire and burn to consumers in use. The study will be part of
the rulemaking record for the proposed standards and satisfies the provisions of section 205 of PL 109-54, which
requires the Environmental Protection Agency (EPA) to assess potential safety issues, including the risk of fire and
burn to consumers in use, associated with the proposed emission standards for nonroad spark-ignition (SI) engines
under 50 horsepower (hp). As is discussed below, this technical study concludes that new emission standards
would not increase the risk of fire and burn to consumers in use. In fact, in a number of circumstances the study
demonstrates a directional decrease in risk.
This study evaluates new exhaust and evaporative emission standards for nonhandheld (NHH) and handheld (HH)
equipment in the Small SI engine category and outboard (OB) and personal watercraft (PWC) engines and vessels
in its Marine SI engine category. The new emission standards addressed by this study include:
• New catalyst-based hydrocarbon plus oxides of nitrogen (HC+NOx) exhaust emission standards for NHH
engines;
• New HC+NOx and carbon monoxide (CO) exhaust emission standards for OB/PWC engines and vessels;
• New fuel evaporative emission standards for NHH and HH equipment; and
• New evaporative emission standards for OB/PWC engines and vessels.
The following summarizes EPA's assessment of the incremental impact on safety of new standards in each of these
four areas. For each new standard, EPA concludes that the forthcoming Phase 3 emission standards may be
implemented without any incremental increase in risk of fire or burn to consumers in use. Furthermore, the testing
and analysis also indicates that compliance with the Phase 3 emissions standards will most likely reduce the risk to
consumers of operating Phase 2 products in these subcategories.
Exhaust emission standards for NHH engines: We conducted the technical study of the incremental risk of catalyst-
based HC+NOx emission standards for NHH engines on several fronts. First, working with the Consumer Product
Safety Commission (CPSC), EPA evaluated CPSC reports and databases and other outside sources to identify those
in-use situations which create fire and burn risk for consumers. Six basic scenarios were identified for evaluation.
Second, EPA conducted extensive laboratory and field testing of both current technology (Phase 2) and prototype
catalyst-equipped advanced technology engines and equipment (Phase 3) to assess the emissions performance and
thermal characteristics of the engines and equipment. EPA also contracted with Southwest Research Institute
(SwRI) to conduct design and process Failure Mode and Effects Analyses (FMEA) comparing Phase 2 and Phase 3
compliant engines and equipment to evaluate incremental changes in risk probability as a way of evaluating the
incremental risk of going from Phase 2 to Phase 3 emission standards. Our technical work and subsequent analysis
of all of the data and information strongly indicate that catalyst-based standards can be implemented without an
incremental increase in the risk of fire or burn to the consumer. In many cases, the designs used for catalyst-based
technology can lead to an incremental decrease in such risk.
Evaporative emission standards for NHH and HH engines and equipment: EPA also evaluated the incremental risk
of fire and burn to consumers for the evaporative emission standards we are considering for NHH and HH
equipment. For both subcategories we are considering fuel tank and fuel hose permeation standards similar to those
in place for other nonroad SI engines and vehicles, such as all-terrain vehicles and off-highway motorcycles. In
addition, for NHH equipment we are considering running loss controls designed to reduce emissions related to fuel
in the tank evaporating to the atmosphere during equipment operation. Working with CPSC, EPA evaluated CPSC
databases to identify those in-use situations which create fire and burn risk for consumers. Fuel leaks from tanks or
fuel hoses on HH and NHH equipment were identified as the major safety concern for evaluation.
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Fuel tanks used on HH and NHH equipment are constructed of different types of materials using different processes
and each has a potentially different approach to controlling tank permeation emissions. EPA evaluated both current
and treated fuel tanks in the laboratory for several years and identified no incremental safety risk related to the
technologies for reducing permeation emissions. Most fuel hoses meet American Society for Testing and Materials
(ASTM) and Society of Automotive Engineers (SAE) standards, and the types of fuel hoses needed to reduce
permeation are in widespread use today. In fact, some lawn and garden equipment already uses low permeation
hose.
Beyond this, in situations where custom fuel hoses are used there are the ASTM and manufacturer specific test
procedures and requirements that assure proper in-use performance. With regard to fuel tanks, there are
manufacturer specific test procedures and requirements which manufacturers apply to current products and will
continue to use in the future. The emissions durability portion of EPA's permeation test procedures inherently
includes the types of evaluations needed to identify the potential for leaks in-use. The FMEA conducted by SwRI
also looked at systems interaction between engine modifications and the fuel system and determined that
permeation controls and running loss controls on NHH fuel tanks would not increase the fire and burn risk
probability but could in fact lead to directionally better systems from a safety perspective. Overall, there is no
incremental safety risk in applying advanced technology to reduced evaporative emissions from HH and NHH
engines and equipment, and to some degree the use of technology can lead to an incremental decrease in risk.
Exhaust emission standards for OB/PWC engines and vessels: EPA is also considering new HC+NOx and CO
exhaust emission standards for OB/PWC engines and vessels. The US Coast Guard (USCG) keeps a close watch
over marine safety issues, and USCG, as well as several other organizations, including SAE, Underwriters
Laboratories (UL), and the American Boat and Yacht Council (ABYC), already have safety standards which apply
to engines and fuel systems used in these vessels. The four-stroke and two-stroke direct injection engine
technologies that are likely to be used to meet the exhaust emission standards being considered by EPA for
OB/PWC are in widespread use in the vessel fleet today. These more sophisticated engine technologies are
replacing two-stroke carbureted engines. These four-stroke and two-stroke direct injection engines meet applicable
USCG and ABYC safety standards and future products will do so as well. The proposed emission standards must be
complementary to the already existing safety standards and our analysis indicates that this is the case. There are no
known safety issues with this technology compared to the two-stroke carbureted engines and arguably the newer
technology engines provide safety benefits due to improved engine reliability in use. Based on the applicability of
USCG and ABYC safety standards and the good in-use experience with advanced technology engines in the current
vessel fleet, EPA believes new emission standards would not create an incremental increase in the risk of fire or
burn to the consumer.
Evaporative emission standards for OB/PWC engines and vessels: EPA also analyzed the incremental impact on
safety for the fuel hose and fuel tank permeation and fuel tank diurnal evaporative emission standards it is
considering for marine vessels. As with the exhaust emission standards, the proposed emission standards must
complement existing USCG, ABYC, and SAE test procedures and safety standards related to fuel hoses for marine
vessels and USCG, UL, and ABYC standards and test procedures covering portable and installed fuel tanks. All of
these standards are designed to address the in-use performance of fuel systems with the goal of eliminating fuel
leaks. The low permeation fuel hoses needed to meet the Phase 3 requirements would need to pass these standards,
and evidence indicates that this would occur. In fact, fuel hoses meeting these requirements are available today.
The low permeation fuel tanks needed to meet the Phase 3 requirements would also need to pass the applicable
USCG, UL, and ABYC standards; work conducted by EPA and vendors supplying the marine tank industry
indicates that the technology needed to meet these standards can be applied without an incremental increase in risk
over current systems.
EPA is also considering fuel tank diurnal emissions standards for fuel tanks used on Marine SI engines and vessels.
For PWC and portable OB fuel tanks, this would likely entail the use of venting control technology already
commonly used in these tanks. For vessels with installed fuel tanks this would likely employ the use of activated
carbon canisters to capture this vapor. Such canisters have been used safely on automobiles for more than 30 years
and a prototype fleet run last summer revealed no safety concerns. Overall, there should be no incremental increase
in risk of fire or burn to consumers in applying advanced technology to reduce evaporative emissions from
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OB/PWC engines and vessels. In fact, the reduction of permeation emissions is likely to incrementally decrease
safety risks from fire in the under floor areas on boats where the tanks and hoses are installed.
In summary, EPA has evaluated the incremental impact on safety focusing on the risk of fire and burn to consumers
associated with the advanced technologies expected to meet the new emission standards EPA is considering for the
Small SI engine and Marine SI engine categories under 50 hp. Laboratory and field testing, the FMEA analyses,,
the mandatory and consensus test procedures and standards which apply to these engines and fuel systems, and the
availability of certain components and engines which already meet the Phase 3 standards lead EPA to conclude that
new emission standards would not cause an incremental increase in risk of fire or burn to consumers in use.
Instead, compliance with the new standards should reduce certain safety concerns presented by current
technologies.
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TABLE OF CONTENTS
EXECUTIVE SUMMARY 1
LIST OF ACRONYMS 7
1. INTRODUCTION 9
A. Background 9
B. Overview 11
2. EPA'S APPROACH TO ASSESSMENT OF THE SAFETY ISSUE 13
A. Scope of As ses sment 13
B. The Small SI Engine Assessment 13
C. Marine SI Assessment 13
3. TECHNICAL BACKGROUND ON NONHANDHELD ENGINES 15
A. Current Technology 15
Class I engines 16
Class II engines 18
B. Current Safety Standards 21
C. In-Use Safety EXPERIENCE 23
CPSC Databases: 24
Discussion of CPSC Data 27
4. SCENARIOS FOR EVALUATION OF NHH ENGINES AND EQUIPMENT 29
a. Summary of Other Information Considered 29
b. Safety Scenarios for Evaluation 30
Scenario 1: Contact burns 30
Scenario 2: Debris fire: 30
Scenario 3: Fires due to fuel leak 31
Scenario 4: Fires related to refueling 31
Scenario 5: Fire related to storage and shutdown 31
Scenario 6: Ignition misfire 31
Scenario 7: Fire due to rich operation 32
5. NHH TEST PROGRAM 33
A. Engine selection 33
B. Engine modifications 34
Class I - 10 g/kW-hr systems 34
Class II - 3.5 g/kW-hr HC+NOx system 40
Class II- 8.0 g/kW-hr HC+NOx systems 43
C. Infrared thermal imaging 45
D. Laboratory test procedures 46
Operation over the Federal A-Cycle 46
Hot Soak Testing 47
After-fire Testing 47
Misfire Testing 48
Simulated Rich Operation 49
E. Field Operation 49
Acquisition ofIR Thermal Images in the Field 54
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6. TEST RESULTS—COMPARISON BETWEEN EPA'S PHASE 3 PROTOTYPES AND CURRENT
ENGINE SYSTEMS 55
A. Emissions Results 55
B. Laboratory test results 55
Surface temperature measurements by infrared thermal imaging - Class I Side-valve Engines 55
Infrared thermal imaging - Class IOHV Engines 59
Infrared thermal imaging - Class II OHV Engines 77
Muffler outlet temperatures - Class I and Class II Engines 89
Run-on after-fire testing 89
Ignition misfire testing 90
Rich Operation 94
C. Field testing Results 96
Surface Temperature Measurements by Infrared Thermal Imaging Taken During Grass Cutting Operations..97
Results of Hot-Soak Tests Conducted in the Field. 98
Idle Testing 103
7. DESIGN AND PROCESS FAILURE MODE AND EFFECTS ANALYSES (FMEA) TO ASSESS NHH
INCREMENTAL SAFETY RISK 104
A. Background 104
B. The Work Conducted by SwRI 105
C. Design FMEA 107
D. Process FMEA 109
E. FMEA Results 109
F. Discussion of Design FMEAs for Classes I and II 110
G. Conclusion Ill
8. CONCLUSIONS - IMPACT OF PHASE 3 EXHAUST STANDARDS ON CLASS I AND CLASS II
NHH ENGINES 130
Scenario 1: Contact burns 130
Scenario Description: Thermal burns due to inadvertent contact with hot surface on engine or equipment. ..130
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 130
Conclusions Based on FMEA of Burn Safety 134
Scenario 2: debris fire 134
Scenario Description: Grass and leaf debris on engine/ equipment 134
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 134
Conclusions Based on FMEA of Debris Fire Safety 135
Scenario 3 Fuel leak 136
Scenario Description: Fires due to fuel leaks on hot surfaces 136
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 136
Conclusions Based on FMEA of Fuel Spills or Leaks 137
Scenario 4: Refueling-related 138
Scenario Description: Fires related to spilled fuel or refueling vapor 138
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 138
Conclusions Based on FMEA of Refueling-Related Safety 138
Scenario 5: Storage and Shutdown 139
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 139
Conclusions Based on FMEA of Shutdown and Storage Safety 139
Scenario 6: Ignition Misfire 140
Scenario Description: Engine malfunction which results in an ignitable mixture of unburnt fuel and air in the
muffler 140
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 140
Conclusions Based on FMEA of Ignition Misfire 141
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Scenario 7: Rich operation
142
Scenario Description: Fire due to operation with richer than designed air-to-fuel ratio in engine or catalyst.
142
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes: 142
Conclusions Based on FMEA of Rich Operation 143
9. SAFETY ANALYSIS OF SMALL SI ENGINE EVAPORATIVE EMISSIONS CONTROL
TECHNOLOGIES 144
A. CURRENT TECHNOLOGY 144
Fuel Evaporative Emissions 144
NHH Equipment 144
HH Equipment 145
B. CURRENT SAFETY STANDARDS 145
C. IN-USE SAFETY EXPERIENCE 146
NHH Equipment 146
HH Equipment 146
D. Emission control system design and SAFETY 147
NHH Equipment 147
HH Equipment 150
E. CONCLUSION 151
10. SAFETY ANALYSIS FOR MARINE SI 152
Marine Engines 152
Marine Vessel Fuel Systems 153
B. IN-USE SAFETY EXPERIENCE 153
Marine Engines and Vessels 153
C. CURRENT SAFETY STANDARDS 154
Marine Engines 154
Marine Vessel Fuel Systems 155
D. Emission control system design 156
Marine Engines 156
Marine Auxiliary Engines 156
Marine Vessels 156
Fuel tanks 157
Diurnal Emissions Control 158
E. ASSESSMENT OF SAFETY IMPACT OF NEW EMISSION STANDARDS 158
New Exhaust Emission Standards for OB/PWC 158
New Exhaust Emission Standards for Marine Auxiliary Generators 158
Fuel Hose Permeation Standards 159
Fuel Tank Permeation Standards 160
Fuel Tank Diurnal Emission Control Standards 160
F. CONCLUSION 161
APPENDIX A - BASIC PRINCIPLES OF INFRARED THERMAL IMAGING 162
IR Temperature Basics 162
Conductive Heat Transfer 162
Convective Heat transfer 162
Radiative heat transfer 162
How the IR Flexcam T and IR Snapshot Camera's convert radiance to temperature 163
APPENDIX B: EMISSIONS RESULTS 165
APPENDIX C - FMEA OF SMALL SI EQUIPMENT AND ENGINES 168
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List of Acronyms
ABYC
American Boating and Yacht Council
ANSI
American National Standards Institute
ASAE
American Society of Agricultural Engineers
ASTM
American Society for Testing and Materials
BP
Barometric Pressure
°C
Degrees Celsius
CAA
Clean Air Act
CAD
Crank Angle Degrees
CARB
California Air Resources Board
Class I
Nonhandheld Engines <225cc
Class II
Nonhandheld Engines >225cc and less than 19kW
CO
Carbon monoxide
CFR
Code of Federal Regulations
CPSC
Consumer Product Safety Commission
cpsi
Cells per square inch
CVS
Constant Volume Sampler
E85
mixture of 85% ethanol and 15% gasoline
ECU
Engine Control Unit
EFI
Electronic Fuel Injection
EPA
Environmental Protection Agency
ETC
Electronic Throttle Control
EVOH
Ethyl Vinyl Alcohol
°F
Degrees Fahrenheit
FMEA
Failure Modes and Effects Analysis
FR
Federal Register
g/kW-hr
Grams per kilowatt hour
HC
Hydrocarbons
HDPE
High-Density Polyethylene
NHH
Non-handheld
HH
Handheld
hp
Horsepower
INDP
In-Depth Investigations (CPSC database)
IPII
Injury/Potential Injury Incident (CPSC database)
IR
Infrared
ISO
International Standards Organization
kW
Kilowatt
LEV
Low Emission Vehicle
MAP
Manifold Absolute Pressure
MIL
Malfunction Indicator Light
NEISS
National Electronic Injury Surveillance System (CPSC database)
NIST
National Institute of Standards and Testing
NFIRS
National Fire Incident Reporting System
NFPA
National Fire Protection Association
NOx
Oxides of nitrogen
NVFEL
National Vehicle and Fuel Emissions Laboratory
OB
Outboard
OEM
Original Equipment Manufacturers
OHV
Overhead Valve
OPEI
Outdoor Power Equipment Institute
Pd
Palladium
PGM
Platinum Group Metal
Ph2
Phase 2
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Ph3
Phase 3
Pt
Platinum
PWC
Personal Water Craft
Rh
Rhodium
ROM
Ride On Mower
RPN
Risk Priority Number
SAE
Society of Automotive Engineers
SD/I
Sterndrive/Inboard
SI
Spark Ignition
SwRI
Southwest Research Institute
TDC
Top dead center
TPS
Throttle Position Sensor
UL
Underwriters Laboratory
US
United States
USD A
United States Department of Agriculture
USCG
United States Coast Guard
VR
Variable Reluctance
WBM
Walk Behind Mower
WOT
Wide open throttle
XLPE
Cross-link polyethylene
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1. Introduction
A. BACKGROUND
Over the past 15 years, the Environmental Protection Agency (EPA) has implemented emission control programs
for nonroad engines and equipment. Section 213 of the Clean Air Act (CAA) authorizes EPA to set emission
standards for nonroad engines and equipment that "achieve the greatest degree of emissions reduction achievable
through the application of technology which the Administrator determines will be available for the engines or
vehicles to which such standards shall apply giving appropriate consideration to the cost of applying such
technology within the period of time available to manufacturers and to noise, energy, and safety factors associated
with the application of such technology." Section 216 of the CAA defines a nonroad engine as "an internal
combustion engine (including the fuel system) that is not used in a motor vehicle or a vehicle used solely for
competition." Nonroad engines are used in a variety of nonroad vehicles and equipment and are primarily powered
by diesel or gasoline. Gasoline-powered engines are frequently referred to as spark-ignition (SI) engines.
EPA's nonroad program regulates nonroad engines and equipment in seven general engine categories. These
categories are further divided into various subcategories or groups depending on what approach is most useful in
distinguishing the particular product and application from others. For example, certain subcategories describe an
engine's or an equipment's application (i.e. snowmobile, personal watercraft, nonhandheld equipment) while other
subcategories include engines of a certain size (i.e. SI engines < 19kW (25hp)). Therefore, each of these seven
engine categories contains further divisions, including engines and equipment with a wide range of horsepower or
performance characteristics. Table 1-1 illustrates the nonroad program and its applicable regulations for these
various subcategories.
Table 1-1 EPA Nonroad Engine Program
Engine Categories
Applicable
Regulations
Date of Last
Significant Rule
Code of Federal
Regulation
Citation
Applicable
Standards
1. Locomotives engines
40 CFR Part 92
April 16,1998
63 FR 18978
Exhaust
2. Marine diesel engines
40 CFR Part 94
December 29,
1999
64 FR 73300
Exhaust
3. Other nonroad diesel engines
40 CFR Parts 89,
1039
June 29, 2004
69 FR 38958
Exhaust
4. Marine SI engines
40 CFR Part 91
October 4, 1996
61 FR 52088
Exhaust
5. Recreational vehicle SI engines
40 CFR Part 1051
November 8, 2002
67 FR 68242
Exhaust &
Evaporative
6. Small SI engines (SI engines <19
kW (or < 30 kW if total
displacement is < 1 liter))
a. Handheld (HH)
b. Nonhandhled (NHH)
40 CFR Part 90
a. Jan 12. 2004
b.Mar 30,1999
a. 69 FR 1824
b. 64 FR 15208
Exhaust
7. Large SI engines (SI engines >19
kW (or > 30 kW if total
displacement is < 1 liter))
40 CFR Part 1048
November 8, 2002
67 FR 68242
Exhaust &
Evaporative
Section 428(b) of the 2004 Omnibus Appropriations bill (PL 108-199) required EPA to consider new emission
standards for nonroad SI engines under 50 horsepower (hp). For purposes of this discussion, 50 hp is about 37
kilowatts (kW). The first three categories in Table 1-1 are only diesel engines so they are not covered by the
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provisions. As shown below, the remaining four categories are all SI engines, with all or at least some or their
product offerings below 50 hp.
Table 1-2 SI Engine HP Distribution
SI Engine Category
Engine Subcategory
Estimated % < 50 hp
Marine SI
Outboard
65
Personal Watercraft
<5
Sterndrive/inboard
0
Recreational SI
All Terrain Vehicle
100
Off-Highway Motorcycle
100
Snowmobile
2
Small SI
Handheld
100
Nonhandheld
100
Large SI
None
40
Standards for Marine SI engines were last promulgated in 1996 and are presently ending their phase-in period.
Recreational SI engine standards were promulgated in 2002, and are beginning their phase-in in 2006. Small SI
engine standards for nonhandheld (NHH) engines (containing Classes I and II) were last promulgated in 1999 and
finish their phase-in next year, 2007. Standards for handheld (HH) (containing Classes III-V) are catalyst-based in
many cases and the implementation approach was revised in a 2004 technology review. These engines do not
complete their phase-in until 2010. Finally, two phases of standards for Large SI engines were promulgated in
2002, with catalyst-based standards and a new test cycle required for 2007.
Based on its assessment of these categories, EPA intends to propose revisions to the emission standards for Marine
SI engines and Small SI NHH engines and equipment for exhaust and evaporative controls and HH equipment for
evaporative controls. Under section 205 of the appropriations bill funding EPA for fiscal year 2006 (section 205 of
PL 109-54) EPA, in coordination with other appropriate federal agencies, must complete and publish a technical
study analyzing the potential safety issues associated with the proposed standards for engines <50hp, including the
risk of fire and burn to consumers. The technical study is to be completed and published before the publication of
the notice of proposed rulemaking. This safety study satisfies the requirements of this provision and will also be part
of the supporting information in the rulemaking.
The safety analysis for NHH exhaust emissions is presented in Chapters 3 through 8. The safety analysis for
evaporative control requirements for NHH and HH are presented in Chapter 9 and for Marine SI requirements in
Chapter 10. The proposed rule is also expected to include the first ever exhaust and evaporative emission standards
for sterndrive/inboard (SD/I) engines and vessels as part of our authority under section 213. However, they are not
addressed in this safety study as they are all over 50hp. The impact on safety of new standards for these engines
and vessels will be addressed in the proposal.
As part of the assessment for the rulemaking, EPA evaluated the performance of the current technology for NHH
engines and equipment (studies for HH and Marine SI were not conducted). EPA's initial efforts focused on
developing a baseline for emissions and general engine performance so that we could assess the potential for new
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emission standards for engines and equipment in this category. This process involved laboratory and field
evaluations of the current engines and equipment. As part of this assessment EPA also reviewed engineering
information and data on existing engine designs and their emissions performance. Using information and experience
gathered in this effort, EPA initiated a testing program designed to evaluate improvements to the emissions
performance of these gasoline engines and to assess the potential safety impacts associated with the use of more
advanced emission control technology.
The technology approaches assessed by EPA for meeting the new standards for Class I (< 225cc engine
displacement) and Class II (>225 cc) NHH engines include exhaust catalyst aftertreatment and improvements to
engine and fuel system designs. In addition to its own testing and development effort, EPA also met with engine
and equipment manufacturers to better understand their designs and technology and to determine the state of
technological progress beyond EPA's Phase 2 standards. EPA's research, development, and testing evaluation
efforts included laboratory and real world field assessments of potential technology applications. In the course of
this work EPA conducted both thorough evaluations of laboratory and field emissions performance as well as
separate assessments of safety issues. The engines EPA used for developing these improved emissions factors were
maintained based on manufacturer specifications. Every engine in the field evaluation was maintained at a level at
least as rigorous as called for in the manufacturer's requirements.
The central focus of our safety assessments for NHH engine exhaust standards has been to understand the potential
incremental safety impact of the application of catalyst-based exhaust emission controls on Class I and Class II
engines. EPA's engineering analysis of the safety of exhaust and evaporative emission controls for NHH and HH
engines and equipment focused on five areas:
1. Engineering analysis and emission testing of current technology Class I and Class II engines and Class I
and Class II engines with properly designed emission control systems capable of achieving exhaust
emission reductions beyond the Phase 2 standards (catalyst-based advanced prototype systems).
2. Exhaust emission and safety assessment testing of Class I and Class II engines in both a stock
configuration and equipped with advanced prototype emission control systems. Engines were tested both
in the laboratory and in the field over a broad range of operating conditions; external exhaust system
surface temperatures were measured using infrared thermal imaging while temperatures for lubricant,
cylinder head and exhaust gases were measured using thermocouple probes.
3. Laboratory analysis of significant off-nominal operating conditions that were identified by engine
manufacturers, original equipment manufacturers (OEMs), and EPA staff.
4. Assessment of the potential safety impacts of evaporative emission control requirements.
5. The completion of design Failure Mode and Effects Analyses (FMEA) for Class I and Class II engines
used in walk-behind and ride-on mowers and three process FMEAs for consumer use of lawn equipment.
These studies were conducted as an additional tool for identifying potential safety concerns in going from
Phase 2 to potential Phase 3 standards.
With regard to marine SI, we focused on safety issues related to incorporating upgraded fuel systems and engine
modifications for both outboard and personal watercraft engines. We also assessed the potential incremental safety
impacts of evaporative emission control requirements for marine SI vessels.
B. OVERVIEW
The remainder of this report is comprised of nine chapters. Following this Introduction, Chapter 2 explains EPA's
basic approach to its assessment of the safety issue. Chapters 3 through 8 address only NHH engines. Chapter 3
gives background on small SI NHH engine technology, the relevant applicable safety standards, in-use experience
related to the safety concerns of interest. Chapter 4 describes the safety issues and concerns raised by the various
parties and identified by EPA and identifies the scenarios to be assessed along with the causal factors. Chapter 5
describes in detail the test methods employed by EPA while Chapter 6 presents the results of the testing. Chapter 7
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describes the design and process FMEAs conducted by Southwest Research Institute (SwRI) and discusses the
safety results in the context of potential Phase 3 standards. Chapter 8 presents EPA's technical conclusions for the
Small SI engine category by assessing the concerns identified in Chapter 4 in light of the technical information and
analyses presented in Chapters 5 through 7. Chapter 9 addresses the evaporative control requirements for
equipment powered by Small SI engines. Finally, Chapter 10 assesses the potential safety impact evaporative and
exhaust emission standards for Marine SI engines and vessels as discussed above. The appendices to this report
contain relevant data and technical information referred to in the text.
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2. EPA's Approach to Assessment of the Safety Issue
A. SCOPE OF ASSESSMENT
As mandated by Section 205, this study addresses four subcategories of nonroad engines and equipment containing
SI engines under 50 hp for which EPA intends to propose revisions to the emission standards. These two categories
are commonly referred to as Small SI and Marine SI. As explained in Chapter 1, the four subcategories include HH
and NHH, in the Small SI engine category, and outboard and personal watercraft engines (OB/PWC), in the Marine
SI engine category. The study does not address the EPA categories where EPA is not intending to propose revisions
to the emission standards. This study also does not address safety issues concerning Marine SI vessels powered by
SD/I engines. EPA intends to propose exhaust and evaporative standards for this Marine SI subcategory. EPA will
address any safety concerns related to SD/I requirements as part of the proposed rule.
For Small SI and Marine SI we are considering new exhaust and/or evaporative emission standards. With regard to
the Small SI category we are considering new exhaust and evaporative standards for nonhandheld equipment and
new evaporative standards for handheld equipment. For Marine SI engines we are considering new exhaust and
evaporative standards for both outboard engines and personal watercraft.
B. THE SMALL SI ENGINE ASSESSMENT
The small SI engines and equipment that we considered in this study have been commercially marketed for over 50
years, are commonly found across the United States (US), and have relatively frequent usage. For example, EPA
estimates that there are over 52 million residential and commercial walk behind lawn mowers and ride-on lawn,
garden, and turf equipment in-use in the United States today. EPA estimates that these are used about 3 billion
hours per year. Thus, there is a large amount of in-use experience with the performance of this equipment over time.
As successive generations of engines and equipment have entered the marketplace there have been improvements to
address consumer satisfaction, performance, safety, and emissions, among other factors. Over this time, consumers
have had a variety of types of performance experiences with this equipment. In some cases problems are related to
engine or equipment design while in others they are related to human interactions. It is not uncommon for both
factors to contribute to a problem.
It is not the purpose of this study to review or generally assess safety or performance issues with current small SI
engines and equipment in-use. This study instead looks at the incremental impact on safety of moving from current
Phase 2 standards to new Phase 3 hydrocarbon plus oxides of nitrogen (HC+NOx) exhaust emission standards for
nonhandheld Small SI Engines which are nominally a 35-40 percent reduction over current Phase 2 emission
standards, as well as fuel evaporative emission control requirements for all Small SI engines Although it was
necessary to understand the performance of Phase 2 products in order to fully characterize the baseline used for this
incremental safety analysis, this study does not assess and does not draw any conclusions on what safety risks, if
any, are presented by current equipment. Instead, EPA took current equipment as the baseline, and evaluated the
incremental impact on safety of moving from this baseline to equipment applying more advanced emissions control
technology. The study does not address any issues not related to the potential proposed rulemaking for small SI
engines, such as concerns about carbon monoxide (CO) exposure or refueling problems related to portable gasoline
containers.
C. MARINE SI ASSESSMENT
EPA intends to propose revisions to the exhaust and evaporative emission standards for Marine SI engines. As with
Small SI engines, the study addresses the incremental impact on safety of going from the current EPA standards to
the standards under consideration. The study addresses both outboard engines and personal watercraft.
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3. Technical Background on Nonhandheld Engines
A. CURRENT TECHNOLOGY
The scope of this study included Class I and Class II engine systems, which relate to residential walk-behind and
riding lawn mowers, respectively. Residential lawn mower equipment was chosen for the following reasons:
1. Lawn mowers and the closely-related category of lawn tractors represent the largest categories of
equipment using Class I and Class II nonroad SI engines. EPA estimates that over 47 million walk-behind
mowers and ride-on lawn and turf equipment are in-use in the US today.
2. These equipment types represent the majority of sales for Small SI engines.
3. CPSC data indicates that more thermal burn injuries associated with lawn mowers occur than with other
NHH equipment; lawn mowers therefore represent the largest thermal burn risk for these classes of
engines.
4. General findings regarding advanced emission control technologies for residential lawn and garden
equipment carry over to commercial lawn and turf care equipment as well as to other NHH equipment
using Class I and Class II engines. Lawn mower design and use characteristics pose unique safety
implications not encountered by other NHH equipment using these engines (i.e. a mower deck collects
debris during operation whereas a pressure washer collects no debris). Thus, other NHH equipment may
employ similar advanced emission control technologies for meeting the proposed standards without a
corresponding concern regarding the safety issues analyzed in this study.
Information in EPA's nonroad emissions model estimates suggests about 1.5 billion lawn mower use events per
year for residential lawn care equipment.1 Much of the equipment is typically operated and refueled by the general
public. The equipment is operated under conditions where grass-clipping and similar debris are often present,
particularly during side-discharge or mulching grass cutting operations. Refueling operations typically occur from
portable containers with no automatic cut-off, and can result in fuel spillage.
Class I product, mostly walk-behind mowers, are produced by both integrated and non-integrated manufacturers.
Integrated manufacturers make both the engine and equipment, non-integrated manufacturers make only one of the
two. In almost all cases the fuel tank and muffler are part of the Class I engine when it leaves the engine
manufacturer. Based on manufacturer estimates provided as part of EPA's emission certification program, there are
about 14 million Class I and Class II engines produced per year. In Class II, which also has integrated and non-
integrated manufacturers, it is not uncommon to have the fuel tank and/or muffler added by the equipment
manufacturer. According to the Outdoor Power Equipment Institute (OPEI), there were about 9 million lawn and
garden units produced in the 2005 model year with the remainder comprised primarily of pressure washers,
generators, tillers, snow throwers, construction, and commercial equipment. Table 3-1 below shows the current
Phase 2 emission standards for Class I and Class II engines.
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Table 3-1 EPA Phase 2 Emission Standards2
Engine Class
HC+NOx Standard
(g/kW-hr)
CO Standard
(g/kW-hr)
Final Phase-In Year
for Large
Manufacturers
Regulatory Useful
Life (hours)
Class I
16.1
610
2007
125,250, or 500
Class II
12.1
610
2005
250, 500, or 1000
Crankcase must be closed. The HC+NOx standards do not apply to engines used in snow equipment. Emission
averaging is allowed to meet the HC+NOx standard. There are no evaporative emission control requirements for
Class I or Class II. The useful life category is determined by the manufacturer.
EPA evaluated the incremental change in key safety parameters for the modification of lawn mowers and lawn
tractors from Phase 2 emissions compliance to meeting potential Phase 3 HC+NOx emission standards of 10.0
g/kW-hr for Class I and 8.0 g/kW-hr for Class II. These standards would be 35-40 percent more stringent than
Phase 2 emission standards on Federal certification fuel. The Phase 3 standards would not change the CO emission
standard for NHH engines.
The potential Phase 3 emission standards would also include measures for controlling fuel evaporative emission
requirements. While we looked at the full range of potential evaporative controls, our present program is focused on
fuel tank and fuel hose permeation emissions, running loss controls, and diffusion losses from freely vented fuel
caps. The fuel systems for Class I and Class II equipment consist of rubber fuel hoses and open-vented fuel tanks
which may be constructed out of metal or plastic. Based on information supplied by manufacturers we estimate that
about 80 percent of Class I and 90 percent of Class II equipment are equipped with plastic fuel tanks. Fuel hoses
used today are typically made out of inexpensive nitrile rubber and there are general industry consensus
performance standards related to hoses which apply.
The following discussion explains the design elements for the type of emission control technology that could be
used to achieve the potential Phase 3 emission standards discussed above. These technical discussions and
information presented below are derived from more than two years of laboratory and field work conducted by EPA
in assessing current Phase 2 engine technology and developing prototype Phase 3 systems.
The North American automotive market is now entering its fourth decade of high-volume production of exhaust
catalysts for light-duty gasoline-powered vehicles since the introduction of catalysts on Chrysler vehicles in 1975.
With the advent of Federal Tier 2 and California Low Emission Vehicle (LEV) II exhaust emission standards, light-
duty and medium-duty vehicles are equipped with catalysts and engine management systems that control NOx, HC,
and CO emissions with greater than 99 percent efficiency relative to previous, non-catalyst engines.
Class I and Class II nonroad SI engines face a number of engineering, safety, and cost challenges that can differ
substantially from those of light duty automotive applications. As a result, Class I and Class II exhaust emission
control systems differ from that of light-duty gasoline vehicles but share some common elements with emission
control systems that are now being applied to small-displacement on-highway motorcycles.
In addition, Class I and II equipment can make use of the advances in materials technology and fuel system designs
that have been made in the automotive industry over the past several decades. These approaches to improved fuel
containment are now being applied to other nonroad applications in anticipation of upcoming evaporative emission
standards.
Class I engines
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Class I engines typically are equipped with integral exhaust and fuel systems and are air-cooled. Significant
applications include walk-behind lawn mowers (largest segment), pressure washers, generator sets and pumps.
There are both overhead valve (OHV) and side-valve (SV) engines used in Class I, but side-valve engines are the
predominant type in Class I, particularly in lawn mower applications. They currently represent about 60 percent of
Class I sales. Exhaust catalyst design for Class I engines must take into account several important factors that differ
from automotive applications:
1. Air-cooled engines run rich of stoichiometry to prevent overheating when under load. Because of this, CO
and HC emissions can be high. Catalyst induced oxidation of a high percentage of available reactants in
the exhaust in the presence of excess oxygen (i.e., lean of stoichiometric conditions) can result in highly
exothermic exhaust reactions and increase heat rejection from the exhaust. For example, approximately 80
to 90 percent of the energy available from catalyst-promoted exhaust reactions is via oxidation of CO.
2. Air-cooled engines have significant HC and NOx emissions that are typically much higher on a brake-
specific basis than water-cooled automotive engine types. Net heat available from HC oxidation and NOx
reduction at rich of stoichiometric conditions is considerably less than that of oxidation of CO at near
stoichiometric or lean of stoichiometric conditions due to the much lower concentrations of NO and HC in
the exhaust relative to CO.
3. Most Class I engines do not have 12-volt DC electrical systems to power auxiliaries and instead are pull
start. Electronic controls relying on 12-volt DC power would be difficult to integrate onto Class I engines
without a significant cost increase.
4. Most Class I engines use inexpensive stamped mufflers with internal baffles. Mufflers are typically
integrated onto the engine and may or may not be placed in the path of cooling air from the cooling fan.
5. The regulatory emission test cycles (A-cycle, B-cycle), manufacturer's durability cycles and some limited
in-use operation data indicate that emissions control should focus primarily on light and part load
operation.
These factors would lead to exhaust catalyst designs for small engines that should differ somewhat from those of
light duty gasoline vehicle exhaust catalysts. Design elements specific to Class I Phase 3 exhaust catalysts would
include:
1. Catalyst substrate volume would be sized relatively small so as to be space-velocity limited. Catalyst
volume for Class I Phase 3 engines would be approximately 10 to 25 percent of the engine cylinder
displacement, depending on cell count, engine-out emission levels, and oil consumption. Catalyst substrate
sizes would be compact, with typical catalyst substrate volumes of approximately 1 to 3 cubic inches. This
would effectively limit mass transport to catalyst sites at moderate-to-high load conditions and reduce
exothermic reactions occurring when exhaust temperature is highest. This is nearly the opposite of the case
of typical automotive catalyst designs. Automotive catalyst volume is typically 50 to 100 percent of
cylinder displacement, with the chief constraints on catalyst volume being packaging and cold-start light-
off performance.
2. Catalyst precious metal loading (Pt-platinum, Pd-palladium, Rh-rhodium) would be kept relatively low,
and formulations would favor NOx and HC selectivity over CO selectivity. We estimate that typical
loading ratios for Phase 3 would be approximately in the range of 30 to 50 g/ft3 (approximately 50 percent
of typical automotive loadings at light-duty vehicle Tier 2 emission levels) and can be Pt:Rh, Pd:Rh or tii-
metallic. Tri-metallic platinum group metal (PGM) loadings that replace a significant fraction of Pt with
Pd would be less selective for CO oxidation and would also reduce the cost of the catalyst. Loading ratios
would be similar or higher in Rh than what is typically used for automotive applications (20-25 percent of
the total PGM mass in small SI) to improve NOx selectivity, improve rich of stoichiometry HC reactions
and reduce CO selectivity.
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3. Catalysts would be integrated into the muffler design. Incorporating the catalyst into the muffler would
reduce surface temperatures, and would provide more surface area for heat rejection. This is nearly the
opposite of design practice used for automotive systems, which generally try to limit heat rejection to
improve cold-start light-off performance. The design for Class I Phase 3 engines would have somewhat
higher surface area and somewhat larger volume than many current Class I muffler designs in order to
promote exhaust heat rejection and to package the catalyst, but would be similar to some higher-end
"quiet" Class I muffler designs. Appropriately positioned stamped heat-shielding and touch guards would
be integrated into Class I Phase 3 catalyst-muffler designs in a manner similar to many Class I Phase 2
mufflers. A degree of heat rejection would be available via forced convection from the cooling fan,
downstream of cooling for the cylinder and cylinder head. This is the case with many current muffler
designs. Heat rejection to catalyst muffler surfaces to minimize "hot spots" can also be enhanced internally
by turning the flow through multiple chambers and baffles that serve as sound attenuation within the
muffler, similar to the designs used with catalyst-equipped lawn mowers sold in Sweden and Germany.
4. Many Class I Phase 3 catalysts would include passive secondary air injection to enhance catalyst efficiency
and allow the use of smaller catalyst volumes. Incorporation of passive secondary air allows halving of
catalyst substrate volume for the same catalyst efficiency over the regulatory cycle. A system for Class I
Phase 3 engines would be sized small enough to provide minimal change in exhaust stoichiometry at high
load conditions so as to limit heat rejection, but would be provide approximately 0.5 to 1.0 points of air-to-
fuel ratio change at conditions of 50 percent of peak torque and below in order to lower HC emissions
effectively in engines operating at air-to-fuel ratios similar to those of current Class I Phase 2 engines.
Passive secondary air systems are preferred. Mechanical or electrical air pumps are not necessary. Passive
systems include stamped or drawn Venturis or ejectors integrated into the muffler, some of which may
incorporate an air check-valve, depending on the application. Pulse-air injection is also a form of passive
secondary air injection. Pulse air draws air into the exhaust port through a check-valve immediately
following the closure of the exhaust valve. Active secondary air (air pump) systems were not considered in
this analysis since they may be cost prohibitive for use in Class I applications due to the need for a
mechanical accessory drive or 12-volt DC power.
5. Class I engines are typically turned off via a simple circuit that grounds the input side of the ignition coil.
Temperature fail-safe capability would, if appropriate, can be incorporated into the engine by installing a
bimetal thermal switch in parallel with the ignition grounding circuit used for turning the engine off. The
switch can be of the inexpensive bimetal disc type in wide-spread use in numerous consumer products
(furnaces, water-heaters, ovens, hair dryers, etc.). To reduce cost, the bimetal switch could be a non-
contact switch mounted to the engine immediately behind the muffler, similar to the installation of bimetal
sensors currently used to actuate automatic chokes on current Phase 2 Class I lawn mower engines.
Class II engines
Almost all Class II engines are air-cooled. Unlike Class I engines, Class II engines are not typically equipped with
integral exhaust systems and fuel tanks. Significant applications include lawn tractors (largest segment),
commercial turf equipment, generator sets and pumps. Overhead valve engines have largely replaced side-valve
engines in Class II, with the few remaining side-valve engines certifying to the Phase II standards using emissions
credits or being used in snow thrower type applications where the HC+NOx standards do not apply. Class II engines
are typically built more robustly than Class I engines. They often use cast-iron cylinder liners, may use either splash
lubrication or full-pressure lubrication, employ high volume cooling fans and in some cases, use significant
shrouding to direct cooling air. Exhaust catalyst design practice for Class II engines will differ depending on the
level of emission control. Class II engine designs are more suitable for higher-efficiency emission control systems
than most Class I engine designs. The design factors are somewhat similar to Class I:
1. Class II engines are mostly air-cooled, and thus must run rich of stoichiometry at high loads. The ability to
operate at air-to-fuel ratios rich of stoichiometry at high load may be more critical for some Class II
engines than for Class I engines due to the longer useful life requirements in Class II. The engines
incorporate more advanced fuel metering and spark control than is typical in Class I, in order to meet the
more stringent Class II Phase 2 emission standards (12.1 g/kW-hr HC+NOx in Class II versus 16.1 g/kW-
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hr in Class I). The heat energy available from CO oxidation is typically somewhat less than the case in
Class I because of slightly lower average emission rates.
2. As with Class I engines, air-cooled Class II engines have significant HC and NOx emissions that are
typically much higher on a brake-specific basis than water-cooled automotive engine types, but generally
with a somewhat higher fraction of NOx in the total regulated HC+NOx emissions and lower CO
emissions than is the case for Class I engines.
3. Most Class II engines are equipped with 12-volt DC electrical systems for starting. Electronic controls
relying on 12-volt DC power could be integrated into Class II engine designs. Low-cost electronic engine
management systems are extensively used in motor scooter applications in Europe and Asia. Both Kohler
and Honda have introduced Class II engines in North America that use electronic engine management
systems.
4. Class II engines use inexpensive stamped mufflers with internal baffles similar to Class I, but the mufflers
are often not integrated onto the engine design and may be remote mounted in a manner more typical of
automotive mufflers. Class II mufflers are often not placed in the direct path of cooling air from the
cooling fan.
5. As with Class I, the regulatory cycles (A-cycle, B-cycle), manufacturer's durability cycles and some
limited in-use operation data indicate that emissions control should focus primarily on light and part load
operation.
Taking these factors into account would point towards exhaust catalyst designs that differ from those of light duty
gasoline exhaust catalysts and differ in some cases from Class I systems. Elements specific to Class II Phase 3
emission control system design using carburetor fuel systems would include:
1. Catalyst substrate volume would be sized relatively small so as to be space-velocity limited. Catalyst
volume for Class II Phase 3 engines would be approximately 33-50 percent of the engine cylinder
displacement, depending on cell count, engine-out emission levels, oil consumption and the useful life
hours to which the engine's emissions are certified. Catalyst substrate sizes would be very compact within
typical mufflers used in Class II, with typical catalyst substrate volumes of approximately 3 to 12 cubic
inches. This would effectively limit mass transport to catalyst sites at moderate-to-high load conditions
and reduce exothermic reactions occurring when exhaust temperature is highest.
2. Catalyst precious metal loading would be kept relatively low, and formulations would favor NOx and HC
selectivity over CO selectivity to minimize heat concerns. We estimate that typical loading ratios for Phase
3 would be approximately in the range of 30 to 50 g/ft3 (approximately 50 percent of typical automotive
loadings) and could be Pt:Rh, Pd:Rh or tri-metallic. Tri-metallic PGM loadings that replace a significant
fraction of Pt with Pd would be less selective for CO oxidation and would also reduce the cost of the
catalyst. Loading ratios would be similar or higher in Rh than what is typically used for automotive
applications (20-25 percent of the total PGM mass in small SI).
3. Catalysts would be integrated into the muffler design. Incorporating the catalyst into the muffler would
reduce surface temperatures relative to the use of a separate catalyst component. The catalyst for Class II
Phase 3 engines would be integrated into mufflers that are similar in volume to today's Class II Phase 2
mufflers. Appropriately positioned stamped heat-shielding and touch guards would be integrated into
Class II Phase 3 catalyst-muffler designs in a manner similar to current product. Class II engines typically
have a much higher volume of cooling air available downstream of the cylinder than Class I engines. Heat
rejection from the cylinder and cylinder head increases the temperature of the cooling air, but it is still
sufficiently below the temperature of exhaust system components to allow its use for forced cooling. Thus
a degree of heat rejection would be available via forced convective cooling of exhaust components via the
cooling fan. However, this would require some additional ducting to supply cooling air to exhaust system
surfaces along with careful layout of engine and exhaust components within the design of the equipment
that it is used to power. Integrated catalyst-mufflers can also use exhaust energy for ejector cooling (see
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chapter 6). Heat rejection to catalyst muffler surfaces to minimize "hot spots" can also be enhanced
internally by turning the flow through multiple chambers and baffles that serve as sound attenuation within
the muffler.
4. Some applications may include secondary air injection to enhance catalyst efficiency. Incorporation of
passive secondary air allows halving of catalyst substrate volume for the same catalyst efficiency over the
regulatory cycle. In many cases, this may not be necessary due to the lower engine-out emissions of Class
II engines. In cases where secondary air is used, it could either be a passive system similar to the
previously described Class I systems, or an active system with an engine driven pump. Pump drive for
active systems could be either 12-volt DC electric or via crankcase pulse, and pump actuation could be
actively controlled using an electric solenoid or solenoid valve. The use of active systems is an option but
seems unlikely.
5. Class II engines are typically turned off via a simple circuit that grounds the input side of the ignition coil.
As with Class I engines temperature fail-safe capability could be incorporated into the engine by installing
a bimetal thermal switch in parallel with the ignition grounding circuit used for turning the engine off,
although application of this may not be suitable for use with ride-on equipment.
6. Higher catalyst efficiency, considerably lower exhaust emissions levels, and improved fuel consumption
are possible with Class II engines, but temperature considerations might necessitate the use of electronic
engine management and open-loop fuel injections systems. In such a case, the design and integration of
the emission control system would more closely resemble automotive applications, but still with some
differences.
Elements specific to Class II Phase 3 emission control system design using electronic engine management to reduce
emissions beyond the nominal 35 percent reduction target would include:
1. Electronic fuel and spark control. Fuel metering would be via a low-cost open-loop fuel injection system
similar to systems currently in production for motor scooters in Europe and Asia. Such systems use far
fewer sensors and components and simpler Engine Control Units (ECU) than typical automotive
applications. Open loop fuel mapping can be based on feedback of manifold absolute pressure (MAP) and
engine oil temperature, with injection timing based on a magnetic signal from the flywheel or an inductive
signal from the ignition system. Air-to-fuel ratio and spark timing can also be tailored at moderate to light-
load conditions to favor engine-out control of HC and CO emissions while still operating sufficiently rich
of stoichiometry to allow good NOx conversion over the catalyst. Such a control strategy would reduce
heat rejection from the catalyst and provide improved engine protection and reduced exhaust temperature
at high-load conditions. Secondary air injection into the exhaust would not be necessary.
2. Larger catalyst volume with higher precious metal loading. Improved air-to-fuel ratio and spark control
allows the use of larger catalyst volumes (50 to 75 percent of engine displacement) with a higher precious
metal loading than is possible with carbureted engines that have higher engine-out CO levels at light to
moderate loads. The advanced engine control system discussed in item 1 above would reduce engine out
CO emissions and thus catalyst exotherms related to further CO oxidation.
3. Catalysts integrated into the muffler design. Catalysts would be integrated into mufflers similar in design
to the systems described for carbureted Class II engines. Muffler volume would be similar to existing
designs.
4. Misfire detection software would be integrated into the ECU that could:
a. notify the user that engine servicing is necessary via illumination of a malfunction indicator light
(MIL);
b. place the engine in a "limp mode" in the event that an engine operating condition is encountered
that has potential safety, engine durability, or emission control system durability implications:
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c. could shut-down the engine under extreme circumstances.
d. ECU software could also integrate an input from a bimetal thermal switch for MIL illumination,
"limp mode" initiation, or engine shut-down.
B. CURRENT SAFETY STANDARDS
An appendix to the SwRI report lists over 30 mandatory and voluntary standards which are, to varying degrees,
applicable to small SI equipment and in some cases specifically to nonhandheld engines.3 The majority of these are
voluntary American National Standards Institute (ANSI) and Society of Automotive Engineers (SAE) standards. US
Department of Agriculture (USDA) requirements are primarily applicable to handheld equipment such as
chainsaws. American Society of Agricultural Engineers (ASAE), International Standards Organization (ISO), and
the American Society for Testing and Materials (ASTM) all have surface temperature requirements.
The existing ANSI standards for turf care equipment standards are sponsored by the Outdoor Power Equipment
Institute. These ANSI standards address engine and equipment safety for small gasoline engines. The predominant
standards followed by the Class I and Class II engine and equipment manufacturers are ANSI B71.1, American
National Standard for Consumer Turf Care Equipment-Walk-Behind Mowers and Ride-On Machines with Mowers-
Safety Specifications and ANSI B71.4, American National Standard for Commercial Turf Care Equipment - Safety
Specification for Consumer Lawn Care and Commercial Lawn Care Equipment.3'4 They are designed to address
operator and by-stander safety. The ANSI standards apply to the engine and exhaust system as well as the complete
equipment product. Within the ANSI standards for residential lawn care equipment, there are three sections that
discuss touch burn safety and prevention of fuel ignition during refueling, with two sections referring to walk-
behind mowers and one section referring to ride-on lawn equipment.
• From ANSI B 71.1, Part II: Walk-Behind Mowers: ,American National Standard for Consumer Turf Care
Equipment-Walk-Behind Mowers and Ride-On Machines with Mowers-Safety Specifications, Part II:
Walk-Behind Mowers:
o "5.2 Heat protection - A guard or shield shall be provided to prevent inadvertent contact with any
exposed components that are hot and may cause burns during normal starting and operation of the
machine."
o "5.3 Fuel ignition protection - Overflow gasoline shall be diverted away from the muffler outlet
area."
• From ANSI B 71.1, Part III: Ride-on mowers, lever steer mowers, lawn tractors, and lawn and garden
tractors:
o "15.2 Heat protection - A guard or shield shall be provided to prevent inadvertent contact with
any exposed components that are hot and may cause burns during normal starting, mounting, and
operation of the machine."
• From ANSI B 71.4, Figure 3, American National Standard for Commercial Turf Care Equipment - Safety
Specification, In section 4.2.4, Operation, Service, Maintenance Instruction (figure 3), the following
information is required in the instruction manual:
o Clean grass and debris from cutting units, drives, mufflers, and engine to help prevent fires. Clean
up oil or fuel spillage.
o Let engine cool before storing and do not store near flame.
" The SwRI report and its appendices are in located in Appendix C of this study.
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o Shut off fuel while storing or transporting. Do not store fuel near flames or drain indoors.
In general these ANSI standards primarily focus on safety labeling, operator instructions, manuals, and a series of
safety tests regarding equipment operation, mower deck safety, prevention of ejection of objects from the deck and
equipment maneuverability. No design standards or surface temperature criteria are specified, nor are standardized
test procedures provided for fire or touch burn safety for lawn care equipment. There are no ANSI standards
specific to fuel tanks or fuel hoses.
• ASAE Standard S440.3 Safety for Powered Lawn and Garden Equipment5 addresses hot surfaces in
section 9 stating:
o 9.1.7 Hot surfaces (engine, hydraulic, transmission, etc) that exceed a temperature of 90°C
(194°F) for nonmetallic surfaces, or 80°C (176°F) for metallic parts while operating at 21°C
(70°F), except surfaces of equipment intended primarily for winter use, which shall be at 5°C
(41°F). All surfaces which exceed 65.5°C (150°F) at 21°C (70°F) ambient and which might be
contacted by the operator during normal starting, mounting, operating, or refueling shall be
indicated by a safety sign located on or adjacent to the surface.
• ISO standard 5395 section 2.2.3 addresses heat protection stating6:
o A guard or shield shall be provided to prevent accidental contact with any exposed engine exhaust
components greater than 10 cm2 and with a hot surface temperature greater than 80° C at 20° C
(+/- 3°C ) ambient temperature during normal operation of the machine.
• ASTM Standard C1055-03, the Standard Guide for Heated System Surface Conditions that Produce
Contact Burn Injuries recommends first determining the acceptable contact time and level of burn
severity7. They list an acceptable contact time of 5 seconds for industrial processes and 60 seconds for
consumer items. The maximum operating surface temperature can then be derived from two equations
given in the standard. A recommendation to install jacketing or insulation is made if the injury level
exceeds the chosen criteria; a redesign to the system is recommended if the criteria still cannot be met after
installing protective measures. Nominally a value of 70°C is established as a level above which action is
necessary.
The CPSC issued a regulation, 16 CFR Part 1205, to prevent users and bystanders from coming into contact with
mower blades8. There are no Federal regulations, standards, or test procedures related to addressing fire or burn risk
with residential lawn equipment.
There are machine standards for noise and other operator and by-stander impacting characteristics in the European
Machinery Directives. These machine standards are referred to during the engine design process. Most of the
machine standards focus on the safety of the cutting blades. There are also installed engine operating tests
designed to address heat exposure of stationary or parked tractors. These specifically focus on grass browning and
surface temperature tests. These tests involve dumping the engine load and either letting the engine idle for two to
three minutes or shutting the engine off. These tests are typically designed to address the level of distress caused to
the grass.
There are a range of threshold temperature specifications that equipment manufacturers require of their engine
suppliers for surface temperatures and exhaust temperatures. Most temperature requirements are for functionality
rather than for safety. These include issues related to ventilation, tire side wall heating (for exhaust exiting near the
rubber front tires), and oil degradation protection.
In the same vein, it should be noted that in discussions with EPA all engine and equipment manufacturers indicated
that they have various proprietary tests they use to address in-use safety. These are applied when engines and fuel
systems are completed by the original engine manufacturer, and it is often the case that the engine manufacturer
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works with and advises the equipment manufacturer on safety specifications and requirements for the safe
application of engines, mufflers, and fuel tanks as appropriate.
C. IN-USE SAFETY EXPERIENCE
Assessing incremental impact on safety risk from applying more advanced emission control technology requires a
thorough understanding of the problems and in-use safety experience with current products. To conduct this
assessment EPA coordinated closely with CPSC. The staff of CPSC provided copies of relevant CPSC technical
reports and provided detail and synopses of relevant information from four key databases. EPA also reviewed
CPSC's public website which contained information on voluntary recall actions.
The technical reports provided by CPSC include the following:
• U.S. Consumer Product Safety Commission. (2004). Hazard Analysis of Power Lawn Mower Studies
Calendar Years 2003 and 1993. Washington DC: Adler, P.; Schroeder, T.9
This report examined data collected from 1983 through 1993 to evaluate the effectiveness of the mandatory
standard addressing blade contact injuries and the ride mower portion of the voluntary ANSI/OPEI B71.1.
Blade-contact and thrown object hazards were examined with walk behind and ride-on mowers.
Additionally, rolling/tipping over hazard was examined in ride-on mowers. All other hazards, including
hot surfaces contact and fire/flame, were categorized as 'other' and were not further addressed by this
report.
• U.S. Consumer Product Safety Commission. (2003). Hazard Screening Report Yard and Garden
Equipment (Product Codes 1400-1464). Washington DC: Rutherford, G., Marcy, N., Mills, A.10
This report compared the risk of different products within the Yard and Garden Equipment category based
on 2001 injury data and 2000 death data. Lawn mowers represented the largest cost associated with injury
and deaths. A common hazard among all yard and garden equipment was a leaking fuel system which was
mostly reported with riding mowers and walk behind mowers. No further information was given specific
to lawn mowers.
• U.S. Consumer Product Safety Commission. (1993). Ride-On Mower Hazard Analysis (1987-1990).
Washington DC: Adler, P.11
This report provides a detailed hazard analysis of lawn mowers for reporting periods 1987-1990; a
comparison was made with lawn mower hazard patterns from 1983-1986. Table 6 indicates that for the
periods 1983-86 and 1987-90, 5-6 percent of all injuries associated with ride-on mowers treated in US
hospital emergency rooms are burns. Lacerations and burns from a hot surface contact occurred to hands
and accounted for 77 percent of all hand injuries.
• U.S. Consumer Product Safety Commission. (1993). Deaths Related to Ride-On Mowers: 1987-1990.
Washington DC: David, J. A.12
A follow-up report to CPSC Rider-On Mower Hazard Analysis (1987-1990) indicates that for the period
1987-1990, 2.5 percent of deaths were fire-related and indicates the fraction of fire-related hospital
emergency room visits to be five percent for 1983-1986 and two percent for 1987-1990., There are
approximately 850 hospital visits related to touching hot surfaces, and nine deaths related to fire for ride-on
mowers for the period 1987-1990. It should be noted that these figures cover only ride-on mowers.
• U.S. Consumer Product Safety Commission. (1988). Hazard Analysis, Ride-On Mowers. Washington DC:
Smith, E.13
23
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This report gives an estimated 6 percent of in-use injuries as being thermal-burn related, such as a hot
muffler or exhaust pipe. In most cases the engine was reported as being off, but the mower was still in use,
which can include making repairs, maintenance, fueling, getting on/off, lifting, pushing, or other.
• U.S. Consumer Product Safety Commission. Thermal Burn Contact-Related Injuries Associated with
Gasoline-Engine Powered Equipment, 1990-19981 Washington DC: Adler, P.14
This report discusses thermal burns exclusively from contact related injuries on gasoline engine powered
equipment for the period 1990 - 1998. This report discusses gasoline engine powered equipment such as
walk behind and riding mowers, chainsaws, rotary tillers, brush cutters. A contact burn injury is
characterized by inadvertent contact with hot components or surfaces on the equipment. Based on the
National Electronic Injury Surveillance System (NEISS) database there were an estimated average of 2,200
contact burn injuries treated in U.S. hospital emergency rooms during the 9 year period. Of these, 17
percent were related to the lower arm/leg and 68 percent were on the hand or finger. First and second
degree burns are 53 percent of the total. Table 3 of this report indicates that 41 percent of burns were
related to the muffler, 13 percent related to the exhaust tailpipe, 13 percent related to engine components,
and 33 percent related to other surfaces. Muffler contact thermal burns were the dominant risk in all the
engine-powered equipment discussed in this report.
In addition, CPSC provided EPA focused extracts related to fire and burn incidents from four different databases.
1. CPSC's NEISS database is comprised of a sample of hospitals that are statistically representative of
hospital emergency rooms nationwide. From the data collected, estimates can be made of the numbers of
injuries associated with consumer products and treated in hospital emergency departments.
2. CPSC's Injury/Potential Injury Incident File (IPII) contains summaries, indexed by consumer product, of
Hotline reports, product-related newspaper accounts, reports from medical examiners, and letters to CPSC.
3. CPSC's In-Depth Investigations (INDP) file contains summaries of reports of investigations into events
surrounding product-related injuries or incidents. Based on victim/witness interviews, the reports provide
details about incident sequence, human behavior, and product involvement.
4. The National Fire Incident Reporting System (NFIRS) is a database of fires attended by the fire service.
NFIRS provides data at the product level and is not a probability sample. The information from the NFIRS
database results are weighted up to the National Fire Protection Association (NFPA) survey to provide
national annual product-level estimates.
US CPSC's public website contains information on voluntary manufacturer recalls dating back over 30 years. In
reviewing this website, EPA reviewed recalls related to small gasoline-powered equipment such as lawn mowers,
generators, pumps, pressure washers, utility vehicles, snow throwers, go-karts, tractors, and engines. In these nine
categories, EPA identified 32 recall actions that were related to either fire or burn risk on gasoline-powered
equipment.
CPSC Databases:
Working closely with CPSC staff, EPA reviewed the databases and recall events to identify those which might have
a bearing on this safety study. Each of these is discussed below.
NEISS: CPSC's National Electronic Injury Surveillance System reported a total of 475 thermal burn injuries
related to gasoline-fueled lawn mowers that were treated in hospital emergency rooms over the five year period
2000-2004.15 The product codes used to create this dataset included walk behind mowers, riding lawn mowers, lawn
tractors and lawn mower product codes that do not specify the type of mower. Based on this period sampling of
NEISS reported cases, there were an estimated 19,072 lawn mower thermal burns injuries treated in emergency
rooms around the United States. Ninety six percent of these injuries were treated and released. Most of the victims
24
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(51%) suffered hand injuries. Other body parts that were injured frequently were finger, lower arm, and lower leg
(about 15%, 13%, and 8% of the cases, respectively).
The descriptive narratives of the NEISS reported cases were reviewed to determine hazard patterns that resulted in
thermal burn injuries. The following hazard patterns were identified:
• Contact Burn: An individual contacts a hot lawn mower component and receives a burn.
• Refueling-Related Fire: Ignition of fuel vapor when an individual was refueling.
In addition, there were two NEISS hazard patterns (shown below) which either had a significant user behavior
component to the problem, which is not a technical issue, or were inadequately described in the records to allow a
laboratory or field assessment of the incremental risk. These two items are assessed primarily in the FMEA.
• Unspecified: The running lawn mower caught fire/exploded for reasons unspecified.
• Maintenance: An individual is performing lawn mower maintenance activities when a fire occurs.
Table 3.2 shows the annual NEISS estimates for both thermal burn injuries associated with gasoline fueled lawn
mowing equipment from 2000-2004 and the portion of these burns that were due to the victim contacting a hot lawn
mower component. There was an estimated average of 3,814 thermal burn injuries per yearb with contact burns
accounting for 88% (3,375) of these injuries. There were no significant differences among the years studied, nor
were there any significant trends detected over these five years.
b Note: The 2000-2004 NEISS estimates are larger than the 1990 - 1998 estimates in report 6, [Thermal Burn Contact-Related
Injuries Associated with Gasoline-Engine Powered Equipment, 1990-1998, Adler, P., because the 2000-2004 data set included
additional product codes such as lawn mowers not specified, tractors other or not specified, powered lawn mowers not specified.
25
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Table 3-2
Annual Estimates of Emergency Room Treated Thermal
Burns From Gasoline-Fueled Lawn Mowing Equipment16
Year
Estimate of
Proportion of Thermal
Thermal Burn
Burn Injuries due to
Injuries
Contact
2000
3,509
92% (3,236)
2001
4,256
85% (3,626)
2002
4,354
92% (3,985)
2003
3,587
84% (3,026)
2004
3,365
89% (3,002)
Total
19,072
88% (16,875)
Mean
3,814
88% (3,375)
IPII and INDP: Gasoline-powered lawn mower records related to thermal burn injuries or potential injuries were
obtained from CPSC's Injury/Potential Injury Incident File and In-Depth Investigation files.17 For the five year
period of January 2000 through December 2004, there were 466 IPII records and 87 INDP records. There were
cases of some duplication in the NEISS, IPII/INDP records because the emphasis was in finding scenarios that can
lead to thermal burn injuries rather than removing duplicate records. EPA and CPSC reviewed every record in these
databases, with the purpose of identifying the prevalence of problems with engine or equipment systems affected by
EPA's potential new exhaust and fuel evaporative emission standards. Several hazard patterns were identified from
the INDP and IPII records that caused or could potentially cause fire and thermal burn injuries. These hazard
patterns fall into two basic categories. In the first, the hazards identified are directly traceable to a technical
performance or failure in a component or subsystem on the engine or are the effect of the characteristics and
performance of the equipment itself. These are shown below:
• Fuel Leaks: fuel leaks from tank installed on equipment, faulty fuel hose or primer bulb, or from faulty or
malfunctioning carburetor
• Debris Fire: Ignition of grass or leaves from hot components on the lawn mower
• Shutdown/Storage: A lawn mower stored or used near combustibles/flammable materials or near an
ignition source such as an appliance with a pilot light results in a fire.
• Engine Backfire/Misfire: The lawn mower backfires resulting in either noise or fire/flames.
• Contact Burn: An individual contacting a hot lawn mower component that results in a burn
• Refueling Related Fire: Ignition of fuel liquid or vapor related to refueling
In addition, there were three hazard patterns (shown below) which either had a significant user behavior component
to the problem which is not a technical issue or were inadequately described in the records to allow a laboratory or
field assessment of the incremental risk. These three items are assessed primarily in the FMEA.
• Maintenance: An individual performing lawn mower maintenance activities that results in a fire
• Tip Over: A riding lawn mower tips over when in use resulting in fuel leaks. It is believed that fuel leaks
from the overturned lawn mower are primarily from the vented gas cap or from the carburetor. In some of
these records, the individual becomes trapped under the riding lawn mower.
• Unspecified: For reasons unspecified, the running lawn mower catches fire/explodes
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NFIRS: The National Fire Incident Reporting System is based on firefighter and first responder reports on incidents
to which they respond. The data compiled by the US Fire Administration and the National Fire Protection
Association is not as complete or precise as that from the NEISS. Nonetheless, the data provided by CPSC estimates
that for 2002 there were 100 fires involving gasoline-fueled lawn mowing equipment and estimates that there were
10 injuries associated with these fires.18
CPSC RECALL INFORMATION
The CPSC website publishes Recalls and Product Safety News, where manufacturers, in cooperation with CPSC,
voluntarily recall products that pose a safety hazard to consumers.19 Recall notices published during the period of
January 2000 to December 2004 were reviewed. During this period there were a total of 22 lawn mowers or lawn
mower engine recalls due to safety issues related to fire and thermal burn injuries. These 22 recall notices affected
approximately 850,000 lawn mower units. Table 3-3 identifies the following hazard patterns from the recall notices:
Table 3-3: Fire/Burn Risk Related Recall Events for Small Gasoline-powered Lawn/Garden Equipment
Problem
Category
Number Recalls
Years Issued
Years Affected
Incidents
Reported
Total Equipment
Involved
Fuel Tank
Leaks
11
2000-2004
1995-2004
2229
742,054
Fuel Hose
Leaks
5
2000-2004
2001-2004
5
4660
Backfire
(Misfire)
2
2002
1998-2001
25
34,000
Refueling Vapor
Ignition
1
2001
1998-2001
28
39,000
Other
3
2000-2004
1999-2003
27
28,300
EPA also identified about 10 other CPSC recalls related to small engines which either were not applicable to lawn
and garden equipment or occurred outside of the five year evaluation period. Most of these were related to fuel
tanks and fuel hoses. This type of problem was also identified in the 2000-2004 lawn mower equipment recalls.
Discussion of CPSC Data
Taken as a whole, the reports and data provided by CPSC are consistent and indicate that the following types of
incidents should be of primary technical concern when evaluating the incremental impact on safety of the more
advanced emissions control technology: burns due to contact with hot surfaces, fuel tank leaks, fuel hose leaks,
refueling vapor ignition, debris fires, shutdown and storage related fires, engine backfire/misfire, and carburetor fuel
leaks.
In the chapters which follow, EPA identifies causative factors which might be contributing to these hazard patterns
and their occurrence in use, and presents data and technical analyses assessing the incremental impact on these
hazard patterns of potential Phase 3 exhaust and fuel evaporative emission standards for Class I and Class II engines
and equipment.
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1 "Estimated Number of Refueling Events for Residential Mowing Equipment," EPA memorandum from Phil
Carlson, March 3, 2006, Docket EPA-HQ-OAR-2004-0008-0331.
2 U.S. Code of Federal Regulations, Title 40, Part 90, §90.103, Tables 2 and 3.
3 ANSI B71.1-2003, "American National Standard for Consumer Turf Care Equipment - Walk-Behind Mowers and
Ride-On Machines with Mowers - Safety Specifications", American National Standards Institute, 2003.
4 ANSI B71.4-2004, "American National Standard for Commercial Turf Care Equipment - Safety Specifications"
American National Standards Institute, 2004.
5 ASAE S440.3, "Safety for Powered Lawn and Garden Equipment", American Society of Agricultural and
Biological Engineers, St. Joseph, Michiganwww.asabe.org, March 2005.
6 ISO 5395, "Power lawn-mowers, lawn tractors, lawn and garden tractors, professional mowers, and lawn and
garden tractors with mowing attachments ~ Definitions, safety requirements and test procedures", International
Organization for Standardization, Geneva, Switzerland, 1990.
7 ASTM C1055-03, "Standard Guide for Heated System Surface Conditions That Produce Contact Burn Injuries",
ASTM International, 2003.
8 U.S. Code of Federal Regulations, Title 16, Part 1205.
9 Docket EPA-HQ-OAR-2004-0008-0321.
10 Docket EPA-HQ-OAR-2004-0008-0322.
11 Docket EPA-HQ-OAR-2004-0008-0323.
12 Docket EPA-HQ-OAR-2004-0008-0332.
13 Docket EPA-HQ-OAR-2004-0008-0329.
14 Docket EPA-HQ-OAR-2004-0008-0320.
15 Docket EPA-HQ-OAR-2004-0008-0327.
16 U.S. Consumer Product Safety Commission, National Electronic Injury Surveillance System database, 2000-
2004.
17 The Injury /Potential Injury Incident File (IPII) can be found at Docket EPA-HQ-OAR-2004-0008-0325. The In-
Depth Investigation (INDP) files can be found at Docket EPA-HQ-OAR-2004-0008-0326.
18 "NFIRS Data on Gasoline-Fueled Lawn Mowing Equipment, 2002," CPSC memo from Risana Chowdhury to
Susan Bathalon, December 7, 2005, Docket EPA-HQ-OAR-2004-0008-0324.
19 U.S. Consumer Product Safety Commission, "Recalls and Product Safety News",
http ://www. cpsc. gov/cpscpub/prerel/prerel.html
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4. Scenarios for Evaluation of NHH Engines and Equipment
A. SUMMARY OF OTHER INFORMATION CONSIDERED
In this chapter, EPA identifies the key scenarios used in evaluating the incremental impact on safety associated with
advanced emission control technology for NHH engines and equipment. The scenarios cover a comprehensive
variety of in-use conditions or circumstances which potentially could lead to an increase in burns or fires. These
may occur presently or not at all, but are included because of the potential impact on safety if they were to occur.
EPA is not identifying these as conditions that will in fact occur, but more as potential or hypothetical conditions
should be evaluated. The focus of the analysis is therefore on the incremental impact on the likelihood or that the
severity of these scenarios and the potential causes occurring from using more advanced emissions control
technology.
In addition to using the CPSC reports and databases, EPA considered additional inputs in identifying the scenarios
for evaluation. These included the following:
• OPEI briefing to EPA entitled: "Discussion of Off-Nominal Operating Conditions for Catalyzed Small
Off-Road SI Engines and Lawn/Garden Equipment," Oct 26, 2005.1
OPEI identified nominal and off nominal conditions and laid out concerns which occur in the lab versus in the field.
According to OPEI, off nominal conditions are defined as unintentional and unavoidable conditions during
equipment operation which are non-trivial infrequency and may be high consequence events leading to significant
increase in fire and heat-related safety hazards. The four general categories of off nominal conditions identified by
OPEI include:
i. An increase in the amount of air present in the muffler/catalyst region
ii. Air/Fuel ratio changes affecting catalyst conversion efficiency
iii. Increase of unburned fuel into muffler/catalyst or on hot surfaces of the equipment
iv. Changes in the cooling air flow management system
• National Association of State Fire Marshals memorandum from Margaret Simonson to James Burns,
"Recommendations for Independent Research Project on Fire Safety of Measures being Considered to
Reduce Emissions of Small Engines in Outdoor Power Equipment," September 22, 2004.2
• Memorandum, from Charles Burnham Applied Safety and Ergonomics to Margaret Simonson, National
Association of State Fire Marshals entitled, "Request for Data: Air Quality Measures for Small Engines
Used with Outdoor Power Equipment," June 18, 2004.3
• Letter from William Guerry, Collier, Shannon, Scott, to Jackie Lourenco entitled Re: "CARB's Catalyst
Durability Study." September 10, 2002.4
• "Lawn-Mower Related Burns," Journal of Burn Care and Rehabilitation, Volume 21, No.8, pp. 403-405.5
• "Literature Survey on Garden Machinery (lawnmowers)" prepared by Dutch Consumer and Safety
foundation for the Inspectorate for Health Protection and Veterinary Public Health, November 3, 2002.6
• Discussion with the National Institute for Standards and Testing (NIST), December 6, 2005.7
• "Durability of Low Emissions Small Off-Road Engines," Southwest Research institute, April, 2004.8
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• Information from meetings, workshops, and discussions with engine and equipment manufacturers
including but not limited to:
o OPEI Presentation to US EPA, May 23, 2005.9
o Public Consultation Meeting, The International Consortium for Fire Safety, Health, and
Environment and US EPA, Briggs and Stratton Corporation, October 5, 2005.10
In addition to these references, EPA has gained valuable empirical experience in the field testing conducted over the
past two years. This testing has increased our understanding of potential failure modes and added to the scope and
depth of our planned assessment.
B. SAFETY SCENARIOS FOR EVALUATION
There are a number of ways in which the scenarios of concern could be identified for evaluation and discussion.
EPA elected an approach which closely mirrors the problems identified in the CPSC data, while including the other
concerns identified in the other sources described in A. above. This provides a comprehensive and methodical
approach to analysis and discussion which is provided in the chapters which follow.
Scenario 1: Contact burns
Scenario Description: Thermal burns due to inadvertent contact with hot surface on engine or equipment.
Potential Causes:
a. muffler surface temperature increases due to debris inhibiting flow of cooling air
b. higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler
or engine
c. muffler temperature increase due to air-to-fuel ratio enleanment caused by calibration drift over time,
fuel system problems or air filter element mal-maintenance
d. exhaust gas leaks increase surface temperatures
e. misfueling: use of highly oxygenated fuel such as E85 (mixture of 85% ethanol and 15% gasoline)
Scenario 2: Debris fire:
Scenario Description: Grass and leaf debris fires on engine/equipment.
Potential Causes:
a. muffler temperature increases due to debris inhibiting flow of cooling air, debris trapped in tight areas
blocks air flow, dries out and heats up
b. higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler or
engine or exhaust system leaks
c. muffler temperature increase due to A/F ratio enleanment caused by calibration drift over time, air
filter element mal-maintenance, or exhaust system leaks
30
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d. exhaust gas leaks increase surface temperatures
e. misfueling: use of highly oxygenated fuel such as E85
Scenario 3: Fires due to fuel leak
Scenario Description: Fires due to fuel leaks on hot surfaces.
Potential Causes:
a. faulty fuel tank
b. faulty fuel line or connection
c. tip-over during maintenance
d. tip over in operation
e. faulty carburetor
f. heat affects fuel tank or fuel line integrity
Scenario 4: Fires related to refueling
Scenario Description: Fires related to spilled fuel or refueling vapor.
Potential Causes:
a. fuel spilled on hot surfaces
b. spilled fuel evaporates or refueling vapors lead to fire indoors
Scenario 5: Fire related to storage and shutdown
Scenario Description: Equipment or structure fire when equipment left unattended after use.
Potential Causes:
a. ignition of nearby easily combustible materials
b. ignition of fuel vapor by an appliance pilot light (or similar open source of ignition)
c. ignition of dry debris on deck
d. ignition of dry debris in field
e. ignition of tarp or other cover over equipment
Scenario 6: Ignition misfire
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Scenario Description: Engine malfunction which results in an ignitable mixture of unburnt fuel and air in the
muffler.
Potential Causes:
a. misfire caused by partial failure in ignition system (single cylinder engines)
b. misfire caused by failure in ignition system, particularly complete failure of ignition for one cylinder
(2 cylinder V-twin engines)
c. after-fire/backfire caused by engine run-on after ignition shut-down due to failure of the engine
flywheel brake or carburetor fuel-cut solenoid
Scenario 7: Fire due to rich operation
Scenario Description: Fire due to operation with richer than designed A/F ratio in engine or catalyst.
Potential Causes:
a. fuel system degradation such as faulty carburetor, oil consumption or carburetor deposits
b. faulty or misapplied choke
c. air filter element mal-maintenance
d. debris blocks catalyst venturi
In addition, through the FMEAs, we assess the hazard patterns identified in Chapter 3 related to equipment fire and
explosion for an unspecified reason.
Chapter 3 laid out the basic NHH technology, discussed the current safety standards affecting design, and analyzed
in-use safety experience. This chapter identifies the key scenarios to evaluate and the causal factors to consider in
this assessment. We turn now to a description of the test methods used in the EPA laboratory and field work for
NHH engines.
1 Docket EPA-HQ-OAR-2004-0008-0310.
2 Docket EPA-HQ-OAR-2004-0008-0311.
3 Docket EPA-HQ-OAR-2004-0008-0312.
4 Docket EPA-HQ-OAR-2004-0008-0313.
5 Docket EPA-HQ-OAR-2004-0008-0314.
6 Docket EPA-HQ-OAR-2004-0008-0315.
7 Docket EPA-HQ-OAR-2004-0008-0316.
8 Docket EPA-HQ-OAR-2004-0008-0317.
9 Docket EPA-HQ-OAR-2004-0008-0318.
10 Docket EPA-HQ-OAR-2004-0008-0319.
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5. NHH Test Program
This chapter describes EPA's laboratory and field testing of Class I and Class II engines and equipment. We
describe the engines selected for testing, the engine's emissions control systems, and the test methodology used to
assess safety of prototype Phase 3 engines compared to current Phase 2 product.
A. ENGINE SELECTION
We selected a total of nineteen nonhandheld SI engines for laboratory and field testing in this study. Twelve of the
engines were Class I engines and were evenly split between side-valve and OHV engine designs from four different
engine families. Eight of the engines were Class II engines, all OHV engine designs from three different engine
families. General specifications for the Class I and Class II engines that were tested are provided in Tables 5-1 and
5-2. The engines were obtained by purchasing residential lawn mowers and lawn tractors from retail stores in SE
Michigan.
The two Class I side-valve engine families selected were certified to U.S. Federal Phase 2 Emission Standards,
without the use of emissions credit, as well as California Air Resources Board (CARB) Tier 2 Emission Standards.
Together these two engine families represented approximately 50% of all gasoline-SI Class I side-valve engine
sales, and they also represented 75% of gasoline-SI Class I side-valve engines certified to Phase 2 for the 2004
model year.
The two Class I OHV engine families selected for testing were also certified to the Phase 2 emission standards.
Together these two engine families represented approximately 46% of all gasoline-SI Class I OHV engine sales, and
approximately 50% of Class I, OHV engines certified to Phase 2 for the 2004 model year.
Table 5-1: Summary of Class I engine and equipment specifications. All of the engines tested were from
residential walk-behind lawn mower applications.
Engine ID numbers
(grouped by engine
family)
243, 244, 245
241,255
258
236, 246, 248, 249,
259
Emissions Standard (as
determined from
"emissions tag")
Federal Phase 2,
CARB Tier 2
Federal Phase 2, CARB
Tier 2
Federal Phase 2, CARB
Tier 2
Federal Phase 2,
CARB Tier 2
Advertised Power (h.p.)
5.5
6.75
6.0
6.0
Maximum Brake Power
(b.h.p)
3.2-3.7
4.3-4.5
3.0
2.9-3.0
Governed Speed @ 75%-
10% of maximum brake
torque (rpm)
2700 - 2900
2800-3100
3160-3260
2700-2900
Engine Displacement
(liters)
0.16
0.19
0.19
0.20
Valve Arrangement
OHV
OHV
Side-valve
Side-valve
Equipment Used for
Field Testing
Self-propelled walk-
behind lawn mower,
configured for
mulching
Not field tested -
obtained from self-
propelled walk-behind
lawn mowers
Not field tested -
obtained from a self-
propelled walk-behind
lawn mower
Self-propelled walk-
behind lawn mower,
configured for
mulching
33
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Two of the three Class II engine families selected for testing were both OHV designs, and together represent
approximately 24% of the gasoline-SI Class II Phase 2 engine sales for the 2004 model year. The third engine
family (engines 254 and 256) is a new design that has superseded one of the other Class II engine families tested
(engines 232 and 233) in high-volume consumer lawn and garden applications.
Table 5-2: Summary of Class II engine specifications. All of the engines tested were from residential lawn tractor
applications.
Engine ID numbers (grouped
by engine family)
231,251,252,253
232,233
254,256
Emissions Standard
(transcribed from "emissions
tag")
Federal Phase 2,
CARB Tier 2
Federal Phase 2,
CARB Tier 2
Federal Phase 2,
CARB Tier 2
Advertised Power (h.p.)
18.0
17.5
20
Maximum Brake Power
(b.h.p) @ 3060 rpm
12.8
12.4
11.8
Governed Speed (rpm) @
75%-10% of maximum
brake torque
2900-3100
2900-3150
3150-3350
Engine Displacement (liters)
0.5
0.49
0.6
Valve Arrangement
OHV
OHV
OHV
Equipment Used for Field
Testing
Residential lawn
tractor w/manual
transmission
Residential lawn
tractor w/manual
transmission
Residential lawn
tractor w/hydrostatic
drive
B. ENGINE MODIFICATIONS
This section describes the advanced emission control systems developed for the engines in section A. Note that
brief descriptions of tested configurations are also included within the tabulated emissions results in Appendix B.
Class I - 10 g/kW-hr systems
EPA conducted a literature search of existing catalyst-muffler designs for Class I engines. Three basic designs
covered under four separate patents showed promise for application to Class I Phase 2 engines. 1,2,3,4 These
designs share a number of common features, including:
• Compact design, being virtually the same size as some standard mufflers available for this engine
• Use of a passive exhaust venturi or exhaust ejector for introduction of secondary air
• Exhaust pulse dampening located upstream of the venturi
• Relatively small substrate volume
One of the catalyst-muffler designs1 was already in mass production by an OEM for use on European walk-behind
lawn mowers (Figure 5-1). EPA purchased several of these units and conducted a preliminary engineering and
chemical analysis. This particular design used a simple, stamped venturi for passive secondary air entrainment and
a small (approximately 20 cc or 1.2 in3) cordierite monolith with 400 cell/square-inch (cpsi) construction common
34
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in automotive applications. The catalyst substrate was retained with a common automotive-type matting material.
PGM loading was approximately 30 g/ft3 with a Pt:Pd:Rh ratio of approximately 5:0:1.
Following initial analysis of the OEM European catalyst-muffler, it was determined that an increase in catalyst
volume might be needed to provide sub-10 g/kW-hr HC+NOx emissions at high hours after taking into
consideration an expected degree of catalyst oil poisoning and degradation of engine-out emissions. Initial
prototype samples were fabricated by lengthening the muffler by 20 mm and doubling the substrate volume within
the production European catalyst-muffler (Figure 5-2). Although increasing substrate volume in this manner
increases exhaust backpressure, for the engine family that this catalyst muffler was tested with there was virtually
identical peak power output at wide-open-throttle (WOT) at the A-Cycle test speed (3060 rpm) for both the
modified catalyst-muffler and the OEM muffler. Similar results were achieved with other catalyst muffler
configurations that tested with other engines. Thus the backpressure increase that resulted from the use of catalysts
within the exhaust systems was not sufficient to impact power output. This may have been in part due to the
relatively small catalyst volumes tested, the geometry of the substrates (generally much lower cell density than
automotive substrates, and also generally "shorter-fatter" geometries), and the exhaust restriction of the substrates
relative to that of other parts of the exhaust system.
Venturi air inlets
Outer shell
20 cc, 400 cpsi cordierite catalyst
substrate with automotive matting
Inner shell
Center divider
2-stage baffle immediately
downstream of exhaust port
Figure 5-1: Details of an OEM catalyst-muffler from a European walk-behind lawn mower application.
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Catalyst-muffler reconfigured
with a second 20 cc substrate
(40 cc total), repositioned inlet
and modified internal baffles.
This is the unit tested with
engine 241.
Catalyst-muffler reconfigured
with a second 20 cc substrate
(40 cc total). This is similar to
the configuration tested with
engine 258.
OEM European Catalyst-muffler
Figure 5-2: Catalyst-muffler from Figure 5-1 (bottom) modified with additional catalyst volume (center) and with
modifications to the inlet and internal baffles to allow use with engine 241 (top).
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The lengthened European catalyst-muffler was further modified by changing the exhaust inlet to allow its use on an
additional engine type (see Figure 5-2). Additional catalysts with different formulation and construction were
obtained from major North American catalyst suppliers (Figure 5-3). Catalyst substrates tested included:
1. 34 cc, 100 cpsi metal monoliths;
2. 44 cc, 200 cpsi metal monoliths;
3. metal-mesh substrates;
4. 22 cc 200 cpsi metal monolith with a 20 mm dia. X 73 mm long tubular pre-catalystc; and
5. the aforementioned 400 cpsi cordierite monoliths, doubled to provide approximately 40 cc catalyst volume
(Figure 5-2).
Ceramic monoliths have been used successfully in OEM applications in Europe, and have proven durable provide
appropriate matting and support for the substrate is provided within the catalyst muffler design. Metal monoliths
are more resistant to shock than ceramic monoliths, and may be easier to package into catalyst mufflers for some
applications, but are generally more expensive. Metal mesh substrates approach the cost of ceramic monoliths, and
have acceptable durability due to recent improvements in substrate packaging and washcoat adhesion. All three
substrate types were tested because they represent the range of types that EPA expects to be used to comply with the
California Tier 3 and the expected Federal Phase 3 standards for different applications.
Most of the prototype catalyst-mufflers contained catalyst substrates with different construction and PGM loading in
the OEM European catalyst-muffler housing. Some designs also incorporated additional heat-shielding or shrouding
(see Figure 5-4). One prototype catalyst-muffler, tested with engine 243, was completely fabricated from scratch
using a tubular venturi and a general layout similar to previous designs (Figure 5-5).3,4 An additional catalyst-
muffler for engine 249 was tested without the use of secondary air and was fit entirely within the standard OEM
muffler.
The tubular pre-catalysts were installed upstream of the secondary-air-venturi, with a 22 cc 200 cpsi monolith
installed downstream of the venturi (Engines 243 and 255). The catalyst-muffler tested with engine 255 is shown in
Figure 5-6.
The PGM loadings on the monolithic substrates ranged from 30 g/ft3 to 50 g/ft3. Generally, higher loadings were
used with smaller substrate volumes to provide a similar overall level of PGM surface area within a smaller
packaging volume. The loading ratio of 5:0:1 (Pt:Pd:Rh) as used with the production catalyst-muffler was the most
common, but loading ratios ranging from 4:0:1 to 0.33:3.66:1 and one Rh-only only were also tested. The specific
loading of any particular catalyst tested and its relationship to particular data results was considered proprietary, but
general trends in emissions versus PGM loading and loading ratio will be discussed within the results section.
When selecting catalyst secondary air configurations to test with each engine, the primary design target was to
achieve less than 10 g/kW-hr HC+NOx emissions at the 125 hour useful life level because this is the most common
for residential walk-behind lawn mowers. A maximum of 7.0 g/kW-hr HC+NOx target was set for low-hour
emissions performance for the Class I residential lawn mower engines to allow for engine and catalyst degradation
over the 125-hour useful life requirements for these engines. Secondary design targets included minimization of
CO oxidation at moderate to high load conditions (e.g., A-cycle modes 1 and 2) and exhaust system surface
temperatures comparable to those of current Phase 2 OEM systems.
The OEM versions of engines 243, 244 and 245 were equipped with mufflers enclosed in shrouds that directed air
flow across the surface of the mufflers for additional cooling of the exhaust system. The catalyst-muffler systems
developed for engines 243, 244, and 245 were equipped with shrouds providing a similar function, but with the air-
outlet of the shroud relocated in order to provide improved air flow over the outer surface of the catalyst-muffler.
0 A tube with a single, perforated channel in which all of the internal surfaces are washcoated.
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These engines also were equipped with an exhaust ejector over the exhaust outlet of the catalyst-mufflers to both
cool the exiting exhaust gases and to provide for additional heat rejection from the surface of the shroud. A similar
shroud and ejector system was tested with engine 249.
Figure 5-3: Some of the catalyst substrate types evaluated by EPA with Class I and Class II engines included (from
left to right) 100 cpsi metal monoliths (in 50 mm and 33 mm diameters); 200 cpsi metal monolith; catalyzed tube
pre-catalysts (in 20 nun and 25 mm diameters); 400 cpsi coridierite (square-oval and round) and metal-mesh. The
50 mm diameter catalyst on the far left was used with Class II engine test configurations. The remaining catalysts
were tested with Class I engines.
Figure 5-4: Engine 236 with catalyst-muffler installed on dynamometer test stand at the U.S. EPA National Vehicle
and Fuel Emissions Laboratory (NVFEL). The muffler was derived from a production European catalyst-muffler.
It was modified to allow installation onto a different engine type, and a 44 cc metal monolith catalyst was
substituted for the original ceramic monolith. A small heat shield was added to prevent heating of the intake
manifold. The catalyst-muffler configurations for engines 246 and 249 were similar, but with different catalyst
substrates and PGM loadings.
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Modified muffler
shroud
Exhaust
ejector
OEM muffler
shroud
OEM exhaust
outlet
Figure 5-5: Engine 243 (left) equipped with a catalyst-muffler, passive venturi-secondaiy-air, muffler air shroud
and exhaust ejector compared to a similar engine (right) with the OEM muffler and muffler air shroud.
Figure 5-6: Catalyst-muffler (left) and OEM muffler (right) tested with engine 255.
Approximate location of 22cc main catalyst
vst I
20mm dia. tube pre-catalvst
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Class II - 3.5 g/kW-hr HC+NOx system
Engines 231 and 232 were fitted with an ECU and components originally developed for the Asian motor-scooters
and small-displacement motorcycles. The fueling logic was speed-throttle-based with barometric pressure (BP) and
MAP correction capability. The OEM ignition system and mechanical speed governing were maintained.
The fuel system consisted of an electronic fuel pump, external regulator, and small fuel injector. The fuel pump
has a flow capacity of 2.5 grams per second at 250 kPa, which was the regulator's pressure setting. The fuel pumps
used were also designed with power consumption minimized to 1 amp. Engine 231 used an in-line fuel pump and
engine 232 used an in-tank fuel pump. The ECU controlled the fuel pump with a pulse-width-modulated low side
drive. The injectors used were a two-hole design with 12 Degree spray cone, and has a static flow of 1.4 grams per
second at the 250 kPa regulated fuel pressure.
The sensors for the ECU were minimized to a throttle position sensor (TPS), air charge temperature sensor, oil
temperature sensor, ECU board-mounted MAP sensor, and crankshaft variable reluctance sensor for a two-tooth
crankshaft target. The throttle position sensor (TPS) required a zero-return spring force to avoid interference with
operation of the engine's mechanical governor. Initially a springless linear potentiometer mounted on the governor
linkage primary control arm was used for TPS. As development progressed, this unit was replaced with a TPS
sensor from an automotive electronic throttle control module.
Catalyst formulations and the air-to-fuel ratio calibration of the open-loop electronic fuel injection (EFI) system
were selected in a manner that prioritized NOx reduction and HC oxidation over CO oxidation. The catalyst-
mufflers were selected for further testing by first screening six different catalysts with varying washcoating
formulations, substrate volume and substrate construction. Specific PGM loadings, loading ratios, and catalyst
construction for the catalysts used in this study were proprietary, but in general loadings were between 50 and 70
g/ft3, and loading ratios varied from 0:5:1 to 5:0:1. Both 200 cpsi and 400 cpsi metal-foil monolithic catalyst
substrates were tested. Catalyst volume varied from approximately 50% to 55% of the engine displacement. A
typical catalyst-muffler is shown in Figure 5-7.
Details of the installation of modified components as installed on a lawn tractor chassis are shown in Figure 5-8.
The engine air shrouding was extended and the routing of cooling air through the chassis of the lawn tractors was
changed to route the cooling air from the engine fan, downstream of the engine, over the catalyst-muffler and
exiting either to the side or the front of the lawn tractor. The resulting forced air cooling reduced exhaust system
temperatures and also prevented debris build-up in the areas adjacent to the exhaust system components.
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Figure 5-7: The photos on the left show the layout of the 3-cliamber OEM Nelson lawn tractor muffler. The
mufflers used with the other Class II lawn tractor engines were very similar except for the inlet-pipe configuration.
OEM mufflers were sectioned and a catalyst monolith was installed between the upper and lower chambers. The
outlet was relocated to facilitate use with an exhaust ejector, and the inlet was flanged to allow use of the catalyst-
muffler in different chassis configurations and to provide the additional clearance necessary for testing the catalyst-
muffler while the engine was installed on the dynamometer. The catalyst mufflers for the 8.0 g/kW-hr
configurations fit entirely w ithin the OEM muffler (upper right and center right). The catalyst-mufflers fabricated
for the 3.5 g/kW-hr configurations (example, lower right) had a cylindrical section that extended above the main
body of the muffler to allow space for additional catalyst volume, and the third chamber was relocated to the top
half of the muffler. Use of an oval monolith would have allowed packaging within the OEM muffler space, but an
appropriate-size oval monolith was not available at the time of testing.
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ECU with
integral MAP
sensor
Throttle-body
injection
Exhaust Approximate
ejector location of catalyst
outlet and muffler
Extension of engine
air- shroud to direct
air flow towards
muffler location
Figure 5-8: Engine 232 installed in a lawn tractor chassis, showing details of the engine and chassis modifications.
The exhaust ejector extends for nearly the entire width of the cavity in which the muffler is housed.
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Class II - 8.0 g/kW-lir HC+NOx systems
The tested configurations of engines 253 and 254 used OEM carburetors and air-to-fuel ratio calibration. No
changes were made to the base Phase 2 configuration of the engine other than those necessary to install the catalyst-
mufflers. Four different catalysts were initially tested with varying PGM loading, loading ratio, substrate volume
and substrate construction, and two were selected for operation in the field. Specific PGM loadings, loading ratios,
and catalyst construction for the catalysts used in this study were proprietary, but in general loadings were between
30 and 40 g/ft3, loading ratios were approximately 5:0:1, and both 200 cpsi metal-foil and 400 cpsi ceramic
monolithic catalyst substrates were tested. Availability of appropriately sized and coated substrates had more
impact on choice of substrate material since performance was comparable between the two substrate types at this
level of emissions control. The catalyst volumes varied from approximately 25% to 40% of the engine
displacement. Photographs of the catalyst-muffler configurations for engines 253 and 254 are shown in Figures 5-9
and 5-10.
Figure 5-9: Engine 253 undergoing dynamometer testing with catalyst-muffler installed. The addition of a single
250cc 400 cpsi ceramic monolith into the OEM muffler and minor physical modifications to the exhaust-muffler
were the only changes made to this Class II, Phase 2 engine. The exhaust-lambda sensor mounted into the exhaust
pipe was used for laboratory measurement purposes only.
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Exhaust
ejector inlet
Exhaust
ejector outlet
Figure 5-10: Engine 254 undergoing dynamometer testing with catalyst-muffler installed (left) and installed in a
lawn tractor chassis (right). The addition of two 79cc, 100 cpsi metal-monolith catalysts into the OEM muffler and
minor modifications of the exhaust-muffler were the only changes made to this Class II, Phase 2 engine.
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C. INFRARED THERMAL IMAGING
The primary experimental method used for comparison of exhaust system, engine, and equipment surface
temperatures during laboratory and field testing was via infrared (IR) thermal imaging.5,6,7 IR thermal imaging is
based on principles originally developed for target finding and surveillance by the U.S. Department of Defense. IR
still images in the laboratory were obtained using an "IR Snapshot" IR imager. Full motion IR imaging in the
laboratory and in the field was obtained using an "IR Flexcam T" infrared imager. Both IR imagers correct the IR
radiance from any single point on the target surface in a manner that a captures precise, accurate representation of
the true temperature at that location. The following assumptions are necessary to allow this sort of analysis:
1. The IR absorption of the air path between the target and the instrument is negligible, and
2. No IR energy is transmitted through the target from sources behind the target.
In order to correct for reflection of the ambient background, it was necessary for the operator of the imager to input
the background temperature. This was monitored in the laboratory and in the field using J-type thermocouples. It
should be noted that during laboratory testing EPA-NVFEL test cells are held at a nearly constant background
temperature of 25 °C ± 1 °C.
The operator of the imager also provided inputs for the targets estimated emissivity. All the primary temperature
targets (Mufflers/Catalysts) were painted with a high temperature flat-black paint with a dull matte finish. This was
used to even out the emissivity over the surface of the object as well as to increase the value of the emissivity of the
object. An emissivity of 0.9 was used for this project. To check the validity of the emissivity assumptions, a
comparison of the surface temperature measured with the IR imager was made to a known surface temperature
measured with a J-type thermocouple. The temperatures were within 1% of agreement.
The IR imagers have the following general specifications:
• They use microbolometer detectors that require no cryogenic cooling.
• The detector elements are square and are located in a rectangular grid.
• The optical path of the camera includes an appropriate band-pass filter for the temperature range of
interest.
• The IR Snapshot Camera has a NIST traceable calibration from 10 °C to 1200 °C with accuracy of 2 °C or
2% of reading.
• The IR FlexCam has a NIST traceable calibration from 0 °C to 600 °C with accuracy of 2 °C or 2% of
reading.
• The lenses for both cameras are made from germanium and are anti-reflective coated for high transmission
in the temperature range of choice.
Both imagers were calibrated using NIST traceable temperature standards prior to the beginning of the IR thermal
imaging tests and at the end of the test program. No change to the calibration curve of either instrument was
necessary between the first and second set of calibrations. Calibration results are provided in Appendix A.
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D. LABORATORY TEST PROCEDURES
Operation over the Federal A-Cvcle
U.S. Federal Phase 2 A-cycle test (table 5-3) was used to gather emissions data and to provide a broad range of
engine operational conditions under which exhaust system surface temperatures could be measured using the
infrared thermal imaging equipment.8 The engine dynamometer test cell was kept a temperature of 25 °C ± 1 °C,
with an absolute humidity of 75 grains-H20/lbm-dry-air. Tests were conducted using a 20 kW (maximum) Edy-
current dynamometer.
IR still images were used during laboratory testing to allow more precise determination of peak temperatures and to
allow further flexibility within the temperature analyses than was possible with the full-motion-video IR imaging.
Some of the engines tested were equipped with a user-selectable governor speed setting. For these engines the
speed setting was kept in the 100% position for A-cycle modes 2, 3, 4, and 5. The user-selectable governor speed
setting was set to 0% (low-speed idle) for mode 6.
Some of the engines had no provision for user adjustment of the governor speed. For these engines, engine
operation occurred with the engine governor controlling engine speed for modes 2, 3, 4, 5 and 6 with no
modifications or adjustments to engine governor operation. Mode 6 was run as a high-speed-idle condition.
In all cases, mode 1 of the A-cycle was obtained via bypassing the governor and operating the engine with a fixed
wide-open-throttle (WOT) and the dynamometer control set to the A-speed (3060 rpm). Torque control provided a
coefficient of variance of 1 % or less in measured torque at WOT.
At each of the 6 steady-state modes of the A-cycle test, IR images were acquired following stabilization of cylinder
head temperature to a value of approximately:
AT/At < 1 °C/minute
where AT is the change in temperature measured with a K-type thermocouple embedded within a sparkplug gasked
for cylinder head temperature measurement, and At is the measured time interval. Depending on the engine tested,
stabilization required between five and ten minutes in A-cycle Mode 1 and approximately five to six minutes for
Modes 2 through 6.
Table 5-3: EPA A-Cycle Intermediate Speed Steady-State Engine Dynamometer Test
EPA A-cycle Mode
1
2
3
4
5
6
Engine Speed (rpm)
3060
100%
governed
100%
governed
100%
governed
100%
governed
0%
governed
(low idle)
Torque
100%
(@ WOT)
75%
50%
25%
10%
0
Cycle Weighting Factor
9%
20%
29%
30%
7%
5%
Notes:
The engine speed governor was disabled for Mode 1, and the engine was operated at WOT with the
dynamometer in speed-control mode set to 3060 rpm. Modes 2-5 were operated with the engine speed
governor set to its 100% position and with the dynamometer in torque-control mode, with percent torque
based on the average Mode 1 value. Mode 6 was a no-load, low idle test point for both Class II engines, and
for engines 243, 244, and 245. Mode 6 was a no-load, high-idle test point for the remaining engines since
these were not equipped with a user-selectable speed setting for the engine governor.
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The limiting factor in the uncertainty of the IR surface temperature measurements was the accuracy (± 2% of point)
of the thermal imagers rather than test to test variability, thus single tests were conducted for each tested
configurations. Catalyst-muffler and OEM muffler configurations for each engine were conducted within one test
day.
Hot Soak Testing
Part way through the test program, EPA began conducting hot soak tests to compare the rate of cooling of catalyst-
muffler equipped engines to that of engines equipped with OEM mufflers. Hot soaks are timed measurements
which are made following the engine shut-down after sustained operation. Laboratory hot soak tests were
conducted following sustained, temperature stabilized operation at 100% load at WOT conditions (A-cycle Mode 1)
and following sustained, temperature stabilized operation at 50% load (A-cycle Mode 3). Hot soak tests were also
conducted in the field following sustained grass cutting operations (see the section on "Field Operation" in this
chapter). The 100% load point represented a worst case test with the highest obtainable exhaust system surface
temperatures. The tested engines were equipped with engine speed governors that could only sustain WOT
momentarily during normal operation. The 50% load point was more representative of temperatures achieved
during moderate to heavy grass cutting conditions, and resulted in comparable surface temperatures to temperatures
measured during field testing. For either the 100% or 50% load operational point, the engine was operated until
stable cylinder head and oil temperature conditions were achieved. Stabilization required approximately six to eight
minutes of operation for the WOT condition and approximately five to six minutes for the 50% load condition,
depending on the engine. The ignition to the engine was then turned off and a timer was started. Infrared thermal
"still" images were taken initially at 30 and 60 seconds following engine shut-down and at 1-minute intervals
thereafter. Manufacturer's recommendations within equipment owner's manuals for equipment using engine-
mounted fuel tanks (e.g., walk-behind lawn mowers) typically recommended waiting 2-minutes after engine shut-
down before opening the cap of the fuel tank. Thus peak surface temperatures 2-minutes after engine shut-down
were compared to the auto-ignition temperature of regular-grade gasoline (approximately 250 °C), particularly for
the hot-soak tests from the 50% load point and for tests of Class I engines that used fuel tanks mounted to the
engine. The manufacturer's recommendations for lawn tractor refueling did not stipulate a specific waiting time
prior to refueling. The 2-minute period appeared to adequately represent common usage of residential lawn
equipment, so this point during the hot soak period was also used for comparison of the Class II engine and lawn
tractor configurations.
After-fire Testing
Two engine manufacturers identified after-fire due to engine run-on following a shut-down under high inertial load
to be a potential safety issue. After-fire can occur when an engine is turning a high inertial load (e.g., a generator).
If the ignition is turned off, and there is no means to physically stop engine rotation, then the inertial load will
temporarily keep the engine spinning. The mechanical governor will pull the carburetor throttle wide open, which
will both reduce engine braking and can allow a full air-fuel charge to enter the engine. Because the ignition is shut
off, the full air-fuel charge exits the exhaust valve and enters the muffler. The air-fuel charge can ignite on hot
surfaces and an "after-fire" flame can propagate through the muffler and exit the muffler or tailpipe. Proper
engineering design typically prevents run-on after-fire from occurring. Most Class I and Class II engines used in
high-inertia applications are equipped with either
1. a flywheel brake to rapidly stop the engine from spinning (within 3 seconds or less), or
2. a fuel cut solenoid that interrupts fuel flow from the float bowl to the carburetor venturi, thus preventing
fuel from flowing into the intake port and out the exhaust port after the ignition is turned off.
Run-on after-fire was encountered with carbureted, catalyst-equipped automobile and light-truck engines in the
1970s and 1980s, particularly with manual transmission vehicles coasting down long grades. One way that the issue
was addressed for these applications was to build simple flame arresting properties into the mufflers.9 Flame
arresting designs route the exhaust gases through channels, passages and/or perforated metal baffles that are
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designed to absorb heat from the gases and thus extinguish a flame front. Flame arresting properties can be directly
incorporated into the sound attenuating baffles within the muffler.
Engine 241 was used for after-fire testing. The after fire testing replicated conditions of engine run-on due to an
inertial load on an engine after the ignition is shut off. Testing occurred at near the end of the regulatory useful life
for the engine (125 hours) following dynamometer aging of the engine and catalyst-muffler. This particular engine
was tested with a standard OEM "shallow-box" style muffler with a central baffle-plate perpendicular to the muffler
inlet that divided the muffler approximately in half, similar to the OEM muffler shown on the right half of Figure 5-
6. This engine and OEM muffler was chosen because it had relatively high exhaust port temperatures and because it
demonstrated a consistent tendency for after-fire immediately following engine shut-down during WOT hot-soak
tests that were conducted. The engine was also tested with a catalyst-muffler with venturi secondary air and 40 cc
cordierite monolith catalyst similar to the one pictured at the top of Figure 5-2. Flame arresting properties were
incorporated into the two-stage baffle located upstream of the secondary air venturi.
The engine was operated at the 100% load, WOT condition on an Eddy-current dynamometer until stable cylinder
head and oil temperature conditions were achieved. The WOT condition was chosen to attain the highest
achievable exhaust gas temperatures and exhaust system surface temperatures. The engine's flywheel brake was
fixed into a disengaged position. The engine ignition was shut-off and the dynamometer load was simultaneously
dropped to zero. The engine continued to spin due to the inertia of the dynamometer for approximately 7 seconds
before stopping completely. This allowed air and fuel to be drawn through the engine and into the exhaust system
without combustion in the engines combustion chamber. The condition simulated shut-down with a high inertial
load and with failure of a fuel-cut solenoid (typically used with generator sets and lawn tractors to prevent after-fire)
or failure of a flywheel brake (used with all walk-behind lawn mowers for blade safety and to prevent after-fire).
Note that federal regulations require cutting blades of walk-behind mowers to stop within 3-seconds of
disengagement of the blade control, and 1- to 2-seconds is typical. 10 There is currently no federal requirement
regarding blade-stopping time for ride-on lawn equipment. There is an ANSI recommendation of 5 seconds for
blade stopping following disengagement of the blade control. 11
Digital video of the after-fire tests was acquired to allow direct comparison of the OEM and catalyst-muffler
configurations. The test was repeated four times for the OEM muffler configuration. Immediately following the
OEM muffler testing, the test was repeated four times using the catalyst muffler.
Misfire Testing
Engine 255 was used for testing under conditions of partial ignition misfire. An optical encoder providing 360
counts per engine revolution (one crank-angle-degree resolution) was installed onto the engine crankshaft output. A
laboratory controller temporarily grounded the ignition coil cut-off circuit based on input from the optical encoder
and the degree of misfire desired. Initially, encoder data was acquired for 360 counts per revolution at a particular
engine operating condition, and a count of up to 1000 engine combustion cycles (2000 engine revolutions) was
initiated. When the ignition coil circuit was grounded, a complete 720 crank angle degrees (CAD) (or two complete
crankshaft revolutions) of ignition misfire would occur. This alleviated the need to track top dead center (TDC) and
spark timing. The series of 1000 cycles could be continuously looped to allow continuous operation at a particular
percentage of ignition misfire. Misfire could be made in equal intervals, so two misfires in 1000 cycles could occur
at cycles 500 and 1000. Similarly, three misfires could occur following 333, 666, and 999 cycles. Other misfire
interval combinations were also evaluated. The cycle count of 1000 was chosen arbitrarily and could be adjusted to
other values to check the effect of duration between misfires or to allow a higher rate of misfire resolution. The
final configuration used during testing utilized random number generation to randomly select the specific cycles on
which misfire would occur, while still allowing selection of the total percentage of misfire events. For example,
during prove-out of the misfire generation, the system was configured to cause 3% of the ignition firings to misfire
over 100 complete engine cycles and the random number generator provided misfire occurrences at cycles 12, 25,
89.
The next step was to determine a reasonable operating condition (speed and load) for operating the engine under
partial misfire. An AC motoring dynamometer was used to map the load provided by the cutting blade during
engine operation over a range of typical engine speeds. This essentially provided a torque curve analogous to a
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"propeller curve" for the conditions under which the cutting blade was spinning but not cutting grass. The cutting
blade torque curve generated was thus established as the minimum torque point for engine operation. The engine
was operated with engine speed controlled by the engine governor, and misfire was initially induced during
operation on the dynamometer along the generated cutting blade torque curve. Operation of the engine beyond 25%
ignition misfire resulted in extremely erratic engine operation and vibration and premature failure of the coupling
between the engine and the dynamometer. When operated at the 25% misfire condition, the erratic engine operation
would be immediately noticeable to the operator, causing engine stumbling, audible misfire and backfire, and
greatly reduced ability for the engine pick up load. Sustained operation at 25% misfire was chosen as the
operational point for analysis of exhaust system surface temperatures. Even this operational point should be
considered a conservative estimate of a maximum misfire level since grass cutting operations and the power-take-
off for the wheel drive system would require more engine torque output than the cutting blade torque curve used
during testing, which was approximately equivalent to torque of the 25% load A-cycle mode 4 test point at the
speed encountered during misfire.
The engine was tested with the OEM muffler and the catalyst-muffler shown in figure 5-6. Following initiation of
sustained 25% misfire and stabilization of exhaust gas temperatures measured at the exhaust port, IR thermal images
were taken of both the OEM muffler and catalyst-muffler configurations to allow comparison of surface
temperatures.
Simulated Rich Operation
Engine 255 was also used for simulated rich operation. A carburetor was modified by changing the main jet to
provide an air-to-fuel ratio number approximately 1.0 to 1.5 units richer than the standard carburetor jetting. This
air-to-fuel ratio was consistent with test results obtained from a similar engine previously tested by EPA (engine
#1514) that returned from field operations running excessively rich. The rich operation was found to be due to a
float-valve that was partially contaminated with debris. 12 The engine was tested in this condition over all 6 modes
of the EPA A-cycle and with both an OEM muffler and with the same catalyst-muffler configuration used for the
misfire testing.
E. FIELD OPERATION
Field operation was conducted to:
1. Obtain operational experience with both OEM and catalyst-equipped engine configurations
2. Provide an accelerated means of accumulating engine hours to assess the emissions of both OEM
Phase 2 and catalyst-equipped engines at either mid-life or near the end of useful life
3. Provide a means to assess surface temperatures of lawn care equipment during grass cutting operations
with the engines installed on equipment chassis
Installation into a chassis was particularly important for the IR thermal imaging analysis of the lawn tractor
applications. The chassis included heat shielding and the ejectors used with the catalyst-muffler configurations
were installed onto the chassis. Cooling air-flow downstream of the engine was also routed through the chassis and
over the catalyst-mufflers to improve heat rejection. These subsystems could not be adequately duplicated on the
engine dynamometer.
The engines were initially run for at least three hours either on the dynamometer, or on the mower-decks while
cutting grass. An additional two to seven hours of dynamometer run-time followed this. Emissions were monitored
during dynamometer testing until stabilized (-10% coefficient of variance in brake-specific HC+NOx for three
repeated measurements), which typically required between five and ten hours of total operation from the new
condition, depending on the engine. The final three repeated measurements were taken as the "low hour" emission
baseline.
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The engines were then installed onto standard walk-behind lawn mowers. For the initial stages of field operations, a
field test apparatus was constructed that could pull up to nine walk-behind mower decks simultaneously through
large fields in Southeast Michigan using a garden tractor (Figures 5-11 and 5-12) to allow a more rapid
accumulation of hours of operation in the field cutting grass. This was done primarily to accelerate the operation of
a large number of Class I, Phase 2 lawn-mowers to generate high-hour emissions results for the purposes of
generating emissions inventory data. Emissions results from the initial stages of field operation can be found in the
Docket to the Nonroad SI Engine Phase 3 rule. 13 The apparatus was equipped with hydraulics that lifted the front
of each mower up when turning around to simulate similar turn maneuvers used during typical operation.
Subsequent stages of field operations, which included all of the Class I and Class II engines for which field data is
reported in this study, were conducted in South Central Texas during the Spring of 2005 (Class II only, Figure 5-
13), in Southwest Tennessee during the fall of 2005 (Class I and Class II, Figure 5-14), and in Florida in early 2006.
In these stages both lawn mowers and lawn tractors were used, and they were operated by individual operators
instead of using the field test apparatus. Mowing was conducted with the lawn mowers and lawn tractors in an
echelon formation in large fields to prevent debris from contacting adjacent equipment. Lawn mowers and lawn
tractors were also segregated to operate in different sections of each field. A total of six walk-behind lawn mowers
were used in grass cutting operations until they reached approximately 110 hours of operation. Of the six lawn
mowers, three used side-valve engines equipped with catalyst-mufflers, two used OHV engines equipped with
catalyst-mufflers, and one used a side-valve engine equipped with an OEM muffler. The two lawn mowers
equipped with OHV engines and catalyst-mufflers were also equipped with air shroud designs that directed air from
the engine cooling fan that exited from the engine cylinder over the outer surface of the catalyst-muffler in a manner
similar to the OEM air shroud design used with these particular lawn mowers. Three of the catalyst-muffler
equipped lawn mowers (both units with the OHV engines and one with the side-valve engine) were additionally
equipped with exhaust ejectors to both reduce the temperatures of the exhaust gases leaving the catalyst-muffler and
to improve heat rejection from muffler and/or air shroud surfaces. Both lawn tractors were equipped with
modifications to engine air shrouding and with exhaust ejectors (see Figure 5.8).
During field operation, up to eight hours of engine run-time per day was possible. Large, level fields were cut. The
run sequence each day was as follows:
1. Each day started by checking the lubricating oil (and adding if necessary) and topping off the fuel tanks.
2. The engines were then started and grass cutting operations commenced. During a workday, engines were
only shut down for refueling or poor weather or cutting conditions. Cutting operations ranged from 2 hours to 9
hours per day, depending on weather.
3. During refueling, oil levels were monitored, and engine oil was added if necessary. Oil consumption was
monitored during the Tennessee field tests.
4. At the end of each full day of operation, debris was cleaned from the mower decks. During the initial stage
of field testing (southeast Michigan), compressed air was used to clean the mower decks and intake air filters.
During the later stages of field operation, mowing decks were brushed clean and air filters were not serviced
between normal maintenance intervals unless a loss of engine performance was noticed by the operator. If air filter
service was required between service intervals due to visible blockage, it typically involved removing the intake air
filter and brushing accumulated debris from the filter prior to reinstallation (engines 243, 244, and 245 only).
5. Major maintenance consisted of changing the lubricating oil (using manufacturer-specified lubricants)d,
air-filters, and spark-plugs at the manufacturers-specified intervals. When intervals were specified by season
instead of hour level, 25-hours of operation was used as one season.
Field operation continued for a total of approximately 110 hours for the Class I engines and 240 hours for the Class
II engines. Afterwards, the engines were removed from the lawn mowers or lawn tractors for dynamometer testing.
d Lubricants were SAE 30 API SL or SAE 10w30 API SM (depending on application). Manufacturer's API
specifications were API SF or better.
50
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¦ KMB&, .
BSjt
• r'r^teJP
I •mm
Figure 5-11: Field test apparatus with lawn mowers cutting grass in Southeast Michigan, late summer 2004. The
apparatus was equipped hydraulic rams to lift the front of each mower to simulate turns at 10-meter intervals. The
mower decks were set to a cutting height of three inches while cutting grass that was approximately five to six
inches in length.
Figure 5-12: The lawn mowers were stopped for refueling, debris clean-off, and basic checks each hour. This took
approximately 30 minutes, so the mowers were cycled between one hour on and half an hour off with a maximum
of eight hours of actual mower running time per day, depending on weather. Regular (87 octane) unleaded pump
gasoline was supplied to the work site using portable plastic gasoline cans with a trigger-nozzle, but no automatic
shut off.
51
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Figure 5-13: Lawn tractor cutting grass in Central Texas in the spring of 2005. Regular (87 octane) unleaded
pump-gasoline was supplied to the work site using portable plastic gasoline cans with pour spouts. Cutting
conditions were relatively dry with a high amount of debris. Grass length varied from approximately five inches to
approximately 18 inches. Mower decks were set to a cutting height of approximately three inches.
52
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Figure 5-14: Lawn mower and Lawn tractor cutting grass in Southeast Tennessee in the fall of 2005. Regular (87
octane) unleaded pump-gasoline was supplied to the work-sight using portable plastic gasoline cans with pour
spouts (same fuel cans as in Texas - see Figure 11). Conditions were cool and wet with a large amount of debris.
Grass length varied from approximately eight inches to approximately 18 inches. Mower decks were set to a cutting
height of approximately three inches. Both wet and dry cutting conditions were encountered. Dry cutting
conditions were accompanied with high levels of debris.
Figure 5-15: Lawn mower and Lawn tractor cutting grass in Florida in early 2006. Regular (87 octane) unleaded
pump-gasoline was supplied to the work-sight using portable plastic gasoline cans with pour spouts. Conditions
were hot and dry with tall try grass and a large amount of debris. Grass length varied from approximately five
inches to approximately twelve inches. Mower decks were set to a cutting height of approximately three inches.
53
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Acquisition of IR Thermal Images in the Field
Both still images and full-motion video infrared imaging was used to collect surface temperature data during grass
cutting operations in the field in Southwest Tennessee and Florida. Full motion video infrared imaging was used to
allow comparison of OEM and catalyst-equipped lawn tractors and lawn mowers while cutting grass in large
(approximately 200-acre), level fields. The video IR imager was mounted onto a tripod and the cutting paths of the
equipment were arranged such that one piece of equipment passed into the range of view for the imager. The
operator of the imager then tracked the equipment for approximately 20 linear feet. Approximately halfway
through, the equipment stopped for 5 seconds directly perpendicular to the imager at a position marked onto the turf
surface to temporarily allow a higher resolution, more precise IR image for each pass in front of the imager. Passes
were taken from both sides of the lawn tractors, and from the exhaust-muffler side of the lawn mowers.
Both full motion video and still imaging was used to measure surface temperatures during timed hot soaks
following sustained (approximately 30-45 minutes) grass cutting with both the lawn tractors and the lawn mowers.
Both Ml motion video and still imaging were also used to measure turf surface temperatures during extended idling
of lawn tractors. Initial measurements conducted during equipment set-up that showed that Turf surface
temperatures underneath and in front of the lawn tractor stabilized after approximately five minutes of idling with
the engine speed setting adjusted to "high". Brief IR measurements of turf surface temperatures following 5 to 30
minutes of idling showed no significant difference versus just five minutes of idling, thus the final measurements of
turf surface temperatures were taken for approximately two minutes of idling following an initial five minutes of
idle for turf surface temperature stabilization.
1 P. A. Sandefur, W.M. Kindness, "Catalytic Converter Having a Venturi Formed From Two Stamped Components",
U.S. Patent No. 5,548,955, 1996.
2 G.J. Gracyalny, P.A. Sandefur, "Multi-Pass Catalytic Converter", U.S. Patent No. 5,732,555, 1998.
3 Y. Yamaki, H. Kaneko, K. Nakazato, "Engine Exhaust Apparatus", U.S. Patent No. 5,431,013, 1994.
4 A. Shiki, M. Nakano, H. Nakazima, "Muffler with Catalyst for Internal Combustion Engine", U.S. Patent No.
4,579,194, 1986.
5 V. Vavilov, V. Demin, "Infrared thermographic inspection of operating smokestacks", Infrared Physics &
Technology, Volume 43, Issues 3-5 , June 2002, Pages 229-232.
6 R. Monti, G. P. Russo, "Non-intrusive methods for temperature measurements in liquid zones in microgravity
environments", Institute of Aerodynamics ", Acta Astronautica, Volume 11, Issue 9 , September 1984, Pages 543-
551.
7 H. Wiggenhauser, "Active IR-applications in civil engineering", Infrared Physics & Technology, Volume 43,
Issues 3-5 , June 2002, Pages 233-238.
8 Title 40, U.S. Code of Federal Regulations, Part 90, Subpart E, Appendix A.
9 S. Mizusawa, "Silencer for and Internal Combustion Engine", U.S. Patent No. 4,124,091, 1978.
10 Title 16, U.S. Code of Federal Regulations, Part 1205.
11 ANSI B71.1-2003, "American National Standard for Consumer Turf Care Equipment - Walk-Behind Mowers
and Ride-On Machines with Mowers - Safety Specifications".
12 "Control of Emissions From Nonroad Spark-Ignition Engines, Vessels, and Equipment Document", Docket ID
"EPA-HQ-OAR-2004-0008-0089", tests 1514-4, 1514-5 and 1514-6.
13 "Control of Emissions From Nonroad Spark-Ignition Engines, Vessels, and Equipment Document", Docket ID
"EPA-HQ-OAR-2004-0008-0089".
54
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6. Test Results—Comparison between EPA's Phase 3 Prototypes
and Current Engine Systems
In this chapter we will discuss the results of laboratory and field testing of the Class I and Class II engines described
in Chapter 5, tables 5-1 and 5-2, respectively.
A. EMISSIONS RESULTS
A summary of the exhaust emissions results for the tested engine configurations over the EPA A-cycle may be
found in Appendix B. Emissions levels of all of the catalyst-configured systems tested were consistent with the
California Tier 3 and the expected Federal Phase 3 emission standards. In many cases, HC+NOx emissions were
well below the expected Phase 3 standards. An increase in exhaust back-pressure was expected with the addition of
catalyst-mufflers to the engines, but engine power output and load response was comparable to that of the engines
using OEM mufflers.
B. LABORATORY TEST RESULTS
Surface temperature measurements by infrared thermal imaging - Class I Side-valve Engines
Engine 258:
Figure 6-1 shows infrared thermal images for A-cycle modes 1, 3 and 5 taken during laboratory testing of engine
258 with a catalyst-muffler and with an OEM muffler following approximately 10 hours of engine break-in and
catalyst "degreening".6 The catalyst-muffler used was the European catalyst-muffler with the stamped secondary-
air-venturi, modified to increase the catalyst substrate volume to approximately 40 cc (2-20 cc 400 cpsi ceramic
monoliths, similar to the "middle" unit in Figure 5-2) as described in Chapter 5. The peak temperatures on the
catalyst-muffler were near the exhaust outlet. The through-bolts attaching the muffler to the engine and one of the
welds between the outer and inner halves of the catalyst-muffler were also at similar temperatures to the outlet.
This particular weld was a result of modifications made to the muffler to increase catalyst volume. Production
mufflers typically use a folded seam rather than a continuous weld to join stamped halves together, and folded
seams tend to hold in less heat.
The peak temperatures for the OEM muffler were at the muffler through-bolts and the lower half of the outside
surface of the muffler, immediately downstream of where the exhaust expands through the muffler baffle. The
OEM muffler peak temperatures were significantly hotter than those of the catalyst-muffler at all six of the A-cycle
test modes, which covered the entire operational range of the engine. The heat-affected surface area above 350 °C
covers a larger area of the OEM muffler at high load than was the case for the catalyst-muffler. While cooler
temperatures of the catalyst-muffler versus the OEM muffler initially seem counterintuitive, the catalyst-muffler has
a number of design elements that allow it to reject heat more effectively than the OEM muffler, including:
1. The catalyst-muffler routes the exhaust gases through three stages of baffles (two pre-catalyst, one post-
catalyst) vs. a single stage baffle for the OEM muffler.
2. The catalyst-muffler has approximately double the external surface area of the OEM muffler to reject heat
over.
3. The catalyst-muffler has a longer internal path (including one flow reversal) to reject heat through.
4. Approximately 25% of the catalyst-muffler surface area is located directly in the cooling air-flow of the
engine fan immediately downstream of the cylinder fins. Very little cooling air reaches the OEM muffler
due to its positioning well forward of where much of the cooling air exhausts from the engine.
e Catalyst degreening involves operation of a catalyst in engine exhaust long enough for an initial degree of thermal
sintering of PGM to occur. This was performed for emissions testing purposes only.
55
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Engine 236
Figure 6-2 shows infrared thermal images for A-cycle modes 1, 3 and 5 taken during laboratory testing of engine
236 following approximately 10 hours of engine break-in and catalyst "degreening". The catalyst-muffler was
similar in construction to the one used with engine 258 except that the catalyst used a 200 cpsi, 44 cc metal
monolith with a tri-metallic washcoating formulation, and the inlet location was changed to allow fitment to engine
236 since this engine is from a different engine family than engine 258.
This engine had peak OEM-muffler temperatures that were 50 to 60 degrees higher than that of engine 258. As a
result, both the catalyst-muffler and OEM muffler surface temperatures were higher for engine 236 than what was
observed for engine 258. Comparing the catalyst-muffler in figure 6-2 to that in figure 6-1, the section of the
catalyst-muffler containing the catalyst substrate was considerably hotter than that in figure 6-1, in part due to lower
air-flow rate from the cooling fan and higher cooling air temperatures for engine 236 relative to engine 258. The
OEM cooling fan was integral to the flywheel and used six constant cross section flat-paddle-type blades. There is
substantial potential to reduce catalyst-muffler surface temperatures for engine 236 via use of a higher efficiency,
higher volume cooling fan and by paying close attention to the routing of cooling air-flow relative to the muffler
position.
As with engine 258, the peak surface temperatures with catalyst-muffler were significantly cooler than those of the
OEM muffler at each of the A-cycle test points. The hottest areas of the catalyst-muffler were the portion of the
muffler that contained the catalyst substrate (the area center-right of the images) and the continuous weld running
along the top of the catalyst-muffler. The hottest area of the OEM muffler was on the outer surface directly
opposite from the exhaust port outlet. The heat-affected surface area above 350 °C was comparable for the OEM
muffler and the catalyst-muffler.
56
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
GOO.O
Maximum surface temperature: 471 °C
50% Load - Mode 3
Maximum surface temperature: 351 °C
10% Load - Mode 5
Maximum surface temperature: 332 °C
OEM Muffler
100% Load - Wide Open Throttle
600.0
Maximum surface temperature: 511 °C
50% Load - Mode 3
Maximum surface temperature: 412 °C
10%Load - Mode 5
Maximum surface temperature: 397 °C
Figure 6-1: Infrared thermal images showing the surface temperatures of exhaust system components for side-valve
engine 258 at low hours, equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1, 3 and 5 of
the A-cycle.
57
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
r 600.0
25.0
Maximum surface temperature: 494 °C
50% Load - Mode 3
Maximum surface temperature: 420 °C
10% Load - Mode 5
Maximum surface temperature: 433 °C
OEM Muffler
100% Load - Wide Open Throttle
-soo.o
Maximum surface temperature: 579 °C
50% Load - Mode 3
Maximum surface temperature: 493 °C
10% Load - Mode 5
Maximum surface temperature: 497 °C
Figure 6-2: Infrared (hernial images showing the surface temperatures of exhaust system components for side-valve
engine 236 at low hours, equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1, 3 and 5 of
the A-cycle.
58
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Infrared thermal imaging - Class IOHV Engines
In some respects, Class I OHV engines present more of a design challenge with respect to exhaust component heat
rejection than their side-valve counterparts. Peak exhaust gas temperatures measured at the muffler inlet can be 50-
100 °C higher at some operating conditions when compared to side-valve engines used in similar walk-behind lawn
mower applications. In some cases, OEM muffler configurations tested incorporated shrouds around the muffler to
enhance heat rejection via forced convection using cooling air from the engine cooling fan (engines 243 and 244).
Other OEM muffler designs for OHV engines were generally similar to those used with side-valve engines (engines
241, 255). The shrouded designs maintained a minimum clearance between the muffler and the shroud to prevent
debris accumulation, similar to the clearances used to prevent debris accumulation within the engine shrouding of
the cylinder and cylinder-head. The catalyst-muffler configurations tested by EPA with engines 243 and 244
incorporated similar shrouding, and in one case (engine 243) used a modified OEM air-shroud.
Engine 241
Figure 6-3 shows infrared thermal images for A-cycle modes 1, 3 and 5 acquired during laboratory testing of engine
241 following approximately 110 hours of dynamometer aging (near the end of useful life). The catalyst-muffler
used was similar to that used with engine 258 (40 cc, 400 cpsi ceramic monolith, top of figure 5-2). The muffler
baffles and muffler inlet were reconfigured, and the muffler did not use through-bolts exposed to the exhaust flow.
No modifications were made to the stamped secondary-air venturi. The exhaust gas temperatures for this OHV
engine family were typically higher than those observed for side-valve engines (e.g., engine 258). Peak surface
temperatures for the catalyst-muffler occurred on the outer muffler shell, immediately downstream of the catalyst
substrate, and on the weld along the lower parting seam of the muffler shell. Peak surface temperatures for the
OEM muffler occurred along the outer-most surface of the muffler shell and near the stub-pipe exhaust outlet. Peak
surface temperatures for the catalyst-muffler were cooler than the OEM muffler for the 100% load, WOT condition,
and were comparable to the OEM muffler over the remaining steady-state operating conditions of the A-cycle. The
OEM muffler's highest surface temperatures generally covered a larger surface area of the outer muffler shell than
was the case for the catalyst-muffler.
Hot soak tests conducted from the 100% load WOT condition show the catalyst-muffler cooler than the OEM
muffler for the first 30 seconds following shutdown (figure 6-4). At one minute following shutdown from WOT,
the temperature decay of the catalyst-muffler decreased due to conductive heat transfer from the internal surfaces to
the outer surfaces of the catalyst-muffler. Thus at 30 seconds after shutdown from WOT, the catalyst-muffler peak
temperatures were approximately the same temperature as the OEM muffler rather than cooler, and at one minute
following shutdown, the catalyst-muffler peak temperatures were approximately 80 °C higher than the OEM
muffler. After approximately two minutes following shutdown from the WOT condition, peak temperatures for the
catalyst-muffler were again comparable to the OEM muffler (figures 6-4 and 6-5).
During hot-soak tests from the 50% load point (mode 3), surface temperatures of the catalyst-muffler and OEM
muffler were comparable throughout the hot-soak period (figures 6-6 and 6-7). The initial hot-soak temperatures
obtained following sustained 50% load operation were also more comparable to exhaust system peak surface
temperatures measured field operation. After approximately 2-minutes following shut-down from 50% load, peak
temperatures of both the OEM muffler and the catalyst-muffler were below 250 °C, which is approximately the
auto-ignition temperature of gasoline. This corresponded well to the manufacturer's recommendations within the
Owner's Manual for this engine that the operator wait two minutes following shut-down before removing the cap to
the fuel tank for refueling.
Engine 255
Figure 6-8 shows infrared thermal images for A-cycle modes 1, 3, and 5 acquired during laboratory testing of
engine 255 with a catalyst-muffler and with an OEM muffler following approximately 10 hours of engine break-in
and catalyst "degreening". The catalyst-muffler used was the same unit shown in figure 5-6. Although engine 255
is from the same engine family as engine 241, the catalyst-muffler has several key differences. In order to
simultaneously enhance emission control performance and heat rejection, part of the catalyst volume was relocated
upstream of the secondary-air-venturi by mounting a catalyzed-tube pre-catalyst in the short length of exhaust pipe
59
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between the exhaust port and the entrance to the muffler body. The catalyst substrate size was reduced, the cell
density was halved, and a metal monolith construction was substituted for the cordierite monoliths used with engine
241. A tri-metallic washcoating formulation was used, although PGM loading was similar to that used with engine
241 on a per-unit of catalyst volume basis. The increased catalyst efficiency of this catalyst-muffler configuration
allowed a reduction in secondary-air entrainment. Two of the four air inlet holes in the stamped venturi were
blocked to reduce the volume of secondary-air flow drawn by the stamped venturi. In the end, the level of
HC+NOx emissions control for the catalyst-muffler tested with engine 255 was approximately equivalent to the
system tested with engine 241, but with approximately 50% less secondary air flow, and an overall reduction in total
catalyst volume and PGM. CO oxidation at low operational hours was reduced from approximately 50% over the
A-cycle to approximately 15%.
Peak surface temperatures for the catalyst-muffler were in the area where the exhaust flow turns 180 degrees,
between the catalyst outlet and the muffler outlet. Peak surface temperatures for the OEM muffler were on the
outer-surface near where the exhaust expands through the muffler baffles. The peak surface temperatures of the
catalyst-muffler were approximately 30 to 60 degrees cooler than the OEM muffler for all six modes of the A-cycle
test and were also reduced relative to the catalyst-muffler tested with engine 241. The heat-affected surface area
above 350 °C for the catalyst-muffler was comparable to that of the OEM muffler.
Engine 244
Figure 6-9 shows infrared thermal images for A-cycle modes 1, 3, and 5 acquired during laboratory testing of
engine 244 with a catalyst-muffler and with an OEM muffler following approximately 10 hours of engine break-in
and catalyst "degreening". The catalyst-muffler used was similar to that used with engine 258, but with a different
catalyst (44 cc, 200 cpsi metal monolith, tri-metallic washcoating formulation). The muffler baffles and muffler
inlet were reconfigured, and the muffler did not use through-bolts exposed to the exhaust flow. A steel shroud was
fabricated to route air-flow over the catalyst-muffler in a manner similar to that of the OEM muffler and shroud
used with this engine. An exhaust ejector was incorporated into the catalyst-muffler shroud design to cool the
muffler outlet (the hottest part on the OEM muffler configuration) and to provide additional cooling to the exhaust
gases exiting the catalyst-muffler. The use of the ejector dropped the peak temperature of exposed surfaces by
approximately 200 °C relative to the OEM configuration over the six modes of the A-cycle test. Exposed surfaces
were below the auto-ignition point of gasoline (-250 °C) at all of the tested conditions, including WOT. The tested
catalyst-muffler configuration maintained 100-200 °C cooler exposed peak surface temperatures for the entire five
minute timed hot-soak period for hot soaks from both the WOT (see Figures 6-10 and 6-11) and 50% load (see
Figures 6-12 and 6-13) conditions when compared to the OEM configuration. The peak temperatures of the shroud
used with the catalyst-muffler increased slightly during the first minute following engine shut-down, and then
decreased throughout the remainder of the timed soak period.
Engine 243
The tests conducted with engine 244 were repeated with a nearly identical engine (engine 243) that also
incorporated further improvements in the design of the catalyst-muffler, air shrouding and exhaust ejector. A
completely different muffler design was used which included a new concentric tube venturi. During development,
secondary-air flow was progressively reduced to minimize CO while maintaining HC+NOx control above 40%
efficiency over the A-cycle. The size reduction of the muffler enabled by the improvements allowed use of a
modified version of the OEM muffler shroud. The exhaust ejector was lengthened approximately 25% to increase
the draw of air through the ejector. The changes resulted in reduced CO oxidation and a further 20 to 40 °C
reduction in external surface temperatures relative to the catalyst-muffler and shroud configuration tested with
engine 244 (figure 6-14). Peak temperatures of exposed surfaces were below 200 °C for all operating points,
including the region near the exhaust outlet from the ejector. During the hot soak from the WOT condition, peak
surface temperatures were similar to the catalyst-muffler tested with engine 244 and approximately 200 °C cooler
than peak temperatures with the OEM system (figures 6-15 and 6-16). Peak temperatures during hot-soak from the
50% load condition were 20-40 °C cooler than the earlier catalyst-muffler configuration, and approximately 100-
300 °C cooler than the OEM system (figures 6-17 and 6-18).
60
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
r 600.0
25.0
Maximum surface temperature: 447 °C
50% Load - Mode 3
Maximum surface temperature: 362 °C
10% Load - Mode 5
Maximum surface temperature: 296 °C
OEM Muffler
100% Load - Wide Open Throttle
rGOO.O
25.0
Maximum surface temperature: 480 °C
50% Load - Mode 3
Maximum surface temperature: 371 °C
10% Load - Mode 5
Maximum surface temperature: 300 °C
Figure 6-3: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 241 at high hours, equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1. 3 and 5
of the A-cycle.
61
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Modified Catalyst-muffler
Maximum surface temperature: 423 °C
r600.0
F2
F
%
n
500
400
I 200
100
25.0
100
25.0
Maximum surface temperature: 396 °C
r 600.0
25.0
Maximum surface temperature: 384 °C
Maximum surface temperature: 324 °C
OEM Muffler
O-seconds
30-seconds
1-minute
2-minutes
Maximum surface temperature: 485 °C
r 600.0
r500
400
300 C
1-200
1-100
125.0
Maximum surface temperature: 418 °C
r 600.0
Maximum surface temperature: 301 °C
-600.0
i-500
i-400
25.0
Maximum surface temperature: 301 °C
Figure 6-4: Infrared thermal images showing the surface temperatures of exhaust system components for engine
241 during a hot-soak period immediately after engine shutdown from sustained operation at WOT, 100% load (A-
cycle mode 1).
62
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A1
¦600.0
500
400
300 C
200
100
25.0
Maximum surface temperature: 265 °C
r 600.0
25.0
Maximum surface temperature: 219 °C
3-minutes
4-minutes
OEM Muffler
m
iff
GOO.O
500
r 400
-300
200
100
25.0
Maximum surface temperature: 258 °C
-GOO.O
25.0
Maximum surface temperature: 218 °C
Figure 6-5: Continuation of the hot-soak shown in figure 6-4.
63
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Modified Catalyst-muffler
600.0
25.0
Maximum surface temperature: 351 °C
Maximum surface temperature: 325 °C
r 600.0
1-500
-400
25.0
Maximum surface temperature: 290 °C
r 600.0
500
25.0
Maximum surface temperature: 247 °C
OEM Muffler
O-seconds
30-seconds
1-minute
2-minutes
Maximum surface temperature
360 °C
Maximum surface temperature
318 °C
288 °C
Maximum surface temperature
Maximum surface temperature:
¦25.0
242 °C
Figure 6-6: Infrared thermal images showing the surface temperatures of exhaust system components for engine
241 during a hot-soak period immediately after engine shutdown from sustained operation at 50% load (A-cycle
mode 3).
64
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Modified Catalyst-muffler
GOO.O
25.0
Maximum surface temperature: 206 °C
r 600.0
i-500
-400
•300 c
25.0
Maximum surface temperature: 176 °C
3-minutes
4-minutes
OEM Muffler
GOO.O
25.0
Maximum surface temperature: 207 °C
r 600.0
i-500
-400
300
X
25.0
Maximum surface temperature: 173 °C
Figure 6-7: Continuation of the hot-soak shown in figure 6-6.
65
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
Maximum surface temperature: 440 °C
50% Load - Mode 3
Maximum surface temperature: 310 °C
10% Load - Mode 5
Maximum surface temperature: 248°C
OEM Muffler
100% Load - Wide Open Throttle
Maximum surface temperature: 470 °C
50% Load - Mode 3
Maximum surface temperature: 360 °C
10% Load - Mode 5
Maximum surface temperature: 296 °C
Figure 6-8: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 255 at low hours, equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1, 3 and 5 of
the A-cycle.
66
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
-eoo.o
Maximum surface temperature: 230 °C
50% Load - Mode 3
Maximum surface temperature: 102 °C
10% Load - Mode 5
A2
1
MOO
-25.0
Maximum surface temperature: 161 °C
OEM Muffler
100% Load - Wide Open Throttle
551 °C
Maximum surface temperature:
50% Load - Mode 3
421 °C
Maximum surface temperature:
10% Load - Mode 5
Maximum surface temperature: 363 °C
Figure 6-9: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 244 at high hours, equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1, 3 and 5
of the A-cycle. The OEM muffler configuration was equipped with a full shroud that directed air-flow over the
muffler. This configuration was largely reproduced for the catalyst-muffler. An exhaust-ejector was also added for
improved shroud and exhaust-gas cooling (dark blue rectangular area).
67
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Modified Catalyst-muffler
[600.0
_ 500
400
300 C
-200
100
25.0
Maximum surface temperature: 228 °C
r 600.0
Maximum surface temperature
234 °C
Maximum surface temperature
240 °C
215 °C
Maximum surface temperature
OEM Muffler
O-seconds
30-seconds
1-minute
2-minutes
Maximum surface temperature
526 °C
527 °C
Maximum surface temperature:
0_
A1
Maximum surface temperature:
A1
-600.0
•500
•400
•300 C
•200
100
25.0
483 °C
•600.0
•500
•400
•300 C
•200
100
Maximum surface temperature: 418 °C
Figure 6-10: Infrared thermal images showing the surface temperatures of exhaust system components for engine
244 during a hot-soak period immediately after engine shutdown from sustained operation at WOT, 100% load (A-
cycle mode 1).
68
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Modified Catalyst-muffler
Maximum surface temperature: 196 °C
r600.0
l500
Maximum surface temperature: 180 °C
r600.0
l500
Maximum surface temperature: 164 °C
OEM Muffler
3-minutes
4-minutes
5-minutes
A1
¦600.0
¦500
•400
•300 C
•200
100
25.0
Maximum surface temperature: 363 °C
r 600.0
25.0
Maximum surface temperature: 319 °C
r 600.0
A1
Maximum surface temperature:
¦500
•400
•300
•200
100
25.0
Figure 6-11: Continuation of the hot-soak shown in figure 6-10.
69
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Modified Catalyst-muffler
[600.0
_ 500
400
300 C
-200
100
25.0
Maximum surface temperature: 168 °C
r 600.0
Maximum surface temperature
173 °C
Maximum surface temperature
176 °C
169 °C
Maximum surface temperature
OEM Muffler
O-seconds
411 °C
Maximum surface temperature:
30-seconds
l*_
A1
Maximum surface temperature:
-600.0
•500
•400
•300 T
•200
100
25.0
389 °C
1-minute
357 °C
Maximum surface temperature:
2-minutes
A
A1
-600.0
¦500
¦400
¦300 C
¦200
¦100
Maximum surface temperature:
25.0
321 °C
Figure 6-12: Infrared thermal images showing the surface temperatures of exhaust system components for engine
244 during a hot-soak period immediately after engine shutdown from sustained operation at 50% load (A-cycle
mode 3).
70
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Modified Catalyst-muffler
Maximum surface temperature: 158 °C
-600.0
Maximum surface temperature: 148 C
Maximum surface temperature: 135 °C
OEM Muffler
3-minutes
4-minutes
5-minutes
A1
¦600.0
¦500
•400
•300 C
•200
100
25.0
Maximum surface temperature: 284 °C
r 600.0
|# _
A1
•500
•400
•300
•200
100
25.0
Maximum surface temperature: 251 °C
r 600.0
•500
•400
•300 c
•200
Maximum surface temperature: 224 °C
•
A1
Figure 6-13: Continuation of the hot-soak shown in figure 6-12.
71
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Catalyst-muffler,
venturi secondary air
100% Load - Wide Open Throttle
-600.0
25.0
Maximum surface temperature: 184 °C
50% Load - Mode 3
Maximum surface temperature: 125 °C
10% Load - Mode 5
Maximum surface temperature: 101 °C
OEM Muffler
100% Load - Wide Open Throttle
551 °C
Maximum surface temperature:
50% Load - Mode 3
421 °C
Maximum surface temperature:
10% Load - Mode 5
Maximum surface temperature: 363 °C
Figure 6-14: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 243 at high hours, equipped with a catalyst-muffler (left) compared to an engine from the same engine
family (engine 244) equipped with an OEM muffler (right) for modes 1, 3 and 5 of the A-cycle. In this case, the
catalyst-muffler used a concentric tube venturi with an annular exhaust inlet. The OEM muffler configuration was
equipped with a full shroud that directed air-flow over the muffler. This configuration was largely reproduced for
the catalyst-muffler via modifications to the OEM shroud. An exhaust-ejector was also added for improved shroud
and exhaust-gas cooling.
72
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Modified Catalyst-muffler
K
600.0
500
400
300 *C
200
100
25.0
Maximum surface temperature: 182 °C
r 600.0
i- 500
I
Maximum surface temperature
164 °C
Maximum surface temperature
177 °C
168 °C
Maximum surface temperature
OEM Muffler
O-seconds
30-seconds
1-minute
2-minutes
Maximum surface temperature
526 °C
527 °C
Maximum surface temperature:
0_
A1
Maximum surface temperature:
A1
-600.0
•500
•400
•300 C
•200
100
25.0
483 °C
•600.0
•500
•400
•300 C
•200
100
Maximum surface temperature: 418 °C
Figure 6-15: Infrared thermal images showing the surface temperatures of exhaust system components for engine
243 (left) and engine 244 (right) during a hot-soak period immediately after engine shutdown from sustained
operation at WOT, 100% load (A-cycle mode 1).
73
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Modified Catalyst-muffler
I
I
600.0
500
400
300
200
100
25.0
Maximum surface temperature: 168 °C
r 600.0
Maximum surface temperature: 183 C
Maximum surface temperature: 162 °C
r 600.0
25.0
Maximum surface temperature: 155 °C
OEM Muffler
3-minutes
4-minutes
5-minutes
6-minutes
A1
¦600.0
¦500
•400
•300 C
•200
100
25.0
Maximum surface temperature: 363 °C
r 600.0
25.0
Maximum surface temperature: 319 °C
r 600.0
A1
Maximum surface temperature:
¦500
•400
•300
•200
100
25.0
Maximum surface temperature: 248 °C
Figure 6-16: Continuation of the hot-soak shown in figure 6-15.
74
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Modified Catalyst-muffler
K
600.0
500
400
300 *C
200
100
25.0
Maximum surface temperature: 115 °C
r 600.0
i- 500
i
Maximum surface temperature
120 °C
Maximum surface temperature
111 °C
111 °C
Maximum surface temperature
OEM Muffler
O-seconds
411 °C
Maximum surface temperature:
30-seconds
l*_
A1
Maximum surface temperature:
-600.0
•500
•400
•300 T
•200
100
25.0
389 °C
1-minute
357 °C
Maximum surface temperature:
2-minutes
A
A1
-600.0
¦500
¦400
¦300 C
¦200
¦100
Maximum surface temperature:
25.0
321 °C
Figure 6-17: Infrared thermal images showing the surface temperatures of exhaust system components for engine
243 (left) and 244 (right) during a hot-soak period immediately after engine shutdown from sustained operation at
50% load (A-cycle mode 3).
75
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Modified Catalyst-muffler
Maximum surface temperature: 132 °C
-600.0
Maximum surface temperature: 112 C
Maximum surface temperature: 113 °C
OEM Muffler
3-minutes
4-minutes
5-minutes
A1
¦600.0
¦500
•400
•300 C
•200
100
25.0
Maximum surface temperature: 284 °C
r 600.0
|# _
A1
•500
•400
•300
•200
100
25.0
Maximum surface temperature: 251 °C
r 600.0
•500
•400
•300 c
•200
Maximum surface temperature: 224 °C
•
A1
Figure 6-18 : Continuation of the hot-soak shown in figure 6-17.
76
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Infrared thermal imaging - Class IIOHV Engines
Infrared thermal images are shown for three of the Class II lawn tractor engine types tested by EPA. It should be
noted that the routing of cooling air through the lawn tractor chassis is important for both engine and exhaust system
cooling. Also, for the catalyst-equipped configurations, the routing of cooling air through the chassis was modified
to enhance cooling of exhaust system surfaces. Forced cooling of this type could not be adequately replicated
during engine dynamometer testing, so the test results presented should be seen as worst case with respect to surface
temperatures. Please refer to the field test results to see comparisons of engines and exhaust configurations as
installed in the lawn tractor chassis.
Engine 231
Figure 6-19 shows infrared thermal images for A-cycle modes 1, 3 and 5 taken during laboratory testing of engine
231 equipped with a catalyst-muffler and EFI compared to an OEM configuration following approximately 10 hours
of engine break-in and catalyst "degreening" and an additional 10 hours of operation accumulated during engine
management system development. The catalyst-muffler used was similar to the one pictured in the lower right of
figure 5-7. The peak temperatures for the catalyst-muffler were on the surfaces of the head-pipe and on the surfaces
adjacent to a series of baffles located in the lower half of the muffler. The peak temperatures of the OEM muffler
were on the surfaces of the head-pipe and on the upper half of the muffler, immediately upstream of the first muffler
baffle. Comparable peak temperatures were found for both the catalyst-muffler and the OEM muffler for all six
steady-state operating modes of the A-cycle. Surface temperatures for both configurations were approximately 100
°C higher than what was measured for the Class I configurations.
Engine 251
Figure 6-20 shows infrared thermal images for A-cycle modes 1, 3 and 5 taken during laboratory testing of engine
251 equipped with a catalyst-muffler and an OEM muffler. Engine 251 was from the same engine family as engine
231. The catalyst-muffler used was similar to the one shown in the middle-right of figure 5-7, but with the outlet on
the bottom of the muffler. Peak surface temperatures for both the catalyst-muffler and the OEM muffler were on
the head-pipe and the region of the muffler immediately downstream of the head-pipe. Comparable peak
temperatures were found for both the catalyst-muffler and the OEM muffler for all six modes of the A-cycle.
Hot soak tests were conducted with this engine from the 50% load condition (see figure 6-21 to 6-23). The cooling
of the catalyst-muffler, as indicated by peak surface temperatures, lagged approximately one minute behind that of
the OEM muffler, probably due to the increased mass of the catalyst-muffler in comparison with the OEM muffler.
The time required for surface temperatures to cool to 250 °C was approximately six minutes for the catalyst-muffler
and five minutes for the OEM muffler.
Engine 254
Figure 6-24 shows infrared thermal images for A-cycle modes 1, 3 and 5 taken during laboratory testing of engine
254 equipped with a catalyst-muffler and an OEM muffler. The catalyst-muffler used on engine 254 differed from
the catalyst muffler used on engine 251 in several ways. The head-pipe used a double-wall construction to reduce
its temperature. The overall substrate volume was reduced and divided into 2 parallel substrates to reduce exhaust
back-pressure. Additionally, 100 cpsi metal-monolith construction was used instead of 200 cpsi, reducing cost and
further reducing exhaust back-pressure. Peak temperatures were comparable between the catalyst-muffler and the
OEM muffler systems for all six modes of the A-cycle. The double-wall construction reduced peak surface
temperatures of the head-pipe used with the catalyst-muffler by approximately 150 °C at moderate to high-load
conditions. Similar double-wall construction could also be applied to other parts of the exhaust system to reduce
peak temperatures in specific locations.
During hot soak testing on engine 254 from sustained operation at WOT, cooling of the catalyst-muffler was
comparable to the OEM muffler for the first 60 seconds, and then lagged behind the OEM system by one to two
minutes for the remainder of the timed hot soak test (see Figures 6-25 to 6-27). During the hot-soak tests from the
50% load condition, the catalyst-muffler peak temperatures over the first 60 seconds cooled off faster than for the
77
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OEM muffler. From approximately two minutes after shut-down to the end of the soak test, the cooling of catalyst-
muffler peak surface temperatures lagged approximately one to two minutes behind those of the OEM muffler,
similar to the WOT hot-soak conditions (see figures 6-28 and 6-29).
EFI w-catalyst, Engine 231
100% Load - Wide Open Throttle - Mode 1
Maximum surface temperature: 558 °C
50% Load - Mode 3
Maximum surface temperature: 512 °C
10% Load - Mode 5
600.0
25.0
Maximum surface temperature: 482 °C
OEM Configuration, Engine 231
100% Load - Wide Open Throttle - Mode 1
-600.0
25.0
Maximum surface temperature: 613 °C
50% Load - Mode 3
£
I
600.0
500
400
300 '
200
100
25.0
Maximum surface temperature: 542 °C
10% Load - Mode 5
c
600.0
500
400
300 '
200
100
25.0
Maximum surface temperature: 470 °C
Figure 6-19: Infrared thermal images showing the surface temperatures of exhaust system components for engine
231 at low hours, equipped with a open-loop EFI and a high-efficiency catalyst-muffler (left) and an OEM muffler
(right).
78
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Figure 6-20: Infrared thermal images showing the surface temperatures of exhaust system components for engine
251 at low hours, equipped with catalyst-muffler (left) and an OEM muffler (right). Both configurations used the
OEM carburetor.
t 600.0
500
r 400
-300 L
1600.0
500
Maximum surface temperature:
50% Load - Mode 3
|| r 200
I
K-25.0
591.7 °C
K 600.0
500
-25.0
Maximum surface temperature: 529.7 °C
10% Load - Mode 5
200
100
25.0
Maximum surface temperature: 445.5 °C
Maximum surface temperature: 599.3 °C
50% Load - Mode 3
600.0
500
400
300
200
Maximum surface temperature: 538.9 °C
10% Load - Mode 5
Maximum surface temperature: 449.7 °C
OEM Carburetor w-catalyst, Engine 251
100% Load - Wide Open Throttle - Mode 1
[600.0
500
OEM Configuration, Engine 251
100% Load - Wide Open Throttle - Mode 1
-600.0
[bUU.L
500
79
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Figure 6-21: Infrared thermal images showing the surface temperatures of exhaust system components for engine
251 during a hot-soak period immediately after engine shutdown from sustained operation at 50% load (A-cycle
mode 3).
600.0
25.0
Maximum surface temperature: 521.1 °C
-eoo.o
0-seconds
30-seconds
1-minute
OEM Carburetor w-catalyst, Engine 251
OEM Configuration, Engine 251
Keoo.0
500
r 400
Maximum surface temperature: 534.1 °C
-G00.0
500
400
r 300 C
L200
Maximum surface temperature: 484.9 °C
-G00.0
500
r 400
Jf-200
1100
25.0
H r 200
|.
*25.0
Maximum surface temperature: 430.0 °C
Maximum surface temperature: 489.4 °C
Maximum surface temperature:
(600.0
500
520.4 °C
80
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OEM Carburetor w-catalyst, Engine 251 OEM Configuration, Engine 251
2-minutes
Maximum surface temperature: 415.7 °C Maximum surface temperature: 356.2 °C
3-minutes
Maximum surface temperature: 358.7 °C Maximum surface temperature: 313.3 °C
4-minutes
Maximum surface temperature: 316.6 °C Maximum surface temperature: 278.7 °C
Figure 6-22: Continuation of the hot-soak shown in figure 6-21.
81
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OEM Carburetor w-catalyst, Engine 251
600.0
-25.0
Maximum surface temperature: 286.3 °C
-G00.0
n
r500
¦400
¦300
-200
100
25.0
Maximum surface temperature: 258.2 °C
-600.0
Mill
Ibuu.L
500
-400
r300
r 200
tr
*25.0
Maximum surface temperature: 234.5°C
OEM Configuration, Engine 251
5-minutes
(600.0
500
2
A1
r 400
¦300
Jt-200
1100
25.0
6-minutes
Maximum surface temperature: 249.4 °C
600.0
at
n
500
¦400
r 300
r 200
100
25.0
7-minutes
Maximum surface temperature: 223.0 °C
-600.0
-25.0
Maximum surface temperature: 201.8 °C
Figure 6-23: Continuation of the hot-soak shown in figures 6-21 and 6-22.
82
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OEM Carburetor w-catalyst, Engine 254
100% Load—Wide Open Throttle - Mode 1
-700.0
r
Maximum surface temperature: 651 °C
Maximum head-pipe temperature: 420 °C
50% Load - Mode 3
Maximum surface temperature: 612 °C
Maximum head-pipe temperature: 483 °C
10% Load - Mode 5
Maximum surface temperature: 587 °C
Maximum head-pipe temperature: 561 °C
OEM Configuration, Engine 254
100% Load - Wide Open Throttle - Mode 1
-700.0
Maximum surface temperature: 651 °C
Maximum head-pipe temperature: 586 °C
50% Load - Mode 3
Maximum surface temperature: 610 °C
Maximum head-pipe temperature: 610 °C
10% Load - Mode 5
n
\
A2
Br
J
700.0
GOO
¦500
¦400
*(
¦300
200
100
25.0
Maximum surface temperature: 577 °C
Maximum head-pipe temperature: 577 °C
Figure 6-24: Infrared thermal images showing the surface temperatures of exhaust system components for engine
254 at low hours, equipped with catalyst-muffler (left) and an OEM muffler (right). Both configurations used the
OEM carburetor.
83
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OEM Carburetor w-catalyst, Engine 254
700.0
*C
25.0
Maximum surface temperature: 649 °C
700.0
25.0
Maximum surface temperature: 648 °C
700.0
25.0
Maximum surface temperature: 584 °C
OEM Configuration, Engine 254
0-seconds
30-seconds
1-minute
Maximum surface temperature: 636 C
Maximum surface temperature: 636 °C
Maximum surface temperature: 585 °C
6-25: Infrared thermal images showing the surface temperatures of exhaust system components for engine 254
during a hot-soak period immediately after engine shutdown from sustained operation at 100% load, WOT (A-cycle
mode 1).
84
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OEM Carburetor w-catalyst, Engine 254
-700.0
25.0
Maximum surface temperature: 494 °C
-700.0
-GOO
-500
-400
Maximum surface temperature: 437 °C
Maximum surface temperature: 384 °C
OEM Configuration, Engine 254
2-minutes
3-minutes
4-minutes
Maximum surface temperature: 446 °C
-700.0
-GOO
-500
-400
Maximum surface temperature: 356 °C
-700.0
-600
I- 500
Maximum surface temperature: 298 °C
6-26: Continuation of the hot-soak shown in figure 6-25.
85
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OEM Carburetor w-catalyst, Engine 254
-700.0
25.0
Maximum surface temperature: 340 °C
-700.0
-GOO
-500
-400
Maximum surface temperature: 292 °C
Maximum surface temperature: 260 °C
OEM Configuration, Engine 254
5-minutes
6-minutes
7-minutes
Maximum surface temperature: 251 °C
-700.0
-GOO
-500
j- 400
-300
°c
¦200
Maximum surface temperature: 215 °C
700.0
25.0
Maximum surface temperature: 187 °C
6-27: Continuation of the hot-soak shown in figures 6-25 and 6-26.
86
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OEM Carburetor w-catalvst, Engine 254
Maximum surface temperature: 620 °C
700.0
Maximum surface temperature: 520 °C
Maximum surface temperature: 479 °C
OEM Configuration, Engine 254
0-seconds
30-seconds
1-minute
Maximum surface temperature: 600 °C
-700.0
-GOO
-500
-400
*C
Maximum surface temperature: 592 °C
-700.0
-600
I- 500
Maximum surface temperature: 493 °C
6-28: Infrared thermal images showing the surface temperatures of exhaust system components for engine 254
during a hot-soak period immediately after engine shutdown from sustained operation at 50% load (A-cycle mode
3).
87
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OEM Carburetor w-catalyst, Engine 254
-700.0
Maximum surface temperature: 424 °C
-700.0
:600
- 500
Maximum surface temperature: 375 °C
r 700.0
7 GOO
-500
Maximum surface temperature: 334 °C
r 700.0
-600
-500
Maximum surface temperature: 298 °C
2-minutes
3-minutes
4-minutes
5-minutes
OEM Configuration, Engine 254
-700.0
Maximum surface temperature: 375 °C
•700.0
600
500
Maximum surface temperature: 302 °C
-700.0
-600
B- 500
Maximum surface temperature: 254 °C
Maximum surface temperature: 215 °C
6-29: Continuation of the hot-soak shown in figure 6-28.
-------
Muffler outlet temperatures - Class I and Class II Engines
Exhaust gas outlet temperatures measured for each of the 6-modes of the A-cycle tests are shown in
Figure 6-30 for representative examples of Class I side-valve, Class I OHV, and Class II OHV engine for
both OEM muffler and catalyst-muffler configurations. The exhaust outlet temperatures for the Class I
catalyst-mufflers were comparable or cooler in comparison with the Class I OEM mufflers. The Class II
catalyst-muffler exhaust outlet temperatures were 30-40 °C higher than the OEM muffler. When mounted
in the lawn tractor chassis, all of the Class II engines tested in the field were equipped with exhaust
ejectors that significantly lowered the exhaust gas temperatures at the outlet via mixing with ambient air.
-»-T Exh Out, 258 w/OEM Muffler
T Exh Out, 258 w/Catalyst
-k- T Exh Out, 244 w/OEM Muffler
T Exh Out, 244 w/Catalyst
-&-T Exh Out, 251 w/OEM Muffler
-®— T Exh Out, 251 w/Catalyst
p\ 500
£ 400
w 300
3
re
*- 200
100
0 J , , , , , , ,
1 2 3 4 5 6
A-Cycle Mode #
Figure 6-30: Exhaust gas outlet temperatures measured during engine dynamometer testing over the 6 steady-state
modes of the A-cycle test for representative Class I side-valve (258) and OHV (244) engines and for a Class II
engine (251). Note that the dashed lines are for OEM muffler configurations, and the solid lines are for catalyst-
muffler configurations.
Run-on after-fire testing
A digital image from one of the tests is presented in Figure 6-31. A full comparison of the OEM muffler and the
catalyst-muffler configurations tested under the same test conditions will require viewing of digital video acquired
during testing. Digital video files may be accessed for viewing via the Phase 3 Nonroad SI Engine Docket and also
from the DVD attached to this study.1 The test conditions are described in Chapter 5.
After-fire was evident for engine 241 for each of the four tests of the high-inertia shut-down conditions tested with
the OEM muffler. This can be seen quite dramatically in digital videos. In many cases, a flash of flame exited the
tailpipe during after-fire (Figure 6-31). In all cases, a series of a sharp "bangs" in the audio track of the videos are
evident, sounding similar to a fire-cracker. The force of the after-fire can be seen in the resulting recoil of the
exhaust collection cone mounted downstream of the tailpipe. It should be noted that the collection cone was
mounted to an approximately 25-lb base located approximately 3 feet below the collection cone.
The tests were repeated four times with the catalyst-muffler, but after-fire was not evident for the four repeats of the
high-inertia shut-down conditions. While the catalyst muffler was adapted from an OEM design, the two-stage
inner baffling differed somewhat in its physical layout (a 3/4" diameter perforated tube followed by a perforated
plate, with 0.125" perforations) and surface area to prevent flame propagation. A degree of flow restriction was
also added near the muffler exit through the use of a serviceable OEM spark arresting screen.
89
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Figure 6-31: Digital image taken of engine 241 during after-fire testing with OEM muffler. A 6" or longer after-
fire flame was observed extending from the tailpipe into the exhaust collection cone, accompanied by a sharp
"bang" similar to a firecracker. Repeated testing of engine 241 under the same conditions with a catalyst-muffler
did not result in after-fire.
Ignition misfire testing
Audible engine misfire, increased engine vibration, and erratic torque output were observed while operating engine
255 at the 25% misfire condition. The misfire condition is clearly visible within the torque, speed, and HC data (see
Figures 6-32 and 6-33) and in digital video taken of engine operation during misfire. Digital video files showing
engine operation during operation at the 25% misfire condition may be accessed for viewing within the Phase 3
Nonroad SI Docket and from the DVD attached to this study1.
Infrared thermal images comparing the tested catalyst-muffler and OEM muffler configurations are presented in
Figures 6-34 and 6-35. The peak temperatures of the catalyst-muffler were approximately 60 °C cooler than the
OEM muffler prior to the onset of ignition misfire. After 30 seconds of operation at 25% random ignition misfire,
the OEM muffler peak temperatures were unchanged and the catalyst-muffler peak temperatures had increased to
approximately the same temperature as the OEM muffler. As misfire progressed, the OEM muffler began to cool
and the catalyst muffler temperatures continued to increase. Temperatures for both configurations stabilized
between three and five minutes of operation. After five minutes of misfire, the catalyst-muffler had approximately
130 °C higher peak surface temperatures than the OEM muffler at the same condition (see Figure 6-34). The
stabilized temperatures of the catalyst-muffler undergoing 25% random misfire were comparable to the OEM
muffler operating normally at a 50% load condition (Figure 6-8). The temperature increase was due to the
exothermic reaction of partially burned fuel components over the catalyst substrate. The catalyst-muffler used with
engine 255 included a number of design elements to limit the exothermic reaction during misfire. These included
dividing the catalyst volume upstream and downstream of the secondary, reducing the amount of secondaiy air, and
choosing a formulation for the upstream pre-catalyst that favored net-rich HC reactions appeared. The design
appeared to be moderately successful at limiting the exotherm since peak temperatures stabilized to less than 400 °C
after approximately three minutes of misfire.
Additional testing was conducted to determine if air-shrouding similar to that used with engines 243 and 244 would
be effective at reducing the peak temperatures of exposed surfaces to temperatures below the corresponding peak
temperatures obtained with the OEM muffler configuration (see Figure 6-35). With the shroud in place, peak
temperatures during misfire testing were reduced substantially, and remained at least 50 °C cooler than the OEM
90
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configuration. Peak temperatures of the shrouded catalyst muffler were relatively constant throughout the five
minutes of misfire. The surface temperature of the shroud adjacent to location of the catalyst within the exhaust
system and the surface temperature of the exhaust ejector outlet increased from approximately 100 °C prior to the
onset of misfire to stabilized temperatures of approximately 180 °C after five minutes of ignition misfire.
- Engine Speed (rpm)
¦ HC (ppmC)
- Muffler Inlet T (°C)
-Torque (Ib-ft)
25%
25%
Misfire
7 8 9
Time (Minutes)
10
11
12
13
50
45
40
—k
o
35
o
X
H
O
30
-Q
C
n>
25
3
F
20
H
15
o
o
10
5
0
14
Figure 6-32: Operational data with engine 255 and OEM muffler showing initial temperature stabilization followed
by approximately five minutes of operation with 25% random ignition misfire. Note that HC concentrations are
from dilute-CVS measurements.
ii\ryf"riy
Engine
HC (ppmC)
Speed
Muffler Inlet T (°q)
Torque (Ib-
6 7
Time (minutes)
Figure 6-33: Operational data with engine 255 and catalyst-muffler showing initial temperature stabilization
followed by approximately five minutes of operation with 25% random ignition misfire. Note that HC
concentrations are from dilute-CVS measurements.
91
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Engine 255 with Catalyst-Muffler Engine 255 with OEM Muffler
& Venturi Secondary Air
0-seconds
Maximum surface temperature: 256 °C Maximum surface temperature: 321 °C
30-seconds
Maximum surface temperature: 318 °C Maximum surface temperature: 322 °C
5-minutes
Maximum surface temperature: 382 °C Maximum surface temperature: 251 °C
Figure 6-34: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 255 at low hours equipped with a catalyst-muffler (left) and an OEM muffler (right). The images were taken
immediately before (top) and after 30 seconds (middle) and five minutes (bottom) of continuous operation at a
condition of 25% random misfire and the minimum torque measured for the lawn mower blade for this application
at 2900 rpm (approximately 25% load or A-cycle mode 4).
92
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Engine 255 with Catalyst-Muffler Engine 255 with OEM Muffler
& Venturi Secondary Air
0-seconds
Maximum surface temperature: 204 °C Maximum surface temperature: 321 °C
30-seconds
Maximum surface temperature: 185 °C Maximum surface temperature: 322 °C
5-minutes
Maximum surface temperature: 197 °C Maximum surface temperature: 251 °C
Figure 6-35: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 255 at low hours equipped with a catalyst-muffler and air shroud (left) and an OEM muffler (right). The
images were taken immediately before (top) and after 30 seconds (middle) and five minutes (bottom) of continuous
operation at a condition of 25% random misfire and the minimum torque measured for the lawn mower blade for
this application at 2900 rpm (approximately 25% load or A-cycle mode 4).
93
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Rich Operation
The 1.0 to 1.5 change in air-to-fuel ratio was achievable for A-cycle modes 1-4 via changes to the main carburetor
jet. During mode 5, the main jet change resulted in a change of 0.7 air-to-fuel ratio, and no change for mode 6.
Figure 6-36 shows a comparison between the air-to-fuel ratio achieved with the OEM carburetor main jet and the
modified carburetor on engine 255. Engine-out CO emissions increased in modes 1 to 4 of the A-cycle by
approximately 40 to 50%. Engine-out HC emission were approximately doubled. Power at WOT increased by
approximately 6%.
Thermal imaging results for operation over modes 1, 3 and 5 of the A-cycle are shown in 6-36. Peak surface
temperatures were comparable between the catalyst-muffler and OEM configurations over all six modes of the A-
cycle. Surface temperatures for the catalyst muffler were virtually unchanged relative to the tests conducted with
the OEM carburetor jetting. Although higher concentrations of CO and HC reactants were available in the exhaust
the richer operation also limited the amount of oxygen available in the exhaust, which limited the exothermic
oxidation reactions of the CO and HC over the catalyst. The richer carburetor jetting reduced the peak surface
temperatures of the OEM muffler by approximately 30 to 40 °C, or to approximately the same peak temperatures as
those of the catalyst-muffler.
15:1
OEM Carburetor
14:1
Main jet modified for rich operation
IS 12:1
611:1
10:1
1
2
3
4
5
A-Cycle Mode #
Figure 6-36: A comparison of air-to-fuel ratio for the first five modes of the A-cycle test.
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Engine 255 with Catalyst-Muffler
& Venturi Secondary Air
100% Load - Wide Open Throttle
Maximum surface temperature: 433 °C
50% Load - Mode 3
A1
Maximum surface temperature: 317 °C
10% Load - Mode 5
1600.0
500
r 400
300 '
E- 200
(6<*
100
25.0
Engine 255 with OEM Muffler
100% Load - Wide Open Throttle
Maximum surface temperature: 450 °C
50% Load - Mode 3
t-600.0
1-500
-400
A1
i- 300 °
1-200
i-100
-25.0
Maximum surface temperature: 320 °C
10% Load - Mode 5
Maximum surface temperature: 244 °C
Maximum surface temperature: 246 °C
Figure 6-37: Infrared thermal images showing the surface temperatures of exhaust system components for OHV
engine 255 at low hours equipped with a catalyst-muffler (left) and an OEM muffler (right) for modes 1. 3 and 5 of
the A-cycle with the carburetor main-jet modified to provide 1-1.5 richer air-to-fuel ratio than the OEM jetting
95
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C. FIELD TESTING RESULTS
During the course of field testing, over 1200 individual refueling events were carried out on six w alk-behind lawn
mowers and four lawn tractors without incident. Of these, four of the lawn mowers and two of the lawn tractors
were equipped with catalyst-mufflers and accounted for over 700 of the refueling events. Auxiliary fuel cans were
kept in close proximity to grass cutting operations and thus refueling typically occurred less than two minutes after
engine shut-down.
During field operations in Tennessee, four of the lawn mowers (all with the same engine type) had unacceptable
levels of debris accumulation in the area of the engine cooling shroud immediately above the cylinder head and on
top of the engine cylinder and required frequent maintenance. The issue was related to the design of the cooling fan
and the fan air-intake and caused maintenance issues with both the OEM and catalyst-equipped configurations of
this engine family. The other two engines from a different engine family that were used during field testing (244,
245) did not have any appreciable debris accumulation within the OEM engine shroud. These two engines used a
small perforated screen attached to the top of the cooling fan to prevent debris above a certain size from entering the
cooling fan and engine shroud. Engines 244 and 245 also used a cooling fan with significantly higher flow (30
curved fan vanes versus six flat-paddle type vanes). Engines 246, 248, and 249 were retrofitted with screens near
the inlet to the cooling fan and no further debris accumulation problems were encountered (see Figure 6-38).
Engine 259
cooling fan
Excessive
debris
accumulation
Engine 245
cooling fan
w/perforated
disc inlet
screen
Fan
intake
screen
Figure 6-38: Engines 246, 248, 249 and 259 had problems with excessive debris build-up underneath the engine
cooling shroud (top, engine 259 shown). Engine 245 had negligible debris build-up on engine and catalyst-muffler
surfaces, even after 110 hours of field operation (bottom left). Note the perforated disc attached to the top of the
cooling fan that prevented debris ingestion with engine 245. An external screen was added near engine fan's air-
intake on engines 246, 248 and 249 to eliminate ingestion of large debris by the engine cooling fan (bottom right).
96
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During hundreds of hours of grass cutting operations there was no discernable difference in operation attributable to
the use of catalyst-mufflers with the lawn mowers or the lawn tractors. All of the lawn mowers were operated to
approximately 100 to 110 hours (within 15-25 hours of the end of useful life). The lawn tractors were operated to
approximately 240 hours (within 10 hours of the end of useful life for engines 231 and 252 and to within 10 hours
of mid-life for engines 232 and 233).
Surface Temperature Measurements by Infrared Thermal Imaging Taken During Grass Cutting Operations
Full motion video infrared thermal images were used to allow surface temperature measurement with the equipment
under load during grass cutting operations. Observations drawn from the videos will be presented in this section. A
full comparison of IR video images from the OEM muffler and the catalyst-muffler configurations tested during
field operations will require viewing of digital video data acquired during testing. Digital video files may be
accessed for viewing via the Phase 3 Nonroad SI Engine Docket and also via the DVD attached to this study.1 The
IR thermal images were acquired at ambient conditions of 18.5 °C (65 °F), 80% relative humidity and little to no
wind for the testing in Tenneessee. The IR thermal images were acquired at ambient conditions of 30 °C (86 °F) ,
46% relative humidity with light 5 to 10 mph winds. The impact of the wind was not readily apparent in the surface
temperature measurements from the equipment, but effect of wind can clearly be seen on the turf surfaces for the IR
video images taken during idling. The grass cutting conditions can be seen in Figures 5-14 and 5-15.
Class I Lawn Mowers
The lawn mower equipped with engine 259 and an OEM muffler was operating with surface temperatures
exceeding 360 °C during cutting of moderate to heavy grass. The lawn mowers equipped with engines 244 and 245
and catalyst-mufflers were operating with surface temperatures of approximately 120 °C and 150 °C, respectively,
during grass cutting in approximately the same location. The lawn mowers equipped with engines 246 and 248 and
catalyst mufflers operated with surface temperatures of approximately 280 °C. The lawn mower equipped with
engine 249 and a catalyst-muffler operated with surface temperatures of approximately 130 °C. In all cases, the
surface temperatures of the lawn mowers equipped with catalyst-muffler configurations were significantly less than
the lawn mower equipped with engine 259 and the OEM muffler. The sub-200 °C temperatures achieved with
engines 244, 245, and 249 are due to the use of air shrouding and forced-air cooling around the muffler and due to
the use of ejector cooling of the exhaust gases and the outer surface of the air shroud. The lower surface
temperatures of the catalyst-mufflers used with engine 244 and 249 relative to that used with engine 245 may have
been due to the reduced use of platinum within their catalyst washcoating formulations. Engine 249 used a
rhodium-only formulation and engine 244 used a formulation that was predominantly palladium with a small
amount of platinum and rhodium. The best combination of emissions control and lower surface temperatures for
these applications appeared to be achievable using a trimetallic washcoating formulation of approximately 30 g/ft3 -
40 g/ft3 PGM that were predominantly palladium with smaller, roughly equivalent amounts of platinum and
rhodium. The rhodium-only catalyst was also comparably effective at achieving low surface temperatures and was
capable of similar emission control performance to the palladium-rich trimetallic formulations at much lower
loading levels (i.e., only slightly higher total PGM cost). The rhodium-only catalyst was also the only catalyst in
this testing capable of reaching EPA's HC+NOx emission targets without the use of passive secondary air. The lack
of secondary air and reduced CO oxidation for engine 249 may have also contributed to its relatively low surface
temperatures during grass cutting.
Class II Lawn Tractors - 3.5 g/kW-hr systems
The lawn tractor equipped with engine 252, which was an OEM muffler and induction system configuration, had
exposed surface temperatures of approximately 150 °C as viewed from both sides of the tractor when cutting
moderate to heavy grass. Note that the view of the exhaust outlet of the muffler was obscured by the OEM touch
guard over the exhaust system. The lawn tractor equipped with engine 231, which had the EFI system and catalyst-
muffler, had exposed surface temperatures of approximately 110 °C. Note that the exhaust outlet housed within the
exhaust ejector was in clear view of the IR Equipment. This temperature was not recorded as an external surface
temperature.
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The lawn tractor equipped with engine 233, which was an OEM muffler and induction system configuration, had
exposed surface temperatures of approximately 220 °C to 280 °C. The lawn tractor equipped with engine 232,
which had the EFI system and catalyst-muffler, had exposed surface temperatures of approximately 200 °C.
In the case of both engine families, exposed surfaces were cooler for the catalyst-muffler equipped engines. This
differed somewhat from the laboratory results, in part due to the more effective cooling of the catalyst-mufflers as
installed in the chassis due to the re-routing of cooling air through the chassis and the addition of the exhaust
ejectors.
Class II Lawn Tractors - 8.0 g/kW-hr systems
The lawn tractor equipped with engine 251, which used an OEM muffler, had exposed surface temperatures of
approximately 200 °C as viewed from both sides of the tractor when cutting moderate to heavy grass, with peaks as
high as 300 to 365 °C. The lawn tractor equipped with engine 253, which had the catalyst-muffler, had exposed
surface temperatures of approximately 115 to 130 °C, with peaks of 160 to 190 °C.
The lawn tractor equipped with engine 256, which used an OEM muffler, had exposed surface temperatures of
approximately 180 °C to 230 °C with peak temperatures of 290 to 320 °C. The lawn tractor equipped with engine
254, which had the catalyst-muffler, also had exposed surface temperatures of approximately 180 to 230 °C and
peak temperatures of 290 to 320 °C.
In the case of both engine families, exposed surfaces were ether comparable (engine 254) or cooler (engine 253) for
the catalyst-muffler equipped engines. This differed somewhat from the laboratory results, in part due to the more
effective cooling of the catalyst-mufflers as installed in the chassis due to the re-routing of cooling air through the
chassis and the addition of the exhaust ejectors.
Results of Hot-Soak Tests Conducted in the Field
Results of the hot soak tests conducted after approximately 30 to 45 minutes of grass cutting are presented in
Figures 6-39 and 6-40 for the lawn mowers and lawn tractors, respectively, for data taken in Tennessee in the fall of
2005 and in Figures 6-41 and 6-42, respectively, for data taken in Florida in early 2006.
Tennessee Tests
At the two minute nominal refueling point following engine shut-down, two of the lawn mowers equipped with
catalyst mufflers (engines 246 and 248) had comparable surface peak surface temperatures to the lawn mower
equipped with the OEM muffler (engine 259). Two of the catalyst-muffler equipped lawn mowers (engines 244 and
249) were significantly cooler than the lawn mower equipped with the OEM muffler. The temperature decrease
with time was more pronounced with the OEM configuration (259). Temperatures for all tested configurations were
comparable at approximately five to six minutes following engine shut-down. Trends in soak temperatures relative
to muffler shrouding and catalyst precious metal composition were similar to those observed during grass cutting.
Catalyst washcoating formulations with higher palladium or rhodium content in place of platinum higher content
tended to start the soak period with lower temperatures. Catalyst-mufflers using air shrouds and exhaust ejectors
also tended to start the soak period with lower temperatures.
Florida Tests
At the two minute nominal refueling point following engine shut-down, all of the catalyst-muffler equipped lawn
mower and lawn tractor configurations had lower peak surface temperatures than the OEM muffler configurations.
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244 w/catalvst
245 w/catalvst
246 w/catalvst
248 w/catalvst
249 w/catalvst
259 OEM muffler
0:00 1:00 2:00 3:00 4:00 5:00 6:00
Time (min.:sec.)
7:00
8:00
9:00 10:00
Figure 6-39: A comparison of peak surface temperatures for six lawn mowers measured using infrared thermal
imaging during hot-soak tests immediately following engine shut-down after approximately 30 minutes of grass-
cutting. At the nominal two minute refueling point, peak temperatures of the catalyst-muffler equipped lawn
mowers were either comparable to (246, 248) or below (245, 244, 249) the lawn mower equipped with an OEM
muffler (259). This data was acquired in SW Tennessee.
Both of the lawn tractors equipped with EFI and catalyst-mufflers (engines 231 and 232) were cooler than the OEM
lawn tractors (engines 233 and 252) at the nominal two minute refueling point after engine shut-down. Surface
temperatures for both EFI and catalyst-muffler configurations were at or below 100 °C for the entire soak period
following engine shut-down. Surface temperatures for the lawn tractor equipped with engine 231 decreased slower
than the lawn tractors equipped with engines 232, 233 and 252. Surface temperatures were comparable for the
configurations with engines 232, 233 and 252 at approximately five to six minutes following engine shut-down.
Engine 231 had higher cylinder head and oil temperatures than engines 232 and 233 (but less than engine 252) and
231 also had somewhat less cooling capacity from the engine fan than engines 232 and 233. It is possible that the
higher chassis and engine temperatures of lawn tractor equipped with engine 231 combined with the increased mass
of the catalyst-muffler reduced the rate of heat transfer from the exhaust system following shut-down.
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200
231 w/EFI&Catalyst
232 w/EFI&Catalyst
180
'Mu
rs
— 233 OEM Configuration
252 OEM Confiauration
160
140
J 120
H 100
0:00
1:00
2:00
3:00
4:00
5:00
6:00
7:00
8:00
9:00 10:00
Time (min.:sec)
Figure 6-40: A comparison of peak surface temperatures for four lawn tractors measured using infrared thermal
imaging during hot-soak tests immediately following engine shut-down after approximately 30-minutes of grass-
cutting. At the nominal 2-minute refueling point, peak surface temperatures for the lawn tractors equipped with EFI
and catalyst mufflers were comparable to (231) or significantly cooler than (232) the OEM configurations (233,
252). Note that engines 232 and 233 are both from one engine family, and that engines 231 and 251 are both from
another engine family (refer to table 5-2). This data was acquired in SW Tennessee.
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0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00
Time (min.:sec.)
Figure 6-41: A comparison of peak surface temperatures for two lawn mowers measured using infrared thermal
imaging during hot-soak tests immediately following engine shut-down after approximately 30 minutes of grass-
cutting. This was a repeat of hot-soak testing for engines 244 and 245 at a higher ambient temperature (30 °C vs.
18.5 °C). and with engine 245 using an OEM muffler. At the nominal two minute refueling point, peak
temperatures of the catalyst-muffler equipped lawn mower (engine 244) was below that the lawn mower equipped
with an OEM muffler (engine 245). The range of surface temperatures encountered were approximately 60 °C
higher than those measured at lower ambient temperature conditions (Figure 6-39). This data was acquired in
Florida.
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253 w/Catalyst
251 w/OEM Muffler
254 w/Catalyst
256 w/OEM Muffler
0:00 1:00 2:00 3:00 4:00 5:00
Time (min.:sec.)
6:00
7:00
8:00
Figure 6-42: A comparison of peak surface temperatures for four lawn tractors measured using infrared thermal
imaging during hot-soak tests immediately following engine shut-down after approximately 30-minutes of grass-
cutting. At the nominal 2-minute refueling point, peak surface temperatures for the lawn tractors equipped with
catalyst mufflers (engines 251 and 256) were significantly cooler than the OEM muffler configurations (engines 251
and 256). Note that engines 251 and 253 are both from one engine family, and that engines 254 and 256 are both
from another engine family (refer to table 5-2). This data was acquired in Florida.
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Idle Testing
The turf surface temperatures for the catalyst-muffler equipped lawn tractors were either comparable (engine 254)
or reduced (engine 253) relative to the turf surface temperatures measured during idling of the lawn tractors with the
OEM mufflers (engines 251 and 256). The variation in turf temperatures was due entirely to wind gusts. Wind
breaks were improvised on two sides of the lawn tractors, but light wind gusts were observed to cause an
approximately 10 °C to 20 °C oscillation in peak turf temperatures measured for engines 254 and 256. Wind was
relatively calm during the measurements with engines 251 and 253, which reduced the variability in peak turf
temperatures to approximately 5 °C to 10 °C. Note that engines 251 and 253 are both from one engine family, and
that engines 254 and 256 are both from another engine family (refer to table 5-2). This data was acquired in
Florida.
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100
r so
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7. Design and Process Failure Mode and Effects Analyses (FMEA)
to Assess NHH Incremental Safety Risk
A. BACKGROUND
In addition to the laboratory and field work described in previous chapters, EPA contracted with Southwest
Research Institute of San Antonio, Texas to conduct design and process Failure Mode and Effects Analyses. The
full text of the SwRI report is contained in an Appendix to this study.
An FMEA is an engineering analysis tool to help engineers and other professional staff on the FMEA team to
identify and manage risk. In an FMEA, potential failure modes, causes of failure, and failure effects are identified.
The primary purpose of the FMEA is to identify those causes of failure modes with the greatest potential for adverse
effect both in terms of frequency of occurrence of the cause of the failure and in the severity of the consequences of
the failure. Within an FMEA the multiplicative product of the numerical values assigned to the frequency of
occurrence of the causal mechanism and severity of the effect of the failure is referred to as risk probability. This
risk probability is used by the FMEA team to rank problems for potential action to reduce or eliminate the causal
factors. The focus of the FMEA is on identifying and prioritizing the causal factors for the failure modes, because
the causal factors are the elements that a manufacturer can consider in order to reduce the adverse effects that might
result from a failure mode. While data is employed to the greatest degree possible, ultimately the process depends
on the professional judgment by members of the FMEA team.
Risk and risk probability are not the same. In traditional safety analysis, risk usually refers to the likelihood of the
occurrence of a hazardous outcome. The occurrence of a hazardous outcome in a given event is much less than the
occurrence of the event itself (e.g., most trip and fall events do not lead to broken bones). In this context, the risk
probability is not the risk that an actual hazardous outcome will occur in a given event, but is a tool to rank the
relative risk of events based on the frequency of the causal factor leading to a failure mode and the severity of the
potential effect of the failure. The frequency used to determine risk probability is the estimate of the frequency of
the potential cause of the failure mode not the frequency of the potential effect(s) if the failure mode were to occur.
For example, one failure mode that was evaluated is backfiring from the engine. One factor that could cause
backfire would be a richer fuel mixture. A richer mixture does not always lead to backfire, if it did then there is
always an increased risk of fire or burn. The FMEA analysis looks at the probability that the causal factor, (the
richer fuel mixture), would occur, and the severity of the outcome if the richer fuel mixture did lead to backfire and
a fire or burn. The analysis does not try to determine the likelihood that richer fuel mixture will in fact lead to fire
or burn, instead, the analyses basically assumes the worst case - the backfire does occur and leads to a fire or burn.
The analysis looks at various failure modes from this worst case perspective, in order to rank the highest priority
issues to address. Thus, for FMEA purposes the risk probability associated with richer fuel mixture may be the same
for all potential outcomes of a richer fuel mixture because the probability of the causal factor of richer fuel mixture
occurring is the same. However, the hazardous outcome of a fire or burn occurring is clearly not the same as the
probability that a richer fuel mixture will occur. Determining hazard risk is beyond the scope of a design or process
FMEA.
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B. THE WORK CONDUCTED BY SwRI
In doing this work for EPA, SwRI used the basic FMEA approach contained in SAE Standard J1739.1 This
approach requires the FMEA team to identify and characterize the systems and subsystems involved and then for
each subsystem list:
1. The item/function being analyzed
2. The potential cause(s)/mechanism(s) of the failure (both primary and contributing, as appropriate)
3. The potential failure mode
4. The potential effect(s) of the failure
5. The classification of the effect
6. The severity of the failure mode
7. The frequency of occurrence of the potential cause(s)/mechanism(s)
8. Risk Probability Number (RPN) [( 6)x(7)]
SAE J1739 provides detailed and helpful guidance to the team on how to set-up and conduct the FMEA. However,
the FMEA is a tool and is often tailored by an FMEA team to help better meet project needs. In this case, looking at
the incremental risk question raised by EPA required SwRI to make adaptations in the way they applied the SAE
protocol. These are described in the full text of the SwRI report attached to this study.
This FMEA covered equipment using Class I and Class II engines. For Class I engines, the equipment identified
was a typical walk-behind lawnmower (WBM). For Class II, the equipment identified was a ride-on lawnmower
(ROM). Two different types of FMEAs were prepared. The first was design FMEAs for both the WBM and ROM.
The second were three process FMEAs covering refueling, maintenance, and shutdown and storage of the
equipment.
These FMEAs were conducted to identify and assess potential differences in risk probability between engines and
equipment meeting EPA Phase 2 emission standards and properly designed engines and equipment meeting
potential EPA Phase 3 emission standards. For Phase 2 Class I and II powered-equipment, SwRI used typical
currently produced equipment/engines. Obviously, production Phase 3 equipment is not available. The
characteristics of properly designed Phase 3 equipment/engine as considered by SwRI are presented in Table 7-1.
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Table 7-1. Projected Phase 3 Engine Characteristics
Item No.
Class I Lawnmower Engine
Class II Ride-on Mower Engine
1
Application of catalyst (moderate activity 30-50%)
designed to minimize CO oxidation, maximize
NOx reduction, with low HC oxidation efficiency
at high exhaust-flow-rates and high HC oxidation
efficiency at low-exhaust flowrates. This design is
expected to minimize catalyst exotherm.
Application of catalyst (moderate activity 30-50%)
designed to minimize CO oxidation, maximize
NOx reduction, with low HC oxidation efficiency
at high exhaust flowrates and high HC oxidation
efficiency at low-exhaust flowrates. This design is
expected to minimize catalyst exotherm.
2
Cooling and shrouding of engine and muffler to
minimize surface temperatures. Use of heat
shielding and/or air-gap insulated exhaust
components to minimize surface temperatures.
Cooling and shrouding of engine and muffler to
minimize surface temperatures. Use of heat
shielding and/or air-gap insulated exhaust
components to minimize surface temperatures.
3
Design flow paths/baffles through the mufflers to
incorporate flame arresting design features, to
improve heat rejection to muffler surfaces and to
spread heat rejection over a large surface area of
the muffler. This will reduce the incidence of
backfire and reduce localized hot spots.
Design flow paths/baffles through the mufflers to
incorporate flame arresting design features, to
improve heat rejection to muffler surfaces and to
spread heat rejection over a large surface area of
the muffler. This will reduce the incidence of
backfire and reduce localized hot spots.
4
Different catalyst substrates (ceramic, metal
monolith, hot tube, metal mesh) can be
successfully used.
Different catalyst substrates (ceramic, metal
monolith, hot tube, mesh) can be successfully
used.
5
The use of air ejectors to cool exhaust gases at the
muffler outlet and to improve cooling of heat
shielding.
The use of air ejectors to cool exhaust gases at the
muffler outlet and to improve cooling of heat
shielding.
6
Use of a small amount of passive supplemental air
to improve exhaust chemistry at light load, but
designed so bulk exhaust remains rich of
stoichiometry at all conditions, and flow-limited at
high exhaust flowrates. This design minimizes
risk of excessive catalyst exotherm.
Use of carburetor recalibration to improve exhaust
chemistry at light load conditions.
7
Use of fuel filter and/or improved design needle
and seat in carburetor to minimize problems
caused by fuel debris.
Improved air/fuel ratio control through tighter
manufacturing tolerances to minimize variation.
8
Improved intake manifold design to reduce intake
manifold leaks.
No anticipated design changes.
9
Cooling system designed to reduce the
accumulation of debris, including the use of a
mesh or screen on cooling fan inlet, when lacking
in current design.
Cooling system designed to reduce the
accumulation of debris.
10
Improved ignition system design to be more
reliable and durable than on Phase 2.
Improved ignition system design to be more
reliable and durable than on Phase 2.
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Table 7-1. Projected Phase 3 Engine Characteristics (continued)
11
Improved component design and manufacturing
processes to reduce air-fuel ratio production
variability to stabilize engine performance and
emissions.
Component changes are not expected. Improved
manufacturing processes to reduce air-fuel ratio
production variability to stabilize engine
performance and emissions.
12
Locate fuel tanks away from heat sources.
Locate fuel tanks away from heat sources.
13
Use of carburetors with appropriate idle circuits,
float-bowl vent, and automatic choke or improved
primer bulb. This will improve fuel system
reliability.
Use of carburetors with appropriate idle circuits,
float-bowl vent, and automatic choke. This will
improve fuel system reliability.
14
Locate the exhaust port away from the
carburetor/fuel line to minimize carburetor
heating.
No anticipated design changes.
15
Improved exhaust system design and materials for
better durability and reliability.
No anticipated design changes.
16
Improved muffler/catalyst/equipment design since
currently, the muffler designs do not incorporate
catalysts.
Improved muffler/catalyst/equipment design since
currently, the muffler designs do not incorporate
catalysts.
17
Evaporative emission controls: hoses, tank, cap,
and evaporative emission control system.
Evaporative emission controls: hoses, tank, cap,
and evaporative emission control system.
18
As Needed: non-contact, bi-metal thermal switch
to disable ignition system to shut engine down in
event of excessive temperature.
As Needed: non-contact, bi-metal thermal switch
to disable ignition system to shut engine down in
event of excessive temperature. Manufacturers
will need to consider the potential trade-off of
disengaging engine power on ride-on equipment if
were to occur on a slope.
C. DESIGN FMEA
The design FMEAs looked at the subsystems/components likely to be modified for compliance with potential Phase
3 exhaust and evaporative emission control requirements and those affected by the modification. Twelve
systems/subsystems were evaluated for both the WBM (Class I) and the ROM (Class II). This broad approach was
deemed essential because of the technical interdependency among these systems in creating power and the potential
interactions among these systems in failure mode situations. The twelve subsystems evaluated included:
1. intake air filter
2. carburetor system
3. governor
4. intake manifold, port, valve, and seals
5. block, power head
6. exhaust valve and seal
7. exhaust manifold, muffler, muffler shroud, and gasket
8. supplemental air (venturi)
9. catalyst
10. cooling system
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11. ignition system
12. fuel tank and line
The design FMEAs were structured and conducted in the following manner: (The reader may find it useful to refer
to the template in Figure 7-1.)
Figure 7-1: Sample FMEA Template
Item
Potential
Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential
Effect(s) of
Failure
Classificatio
n
of Effect
Sev
Ph
2
Occur
Ph 2
RPN
Ph
2
RPN
Ph 3
Sev
Ph
3
Occur
Ph 3
RPN
Delta
(Ph 2
vs. Ph
3)
Notes
First the system and function were identified. Next, for each item identified, each cell of the columns of the FMEA
was completed. This relied heavily on SwRI's understanding of small engines, combustion, fuels, and how the
primary and contributing causes can translate into potential failure modes. The failure modes of the subsystem were
often identified as a potential cause (primary or contributing) of a potential failure mode of other engine system.
Once the potential failure modes were identified, the team ranked the estimated occurrence rate. Then the team
identified the potential effects (usually more than one) and ranked their individual severity. Information from the
CPSC databases discussed in Chapter 4 was instrumental in linking potential failure modes and effects. The
rankings for the severity of the failure mode and the frequency of occurrence of potential cause were drawn from
the tables (shown below) which were taken from the SwRI report. For the severity classification any failure mode
involving a potential burn or fire was ranked as a 9 or 10, respectively, while an increase in the risk of fire or burn
was ranked as a 9. The final steps in the FMEA process were to assign the effect to one of four classes (safety,
regulatory compliance, performance, other) and to calculate the risk probability number for each row by multiplying
the occurrence and severity values. The entire process was completed for each of the twelve subsystems for the
WBM Phase 2, WBM Phase 3, ROM Phase 2, and ROM Phase 3 equipment. Calculating the delta RPN shown in
the template required a subtraction of the RPN value for the Phase 2 and Phase 3 analysis for each item. The full
results for these four design FMEAs are in the attached SwRI reports.
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Table 7-2: Severity Ranking Scale
Ranking
Effect
Severity of Effect - Customer
10
Hazardous
Hazardous effect. Safety Related. Regulatory non-
compliant
9
Serious
Potential hazardous effect. Able to stop without mishap.
Regulatory compliance in jeopardy.
8
Extreme
Item inoperable, but safe. Customer very dissatisfied
7
Major
Performance severely affected, but functional and safe.
Customer dissatisfied
6
Significant
Performance degraded, but operable and safe. Customer
experiences discomfort
5
Moderate
Performance moderately affected. Fault on non-vital
requires repair. Customer experiences some
dissatisfaction
4
Minor
Minor effect on performance. Fault does not require
repair. Non-vital fault always noticed. Customer
experiences minor nuisance.
3
Slight
Slight effect on performance. Non-vital fault noticed most
of the time. Customer slightly annoyed.
2
Very Slight
Very slight effect on performance. Non-vital fault may be
noticed. Customer is not annoyed.
1
None
No effect.
Table 7-3: Occurrence Ranking Scale.
Ranking
Probability
Likely Failure Rates
10
Almost Certain
Greater than / Equal to 1 in 2
9
Very High
1 in 3
8
High
1 in 8
7
Moderately High
1 in 20
6
Medium
1 in 80
5
Low
1 in 400
4
Slight
1 in 2000
3
Very Slight
1 in 10,000
2
Remote
1 in 50,000
1
Almost Impossible
<1 in 500,000
Note 1: For the Design FMEA the Occurrence Ranking is related to the design life of the equipment.
Note 2: For the Process FMEA the Occurrence Ranking is related to a one-year operation period.
D. PROCESS FMEA
As discussed in Chapter 4, input received from various sources and the CPSC databases revealed three processes
which to some degree lead to problems in-use. The process FMEAs conducted by SwRI addressed refueling,
equipment shut down and storage, and maintenance (equipment cleaning, oil/filter change, spark plug change, blade
sharpening, and drive belt replacement). While some of the information and results from the design FMEA would
carry across to the process FMEAs (e.g., air filter problems), a key difference between the analyses of these
activities in the design and process FMEAs is the introduction of the operator as a factor. Otherwise, the process
FMEAs were conducted very much like the design FMEAs, with heavy reliance on the SwRI technical expertise
and inputs gleaned from the CPSC databases.
E. FMEA RESULTS
The purpose of the FMEAs was to identify and assess change in engines, equipment, and operation that could
potentially impact safety when moving from Phase 2 compliant product to Phase 3 compliant product. To meet this
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objective there were two further steps necessary to put the FMEA results in a format useful for this study. The first
is related to the "Classification of Effect" column. Above we indicated that the study divided all of the potential
effects into one of four categories; of those four, only safety is relevant here. Second, as was presented above, the
analysis should be presented in a format that shows incremental RPN differences between Phase 2 and Phase 3
product. The differences between the outcomes of the Phase 2 and Phase 3 design and process FMEAs are
instructive in characterizing potential safety concerns in each category and identifying potential incremental safety
risks. This is possible because the delta RPN number is indicative of the incremental change in risk from the
engineering perspective. From the viewpoint of a designer, a positive delta RPN would indicate a directional
reduction in the incremental risk, a zero value would represents essentially no incremental change, and a negative
delta RPN would suggest a directional increase in risk. Tables 7-4 to 7-8, shown below, present the design and
process FMEA results for the safety-related items from the attached SwRI report.
F. DISCUSSION OF DESIGN FMEAs FOR CLASSES I AND II
A review of the analyses presented in Tables 7-4 and 7-5 clearly indicates that for both the WBM (Class I) and
ROM (Class II) FMEAs, the overall FMEAs are comparable for Phase 2 and the Phase 3 compliant equipment.
Table 7-4 presents the safety-related items of the FMEA for WBMs. In the WBM (Class I engine) FMEA, SwRI
identified 24 failure modes with the potential for an impact on safety. In comparing the Phase 3 and Phase 2 RPNs,
11 indicated a positive RPN delta and thus the potential for a directional improvement in safety, while one indicated
a negative RPN delta and thus the potential for a directional degradation in safety, and 12 indicated no overall
change in RPN. Similarly, Table 7-5 presents the safety-related items of the FMEA for ROMs. In the ROM (Class II
engine) FMEA, SwRI identified 25 failure modes with the potential for an incremental safety effect. In comparing
the Phase 3 and Phase 2 RPNs, 8 indicated a positive RPN delta and thus the potential for a directional improvement
in safety, while one indicated a negative RPN delta and thus the potential for a directional degradation in safety, and
16 indicated no overall change in RPN.
Chapter 4 identified seven scenarios for evaluation, and indeed the FMEAs also identified many of the potential
causes listed in Chapter 4 as potential failure modes. The FMEA outcomes for these items will be discussed further
in Chapter 8.
There was one hazard pattern identified in the CPSC IPII database where the cause was unknown. In Chapter 3 this
is identified as "Unspecified: For reasons unspecified, the running lawn mower catches fire/explodes." With no
detail, it is not wise to speculate on the specific cause(s) of these events. While these types of incidents are not
directly addressed in the FMEA a review of the FMEA tables and the details on incidents of this nature may provide
some perspective. Major engine malfunction is addressed in the Class I and Class II FMEAs with the conclusion
that there is no change in risk probability number. Also, fuel line and fuel tank leak or failure is assessed in the
Class I and Class II design FMEAs with the general conclusion that the possibility that some manufacturers may
move fuel tanks to address fuel evaporative emission controls could at least directionally reduce the risk probability
number for Phase 3 versus Phase 2 equipment. In addition, the Class I and Class II FMEAs indicate a lower risk
probability number for debris fires for a properly designed Phase 3 system compared to a current Phase 2 system.
Thus, based on this assessment, to the degree that these types of potential causes lead to fire in operation, EPA
believes that in an overall sense there will not be an increase in this type of fire for a properly designed Phase 3
system.
The design FMEAs looked at the subsystems/components likely to be modified for compliance with potential Phase
3 exhaust and evaporative emission control requirements and those affected by the modification. Twelve
systems/subsystems were evaluated for both the WBM (Class I) and the ROM (Class II). This broad approach was
deemed essential because of the technical interdependency among these systems in creating power and the potential
interactions among these systems in failure mode situations. The potential effect of failure modes on the catalyzed
muffler performance was considered in each item evaluated. No system or subsystem was considered in isolation.
Considering this systems view and the interactions among the subsystems it is worthwhile to discuss the issue of
enleanment, an increase in the intake A/F ratio above the design value. This can occur because of an increase in
the available air or a decrease in the available fuel, and is usually a result of a failure of a component or subsystem
upstream of the exhaust manifold. Concerns have been expressed that enleanment on an engine with a catalyzed
110
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muffler could lead to fire and burn risk because the activity of the catalyst would enhance CO oxidation in the
presence of the extra air. However, increased oxidation also occurs in a non-catalyst muffler because the muffler
acts like a thermal reactor.
Even without potential failures exhaust system surface temperatures are above the levels needed for contact burns to
occur. With enleanment the surface temperatures would still be above the temperatures needed for thermal burns to
occur. The FMEA identified three potential failure modes related to leaner mixtures, including situations where the
air filter, the carburetor, or the intake air manifold failed to function as designed. For all three potential failure
modes even with the potential for hotter exhaust gas, hotter exhaust system surface temperatures, and/or hotter
engine surface temperatures, the RPN related to fire and burn risk is zero or improved for Phase 3 compared to
Phase 2.
The Phase 3 catalyzed system incorporates improvements which will reduce the surface temperature exposed to the
user. The improvements include cooling air from the fan directed over the muffler and the heat shield designed to
cover the entire muffler and direct that cooling air around the muffler and out designated areas for maximum
muffler cooling. Therefore, increased temperatures resulting from differing exhaust conditions would not result in a
significant increased temperature to the user over that of a Phase 2 system experiencing the same exhaust
conditions.
Process FMEAs
SwRI also performed process FMEAs on the WBM and the ROM to assess potential failure modes and effects for
three of the most common events in the life cycle of the engine and equipment. These included refueling, shutdown
and storage, and maintenance. A review of the information provided by CPSC indicates current in-use safety
problems in all three areas.
First, with regard to refueling, in Table 7-6, SwRI identified 25 aspects of the operation with potential impacts on
safety. Of these, 12 involved the actual dispensing of fuel from a gas can into the equipment tank. SwRI's analysis
indicated no change in RPN for Phase 2 and Phase 3 equipment for any of the 25 events involving refueling.
The second process FMEA (Table 7-7) involved shutdown and storage of equipment after use. The IPII data base
provided by CPSC included a number of situations where, for various reasons, equipment stored either outdoors or
indoors after use led to a grass or structure fire. In most cases the causes were not clear, but were presumably related
to grass/leaf debris or combustible material coming into contact with hot surfaces or the ignition of fuel vapor by
sources not related to the mower unit. SwRI identified 15 items with potential safety implications related to
shutdown and storage. In none of these did the FMEA indicate any differences in RPN between Phase 2 and Phase
3 equipment.
The third process FMEA (Table 7-8) involved different aspects of common maintenance practices including
cleaning equipment, changing the oil/filter, changing the spark plug, sharpening the cutting blade, and replacing the
drive belt. Of the 16 different items identified, SwRI identified five in which the RPN improved slightly. In each of
these, the potential for fuel spillage on the operator or on hot surfaces during maintenance would be reduced
because of tank and cap changes brought on by potential EPA fuel evaporative emission control requirements.
G. CONCLUSION
The RPN values are the output from the FMEA which the engineer would use to rank and prioritize actions which
might be taken to reduce potential risk. Since EPA is most interested in assessing the incremental risk of going from
Phase 2 to Phase 3, the delta RPN as presented in the SwRI analyses is instructive in understanding how design and
performance changes on the engines/equipment might affect in-use fire and burn risk.
When comparing the delta RPN results for the Phase 2 WBM and Phase 3 WBM design FMEAs and comparing the
delta RPN results for the Phase 2 ROM and Phase 3 ROM design FMEAs the engineer would conclude that the
Phase 3 equipment does not present an increase in risk of fire and burn relative to Phase 2. The FMEAs for both
WBMs and ROMs give comparable and in some cases directionally positive results. The engineer's decisions on
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ranking and prioritizing risks to address would not be significantly different for a properly designed Phase 3 system
compared to a current Phase 2 system.
An inspection of the RPN delta columns in Tables 7-4 to 7-8 shows only modest changes. The vast majority of
RPN deltas were positive or zero for the safety classification indicating either a directional improvement or no
change in risk. This indicates that from the FMEA perspective, the potential causes identified in the seven scenarios
in Chapter 4 would not be worse for a properly designed Phase 3 system and some would be better.
This analysis includes a catalyzed muffler in the Phase 3 systems. Since a Phase 2 system does not have a catalyzed
muffler, the potential exists to identify failure modes related to the inclusion of the catalyst in the muffler. In the
Phase 3 WBM and ROM FMEAs, the catalyzed muffler was considered in every item evaluated. In the beginning
of this chapter EPA discussed that the rationale for selecting twelve subsystems in the WBM and ROM FMEAs,
was to ensure that the analyses captured the technical interdependency among these subsystems in creating power
and the potential interactions among these systems in failure mode situations. That is to say, problems in air intake,
ignition, carburetion, fuel storage etc all had the potential to manifest themselves as causal effects for fire or burn
problems related to the catalyzed muffler. However, of the approximately twenty five items evaluated in both the
WBM and ROM design FMEAs where the catalyst was considered in each item, the analyses identified only one
type failure mode which led to a negative delta RPN. The vast majority had a positive or zero delta RPN leading to
the conclusion catalyst-equipped WBMs and catalyst-equipped ROMs can be implemented without an increase in
risk of fire or burn.
The one item with a negative delta RPN in both the Class I and Class II design FMEAs was related to either an
incorrect or improperly installed catalyst in the muffler where there was not one in the Phase 2 system. In this case,
the FMEA performed its intended function - to identify for the designer potential failure modes and effects to allow
for an appropriate response as necessary. In this case the severity was rated a 10 based on burn or fire concerns and
the frequency of the failure was rated as a 2 (remote) by SwRI. The chance of this occurring truly seems remote
since catalyst geometries will by definition partially eliminate mistakes (the wrong catalyst won't fit in the space
allocated) and there are very tight finite limits on catalyst wash coating which would limit the severity.
Conceptually, this potential problem is similar to one not identified in the Phase 2 FMEAs, that being the mis-
installation of the muffler or an incorrect muffler. In this case there would be potential problems related to
backpressure or changes in cooling air flow which could affect fire and burn risk. No such problems were identified
in the CPSC databases. Nonetheless, if the FMEA team decided to address this concern for Phase 3 engines there
are a number of approaches including QA/QC processes to address potential catalyst vendor or installation problems
or improved heat shielding. Thus, EPA does not see this potential failure mode as creating an in-use risk.
1 SAE J1739, "Potential Failure Mode and Effects Analysis in Design (Design FMEA) and Potential Failure Mode
and Effects Analysis in Manufacturing and Assembly Processes (Process FMEA) and Effects Analysis for
Machinery (Machinery FMEA)", SAE International, August 2002.
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Table 7-4: Class I Safety FMEA Items
Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta (Ph
2 vs Ph 3)
Notes
1
Intake Air
Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
richer
mixture
backfire
fire or burn
1 Safety
10
3
30
20
10
2
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
2
Intake Air
Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
leaner
mixture
hotter exhaust
fire or burn
1 Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
there will be no increase in burn risk with the application of a
properly designed catalyst. The effect could be mitigated by
the presence of a thermal switch.
3
Carburetor
System
Restriction in fuel
passages, wrong
jets in production
or production
variability
leaner
mixture
Higher
temperature in
engine and
catalyst
fire or burn
1 Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. Any
effect that the catalyst might have on temperature level is
offset by the expected improvements in air cooling of the
manifold system on Phase 3 products. If the change in
temperature is significant the effect could be mitigated by the
presence of a thermal switch.
4
Carburetor
System
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer
mixture
backfire
fire or burn
1 Safety
10
5
50
40
10
4
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
5
Carburetor
System
gasket failure, or
needle valve stuck
open, or cracked
primer bulb
leakage of
fuel to
mower deck,
air filter or
elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1 Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because
exposed muffler temperatures are nominally equivalent. Fuel
can be ignited by hot surfaces or the ignition system.
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta (Ph
2 vs Ph 3)
Notes
6
Carburetor
System
gasket failure, or
needle valve stuck
open, or cracked
primer bulb
leakage of
fuel to
mower deck,
air filter or
elsewhere
(i.e. out of air
filter)
fuel puddles
fire or burn
1 Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst because
exposed muffler surfaces have been shown to be nominally
equivalent in Phase 2 (no catalyst) and Phase 3 (catalyzed)
prototype systems.
7
Governor
Malfunction-
ing governor
open governor
causes engine
overspeed
catastrophic
failure (potential
injury due to
flying parts)
1 Safety
9
2
18
18
9
2
0
Engine failure caused by overspeed. The rankings are the
same with or without a catalyst.
8
Intake
Manifold
None
Crack or leak in
manifold
leaner
mixture
Engine,
exhaust
system and
catalyst run
hotter
fire or burn
1 Safety
10
9
90
40
10
4
50
The lower occurrence for Phase 3 is due to the expected
improvement of the manifold system for Phase 3 products.
The effect could be mitigated by the presence of a thermal
switch.
9
Block
Higher thermal
load
higher
engine
temperatures
Engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
catastrophic
failure (potential
injury due to
flying parts)
1 Safety
9
4
36
36
9
4
0
Engine failure caused by excessive temperatures. The
rankings are the same with or without a catalyst. The effect
could be mitigated by the presence of a thermal switch.
10
Block
Higher thermal
load
higher
engine
temperatures
Engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
fire or burn
1 Safety
10
4
40
40
10
4
0
Engine failure can result in contact with hot metal or fluids.
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
11
Exhaust
Manifold
None
loosening of
muffler,
manifold or
failed gasket
(gasket is
less common
on Class I
vertical shaft
engines)
exhaust leak
fire or burn
1 Safety
10
6
60
40
10
4
20
The lower Phase 3 occurrence is due to the Phase 3 improved
exhaust system design.
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta (Ph
2 vs Ph 3)
Notes
12
Exhaust
Manifold
Debris
accumulation
reduction in
engine
cooling and
increased
muffler
temperatures
ignition of
debris
adjacent to
muffler
fire
1 Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and control of
debris accumulation. In addition, fan inlet screens are
expected on all Phase 3 engines. The failure mode could be
mitigated by the presence of a thermal switch.
13
Exhaust
Manifold
removal or
mechanical
failure of the
shroud
loss of muffler
shroud
fire or burn
1 Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and shroud design.
14
Catalyst
None
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
excessive
catalyst
performance
fire or burn
1 Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does
not have a catalyst. For Phase 3, the severity ranks high due
to the potential safety impact. The effect could be mitigated
by the presence of a thermal switch.
15
Cooling
System
cooling
system
shroud failed
loss of cooling
to engine block
and muffler
system
burn risk
1 Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
16
Cooling
System
None
plugging of
cooling
passages
due to debris
reduction of
engine cooling
burn risk
1 Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design
features for Phase 3 results in a slight reduction in
Occurrence. The effect could be mitigated by the presence of
a thermal switch.
17
Ignition
System
None
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module
failure
weak or
intermittent
spark (misfire)
excessive
muffler or
catalyst
temperatures
and increased
burn risk
1 Safety
9
5
45
27
9
3
18
The lower occurrence for the Phase 3 is due to the improved
ignition system for Phase 3 products. The effect could be
mitigated by the presence of a thermal switch.
18
Ignition
System
plug bad, short in
plug wire, failed
coil, loose
flywheel, magneto
loss of spark
backfire
(misfire)
fire or burn
1 Safety
10
6
60
40
10
4
20
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta (Ph
2 vs Ph 3)
Notes
19
Fuel Tank
leak of tank
or line
fuel puddles
fire or burn
1 Safety
10
5
50
40
10
4
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
20
Fuel Tank
None
leak of tank
or line
fuel puddles
operator fuel
exposure
1 Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
21
Fuel Tank
None
leak of tank
or line
fuel leaks on
hot component
fire or burn
1 Safety
10
4
40
30
10
3
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
22
Fuel Tank
NRfJP muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel puddles
fire or burn
1 Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
23
Fuel Tank
High muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel puddles
operator fuel
exposure
1 Safety
9
3
27
18
9
2
9
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
24
Fuel Tank
High muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel leaks on
hot component
fire or burn
1 Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst. The
exposed muffler temperatures are nominally equivalent.
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Table 7-5: Class II Safety FMEA Items
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
1
Intake Air Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
richer mixture
backfire
fire or burn
1 Safety
10
2
20
20
10
2
0
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. The occurrence
is held the same for Phase 2 and 3 in this case since Class II,
Phase 2 products are already judged to have a relatively low
occurrence of backfire due to intake filter issues.
2
Intake Air Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
leaner mixture
hotter
exhaust
fire or burn
1 Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
there will be no increase in fire or burn risk with the
application of a properly designed catalyst. The effect could
be mitigated by the presence of a thermal switch.
3
Carburetor
System
Restriction in
fuel passages,
wrong jets in
production, or
choke stuck
open, or
production
variability. Fuel
injection system
fuel pump or
fuel pressure
regulator
failure. Fuel
filter or injector
restriction.
Injector wiring
connection
degraded.
MAP, ECM, or
02 sensor
failure.
leaner mixture
higher
temperature
in engine and
Catalyst
fire or burn
1 Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst. Any
effect that the catalyst might have on temperature level is
offset by the expected improvements in air cooling of the
manifold system on Phase 3 products. If the change in
temperature is significant the effect could be mitigated by the
presence of a thermal switch.
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Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Float breaks,
debris in float
needle, or
wrong jets in
production,
choke stuck
4
Carburetor
System
closed, or
production
variability. Fuel
injection fuel
system fuel
pressure
regulator
failure. Fuel
injector stuck
open. MAP,
ECM, 02
sensor failure.
richer mixture
backfire
fire or burn
1 Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
5
Carburetor
System
gasket failure,
or needle valve
stuck open, or
fuel pump /
regulator leak
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1 Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because
exposed muffler temperatures are nominally equivalent. Fuel
can be ignited by hot surfaces or the ignition system.
6
Carburetor
System
gasket failure,
or needle valve
stuck open, or
fuel pump /
regulator leak
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel puddles
fire or burn
1 Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
exposed muffler surfaces have been shown to be nominally
equivalent in Phase 2 (no catalyst) and Phase 3 (catalyzed)
prototype systems.
7
Carburetor
System
ECM failure,
solenoid return
spring
breakage
causes fuel
cutoff solenoid
open failure
fuel flow into
and from
engine
fuel puddles
fire or burn
1 Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst.
118
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
8
Governor
None
malfunctioning
governor
open
governor
causes
engine
overs peed
catastrophic failure
(potential injury due
to flying parts)
1 Safety
9
2
18
18
9
2
0
Engine failure caused by overs peed. The rankings are the
same with or without a catalyst.
9
Intake Manifold
Crack or leak in
manifold
leaner mixture
engine,
exhaust
system and
catalyst run
hotter
fire or burn
1 Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
10
Intake Manifold
Intake manifold
leak causes
MAP to read
higher pressure
richer mixture
backfire
fire or burn
1 Safety
10
3
30
30
10
3
0
The failure relates to fuel Injected engines. EPA
demonstrated that the backfire impact was reduced with the
addition of a properly designed catalyzed muffler system for
Class I. However, since the design quality of the Class II
equipment mufflers is very good on Phase 2, the impact of
adding the catalyst is minimal.
11
Block
Higher thermal
load
higher engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
catastrophic failure
(potential injury due
to flying parts)
1 Safety
9
3
27
27
9
3
0
Engine failure caused by excessive temperatures. The
rankings are the same with or without a catalyst. The effect
could be mitigated by the presence of a thermal switch.
12
Block
Higher thermal
load
higher engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
fire or burn
1 Safety
10
3
30
30
10
3
0
Engine failure can result in contact with hot metal or fluids.
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
13
Exhaust
Manifold
None
cracked
muffler,
manifold or
failed gasket
exhaust leak
fire or burn
1 Safety
10
4
40
30
10
3
10
The lower Phase 3 occurrence is due to the Phase 3
definition of improved exhaust system design.
14
Exhaust
Manifold
Debris
accumulation
reduction in
engine cooling
/ increased
muffler
temperatures
ignition of
debris
adjacent to
muffler
fire
1 Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and control of
debris accumulation.
119
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
15
Exhaust
Manifold
None
removal or
mechanical
failure
loss of
muffler
shroud
fire or burn
1 Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting design for cooling and shroud
design.
16
Catalyst
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
increased
catalyst
performance
fire or burn
1 Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does
not have a catalyst. For Phase 3, the severity ranks high due
to the potential safety impact. The effect could be mitigated
by the presence of a thermal switch.
17
Cooling
System
None
plugging of
cooling
passages due
to debris
reduction of
engine
cooling
burn risk
1 Safety
9
4
36
27
9
3
9
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
18
Cooling
System
None
cooling system
shroud failed
loss of
cooling
burn risk
1 Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
19
Ignition System
None
plug bad, short
in plug wire,
failed coil,
loose flywheel,
magneto,
ignition
module failure
weak or
intermittent
spark, or loss
of ignition in
one of two
cylinders
(misfire)
excessive muffler or
catalyst
temperatures and
increased burn risk
1 Safety
9
3
27
27
9
3
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
20
Ignition System
bad plug, short
in plug wire,
failed coil, loose
flywheel,
magneto
loss of spark
Backfire
(misfire)
fire or burn
1 Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
21
Fuel Tank
None
leak of tank or
line
fuel puddles,
or sprays
fire or burn
1 Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
22
Fuel Tank
None
leak of tank or
line
fuel puddles,
or sprays
operator fuel
exposure
1 Safety
9
3
27
18
9
2
9
The rankings are the same with or without a catalyst.
23
Fuel Tank
Equipment tip
over, material
failure,
component
failure
leak of tank or
line
fuel contacts
hot
component
fire or burn
1 Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
120
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
24
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel puddles
or sprays
fire or burn
1 Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
25
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel puddles
or sprays
operator fuel
exposure
1 Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst.
26
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel contacts
hot
component
fire or burn
1 Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
121
-------
Table 7-6: Refueling Process FMEA
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
1
Shut off engine
failed to shut engine
off
engine
running
risk of refueling while
engine running and a
potential of a fire or burn
1_Safety
9
2
18
No difference between Phase 2 and
Phase 3 expected. Thermal images
indicate that at idle operation the
maximum surface temperatures are
comparable for Phase 2 and Phase 3
designs.
2
Open mower cap
overpressure of fuel
tank
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
3
Open mower cap
overpressure of fuel
tank
spillage (hot
fuel, full tank,
pressurized
tank - i.e. vent
blocked)
spillage onto hot
surfaces and a potential
of a fire or burn
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
4
Open mower cap
overpressure of fuel
tank
fire
1_Safety
10
2
20
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
5
Remove fuel can
cap
operator behavior
Fail to open
vent
fuel spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
6
Remove fuel can
cap
hot fuel and high
pressure(high
temperature storage,
heating from sunlight)
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
7
Remove fuel can
cap
hot fuel and high
pressure(high
temperature storage,
heating from sunlight)
fuel spray
upon opening
cap/vent
spillage
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
8
Remove fuel can
cap
operator behavior
spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
9
Remove fuel can
cap
operator behavior
vapor released from can
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
122
-------
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
10
pick up can and
pour
fuel spill
fuel puddle on
equipment
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
11
pick up can and
pour
fuel spill
fuel spill into
fan inlet
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
12
pick up can and
pour
fuel spill
fuel over the
cowling and
makes contact
with a hot
exhaust
system
component
fuel fire
1_Safety
10
4
40
A safety concern, but effectively no
difference between Phase 2 and Phase
3 expected. Thermal imaging cross-
validation studies indicated that "...the
application of a catalyst to a small
gasoline engine does not increase, and
can actually lower, exhaust system
surface temperatures..."
13
pick up can and
pour
fuel spill
spill on
operator
and/or
bystander
fuel exposure
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
14
pick up can and
pour
fuel spill
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
15
pick up can and
pour
fuel spill
spillage on
surrounding
areas
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
16
pick up can and
pour
fuel spill
creates combustible
material
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
17
pick up can and
pour
material failure
gas can
cracks
fuel spill and potential of
fire or burn
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
18
pick up can and
pour
engine running
refuel while
running
spill fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
19
pick up can and
pour
engine running
fuel vapor ignites
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
20
pick up can and
pour
static charge
spark
fire or explosion
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
123
-------
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
21
pick up can and
pour
gas cap on can is not
secure
spillage on
surrounding
areas
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
22
Recap the Mower
Tank
failure to recap mower
tank
fuel spillage or
vapor release
onto
equipment or
operator
during
operation
fire
1_Safety
10
3
30
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
23
Recap the Mower
Tank
failure to recap mower
tank
fuel exposure
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
24
Restart
fuel on the equipment
ignition
component
failure
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
25
Restart
fuel or debris left on
the equipment
hot surfaces
ignites
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
124
-------
Table 7-7: Shutdown and Storage Process FMEA
Shutdown and Storage Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
1
Engine Shut Down
ignition cut off and
engine brake fail (and
engine does not shut
off)
engine left
running, and
operator may
pull plug wire
to stop
high surface
temperatures, and risk
of fuel ignition from high
voltage spark and risk
of shock
1_Safety
9
2
18
No difference between Phase 2 and Phase
3 expected
2
Engine Shut Down
engine won't stop and
operator goes for help
untended
operation
bystander gets injured
by burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
3
Engine Shut Down
engine won't stop and
operator goes for help
debris fire
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
4
Engine Shut Down
engine won't stop and
operator pulls plug
wire
risk of fuel
ignition due to
high voltage
spark
fire or burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
5
Engine Shut Down
engine won't stop and
operator pulls plug
wire
operator
contacts hot
component
burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
6
Equipment Storage
cover with tarp while
engine hot (any
material)
tarp ignites
fire ignites adjacent
materials
1_Safety
10
2
20
Tarp ignites and fire could spread. No
impact due to addition of a catalyst.
7
Equipment Storage
cover with tarp while
engine hot (any
material)
fire damages equipment
1_Safety
10
2
20
Tarp ignites and fire could spread. No
impact due to addition of a catalyst.
8
Equipment Storage
store in or near
garage or shed when
engine hot
equipment
ignites
combustible
material
structural fire
1_Safety
10
1
10
Surrounding material could ignite. No
impact due to addition of a catalyst. Data
available does not support a higher
occurrence ranking.
9
Equipment Storage
store in or near
garage or shed when
engine hot
water heater
pilot light
ignites
gasoline vapor
from leak, spill
or refueling
structural fire
1_Safety
10
1
10
Gas vapor could ignite. No impact due to
addition of a catalyst. Data available does
not support a higher occurrence ranking.
10
Equipment Storage
store in or near
garage or shed when
engine hot
Spilled fuel or
debris on
mower deck
ignites
Equipment or structural
fire
1_Safety
10
1
10
Debris on the mower deck could ignite. No
impact due to addition of a catalyst. Data
available does not support a higher
occurrence ranking.
125
-------
Shutdown and Storage Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
11
Equipment Storage
store in or near
garage or shed when
engine hot
operator
and/or
bystander
contacts hot
component
burn
1_Safety
10
2
20
No impact due to addition of a catalyst.
12
Equipment Storage
park equipment on
combustible debris
debris ignites
debris fire
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
13
Equipment Storage
park equipment on
combustible debris
structural fire
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
14
Equipment Storage
park equipment on
combustible debris
bystander gets injured
by burn
1_Safety
10
2
20
No impact due to addition of a catalyst.
15
Equipment Storage
park equipment on
combustible debris
fire damages equipment
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
126
-------
Table 7-8: Maintenance Process FMEA
Maintenance Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
1
Cleaning Equipment
Tip equipment to clean
underneath
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
2
Cleaning Equipment
Tip equipment to clean
underneath
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
3
Cleaning Equipment
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
4
Change Oil / Filter
Improper maintenance
spill oil
operator exposure to
oil
1_Safety
9
9
81
No difference between Phase 2
and Phase 3 expected
5
Change Oil / Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
6
Change Oil / Filter
Tip equipment for
maintenance
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
7
Change Oil / Filter
Tip equipment for
maintenance
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
8
Change Air Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
9
Change Spark Plug
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
10
Change Spark Plug
testing for spark
spark ignites fuel
fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
11
Sharpen Blade
tipping equipment for
blade access
equipment falls
personnel injury
1_Safety
10
5
50
No difference between Phase 2
and Phase 3 expected
12
Sharpen Blade
tipping equipment for
blade access
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
127
-------
Maintenance Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
13
Sharpen Blade
Improper reassembly
spill fuel or oil
personnel injury
1_Safety
10
1
10
No difference between Phase 2
and Phase 3 expected
14
Replace Drive Belt
wrong belt installed
belt slips or does
not engage
belt fire / debris fire
1_Safety
10
4
40
No difference between Phase 2
and Phase 3 expected
15
Replace Drive Belt
belt installed
incorrectly
belt slips or does
not engage
belt fire / debris fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
16
Replace Drive Belt
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
-------
129
-------
8. Conclusions - Impact of Phase 3 Exhaust Standards on Class I
and Class II NHH Engines
In this chapter, EPA draws conclusions based upon:
1. the results of laboratory testing conducted with EPA prototypes of engines with Phase 3 exhaust emissions
control systems,
2. the results of laboratory testing conducted with current Phase 2 engines, and
3. the results of the FMEA for each of the key scenarios used to evaluate the incremental risk associated with
advanced emission control technology for NHH engines and equipment.
In all cases, based on the data presented in this report, EPA concludes that the catalyst-based Phase 3 standard
under consideration poses no incremental increase in the risk of fire or burn for Class I and Class II NHH
engines.
SCENARIO 1: CONTACT BURNS
Scenario Description: Thermal burns due to inadvertent contact with hot surface on engine or equipment.
Potential Causes:
a. muffler surface temperature increases due to debris inhibiting flow of cooling air
b. higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler or
engine
c. muffler temperature increase due to air-to-fuel ratio enleanment caused by calibration drift over time, fuel
system problems or air filter element mal-maintenance
d. exhaust gas leaks increase surface temperatures
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
a. Muffler surface temperature increases due to debris inhibiting flow of cooling air. Engines equipped with
catalyst-mufflers showed no greater propensity to trap debris than those equipped with OEM mufflers,
even during operation in high-debris environments in the field. Both laboratory and field testing showed
that properly designed catalyst-mufflers could achieve comparable, or even cooler, surface temperatures
relative to today's OEM muffler designs. EPA did find evidence of cooling air being blocked by debris
during field testing for some engine designs, regardless of exhaust system configuration (see figure 6-36).
A partially blocked cooling system could potentially limit the amount of cooling air available for forced
convective cooling of the exhaust system, and this could occur whether or not the engine is equipped with
a catalyst. Engines 244 and 245 in Class I and all of the Class II engines tested were designed with coarse
screens on the inlet to the cooling fan. Engines with properly designed cooling fan air-inlet screens had
minimal or no issues regarding debris ingestion and blockages within the engine cooling system. Debris
build-up on muffler surfaces did not occur on engines equipped with air-shrouding for muffler or catalyst-
muffler cooling. Properly designed systems were capable of grass cutting operations to near the end of
useful life with minimal build-up of debris either within the cooling system or on exhaust system surfaces
(engines 231, 232, 233, 244, 245, 251). These grass cutting operations included high-debris conditions
that led to nearly complete blockage of the cooling systems on engines 246, 248, 249 and 259. Retrofitting
the engines with a screen near the air-inlet to the cooling fan resolved the debris-blockage issue.
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b. Higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler or
engine: EPA laboratory testing and field testing clearly indicate that comparable, or even cooler, surface
temperatures can be achieved for properly designed catalyst-mufflers relative to today's OEM mufflers
(see Chapter 6). Most Phase 2-compliant engines already have sufficient cooling-air capacity to manage
heat rejection from properly designed catalyst-mufflers, and cooling system designs will be carried or
improved for Phase 3 engines. Proper catalyst design for minimizing heat load includes the use of catalyst
designs that minimize of CO oxidation through careful selection of catalyst size, washcoating composition
and PGM loading. Comparisons of surface temperatures between OEM muffler and catalyst-muffler
configurations for a broad range of engine families and operational conditions are presented within Chapter
6.
c. Muffler temperature increase due to air-to-fuel ratio enleanment caused by calibration drift over time, fuel
system problems or air filter element mal-maintenance: Conditions of richer and leaner air-to-fuel ratios,
as well as little to no change in air-to-fuel ratio, have been observed on the engines EPA has tested as they
have accumulated hours, and can occur whether the engine is equipped with a catalyst-muffler or with
current OEM muffler designs. Leaner air-to-fuel ratios tend to lead to increased exhaust gas temperatures.
While exhaust temperatures would increase regardless of the presence of a catalyst, the concern is that
excessive exhaust system surface temperatures would occur if the engine operated near or lean of
stoichiometry due to the increased availability of oxygen in the exhaust for CO oxidation over the catalyst.
The only induction system problem that EPA has observed as a consistent cause of lean operation at high
hours has been a failure of the seal between the carburetor and intake manifold with one particular family
of Class I engine. This particular engine family uses a plastic, tubular intake manifold design without a
manifold flange onto which the carburetor can directly mount. Instead, the carburetor seals to the manifold
tube by deforming an O-ring located between the carburetor, a carburetor support, and the tube. With this
design, a flat-spot often wears onto the O-ring over time due to engine vibration and insufficient support of
the weight of the carburetor, resulting in an air leak into the induction system that bypasses the carburetor
and causes lean operation. This was a common occurrence during field aging of lawn mower engines in
southeast Michigan with three out of four engines from the same engine family as engine 258 having an
intake manifold O-ring failure and subsequent induction leak with lean operation. Some of the engines that
had intake-manifold gasket failures in the field were tested by EPA, and then sent to an independent
laboratory for tear-down and inspection. The engines were at or close to catastrophic mechanical failure
(complete inoperability), and in one case the engine could not be started and run on the dynamometer for
testing. These engines had:
1. Greatly reduced power output (up to 40% lower)
2. Very poor load pickup
3. Failed head gaskets
4. Cylinder head temperatures exceeding 300 °C and oil temperatures of 180 to 200 °C at high loads
5. Greatly increased oil consumption, due to cylinder bore distortion and loss of oil viscosity at high
temperatures
6. Visible smoke coming from the exhaust (see Figure 8-1)
In the event of an induction system failure resulting in a severe manifold air leak and lean-of-
stoichiometric operation, an increased catalyst exotherm would occur as long as the catalyst is active. Net
lean operation with an air-cooled engine at above moderate load conditions would also result in engine
damage, and would likely result in deactivation of the catalyst from both thermal sintering and oil-
poisoning. In extreme cases, lean operation and high oil consumption may lead to substrate failure or
plugging of the monolith which may result in engine inoperability.
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Figure 8-1: Smoke plume at idle from Class I engine with failed intake manifold and head gasket.
Use of a proper intake manifold design with positive sealing through a flat intake manifold flange, along
with proper mechanical support of the mass of the carburetor minimizes the likelihood of lean-drift of the
air-to-fuel ratio over time. Other engine families tested by EPA that used more typical flat-flange-
mounting systems on their intake manifolds or, in some cases, direct mounting of a side-draft carburetor to
the intake port with no manifold, together with robust carburetor support did not exhibit any significant
trend towards lean operation at high hours.
Catalyst deactivation is an emissions compliance issue, engine manufacturers will need to use robust intake
manifold designs and carburetor supports in order to comply with the Phase 3 emissions regulations to the
end of the engines' useful life. Such designs should reduce or eliminate the occurrence of lean air-to-fuel
ratio drift, and should improve both the safety and the durability of Phase 3 engines relative to today's
Phase 1 and Phase 2 engines. Another alternative for walk-behind lawn mowers would be to entirely
prevent operation of a malfunctioning engine via the use of a low cost (<$1.00), self-resetting bimetal-disk
thermal switch to shut down the engine's ignition system if a pre-set temperature is exceeded. Bimetal
devices are already commonly used on Class I lawn mower engines to provide automatic choke activation,
and are non-contact devices that are mounted directly behind the muffler to sense exhaust heat.
Noncontact bimetal shut-off switches are used in a wide variety of consumer products, including portable
hair-driers, irons, battery-electric lawn mowers, home water heaters and clothes driers.
The impact of air filter mal-maintenance on emissions and air-to-fuel ratio has been significantly reduced
since the advent of the Phase 2 emission standards in the US. The majority of carburetors used with Phase
2 engines are equipped with float bowl venting that provides compensation for air-filter mal-maintenance.
Thus changes in carburetor air-inlet restriction are already largely compensated for by design.
d. Exhaust system leaks: The hypothesis is that an exhaust leak would allow significant air entrainment into
the exhaust system upstream of the catalyst, leading to increased CO oxidation and increased catalyst-
muffler surface temperatures. The layout of existing Class I and Class II exhaust systems would make the
occurrence of this phenomenon extremely unlikely. The relatively close coupled exhaust systems used by
Class I and Class II engines along with the exhaust restriction imposed by the muffler and catalyst would
cause exhaust leaks out of the exhaust system, but would limit ambient air leakage into the exhaust system
to a negligible level since the pressure pulsations in the exhaust are entirely or nearly entirely at a higher
pressure than ambient.
Controlled "leakage" of air into exhaust systems is used as a method of providing secondary air for exhaust
catalyst systems. Examples include the stamped venturi used by European catalyst-mufflers on Class I
engines (see figure 5-1) and the check-valve pulse-air systems used with some motorcycle catalyst systems
and used by automobiles in the 1980s and early 1990s. It is highly unlikely that an exhaust leak would
occur in a manner that would produce the exact shape and exhaust flow restriction necessary for venturi
induction of air into the exhaust.
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Pulse-air systems rely on exhaust gas pulsation to just below ambient pressure to draw air into the exhaust
through a check-valve. Such systems rely on the fact that exhaust traveling through a long pipe has inertia
and the flow is compressible. Between exhaust valve events, the inertia of the exhaust gases can create
temporary conditions at which the exhaust gases are below ambient pressure, allowing ambient air to be
entrained into the exhaust system. While the pulse-air phenomenon has been used successfully with
catalyst systems in numerous automotive and motorcycle applications, attempts to apply pulse-air systems
to Class I and Class II engines have not been successful. Class I lawn mower mufflers are most often
mounted directly to the exhaust port, although some are mounted up to 4-inches downstream of the exhaust
port. Class II lawn tractor mufflers are mounted approximately 8-inches to 2-feet downstream of the
exhaust port. EPA attempted to apply check-valve pulse air systems to both Class I and Class II engines
during early development of exhaust catalyst systems in support of the Phase 3 rule. With such close
coupling of the exhaust system, the inertia of the exhaust gases traveling from the exhaust port and the
exhaust system upstream of the catalyst-muffler resulted in exhaust pressure that did not fall below ambient
pressure between exhaust valve closing and opening events, and thus there was no net change in exhaust
stoichiometry. Similarly, EPA expects that leakage in these systems would obey physics and result in
exhaust gases traveling from the higher pressures found within the exhaust system to the lower pressures
found in the ambient without any significant amount of air moving in the opposite direction.
Temperatures above the human skin burn threshold exist with current production OEM mufflers under a broad
range of normal operating conditions. Proper design and layout of the exhaust system can minimize occurrences of
touch-burns regardless of whether or not the exhaust system incorporates a catalyst or if a system fault occurs. EPA
demonstrated similar or cooler operating temperatures for properly-designed catalyst-mufflers compared to today's
OEM mufflers (see Chapter 6). Catalyst-mufflers equipped with air shrouds and exhaust ejectors in some cases
resulted in systems that were significantly cooler than many current OEM muffler designs.
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Conclusions Based on FMEA of Burn Safety
The potential for increased temperature which could increase thermal burns was assessed in various engine
subsystems and processes within the FMEA. In the FMEA protocol, if the effect of the potential failure was burn or
increased burn risk the item was given a severity classification of 9. There were 58 items in the 5 FMEAs which
indicated burn or increased burn risk as the potential effect of failure. As can be seen in Table 8-1 below, there was
not a significant change in risk probability for burns in going from a Phase 2 engine to a properly designed Phase 3
system. Overall, 17 items in the five FMEAs indicated the potential for a small improvement in risk probability,
two indicated the potential for a small degradation, and 39 indicated no change.
Table 8-1: Burns Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Number with
Number with
Number with
Burn as the Potential
Potential
No Change
Potential
Effect of Failure
Improvement
Degradation*
Design
Class I:
19
10
8
1
Class II:
21
7
13
1
Process
Refueling:
8
0
8
0
Shutdown/Storage:
5
0
5
0
Maintenance:
5
0
5
0
* These two items are discussed in Chapter 7, section G.
SCENARIO 2: DEBRIS FIRE
Scenario Description: Grass and leaf debris on engine/ equipment
Potential Causes
a. muffler surface temperature increases due to debris inhibiting flow of cooling air, debris trapped in tight
areas blocks air flow, dries out and heats up
b. higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler or
engine
c. muffler temperature increase due to air-to-fuel ratio enleanment caused by calibration drift over time, fuel
system problems or air filter element mal-maintenance
d. exhaust gas leaks increase surface temperatures
e. misfueling: use of highly oxygenated fuel such as E85
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
a. Muffler temperature increases due to debris inhibiting flow of cooling air, debris trapped in tight areas
blocks air flow, dries out and heats up: As mentioned in the previous section on touch burns, engines
equipped with properly-designed catalyst-mufflers have no greater propensity to trap debris than those
equipped with OEM mufflers, and have successfully operated to full useful life in the field under
conditions that included high-debris environments. Both laboratory and field testing have shown that
properly designed catalyst-mufflers can achieve comparable, or even cooler, surface temperatures relative
to today's OEM muffler designs. The combination of air shrouding and the use of exhaust ejectors can be
expected to provide significant improvements in prevention of debris build-up and debris ignition by
lowering surface temperatures, lowering exhaust gas outlet temperatures, and improving debris clearance
over hot exhaust system surfaces.
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b. Higher temperatures on mower deck or around muffler due to higher radiant heat load from muffler or
engine or exhaust system leaks: As mentioned in the previous section on touch burns, EPA laboratory
testing and field testing clearly indicates that comparable, or even cooler, surface temperatures can be
achieved for properly designed catalyst-mufflers relative to today's OEM mufflers (see Chapter 6).
Systems using forced-air cooling and exhaust ejectors will actually radiate significantly less onto mower
deck surfaces than many existing OEM muffler systems.
c. Muffler temperature increase due to air-to-fuel ratio enleanment caused by calibration drift over time, air
filter element mal-maintenance, or exhaust system leaks: As mentioned in the previous section on touch
burns, air-to-fuel ratio drift can be largely eliminated via moderate improvements to induction system
designs. Such improvements will be necessary in order to comply with Phase 3 emission standards at full
useful life, and will result in improvements to both engine durability and safety. A low-cost bimetal
ignition cut-off switch could also be used for walk-behind lawn mower applications to prevent excessive
exhaust system surface temperatures in the event of a system failure causing excessively lean operation.
d. Exhaust gas leaks increase surface temperatures'. As mentioned in the previous section on touch burns,
the exhaust backpressure and layout of Class I and Class II exhaust systems will result in leaks of exhaust
gases out of the system, but not air into the system. Thus exhaust leakage cannot appreciably change
exhaust stoichiometry, increase CO oxidation, or increase catalyst-muffler temperatures.
e. Misfueling: use of highly oxygenated fuel such as E85: Misfueling a Phase 3 Class I or Class II engine
with E85 would most likely result in an engine incapable of starting. While E85 is not yet widely available
in the U.S., its use is increasing in centrally fueled fleets. The air-to-fuel of ratio of an engine with a
similar carburetor calibration to today's Phase 2 engines would be beyond the lean-flammability limit for
sustaining E85 combustion if the tank were completely filled with E85. Misfueling with a lesser amount of
E85 would result in anything from no effect at all to lean-misfire or inoperability depending on the ratio
with which it is blended with gasoline. A significant degree of lean misfire would rapidly deactivate the
catalyst, posing emissions compliance issues but not necessarily safety issues. The carburetor calibration
of Phase 3 engines would likely follow current Phase 2 design practice and would allow engine operation
on up to 10% ethanol in a gasoline blend. Misfueling beyond 10% ethanol would result in leaner than
normal exhaust stoichiometry, but would not necessarily result in higher exhaust gas temperatures.
Ethanol has a lower net heat of combustion than gasoline, which effectively would "de-rate" engine power
output. Ethanol also can evaporatively cool the intake charge. Both effects would contribute to lowering
combustion and exhaust temperatures.
Temperatures capable of causing debris ignition occur under normal operating conditions with current production
OEM mufflers. Proper design and layout of the exhaust system are necessary to minimize occurrences of debris
ignition regardless of whether or not the exhaust system incorporates a catalyst. EPA demonstrated similar or
cooler operating temperatures for properly-designed catalyst-mufflers compared to today's OEM mufflers.
Catalyst-mufflers equipped with air-shrouds and exhaust ejectors in some cases resulted in systems that were
significantly cooler than many current OEM muffler designs, and such designs would be expected to decrease,
rather than increase, the incidence ignition of debris. Current OEM designs and EPA testing have demonstrated that
air-shrouding and forced-air cooling can be incorporated into the exhaust system designs in a manner that not only
results in negligible accumulation of debris on hot exhaust system surfaces, but can even assist with clearing debris
from hot exhaust system surfaces if proper attention is paid to cooling air velocity and maintaining sufficient gaps
within the shrouding around the exhaust system. Testing results for extended idling under dry, high debris
conditions show that turf surface temperatures rapidly stabilize (under five minutes) and also demonstrate that turf
surface temperatures under and adjacent to lawn tractors equipped with catalyst-muffler can be comparable, or even
cooler than, turf surface temperatures underneath and adjacent to current lawn tractors equipped with OEM mufflers
(see Chapter 6).
Conclusions Based onFMEA of Debris Fire Safety
The potential for increased temperature which could exacerbate the possibility for debris fires was identified as a
potential effect of failure in the Class I and Class II engine subsystems and the refueling and storage/shutdown
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process FMEAs. In the FMEA protocol, if the effect of the potential failure was fire or increased fire risk the item
was given a severity classification of 10 or 9, respectively. There were 23 items in the four FMEAs which indicated
fire or increased fire risk related to debris as the potential effect of failure (e.g., not related to fuel or backfire). As
can be seen in Table 10-2, below, there were not significant changes in risk probability for debris fires in going
from current Phase 2 engines to a properly designed Phase 3 system. Overall, seven items in the four FMEAs
indicated the potential for a small improvement in the risk probability, two indicated the potential for a small
degradation, and 14 indicated no change.
Table 8-2: Debris Fire Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Number with
Number with
Number with
Debris Fire as the
Potential
No Change
Potential
Potential Effect of
Improvement
Degradation*
Failure
Design
Class I:
8
4
3
1
Class II:
8
3
4
1
Process
Refueling:
1
0
1
0
Shutdown/Storage:
6
0
6
0
* These two items are the same as indicated for contact burn since the potential effect was fire or burn. These two
items are discussed in Chapter 7, section G.
SCENARIO 3 FUEL LEAK
Scenario Description: Fires due to fuel leaks on hot surfaces
Potential Causes:
a. faulty fuel tank
b. faulty fuel line or connection
c. tip-over during maintenance
d. tip over in operation
e. faulty carburetor
f. heat affects fuel tank or fuel line integrity
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
The faults encountered due to fuel leakage can potentially occur with equal frequency for engines equipped with
current OEM muffler designs or with catalyst-mufflers. As indicated above, EPA's testing has shown that properly
designed catalyst-muffler systems can achieve comparable, or even cooler, surface temperatures relative to today's
OEM muffler designs. Additionally, proper catalyst-muffler thermal management as demonstrated in EPA's test
program will result in no significant increase in heat load on fuel system components. Surface temperatures above
the auto-ignition temperature for gasoline occur during normal operation for engines equipped with both OEM
mufflers and engines equipped with catalyst-mufflers; thus, an equal potential exists for ignition of fuel on hot
surfaces if a leak or spillage occurs. Because the Phase 3 regulations address evaporative and running loss
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emissions, EPA expects that the frequency and severity of fuel leakage and fuel-related fires will be reduced relative
to today's Phase 1 and Phase 2 equipment. Compliance with Phase 3 standards will require improvements in tank
materials, fuel line materials and fuel line connections, and will reduce the likelihood of failure and/or leakage.
Running loss controls on lawn tractors will likely require replacement of front-mounted (engine compartment
mounted) fuel tanks with rear-mounted fuel tanks, moving both refueling operations and spillage in the event of
turn-over into a location that is further away from hot engine components. Phase 3 compliant venting systems also
include cap designs which have the propensity to reduce fuel loss in the event of tipping of equipment either
inadvertently or during maintenance. Fuel leakage during maintenance and storage can also be limited to the
quantity of fuel in the carburetor float-bowl by equipping lawn mowers and lawn tractors with inexpensive, positive
fuel cut-off valves. Fuel cut-off valves are frequently used in consumer lawn-care products.
Conclusions Based on FMEA of Fuel Spills or Leaks
The potential for increased fuel leaks or spills from equipment creating a fire risk was identified as a potential effect
of failure in the Class I and Class II engine subsystems and the maintenance process FMEA. In the FMEA protocol,
if the effect of the potential failure was fire or increased fire risk the item was given a severity classification of 10 or
9, respectively. There were 16 items in the three FMEAs which indicated fire or increased fire risk related to fuel
spill or leak from equipment as the potential effect of failure. As can be seen in Table 8-3, below, there were modest
positive changes in risk probability for fuel spill or leak related fires in going from current Phase 2 engines to a
properly designed Phase 3 system. Overall, eight items in the three FMEAs indicated the potential for a small
improvement in risk probability, none indicated the potential for degradation, and eight indicated no change. The
positive changes were related to improved fuel tank designs related to fuel evaporative emission control
requirements.
Table 8-3: Fuel Leak or Spill Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Number with
Number with
Number with
Fuel-Related Fire as
Potential
No Change
Potential
the Potential Effect of
Improvement
Degradation
Failure
Design
Class I:
6
3
4
0
Class II:
7
2
5
0
Process
Maintenance:
3
3
0
0
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SCENARIO 4: REFUELING-RELATED
Scenario Description: Fires related to spilled fuel or refueling vapor
Potential Causes:
a. fuel spilled on hot surfaces
b. spilled fuel evaporates or refueling vapors lead to fire indoors
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
EPA field test hot-soak data showed that at the manufacturer's specified minimum two minute refueling point after
engine shutdown, exhaust system surface temperatures for properly designed catalyst-muffler systems were
comparable or cooler than current OEM mufflers. The field tests also showed that exposed surface temperatures
rapidly decayed to below the autoignition temperature for gasoline after engine shut-down for all of the lawn tractor
and lawn mower configurations tested (see Chapter 6).
Based on CPSC NEISS cases for the five year period of 2000-2004, there was an estimated yearly average of 3,814
emergency room treated thermal burn injuries associated with lawn mowers. Refueling activities accounted for
approximately 7% of these injuries. EPA estimates that approximately 1.5 billion refueling events occur per year
for lawn and garden equipment. While CPSC NEISS cases involved fires from refueling events, the relative
infrequency of refueling fires in comparison with the very large number of refueling events demonstrates that fires
from refueling of lawn and garden equipment are relatively infrequent. The surface temperature data indicates that
the relative infrequency of refueling fires with this equipment is probably due to surface temperatures rapidly
decreasing to below the minimum gasoline surface ignition temperature of approximately 280 °C.' This rapid
decrease in surface temperatures is comparable equivalent between Phase 2 and expected Phase 3 system
configurations (see Chapter 6, section C).
Refueling of lawn mowers or lawn tractors in enclosed areas is hazardous and recommendations against this
practice are included in equipment owner's manuals. EPA's field and laboratory data showed that properly
designed catalyst-muffler systems can achieve comparable, or even cooler, surface temperatures relative to today's
OEM muffler designs. While refueling in an enclosed area is certainly inadvisable under any circumstances, such
misuse with a Phase 3 lawn mower or lawn tractor would not pose any additional fire risk beyond the already
considerable risk of this practice with current Phase 1 and Phase 2 equipment.
The required changes to fuel systems that will be necessary for compliance with Phase 3 permeation and running
loss emissions standards will also reduce the potential for refueling fires for lawn tractors. Relocation of fuel tanks
from the engine compartment to the rear of lawn tractors will greatly reduce the likelihood of spilled fuel coming
into contact with hot engine surfaces.
Conclusions Based onFMEA of Refueling-Related Safety
The potential for refueling-related fires where the equipment was involved was identified as a potential effect of
failure in the refueling process FMEA (see Table 7-6). There were 11 items in the FMEA which indicated fire
related to refueling as the potential effect of failure. As can be seen in Table 8-4 below, while fuel evaporative
emission controls present the possibility for improvement, overall there was no change in risk probability for
refueling-related fires in going from current Phase 2 engines to a properly designed Phase 3 system.
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Table 8-4: Refueling Related Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Refueling-Related Fire
as the Potential Effect
of Failure
Number with
Potential
Improvement
Number with
No Change
Number with
Potential
Degradation
Process
Refueling:
11
0
11
0
SCENARIO 5: STORAGE AND SHUTDOWN
Scenario Description: Equipment or structure fire when equipment left unattended after use.
Potential Causes:
a. ignition of nearby easily combustible materials
b. ignition of fuel vapor by pilot light
c. ignition of dry debris on deck
d. ignition of dry debris in field (lawn tractors)
e. ignition of tarp or other cover thrown over equipment
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
Surface temperatures during hot soak conditions following engine shut-down were comparable between equipment
tested by EPA with catalyst-mufflers and with OEM mufflers (see Chapter 6). Conditions certainly exist under
which combustible materials can be ignited if the equipment is misused, mal-maintained, or stored improperly. The
relative frequency of incidences of this sort should be no different for Phase 3 lawn mowers and lawn tractors than
is the case for current Phase 1 and Phase 2 equipment. Throwing a tarp over a recently run lawn mower can result
in ignition of the tarp regardless of whether or not the lawn mower is equipped with a catalyst-muffler.
While it is certainly inadvisable to store lawn tractors and lawn mowers in enclosures with open flames (e.g.,
storage of equipment in an attached garage near a water heater or furnace), the frequency of ignition of fuel vapor
by pilot lights should be reduced with Phase 3 equipment relative Phase 1 and Phase 2 equipment. This is due to the
reduction in volatile organic compound concentrations in the immediate vicinity of the equipment through the use of
evaporative emissions controls that comply with the Phase 3 emission standards.
Conclusions Based on FMEA of Shutdown and Storage Safety
The potential for ignition of fuel or other adjacent materials was assessed in the shutdown and storage process
FMEA. There were 10 items in the FMEA which indicated fire or increased fire risk related to shutdown and
storage (see Table 7-7) as the potential effect of failure. As can be seen in Table 8-5 below, there were no changes
in risk probability for storage and shutdown related fires in going from current Phase 2 engines to a properly
designed Phase 3 system. This is the case because the hot surface cool down profiles for Phase 2 equipment and
properly designed Phase 3 equipment are comparable.
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Table 8-5: Shutdown and Storage FMEA Safety Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Shutdown/Storage Fire
as the Potential Effect
of Failure
Number with
Potential
Improvement
Number with
No Change
Number with
Potential
Degradation
Process
Shutdown/Storage:
10
0
10
0
SCENARIO 6: IGNITION MISFIRE
Scenario Description: Engine malfunction which results in an ignitable mixture of unburnt fuel and air in the
muffler.
Potential Causes:
a. misfire caused by partial failure in ignition system (single cylinder engines)
b. misfire caused by failure in ignition system, particularly complete failure of ignition for one cylinder (2
cylinder V-twin engines)
c. after-fire/backfire caused by engine run on after ignition shut-down due to failure of the engine flywheel
brake or carburetor fuel-cut solenoid
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
Ignition misfire can rapidly result in catalyst deactivation. Because of this, EPA predicts that ignition system
improvements that include use of higher output ignition coils and higher-quality ignition wires will be necessary to
ensure compliance with the Phase 3 emission standards. These improvements will decrease the incidence of
ignition misfire relative to Class 1 and Class 2 equipment. Still, of the potential failure modes that can occur,
ignition misfire is the condition of most concern with regards to the use of catalyst-mufflers with Class I lawn
mowers and Class II lawn tractors. This is the only condition that has been identified that provides both excess fuel
and excess air simultaneously to exhaust system internal surfaces in a proportion that can support combustion.
a. Single-cylinder engine misfire: The design approach taken by EPA to address ignition misfire with engine
255 was to divide the catalyst volume between locations upstream and downstream of secondary air
entrainment ("pre-catalyst" and "main catalyst"). These changes improved catalyst efficiency relative to
total catalyst volume, and allowed a reduction in the amount of secondary air used. The reduction in
secondary air reduced CO oxidation and reduced surface temperatures during normal operation. This
resulted in surface temperatures below that of the OEM muffler during normal operation, and allowed
further engineering margin for a temperature increase to occur with the catalyst-muffler during misfire.
The pre-catalyst was also optimized for relatively rich operation (similar to 2-stroke catalyst applications)
and reduced HC emissions upstream of the entrainment of secondary air both during normal operation and
during misfire. This allowed the use of a smaller main catalyst downstream of the secondary air. During
misfire, the smaller, space-velocity limited main catalyst was overwhelmed with reactants, thus reducing
heat rejection from the main catalyst during misfire. A moderate but manageable increase in temperature
was observed for this system, and surface temperatures during misfire were still within 60 °C of normal
operating temperatures with the standard muffler. Use of air-shrouding, forced-air cooling of the exhaust
and use of an exhaust ejector was more than sufficient to counter the impact of misfire on catalyst-muffler
surface temperatures. An alternative approach would be to use a low cost, self-resetting bimetal-disk
thermal switch to shut down the engine's ignition system if high temperatures are encountered near exhaust
system surfaces due to a partial ignition system failure.
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b. V-twin ignition misfire: Conditions exist under which lawn tractors equipped with V-twin engines can
operate with one cylinder's ignition system completely deactivated and operate in a manner in which the
failure may not be immediately apparent to the operator of the equipment. This is potentially a more
hazardous condition than could occur with ignition misfire from a single cylinder engine since a full air
and fuel charge from the deactivated engine cylinder can mix with the hot exhaust gases from the active
engine cylinder and impinge on hot surfaces within the muffler. A similar degree of misfire with a single
cylinder engine would result in engine stalling. One solution would be to divide the exhaust system such
that there is one small catalyst substrate for each of the two cylinders of the V-twin. This could be
accomplished with two catalyst mufflers, or with a single catalyst muffler with completely separate flow-
paths for each cylinder. In the case of full ignition misfire on one cylinder, the exhaust gases would
rapidly cool to below the light-off temperature for HC over the catalyst for the section of the catalyst-
muffler fed by non-firing cylinder.
c. After fire caused by engine run-on after shutdown: EPA testing demonstrated that a properly designed
catalyst-muffler can reduce the incidence of after-fire during run-on relative to a current OEM muffler
system (see Chapter 6). Design principles for preventing after-fire flame propagation in mufflers are well
understood, and can be incorporated into a muffler's baffles and internal passages, and can be combined
with spark arresting at the muffler outlet.
Conclusions Based on FMEA of Ignition Misfire
The potential for an increase in misfire-related phenomena to cause an increase in fires or burns was assessed as a
potential effect of failure in the Class I and Class II engine subsystems. In the FMEA protocol, if the effect of the
potential failure was burn, fire or increased fire risk the item was given a severity classification of 9 or 10. There
were four items in the two FMEAs which listed fire or increased burn risk related to misfire as the potential failure
mode. As can be seen in Table 8-6, below, there were modest positive changes in risk probability for misfire in
going from current Phase 2 engines to a properly designed Phase 3 system. Overall, three items in the two FMEAs
indicated the potential for a small improvement, none indicated the potential for degradation, and one indicated no
change. The positive changes were related to the expected improvements in the ignition system for a properly
designed Phase 3 system.
Table 8-6: Misfire Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with
Number with
Number with
Number with
Misfire Potential
Potential
No Change
Potential
Failure Mode
Improvement
Degradation
Design
Class I:
2
2
0
0
Class II:
2
1
1
0
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SCENARIO 7: RICH OPERATION
Scenario Description: Fire due to operation with richer than designed air-to-fuel ratio in engine or catalyst.
Potential Causes:
a. fuel system degradation such as faulty carburetor, oil consumption or carburetor deposits
b. faulty or misapplied choke
c. ignition system failure
d. air filter element mal-maintenance
e. debris blocks catalyst venturi
Conclusions Based on EPA Testing of Phase 2 engines and Phase 3 Prototypes:
Based on EPA testing, the impact of richer air-to-fuel ratios appears to be minimal with respect to exhaust surface
temperatures (figure 6-35) on both OEM muffler and properly designed catalyst-muffler systems. This is not
surprising since during rich operation, exhaust gas oxygen concentrations are low and thus CO oxidation is reduced.
Extremely rich air-to-fuel ratios could cause after-fire in the muffler at some conditions. This was not observed in
EPA testing at rich air-to-fuel ratio conditions for either the OEM muffler or the catalyst-muffler, or in earlier tests
of an engine with a malfunctioning carburetor float valve (engine #1514)10. EPA's work with run-on after-fire
suggests that with proper design, flame-arresting can be easily incorporated into catalyst-muffler designs to reduce
the incidence of after-fire for catalyst-mufflers relative to current OEM mufflers. Overly rich air-to-fuel ratios pose
an emissions compliance issue by increasing engine-wear and engine-out emission degradation over time and by
reducing catalyst efficiency by partial deactivation of the catalyst through coking of catalyst surfaces. In order to
comply with Phase 3 regulations at engine full useful life, it is expected that manufacturers will eliminate the use of
manual chokes and switch to the use of either automatic chokes or priming bulbs. This has largely occurred already
with Phase 2 Class I engines.
a. Fuel system degradation: This would be an emissions compliance issue, but would not result in any
difference in safety for Phase 3 equipment relative to existing Phase 1 and Phase 2 equipment.
b. Faulty or misapplied choke: The resulting overly-rich air-to-fuel ratios pose an emissions compliance
issue by increasing engine-wear and engine-out emission degradation over time, and by reducing catalyst
efficiency by partial deactivation of the catalyst through the coking of catalyst surfaces, but would not
result in any differences in safety for Phase 3 equipment relative to existing Phase 1 and Phase 2
equipment. In order to comply with Phase 3 regulations at engine full useful life, it is expected that
manufactures will eliminate the use of manual chokes and switch to the use of either automatic chokes or
priming bulbs. This has largely occurred already with Phase 2 Class I engines.
c. Ignition system failure: Ignition system failure is not related to rich operation. As such, it is covered
separately under scenario 6.
d. Air filter element mal-maintenance: The impact of air-filter mal-maintenance on emissions and air-to-fuel
ratio has been significantly reduced since the advent of the Phase 2 emission standards. The majority of
carburetors used with Phase 2 engines are equipped with float bowl venting that provides compensation for
a degree air-filter mal-maintenance. Thus changes in carburetor air-inlet restriction are already largely
compensated for by design. Extreme blockage of the air filter element resulting in rich operation would
increase exhaust emissions, but based on EPA test results would not result in any difference in safety for
Phase 3 equipment relative to existing Phase 1 and Phase 2 equipment.
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e. Debris blocks catalyst venturi: The impact of debris blockage of catalyst venturi would be increased
emissions and reduced heat rejection at some conditions. While this would pose an emissions compliance
issue, EPA would not expect any safety-related impact from venturi air-inlet blockage. The venturi of the
European catalyst-muffler design (figure 5-1) is located in a low-debris area in its OEM application. The
venturi inlet was similarly located in low debris locations in EPA's applications of this basic design to two
different engine families used with four of the engines in the field operations in southwest Tennessee
(engines 244, 245, 246, and 248). These systems were operated to near the end of useful life and none
experienced any significant degree of venturi blockage.
Conclusions Based on FMEA of Rich Operation
Rich operation was identified as a potential safety concern by one organization. Within the Class I and Class II
design FMEAs there were only five situations identified where a rich mixture could potentially create a safety
problem. In each case, the potential effect of the failure was backfire. To some degree these problems are
redundant with misfire as discussed above. Rich operation can lead to other potential failure effects such hard
starting, general degradation of performance, or emissions increases but in no other scenario was there a potential
safety issue identified.
Table 8-7: Backfire Safety FMEA Summary - Incremental Change from Phase 2 to Phase 3
FMEA Type
Number of Items with Backfire
Number with
Number
Number with Potential
Potential Failure Mode
Potential
with No
Degradation
Improvement
Change
Design
Class I:
2
2
0
0
Class II:
3
1
2
0
1 American Petroleum Institute, "Ignition Risk of Hydrocarbon Vapors by Hot Surfaces in Open Air", Table 3:
Open Air Ignition Tests Under Normal Wind and Convection Current Conditions, API Publication #2216, January
1991.
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9. Safety Analysis of Small SI Engine Evaporative Emissions Control
Technologies
A. CURRENT TECHNOLOGY
Fuel Evaporative Emissions
EPA intends to propose standards for evaporative emission control requirements for NHH and HH equipment.
Evaporative emissions refer to gasoline vapor lost to the atmosphere from a number of mechanisms including:
1. permeation: These emissions occur when fuel vapor works its way through the material used in the fuel
system. Permeation occurs most commonly through plastic fuel tanks and rubber fuel hoses.
2. diurnal: These emissions result from temperature changes throughout the day. As the day gets warmer, the
fuel temperature increases and the fuel evaporates into the atmosphere. This is sometimes referred to as
breathing losses.
3. diffusion: These emissions result from vapor exiting through a vent path to the atmosphere regardless of
changes in temperature. This occurs due to the vapor concentration gradient between vapor in the tank or
hose and the outside atmosphere.
4. running loss: These emissions are similar to diurnal emissions except that the heating of the fuel is caused
by engine operation.
5. refueling: These emissions occur when vapors displaced from the fuel tank escape when fuel is dispensed
into the tank.
6. hot soak: These emissions occur from hot fuel cooling after engine shutdown. Traditionally they can
emanate from the fuel tank or the carburetor.
7. spillage: These emissions occur when fuel is spilled by the user during refueling events.
The following sections describe the current technological designs for NHH and HH equipment that will be impacted
by the potential Phase 3 evaporative emissions standards.
NHH Equipment
NHH equipment refers generally to gasoline-powered equipment that does not require operator support for its
operation. It can be free standing, such as a pressure washer or generator, or wheel-based, such as a walk-behind
lawnmower, a ride-on mower, or a cultivator. We are considering fuel tank and fuel hose permeation standards,
diffusion, and running loss control requirements for NHH equipment.
Fuel tanks for NHH equipment are often mounted on or near the engine. Due to the small size of the tanks and
equipment, and to aid in stability in typical Class I applications, the fuel tanks are often mounted directly on the
engines. Tank volumes are normally < 0.5 gallon and are made of either metal or high density polyethylene
(HDPE). Class I applications normally have only one fuel tank. For Class II equipment, it is more common for fuel
tanks to be mounted near the engine on the chassis as opposed to directly on the engine. For example, some ride-on
mowers mount the fuel tank in the engine compartment. For equipment with rear-mounted engines it is not
uncommon to have the fuel tank in the rear as well. Tank volumes are normally >1.5 gallons and it is common to
have two higher capacity (> 5 gallon) dual tanks on larger commercial equipment. Class II equipment tanks are
normally made of injection or blow-molded HDPE or rotomolded cross link polyethylene (XLPE).
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Generally, the fuel systems on Class I and Class II equipment have no rollover valves or other mechanisms to
prevent fuel from spilling on the engine or equipment when the equipment is tipped on its side or turned over.
Some tanks use tortuous venting paths in the fuel caps, which also restrict fuel flow, but others simply use holes in
the fuel caps for venting which would also allow fuel to spill out of the tanks at higher flow rates. Fuel tank caps
are primarily made of plastic and typically do not have a tether to prevent loss of the cap. Running loss emissions
from fuel tank heating during operation are typically vented through the fuel cap.
NHH equipment uses a variety of fuel hose constructions. They may be extruded rubber hose meeting SAE J30R7
requirements or they may use a multi-layer hose such as would meet SAE J30R9. Typical materials used are nitrile
rubber, and in some cases, fluoroelastomers.
HH Equipment
HH equipment refers generally to gasoline-powered tools that are supported by the user during operation. This
category includes chainsaws, string trimmers, leaf blowers, and other similar equipment. EPA is considering fuel
hose and fuel tank permeation standards and diffusion control requirements for HH equipment.
Fuel tanks on HH equipment are typically molded out of either nylon or polyethylene. Most of these tanks are < 0.5
gallons in capacity and in some cases much less. With some equipment, instead of a tank being attached as part of
the overall equipment assembly, the fuel tank is structurally integrated into the body of the equipment. This design
approach is used in common applications such as chainsaws, hedge trimmers, and brush cutters. This construction
helps to provide structural strength to the equipment and results in the fuel tank being molded out of the same
material as the rest of the body. In these cases, nylon is typically used due to the favorable heat resistance and
stiffness characteristics it offers. The fuel tanks used in HH equipment may either be vented to the atmosphere or
they may be sealed. Manufacturers often seal the fuel tanks to prevent spillage during use. This is especially
common on tools such as chainsaws where the equipment is regularly turned over during normal use.
HH equipment uses a variety of fuel hose constructions. They may be extruded rubber hose or may be molded into
custom forms. Typical materials used are nitrile rubber, polyurethane, polyvinyl chloride, and in some cases,
fluoroelastomers. According to the Outdoor Power Equipment Institute, the vast majority of HH equipment has
total fuel hose lengths of less than 15 cm.
B. CURRENT SAFETY STANDARDS
The current safety standards for NHH equipment are discussed in Chapter 3. At this point there are no mandatory or
general industry consensus standards related to safety practices or standards for fuel tanks or fuel hoses used in
NHH or HH equipment. One exception to this is UL 1602 which does present guidelines for the construction of
gasoline-powered edgers.
Although industry wide standards are not used, extensive product qualification and durability testing is performed.
According to industry sources, manufacturers typically soak tanks at an elevated temperature on various fuels to test
for fuel compatibility. In addition, most manufacturers perform impact tests on their fuel tanks. Impact tests vary
by manufacturer and can be performed using drop testing, pendulum swung hammers, or sharp point impact. Other
procedures that manufacturers have stated that they use for evaluating fuel tank durability include pressure tests and
vibration tests.
Most NHH equipment use hose meeting SAE J30 R7 standards. As discussed below, these standards include a long
list of durability tests. One engine and equipment manufacturer that does not use hose labeled as SAE J30 R7 stated
that they use similar pliability and durability tests as are in the SAE recommended practice. In addition, they test for
abrasion resistance and the minimum load required for pulling the hose off of a fitting. They stated that they use the
hose pull of load specified in ANSI B71.3. Although this standard is intended for snow throwers, the pull off
requirement can be applied to other applications.
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HH equipment manufacturers typically use fuel hoses made of polyurethane, nitrile rubber, or polyvinyl chloride.
For edgers, the hose must meet a number of durability requirements according to UL 1602. These durability
requirements include ultraviolet light exposure, dry heat aging, fuel resistance, and low temperature flexibility.
Industry sources have stated that they also perform heat resistance testing and pull off testing on this hose and use
the same fuel hose for the rest of their equipment. HH equipment manufacturers also use molded nitrile or
fluoroelastomer hoses on some of their equipment. Industry sources stated that they perform a number of durability
tests on these hoses as well which include fuel resistance, a pull off load requirement, heat resistance, cold
temperature flexibility, and vibration resistance.
ASTM also provides guidance for hose durability testing. ASTM D1149 provides test procedures for determining
cracking in the hose that may occur from ozone exposure. ASTM D471 describes test procedures for determining
the resistance of rubber products to a number of test fuels. ASTM D380 references these test methods and describes
several additional durability tests for fuel hose. These additional tests include tensile strength, elongation, adhesion,
pressure tests, low temperature exposure, tension, and hot air aging. One equipment manufacturer specifically
stated that they use these test procedures. In addition, all of these ASTM test methods are referenced in SAE J30.
In addition to the above testing, manufacturers often operate the equipment in the field for extended periods of time
to evaluate durability. Among other things, these evaluations give manufacturers the ability to evaluate the
performance of the fuel tanks, hose, and connections. The use of these durability tests can affect safety in that
manufacturers are able to look for defects that may lead to fuel leaks in the field.
Industry sources have also stated that they test for fuel overflow on their NHH equipment. These sources have
referenced ANSI standards B17.1 for lawnmowers, B17.3 for snow throwers, and B17.4 for commercial turf
equipment. These standards basically require that there be a shield or other method to prevent any fuel overfill
during refueling from spilling onto an ignition source such as the muffler or non-insulated electrical wire.
C. IN-USE SAFETY EXPERIENCE
As discussed in earlier chapters, assessing incremental risk requires an understanding of the problems and in-use
safety experience with current products. For this analysis we used data from CPSC's website regarding NHH and
HH equipment. The CPSC website publishes Recalls and Product Safety News, where manufacturers, in
cooperation with CPSC, voluntarily recall products that pose a safety hazard to consumers. Recall notices published
during the period of January 2000 to December 2004 were reviewed. Our analysis focused only on incidences that
were relevant to the fuel systems that may be affected by potential Phase 3 emission standards.
NHH Equipment
The in-use safety discussion for NHH equipment in Chapter 3 includes issues related to potential evaporative
emission control technology. During the period of January 2000 to December 2004, there were a total of 22 lawn
mowers or lawn mower engines recalls due to safety issues related to thermal burn injuries. These 22 recall notices
affected approximately 850,000 lawn mower units. In the same time period, CPSC reported 11 recalls for fuel tank
leaks and five recalls for fuel line leaks. Chapter 3 presents CPSC Injury/Potential Injury Incident File and In-
Depth Investigations related to lawn mower fuel leak incidents.
HH Equipment
In reviewing the CPSC Recall website, EPA reviewed recalls related to gasoline-powered HH equipment such as
blowers, trimmers, edgers, chainsaws, augers, and brush cutters. From 2000 to 2004, EPA identified 11 recalls
categorized as fire/burn hazards. Of these 11 recall actions, three were associated with potential fuel leakage from
hoses, seven were associated with potential fuel leakage from tanks, and one was related to flames in the engine
exhaust. These 11 recall actions included more than 80 percent of the HH equipment recalled in that time period.
EPA recognizes that a list of voluntary recalls does not provide details on injuries associated with fires and burns.
However, as shown with NHH equipment in Chapter 3, recall notices do provide a good indication of what the
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safety issues are for a given class of equipment. Based on this, our analysis of incremental risk should focus on fire
and burn hazards related to fuel leaks and spills arising from the use of technology to control fuel hose or fuel tank
permeation emissions.
D. EMISSION CONTROL SYSTEM DESIGN AND SAFETY
NHH Equipment
We are considering evaporative emission standards for Small SI engines in the Class I and Class II subcategories.
These standards include the control of the permeation of fuel vapors through nonmetallic fuel system components,
such as rubber fuel hoses and plastic fuel tanks, and the control of fuel vapor vented out of the fuel system. This
section discusses the various evaporative emission control approaches under consideration and what impacts these
control strategies may have on safety. When evaluating potential safety impacts of evaporative emission control, we
considered primarily the chance of a fuel hose or fuel tank liquid leak or a combustible fuel vapor reaching an
ignition source, such as a hot exhaust system, when the engine is in use. Thus component durability is a key issue.
Fuel hoses
Most NHH equipment uses rubber hose for delivering gasoline from the fuel tank to the engine. The typical fuel
hose construction is a nitrile rubber hose with a protective cover for abrasion resistance. To meet the fuel hose
permeation standards under consideration, manufacturers would be able to use this hose construction except that an
additional barrier layer would need to be added to minimize permeation fuel through the hose material. A typical
barrier material would likely be a fluoroelastomer or fluoroplastic material. Barrier hose constructions are used
widely in automotive applications and even on some Class II engines. The lines used today typically meet SAE and
ASTM standards; in most cases fuel hose meeting the SAE J30R7 is used. In addition, manufacturers commonly
specify minimum loads to pull their fuel hose off of the connecting barbs. One example of a published
recommended minimum pull off load is 10 lbs specified in ANSI B71.3.
Fuel hose under the SAE J30 R7 rating must pass a number of tests designed to measure the durability of the hose.
These tests include a burst pressure, tensile strength and elongation, dry heat resistance, oil resistance, ozone
resistance, kink resistance, and several fuel exposure tests. The fuel resistance tests include repeating most of the
above tests after soaking the hose with both ASTM fuel Cf and a test fuel made up of 85 percent ASTM fuel D
blended with 15 percent ethanol. In addition, to test for "sour fuel" resistance, the hose is tested for tensile strength
and elongation after being exposed to a test fuel made up of ASTM Fuel B and sufficient t-butyl hydroperoxide to
achieve a specified peroxide level. Finally, the hose is tested for permeation on ASTM fuel C. In addition, the SAE
requirements include an adhesion test which sets a minimum load required to separate the tube from the protective
cover
EPA's fuel hose permeation requirements must be met using EPA test procedures. However, past testing indicates
that many hoses meeting the SAE J30 R9, R11A, or R12 requirements will meet EPA permeation requirements.
Hoses meeting R9 or better specifications would also have to meet all other durability requirements associated with
the SAE J30 standard as described in the preceding paragraph. Barrier hoses constructed today are generally higher
quality hose that also have better temperature resistance than non-barrier hose. For instance, SAE J30 R9 hose must
meet a dry heat resistance test based on 150°C heat aging compared to 125°C for R7 hose. According to one hose
manufacturer, heat resistance is primarily a function of the cover material rather than the permeation barrier material
itself. This should directionally address current concerns related to fuel lines droping under radiant load.
Furthermore, the barrier materials are made of rubber compounds that are resistant to permeation by gasoline,
including ethanol blends and oxidized ("sour") gasoline. This fuel resistance not only protects against chemical
attack, but also limits swelling due to the permeation of fuel. By limiting the swelling and contracting (drying)
cycles and chemical attacks that may cause the hose to become brittle, the hose may resist cracking as well. Finally,
the barrier layers are thin and are not expected to lead to any significant differences in hose flexibility or ability to
retain connections within the fuel system. Based on the rigorous nature of the SAE testing requirements and the
f These ASTM fuels are blends of isooctane/toluene: B=70%/30%, C=50%/50%, D=60%/40%.
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essentially universal use of hoses meeting SAE specification in NHH applications, we expect no increase in fuel
hose leaks associated with the use of low permeation fuel hose relative to current fuel hose. The hose which would
be used is commercially available today.
Fuel tanks
Fuel tanks on NHH equipment are usually constructed of HDPE through a blow molding or injection molding
process. There are still a few models, some with very high sales, using metal tanks. Some of the larger NHH
equipment, such as commercial turf care equipment, uses fuel tanks constructed of XLPE. XLPE is thermoset
which means that that a reaction takes place in the plastic during molding (at an engineered temperature) which
creates the cross-link structure. HDPE and XLPE have poor fuel permeation resistance characteristics while metal
tanks do not permeate. There are several technological approaches that can be used to reduce gasoline permeation
through plastic fuel tanks (HDPE and XLPE). These approaches include surface treatments, barrier constructions,
and alternative materials.
Surface treatments, such as fluorination and sulfonation, could be used to meet the standard that EPA is considering.
These treatments are performed as a secondary step after the fuel tank is molded; both create a thin layer on the
inner or outer surfaces of the fuel tank that acts as a barrier to permeation. In fluorination, a barrier is created on
both the inner and outer surfaces while in sulfonation, it is created only on the inner surface. These treatments do
not materially change the construction of the fuel tank and are not expected to affect the durability of the fuel tanks
because the barrier is not thicker than 20 microns thick and does not affect the tank wall material which is typically
3-6 mm thick. These approaches are both used to meet the current California gasoline permeation standards for
portable fuel cans.
Multi-layer fuel tank constructions which create a barrier to permeation have been used in automotive applications
for many years. The most common approach is to mold a thin layer of ethyl vinyl alcohol (EVOH) inside a HDPE
shell. This approach is commonly used in high production volume, blow-molded fuel tanks but could be used in
lower production volumes through a molding process known as thermoforming. Another approach available for
blow-molded fuel tanks is to blend a small amount of EVOH directly into the HDPE. During molding, the EVOH
creates non-continuous overlapping barrier platelets which restrict permeation. For each of these technologies, the
barrier material is only a small percentage of the total makeup of the fuel tank. In addition, adhesion layers are used
between the barrier and the HDPE shell to prevent the layers from pulling apart. These technologies have the
advantage of having been in use for many years and having been demonstrated in automotive and other applications
with no safety issues. Automotive manufacturers require the fuel tanks to meet wide range of durability tests on
these fuel tanks including fuel exposure, flame tests, and low temperature drop impact tests.
Rotationally molded XLPE tanks would use one of several techniques to reduce permeation. In the first technique
nylon, which has good permeability properties, is applied as an inner shell inside the fuel tank. The manufacturer
has demonstrated that the nylon has an excellent bond with the XLPE.1 As a result of this bond and the strength of
the nylon, this construction offers strong resistance to impact. Testing at Imanna Laboratory, Inc. showed that a
tank of this construction met the United States Coast Guard (USCG) durability requirements described in chapter 10
which include impact testing and flame resistance.2 Another new approach for XLPE tanks is to coat the tank with
a low permeation epoxy in a secondary step after molding. This approach does not change the basic fuel tank
construction but only adds an outer layer similar in thickness as a coat of paint. A third approach for reducing
permeation would be to rotomold the fuel tanks out of lower permeation materials such as nylons, acetal
copolymers, or thermoplastic polyesters. Materials manufacturers have been working for years on engineered
plastics that are compatible with the molding processes and design requirements of today's fuel tanks.
In the case where manufacturers make any changes to their fuel tanks, such as materials or geometry, they must
evaluate the effect of these changes on their product. There are no standard procedures for evaluating the safety
characteristics of these fuel tanks. Each vendor or manufacturer has developed their own tests to ensure
performance. Examples of these durability tests include impact testing, temperature testing, and fuel exposure
testing. It should be noted that EPA's permeation test procedures (contained in 40 CFR 1051.515) incorporate test
requirements which will help to ensure the in-use integrity of these tanks. Current requirements include extended
time of fuel soak in a 10 percent ethanol/gasoline blend, slosh testing, pressure-vacuum cycling, and prolonged
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exposure to ultraviolet light. Because there are not set industry standards for durability testing of fuel tanks, it may
be helpful to consider additional tests which could address emissions durability such as high and low temperature
cycling.
In none of these three approaches (surface treatment, barrier construction, and alternative materials) would EPA
expect there to be an adverse incremental impact on safety. Surface treatments and barrier construction are used in
portable and installed fuel tanks today. The choice of proper materials and construction durability is important and
we believe that the manufacturer specific test procedures and production audits and EPA requirements are sufficient
to ensure that there will be no increase in the types of fuel leaks that lead to fire and burn risk in use. There is also
the potential for at least a directional improvement in safety in Phase 3 standards associated with reducing
permeation of fuel vapor from the equipment in a closed space such as a shed or garage.
Running Loss
We are also considering several approaches to reducing the evaporative emissions associated with direct venting of
fuel vapors from the fuel tank. We focus primarily on running loss venting emissions. When equipment is
operating, the fuel is heated by the engine, the exhaust system, and possibly the hydraulic system. We are
considering two primary approaches to controlling running loss venting emissions.
First, the equipment could be designed to minimize heat reaching the fuel tank. This could be achieved through
heat shielding, changing from metal to plastic tanks, or by relocating the fuel tank further from heat sources. In the
case of Class I equipment, the fuel tank could be moved away from the muffler to the opposite side of the engine
block. On Class II equipment, there would be more room on the equipment to move the tank away from heat
sources such as the engine or exhaust system. Overall, EPA expects this would be the preferred approach since it
would be the least expensive way to comply with the test procedures and emissions standards under consideration.
If the fuel tank is moved away from heat sources, the likelihood of fuel spilling on a hot surface during refueling
would also be reduced. Heat shielding and changing tank material would also reduce heat getting to the fuel.
Changing from metal to plastic tanks where practical would also substantially reduce running loss emissions and the
overall hot surface area.
The second approach to controlling running loss emissions would be to route the vapor to the engine intake to be
burned by the engine. A restriction would need to be placed in the vent line to the engine to keep the engine
manifold vacuum from drawing too much vapor from the fuel tank. This restriction could be in the form of a
limited flow orifice or a valve. This would have the additional benefit of acting as a rollover valve since the
limiting orifice or valve restricting vapor flow would inhibit fuel flow from the tank if the equipment was inverted.
Even without moving the fuel tank, the equipment could be designed to prevent fuel spillage during refueling from
reaching hot surfaces that could ignite the fuel. As discussed above, some manufacturers design their equipment to
prevent fuel overfill from reaching these hot surfaces consistent with ANSI B71.1, B71.3, and B71.4.
To control diffusion-related venting emissions, manufacturers could make use of fuel caps with no venting or with
venting through a tortuous path. These caps, which are used in some applications today, would reduce fuel spillage
when the equipment is turned over or even due to sloshing in the fuel tank. The chance of a fuel cap being lost
could be reduced with a tether which could reduce the chance of fuel spillage due to open or improperly plugged fill
necks. We would expect to accomplish this type of control as part of our running loss control requirements.
Conclusion
NHH equipment is capable of achieving reductions in fuel tank permeation, fuel hose permeation, and fuel tank
vapor venting emissions without an adverse incremental impact on safety.
For fuel hoses and fuel tanks the applicable consensus standards, manufacturer specific test procedures and EPA
requirements are sufficient to ensure that there will be no increase in the types of fuel leaks that lead to fire and burn
risk in use. The running loss control program being considered by EPA will create requirements that will reduce risk
of fire in use. Moving fuel tanks away from heat sources, improving cap designs to limit leakage on tip over, and
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requiring a tethered cap will all help to eliminate conditions which lead to in-use problems related to fuel leaks and
spillage.
Furthermore, reductions in permeation emissions and the techniques for reducing running loss emissions are likely
to have a salutary impact on the overall safety of NHH systems. The evaporative emission standards under
consideration would lead to significant reductions in fuel vapor emitted to the atmosphere. This is especially
important in closed spaces because evaporative emissions occur regardless of whether the equipment is operated
(i.e. a piece of equipment stored in a shed with fuel in the tank continues to permeate and vent fuel vapor into the
shed); such controls could prevent vapor concentrations in closed spaces from becoming high enough for the vapor
to reach a flammable mixture. Exposing the fuel tank to less heat may also reduce post shutdown hot soak
emissions from the tank.
HH Equipment
We are considering fuel hose and fuel tank permeation emission standards for HH equipment. The standards and
test procedures would be similar to those discussed above for NHH engines.
Fuel Hose
For the most part there are no significant differences in the fuel hose related safety issues for NHH and HH engines
and equipment. Although somewhat different constructions are used today, manufacturers perform many durability
tests on HH hose as well. These tests are described above. HH equipment manufacturers can make use of the same
low permeation hose materials and constructions described above for NHH equipment. These low permeation hose
constructions use a fluoroelastomer or fluoroplastic material as a barrier. Alternatively, the entire fuel hose could be
molded from a fluoroelastomer.
In some applications, molded fuel hoses are used rather than simple extruded fuel hose. These fuel hoses are
typically either molded out of nitrile rubber or a fluoroelastomer. Fluoroelastomers are essentially rubber
impregnated with fluorine which results in good fuel permeation resistance. Manufacturers of equipment that may
be used in cold weather have stated that they must use nitrile rubber because the fluorelastomer material may
become brittle at very low temperatures. While they have presented data supporting this claim, it was based on a
fluoroelastomer without a low temperature additive package. Fluoroelastomers used in automotive applications use
low temperature additive packages and are designed for strength at temperatures as low as -40°C. In addition, at
least one snowmobile manufacturer has recently begun using a low temperature fluoroelastomer for its fuel system
seals. Fuel hose meeting SAE and ASTM standards is available today which meets a widespread set of safety and
durability requirements.
Manufacturers have claimed that barrier hoses are stiffer and may not hold on to hose connections as well as nitrile
rubber hose. The barriers used in low permeation hose are thin and, in our evaluation, barrier hose is not noticeably
different in stiffness than nitrile hose and fits well over typical hose barbs used today. If a manufacturer felt it was
necessary, there is a wide range of fuel hose clamps available today.
Manufacturers have indicated that they would perform durability testing on any new hose constructions they were to
use. These tests are described above. In addition, manufacturers have stated that they would test the low
permeation hose on their equipment under field testing. Based on these practices and the properties of the low
permeation materials discussed above, the low permeation fuel hose requirements being considered by EPA would
not lead to an increase in fuel leaks or risk of fire or burn in use.
Fuel Tanks
Most fuel tanks on HH equipment are made of HDPE. EPA expects emission reductions would be achieved
through the surface treatments or barrier technologies identified for NHH equipment and that the in-use safety
experience would be similar. The surface treatments described above were fluorination and sulfonation. The
barrier treatments described above included a thin EVOH barrier layer within a HDPE shell and non-continuous
barrier platelets created by blending the EVOH into the HDPE prior to molding. As discussed above, the surface
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treatments do not change the construction of the fuel tank but only put a microscopic barrier on the outer surface.
The barrier technologies only make up a small fraction of the total material of the fuel tank and have been long
demonstrated in automotive and other applications.
Manufacturers of equipment with structurally integrated fuel tanks have stated that they must use nylon because of
its structural qualities. An additional advantage of nylon is that it has lower permeation rates than HDPE.
However, on test fuel containing ethanol, the permeation rate through nylon fuel tanks is still slightly higher than
the permeation standard under consideration. Under the program we are considering, EPA expects that
manufacturers using nylon in their structurally integrated tanks will be able to continue to do so. Thus, EPA expects
there will be no change and thus no increase in risk.
Conclusion
HH equipment is capable of achieving reductions in fuel tank permeation and fuel hose permeation without an
adverse incremental impact on safety. For fuel hoses and fuel tanks the applicable consensus standards,
manufacturer specific test procedures and EPA requirements are sufficient to ensure that there will be no increase in
the types of fuel leaks that lead to fire and burn risk in use. The evaporative emission standards under consideration
would lead to significant reductions in fuel vapor emitted to the atmosphere. This is especially important in closed
spaces because evaporative emissions occur regardless of whether the equipment is operated; such controls could
prevent vapor concentrations in closed spaces from becoming high enough for the vapor to reach a flammable
mixture.
E. CONCLUSION
EPA has reviewed the fuel hose and fuel tank characteristics for NHH and HH equipment and evaluated control
technology which could be used to reduce evaporative emissions from these two subcategories. This equipment is
capable of achieving reductions in fuel tank and fuel hose permeation without an adverse incremental impact on
safety. For fuel hoses and fuel tanks, the applicable consensus standards, manufacturer specific test procedures and
EPA requirements are sufficient to ensure that there will be no increase in the types of fuel leaks that lead to fire and
burn risk in use. Instead, these standards will reduce vapor emissions both during operation and in storage. That
reduction, coupled with some expected equipment redesign, is expected to lead to reductions in the risk of fire or
burn without affecting component durability. Additionally, the running loss control program being considered by
EPA for NHH equipment will lead to changes that are expected to reduce risk of fire in use. Moving fuel tanks
away from heat sources, improving cap designs to limit leakage on tip over, and requiring a tethered cap will all
help to eliminate conditions which lead to in-use problems related to fuel leaks and spillage. Therefore, EPA
believes that the application of emission control technology to reduce evaporative emissions from these two
subcategories will not lead to an increase in incremental risk of fires or burns and in some cases is likely to at least
directionally reduce such risks.
1 O'Brien, G., Partridge, R., Clay, B., "New Materials and Multi-Layer Rotomolding Technology for Higher
Barrier Performance Rotomolded Tanks," Atofina Chemicals, 2004, Docket EPA-HQ-OAR-2004-0008-0044.
2 Partridge, R., "Petro-Seal for Ultra-low Fuel Permeation; Evaporative EPA Emissions from Boat Fuel Systems,"
Arkema, Presentation at the 2004 International Boatbuilders' Exhibition and Conference, October 25, 2004, Docket
EPA-HQ-OAR-2004-0008-0252.
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10. Safety Analysis for Marine SI
This section gives an overview of Marine SI engines and vessels that may be impacted by further exhaust and
evaporative emission control requirements. It also provides the technical basis and analysis for our assessment of
the incremental impact on safety of potential marine SI exhaust and fuel evaporative emission standards
A. CURRENT TECHNOLOGY
Marine Engines
Marine SI engines are typically grouped into the following categories:
1. Outboards (OB). These are engines mounted on the stern of a boat with the entire engine and drive
assembly external to the hull. Outboards range in power from less than 2 horsepower (hp) to more than
250 hp. More than half of the outboards sold in the US are less than 50 hp.
2. Personal watercraft (PWC). These vessels are generally intended for 1-3 riders where the riders sit (or
stand) on top of the vessel with their legs straddling it. Examples of PWC include Jet skis, Wave runners
and Sea Doo watercraft. Traditional PWC sold today are all above 50 hp, but some lower power specialty
applications, such as motorized surfboards, fall into this category as well.
3. Sterndrives and Inboards (SD/I). These engines are typically built by adding marine components to
automotive engine blocks and range in power from about 130 hp to more than 1000 hp. A stern drive
engine (also known as an inboard/outboard) is mounted in the stern of the boat and has a direct drive
through the hull similar to an outboard drive. An inboard engine is generally mounted in the center or rear
of the vessel and the engine is linked to the propeller by a drive shaft.
4. Marine auxiliary engines. These are small engines used on boats for auxiliary power. Although they are
currently categorized as Class I NHH engines (and in some cases Class II NHH engines), they have
features that are unique to marine applications. Specifically, they make use of their environment to water-
cool the engine and water-jacket the exhaust.
This study focuses on engines less than 50 hp. For this reason we only include OB, PWC, and marine generator sets
in the following discussion.
To meet existing emission standards, OB and PWC manufacturers are converting much of their product mix from
traditional crankcase scavenged carbureted two-stroke engines to either four-stroke engines or two-stroke direct
injection engines. Smaller four-stroke engines (<25 hp) are anticipated to continue to use carburetion; however,
electronic fuel injection is becoming popular on larger engines.
PWCs have a fuel tank integrated into the vessel/engine structure and all is sold as a unit. OB engines are self
contained power units but typically do not have an attached fuel tank. Either a portable fuel tank is used with the
engine (mostly for smaller engines) or the engine is connected to a fuel tank in the vessel that is permanently
installed by the boat builder.
As stated above, engines used in marine generator sets are water cooled with water-jacketed exhaust. The purpose
of the water-jacketing is to maintain low surface temperatures to minimize exhaust system temperatures. These
engines are often packaged in small compartments on boats and could overheat if they relied solely on ambient air
for the cooling system. Two engine manufacturers currently dominate this niche market. Recently, both
manufacturers have introduced models with electronic fuel injection and catalysts in the exhaust system and have
stated their intentions to convert to catalyzed engines in the near future. Catalyst technology has been driven by the
desire to reduce carbon monoxide emissions. Known carbon monoxide poisonings have been disproportionately
high among boats with generators compared to other vessels.
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Marine Vessel Fuel Systems
The marine vessels under consideration here include those powered by OB and PWC engines. The marine industry
has both mandatory and voluntary standards for boat construction (discussed below) which include requirements for
fuel system components such as fuel hoses and fuel tanks.
Vessels powered with OB engines use both portable and installed tanks. Portable marine fuel tanks, which are used
primarily with small OB engines, are normally 5-6 gallons. They are normally designed of blow-molded HDPE.
They are designed with a quick connect fitting for the fuel hose which closes and seals the system when not in use.
Outboard vessels with installed fuel tanks primarily use roto-molded XLPE fuel tanks. However, fuel tanks made
of aluminum or fiberglass are also used, primarily on larger vessels. These tanks range in capacity from 12 gallons
to well over 100 gallons. Outboard vessels with installed tanks generally follow the recommended industry practice
of venting the fuel tank though a hose which extends to the outside of the hull. Thus diurnal emissions are
uncontrolled.
Fuel tanks used on PWC are installed by the vessel manufacturer. They range in size from 4-18 gallons and are
usually constructed of blow-molded HDPE. Fuel tanks on PWC are sealed with pressure relief valves so there are
low diurnal emissions. The purpose of sealing the fuel tank is to prevent fuel spillage into the water during use.
Fuel hoses include those carrying liquid fuel as well as those carrying fuel vapor. OB engines employ fuel hoses on
the engine and come with a fuel hose to be connected to the portable or the installed fuel tank. For those OB engines
with installed fuel tanks, there is a fuel fill hose through which gasoline enters the fuel tank and another smaller
diameter hose used to vent the fuel tank. Fuel hose is generally constructed of polyvinyl chloride or nitrile rubber
with an abrasion-resistant cover and often a braid or wire reinforcement. The fuel, vent, and fill neck hoses can
range from only a few feet in length to dozens of feet in length depending on the size of the vessel, the location of
the fuel tank and engine, and the location of the tank vents and fill caps. For portable fuel tanks, the hose is
generally about 6 feet in length and includes quick connections at both ends and a rubber primer bulb in the middle.
Portable fuel tanks vent through a fuel cap mounted directly on the fuel tank so there is no vent hose.
PWC come with a fully installed fuel system. The fuel hoses include those used to route fuel to the engine as well as
those used to draw fuel from the installed fuel tank. These tanks are normally top fill so there is no appreciable fuel
fill neck involved.
B. IN-USE SAFETY EXPERIENCE
As discussed in earlier chapters, assessing incremental risk requires an understanding of the problems and in-use
safety experience with current products. For this analysis we used data available on the USCG website for marine
vessels. Presented below are incidences that are relevant to the engine/equipment subsystems that may be affected
by our emission standards.
Marine Engines and Vessels
The USCG website (www.uscgboating.org) includes boating statistics developed from the recreational boat
numbering and casualty reporting systems. The most recent publication on these statistics is "Boating Statistics -
2004" which includes a five year summary of boating accidents. The table 10-1 presents boating accidents related
to fuel fires.
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Table 10-1: Coast Guard Five Year Summary of Fuel Related Fires
Type of Accident
Year
Incidences
Fatalities
Injuries
Fire or Explosion of Fuel
2004
162
4
158
2003
142
7
68
2002
160
4
82
2001
153
2
73
2000
183
2
93
The above statistics only include incidences that are reported to USCG under 33 CFR 173.55. Because this
regulation places minimum thresholds on property damage or treatment requirements, incidences may go
unreported. Additionally, the USCG report does not provide any more detail on the causes of the fuel related fires.
Even looking into the incidence reports, details are not generally given on the source of the fuel or fuel vapor
leading to the fire or explosion. In many of the incidence reports the operator stated that they had just started their
engine when the fire started. Recommended practice is to run a blower to remove fuel vapor from the engine
compartment prior to starting the engine. The purpose of this is to remove fuel vapor that could be a fire hazard.
This fuel vapor may come from fuel spillage, leaks in the fuel system, and/or permeation through plastic tanks and
rubber hoses.
C. CURRENT SAFETY STANDARDS
The marine industry is regulated for safety primarily by USCG. In addition, USCG standards are supplemented by
voluntary standards created by the American Boat and Yacht Council (ABYC) Reference is also made to SAE and
Underwriters Laboratories tests and standards. These standards cover a wide range of boating safety issues which
include engine installations and fuel system requirements. All of the technologies being considered for controlling
exhaust and evaporative emissions from marine engines are covered by these safety requirements. These include:
33 CFR 183 Subparts J and K
ABYC H-2, H-24, H-25, P-l, and TH-23
UL 1102 and 1185
SAE J1527 and J2046
Marine Engines
The primary safety issues related to exhaust emission controls pertain to maximum exhaust system surface
temperatures, the risk of exhaust system leaks (i.e. carbon monoxide) into the vessel, and the risk of flammable
gasoline vapor mixtures around an engine. As discussed above, marine engines used in recreational vessels
typically have water-jacketed exhaust to minimize the temperature of exposed surfaces.
USCG safety requirements for boats and associated equipment are contained in 33 CFR 183. Subpart J deals
specifically with fuel systems on boats and includes specifications for fuel pumps and carburetors on the engine.
The scope of Subpart J includes all gasoline propulsion and auxiliary marine engines, excluding outboards. These
regulations state that the fuel pump must be on the engine or within 12 inches of the engine and that it must not leak
fuel even if the diaphragm fails. These regulations also limit the amount that a carburetor may leak under several
specified conditions and require anti-siphon valves and fuel shut off valves under specific conditions. The purpose
of these requirements is to minimize the risk of fuel spilling into the boat. In addition 46 CFR part 58 includes
installation requirements for gasoline marine engines. These installation requirements include backfire flame
control, drip collectors for carburetors, cooling or insulation for the exhaust system, and safe exhaust pipe
installations. These regulations do not apply to OB engines because they are not considered to be permanently
installed. Supplemental recommended practice for electric fuel transfer pumps is included in ABYC H-24 which
specifies delivery hose length, outlet pressure, and when the pump may be energized.
The only USCG safety standards that directly apply to OB engines are in 33 CFR 183, Subpart L. These standards
require that outboards capable of a minimum specified thrust must be equipped with a device to prevent the OB
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from being started in gear. USCG has not promulgated further safety standards for OB engines primarily because
the need has not been demonstrated for further regulation.
USCG standards for ventilation of vapors from boats with gasoline engines (auxiliary or propulsion) are contained
in 33 CFR 183, Subpart K. Subpart K requires that each compartment containing a gasoline engine be open to the
atmosphere or be vented by a blower system. Where a powered ventilation system is required, USCG requires a
label stating "Warning—gasoline vapors can explode. Before starting engine, operate blower for 4 minutes and
check engine compartment bilge for gasoline vapors." These ventilation requirements are supplemented by ABYC
H-2 which also requires compartments with non-metallic fuel tanks to be vented to atmosphere.
ABYC P-l states that all surfaces on the exhaust system on permanently installed marine engines that may come
into contact with persons or gear must be at or below 200°F or have protective guards, jacketing, or covers.
ABYC also details recommended practices for minimizing the risk of CO exposure on boats. These recommended
practices are described in ABYC TH-23 which is a technical report intended for design, construction, and testing
criteria to identify and minimize the presence of CO around a boat with a gasoline propulsion or auxiliary marine
engine.
Marine Vessel Fuel Systems
The primary safety issue regarding marine fuel systems is to prevent fuel from leaking into the boat. USCG
requirements for marine fuel systems are located in 33 CFR 183, Subpart J. Subpart J deals specifically with fuel
systems on boats and contains durability and other design requirements for fuel tanks and fuel hoses. It should be
noted that Subpart J applies to all boats that have gasoline engines (propulsion and/or auxiliary), except for OB
engines. However, ABYC H-24 supplements 33 CFR 183 and extends these practices to all boats with gasoline fuel
systems, including OB engines. Some smaller boats do not have installed gasoline fuel systems. Operators of these
boats use OB engines attached to portable fuel tanks which are covered by ABYC H-25. Specifications for marine
fuel hoses and fuel tanks are discussed below.
Fuel Hoses
Both 33 CFR 183 and ABYC H-24 reference SAE J1527 for the proper design of marine fuel hoses. The USCG
regulations and SAE recommended practice distinguishes between Type A and Type B fuel hose. Type A fuel hose
normally contains liquid fuel while Type B hose normally contains no liquid fuel. Both hose types are subject to the
2Vi minute flame test under 33 CFR 183, Subpart J; however, Type B hose has a more relaxed permeation
requirement.. In addition, both types of hose must still be self extinguishing within 60 seconds when burned. SAE J
1527 includes several other durability tests including abrasion resistance, burst pressure, vacuum collapse, cold
temperature flexibility, tensile strength and elongation, oil resistance, ozone resistance, and fuel resistance tests on
ASTM fuel C and a test fuel containing 85 percent ASTM fuel C and 15 percent methanol. The fuel resistance tests
state that the hose must meet maximum tensile change, elongation change, and volume changes after being
immersed in the test fuels. Also, SAE J1527 specifies maximum allowable permeation rates on the two test fuels.
Finally, this recommended practice includes an adhesion test which sets a minimum load required to separate the
tube from the protective cover.
PWC manufacturers generally use an alternative recommended practice provided under SAE J2046 for their fuel
system designs. This recommended practice includes tests and limits for tensile strength and elongation, dry heat
resistance, ozone resistance, oil heat resistance, burst pressure, vacuum collapse, cold temperature flexibility, and
resistance to ASTM fuel C. This fuel resistance includes immersing the hose in fuel and testing the tensile change,
elongation change, and volume change. Also, a permeation limit is set for ASTM fuel C. In addition, SAE J2046
contains an adhesion test which sets a minimum load for separating the tube and cover. Finally, this recommended
practice includes a 2Vi minute flame test for the entire fuel system.
For fuel hose used with portable fuel tanks, UL 1185 recommends that fuel hose meet the USCG Type A or Type B
standards discussed above.
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Fuel Tanks
33 CFR 183 Subpart J includes several specifications and durability tests for marine fuel tanks which are installed in
vessels with gasoline propulsion or auxiliary engines, excluding OB engines. These fuel tank specifications include
prohibited materials, labeling requirements, and a limit on the pressure in the fuel tank of 80 percent of the pressure
marked on the label that the tank can withstand without leaking (at least 3 psi). The fuel tanks must pass several
durability tests without leaking. These durability tests include a static pressure test, a shock test, a pressure impulse
test (25,000 cycles from 0-3 psi), a slosh test (500,000 cycles ± 15° from level), and a 2Vi minute fire test.
ABYC H-24 supplements 33 CFR 183 and extends these practices to all gasoline powered boats with installed fuel
tanks, including those using OB engines. One notable addition is that ABYC H-24 requires a 5/8" ID vent hose to
prevent pressure from building up in the fuel tank. Additional requirements are contained in UL 1102 which
references ASTM H-24 and 33 CFR 183, Subpart J. These additional requirements include shock testing of fittings,
a static pressure test, and requirements for gaskets to be tested for fuel and oil resistance and atmospheric aging.
ABYC H-25 defines recommended practices for the design of portable marine fuel tanks. These specifications
include requirements for color (red), UV inhibitors, mechanical strength from -18°C to 60°C, labeling, and vent
openings that can be closed so that they are liquid and vapor tight. This recommended practice includes several
durability tests as well. These durability tests include a low temperature drop test, exposure to a test fuel of 85
percent ASTM fuel C blended with 15 percent methanol, and an expansion and contraction test. UL 1185 includes
additional requirements including standards for fittings and accessories integral to the portable fuel tank such as the
fuel hose and the quick connect fittings. Additional tests for the fuel tank include vibration, durability of vent and
fill closures, fitting impact, permeation, light and water exposure, and a fire test. In addition there are requirements
for gaskets to be tested for fuel and oil resistance and atmospheric aging.
D. EMISSION CONTROL SYSTEM DESIGN
Marine Engines
We expect to propose emission standards for OB and PWC that will require significant upgrades in fuel systems and
calibration. These standards are expected to eliminate carbureted two-stroke engines from the market. These 2-
stroke engines have short-circuiting losses in the cylinder due to the intake and exhaust valves being open at the
same time. As a result, 25 percent or more of the fuel passes through the engine unburned. Over the past decade,
manufacturers have introduced lower emitting four-stroke or direct-injection two-stroke engines across their entire
product lines. We anticipate that further emission controls will result in manufacturers discontinuing their older
carbureted two-stroke engine lines and selling only their cleaner four-stroke or direct-injection two-stroke designs.
We do not expect that the potential exhaust emission standards would require after-treatment technology for control
of exhaust emissions. We are not anticipating the use of new technology to meet the exhaust emissions standards
but only the expanded use of current cleaner technologies.
Marine Auxiliary Engines
These are small engines used on boats for auxiliary power, in most cases for electric power generation. Although
they are currently categorized as Class INHH engines (and in some cases Class IINHH engines), they have features
that are unique to marine applications. Specifically, they make use of their environment to water-cool the engine
and water-jacket the exhaust. Marine auxiliary engine manufacturers have aggressively pursued the development of
advanced emission control technology for these products in response to market place concerns. These systems use
catalytic converters inside of a water-jacketed system and electronic feedback controls to give optimum air to fuel
ratio. This emission control approach allows for very low exhaust emission levels relative to current NHH HC+NOx
and CO emission standards.
Marine Vessels
We have already proposed evaporative emission standards for vessels powered by Marine SI engines that are
similar in scope to those discussed above for nonhandheld land-based engines. These include fuel hose and fuel
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tank permeation control. Also, while we are not proposing standards for controlling vessel running loss emissions,
we have already proposed standards requiring the control of diurnal emissions.
Fuel Hose
Most marine vessels using SI engines use polyvinyl chloride or nitrile rubber hose to deliver gasoline from the fuel
tank to the engine. To meet the fuel hose permeation standards under consideration, manufacturers would be able to
use the current basic type of hose construction except that an additional barrier layer would need to be added to the
construction. A typical barrier material would likely be a fluoroelastomer or fluoroplastic material. Current fuel
lines used in marine applications meet USCG and ABYC standards for flame resistance and durability as well as
requirements for fuel system fittings and clamps. The barrier layers needed to control permeation are thin and are
not expected to lead to any significant differences in hose flexibility or ability to retain connections within the fuel
system. The hose which could be used is commercially available today.
Fuel tanks
Marine fuel tanks include portable tanks constructed of HDPE and installed fuel tanks made of XLPE, aluminum,
and fiberglass. Portable fuel tanks made of HDPE are used in PWCs and with lower horsepower OB engines.
Aluminum, fiberglass, and XLPE are used in installed tanks in vessels using higher horsepower OB engines.
HDPE, XLPE, and fiberglass have poor permeation resistance characteristics. Fuel does not permeate through
aluminum tanks. As was the case with NHH engines and equipment, there are several technological approaches that
can be used to reduce gasoline permeation through plastic fuel tanks. These approaches include surface treatments,
barrier constructions, and alternative materials.
Surface treatments, such as fluorination and sulfonation, do not materially change the construction of the fuel tank.
These treatments are performed as a secondary step after the fuel tank is molded and create a thin layer on the
surfaces of the fuel tank that acts as a barrier to permeation. In fluorination a barrier is created on both the inner and
outer surfaces while in sulfonation it is created only on the inner surface. These treatments do not materially change
the construction of the fuel tank and are not expected to affect the durability of the fuel tank because the barrier is
less than 20 microns thick. Surface treatments are used to meet the California gasoline permeation standards for
portable fuel cans.
Multi-layer fuel tank constructions which create a barrier to permeation have been used in automotive applications
for many years. The most common approach is to mold a thin layer of ethyl vinyl alcohol (EVOH) inside a HDPE
shell. This approach is commonly used in high production volume, blow-molded fuel tanks and can be used in
lower production volumes through a molding process known as thermoforming. Another approach available for
blow-molded fuel tanks is to create a non-continuous barrier by blending a small amount of EVOH directly into the
HDPE. During molding, the EVOH creates overlapping barrier platelets which restrict permeation. For each of
these technologies, the barrier material is only a small percentage of the total makeup of the fuel tank. Non-
continuous barriers can reduce permeation by more than 85 percent while continuous barriers can achieve more than
a 99 percent reduction in permeation. These technologies have the advantage of having been in use for many years
and having been applied in various applications. Automotive manufacturers require these fuel tanks to meet
durability specifications similar to those required by the US Coast Guard.
Rotationally molded XLPE tanks would be able to make use of barrier technologies. In one technique nylon, which
has good permeability properties, is applied as an inner shell inside the fuel tank. The manufacturer has
demonstrated that the nylon has an excellent bond with the XLPE.1 As a result of this bond and the strength of the
nylon, this construction offers strong resistance to impact. Testing at IMANNA labs showed that a tank of this
construction met the USCG durability requirements in 33 CFR 183, Subpart J which includes impact testing and
flame resistance.2 As a result of this bond and the strength of the nylon, the construction meets the USCG impact
and flame resistance requirements discussed above. In addition, emission testing has shown good permeation
control performance compared to baseline. Another new approach for XLPE tanks is to coat the tank with a low
permeation epoxy in a secondary step after molding.3 This approach does not change the basic fuel tank
construction but only adds an outer layer similar in thickness as a coat of paint. In addition, an intumescent additive
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has been developed which can be added to the epoxy coating for additional flame resistance. Emission testing on
this technology has also shown good emission control performance.
Fiberglass fuel tanks can meet low permeation requirements through the use of a nanocomposite barrier layer. This
barrier layer is composed of fiberglass impregnated with microscopic fibers of treated volcanic ash. A company
named ECSI has developed this technology for use in marine fuel tanks. Through testing, ECSI has demonstrated
this technology to meet USCG and ABYC standards for fuel system mechanical strength requirements.4 In
addition, emission testing has shown good emission control performance.
Diurnal Emissions Control
As was discussed in the beginning of Chapter 9, diurnal emissions occur when the rising ambient temperature heats
the fuel inside the fuel tank and displaces the fuel vapors created through fuel tank vents. In the cases where these
venting emissions are high, a combustible fuel vapor concentration could occur if the vapor is vented into an
enclosed space such as the confines a vessel. In addition, fuel vapor vents create a path for fuel to spill out of the
fuel system during refueling or when fuel sloshing occurs.
The simplest approach to controlling diurnal emissions is simply to close the tank vent. Under this scenario, when
the tank heats up, pressure would build in the fuel tank, but no fuel vapor would be vented to the atmosphere.
Pressure would be limited with a pressure relief valve that would open at higher pressures. In addition, a vacuum
relief valve would be needed to prevent a vacuum in the fuel tank which could restrict fuel delivery to the engine
and cause the engine to stall. This is really only an option for smaller tanks where the potential for significant
geometric shape deformation under pressure is small. Portable marine fuel tanks are designed to be sealed when not
in use, and PWC use sealed fuel tanks (with pressure relief valves) to prevent spillage during operation. Leakage
from these tanks is normally not into a confined space such as a vessel bilge.
Another well developed approach to controlling diurnal emissions has been used in automobiles for over 30 years.
In this approach a plastic canister containing activated carbon is placed in the vent line. This carbon canister
collects fuel vapor vented from the fuel tank as it breathes during the day. The canister could then be either actively
or passively purged. Active purging refers to drawing the vapor to the engine to be burned. Passive purging refers
to removing gasoline vapor stored on the activated carbon through the air naturally drawn into the fuel tank through
the vent line during cooling periods. Canister systems represent a simple technology that has long been
demonstrated in various applications without safety issues.5
E. ASSESSMENT OF SAFETY IMPACT OF NEW EMISSION STANDARDS
New Exhaust Emission Standards for OB/PWC
Because we are not anticipating the use of new technology to meet the exhaust emissions standards, we do not
believe that further emission control will result in an incremental safety risks relative to the current mix of
technology. Current 4-stroke and 2-strke direct injection technologies are more sophisticated than the older
carbureted two-stroke design and have been used for nearly a decade. Although there were some early technical
issues with two-stroke direct injection engines, these issues have been largely resolved though significant
engineering efforts. As a result of these engineering efforts, the newer 4-stroke and 2-stroke direct injection
technologies are actually more reliable than older designs. In addition, they are more fuel efficient which allows for
greater range and, arguably a lower chance of running out of fuel. These improvements in reliability and range
would be expected to improve safety issues related to being stranded at sea.
New Exhaust Emission Standards for Marine Auxiliary Generators
Manufacturers of marine auxiliary engines are leading the way in new exhaust emission control technology in the
marine sector. Even with catalysts packaged in the exhaust manifold, these engines have low surface temperatures
because the exhaust manifolds containing the catalysts are water-jacketed with surface water drawn and returned to
the ambient source to cool the exhaust system. With water jacket cooling EPA does not anticipate any heat-related
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problems or increase in fire due to catalysts. In addition, these systems are electronically controlled with feedback
systems that can be used to detect problems with the engine before they become problematic. Finally, a safety
benefit is achieved by the very large reduction in CO emissions from these engines. This reduction in CO will
benefit not only the boat operators but swimmers and other individuals in the vicinity of the boat.
Fuel Hose Permeation Standards
Low permeation fuel hose subject to the USCG requirements would still need to meet the requirements specified in
SAE J1527 and discussed above. In fact, one manufacturer is selling barrier fuel hose today that meets the USCG
requirements and is used by several boat builders. This hose meets the permeation requirements we are considering.
This hose construction is similar to baseline hose constructions except that a barrier layer is added. In the same
way, manufacturers of PWC and portable fuel tanks, would still be expected to comply with SAE J2046 and UL
1185 respectively. To meet the fuel hose permeation standards under consideration, manufacturers would be able to
use the existing hose constructions except that an additional barrier layer would need to be added to minimize
permeation fuel through the hose material.
Low permeation fuel hose will have no negative implications for safety and may have some benefits. The addition
of a barrier layer would not require a change in the general construction of the hose. In addition, barrier materials
are made of compounds that are resistant to permeation by gasoline, including ethanol blends and oxidized ("sour")
gasoline. This fuel resistance not only protects against chemical attack, but also limits swelling due to the
permeation of fuel. By limiting the swelling and contracting (drying) cycles and chemical attacks that may cause
the hose to eventually become brittle, the hose may better resist cracking as well. The barrier hose may reduce
concentrations of fuel vapor in confined spaces where the fuel hoses are routed such as the engine compartment,
vessel bilge, or other areas in the hull where the fuel tank may be located.
This lower concentration could help prevent a flammable mixture of fuel vapor from forming within the confines of
the vessel. It should be noted that low permeation fuel hose is available today and is used by many boat builders.
Fuel system fittings and clamps are also covered by the USCG and ABYC standards. These specifications require
the fittings to have a bead, flare, or other grooves to help prevent the hose from pulling off the fittings. Clamps
must be corrosion resistant, not cut the hose, and resist one pound tensile force. In addition, all fittings, joints, and
connections must be easily accessible for inspection and maintenance. With any changes in hose constructions, boat
builders would still need to design their connections to meet these requirements. As some boat builders are using
low permeation fuel hose today, they are also using corresponding fittings and clamps.
159
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Fuel Tank Permeation Standards
In any situation where a manufacturer makes changes to fuel tanks, such as materials or geometry, they must
evaluate the potential safety effects of these changes. Under current industry practices new fuel tank designs are
durability tested under the USCG requirements and ABYC and UL recommended practice described above. These
tests include pressure impulse, fuel and oil exposure, atmospheric aging, slosh, shock, and flame resistance.
The techniques suggested above would also meet the USCG and ABYC durability requirements including the flame
test
We expect that the use of low permeation fuel tanks will have no negative implications for safety and may have
some benefits. Permeation barriers could minimize permeation of the fuel into the tank walls and reduce any
negative effects of fuel exposure. In addition, low permeation fuel tanks would lead to reduced concentrations of
fuel vapor in confined spaces in the vessel hull where the fuel tank is located; a lower fuel vapor concentration
means a reduced risk of fire. The choice of proper materials and construction durability is also important.
Under our current permeation requirements for recreational vehicles, we require durability testing as part of the fuel
tank permeation test procedure. Prior to the permeation test, the fuel tank is filled with gasoline containing 10%
ethanol and soaked for 20 weeks at 28±5°C. In addition, the fuel tank is subject to a pressure vacuum test made up
of 10,000 cycles from -0.5 to 2.0 psi, a slosh test made up 1 million cycles where the tank is rocked ±°15, and a 240
hour UV exposure test. Although these tests are intended to help ensure the long term effectiveness of the
permeation control technology, they also inherently assess the durability of the fuel tank as well.
Fuel Tank Diurnal Emission Control Standards
Portable fuel tanks are currently designed to be pressurized through a manual control valve on the vent. The use of
a sealed tank with vacuum relief would not add to the pressure experienced by the fuel tank and therefore offer no
incremental safety risk. The vacuum relief valve could offer a safety benefit in that it could prevent occurrences of
engine stalling that may occur if the operator were to forget to open the manual valve prior to starting the engine.
PWC fuel tanks are already using sealed fuel systems with pressure relief valves. We expect that this design would
meet the emission control requirements under consideration.
Carbon canisters do not present an incremental risk to safety for marine vessel use. These canisters are passive
systems in the vent line and create nothing more than nominal backpressure on the tank. The use of the carbon
canister can have positive safety implications. First, the carbon will collect vapor from the fuel tank which will
result in less gasoline vapor which can infiltrate the engine and bilge areas on the boat. Second, the design of the
diurnal control system will include a mechanism to prevent fuel from entering the vent hose during refueling. This
mechanism could be as simple as a small orifice between the fuel tank and the canister that would be sized to limit
fuel from entering the vent hose during refueling but be large enough to prevent a restriction on vapor flow during
diurnal breathing. For an average fuel tank, this orifice would be on the order of 1mm in diameter. This could help
reduce fuel spillage that sometimes occurs today from the vent line during refueling. Because the fuel tank would
need to vent through the canister to achieve the emission reductions, the fuel cap would need to form a vapor tight
seal. Four boat manufacturers installed carbon canisters last summer on a total of fourteen boats as part of a
demonstration project. At the end of the summer, all of the canisters were still operating properly and no safety
incidences were reported.6
160
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F. CONCLUSION
EPA reviewed the characteristics of marine engines less than 50 horsepower and evaluated the emission control
technologies used to reduce exhaust emissions from these engines. EPA also reviewed the fuel system
characteristics for marine vessels using these engines and evaluated emission control technologies which could be
used to reduce fuel evaporative emissions from these two subcategories. Marine engines including marine auxiliary
engines must meet USCG standards related to safety. In addition, it is industry practice to meet ABYC
requirements. There are thousands of 4-stroke and 2-stroke direct injection engines in the fleet today which would
meet the exhaust emission standards being considered by EPA. Based on the fact that the technology needed to
meet the standards we are considering is already in use in both OB and PWC engines, EPA does not believe that the
technology needed to meet new standards would result in an increase of risk of fire and burn to consumers in use.
With regard to fuel hoses, fuel tanks, and diurnal controls, there are rigorous USCG, ABYC, UL, and SAE
standards which manufacturers will continue to meet for fuel system components. In addition, USCG and others
would be able to expand their requirements in response to new fuel systems designs if they saw the need to do so.
Furthermore, the EPA permeation certification requirements related to emissions durability will add an additional
layer of assurance. Low permeation fuel hoses are used safely today in many marine vessels. Low permeation fuel
tanks and diurnal emission controls have been demonstrated in various applications for many years without an
increase in safety risk.
Furthermore, a properly designed fuel system with fuel tank and fuel hose permeation controls and diurnal emission
controls would reduce the fuel vapor in the boat, thereby reducing the opportunities for fuel related fires. In
addition, using improved low permeation materials coupled with designs meeting USCG and ABYC requirements
should reduce the risk of fuel leaks into the vessel. EPA believes that the application of emission control
technologies on marine engines and vessels for meeting the proposed evaporative emissions standards would not
lead to an increase in incremental risk of fires or burns.
1 O'Brien, G., Partridge, R., Clay, B., "New Materials and Multi-Layer Rotomolding Technology for Higher
Barrier Performance Rotomolded Tanks," Atofina Chemicals, 2004, Docket EPA-HQ-OAR-2004-0008-0044.
2 Partridge, R., "Petro-Seal for Ultra-low Fuel Permeation; Evaporative EPA Emissions from Boat Fuel Systems,"
Arkema, Presentation at the 2004 International Boatbuilders' Exhibition and Conference, October 25, 2004, Docket
EPA-HQ-OAR-2004-0008-0252.
3 Bauman, B., "Advances in Plastic Fuel Tanks," Fluoro-Seal International, Presentation at the 2004 International
Boatbuilders' Exhibition and Conference, October 25, 2004 Docket EPA-HQ-OAR-2004-0008-0036.
4 Chambers, J., "Marine Fuel Containment... A Permanent Solution," Engineered Composite Structures,
Presentation at the 2004 International Boatbuilders' Exhibition and Conference, October 25, 2004 Docket EPA-HQ-
OAR-2004-0008-0037.
5 "Stopping Vehicle Fires & Reducing Evaporative Emissions: The Need to Control Gasoline & Alcohol Blend
Volatility," Center for Auto Safety, March 1988, Docket EPA-HQ-OAR-2004-0008-0330.
6 Tschantz, M., "Summer Test Program Carbon Analysis," Meadwestvaco Corporation, Presentation at the 2005
International Boatbuilders' Exhibition and Conference, October 20, 2005 Docket EPA-HQ-OAR-2004-0008-0290.
161
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Appendix A - Basic principles of Infrared thermal imaging1
IR TEMPERATURE BASICS
Temperature is a measure of the thermal energy contained by an object; the degree of hotness or coldness of an
object is measurable by a number of means and is defined by temperature scales. Temperature, in turn, determines
the direction of net heat flow between two objects.
There are three modes of heat transfer, conduction, convection and radiation. All heat is transferred by means of
one or another of these three modes, infrared thermography is most closely associated with radiative heat transfer,
but it is essential to understand all three in order to comprehend the significance of IR Thermograms.
CONDUCTIVE HEAT TRANSFER
Conductive heat transfer is the transfer of heat in stationary media. It is the only mode of heat flow in solids, but
can also take place in liquids and gases. It occurs as a result of atomic vibrations and (in solids) and molecular
collisions (in liquids). Whereby energy is moved, one molecule at a time, from higher temperature sites to lower
temperature sites.
CONVECTIVE HEAT TRANSFER
Convective heat flow takes place in a moving medium and is almost always associated with transfers between a
solid and a moving fluid (such as air). Free convection takes place when the temperature differences necessary for
heat transfer produce density changes in the fluid and the warmer fluid rises as a result of increased buoyancy.
Forced convection takes place when an external driving force, such as a cooling fan, moves the fluid.
RADIATIVE HEAT TRANSFER
Radiative heat transfer is unlike the other two modes in several respects:
• It can propagate through a vacuum
• It occurs by electromagnetic emission and absorption.
• It occurs at the speed of light and behaves in a manner similar to light
While conductive and convective heat transferred between points is linearly proportional to the temperature
difference between them, the energy radiated from a surface is proportional to the fourth power of its absolute
temperature. The radiant thermal energy is transferred between two surfaces is proportional to the third power of
the temperature difference between the surfaces.
Thermal infrared radiation leaving a surface is called radiant exitance or radiosity. It can be emitted from the
surface, reflected off a surface, or transmitted through a surface. The total radiosity is equal to the sum of the
emitted component, reflected component and the transmitted component. The surface temperature, however, is only
related to the emitted component.
The measurement of thermal infrared radiation is the basis for non-contact temperature measurement and IR
thermography. Like light energy, thermal radiation is a photonic phenomenon that occurs in the electromagnetic
spectrum. While light energy takes place in the visible portion of the spectrum, radiative heat transfer takes place in
the infrared portion of the spectrum.
All target surfaces warmer than absolute zero radiate energy in the infrared spectrum. Very hot targets radiate
visibly as well. IR thermal imagers measure and display images of this infrared radiated energy.
162
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From the point of view of IR radiation characteristics, there are three types of target surfaces; blackbodies,
graybodies and non-graybodies (also called spectral bodies). A black body radiator is defined as "a theoretical
surface having unit emissivity at all wavelengths and absorbing all radiant energy impinging upon it" Emissivity is
defined as the ratio of radiant energy emitted from a surface to the energy emitted from a blackbody surface at the
same temperature. Although blackbody radiators are theoretical and do not exist in practice, the surface of most
solid objects are graybodies, that is, surfaces with emissivities that are fairly constant with wavelength.
Total radiosity available to a measuring device from a target surface has three components: emitted energy, reflected
energy and energy transmitted through the target surface. If the target is a blackbody emitter, it has an emissivity
equal to one, and it will reflect and transmit no energy. If the target is a graybody emitter, then it will resemble a
black body in spectral distribution, but since its emissivity is less than one, it may also reflect and/or transmit
energy. If the target is a non-graybody emitter, it may also emit, reflect and transmit energy. Since only the emitted
component is related to temperature of the target surface it becomes apparent that a significant step in making IR
temperature measurements is eliminating or compensating for the other two components.
Infrared radiation from the target passes through some transmitting medium on its way to the infrared instrument. If
the medium is a vacuum then there is no loss of energy, but most infrared measurements are mad through air. The
effect of atmospheric gases can be ignored for short distances, such as a few meters.
HOW THE IR FLEXCAM T AND IR SNAPSHOT CAMERA'S CONVERT RADIANCE TO TEMPERATURE
The IR Flexcam T and IR Snapshot imagers correct the infrared radiance from any single point on the target surface,
so as to approach the true temperature measurements at that location. To do this, it first assumes that the IR
absorption of the air path between the target and the instrument is negligible. It also assumes that there is no IR
energy transmitted through the target from sources behind the target. In order to correct for reflection of the
ambient background it requires the operator to input the background temperature. Note that the EPA-NVFEL test
cells are held at a temperature of 25C +/- 1C.
The operator also inputs the targets estimated emissivity. All the targets of interest (Mufflers/Catalysts/Heat
Shields) have been painted with a high temperature flat-black paint which has a very dull matte finish. This is used
to even out the emissivity of the object over the surface as well as to increase the value of the emissivity of the
object. An emissivity of 0.9 was used for this project. To check the validity of the emissivity assumptions, a
comparison of the surface temperature measured with the IR imager was made to a known surface temperature
measured with a thermocouple. The temperatures were within 1% of agreement.
The IR imagers used for EPA's test program have the following general specifications. They use microbolometer
detectors that require no cryogenic cooling. The detector elements are square and are located in a rectangular grid.
The optical path of the camera includes an appropriate band-pass filter for the temperature range of interest. The IR
Snapshot Camera has a NIST traceable calibration from 10C to 1200C with accuracy of 2C or 2% of reading. The
IR FlexCam has a NIST traceable calibration from 0C to 600C with accuracy of 2C or 2% of reading. The lenses
for both cameras are made from germanium and are anti-reflective coated for high transmission in the temperature
range of choice.
The calibration of both the IR Flexcam and IR Snapshot was repeated on January 11, 2006. Both imagers were
within the manufacturer's accuracy specifications, thus neither imager required calibration adjustment. The
calibration results are presented in Tables A-l and A-2.
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Table A-l: Summary of results for the validation of temperature calibrations for the "FlexCamT" and "FLIR"
imagers. Both imagers were adjusted to account for the emissivity of the temperature targets and an ambient
temperature of 25°C.
EPA IR Flexcam T
Point Temperature
(°C)
Emissivity of
Temperature
Target
0.98
0.93
0.97
0.93
Target
Temperature
(°C)
5
100
350
600
4.6
99.1
351.8
590.1
Briggs & Stratton FLIR
Point
Temperature
(°C)
4.9
102
350
602
Average
Temperature
(°C)
5.6
101.6
351.5
601.6
Table A-2: Summary of results for the validation of temperature calibration for the EPA "IR Snapshot" imager.
Emissivity of
Temperature
Target
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
0.98
Target
Temperature
(°C)
5
20
37
50
75
100
240
300
350
600
700
800
900
1000
1100
1200
Average
Temperature
(°C)
3.51
19.57
36.44
49.19
74.18
98.99
239.8
301.85
350.88
594.65
694.06
793.47
901.97
986.42
1091.14
1192.84
1 Adapted from the IR Flexcam T and IR Snapshot Operating Manuals, Infrared Solutions Inc., Plymouth, MN,
2004.
164
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Appendix B: Emissions Results
Table B-l: Emissions summary - Class I OHV engines at low (10-20) hours.
Engine
Tested
Configuration
HC+NOx
(g/kW-hr)
NOx
(g/kW-hr)
HC
(g/kW-hr)
CO
(g/kW-hr)
241
OEM
10.6 ±0.5
3.0 ±0.3
7.6 ±0.3
313 ±29
241
Catalyst-muffler,
venturi air
3.9 ±0.2
1.45 ±0.2
2.5 ±0.3
138 ±46
255
OEM
11.2
3.2
8.0
340
255
Catalyst-
muffler*, venturi
air
5.0
0.7
4.3
288
2982
OEM
8.4 ±0.5
4.4 ±0.4
4.0 ±0.3
161 ± 15
2982
Catalyst-muffler,
venturi air**
4.9 ±0.3
2.8 ±0.2
2.2 ±0.3
85 ± 10
243
OEM
13.4 ±0.9
4.6 ±0.3
9 ± 1
351 ± 13
243
Catalyst-muffler,
venturi air"*
7 ± 1
1.8 ±0.2
5 ± 1
334 ±50
244
OEM
11.0
1.8
9.2
517
244
Catalyst-muffler,
venturi air
7.2
1.1
6.1
433
245
OEM
10.9
2.4
8.5
472
245
Catalyst-muffler,
venturi air
5.6
0.6
5.0
381
Notes:
Engines 241, 255, and 2982 are from the same engine family.
Engines 243, 244, and 245 are from the same engine family
*Tubular pre-catalyst, 22cc 200 cpsi metal monolith downstream of stamped secondary-air venturi
**35 cc, 100 cpsi metal monolith, stamped secondary-air venturi.
*** Reduced substrate volume, tubular venturi.
Stamped Venturis used were based on the OEM design.
"±" values represent 95% confidence intervals for a 2-sided t-test, for 3 to 4 replicate measurements.
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Table B-2: Emissions summary - Class I side-valve engines at low (10-20) hours.
Engine
Tested
HC+NOx
NOx
HC
CO
Configuration
(g/kW-hr)
(g/kW-hr)
(g/kW-hr)
(g/kW-hr)
6820
OEM
10.8 ±0.5
2.2 ±0.2
8.7 ±0.6
458 ±45
258
OEM
10.5
2.5
8.1
487
258
Catalyst-muffler,
venturi air
6.7
1.2
5.5
380
236
OEM
15.2 ±.2
3.0 ±0.8
12.1 ±0.8
380 ±38
236
Catalyst-muffler,
venturi air
4.9 ±0.6
0.90 ±0.05
4.0 ±0.7
218 ±62
246
OEM
12.4
1.8
10.6
490
246
Catalyst-muffler,
venturi air
5.6
0.8
4.8
333
248
OEM
12.0
3.0
9.0
403
248
Catalyst-muffler,
venturi air
4.6
0.8
3.8
294
249
OEM
11.3
3.0
8.3
413
249
Catalyst-muffler,
(no secondary
air)*
6.3
0.9
5.4
351
Notes:
Engines 6820 and 258 were from the same engine family, and used identical catalyst muffler designs.
Engines 236, 246, and 249 were from the same engine family.
Stamped Venturis used were based on the OEM design.
"±" values represent 95% confidence intervals for a 2-sided t-test, for 3 to 4 replicate measurements.
The catalyst-muffler for engine 6820 was not available until just prior to the initiation of field aging - emissions
measurements at low-hours were not conducted.
*Rh-only catalyst
Table B-3: Emissions summary - Class IOHV and side-valve engine tested at high (>110) hours.
Engine
Tested
Configuration
HC+NOx
(g/kW-hr)
NOx
(g/kW-hr)
HC
(g/kW-hr)
CO
(g/kW-hr)
241 (OHV)
OEM
13.4 ±0.6
5.2 ±0.4
8.1 ±0.6
266 ±9
241
Catalyst-muffler,
venturi air
6.6 ±0.2
3.2 ±0.2
3.4 ±0.1
180 ±4
2982 (OHV)
OEM
10.2 ±0.4
6.1 ±0.4
4.1 ±0.2
148 ±6
2982
Catalyst-muffler,
venturi air
7.0 ±0.4
4.5 ±0.3
2.5 ±0.2
85 ±6
6820 (side-
valve)
OEM
15.4 ±0.4
2.6 ±0.5
13 ± 1
380 ± 42
6820
Catalyst-muffler,
venturi air
9.4 ±0.7
2.8 ± 1
6.6 ±0.8
168 ± 19
Notes:
"±" values represent 95% confidence intervals for a 2-sided t-test, for 3 to 4 replicate measurements.
166
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Table B-4: Emissions summary - Class II OHV engines at low (10-40) hours.
Engine
Tested
Configuration
HC+NOx
(g/kW-hr)
NOx
(g/kW-hr)
HC
(g/kW-hr)
CO
(g/kW-hr)
231
OEM
7.0 ± 1
3.0 ±0.6
4 ± 1
333 ±60
231
EFI
6.9
3.0
3.8
308
231
EFI, catalyst-
muffler
1.8 ±0.4
0.6 ±0.2
1.3 ±0.5
120 ± 29
251
OEM
9.2
5.9
3.3
228
251
catalyst muffler
3.1 ±0.3
0.9 ±0.6
2.8 ±0.4
245 ± 93
252
OEM
9.1 ±0.8
7.3 ±0.8
1.8 ±0.2
188 ±33
253
OEM
6.9 ±0.4
3.0 ±0.1
4.0 ±0.5
380 ±23
253
catalyst muffler
4.5 ±0.1
0.29 ±0.01
4.2 ±0.1
529 ± 11
232
OEM
8.5 ±0.5
2.25 ±0.08
6.2 ±0.5
475 ± 29
232
EFI
8.0 ±0.3
4.4 ±0.3
3.7 ±0.6
274 ± 42
232
EFI, catalyst-
muffler
2.2 ±0.1
0.8 ±0.2
1.4 ±0.2
154 ±27
233
OEM
8.1 ±0.7
2.2 ±0.3
6.0 ±0.4
459 ± 24
Table B-5: Pre- and Post-catalyst emissions for a Carbureted 400cc Class II engine after 50, 300, and 500 hours of
operation.
Engine
Tested
Accumulated
HC+NOx
NOx
HC
CO
Configuration
Hours of
Engine
Operation
(g/kW-hr)
(g/kW-hr)
(g/kW-hr)
(g/kW-hr)
142
OEM
50
6.56 ±0.03
2.8 ±0.1
3.74 ±0.07
300 ± 15
142
Catalyst
50
2.5 ±0.6
0.12 ±0.06
2.3 ±0.6
282 ± 47
142
OEM
300
7.27 ±0.18
3.60 ±0.08
3.7 ±0.1
238 ±4
142
Catalyst
300
3.5 ±0.04
0.367 ±
0.002
3.15 ±0.04
263 ±9
142
OEM
500
9.8 ±0.1
6.4 ±0.2
3.4 ±0.1
165 ±7
142
Catalyst
500
2.8 ±0.7
0.7 ±0.2
2.1 ±0.5
170 ± 26
Notes:
The catalyst tested with engine 142 is a duplicate of the unit tested within the catalyst-muffler of engine 253.
167
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&EFA Office of Transportation EPA420-R-06-006
United States and Air Quality March 2006
Environmental Protection —
EPA Technical Study on the
Safety of Emission Controls
for Nonroad Spark-Ignition
Engines < 50 Horsepower
Appendix C -
Design/Conduct Failure
Modes and Effects Analysis
for Small SI Equipment and
Engines
-------
EPA420-R-06-006
March 2006
EPA Technical Study on the Safety of
Emission Controls for
Nonroad Spark-Ignition Engines < 50 Horsepower
Appendix C -
Design/Conduct Failure Modes and Effects Analysis for
Small SI Equipment and Engines
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
Prepared for EPA by
Southwest Research Institute
Engine, Emissions, & Vehicle Research Division
EPA Contract No. EP-C-05-018
Work Assignment No. 0-10
-------
EXECUTIVE SUMMARY
The U.S. Environmental Protection Agency (EPA) issued Work Assignment 1-10,
"Design/Conduct FMEAs for Small SI Equipment and Engines" to Southwest Research
Institute® (SwRI®). The work was to analyze the potential safety impact of possible Phase 3
emissions standards, which include a 35% reduction in HC+NOx exhaust emissions and
evaporative emission standards on small spark-ignited (SI) engines (<19kW). The standards are
expected to result in the use of exhaust catalysts and evaporative emission control systems on
small spark-ignited (SI) engines (<19kW). Since catalysts are exothermic (a process that
produces heat) in operation, the addition of catalysts to future products required that potential
incremental safety impacts be evaluated and understood.
A team of representatives from SwRI, EPA, and Consumer Product Safety Commission
(CPSC) contributed to the completion of this work assignment. The EPA set the direction for the
study and provided data and technical information on the Phase 2 and Phase 3 products under
review. The CPSC provided product safety information from multiple databases which was
helpful in identifying potential failure modes for the study. SwRI contributed the experienced
engine experts, the FMEA process experience and conducted the independent FMEA analysis.
A Design Failure Mode and Effects Analysis (FMEA) format was selected to evaluate the
incremental safety impact between existing Phase 2 products (current production models) and the
expected Phase 3 products. The scope of the assignment included Class I and Class II engine
systems, which relate to walk-behind and riding lawn mowers, respectively. These equipment
types represent the majority of sales for small SI engines and this is also the area where EPA has
received comment from various stakeholders in pre-proposal discussions. A Process FMEA
format was chosen to evaluate common human interactions with the mower equipment. Three
Process FMEAs were conducted to evaluate the safety impact associated with equipment
refueling, storage, and maintenance. These FMEA results were then used to assess if the
addition of a catalyst or fuel evaporative emission control would pose any incremental safety
impact associated with these processes.
The SAE J1739 FMEA procedure was the basis for the format for the FMEA. This
document states that "An FMEA can be described as a systematic group of activities intended to:
(a) recognize and evaluate the potential failure of a product/process and the effects of that failure,
(b) identify actions that could eliminate or reduce the chance of the potential failure occurring,
and (c) document the process. It is complementary to the process of defining what a design or
process must do to satisfy the customer".
The FMEA process identifies Potential Failure Modes and Potential Effect(s) of Failure.
Each Potential Effect(s) of Failure is classified with regards to Safety, Regulatory, Performance,
or Other. The main focus of this analysis was to draw attention to the Safety related items. The
Risk Priority Number (RPN) was calculated for Phase 2 and prototype Phase 3 engines for each
line item in the FMEA. The delta RPN was calculated by subtracting RPN (Phase 2) from RPN
(Phase 3): Delta RPN = Ph3 RPN - Ph2 RPN.
Three cases were observed in the analysis:
i
-------
a. Delta RPN = 0: Many Safety line items show no significant changes in Risk
Priority Number (RPN) between current Phase 2 prototype Phase 3 engines.
b. Delta RPN > 0: A number of Safety line items show that RPN is reduced in the
prototype Phase 3 engines due to improved design and better reliability.
c. Delta RPN < 0: One Safety line item in each Class (I & II) shows that the RPN is
higher for the Phase 3 engine.
The Phase 3 engine definition within this report (Table 3) is the basis for the Phase 3
engine system analyzed in this analysis. It is based on a number of engine prototypes, catalyst
prototypes, thermal data, field, dyno and emission testing by EPA. The main features of this
engine over the majority of existing Phase 2 engines include:
a. Application of catalyst (moderate activity 30-50%) designed to minimize CO
oxidation, maximize NOx reduction, with low HC oxidation efficiency at high
exhaust-flow-rates and high HC oxidation efficiency at low-exhaust flowrates.
This design is expected to minimize catalyst exotherm.
b. Cooling and shrouding of engine and muffler to minimize surface temperatures.
Use of heat shielding and/or air-gap insulated exhaust components to minimize
surface temperatures.
c. Improved component design and manufacturing processes to reduce Air-Fuel
ratio production variability to stabilize engine performance and emissions.
d. Evaporative emission controls: hoses, tank, cap, and running loss system.
The prototype Phase 3 engine evaluated by the FMEA team had less potential to cause
fires and operator burns than some equipment now in production. EPA's thermal data on Phase
2 and Phase 3 product showed muffler heat shield temperatures were equivalent or cooler.
EPA is considering evaporative requirements, some of which will also reduce the
occurrence of fuel leaks, and subsequently fire and burn risks. Leaks will be reduced during
tipping of equipment with the following controls to reduce running loss emissions: 1) use of fuel
caps with no venting or with venting through a tortuous path (to control diffusion-related venting
emissions), and 2) a restriction, a limited flow orifice or a valve, placed in the vent line to the
engine to keep the engine manifold vacuum from drawing too much vapor from the fuel tank
(route the vapor to the engine intake to be burned by the engine). Other possibilities to reduce
fuel leakage include moving the fuel tanks away from heat sources and using a tethered cap.
Leaks from the tanks and lines will be lessened due to the material improvements likely to be
made to reduce permeation from these components.
11
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Three processes were identified for FMEA analysis: refueling, equipment storage, and
maintenance. The FMEAs were done to identify if there could be any potential for increased
concern of Phase 3 engine systems with catalyst mufflers compared to the current Phase 2
product. Due to the fact that these processes are done with the engine off, the processes were
analyzed with respect to worst case outcomes after shut-off It was concluded that there were no
additional areas of concern with Phase 3 prototypes versus Phase 2 engine designs. This was
based on redesign associated with meeting Phase 3 fuel evaporative emission control
requirements and EPA's thermal data that showed the muffler's hot soak temperatures were
comparable, or potentially reduced, with properly designed Phase 3 catalyst systems. In case of
fuel spills due to tipping of equipment, there is the potential for lower occurrence ranking due to
fuel system modifications and upgrades associated with meeting the fuel evaporative emission
control requirements EPA is considering. Reductions in vapor emissions during storage would
occur as a result of using less permeable tanks and lines.
in
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TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1
2.0 I'Mi:A BACKGROUND / DESCRIPTION 3
3.0 THE SWRI APPROACH FOR THE SMALL ENGINE FMEA PROJECT 4
A. FMEA Team Make-up 4
B. Cases to be studied 5
C. Definitions and Constraints for this study 10
D. Sources of Data and Information 13
E. FMEA Process and Documentation Structure 15
4.0 DISCUSSION OF RESULTS 20
5.0 CONCLUSIONS 45
ATTACHMENTS:
Attachment 1 EPA Statement of Work
Attachment 2 Reference Photographs of Phase 2 and Prototype Phase 3 Hardware at EPA
Attachment 3 Notes on Class II Soak Data from EPA
Attachment 4 List of Standards Reviewed for the FMEA Study
Attachment 5 Example: A Typical FMEA Report Format
Attachment 6 Example: The Modified FMEA Report Format used in W. A. 1-10
Attachment 7 Representation of the Catalyst Control Volume
Attachment 8 Class I Design FMEA Report
Attachment 9 Class II Design FMEA Report
Attachment 10 Process FMEA Report - Refueling Process for Class I and Class II, Phase 2 and
Phase 3 Equipment
Attachment 11 Process FMEA Report - Shutdown and Equipment Storage Process for Class I
and Class II, Phase 2 and Phase 3 Equipment
Attachment 12 Process FMEA Report - Equipment and Engine Maintenance for Class I and
Class II, Phase 2 and Phase 3 Equipment
Attachment 13 Ignition Property Data of Various Materials and Human Skin Damage at
Elevated Temperature/Radiant Heat Exposure Data
iv
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LIST OF FIGURES
Page
Figure A2-1. Stock Briggs Quantum Side Valve Complete Engine 1
Figure A2-2. Stock Briggs Quantum European Catalytic Muffler 1
Figure A2-3. Stock Briggs Quantum SV Close up of Front of European Catalytic Muffler 2
Figure A2-4. Stock Briggs Quantum SV Close up of Back of European Catalytic Muffler 2
Figure A2-5. Stock Briggs Quantum SV European Catalytic Muffler Shroud 3
Figure A2-6. Stock Briggs Quantum SV European Catalytic Muffler Interior 3
Figure A2-7. Stock Briggs Quantum SV Center European Catalytic Muffler Interior with
Substrate Removed 4
Figure A2-8. Stock Briggs Quantum SV European Catalytic Muffler Supplemental Air Venturi 4
Figure A2-9. Stock Honda GVC 160 without Muffler 5
Figure A2-10. Stock Honda GVC 160 Muffler with Shroud 5
Figure A2-11. EPA Prototype Catalyzed Muffler in Shroud for Honda GVC 160 6
Figure A2-12. EPA Prototype Muffler with Exhaust Gas Cooling Air Ejector Around Exhaust
for Honda GVC 160 6
Figure A2-13. EPA Prototype Muffler Air Ejection Tube for Honda GVC 160 7
Figure A2-14. EPA Prototype Muffler Ceramic Substrate for Honda GVC 160 7
Figure A2-15. Tube Catalyst for Insertion in Exhaust Port 8
Figure A2-16. Prototype Low Cell Density Metal Substrate Catalyst 8
Figure A2-17. Wire Mesh Catalyst in Muffler 9
Figure A2-18. Wire Mesh Catalyst Removed from Muffler 9
Figure A2-19. Stock Honda GVC 160 Mower 10
Figure A2-20. Briggs 6.Quantum with Briggs European Catalyzed Muffler 10
Figure A2-21. Briggs Intek Engine with Dual Substrate European Muffler and Cooling Air Duct
11
Figure A2-22. Stock Briggs Intek Engine with Stock Muffler 11
Figure A2-23. Stock Tecumseh LV195BA 12
Figure A2-24. Briggs Dual Metallic Substrate European Muffler on Tecumseh LV195BA 12
Figure A2-25. Stock Kawaski FH 60ID Intake Air 13
Figure A2-26. Stock Kawasaki FH 60ID Muffler 13
Figure A2-27. Kawasaki FH 601D Muffler with Air Injection & Catalyst 14
Figure A2-28. Triple Pass Catalyst with Double Wall 14
Figure A2-29. Stock Muffler with Inserted Catalyst 15
Figure A2-30. Stock Muffler with Inserted Catalyst 15
Figure A2-31. High Efficiency Dual Catalyst Ahead of Muffler 16
Figure A2-32. Briggs Intek 31P777 Showing No Head Cooling Fins 16
Figure A2-33. Kohler CH26 With Stock Muffler without Catalyst, With EFI With Ego Sensor
Feedback 17
Figure A2-34. Kohler Catalyzed Muffler for CH26 EFI Engine with Feedback Ego Sensor 17
Figure A2-35. Prototype Briggs 31P777 Intek with Oil Cooler 18
Figure A2-36. Prototype Briggs 31P777 Intek With Air Ducted To Catalyst Muffler 18
Figure A2-37. Prototype Briggs 31P777 Intek Close-Up of ECU & Fuel Injector 19
Figure A2-38. Stock Briggs 31P777 Intek on Riding Mower 19
Figure A2-39. Stock Kohler CV490 Riding Mower 20
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Figure A2-40. Kohler CV490 Riding Mower with Catalyzed Muffler & Modified Shroud
Cooling & EFI 20
Figure A3-1. Time (Minutes after Shutdown) 2
Figure A3-2. Time (Minutes after Shutdown) 3
Figure A3-3. Time (Minutes after Shutdown) 3
Figure A13-1. Temperature-Time Relationship for Burns [2] 7
LIST OF TABLES
Page
Table 1. EPA Phase 3 Concept Emission Standards 5
Table 2. Summary of Attachment 2 Photographs 6
Table 3. Projected Phase 3 Engine Characteristics for the FMEA 12
Table 4. Severity Ranking Definitions 18
Table 5. Occurrence Ranking Definitions 18
Table 6. FMEA Systems Evaluated 20
Table 7. Class I Safety FMEA Items 24
Table 8. Class II Safety FMEA Items 29
Table 9. Refueling Process FMEA 35
Table 10. Shutdown and Storage Process FMEA 39
Table 11. Maintenance Process FMEA 43
Table A3 - 1. Muffler Temperature Field Soak Data vs. Time 1
Table A13-1. Ignition Temperatures of Various Materials [3] 2
Table A13-2. Typical Values of the Minimum Auto-Ignition Temperature for Flammable Gases
and Vapors [4] 3
Table A13-3. Piloted Ignition Temperatures of Various Woods [1] 3
Table A13-4. Tube Furnace Tests for the Auto-Ignition Temperature of Cellulose Filter Paper [5]
4
Table A13-5. Auto-Ignition of Filter Paper from Hot-Air Blower 4
Table A13-6. Hotplate Ignition Temperature of Some Fabrics [5] 5
Table A13-7. Auto-Ignition of Cotton Fabric From a Hot-Air Blower 5
Table A13-8. Hot Surface Ignition Temperatures for Carpets [5] 5
Table A13-9. Flammability Limits, Quenching Distances, and Minimum Ignition Energies For
Various Fuels [3'5] 6
Table A13-10. Effects of Thermal Radiation 6
vi
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LIST OF ACRONYMS / ABBREVIATIONS
ASTM
American Society for Testing and Materials
ANSI
American National Standards Institute
ASAE
American Society of Agricultural Engineers
C
Centigrade
CEC
Coordinating European Council
CFR
Code of Federal Regulations
CO
Carbon Monoxide
CPSC
Consumer Product Safety Commission
ECM
Engine Control Module
EEC
European Economic Community
EGO
Exhaust-Gas-Oxygen
EFI
Electronic Fuel Injection
EPA
U.S. Environmental Protection Agency
F
Fahrenheit
FMEA
Failure Mode and Effects Analyses
HC
Hydrocarbon
ISO
International Standards Organization
INDP
In-Depth Investigations
IPII
Injury/Potential Injury Incident File
kg
Kilogram
MAP
Manifold Absolute Pressure)
NEISS
National Electronic Injury Surveillance System
NFIRS
National Fire Incident Reporting System
NFPA
National Fire Protection Association
NOx
Nitrous Oxide
NMMA
National Marine Manufacturers Association)
NVFEL
National Vehicle and Fuel Emissions Laboratory
02
Oxygen
OEM
Original Equipment Manufacturer
OHV
Overhead Valve
RPN
Risk Priority Number
SAE
Society of Automotive Engineers
SI
Spark Ignited
SwRI®
Southwest Research Institute®
sv
Side Valve
TBoil
Boiling Temperature
Tig
Ignition Temperature
tic,
Ignition Time
USD A
United States Department of Agriculture
O
Degree
^max
Equivalence Ratio
vii
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1.0 INTRODUCTION
The U.S. Environmental Protection Agency (EPA) issued Work Assignment 1-10,
"Design/Conduct FMEAs for Small SI Equipment and Engines" to Southwest Research
Institute® (SwRI®) to analyze the potential safety impact of new emission standards, which are
expected to result in the use of exhaust catalysts and evaporative emissions control systems on
small spark-ignited (SI) engines (<19kW). Please see Attachment 1 for the work assignment
details. The overall product population in this market is dominated by walk-behind mowers
(Class I) and ride-on (Class II) lawn and garden equipment. Based on the Consumer Product
Safety Commission's National Electronic Injury Surveillance System (NEISS) database from
2000 through 2004 there were significantly more thermal burns associated with lawn mowers
than for generators and power washers. The CPSC recall database for the same period also
included many more recalls for fire and burn associated with lawn and garden equipment than
any other product. Consequently, the walk-behind and ride-on mower engines represented the
primary focus of this study.
The objective of this work assignment was to design and perform Failure Mode and
Effects Analyses (FMEA) on Class I and Class II engine systems. The FMEA technique is an
industry-accepted tool that is used to assess product risk associated with potential failure modes.
This FMEA study was focused on identifying and assessing the potential incremental safety
impact between the current engine products that meet the Phase 2 emission standards, and future
engine designs for expected Phase 3 emission standards. It is expected that a number of
improvements in engine design including air-fuel ratio control and a catalyst will be utilized to
meet Phase 3 emissions standards. SwRI has conducted a Design FMEA with the existing Phase
2 product (current production models) compared to the expected Phase 3 product. The analyzed
configurations of Phase 3 products were based on Phase 2 engine models that have been
modified by the EPA to meet the new emissions requirements. The modifications are listed in
Table 3.
The SwRI FMEA team represents 100 years of experience in engine design, development
and testing. The expertise used in the assessment of the Phase 2 and Phase 3 products included:
engineering judgment, engineering expertise, engine test experience with this class of product,
previous experience applying catalysts to this type of product, review of Phase 3 engine
prototypes and data from the EPA, review of data from the CPSC, and personal knowledge of the
product from a consumer perspective.
The Work Assignment included four main tasks:
Task 1:
SwRI was to select a team of experts and define the approach to be taken to conduct the
FMEA assessments. The team was selected and the approach was to use the Design and Process
FMEA methods as a guide for the subsequent analysis.
Task 2:
SwRI presented an overall plan that described how the FMEA would be conducted. SwRI
reviewed the catalyst concepts and data for the tests conducted by the EPA that evaluated
1
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catalyst-equipped prototype engines and equipment. EPA provided engineering expertise that
assisted in this analysis process. The CPSC provided product safety information from multiple
databases which was helpful during the Failure Mode and Effects Analysis (FMEA) study. Brief
descriptions of these databases are indicated below:
• CPSC's National Electronic Injury Surveillance System (NEISS) is comprised of a
sample of hospitals that are statistically representative of hospital emergency rooms
nationwide. From the data collected, estimates can be made of the numbers of injuries
associated with consumer products and treated in hospital emergency departments.
• CPSC's In-Depth Investigations (INDP) file contains summaries of reports of
investigations into events surrounding product-related injuries or incidents. Based on
victim/witness interviews, the reports provide details about incident sequence, human
behavior, and product involvement.
• CPSC's Injury/Potential Injury Incident File (IPII) contains summaries, indexed by
consumer product, of Hotline reports, product-related newspaper accounts, reports
from medical examiners, and letters to CPSC.
• The National Fire Incident Reporting System (NFIRS) is a database of fires attended
by the fire service. NFIRS provides data at the product level and is not a probability
sample. The information from the NFIRS database is weighted up to the National Fire
Protection Association (NFPA) survey to provide national annual product-level
estimates.
• In addition the SwRI team had access to the recall summaries posted at CPSC's
public website.
Task 3:
SwRI conducted an FMEA considering multiple engines and pieces of equipment. The
FMEA was performed for the Phase 2 and prototype Phase 3 small-spark ignited (SI) engines
and related equipment. This was performed for both Class I and Class II engines. The analysis
was based on the SwRI FMEA team's knowledge of Phase 2 products and the Phase 3 hardware
configurations provided by EPA. Three Process FMEAs were also performed, to assess the
potential increase in safety impact associated with the use of the lawncare equipment. The
FMEA team included staff from EPA and CPSC, as well as SwRI.
Task 4:
The final report is presented as the primary task requirement that was generated from the
FMEAs. Future presentations by SwRI in support of this project will be provided as requested
by EPA.
2
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2.0
FMEA BACKGROUND / DESCRIPTION
The Failure Mode and Effects Analysis (FMEA) is one of many quality improvement
techniques that have been developed and successfully applied in industry over the last 40 years.
The FMEA process focuses on potential failures and the resulting effects, and is recommended
by a number of U.S. and International Standards organizations. The FMEA is a tool that
systematically evaluates potential product hazards, effects, and the likelihood of those potential
hazards occurring. It also provides a systematic means for estimating risk. The FMEA guide
used throughout this study was the SAE standard, J1739. This analysis was conducted using the
Design FMEA and Process FMEA formats.
The methodology of a Design FMEA has four primary aspects: (1) use of a systematic
approach and sound engineering judgment to anticipate how and how often a particular design
could fail to perform its intended function, (2) identification of the likely consequences of the
failures, (3) to clearly identify the critical failure modes, and (4) to identify the actions necessary
(typically controlled by the manufacturer) to eliminate or reduce the risk associated with the
potential failure modes.
The Process FMEA technique is similar to that described for the Design FMEA except
that the Process FMEA addresses how and how often processes can fail to result in the intended
outcome, rather than how and how often components can fail to perform the intended function.
A FMEA is conducted by a team of people (typically 4 to 6 members), and is not
effective if the FMEA is completed by a single person. The selection of the members of the
team is important. The team should consist of cross-functional members, if possible, to promote
a variety of perspectives. The most effective FMEA teams are comprised of members who have
technical knowledge of the subject, and who are willing to participate in open discussions and be
willing to accept team consensus to reach the best assessment. The team leader is typically a
process leader and facilitator of the FMEA. Typically, the FMEA process is used to identify a
wide range of product problems including performance, safety, durability, and other user
satisfaction issues. This study focused on the incremental safety impact associated with the
application of catalysts to small SI engines and equipment.
As with any tool, there are limitations to the FMEA process. The FMEA process is very
detailed, to the point of being tedious and time consuming when complex systems are being
analyzed. The FMEA technique deals primarily with single point failures, and usually does not
address the effect of combinations of failures. It is important to capture all of the practical
failure modes, while avoiding highly improbable failure modes that are of minimal consequence.
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3.0
THE SWRI APPROACH FOR THE SMALL ENGINE FMEA PROJECT
A. FMEA Team Make-up
The team selection is critical for an FMEA process. The SwRI team was selected
considering the knowledge and expertise required for conducting the subject FMEA. Team
members are engineers and have the technical skills required for the task. In addition, the team
members have skills beyond the requisite technical skills which allow a broader view of the
problem.
The SwRI FMEA team consisted of four core team members and one reviewer. All are
experienced SwRI staff members. Brief resumes are included below:
Jeff White (Core Team): Mr. White has been contributing to the development of cleaner
engines and vehicles for over 25 years. Mr. White has performed emission research programs
for a wide range of applications including light-duty vehicles, heavy-duty truck and bus engines,
and many types of small and nonroad engines. Jeff and his colleagues have performed numerous
studies on small engines, focusing principally on development of strategies and technologies to
reduce emissions. Work has addressed both 2-stroke and 4-stroke designs, as well as diesel and
alternative-fueled engines.
Tom Boberg (Core Team): Mr. Boberg is the FMEA team leader, facilitator and an experienced
FMEA process user. He has 27 years experience with the design, development and production
release of engines. He currently is Manager of the Gas and Large Engine Section at SwRI. Tom
has previously participated in several dozen of Design and Process FMEA analyses over the last
13 years as a participant, leader and facilitator.
Jim Carroll (Core Team): Mr. Carroll has 25 years experience in off-highway engines and
emissions testing. He has managed projects for engine certification, emissions development,
catalyst development, component durability, emissions reduction and test cycle procedure
development. He has worked with off-road engines for 15 years and has participated in baseline
studies for regulatory agencies, and emission reduction strategy development and engine
certification.
Kevin Castile (Core Team): Mr. Castile has over 23 years of experience in the engine lubricants
industry. He is currently the Project Manager of the Leisure Marine and Small Engine
Lubricants Section. Over the last seven years he has authored, co-authored, and updated industry
standard lubricant specifications for ASTM (American Society for Testing and Materials), CEC
(Coordinating European Council), ISO (International Standards Organization), and NMMA
(National Marine Manufacturers Association).
Barry Badders (Reviewer): Mr. Badders has a Bachelors Degree in Mechanical Engineering
with an emphasis on thermal systems, heat transfer and fluid dynamics. Mr. Badders will be
obtaining his Masters Degree in Fire Protection Engineering from the University of Maryland in
May 2006. After obtaining his undergraduate degree, he worked as a consultant for 4.5 years,
during which time he received his Professional Engineer's License in the state of Texas and
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Florida. Mr. Badders works in the Southwest Research Institute's Department of Fire
Technology as a group leader responsible for the Engineering and Research Section. His job
functions include fire modeling using computational fluid dynamics and finite element methods.
He also conducts research and customized testing to study the effects of fire and related
phenomena.
B. Cases to be studied
The purpose of this Work Assignment was to identify and assess incremental safety
impact between the current, Phase 2 versions of a number of small SI equipment/engines, and the
same equipment and engines that have been modified to meet Phase 3 concept emission
standards. As part of their technology assessment work, EPA modified a number of OEM Phase
2 engine and equipment configurations in such a manner that they met the exhaust emission
standards being considered by EPA staff. The emission standards that are under consideration by
EPA are shown in Table 1, below.
Table 1. EPA Phase 3 Concept Emission Standards
Exhaust Emissions
HC+NOx*
g/kW-hr
CO
g/kW-hr
Year
Useful Life
(hours)
Class I
10.0
610
2010
125/250/500
Class II
8.0
610
2011
250/500/1000
Classes 3-5
No Changes
*HC+NOx standard is based on averaging; new standards would not apply to snow equipment.
Evaporative Cont
rols
Class I
Class II
Classes 3-5
Standard
Hose and Tank
Permeation
2009
2009
2009
15 g/mA2& 1.5
g/mA2
Running Loss
2010
2011
n/a
Design/Test
Following the initial meeting with the EPA, the scope of the FMEA was refined to
include conducting two Design FMEAs and three Process FMEAs. The Design FMEAs focused
on potential subsystem/component failures of Class I and Class II lawn mower products. The
Process FMEAs relate to user activities of equipment refueling, equipment storage, and engine
maintenance. These activities were supported by the detailed review of Class I and Class II,
Phase 2, and prototype Phase 3 engines and equipment available at the EPA in Ann Arbor,
Michigan on October 3rd and 4th 2005. The equipment that was reviewed is listed in Table 2.
Table 2 is a summary of Attachment 2 which presents photographs of production, Phase 2, lawn
and garden equipment and prototype Phase 3 engines and modified equipment. Figures A2-1
through A2-24 shows Class I engines, catalysts, mufflers, and equipment; Figures A2-25 through
A2-41 show Class II engines, catalysts, mufflers, and equipment. These images document the
design changes implemented by the EPA in the course of their Phase 3 design impact analysis.
5
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Table 2. Summary of Attachment 2 Photographs
Figure
No.
Figure - Title
Notes
A2-1
Stock Briggs Quantum Side Valve Complete
Engine
Purchased locally by EPA
A2-2
Stock Briggs Quantum European Catalytic
Muffler
Three stamped steel parts, plus mat-wrapped
ceramic catalyst (400cpsi, 20 cc)
A2-3
Stock Briggs Quantum SV Close-Up Of
Front Of European Catalytic Muffler
Muffler is direct replacement for non-
catalyzed muffler, available from Briggs
distributors. Note Briggs logo on right.
A2-4
Stock Briggs Quantum SV Close-Up Of
Back Of European Catalytic Muffler
Supplemental air inlets are visible.
A2-5
Stock Briggs Quantum SV European
Catalytic Muffler Shroud
Outlet side of muffler.
A2-6
Stock Briggs Quantum SV European
Catalytic Muffler Interior
Center stamping and catalyst.
A2-7
Stock Briggs Quantum SV Center European
Catalytic Muffler Interior With Substrate
Removed
Center stamping with catalyst removed
showing catalyst and wrap
A2-8
Stock Briggs Quantum SV European
Catalytic Muffler Supplemental Air Venturi
Venturi is formed at supplemental air inlet.
Muffler located at exhaust port connection
helps homogenize exhaust gas mixture.
A2-9
Stock Honda GVC 160 Without Muffler
Cooling air flow directed toward muffler by
upper block casting.
A2-10
Stock Honda GVC 160 Muffler With Shroud
Muffler with air cooling shroud and touch
guard.
A2-11
EPA Prototype Catalyzed Muffler In Shroud
For Honda GVC 160
Prototype catalyzed muffler and shroud. Air
injection by internal venturi with air in
through external pipe.
A2-12
EPA Prototype Muffler With Exhaust Gas
Cooling Air Ejector Around Exhaust For
Honda GVC 160
Ejector tube around exhaust outlet draws
cooling air across outlet though exhaust flow
dynamics.
A2-13
EPA Prototype Muffler Air Ejection Tube
For Honda GVC 160
Cooling air ejector tube.
A2-14
EPA Prototype Muffler Ceramic Substrate
For Honda GVC 160
Ceramic substrate encased in steel mounting
support.
A2-15
Tube Catalyst For Insertion In Exhaust Port
First low surface area controls catalyst
activity, reduces plugging, and reduces cost.
A2-16
Prototype Low Cell Density Metal Substrate
Catalyst
Low cell density controls exothermic
reactions.
A2-17
Wire Mesh Catalyst In Muffler
Metal mesh substrate controls catalytic
activity, and reduces plugging.
A2-18
Wire Mesh Catalyst Removed From Muffler
Substrate removed showing support structure
in muffler.
A2-19
Stock Honda GVC 160 Mower
Purchased locally by EPA.
A2-20
Briggs QUANTUM SV With Briggs
European Catalyzed Muffler
Briggs engine with muffler from Fig. 2 plus
touch shield. Additional catalyst, spark
arrestor, and exhaust flow diffuser added to
muffler
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A2-21
Briggs Intek OHV Engine With Dual
Substrate European Muffler And Cooling Air
Duct
EPA prototype catalyzed muffler. Additional
catalyst added to muffler. Shroud at top of
muffler to divert cooling air behind muffler.
A2-22
Stock Briggs Intek OHV Engine With Stock
Muffler
Purchased locally by EPA.
A2-23
Stock Tecumseh LV195EA
Purchased locally by EPA.
A2-24
Briggs Dual Metallic Substrate European
Muffler On Tecumseh LV195EA
Catalyzed muffler purchased from Briggs in
Europe.
A2-25
Stock Kawasaki FH 60ID
Purchased locally by EPA
A2-26
Stock Kawasaki FH 60ID Muffler
Stock muffler for comparison to Fig. 27.
A2-27
Kawasaki FH 60ID With Air Injection &
Catalyst
EPA prototype catalyzed muffler. Air
injection tube at top center. Secondary air is
injected between two Palladium Rhodium
converters.
A2-28
Triple Pass Catalyst With Double Wall
fabricated by EPA.
Double wall reduces surface temperature and
fire and burn risk.
A2-29
Stock Muffler for Kohler CV490 With
Inserted Catalyst
Stock Class II muffler modified with catalyst
and then re-assembled.
A2-30
Stock Muffler for Kohler CV490 With
Inserted Catalyst
Stock Class II muffler modified with catalyst
and then re-assembled.
A2-31
High Efficiency Dual Catalyst Ahead Of
Muffler fabricated by EPA.
Class II muffler modified by attaching dual
catalyst ahead of muffler.
A2-32
Briggs Intek OHV 31P777 Showing No Head
Cooling Fins
Head cooling achieved through conduction
from cylinder, plus air convection. Note tight
shrouding around cylinder to duct cooling air.
A2-33
Kohler CH26 With Stock Muffler Without
Catalyst, With EFI With EGO Sensor
Feedback
EGO (Exhaust Gas Oxygen) Closed-loop
air/fuel ratio control system added to engine.
A2-34
Kohler Catalyzed Muffler For CH26 EFI
Engine With Feedback EGO Sensor
Catalyzed muffler for Kohler in Fig. 33 with
oxygen sensor.
A2-35
Prototype Briggs 31P777 Intek with Oil
Cooler
Stock engine had 140C oil temperature.(no
cooling fins on head). Oil cooler (thermostat
opens @110 °C) added to reduce high
temperature in order to age 250 hour motor to
500 hours.
A2-36
Prototype Briggs 31P777 Intek With Air
Ducted To Catalyst Muffler with open loop
EFI
Additional shrouding ducts the cooling air
from the engine past exhaust system, and
reduces debris collection.
A2-37
Prototype Briggs 31P777 Intek Close-Up Of
ECU & Fuel Injector
ECU and fuel injector from Asian motorcycle.
The Intake manifold modified by EPA to
accept injector.
A2-38
Stock Briggs 31P777 Intek on Riding Mower
Purchased locally by EPA.
A2-39
Stock Kohler CV490 Riding Mower
Purchased locally by EPA.
A2-40
Kohler CV490 Riding Mower With
Catalyzed Muffler & Modified Shroud
Cooling & EFI
Additional shrouding ducts cooling air from
engine past the exhaust system, to reduce
debris collection.
Prototype Phase 3 engines were developed by EPA to demonstrate that small SI engines
can meet tighter emission standards at reasonable cost without an incremental increase in safety
7
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risk. To that end, four Class I engines were chosen which represent 75 percent of the market's
sales, and two Class II engines were chosen which represent 25 percent of the market. The Class
II engine market is not dominated by a few sales leaders as is the case with Class I engines. EPA
chose a variety of engines that included side-valve (SV) and overhead-valve (OHV) designs,
low- and high-cost engines, and both residential-use and commercial-use engines.
During the course of EPA's technology assessment, it investigated a range of engine
control and aftertreatment technologies to reduce emissions. These included the application of
alternative catalytic converter substrates such as ceramic (Figures A2-7 and A2-14), wire mesh
(Figures A2-17), metal tube (Figure A2-15), and metal foil (Figure A2-16). The substrates were
coated with a range of washcoat materials and noble metal loadings to control emission reduction
efficiency and exhaust system temperature.
One of the catalytic converters tested was a production design from the European market
(Figure A2-3). The rest of the test catalytic converters were fabricated and installed by EPA after
modifying a production muffler (Figures A2-13 for Class I and A2-29 for Class II) or by placing
the catalyst ahead of the production muffler (Figure A2-31).
EPA's criteria for choosing catalyst formulations included:
minimize heat rejection
provide appropriate level of emission control and durability
minimize cost
Catalytic converters are exothermic (gives off heat). The addition of a catalyst increases
the total mass of the exhaust system and will retain heat. With this being considered, the EPA
objective for Phase 3 engines was that prototype exhaust system designs was to control surface
temperatures to the current Phase 2 engine temperature levels. Infrared imaging equipment was
used to measure both production and prototype engine surface temperatures during operation in
the laboratory, in the field, and after the engines were turned off.
Thermal images and temperature levels measured by the imaging equipment were
supplied to the FMEA team by EPA. These data showed that several prototype Phase 3 systems
exhibited much lower peak surface temperatures during operation and hot soak than current
Phase 2 systems. Peak temperatures are important because they represent the point of greatest
risk for fire and burn.
Noble metals used by catalyst manufacturers to promote emission reduction include
platinum (Pt), palladium (Pd), and rhodium (Rh). The catalyst reduction efficiencies are a
function of a number of variables including: catalyst formulation, exhaust gas composition, the
exhaust gas temperature, and the exhaust gas flow rate. The catalyst operating temperature is
dictated by the reduction efficiency. Carbon monoxide is oxidized within the converter to
carbon dioxide in the presence of oxygen. Since these engines have higher concentrations of CO
than HC or NOx, the CO conversion is the primary source of exotherm in the exhaust system.
The EPA's study found that a loading ratio of Pt:Pd:Rh of 1:3:1 had an advantage in reducing the
peak temperature due to CO conversion. About one-half of the final prototype exhaust systems
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used catalysts with a 1:3:1 ratio and the other half of the converters used catalysts with a 3:1:1
ratio.
Small air-cooled engines such as these tend to run with combustion mixtures or air/fuel
ratios which are fuel rich. This means that there is more fuel than required for the volume of
combustion air drawn into the engine. The excess fuel keeps combustion temperatures low
because it acts as a heat sink much like a mist. In the engine, most of the oxygen is consumed
through combustion. Without sufficient oxygen in the exhaust, a catalyst cannot completely
oxidize hydrocarbons or carbon monoxide. Although reducing the amount of fuel (enleanment)
introduced into the engine would free more oxygen, the higher operating temperatures resulting
from leaner operation could adversely affect engine durability. Therefore, EPA investigated the
use of both passive and active supplemental air systems, which added air to the exhaust before
the catalyst. Passive supplemental air systems rely on an integral venturi in the exhaust pipe to
drawn in ambient air (Figure A2-4 and A2-8 show ambient air inlets and venturi location).
Active systems use a pump to force air into the exhaust system (Figures A2-11 and A2-27 show
a supplemental air tube into the muffler). However, as the Table 3 definition of Class II engines
shows, supplemental air is not required for Class II catalyst systems.
Supplementing efforts to reduce surface temperatures, EPA also investigated designs to
reduce the likelihood of debris, such as grass cuttings, accumulating on or near the prototype
exhaust systems. Cooling system air was ducted to flow additional air around the exhaust
system, and larger ducting channels were included to reduce plugging of the cooling air flow
passages by debris.
EPA investigated exhaust system temperature control using various methods, as follows:
1) Some of the catalytic converters were placed within production mufflers close to the
muffler's inlet to produce a larger cooling volume after the converter.
2) Some of the mufflers had internal baffles added to redirect the exhaust flow along a
longer path before exiting the muffler.
3) The catalyst coatings were designed for lower reduction efficiencies that still met the
potential emission standards, but did not create an excessive exothermic reaction as
often occurs with high CO conversion efficiencies.
4) The catalyst surface area was controlled by using small catalysts (Figure A2-14) or
catalysts with low cell density (Figures A2-15, A2-16, and A2-17).
5) Simple shrouds were placed around the muffler similar to production systems (Figure
A2-10) or double walls were added around the muffler (Figure A2-28).
6) More elaborate cooling systems were also utilized which ducted engine cooling air
around the catalyzed muffler (Figures A2-21 and A2-24, note the non-shrouded
equipment in Figure A2-23), or shrouded and ducted cooling air around the whole
exhaust system (Figures A2-36 and A2-40, note the non-shrouded equipment in
Figure A2-39).
7) An exhaust flow diffuser was incorporated at the muffler outlet to direct hot exhaust
(Figures A2-20 and A2-21).
8) EPA mounted an ejector around the exhaust pipe at the muffler exit (Figure A2-12).
By placing an open-ended shroud around the exhaust pipe, the ejector utilizes the
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exhaust flow within the shroud to draw cooling air from the other end of the ejector.
The ejector thus rapidly cools the muffler's surface and its exhaust gases, and shrouds
the hot exhaust pipe exit.
EPA installed fuel injection systems on three Class II engines (Figures A2-33, A2-35,
and A2-40). The fuel injection systems replaced the carburetors on these engines with a throttle
body to control air flow, and a small injector and engine control module (ECM) from an Asian
moped. The ECM controls the fuel injector flow by measuring engine speed and the intake
manifold pressure, and then looking up the correct fuel flow from an internal data table. The
ECM system also has the capability to be operated in closed-loop control by sensing the exhaust
oxygen level with an exhaust-gas-oxygen (EGO) sensor in the exhaust pipe (Figure A2-34 at top
left). The EGO sensor signals the ECM when the air/fuel mixture is leaner or richer than
stoichiometry (exact air-fuel mixture for complete combustion) and the fuel injector flow is
adjusted by the ECM to add or subtract fuel accordingly. The use of fuel injection systems was
only investigated with larger Class II engines because of higher cost, and because the larger
engines have cooling systems which are more effective in controlling the increased combustion
temperatures due to enleanment. This analysis does consider carbureted engines, however,
prototypes were not available at the time of this report.
C. Definitions and Constraints for this study
The Phase 2, Class I and Class II engines and equipment in this study were defined to be
typical of current non-catalyst, production, consumer products. "Typical" in this case means the
product has average features and performance. The team used this definition throughout the
analysis.
It was useful for the team and the FMEA review process to clearly define the specific
characteristics of Class I and Class II product. This was accomplished by listing the major
differences between Class I and the Class II products. The differences between small spark
ignited, Class II engines (equal to or greater than 225 cubic centimeters displacement and less
than 19 kilowatts of rated power) and Class I engines (less than 225 cubic centimeters
displacement and less than 19 kilowatts of rated power) include:
1. The Class II engine is larger in physical size.
2. The Class II engine has higher power.
3. The Class II engine has a wider range of quality in design, materials, fuel lines, fuel
tanks, location of the fuel tank, engine, and mufflers.
4. The Class II engine intake manifolds are of higher quality and more robust.
5. The Class II engine exhaust system is more robust.
6. The Class II engine cylinder head temperatures are normally lower in general,
(exceptions: engines without cylinder head cooling fins)
7. The Class II engine cooling fins are larger and wider apart which reduces the
possibility of debris buildup.
8. The Class II engine heat rejection from exhaust is substantial, and may radiate to
ground.
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9. The Class II engine mufflers are remotely mounted from engine, and closer to the
ground than Class I designs.
10. The Class II engine mufflers are often supplied by the equipment (not engine)
manufacturer.
11. The Class II engine carburetors are typically of higher quality and have a wider
functional range (low idle to rated power).
12. The Class II engine carburetors have idle fuel circuits, and altitude compensation.
13. The Class II engines are typically equipped with fuel cutoff solenoid in float bowl.
14. The Class II engine can have automatic chokes on the carburetors. (Honda has
mechanical timer, some use exhaust heat and a bi-metallic choke control)
15. The Class II engine will typically be of an over head valve (OHV) design.
16. Some Class II engines are 2-cylinder designs. This means that the engines can
operate on one cylinder and be more prone to backfire.
17. The Class II equipment fuel tanks are often supplied by equipment (not engine)
manufacturer.
18. The Class II equipment is more prone to accidental rollover. (Note: this is expected
to be true, but intentional tipping of Class I equipment is very high for maintenance
activity).
19. The Class II equipment has more fuel capacity and more fuel is resident in the fuel
system components.
20. The Class II engines are used on a wider range of equipment.
21. For two-cylinder, Class II engines, a loss of ignition in one cylinder may overheat a
catalyst if the engine continues to operate.
22. Class II engine fuel injection systems with a closed-loop control may be employed.
(Westerbeke, and Kohler already sell fuel-injected, CL-control generators with
catalysts.)
23. Most Class II engines have electric starters and alternators.
24. The Class II engines are more durable and most are designed to be durable in
commercial operation.
25. Some Class II engines have high pressure lubrication systems.
26. The Class II equipment, typically locates the operator closer to the engine, (i.e.
Riding mowers, and turf equipment).
27. The Class II equipment fuel tank can be remotely mounted from engine.
In addition to the above Class I and Class II information, it was equally important to
define the characteristics of Phase 3 products. A list of characteristics was created in co-
operation with EPA to more clearly describe the Class I and Class II, Phase 3 products for this
study. It is acknowledged that some of the characteristics listed in Table 3 currently appear on
Phase 2 products, but it was projected that all Phase 3 engines will have these design,
manufacturing and quality improvements. This characterization process was necessary since
production Phase 3 engines and equipment are not yet available. The characteristics of Phase 3
products adopted for the purpose of conducting this study are shown in Table 3.
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Table 3. Projected Phase 3 Engine Characteristics for the FMEA
Item No.
Class I Lawnmower Engine
Class II Ride-on Mower Engine
1
Application of catalyst (moderate activity 30-
50%) designed to minimize CO oxidation,
maximize NOx reduction, with low HC
oxidation efficiency at high exhaust-flow-
rates and high HC oxidation efficiency at low-
exhaust flowrates. This design is expected to
minimize catalyst exotherm.
Application of catalyst (moderate activity 30-
50%) designed to minimize CO oxidation,
maximize NOx reduction, with low HC
oxidation efficiency at high exhaust flowrates
and high HC oxidation efficiency at low-
exhaust flowrates. This design is expected to
minimize catalyst exotherm.
2
Cooling and shrouding of engine and muffler
to minimize surface temperatures. Use of heat
shielding and/or air-gap insulated exhaust
components to minimize surface
temperatures.
Cooling and shrouding of engine and muffler
to minimize surface temperatures. Use of heat
shielding and/or air-gap insulated exhaust
components to minimize surface
temperatures.
3
Design flow paths/baffles through the
mufflers to incorporate flame arresting design
features, to improve heat rejection to muffler
surfaces and to spread heat rejection over a
large surface area of the muffler. This will
reduce the incidence of backfire and reduce
localized hot spots.
Design flow paths/baffles through the
mufflers to incorporate flame arresting design
features, to improve heat rejection to muffler
surfaces and to spread heat rejection over a
large surface area of the muffler. This will
reduce the incidence of backfire and reduce
localized hot spots.
4
Different catalyst substrates (ceramic, metal
monolith, hot tube, metal mesh) can be
successfully used.
Different catalyst substrates (ceramic, metal
monolith, hot tube, mesh) can be successfully
used.
5
The use of air ejectors to cool exhaust gases at
the muffler outlet and to improve cooling of
heat shielding.
The use of air ejectors to cool exhaust gases at
the muffler outlet and to improve cooling of
heat shielding.
6
Use of a small amount of passive
supplemental air to improve exhaust
chemistry at light load, but designed so bulk
exhaust remains rich of stoichiometry at all
conditions, and flow-limited at high exhaust
flowrates. This design minimizes risk of
excessive catalyst exotherm.
Use of carburetor recalibration to improve
exhaust chemistry at light load conditions.
7
Use of fuel filter and/or improved design
needle and seat in carburetor to minimize
problems caused by fuel debris.
Improved air/fuel ratio control through tighter
manufacturing tolerances to minimize
variation.
8
Improved intake manifold design to reduce
intake manifold leaks.
No anticipated design changes.
9
Cooling system designed to reduce the
accumulation of debris, including the use of a
mesh or screen on cooling fan inlet, when
lacking in current design.
Cooling system designed to reduce the
accumulation of debris.
10
Improved ignition system design to be more
reliable and durable than on Phase 2.
Improved ignition system design to be more
reliable and durable than on Phase 2.
11
Improved component design and
manufacturing processes to reduce air-fuel
ratio production variability to stabilize engine
performance and emissions.
Component changes are not expected.
Improved manufacturing processes to reduce
air-fuel ratio production variability to stabilize
engine performance and emissions.
12
Locate fuel tanks away from heat sources.
Locate fuel tanks away from heat sources.
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13
Use of carburetors with appropriate idle
circuits, float-bowl vent, and automatic choke
or improved primer bulb. This will improve
fuel system reliability.
Use of carburetors with appropriate idle
circuits, float-bowl vent, and automatic
choke. This will improve fuel system
reliability.
14
Locate the exhaust port away from the
carburetor/fuel line to minimize carburetor
heating.
No anticipated design changes.
15
Improved exhaust system design and
materials for better durability and reliability.
No anticipated design changes.
16
Improved muffler/catalyst/equipment design
since currently, the muffler designs do not
incorporate catalysts.
Improved muffler/catalyst/equipment design
since currently, the muffler designs do not
incorporate catalysts.
17
Evaporative emission controls: hoses, tank,
cap, and evaporative emission control system.
Evaporative emission controls: hoses, tank,
cap, and evaporative emission control system.
18
As Needed: non-contact, bi-metal thermal
switch to disable ignition system to shut
engine down in event of excessive
temperature.
As Needed: non-contact, bi-metal thermal
switch to disable ignition system to shut
engine down in event of excessive
temperature. Manufacturers will need to
consider the potential trade-off of disengaging
engine power on ride-on equipment if were to
occur on a slope.
I). Sources of Data and Information
The FMEA study used several sources of information, as outlined below:
SwRI FMEA Team Member Experience:
The team's personal and professional experience with the type of equipment being
analyzed was used to conduct the FMEA. This included the creation of the FMEA report
formats. SwRI's staff and titles can be found in Section 3-A.
Environmental Protection Agency (EPA) Staff Input
Technical discussions and review of the available OEM and prototype hardware with
EPA provided the detailed technical information and insight that was necessary for the review.
Thermal test data of OEM and prototype hardware provided a basis for decisions on thermal
issues. A sample and a brief discussion of the thermal image data provided by EPA are shown in
Attachment 3. EPA staff also acted as a consultation team to the FMEA tables and report.
The EPA NVFEL staff members assisting with the FMEA include: Glenn Passavant -
Non-Road Center Director; Joe McDonald - Mechanical Engineer, NVFEL; and Cheryl Caffrey
- Mechanical Engineer, NVFEL
Consumer Product Safety Commission (CPSC) Staff Input
CPSC staff provided real-world scenarios of operator burns and fires associated with
spark-ignition lawn mowers. Four databases were used to compile the data; the U.S. Consumer
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Product Safety Commission's National Electronic Injury Surveillance System (NEISS), Injury
and Potential Injury Incidents (IPII), In-Depth Investigations (INDP) and the U.S. Fire
Administrator's National Fire Incident Reporting System (NFIRS). Where possible, the data
spanned a five-year period, 2000 - 2004. CPSC staff also provided review and input to the
FMEA tables and report. The CPSC Directorate for Engineering Sciences staff assisting with the
FMEA include -Susan Bathalon, Mechanical Engineer, John Murphy, Mechanical Engineer, and
Sarah Brown, Engineering Psychologist in the Human Factors Division.
References:
SwRI performed a literature search to identify documents related to this study.
Attachment 4 lists the documents found in the literature search. These documents were reviewed
by the team to identify current safety specifications for small off road engines (<19 kW). The
information in these references was used by the team to:
1. Identify the maximum allowable operating temperatures in available standards and
guidelines:
• Consumer Turf Care Equipment:
o "A guard or shield shall be provided to prevent inadvertent contact with
any exposed components that are 'hot' and may cause burns during
normal starting and operation of the machine" from ANSI B71.1
o "All surface which exceed 65.5° C (150° F) at 21° C (70° F) ambient and
which might be contacted by the operator during normal starting,
mounting, operating or refueling shall be indicated by a safety sign located
on or adjacent to the surface." From ASAE S440.3
• Commercial Turf Care Equipment:
o "Lawn and garden equipment requires a shield if temperatures exceed 90
°C for non-metallic surfaces and 80° C for metallic surfaces" for ANSI
B71.4;
o "Hot surfaces (engine, hydraulic, transmissions, etc.) that exceed a
temperature of 90° C (194° F) for nonmetallic surfaces, or 80° C (176° F)
for metallic parts while operating at 21° C (70° F)" for ANSI B71.4;
• Multi-position Small Engine (handheld engine):
o "Temperatures shall not exceed 550° F for exposed surfaces and 475° F
for exhaust gases" per USDA Forest Service Standard 5100-1 as tested
under SAE J335 test procedure).
NOTE: This search did not locate a mandatory standard which defined temperature limits for
surfaces on consumer lawn and garden equipment. The standards listed above are voluntary
only. There are regulations/guidelines for spark arresters used in off highway vehicles (SAE
J350, SAE J342), handheld equipment engines (SAE J335) and other small engines.
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2. Identify the control volume used for the Design FMEA studies (see Attachment 7 for
this study's Control Volume).
3. Identify how previous equipment safety documents were related to this FMEA study;
surface temperatures, debris fires, and safe handling and operation. (See Attachment
4).
4. Identify the current safety concerns of regulatory and standard setting organizations
relative to sparks, surface temperatures, fire suppression, noise, operator safety and
test procedures.
The literature search information allowed the team to understand the different
perspectives that exist when considering product safety. Attachment 13 discusses: (1) auto
ignition; (2) what constitutes a fire; (3) what constitutes a burn (temperature, material and
exposure.
E. FMEA Process and Documentation Structure
The typical FMEA process is defined in detail in SAE standard 1739. In an effort to help
the reader understand the mechanics and structure of the FMEA process, a summary explanation
is provided below.
The FMEA process is not rigidly dictated. There is considerable leeway for the FMEA
team to deviate from the SAE standard in order to best suit the requirements of a specific review.
In the case of this Work Assignment FMEA, the team created a worksheet format structure, and
developed a ranking process that was appropriate for the study of Class I and Class II lawn
mower engines from a safety perspective.
In Attachment 5, a typical Design FMEA worksheet format is presented. This format is
similar to the Design FMEA worksheet format that is shown as an example in the SAE standard
1739. Attachment 6 presents the worksheet format that the FMEA team chose for this study.
When comparing the two examples, several differences can be seen, and these are explained
below:
Column Positions:
The column positions of the worksheet were modified considerably for this study. The
team felt that the resulting format was easier to follow.
Added Columns:
The worksheet (Attachment 6) included a Contributing Cause column to assist the team
in the evaluation process. In some cases, a secondary cause was identified, but in other cases a
primary cause was felt to be sufficient. The addition of the Contributing Cause information does
not alter the fact that the FMEA only addresses single point failures as previously discussed in
Section 2 above. Since the study was to evaluate the incremental differences between Phase 2
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and Phase 3 equipment, ranking columns were added for both phases. In effect, both a Phase 2
FMEA and a Phase 3 FMEA were performed within each Design FMEA process for both the
walk-behind and ride-on mowers.
To classify the Effects of the failure modes, a "Classification of Effect' column was
added to distinguish between (1) Safety, (2) Regulatory, (3) Performance, and (4) Other Effects.
Severity, Occurrence and Risk Priority Number columns were added for Phase 3 engines
to provide a side-by-side comparison with Phase 2 engines. Finally, a column was added to
show the difference between the Phase 2 and the Phase 3 RPN (RPN Delta).
Deleted Columns
The Detection value column was deleted from the FMEAs. Detection is useful
principally in FMEAs where the team that is responsible for the analysis has direct knowledge of
their organizations' ability to detect design problems before the product is released to the market.
In the case of this Work Assignment, the team is composed of people that are independent of any
specific engine manufacturer. Consequently, direct understanding of the detection process was
limited. Detection also can differ considerably among Class I and Class II engine manufacturers
and equipment OEM's. Further, if Detection were to be utilized, the team decided that all
detection numbers would have to be the same by default, due to the limited knowledge of and the
variance among manufacturers' processes. Therefore, removing the Detection ranking number
from the process had no effect on the relative Risk Priority Number rankings. As a result, it was
decided that the ranking parameter of Detection would not be considered, and would not be part
of the FMEA analysis or the FMEA worksheet.
To understand the FMEA process, it is important to understand the definitions of the
terms used.
1. Risk Priority Number (RPN): This is one of the primary output of the FMEA process.
The RPN value is the product of the ranking values. In this study, the RPN is the
product of the Severity Ranking and the Occurrence Ranking (S x O = RPN). The
RPN is used to classify the failure modes to help identify which modes are likely to
be the most serious. In industry the RPN values from the FMEA would be used to
direct the efforts to make improvements to the product or process (The corrective
action is typically targeted for completion prior to production release of the product in
question). A high failure mode RPN does not always suggest a high occurrence.
When failure modes are associated with Effects (see item 4 below) that have a high
Severity ranking (see 5 below) the RPN suggests that if the failure mode does occur
(no matter how remote), a serious consequence potentially could result. Typically,
any FMEA line item with a severity ranking of 9 or 10 requires that a study be
conducted to assess how the potential failure mode that could result in the serious
consequences could be mitigated.
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2. Potential Failure mode: A means by which a component, subsystem or system could
potentially fail. In the typical FMEA process the definition of failure modes is a
speculative process and defines a failure that "could" happen.
3. Potential Cause: This is the identification of the potential cause of the failure mode.
This is often an indication of a potential component or system design flaw or
weakness which leads to a failure of the subsystem or system to perform the intended
function. The failure could be due to a direct failure of the component or system, or
could be caused by external factors. There should be at least one cause identified for
each potential failure mode. In some cases, a contributing cause was identified, but in
other cases a primary cause was felt to be sufficient.
4. Potential Effects of Failure: The potential effects of the failure are the results of the
component, subsystem or system failing to perform the intended function. Safety
effects should be explicitly identified. EPA field data and CPSC real world incidents
were helpful in identifying some potential effects of failure. There is usually the
potential of multiple effects associated with each potential failure mode, including
"no effect".
5. Severity. This is a ranking parameter which is an assessment of the relative
seriousness of an effect for any failure mode. Typically, the range of ranking values
is between 1 and 10 (never zero). Each effect needs to be ranked for severity. Table
4 presents the definitions used in this analysis for the Severity Ranking. In this study
the effect "burn risk" was assigned a severity ranking of 9; the effect: "increased risk
of fire or burn" was ranked a severity 9; and "fire" was ranked a severity of 10.
6. Occurrence: This is a ranking parameter which is an assessment of the likelihood
that the potential failure mode (which is the result of the cause or causes) will happen.
Typically, the range of ranking values is between 1 and 10 (never zero). Table 5
presents the definitions used in this analysis for the Occurrence Ranking. Note: The
Occurrence is related to the failure mode, not the Effect of the failure mode.
The Severity and Occurrence tables were developed by the SwRI team. The Dyadem
FMEA-Pro software used to manage the FMEA process came with pre-installed Severity,
Occurrence, and Detection tables. However, the SwRI team decided that the Dyadem definitions
for the Severity and for the Occurrence ranking were more typical of automotive products, and
needed revision. The team chose definitions, which better represents Class I and Class II small
engines. The ranking values and definitions are shown in Tables 4 and 5 shown below.
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Table 4. Severity Ranking Definitions
Ranking
Effect
Severity of Effect - Customer
10
Hazardous
Hazardous effect. Safety Related. Regulatory non-compliant
9
Serious
Potential hazardous effect. Able to stop without mishap. Regulatory
compliance in jeopardy.
8
Extreme
Item inoperable, but safe. Customer very dissatisfied
7
Major
Performance severely affected, but functional and safe. Customer dissatisfied
6
Significant
Performance degraded, but operable and safe. Customer experiences
discomfort
5
Moderate
Performance moderately affected. Fault on non-vital requires repair.
Customer experiences some dissatisfaction
4
Minor
Minor effect on performance. Fault does not require repair. Non-vital fault
always noticed. Customer experiences minor nuisance.
3
Slight
Slight effect on performance. Non-vital fault noticed most of the time.
Customer slightly annoyed.
2
Very Slight
Very slight effect on performance. Non-vital fault may be noticed. Customer is
not annoyed.
1
None
No effect.
Table 5. Occurrence Ranking Definitions
Ranking
Probability
Likely Failure Rates
10
Almost Certain
Greater than / Equal to 1 in 2
9
Very High
1 in 3
8
High
1 in 8
7
Moderately High
1 in 20
6
Medium
1 in 80
5
Low
1 in 400
4
Slight
1 in 2000
3
Very Slight
1 in 10,000
2
Remote
1 in 50,000
1
Almost Impossible
<1 in 500,000
Note 1: For the Design FMK4 the Occurrence Ranking is related to the design life of the equipment.
Note 2: For the Process FMEA the Occurrence Ranking is related to a one-year operation period.
The Design and Process FMEA methodology for this work consisted of the following
steps:
1. Define the system to be studied (ref: Attachment 7)
• This activity depends on the project scope and relies on the expertise of the team
members.
2. List the items in the system
• This activity is intended to make sure each team member is well versed in the sub
elements of the system or component being evaluated.
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3. List the major functions of each item or element
• This activity is intended to make sure that the team has identified all of the main
functions of the system or component being studied.
4. Anticipate the possible Failure Modes for each item
• This activity uses experience and engineering judgment to identify the most likely
ways the system or component could fail.
5. Consider possible Causes
• Determine what could be the cause of the failure mode.
6. Determine the potential effects of each failure mode
• This activity develops a list of what the team members would expect to be the
possible results or effects of the particular failure mode.
7. Rank the Severity of the potential effect of the failure mode
• This activity is based on experience and judgment. The team defines the severity
of the effect and assigns a Severity value.
8. Determine the likelihood that the particular failure mode would occur
• This activity requires the team estimates or use data to project how often the
particular failure would likely occur and assigns an Occurrence value.
9. The Risk Priority Number (RPN)
• This is calculated by multiplying the Severity ranking value of the potential effect
of the failure mode by the Occurrence ranking value. The RPN parameter relates
to each failure mode and is a primary output of the FMEA analysis. It is intended
to drive focus on the areas needing product improvement. The highest ranked
potential failures should get further attention and the lowest ranked items may not
be addressed at all.
10. Perform Failure Analysis on Phase 2 and Phase 3 engines
• Since the study considered incremental changes between Phase 2 and Phase 3
engine; each had to be analyzed and ranked separately.
11. RPN Delta (Phase 2 versus Phase 3)
• This value is the difference between the Phase 3 RPN and the Phase 2 RPN. A
positive number suggests an improvement for Phase 3.
The ranking process for an FMEA is adapted to the particular study being conducted. In
the case of this FMEA, the Occurrence of the Failure Mode and the Severity of the Effects were
ranked using the list of criteria presented in Tables 4 and 5. The ranking definitions and the
specific ranking process were established by consensus of the team. The ranking process is
generally unique for each study and team. One exception is that any Effect of a Failure that is
defined as hazardous or potentially hazardous is ranked as a 10 or 9, respectively. In addition, in
this study parallel Design FMEAs were conducted for Phase 2 and Phase 3 engines in order to
identify the expected incremental risk.
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4.0 DISCUSSION OF RESULTS
OVERVIEW
This FMEA was conducted to identify and assess potential safety differences between
engines/equipment meeting EPA Phase 2 emission standards and engines/equipment meeting
potential EPA Phase 3 standards. This analysis covered both equipment using Class I (<225cc)
and Class II (>225cc) engines. For the Class I engines, the equipment identified were a typical
walk behind lawnmower. For Class II, the equipment identified was a typical ride on mower.
Two different types of FMEAs were prepared. The first was a Design FMEA. This was
prepared for Class I and Class II engines. The second was a Process FMEA. This was prepared
for the processes of refueling, maintenance and storage of the aforementioned equipment. The
Design FMEAs will be discussed first followed by the Process FMEAs, and then more general
conclusions about the work. The complete tables of results for the two Design FMEAs for Class
I and Class II engines/equipment can be found in Attachments 8 and 9. The complete tables of
results for the three Process FMEAs for refueling, maintenance and storage can be found in
Attachments 10, 11, and 12, respectively.
Design FMEA
The Design FMEAs were completed using a systems approach. The system, subsystem
and components most likely to be modified for compliance with potential exhaust and
evaporative requirements were considered. Twelve systems/subsystems were evaluated. This
was deemed an essential part of the process because of the technical interdependency of these
systems, and the potential interaction among these systems in potential failure mode situations.
The twelve systems evaluated included those listed in Table 6.
Table 6. FMEA Systems Evaluated
1
Intake air filter
7
Exhaust manifold, muffler,
muffler shroud and gasket
2
Carburetor system
8
Supplemental air (Class I only)
3
Governor
9
Catalyst (monolith, matting)
4
Intake manifold, port, valve and seals
10
Cooling system
5
Block
11
Ignition system
6
Exhaust valve and seal
12
Fuel tank and line
The Design FMEAs were structured and conducted in the following manner.
1. The systems and functions were identified.
2. Inputs for the row items of each system/function combination were determined (Potential
Cause (Contributing), Potential Cause (Primary), Potential Failure Modes, Potential
Effect(s) of Failure).
20
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3. Ranking were established for Severity and Occurrence.
4. Values were assigned for the Phase 2 engine: Occurrence of the Potential Failure Mode
and Severity of the Potential Effect(s) of Failure
5. Values were assigned for the Phase 3 engine: Occurrence of the Potential Failure Mode
and Severity of the Potential Effect(s) of Failure
6. Calculation of RPN's for Phase 2 and Phase 3 and calculation of difference in RPN
(Phase 3-Phase 2)
7. Include notes to describe important items in the decision making for each line item.
8. Classify the Effect (Safety, Regulatory, Performance, Other)
This work leaned heavily on the teams understanding of engines, combustion, fuels and
how primary and contributing causes can translate into potential failure modes. Each member of
the team was given opportunity to add input and speak to the need for refinement and changes.
The reports and data provided by CPSC were important and identified some of the potential
failure modes and effects.
Process FMEAs
Input received from various sources and the CPSC reports and data revealed processes
which led to potential problems in use. EPA felt that specific analysis of these three areas was
important because they represent typical life-cycle use for the product. The Process FMEAs
conducted by the team included refueling, maintenance, and storage. While some of the
information and results from the Design FMEAs carry across to the Process FMEAs, the
difference is in the introduction of the operator to perform these functions. These Process
FMEAs were completed with heavy reliance on the technical information, the expertise of the
team members and input from the CPSC reports and data.
RESULTS
Complete FMEA summaries are included in the Attachments 8 through 12. A subset of
these results that relate only to safety items are presented in Tables 7 through 11. Tables 7 and 8
cover Class I and Class II Design FMEA safety items, and Tables 9 through 11 cover refueling,
shutdown and storage, and maintenance Process FMEA safety items, respectively.
Design FMEAs - Discussion of Safety Tables for Class I and Class II
In Table 7, Class I engine FMEA safety items are grouped by systems/subsystems, i.e.
intake air filter, carburetor system, governor, and others as presented in Table 6. Intake air filter
failures (dirty, missing filters) can cause engine operation to switch either richer or leaner. Richer
operation (reference item 1) could cause a backfire, which could result in a fire or burn. Fire or
burn is always classified with a severity of 10. The team rated the occurrence of this failure mode
to be reduced for the Phase 3 product relative to the Phase 2 product. This difference is based on
21
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experience with EPA prototype Phase 3 engines, which showed reduced incidence of backfire
with catalyst, principally due to the flame arresting function provided by the catalyst. For intake
air failure mode (reference item 2), a leaner mixture can create slightly higher exhaust
temperatures. Since baseline (non-failure mode) exhaust temperatures are already high enough to
cause burns, this failure mode only incrementally increases severity of the burn. Since catalyst
application does not increase the occurrence of the failure mode, the RPN values are the same for
Phase 2 and 3 products. This increase could be mitigated by application of a thermal cutoff
switch, designed to shut the engine off at a specified temperature.
The next four failure modes (reference items 3 through 6) have to do with the carburetor
system. Restrictions in fuel passages (reference item 3) could result in higher engine and/or
catalyst temperatures with the resulting potential effect of a fire or touch burn. This effect rates a
severity of 10. While the Phase 3 engine's catalyst may increase the thermal load around the
engine, the improvements in manifold air cooling will mitigate these effects. The RPN rankings
are thus the same for Phase 2 and Phase 3 product. As is the case above, this effect could be
mitigated for either Phase 2 or 3 products by application of a thermal cutoff switch.
Carburetor system failure mode (reference item 4), backfire, is caused by a richer mixture
which can be caused by float malfunctions, a stuck choke, or other causes. As in the case of the
intake air filter associated backfire, (reference item 1) the team felt the incidence of this would
be reduced with catalyst application, thus resulting in a reduced RPN for the Phase 3 product.
Carburetor system failure modes (reference item 5 and 6) involve fuel leakage to a
surface where it can potentially be ignited, causing a fire or burn (severity 10). The incidence of
this occurring was rated the same with or without a catalyst since adequate ignition temperatures
are already present in existing Phase 2 product. Also, fuel can be ignited by the ignition system,
which is present in both Phase 2 and Phase 3 product.
A governor malfunction, where the governor does not close the throttle can result in an
overspeed, which can cause mechanical engine failure where parts fail or come apart due to
excessive speed (reference item 7). Occurrence of this type of failure is very low, and is the same
with or without a catalyst.
A significant crack or leak in the intake manifold (reference item 8) can result in a leaner
mixture which could lead to increased temperatures in the exhaust systems or catalyst. Potential
effects are fire or burn (severity 10). The Phase 3 engine has a significantly lower occurrence due
to improvement in intake manifold system design, including the use of gaskets. SwRI recently
performed a teardown and inspection of 10, field aged, Class I, Phase 2 engines. Eight of the 10
were found to have leaky intake manifolds. This type of problem will need to be addressed on
Phase 3 products to assure in-use emissions compliance.
Engine failures can be caused by excessive temperatures (reference 9 and 10). This can
result from higher thermal loads due to higher engine loading or a mechanical problem.
Sufficiently high temperatures can cause failure or seizure of an internal component, rendering
the engine non-functional. A catastrophic engine failure could create a safety hazard from flying
debris or an engine fire. In both cases, the occurrence is rated to be the same with or without a
22
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catalyst. As discussed above, these failure modes could be mitigated for either Phase 2 or 3
products by application of a thermal cutoff switch.
The next three failure modes (reference itemsl 1 through 13) are related to problems with
the exhaust manifold. Gasket failures can cause leaks which can cause burns. Occurrence of this
failure mode is reduced for Phases 3 product due to the use of improved exhaust system designs
and/or improved materials. Debris accumulation around the exhaust manifold can result in a fire
(reference item 12). Occurrence of this failure mode is reduced for Phase 3 product due to
improved designs of the cooling air ducting systems. Another potential failure mode is the loss of
the muffler shroud. This can also result in fire or burn. Occurrence of this failure mode is again
reduced due to improvement in the design of the air ducting system. Thus in all three cases, RPN
ratings for exhaust manifold related failure modes are reduced with Phase 3 product, principally
due to improvements in design. These same improvements could be effected in Phase 2 product,
if desired.
The next failure mode is associated with the catalyst system. The RPN value is higher for
Phase 2 due to the absence of catalyst on the Phase 2 product. If in manufacturing, the incorrect
catalyst were installed on the engine or the catalyst was installed improperly (reference item 14),
excessive temperatures could result if the catalyst has higher catalytic activity than the proper
catalyst for that engine. It should be noted that the occurrence of this failure mode for Phase 3
product is relatively low. Further, the occurrence of this mode can be reduced by application of a
thermal cutoff switch if the design team determined it was needed.
The next two failure modes result from problems with the cooling system (reference
items 15 and 16). A failure of the cooling system shroud (reference item 15) that directs cooling
air can result in higher temperatures that present a burn risk. Presence of a catalyst has no effect
of the occurrence or severity of this failure and thus Phase 2 and Phase 3 products have the same
RPN. The pluggage of cooling passages by debris will tend to increase the component
temperatures and could result in a burn risk. Due to the expected design improvements in the
cooling system features of the Phase 3 product, the Phase 3 RPN is lower than the Phase 2
product. These problems associated with the cooling system could be mitigated, again, by the use
of a thermal cutoff switch.
Ignition system problems can cause a variety of failure modes. A bad spark plug or
ignition wire or a problem with the ignition module or the magneto can result in a weak or
intermittent spark (reference item 17). This can potentially result in higher muffler and catalyst
temperatures and an increased burn risk. Ignition system problems can also result in misfire
(reference item 18), which can cause a fire of burn. Phase 3 RPN is less than that for Phase 2
product due to the reduced incidence of backfire when a catalyst is applied, as demonstrated by
EPA.
Fuel tank problems can present possibilities for fuel leaks which can result in fires or
burns. High muffler or catalyst temperatures could melt nearby fuel lines resulting in a fuel leak.
For reference items 19, 20, 21, 22 and 23, the application of fuel evaporative emission controls
will reduce leak occurrence, resulting in lower RPNs for Phase 3 product. For the other three
cases, the presence of a catalyst does not affect the rankings; they are the same with or without a
catalyst.
23
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Table 7. Class I Safety FMEA Items
Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
1
Intake Air
Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
richer
mixture
backfire
fire or burn
1_Safety
10
3
30
20
10
2
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
2
Intake Air
Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
leaner
mixture
hotter exhaust
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
there will be no increase in burn risk with the application of a
properly designed catalyst. The effect could be mitigated by
the presence of a thermal switch.
3
Carburetor
System
Restriction in fuel
passages, wrong
jets in production
or production
variability
leaner
mixture
higher
temperature in
engine and
catalyst
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. Any
effect that the catalyst might have on temperature level is
offset by the expected improvements in air cooling of the
manifold system on Phase 3 products. If the change in
temperature is significant the effect could be mitigated by the
presence of a thermal switch.
4
Carburetor
System
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer
mixture
backfire
fire or burn
1_Safety
10
5
50
40
10
4
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
5
Carburetor
System
gasket failure, or
needle valve stuck
open, or cracked
primer bulb
leakage of
fuel to
mower deck,
air filter or
elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because
exposed muffler temperatures are nominally equivalent. Fuel
can be ignited by hot surfaces or the ignition system.
24
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
6
Carburetor
System
gasket failure, or
needle valve stuck
open, or cracked
primer bulb
leakage of
fuel to
mower deck,
air filter or
elsewhere
(i.e. out of air
filter)
fuel puddles
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst because
exposed muffler surfaces have been shown to be nominally
equivalent in Phase 2 (no catalyst) and Phase 3 (catalyzed)
prototype systems.
7
Governor
None
Malfunction-
ing governor
open governor
causes engine
overspeed
catastrophic
failure (potential
injury due to
flying parts)
1_Safety
9
2
18
18
9
2
0
Engine failure caused by overspeed. The rankings are the
same with or without a catalyst.
8
Intake
Manifold
Crack or leak in
manifold
leaner
mixture
engine,
exhaust
system and
catalyst run
hotter
fire or burn
1_Safety
10
9
90
40
10
4
50
The lower occurrence for Phase 3 is due to the expected
improvement of the manifold system for Phase 3 products.
The effect could be mitigated by the presence of a thermal
switch.
9
Block
Higher thermal
load
higher
engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
catastrophic
failure (potential
injury due to
flying parts)
1_Safety
9
4
36
36
9
4
0
Engine failure caused by excessive temperatures. The
rankings are the same with or without a catalyst. The effect
could be mitigated by the presence of a thermal switch.
10
Block
Higher thermal
load
higher
engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
fire or burn
1_Safety
10
4
40
40
10
4
0
Engine failure can result in contact with hot metal or fluids.
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
11
Exhaust
Manifold
None
loosening of
muffler,
manifold or
failed gasket
(gasket is
less common
on Class I
vertical shaft
engines)
exhaust leak
fire or burn
1_Safety
10
6
60
40
10
4
20
The lower Phase 3 occurrence is due to the Phase 3 improved
exhaust system design.
25
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
12
Exhaust
Manifold
Debris
accumulation
reduction in
engine
cooling and
increased
muffler
temperatures
ignition of
debris
adjacent to
muffler
fire
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and control of
debris accumulation. In addition, fan inlet screens are
expected on all Phase 3 engines. The failure mode could be
mitigated by the presence of a thermal switch.
13
Exhaust
Manifold
None
removal or
mechanical
failure of the
shroud
loss of muffler
shroud
fire or burn
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and shroud design.
14
Catalyst
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
excessive
catalyst
performance
fire or burn
1_Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does
not have a catalyst. For Phase 3, the severity ranks high due
to the potential safety impact. The effect could be mitigated
by the presence of a thermal switch.
15
Cooling
System
None
cooling
system
shroud failed
loss of cooling
to engine block
and muffler
system
burn risk
1_Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
16
Cooling
System
None
plugging of
cooling
passages
due to debris
reduction of
engine cooling
burn risk
1_Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design
features for Phase 3 results in a slight reduction in
Occurrence. The effect could be mitigated by the presence of
a thermal switch.
17
Ignition
System
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module
failure
weak or
intermittent
spark (misfire)
excessive
muffler or
catalyst
temperatures
and increased
burn risk
1_Safety
9
5
45
27
9
3
18
The lower occurrence for the Phase 3 is due to the improved
ignition system for Phase 3 products. The effect could be
mitigated by the presence of a thermal switch.
18
Ignition
System
plug bad, short in
plug wire, failed
coil, loose
flywheel, magneto
loss of spark
backfire
(misfire)
fire or burn
1_Safety
10
6
60
40
10
4
20
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
26
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Class I Safety FMEA Items
Ref. Item
No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure Modes
Potential
Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
19
Fuel Tank
None
leak of tank
or line
fuel puddles
fire or burn
1_Safety
10
5
50
40
10
4
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
20
Fuel Tank
None
leak of tank
or line
fuel puddles
operator fuel
exposure
1_Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
21
Fuel Tank
None
leak of tank
or line
fuel leaks on
hot component
fire or burn
1_Safety
10
4
40
30
10
3
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
22
Fuel Tank
High muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel puddles
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
23
Fuel Tank
High muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel puddles
operator fuel
exposure
1_Safety
9
3
27
18
9
2
9
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
24
Fuel Tank
High muffler or
catalyst
temperatures near
fuel lines
fuel tank or
line melted
fuel leaks on
hot component
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst. The
exposed muffler temperatures are nominally equivalent.
27
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Table 8 presents a summary of Class II engine FMEA safety items. In many cases, Class
II engine safety items are similar or identical to those for Class I engines. Discussion will focus
or areas with significant differences.
While most Class II engines currently use carburetors, several use fuel injection systems
and it is likely more will do so in the future. Carburetor system items (reference items 3 through
7) can be caused by either carburetor or fuel injection system problems. Fuel pump or pressure
regulator failures can cause the leaner mixture problem in reference item 3. This can also be
caused by fuel filter or injector restrictions, or problems with injection system wiring, or MAP
(manifold absolute pressure) sensors, ECMs (engine control modules), or by oxygen (02) sensor
failures. For backfire failure modes associated with carburetors (reference item 4), the catalyst
will reduce incidence of backfire, as demonstrated by EPA, thus producing lower RPN values for
the Phase 3 product.
Another type of fuel injection system failure is presented in reference item 7, where an
ECM or a solenoid valve return spring failure could allow fuel to flow into a non running engine.
This could puddle or leak from the engine, and could ignite causing a fire. This failure mode is
unaffected by the presence of a catalyst; thus the RPN values are the same for Phase 2 and 3
engines.
For Class II engines with a MAP sensor, a leak in the intake manifold can cause the MAP
to read a higher pressure that would command a richer mixture (reference item 10). This could
produce a backfire, potentially causing a fire or burn. RPN values are the same with or without a
catalyst.
Another type of failure mode more specific to Class II products is equipment tip-over.
This can happen where the operator is mowing on a slope, for example, and reaches an angle
where the equipment rolls over (reference item 23). In such cases, fuel can leak from the fuel
tank and potentially catch fire. The evaporative emission controls expected for Phase 3 will
reduce the leak occurrence, and thus the Phase 3 RPN is also lower. Available data suggests the
Phase 3 product could have directionally cooler exhaust system temperatures as demonstrated by
EPA. Cooler exhaust temperature will improve the risk of fire due to equipment tip over further.
28
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Table 8. Class II Safety FMEA Items
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
1
Intake Air Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
richer mixture
backfire
fire or burn
1_Safety
10
2
20
20
10
2
0
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. The occurrence
is held the same for Phase 2 and 3 in this case since Class II,
Phase 2 products are already judged to have a relatively low
occurrence of backfire due to intake filter issues.
2
Intake Air Filter
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
leaner mixture
hotter
exhaust
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
there will be no increase in fire or burn risk with the
application of a properly designed catalyst. The effect could
be mitigated by the presence of a thermal switch.
3
Carburetor
System
Restriction in
fuel passages,
wrong jets in
production, or
choke stuck
open, or
production
variability. Fuel
injection system
fuel pump or
fuel pressure
regulator
failure. Fuel
filter or injector
restriction.
Injector wiring
connection
degraded.
MAP, ECM, or
02 sensor
failure.
leaner mixture
higher
temperature
in engine and
Catalyst
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst. Any
effect that the catalyst might have on temperature level is
offset by the expected improvements in air cooling of the
manifold system on Phase 3 products. If the change in
temperature is significant the effect could be mitigated by the
presence of a thermal switch.
29
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Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Float breaks,
debris in float
needle, or
wrong jets in
production,
choke stuck
4
Carburetor
System
closed, or
production
variability. Fuel
injection fuel
system fuel
pressure
regulator
failure. Fuel
injector stuck
open. MAP,
ECM, 02
sensor failure.
richer mixture
backfire
fire or burn
1_Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
5
Carburetor
System
gasket failure,
or needle valve
stuck open, or
fuel pump /
regulator leak
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because
exposed muffler temperatures are nominally equivalent. Fuel
can be ignited by hot surfaces or the ignition system.
6
Carburetor
System
gasket failure,
or needle valve
stuck open, or
fuel pump /
regulator leak
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel puddles
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because
exposed muffler surfaces have been shown to be nominally
equivalent in Phase 2 (no catalyst) and Phase 3 (catalyzed)
prototype systems.
7
Carburetor
System
ECM failure,
solenoid return
spring
breakage
causes fuel
cutoff solenoid
open failure
fuel flow into
and from
engine
fuel puddles
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst.
30
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
8
Governor
None
malfunctioning
governor
open
governor
causes
engine
overspeed
catastrophic failure
(potential injury due
to flying parts)
1_Safety
9
2
18
18
9
2
0
Engine failure caused by overspeed. The rankings are the
same with or without a catalyst.
9
Intake Manifold
Crack or leak in
manifold
leaner mixture
engine,
exhaust
system and
catalyst run
hotter
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
10
Intake Manifold
Intake manifold
leak causes
MAP to read
higher pressure
richer mixture
backfire
fire or burn
1_Safety
10
3
30
30
10
3
0
The failure relates to fuel Injected engines. EPA
demonstrated that the backfire impact was reduced with the
addition of a properly designed catalyzed muffler system for
Class I. However, since the design quality of the Class II
equipment mufflers is very good on Phase 2, the impact of
adding the catalyst is minimal.
11
Block
Higherthermal
load
higher engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
catastrophic failure
(potential injury due
to flying parts)
1_Safety
9
3
27
27
9
3
0
Engine failure caused by excessive temperatures. The
rankings are the same with or without a catalyst. The effect
could be mitigated by the presence of a thermal switch.
12
Block
Higherthermal
load
higher engine
temperatures
engine failure
(internal
component
seizure,
broken valve
or spring,
excess wear)
fire or burn
1_Safety
10
3
30
30
10
3
0
Engine failure can result in contact with hot metal or fluids.
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
13
Exhaust
Manifold
None
cracked
muffler,
manifold or
failed gasket
exhaust leak
fire or burn
1_Safety
10
4
40
30
10
3
10
The lower Phase 3 occurrence is due to the Phase 3
definition of improved exhaust system design.
14
Exhaust
Manifold
Debris
accumulation
reduction in
engine cooling
/ increased
muffler
temperatures
ignition of
debris
adjacent to
muffler
fire
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting for cooling and control of
debris accumulation.
31
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
15
Exhaust
Manifold
None
removal or
mechanical
failure
loss of
muffler
shroud
fire or burn
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the
improvement of the air ducting design for cooling and shroud
design.
16
Catalyst
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
increased
catalyst
performance
fire or burn
1_Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does
not have a catalyst. For Phase 3, the severity ranks high due
to the potential safety impact. The effect could be mitigated
by the presence of a thermal switch.
17
Cooling
System
None
plugging of
cooling
passages due
to debris
reduction of
engine
cooling
burn risk
1_Safety
9
4
36
27
9
3
9
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
18
Cooling
System
None
cooling system
shroud failed
loss of
cooling
burn risk
1_Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
19
Ignition System
None
plug bad, short
in plug wire,
failed coil,
loose flywheel,
magneto,
ignition
module failure
weak or
intermittent
spark, or loss
of ignition in
one of two
cylinders
(misfire)
excessive muffler or
catalyst
temperatures and
increased burn risk
1_Safety
9
3
27
27
9
3
0
The rankings are the same with or without a catalyst. The
effect could be mitigated by the presence of a thermal switch.
20
Ignition System
bad plug, short
in plug wire,
failed coil, loose
flywheel,
magneto
loss of spark
Backfire
(misfire)
fire or burn
1_Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can
cause a fire or burn. EPA demonstrated that the backfire
incidence was significantly reduced with the addition of a
properly designed catalyzed muffler system. That fact drives
a reduction in the Occurrence ranking.
21
Fuel Tank
None
leak of tank or
line
fuel puddles,
or sprays
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
22
Fuel Tank
None
leak of tank or
line
fuel puddles,
or sprays
operator fuel
exposure
1_Safety
9
3
27
18
9
2
9
The rankings are the same with or without a catalyst.
23
Fuel Tank
Equipment tip
over, material
failure,
component
failure
leak of tank or
line
fuel contacts
hot
component
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design
features for Phase 3 is expected to result in a slight reduction
in Occurrence. The evaporative emission controls will
reduce leak occurrence
32
-------
Class II Safety FMEA Items
Ref. No.
Item
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential
Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
24
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel puddles
or sprays
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
25
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel puddles
or sprays
operator fuel
exposure
1_Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst.
26
Fuel Tank
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel contacts
hot
component
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
33
-------
Process FMEAs - Discussion of Safety Tables
Tables 9-11 summarize safety related failure modes and effects for Class I and Class II
engines. These tables are for Process FMEAs, which consider failure modes which can occur in
the course of a process or an operation. Table 9 considers engine refueling. Table 10 addresses
the process of engine shutdown and storage; and Table 11 is for maintenance processes.
Safety issues associated with refueling principally involve fuel spillage which can result
in a fire. Refueling failure mode, reference item 1, involves a scenario where the operator has not
shut off the engine before refueling (Table 9). The potential effect of this failure mode is the risk
of refueling while the engine is still running. Thermal images taken by EPA of current Phase 2
product and prototype Phase 3 product indicate that exhaust surface temperatures at idle are
similar. In addition, EPA is not expected to propose measures to reduce spillages related to the
refueling process as part of its Phase 3 rulemaking. Since the thermal characteristics between
Phase 2 and Phase 3 products are expected to be similar and the human factors associated with
the refueling process are the same in each case, the RPN values are ranked equally for the Phase
2 and Phase 3 products for all refueling process scenarios.
34
-------
Table 9. Refueling Process FMEA
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
1
Shut off engine
failed to shut engine
off
engine
running
risk of refueling while
engine running and a
potential of a fire or burn
1_Safety
9
2
18
No difference between Phase 2 and
Phase 3 expected. Thermal images
indicate that at idle operation the
maximum surface temperatures are
comparable for Phase 2 and Phase 3
designs.
2
Open mower cap
overpressure of fuel
tank
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
3
Open mower cap
overpressure of fuel
tank
spillage (hot
fuel, full tank,
pressurized
tank - i.e. vent
blocked)
spillage onto hot
surfaces and a potential
of a fire or burn
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
4
Open mower cap
overpressure of fuel
tank
fire
1_Safety
10
2
20
A safety concern, but no significant
difference between Phase 2 and Phase
3 expected. (Phase 3 tank venting
could be a slight improvement)
5
Remove fuel can
cap
operator behavior
Fail to open
vent
fuel spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
6
Remove fuel can
cap
hot fuel and high
pressure(high
temperature storage,
heating from sunlight)
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
7
Remove fuel can
cap
hot fuel and high
pressure(high
temperature storage,
heating from sunlight)
fuel spray
upon opening
cap/vent
spillage
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
8
Remove fuel can
cap
operator behavior
spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
9
Remove fuel can
cap
operator behavior
vapor released from can
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
35
-------
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
10
pick up can and
pour
fuel spill
fuel puddle on
equipment
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
11
pick up can and
pour
fuel spill
fuel spill into
fan inlet
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
12
pick up can and
pour
fuel spill
fuel over the
cowling and
makes contact
with a hot
exhaust
system
component
fuel fire
1_Safety
10
4
40
A safety concern, but effectively no
difference between Phase 2 and Phase
3 expected. Thermal imaging cross-
validation studies indicated that "...the
application of a catalyst to a small
gasoline engine does not increase, and
can actually lower, exhaust system
surface temperatures..."
13
pick up can and
pour
fuel spill
spill on
operator
and/or
bystander
fuel exposure
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
14
pick up can and
pour
fuel spill
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
15
pick up can and
pour
fuel spill
spillage on
surrounding
areas
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
16
pick up can and
pour
fuel spill
creates combustible
material
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
17
pick up can and
pour
material failure
gas can
cracks
fuel spill and potential of
fire or burn
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
18
pick up can and
pour
engine running
refuel while
running
spill fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
19
pick up can and
pour
engine running
fuel vapor ignites
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
36
-------
Refueling Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
20
pick up can and
pour
static charge
spark
fire or explosion
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
21
pick up can and
pour
gas cap on can is not
secure
spillage on
surrounding
areas
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
22
Recap the Mower
Tank
failure to recap mower
tank
fuel spillage or
vapor release
onto
equipment or
operator
during
operation
fire
1_Safety
10
3
30
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
23
Recap the Mower
Tank
failure to recap mower
tank
fuel exposure
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
24
Restart
fuel on the equipment
ignition
component
failure
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
25
Restart
fuel or debris left on
the equipment
hot surfaces
ignites
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
37
-------
Table 10 presents failure modes that can occur during equipment shutdown and storage.
In several cases, failures can result from inability to shut the engine off. The operator can be
burned while trying to disconnect the spark plug wire. Another failure mode can occur if the
operator covers the equipment with a tarp while it is still hot. The tarp could catch fire and
damage the equipment or even cause a structural fire if the equipment had been moved indoors.
Fires can also result from storage of hot equipment on or next to combustible materials, such as
newspapers. In all cases, there are no differences between RPNs for Phase 2 and Phase 3
equipment.
38
-------
Table 10. Shutdown and Storage Process FMEA
Shutdown and Storage Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
1
Engine Shut Down
ignition cut off and
engine brake fail (and
engine does not shut
off)
engine left
running, and
operator may
pull plug wire
to stop
high surface
temperatures, and risk
of fuel ignition from high
voltage spark and risk
of shock
1_Safety
9
2
18
No difference between Phase 2 and Phase
3 expected
2
Engine Shut Down
engine won't stop and
operator goes for help
untended
operation
bystander gets injured
by burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
3
Engine Shut Down
engine won't stop and
operator goes for help
debris fire
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
4
Engine Shut Down
engine won't stop and
operator pulls plug
wire
risk of fuel
ignition due to
high voltage
spark
fire or burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
5
Engine Shut Down
engine won't stop and
operator pulls plug
wire
operator
contacts hot
component
burn
1_Safety
10
2
20
No difference between Phase 2 and Phase
3 expected
6
Equipment Storage
cover with tarp while
engine hot (any
material)
tarp ignites
fire ignites adjacent
materials
1_Safety
10
2
20
Tarp ignites and fire could spread. No
impact due to addition of a catalyst.
7
Equipment Storage
cover with tarp while
engine hot (any
material)
fire damages equipment
1_Safety
10
2
20
Tarp ignites and fire could spread. No
impact due to addition of a catalyst.
8
Equipment Storage
store in or near
garage or shed when
engine hot
equipment
ignites
combustible
material
structural fire
1_Safety
10
1
10
Surrounding material could ignite. No
impact due to addition of a catalyst. Data
available does not support a higher
occurrence ranking.
9
Equipment Storage
store in or near
garage or shed when
engine hot
water heater
pilot light
ignites
gasoline vapor
from leak, spill
or refueling
structural fire
1_Safety
10
1
10
Gas vapor could ignite. No impact due to
addition of a catalyst. Data available does
not support a higher occurrence ranking.
10
Equipment Storage
store in or near
garage or shed when
engine hot
Spilled fuel or
debris on
mower deck
ignites
Equipment or structural
fire
1_Safety
10
1
10
Debris on the mower deck could ignite. No
impact due to addition of a catalyst. Data
available does not support a higher
occurrence ranking.
39
-------
Shutdown and Storage Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
11
Equipment Storage
store in or near
garage or shed when
engine hot
operator
and/or
bystander
contacts hot
component
burn
1_Safety
10
2
20
No impact due to addition of a catalyst.
12
Equipment Storage
park equipment on
combustible debris
debris ignites
debris fire
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
13
Equipment Storage
park equipment on
combustible debris
structural fire
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
14
Equipment Storage
park equipment on
combustible debris
bystander gets injured
by burn
1_Safety
10
2
20
No impact due to addition of a catalyst.
15
Equipment Storage
park equipment on
combustible debris
fire damages equipment
1_Safety
10
2
20
Surrounding material could ignite. No
impact due to addition of a catalyst.
40
-------
The Equipment/Engine Maintenance Process FMEA is included in Attachment 12. Table
11 addresses only the maintenance processes with potential safety effects. These include
cleaning the equipment, changing the oil and filter, changing the spark plug, sharpening the
mower blade, and replacing the drive belt. Possible failure modes and resulting effects can
include burns from contact with hot surfaces, fires caused by fuel or oil spillage, or personal
injury from equipment tip over. Additionally, if the drive belt is improperly installed, it can slip
and get very hot, potentially causing a fire. For the fuel spillage scenarios, vapor control
requirements will reduce the occurrence of fuel spillage with Phase 3 product. For all other
cases, the presence of a catalyst does not increase the RPN value above that for Phase 2 product.
Although a Process FMEA was not conducted to specifically address lack of maintenance
of Class I or Class II engines, the causes, failure modes, and effects due to lack of maintenance
are addressed within the Equipment/Engine Maintenance Process FMEA and/or the Design
FMEAs. The maintenance processes which are typically performed by the equipment operator
which, if neglected, could have incremental effects with operation of Phase 3 engines are as
follows:
1. Equipment Cleaning: The Equipment/Engine Maintenance Process FMEA does not
address lack of cleaning. However, Sections 10 and 9 "Cooling System" of the
Class I and Class II Design FMEAs (Attachments 8 and 9) respectively, do address
plugging of cooling passages by debris. The Occurrence and RPN associated with
plugging due to lack of cleaning is expected to be reduced with Phase 3 engines.
2. Engine Oil and Oil Filter Maintenance: In Attachment 12, reference number 10
addresses lack of maintenance. In addition, if engine oil was not replaced or kept at
an adequate level, the effects due to a higher thermal load is identified in Item 5
"Block, Power Head" in Attachments 8 and 9. No difference between Phase 2 and
Phase 3 engines is expected.
3. Air Filter Maintenance: Lack of maintenance is described in references 25 and 26 of
Attachment 12. The effects in Attachment 12 are general, however, in the Design
FMEAs specific effects due to the two Potential Causes (Primary) are identified in
Item 1 "Intake Filter". For example, a richer or leaner mixture could result if the air
filter was not maintained or replaced at regular intervals. A reduction in safety
related RPN, and an increased in RPN associated with failing to meet emissions
regulations were identified due to filter degradation.
4. Spark Plug Maintenance: The cause, failure, and effect that could be envisaged from
lack of maintenance of the spark plug is addressed in reference 28 of Appendix 12,
and in Items 11 and 10 "Ignition System" of the Class I and Class II engine Design
FMEAs, respectively. No increased safety related RPN was identified, however,
there is an incremental RPN associated with failing to meet emissions regulations
due to a lack of maintenance.
5. Carburetor Maintenance: Lack of maintenance of the carburetor is not addressed in
the Equipment/Engine Maintenance Process FMEA. However, if carburetor
41
-------
maintenance was not performed causing restricted fuel passages or allowing debris
accumulation in the float bowl, these contributing causes are identified in Item 2
"Carburetor or Fuel Injection System" in the Design FMEAs. A reduction in safety
related RPN, and an increased RPN associated with failing to meet emissions
regulations were identified due to fuel passage restriction or debris accumulation
within the fuel system.
42
-------
Table 11. Maintenance Process FMEA
Maintenance Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
1
Cleaning Equipment
Tip equipment to clean
underneath
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
2
Cleaning Equipment
Tip equipment to clean
underneath
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
3
Cleaning Equipment
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
4
Change Oil / Filter
Improper maintenance
spill oil
operator exposure to
oil
1_Safety
9
9
81
No difference between Phase 2
and Phase 3 expected
5
Change Oil / Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
6
Change Oil / Filter
Tip equipment for
maintenance
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
7
Change Oil / Filter
Tip equipment for
maintenance
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
8
Change Air Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
9
Change Spark Plug
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
10
Change Spark Plug
testing for spark
spark ignites fuel
fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
11
Sharpen Blade
tipping equipment for
blade access
equipment falls
personnel injury
1_Safety
10
5
50
No difference between Phase 2
and Phase 3 expected
12
Sharpen Blade
tipping equipment for
blade access
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
43
-------
Maintenance Process FMEA
Ref. Item
No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
13
Sharpen Blade
Improper reassembly
spill fuel or oil
personnel injury
1_Safety
10
1
10
No difference between Phase 2
and Phase 3 expected
14
Replace Drive Belt
wrong belt installed
belt slips or does
not engage
belt fire / debris fire
1_Safety
10
4
40
No difference between Phase 2
and Phase 3 expected
15
Replace Drive Belt
belt installed
incorrectly
belt slips or does
not engage
belt fire / debris fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
16
Replace Drive Belt
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
44
-------
5.0 CONCLUSIONS
Design FMEAs
The safety summary tables for the Design FMEAs for Class I and Class II engines
contain 49 potential failure modes. For 28 of these, there was no difference in Risk Priority
Number (RPN) between Phase 2 and Phase 3 product designs. There are also 19 potential failure
modes for which there is a decreased RPN due to improvements in Phase 3 product design, and
two for which there is an increased RPN.
As can be seen in Table 3, EPA's Phase 3 designs improve on Phase 2 designs in several
key areas. EPA's Phase 3 design includes features which are key to implementing catalyst-based
standards and fuel evaporative emission controls, with overall comparable or lower RPNs, which
helps to address safety-related shortcomings in the current Phase 2 engines evaluated. Data
supplied by EPA showed comparable or better results in key areas such as exhaust system
surface temperatures, backfire/misfire performance, and post use cool down.
Overall, the Design FMEAs indicate that from a safety perspective, Phase 3 designs can
be comparable, if not directionally better than Phase 2 for both Class I and Class II products.
This FMEA report relies on laboratory and field data collected by the EPA which shows
that the use of catalyst on small SI engines, if properly designed, could result in exhaust system
temperatures which are comparable or lower than current product in the marketplace. The main
features of EPA's Phase 3 system design include use of cooling air from the fan to flow across
the catalyzed muffler and engine block, control of CO emission reductions to reduce the CO
oxidation exotherm, and a properly designed and located heat shield. However, as is the case
with mufflers on current product, thermal images taken of catalyzed mufflers show that
temperatures are still above the second degree burn temperature for skin.
It is the nature of the FMEA process to consider interdependencies and interactions
among subsystems. That is, the FMEA looks at how a failure of as subsystem or component to
properly perform its intended function can affect other subsystems and components. In this way,
potential effects on the catalyzed muffler and changes in catalyst performance affecting safety
were considered in every item of the Phase 3 analyses. The same is true for the fuel system and
fuel system components impacted by fuel evaporative emission controls.
The potential failure modes that represent the two Class I and Class II negative difference
RPNs involved the use of an improper catalyst or a mis-installation of a catalyst.
- The engine manufacturer selected a catalyst with the wrong specification or assembled
the wrong catalyst component on the engine and the catalyst converted more CO than
expected which resulted in increased catalyst temperatures.
While the probability of this failure was ranked as remote, if this was to occur, the failure
has the potential to result in higher temperatures of the catalyst muffler/shroud system with the
potential effect of risk or a fire or burn.
45
-------
With regard to burn, this potential effect of failure is probably better characterized as the
potential for a more severe (thermal) burn than an increase in the occurrence of thermal burn
since Phase 2 exhaust system temperatures are already high enough to cause a thermal burn. In
order to have an increase in the occurrence of thermal burn, the designs would have to create a
situation where the operator has more frequent contact with the muffler area. During the use of
this equipment with Phase 3 engines, the operator need not access the area of the muffler any
more frequently than with the current Phase 2 product.
If temperatures of the catalyst muffler/shroud system were to increase beyond those of
current product, the incidence of fires may still be the same. This is based on the fact that in
order for a fire to happen, the surface temperatures on current products are often above the
ignition temperature for combustibles such as dry debris or fuel. In this study, the catalyst
mufflers replace the existing mufflers in current locations, but EPA is projecting improvements
in cooling approaches to reduce surface temperatures. If the engine or equipment manufacturer
elected, it could reduce burn risk by incorporating a bimetallic thermal cutoff switch which
would shut off the engine if temperatures exceeded a selected value. This would result in a
decrease in the risk of fire or burn. This approach could be used with current Phase 2 product, as
well.
Process FMEAs
Three processes were identified for FMEA analysis: refueling, equipment storage, and
maintenance. The Process FMEAs were done to identify if there could be any potential for
increased concern of Phase 3 engine systems with catalyst mufflers compared to the current
Phase 2 product. Due to the fact that these processes are mostly done with the engine off, the
processes were analyzed primarily with respect to worst case outcomes after shut-off It was
concluded that there were no additional areas of concern with Phase 3 prototypes versus Phase 2
engine designs. This was based on EPA's thermal data that showed the muffler's hot soak
temperatures were comparable, or potentially reduced, with properly designed Phase 3 catalyst
systems. In some cases, there was the potential for improvement due to fuel system
modifications and upgrades associated with meeting the fuel evaporative emission control
requirements EPA is considering.
46
-------
ATTACHMENT 1
EPA STATEMENT OF WORK
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Attachment 1 P-4
-------
ATTACHMENT 2
REFERENCE PHOTOGRAPHS OF PHASE 2 AND PROTOTYPE
PHASE 3 HARDWARE AT EPA
-------
FIGURE A2-1. STOCK BRIGGS QUANTUM SIDE VALVE COMPLETE ENGINE
FIGURE A2-2. STOCK BRIGGS QUANTUM
EUROPEAN CATALYTIC MUFFLER
Attachment 2 P-1
-------
FIGURE A2-3. STOCK BRIGGS QUANTUM SV CLOSE UP OF
FRONT OF EUROPEAN CATALYTIC MUFFLER
FIGURE A2-4. STOCK BRIGGS QU ANTUM SV CLOSE UP OF
BACK OF EUROPEAN CATALYTIC MUFFLER
Attachment 2 P-2
-------
FIGURE A2-5. STOCK BRIGGS QUANTUM SV EUROPEAN
CATALYTIC MUFFLER SHROUD
*
FIGURE A2-6. STOCK BRIGGS QUANTUM SV EUROPEAN
CATALYTIC MUFFLER INTERIOR
Attachment 2 P-3
-------
-
FIGURE A2-7. STOCK BRIGGS QUANTUM SV CENTER EUROPEAN
CATALYTIC MUFFLER INTERIOR WITH SUBSTRATE REMOVED
FIGURE A2-8. STOCK BRIGGS QUANTUM SV EUROPEAN
CATALYTIC MUFFLER SUPPLEMENTAL AIR VENTURI
Attachment 2 P-4
-------
FIGURE A2-9. STOCK HONDA GVC 160 WITHOUT MUFFLER
FIGURE A2-10. STOCK HONDA GVC 160 MUFFLER WITH SHROUD
Attachment 2 P-5
-------
FIGURE A2-11. EPA PROTOTYPE CATALYZED MUFFLER IN SHROUD
FOR HONDA GVC 160
FIGURE A2-12. EPA PROTOTYPE MUFFLER WITH EXHAUST GAS COOLING
AIR EJECTOR AROUND EXHAUST FOR HONDA GVC 160
Attachment 2 P-6
-------
FIGURE A2-13. EPA PROTOTYPE MUFFLER AIR EJECTION TUBE FOR
HONDA GVC 160
FIGURE A2-14. EPA PROTOTYPE MUFFLER CERAMIC SUBSTRATE
FOR HONDA GVC 160
Attachment 2 P-7
-------
FIGURE A2-15. TUBE CATALYST FOR INSERTION IN EXHAUST PORT
FIGURE A2-16. PROTOTYPE LOW CELL DENSITY METAL SUBSTRATE
CATALYST
Attachment 2 P-8
-------
FIGURE A2-17. WIRE MESH CATALYST IN MUFFLER
FIGURE A2-18. WIRE MESH CATALYST REMOVED FROM MUFFLER
Attachment 2 P-9
-------
FIGURE A2-19. STOCK HONDA GVC160 MOWER
FIGURE A2-20. BRIGGS 6.QUANTUM WITH BRIGGS EUROPEAN
CATALYZED MUFFLER
Attachment 2 P-10
-------
FIGURE A2-21. BRIGGS INTEK ENGINE WITH DUAL SUBSTRATE
EUROPEAN MUFFLER AND COOLING AIR DUCT
FIGURE A2-22. STOCK BRIGGS INTEK ENGINE WITH STOCK MUFFLER
Attachment 2 P-l 1
-------
FIGURE A2-23. STOCK TECUMSEH LV195BA
FIGURE A2-24. BRIGGS DUAL METALLIC SUBSTRATE EUROPEAN MUFFLER
ON TECUMSEH LV195BA
Attachment 2 P-12
-------
FIGURE A2-25. STOCK KAWASKI FH 601D INTAKE AIR
EKflRlA
FIGURE A2-26. STOCK KAWASAKI FH 601D MUFFLER
Attachment 2 P-13
-------
FIGURE A2-27. KAWASAKI FH 601D MUFFLER WITH AIR INJECTION
& CATALYST
FIGURE A2-28. TRIPLE PASS CATALYST WITH DOUBLE WALL
Attachment 2 P-14
-------
FIGURE A2-29. STOCK MUFFLER WITH INSERTED CATALYST
FIGURE A2-30. STOCK MUFFLER WITH INSERTED CATALYST
Attachment 2 P-l 5
-------
FIGURE A2-31.
HIGH EFFICIENCY DUAL CATALYST AHEAD OF MUFFLER
FIGURE A2-32. BRIGGS INTEK 31P777 SHOWING NO HEAD COOLING FINS
Attachment 2 P-16
-------
FIGURE A2-33. KOHLER CH26 WITH STOCK MUFFLER WITHOUT CATALYST,
WITH EFI WITH EGO SENSOR FEEDBACK
FIGURE A2-34. KOHLER CATALYZED MUFFLER FOR CH26 EFI ENGINE
WITH FEEDBACK EGO SENSOR
Attachment 2 P-l 7
-------
FIGURE A2-35. PROTOTYPE BRIGGS 31P777 INTEK WITH
OIL COOLER
FIGURE A2-36. PROTOTYPE BRIGGS 31P777 INTEK WITH AIR DUCTED
TO CATALYST MUFFLER
Attachment 2 P-l 8
-------
FIGURE A2-37. PROTOTYPE BRIGGS 31P777 INTEK CLOSE-UP OF ECU
& FUEL INJECTOR
FIGURE A2-38. STOCK BRIGGS 31P777 INTER ON RIDING MOWER
Attachment 2 P-19
-------
FIGURE A2-39. STOCK KOHLER CV490 RIDING MOWER
FIGURE A2-40. KOHLER CV490 RIDING MOWER WITH CATALYZED
MUFFLER & MODIFIED SHROUD COOLING & EFI
Attachment 2 P-20
-------
ATTACHMENT 3
NOTES ON CLASS II SOAK DATA FROM EPA
-------
Notes on Class II Soak Data from EPA
Table 3-1 shows muffler surface temperature data taken from thermal images of Class II
engines that were brought up to normal operating temperature and then shut down in order to
document the temperature over time. All catalysts tested met proposed Class II Phase 3
standards. Data from Table 3-1 and Figure 3-1, show that with proper selection of catalyst and
exhaust system engineering, the prototype Briggs & Stratton INTEK engine's maximum muffler
surface temperatures do not exceed stock exhaust temperatures. In addition, Figure 3-1 shows
that prototype exhaust hot soak temperature profiles can closely match those measured in the
stock configuration. The muffler with catalyst D showed the highest surface temperatures; it was
the most efficient and produced HC+NOx emission test results significantly below results from
tests using catalysts A and B.
Table A3 -1. Muffler Temperature Field Soak Data vs. Time
TEST CONFIGURATIONS
MAXIMUM OBSERVED TEMPERATURE, °C
Time, minutes from shutdown
0
1
2
3
4
5
6
Stock B&S Intek Plus
478
342
221
212
175
145
122
Prototype B&S EFI with Catalyst D
459
425
386
352
321
298
275
Prototype B&S EFI with Catalyst A
460
280
226
183
153
133
118
Prototype B&S EFI with Catalyst B
517
425
332
279
239
212
Stock Kohler CV490 with muffler
441
351
285
224
187
157
137
Prototype Kohler CV490 EFI with
Catalyst F
515
478
405
353
316
286
261
Prototype Kohler CV490 EFI with
Catalyst E
610
482
401
356
321
290
268
B&S INTEK Plus Stock Tractor (in-
chassis data)
265
221
179
157
94.3
87
Prototype B&S INTEK Plus EFI Tractor
with Catalyst D (in-chassis data)
138
144
149
145
138
135
133
Attachment 3 P-l
-------
B&S INTEK 31P777 Exhaust Soak Temperatures
600
500
rr 400
5 300
100
0
1
2
3
4
5
6
Stock B&S Intek Plus B&S EFI with Catalyst D
B&S EFI with Catalyst A B&S EFI with Catalyst B
FIGURE A3-1. TIME (MINUTES AFTER SHUTDOWN)
Figure 3-2 shows data from a B&S INTEK equipped tractor with a stock and a modified muffler
with catalyst D. Shrouding around the engine and exhaust system was modified in order to
control maximum surface temperatures while using catalyst D. Figure 3-2 shows that with
proper cooling system design, exposed surface temperatures can be much lower than current
non-catalyst designs, and that they remain below grass ignition temperatures (350-400 °C per
Attachment 13) during a hot soak.
Figure 3-3 shows surface temperature data from a Kohler CV490 in stock and modified muffler
configurations. The line for catalyzed muffler F indicates that maximum temperatures upon shut
down were 74 °C higher than the stock muffler, and maintained a -130 °C higher temperature
than stock during the soak. With catalysts F and E, the Kohler engine met the proposed Class II
Phase 3 standards.
The catalyst D data shown in Figure 3-2 and the catalyst A data in Figure 3-1 illustrate why
many failure modes in the FMEAs have lower probabilities of occurrence for Phase 3 engines
than for Phase 2 engines. However, there is also data in Table 3-1 and Figures 3-1 and 3-3 that
shows the need for sound engineering of Phase 3 designs.
Attachment 3 P-2
-------
B&S Field Test Soak Temperatures
(shroud and force-air cooling)
400
350
300
250
200
100
50
0
0
1
2
3
4
5
6
Time (min)
—B&S INTEK Plus Stock Tractor (in-chassis data)
B&S INTEK Plus EFI Tractor with Catalyst D (in-chassis data)
FIGURE A3-2. TIME (MINUTES AFTER SHUTDOWN)
Kohler CV490 Exhaust Soak Temperature
700
600
500
O
* 400
D
¦*—i
-------
ATTACHMENT 4
LIST OF STANDARDS REVIEWED FOR THE FMEA STUDY
-------
Ref.
Standard Ref.
Date
Title
Group
4-1
ANSI B175.1
January-00
Power Tools-Gasoline- Powered Chain Saws - Safety
Requirements
ACTV-CURR
4-2
ANSI B175.2
January-00
Power Tools-Hand-Held and Backpack, Gasoline-Engine-
Powered Blowers
ACTV-CURR
4-3
ANSI B175.3
January-03
Outdoor Power Equipment-Grass Trimmers and Bushcutters-
Safety Requirements
ACTV-CURR
4-4
ANSI B71.1
September-
05
Consumer Turf Care Equipment Walk-Behind Mowers and Ride-
On Machines with Mowers Safety Specifications
ACTV-CURR
4-5
ANSI B71.3
January-05
Snow Throwers - Safety Specifications
ACTV-CURR
4-6
ANSI B71.4
January-04
Commercial Turf Care Equipment - Safety Specifications
ACTV-CURR
4-7
ANSI B71.6
February-
00
Powered Shredder/Grinders,Shredder/Baggers, Chippers,and
Walk-Behind Chipper/Vacuums-Safety Specifications
ACTV-CURR
4-8
ANSIB71.7
January-85
Powered Log Splitters - Safety Specifications
INAC-WDRN
4-9
ANSIB71.8
January-96
Outdoor Power Equipment - Walk-Behind Powered Rotary Tillers
and Hand Supported Cultivators - Safety Specifications
ACTV-CURR
4-10
SAE J997
SAE J997 Spark Arrester Test Carbon (establishes physical
properties required of SAE Coarse Test Carbon and SAE Fine
Test Carbon)
SAE
4-11
SAE J350
January-91
SAE J350 Spark Arrester Test Procedure for Medium Size
Engines (motorcycles, highway trucks, agricultural tractors,
industrial tractors
SAE
4-12
SAE J335
June-95
Multiposition Small Engine Exhaust System Fire Ignition
Suppressions
SAE
4-13
EEC Council Directive
December-
78
EEC Council Directive of 19 Dec 1978 - noise emission of
construction plant and equipment
EEC
4-14
EEC Council Directive
September-
84
EEC Council Directive of 17 Sept 1984 - permissible sound
power levels of lawnmowers
EEC
4-15
EEC Council Directive
April-87
EEC Council Directive of 7 April 1987 - amendment to 17 Sept
1984 (adapting to technical progress)
EEC
4-16
ASAE S440.3
March-05
Safety for Powered Lawn and Garden Equipment
ASAE
4-17
16 CFR 1205
January-05
Safety for Walk-behind Power Lawn Mowers
CFR
Attachment 4 P-l
-------
Ref.
Standard Ref.
Date
Title
Group
4-18
PMS 430-1 NFES #1363
June-02
Spark Arrester Guide - General Purpose and Locomotive
(GP/Loco)
National Wildfire
Coordinating Group
4-19
PMS 430-2 NFES #2363
June-03
Spark Arrester Guide - Muitiposition Small Engines (MSE)
National Wildfire
Coordinating Group
4-20
5100-Fire Management
9151 1801
April-91
Fire Investigation Procedure For Multipurpose Small Engines
&General Purpose Spark Arrester Exhaust Systems
USDA - Forest Service
4-21
5100-Fire Management
0551 1803-SDTDC
July-05
Manufacturer Submission Procedure for the Qualification
Testing of General-purpose, Screen, and Locomotive Spark
Arrester Exhaust Systems
USDA - Forest Service
4-22
5100-Fire Management
9151 1804
August-91
Standard Test Procedure for Chain Saw Spark Arrester
Exhaust Systems
USDA - Forest Service
4-23
5100-Fire Management
9951 1805-SDTDC
August-99
Standard Test Procedure for General Purpose Spark Arresters
USDA - Forest Service
4-24
5100-Fire Management
9151 1202
January-91
Spark Arrester Test Carbon Replacement Study - Final
Report
USDA - Forest Service
4-25
Fire Management Tech
Tips
5100 0351 1304-SDTDC
May-03
An Introduction to Spark Arrestors: Spark Arresters and the
Prevention of Wildland Fires
USDA - Forest Service
Technology &
Development Program
4-26
Fire Management Tech
Tips
5100 0351 1305-SDTDC
May-03
Muitiposition Small-Engine Spark Arresters: Spark Arresters
and the Prevention of Wildland Fires
USDA - Forest Service
Technology &
Development Program
4-27
Fire Management Tech
Tips
5100 0351 1306-SDTDC
May-03
General-Purpose Spark Arresters: Spark Arresters and the
Prevention of Wildland Fires
USDA - Forest Service
Technology &
Development Program
4-28
Fire Management Tech
Tips
5100 0351 1307-SDTDC
May-03
Off-Highway Vehicle Spark Arrestors: Spark Arresters and the
Prevention of Wildland Fires
USDA - Forest Service
Technology &
Development Program
4-29
RFQ-R5-15-03-073
April-91
Fire Plan for Construction and Service Contracts (Attachment
to Contract) (Ref: FSH 6309.32 and 6309.11)
USDA - Forest Service
A-30
SDTDC
Fire Investigation Report
Forest Service
4-31
515-MW-01
December-05
Specification for Mowers, Power, Rotary, Walk-Behind
Texas Specification
Attachment 4 P-2
-------
Ref.
Standard Ref.
Date
Title
Group
4-32
ANSI C 1055-03
Standard Guide for Heated System Surface Conditions that
Produce Contact Burns
ANSI
4-33
UL 1602
Gasoline Engine Powered, Rigid Cutting-Member Edgers and
Edger Trimmers
UL
4-34
ISO 5395:1900 (E)
Powered Lawn-mowers, Lawn Tractors, Lawn and Garden
Tractors, Professional Mowers, and Lawn and Garden
Tractors with Mowing Attachments - Definitions, Safety
Requirements and Test Procedures. Section 2.2.3 Heat
Protection
ISO
Attachment 4 P-3
-------
ATTACHMENT 5
EXAMPLE: A TYPICAL FMEA REPORT FORMAT
-------
System: Phase 3 (vs. Phase 2), Small Off Road Engines ( Subsystem: Exhaust,
Class I and II Lawn Mowers)
Component: Manifold
Item Selected: gasket
Item Function Selected: 1. seals
0
c
c
u
r
Current
Design
Control
PREVENT
IONS
Current
Design
Control
DETECT
IONS
D
e
t
e
c
R
Recommendations
Action Results
Potential
Failure
Modes
Potential
Effect(s)
of
Failure
S
e
V
Potential
Cause /
Mechanism
of Failure
P
N
Recommendation
Resp
Target
Completion
Date
Actions
Taken
Effect
Date
S
e
V
0
c
c
u
r
D
e
t
e
c
R.P.N.
%
Reduc
tion
Attachment 5 P-l
-------
ATTACHMENT 6
EXAMPLE: THE MODIFIED FMEA REPORT FORMAT USED
IN W.A. 1-10
-------
EXAMPLE: Modified DESIGN FMEA Format
Item Selected: LBffiSlEllflillEfl
Item Function Selected: 1. filter air
Subsystem: Catalyst System Control Volume
Component: Intake, Cooling Air, Power
Cylinder, Exhaust, Block, Equipment
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s)
of Failure
Classification of
Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
Difference in
RPN (Phase 3
vs. Phase 2)
Notes
noise
4_Other
3
3
9
6
3
2
3
EPA demonstrated that the backfire incidence was
significantly reduced with the addition of a catalyst. jhat
fact drives a reduction in the Occurrence ranking.
Degradation or tear of
filter element, wrong
filter or dirty or missing
filter. Prefilter not oiled
richer mixture
backfire
flame out of muffler
4_Other
4
3
12
8
4
2
4
In this case it is assumed that a momentary flame does
not cause a safety issue. EPA demonstrated that the
backfire incidence was significantly reduced with the
addition of a catalyst. That fact drives a reduction in the
Occurrence ranking.
fire or burn
1_Safety
10
3
30
20
10
2
10
A backfire could cause a fire or burn. However, EPA
demonstrated that the backfire incidence was significantly
reduced with the addition of a catalyst. That fact drives a
reduction in the Occurrence ranking.
Degradation or tear of
filter element, wrong
filter or dirty or missing
filter. Prefilter not oiled
leaner mixture
hotter exhaust
no effect
4_Other
1
3
3
3
1
3
0
The rankings are expected to be the same with or without
a catalyst.
Attachment 6 P-l
-------
ATTACHMENT 7
REPRESENTATION OF THE CATALYST CONTROL VOLUME
-------
Heat In / Out of the
CV (conduction,
convection, radiation)
AMBIENT AIR IN/
OUT of the CV
Cooling Air (fan, shrouds, vanes,etc)
Ignition System: (spark plug, coil,
points, wires)
Air from
control
Volume
V
Intake
(air filter, carburetor,
fuel feed,intake port,
intake valve...)
Power Cylinder
(piston, rings,
head, block,
crankcase, crank,
Exhaust
(exh valve, port, seals,
attachments, muffler,
spark arrester,
supplemental air)
Equipment (mower deck, fuel tank,
controls)
~
Exhaust into the
Control Volume
4
System Control
Volume Boundary
Fuel and oil vapors
into and out of the CV
Attachment 7 P-l
-------
ATTACHMENT 8
CLASS I DESIGN FMEA REPORT
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Selected: fl
Item Function Selected: 1. filter air
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
richer mixture
backfire
noise
4_Other
3
3
9
6
3
2
3
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a properly designed catalyzed muffler system. That fact drives a reduction
in the Occurrence ranking.
flame out of muffler
4_Other
4
3
12
8
4
2
4
In this scenario, a momentary flame does not cause a safety issue,
demonstrated that the backfire incidence was significantly reduced with the addition
of a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
fire or burn
1_Safety
10
3
30
20
10
2
10
In this scenario, the backfire is of such intensity that it can cause a fire or burn. EPA
demonstrated that the backfire incidence was significantly reduced with the addition
of a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
Prefilter not oiled
leaner mixture
hotter exhaust
no effect
4_Other
1
3
3
3
1
3
0
The rankings are the same with or without a catalyst.
muffler failure (crack,
oxidation, breakage,
internal damage)
3_Performance
6
3
18
18
6
3
0
Mechanical failure caused by excessive temperature. The rankings are the same
with or without a catalyst. The effect could be mitigated by the presence of a thermal
switch.
engine failure (internal
component seizure,
broken valve or spring,
excess wear)
3_Performance
8
3
24
24
8
3
0
Engine failure caused by excessive combustion temperatures. This is considered to
be a failure of the engine contained to internal components and does not put the user
at risk. The rankings are the same with or without a catalyst. The effect could be
mitigated by the presence of a thermal switch.
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because there will be no
increase in burn risk with the application of a properly designed catalyzed muffler
system. The effect could be mitigated by the presence of a thermal switch.
catalyst overheats and
fails (substrate cracks,
washcoat spalling,
noble metal sintering,
alumina phase
change, crystallite
growth)
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
Attachment 8 P-l
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
2. carburetor system
Item Selected: [
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer mixture
backfire
noise
4_Other
3
5
15
12
3
4
3
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a properly designed catalyzed muffler system. That fact drives a reduction
in the Occurrence ranking.
flame out of muffler
4_Other
4
5
20
16
4
4
4
In this case it is expected that a momentary flame does not cause a safety issue.
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a properly designed catalyzed muffler system. That fact drives a reduction
in the Occurrence ranking.
fire or burn
1_Safety
10
5
50
40
10
4
10
In this scenario, the backfire is of such intensity that it can cause a fire or burn. EPA
demonstrated that the backfire incidence was significantly reduced with the addition
of a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer mixture
cooler exhaust
and catalyst
no effect
4_Other
1
5
5
5
1
5
0
The rankings are the same with or without a catalyst.
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer mixture
engine power
loss
degraded performance
3_Performance
5
5
25
25
5
5
0
The rankings are the same with or without a catalyst.
too many primer
bulb pumps
richer mixture
engine stalls
Nuisance to customer.
3_Performance
4
6
24
24
4
6
0
The rankings are the same with or without a catalyst.
Attachment 8 P-2
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
2. carburetor system
Item Selected: \
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Restriction in fuel
passages, wrong
jets in production,
or choke stuck
open, or
production
variability.
leaner mixture
engine won't
start
inoperable and needs
repair
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed or
production
variability
richer mixture
engine won't
start
inoperable
3_Performance
8
5
40
40
8
5
0
The rankings are the same with or without a catalyst.
stuck choke
(open)
leaner mixture
engine won't
start
inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
crack primer bulb
leaner mixture
engine won't
start
inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
Attachment 8 P-3
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
2. carburetor system
Item Selected: [
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Restriction in fuel
passages, wrong
jets in production
or production
variability
leaner mixture
higher
temperature in
engine and
catalyst
no effect
4_Other
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
muffler failure (crack,
oxidation, breakage,
internal damage)
3_Performance
6
4
24
24
6
4
0
Mechanical failure caused by excessive temperature. The rankings are the same
with or without a catalyst. The effect could be mitigated by the presence of a thermal
switch.
engine failure (internal
component seizure,
broken valve or spring,
excess wear)
3_Performance
8
4
32
32
8
4
0
Engine failure caused by excessive combustion temperatures. The rankings are the
same with or without a catalyst. The effect could be mitigated by the presence of a
thermal switch.
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. Any effect that the catalyst
might have on temperature level is offset by the expected improvements in air cooling
of the manifold system on Phase 3 products. The effect could be mitigated by the
presence of a thermal switch.
catalyst overheats and
fails (substrate cracks,
washcoat spalling,
noble metal sintering,
alumina phase
change, crystallite
growth)
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
Attachment 8 P-4
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
2. carburetor system
Item Selected: [
Item Function Selected: 2. throttles the air
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Throttle shaft
wear
significant air
leak around
shaft
degraded load
control
degraded performance
3_Performance
4
3
12
12
4
3
0
The rankings are the same with or without a catalyst.
Throttle shaft
wear
butterfly /
linkage failure
lack of load
control
engine will only idle
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
Throttle shaft
wear
slight air leak
around shaft
leaner mixture
no effect
4_Other
1
3
3
3
1
3
0
The rankings are the same with or without a catalyst.
Item Selected:
Item Function Selected: 3. stores fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
gasket failure, or
needle valve
stuck open, or
cracked primer
bulb
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
engine dies due
to lack of fuel or
excess of fuel
engine inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
gasket failure, or
needle valve
stuck open, or
cracked primer
bulb
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because exposed muffler
temperatures are nominally equivalent. Fuel can be ignited by hot surfaces or the
ignition system.
gasket failure, or
needle valve
stuck open, or
cracked primer
bulb
leakage of fuel
to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel puddles
no effect
4_Other
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
needs repair
3_Performance
5
4
20
20
5
4
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst because exposed muffler
surfaces have been shown to be nominally equivalent in Phase 2 (no catalyst) and
Phase 3 (catalyzed) prototype systems.
Attachment 8 P-5
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Selected: EHflTOffiCT
Item Function Selected: 1. controls engine speed and load
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
malfunctioning
governor
closed governor
prevents the
engine from
making power
equipment inoperable
3_Performance
8
4
32
32
8
4
0
Insufficient power available to perform the job. The rankings are the same with or
without a catalyst.
None
malfunctioning
governor
open governor
causes engine
overs peed
higher exhaust
temperatures
3_Performance
2
2
4
4
2
2
0
The rankings are the same with or without a catalyst.
engine failure (internal
component seizure,
broken valve or spring,
excess wear)
3_Performance
9
2
18
18
9
2
0
Engine failure caused by overspeed. The rankings are the same with or without a
catalyst.
catastrophic failure
(potential injury due to
flying parts)
1_Safety
10
2
20
20
10
2
0
Engine failure caused by overspeed. The rankings are the same with or without a
catalyst.
None
malfunctioning
governor
poor load
control
degraded engine
performance
3_Performance
6
5
30
30
6
5
0
The rankings are the same with or without a catalyst.
Item Selected:
Item Function Selected: 1. Transfer the air /fuel mixture to the intake valve
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Crack or leak in
manifold
leaner mixture
catalyst
overheats and
fails (substrate
cracks,
wash coat
spalling, noble
metal sintering,
alumina phase
change,
crystallite
growth)
loss of emission
control
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
Attachment 8 P-6
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
4. intake manifold, port, valve and seals
Item Selected: \
Item Function Selected: 1. Transfer the air / fuel mixture to the intake valve
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Crack or leak in
manifold
leaner mixture
change in
power
degraded engine
performance
3_Performance
4
9
36
20
4
5
16
The lower occurrence for Phase 3 is due to the improvement of the manifold system
for Phase 3 products.
no effect
4_Other
1
9
9
4
1
4
5
The lower occurrence for Phase 3 is due to the expected improvement of the manifold
system for Phase 3 products.
Crack or leak in
manifold
engine, exhaust
system and
catalyst run
hotter
muffler failure
3_Performance
6
9
54
24
6
4
30
The lower occurrence for Phase 3 is due to the expected improvement of the manifold
system for Phase 3 products. The effect could be mitigated by the presence of a
thermal switch.
leaner mixture
engine failure
3_Performance
8
9
72
32
8
4
40
The lower occurrence for Phase 3 is due to the expected improvement of the manifold
system for Phase 3 products. The effect could be mitigated by the presence of a
thermal switch.
fire or burn
1_Safety
10
9
90
40
10
4
50
The lower occurrence for Phase 3 is due to the expected improvement of the manifold
system for Phase 3 products. The effect could be mitigated by the presence of a
thermal switch.
Crack or leak in
manifold
leaner mixture
engine failure
(internal
component
seizure, broken
valve or spring,
excess wear)
inoperable
3_Performance
8
3
24
16
8
2
8
The lower occurrence for the Phase 3 is due to the improvement of the manifold
system for Phase 3 products. The effect could be mitigated by the presence of a
thermal switch.
Crack or leak in
manifold
leaner mixture
engine stalls
inoperable
3_Performance
8
4
32
24
8
3
8
The lower occurrence for Phase 3 is due to the improvement of the manifold system
for Phase 3 products.
None
damaged
valve
leaky intake
valve
power loss
3_Performance
5
4
20
15
5
3
5
The lower Phase 3 occurrence due to the improved Phase 3 cooling and fuel control,
which could reduce cases of excessive temperature that could damage valves.
leaky intake
manifold gasket
head gasket
failure
loss of
compression
degraded engine
performance
3_Performance
7
8
56
35
7
5
21
The lower Phase 3 occurrence due to the improved Phase 3 cooling and fuel control,
which could reduce cases of excessive temperature that could damage the manifold
and head gasket.
Attachment 8 P-7
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
5. block, power head
Item Selected: fj
Item Function Selected: 1. Produces power
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Higher thermal
load
higher engine
temperatures
engine failure
(internal
component
seizure, broken
valve or spring,
excess wear)
inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
catastrophic failure
(potential injury due to
flying parts)
1_Safety
9
4
36
36
9
4
0
Engine failure caused by excessive temperatures. The rankings are the same with or
without a catalyst. The effect could be mitigated by the presence of a thermal switch.
fire or burn
1_Safety
10
4
40
40
10
4
0
Engine failure can result in contact with hot metal or fluids. The rankings are the
same with or without a catalyst. The effect could be mitigated by the presence of a
thermal switch.
None
ring, cylinder
or valve wear
or leakage
increased oil
consumption
catalyst poisoning due
to lubricant
components
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
None
ring, cylinder
or valve wear
or leakage
increased oil
consumption
smoke
3_Performance
3
9
27
27
3
9
0
The rankings are the same with or without a catalyst.
no effect
4_Other
1
9
9
9
1
9
0
The rankings are the same with or without a catalyst.
6. exhaust valve and seal
Item Selected: [
Item Function Selected: 1. seal combustion chamber
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Burn or warped
valve
head warpage
engine damage
inoperable
3_Performance
8
3
24
24
8
3
0
The rankings are the same with or without a catalyst.
higher exhaust and
catalyst temperature
3_Performance
4
4
16
12
4
3
4
Valve leakage permits hot cylinder gases to escape into exhaust system. The lower
Phase 3 occurrence ranking is due to the Phase 3 improved design and/or materials.
The effect could be mitigated by the presence of a thermal switch.
Excessive engine
temperature or
wear
burned or
valve leakage
backfire
3_Performance
5
4
20
15
5
3
5
The lower Phase 3 occurrence due to the Phase 3 improved cooling and fuel control
which would reduce cases of excessive temperature that would damage valves.
warped valve
lower power
3_Performance
5
4
20
15
5
3
5
The lower Phase 3 occurrence due to the Phase 3 improved cooling and fuel control
which would reduce cases of excessive temperature that would damage valves.
allow unburned fuel
and oil to reach the
catalyst
2_Regulatory
1
1
1
27
9
3
-26
The lower Phase 3 occurrence due to the Phase 3 improved cooling and fuel control
which would reduce cases of excessive temperature that would damage valves.
Attachment 8 P-8
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
7. exhaust manifold, muffler, muffler shroud and gaske
Item Selected: [
Item Function Selected: 1. seals exhaust and directs exhaust and muffles noise
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
loosening of
muffler,
manifold or
failed gasket
(gasket is less
common on
Class I vertical
shaft engines)
exhaust leak
increased emissions
2_Regulatory
1
6
6
36
9
4
-30
The RPN difference is due to the regulatory requirement of Phase 3 and the
increased severity. Also, the lower occurrence for the Phase 3 is due to the improved
exhaust system design.
increased noise
3_Performance
6
6
36
24
6
4
12
The lower occurrence for the Phase 3 is due to the improved design of the engine.
fire or burn
1_Safety
10
6
60
40
10
4
20
The lower Phase 3 occurrence is due to the Phase 3 improved exhaust system
design.
heat surrounding
components reducing
their durability
3_Performance
4
6
24
16
4
4
8
The lower occurrence for the Phase 3 is due to the improved design of the engine.
Debris
accumulation
reduction in
engine cooling
and increased
muffler
temperatures
ignition of debris
adjacent to
muffler
fire
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the improvement of the air ducting for
cooling and control of debris accumulation. In addition, fan inlet screens are
expected on all Phase 3 engines. The failure mode could be mitigated by the
presence of a thermal switch.
None
removal or
mechanical
failure
loss of muffler
shroud
fire or burn
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the improvement of the air ducting for
cooling and shroud design.
Item Selected:
Item Function Selected: 1. provides supplemental air to catalyst and leans the mixture
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
cracks in
supplemental
air system
mechanical
failure
reduced supplemental
air and catalyst
performance
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
None
external
debris
system plugs
reduced supplemental
air and catalyst
performance
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Attachment 8 P-9
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Selected:
Item Function Selected: 1. reduce emissions (HC NOx CO)
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Lean mixture or
engine overspeed
excessive
catalyst
temperatures
catalyst
overheats and
fails (substrate
cracks,
wash coat
spalling, noble
metal sintering,
alumina phase
change,
crystallite
growth)
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
increased engine back
pressure with
degraded performance
3_Performance
1
1
1
6
3
2
-5
The performance change is small. The failure mode could be mitigated by the
presence of a thermal switch.
Engine wear
release of
engine
metallic debris
catalyst plugs
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
increased engine back
pressure
3_Performance
1
1
1
6
3
2
-5
The performance change is small.
Rich mixture
soot coats
catalyst
deactivates
catalyst
increased emissions
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
excessive
catalyst
performance
reduced emissions
3_Performance
1
1
1
2
1
2
-1
The performance change is small.
slightly higher
temperatures
3_Performance
1
1
1
2
1
2
-1
The performance change is small.
fire or burn
1_Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential safety impact. The effect could
be mitigated by the presence of a thermal switch.
Manufacturing,
material problem
or vibration
catalyst mat
failure
mechanical
failure of
ceramic
monolith
catalyst
increased emissions
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
change engine back
pressure
3_Performance
1
1
1
9
3
3
-8
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks higher due to the catalyst being present.
Engine wear
excessive
lubricant
consumption
poison
deactivation due
to lubricant
components
increased emissions
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks higher due to the potential regulatory non-compliance.
Replicates failure modes from power cylinder rankings.
Attachment 8 P-10
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Selected:
Item Function Selected: 1. reduce emissions (HC NOx CO)
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
Manufacturing or
supplier problem
defective or
wrong catalyst
poor catalyst
performance
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Fuel or ignition
system
malfunction
increased
thermal load
from catalyst
potential
damage to
engine, catalyst
or components
poor performance
3_Performance
1
1
1
18
6
3
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks higher due to the catalyst being present. The failure
mode could be mitigated by the presence of a thermal switch.
reduced engine
durability
3_Performance
1
1
1
18
6
3
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks higher due to the catalyst being present. The failure
mode could be mitigated by the presence of a thermal switch.
engine failure
3_Performance
1
1
1
24
8
3
-23
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks higher due to the catalyst being present. The failure
mode could be mitigated by the presence of a thermal switch.
Item Selected:
Item Function Selected: 1. Provides cooling air to engine and components
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
material
failure or
loose bolt
fan / flywheel
fails
engine stops
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
engine overheats and
stalls
3_Performance
7
2
14
14
7
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
loss of cooling
to engine block
and muffler
system
burn risk
1_Safety
9
2
18
9
9
1
9
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
None
cooling
system shroud
failed
engine failure
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
hotter engine
3_Performance
1
2
2
2
1
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
higher exhaust surface
temperatures
3_Performance
1
2
2
2
1
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated
by the presence of a thermal switch.
Attachment 8 P-l 1
-------
Class I Design FMEA
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Selected:
Item Function Selected: 1. Provides cooling air to engine and components
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
engine overheats and
stalls
3_Performance
5
5
25
20
5
4
5
By definition of the Phase 3 product, the improved design features for Phase 3
results in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
engine failure
3_Performance
8
5
40
32
8
4
8
By definition of the Phase 3 product, the improved design features for Phase 3
results in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
None
plugging of
cooling
passages due
to debris
reduction of
engine cooling
burn risk
1_Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design features for Phase 3
results in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
hotter engine
3_Performance
1
5
5
4
1
4
1
By definition of the Phase 3 product, the improved design features for Phase 3
results in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
higher exhaust surface
temperatures
3_Performance
1
5
5
4
1
4
1
By definition of the Phase 3 product, the improved design features for Phase 3
results in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
Item Selected:
Item Function Selected: 1. provides timed spark
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
plug bad, short in
plug wire, failed
coil, loose
flywheel,
magneto
loss of spark
backfire (misfire)
noise
3_Performance
3
6
18
12
3
4
6
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a catalyst. That fact drives a reduction in the Occurrence ranking.
Flame out of muffler
3_Performance
4
6
24
16
4
4
8
In this scenario, a momentary flame does not cause a safety issue,
demonstrated that the backfire incidence was significantly reduced with the addition
of a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
fire or burn
1_Safety
10
6
60
40
10
4
20
In this scenario, the backfire is of such intensity that it can cause a fire or burn. EPA
demonstrated that the backfire incidence was significantly reduced with the addition
of a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
Attachment 8 P-12
-------
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Item Function Selected: 1. provides timed spark
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
weak or
intermittent
spark
excessive
catalyst
temperatures
catalyst overheats and
fails (substrate cracks,
washcoat spalling,
noble metal sintering,
alumina phase
change, crystallite
growth)
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module failure
loss of spark
engine stalls and
unburned fuel pumped
through engine
resulting in high
catalyst temperatures
3_Performance
7
5
35
24
8
3
11
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products.
engine stalls and won't
run
3_Performance
8
5
40
24
8
3
16
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products.
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module failure
spark timing
changes
engine stalls and won't
run
3_Performance
8
4
32
16
8
2
16
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products.
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module failure
weak or
intermittent
spark (misfire)
degraded engine
performance
3_Performance
6
5
30
18
6
3
12
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products.
potentially higher
muffler / catalyst
temperatures
3_Performance
2
5
10
9
3
3
1
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products. The effect could be mitigated by the presence of a thermal switch.
engine stalls and won't
run
3_Performance
8
5
40
24
8
3
16
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products.
excessive muffler or
catalyst temperatures
and increased burn
risk
1_Safety
9
5
45
27
9
3
18
The lower occurrence for the Phase 3 is due to the improved ignition system for
Phase 3 products. The effect could be mitigated by the presence of a thermal switch.
Attachment 8 P-13
-------
Class I Design FMEA
Item Selected:
Item Function Selected: 1. Contains fuel and conveys to engine
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph 2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Notes
None
leak of tank or
fuel leaks on hot
needs repair
3_Performance
5
4
20
15
5
3
5
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
line
component
fire or burn
1_Safety
10
4
40
30
10
3
10
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
High muffler or
catalyst
temperatures
near fuel lines
Fuel tank or
line melted
fuel leaks on hot
component
needs repair
3_Performance
5
2
10
10
5
2
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst. The exposed muffler
temperatures are nominally equivalent.
needs repair
3_Performance
5
5
25
20
5
4
5
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
None
leak of tank or
line
fuel puddles
fire or burn
1_Safety
10
5
50
40
10
4
10
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
operator fuel exposure
1_Safety
9
5
45
36
9
4
9
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
needs repair
3_Performance
5
3
15
10
5
2
5
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
High muffler or
catalyst
temperatures
near fuel lines
Fuel tank or
line melted
fuel puddles
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
operator fuel exposure
1_Safety
9
3
18
18
9
2
9
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
Phase 2 versus Phase 3, Small Off-Road Engines,
Class I, Walk-behind Lawn Mowers
Attachment 8 P-14
-------
ATTACHMENT 9
CLASS II DESIGN FMEA REPORT
-------
Item Function Selected: 1. filter air
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
noise
4_Other
3
2
6
6
3
2
0
The rankings are the same with or without a catalyst.
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
richer mixture
backfire
Flame out of muffler
4_Other
4
2
8
8
4
2
0
In this scenario, a momentary flame does not cause a safety issue. FpA
demonstrated that the backfire incidence was significantly reduced with the addition of
a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
fire or burn
1_Safety
10
2
20
20
10
2
0
In this scenario, the backfire is of such intensity that it can cause a fire or burn. Fp»
demonstrated that the backfire incidence was significantly reduced with the addition of
a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
no effect
4_Other
1
3
3
3
1
3
0
The rankings are the same with or without a catalyst.
muffler failure (crack,
oxidation, breakage,
internal damage)
3_Performance
6
3
18
18
6
3
0
Mechanical failure caused by excessive temperature. The rankings are the same with
or without a catalyst. The effect could be mitigated by the presence of a thermal
switch.
Degradation or
tear of filter
element, wrong
filter or dirty or
missing filter.
leaner mixture
hotter exhaust
engine failure (internal
component seizure,
broken valve or
spring, excess wear)
3_Performance
8
3
24
24
8
3
0
Engine failure caused by excessive combustion temperatures. This is considered to
be a failure of the engine contained to internal components and does not put the user
at risk. The rankings are the same with or without a catalyst. The effect could be
mitigated by the presence of a thermal switch.
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because there will be no increase
in fire or burn risk with the application of a properly designed catalyzed muffler system.
The effect could be mitigated by the presence of a thermal switch.
Catalyst overheats
and fails (substrate
cracks, washcoat
spalling, noble metal
sintering, alumina
phase change,
crystallite growth)
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
Attachment 9 P-l
-------
2. carburetor or fuel injection system
Item Selected: \
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
no effect
4_0ther
1
3
3
3
1
3
0
The rankings are the same with or without a catalyst.
Restriction in fuel
passages, wrong
jets in production,
muffler failure (crack,
oxidation, breakage,
internal damage)
3_Performance
6
3
18
18
6
3
0
Mechanical failure caused by excessive temperature. The rankings are the same with
or without a catalyst. The effect could be mitigated by the presence of a thermal
switch.
open, or
production
variability. Fuel
injection system
fuel pump or fuel
leaner mixture
higher
temperature in
engine failure (internal
component seizure,
broken valve or
spring, excess wear)
3_Performance
8
3
24
24
8
3
0
Engine failure caused by excessive combustion temperatures. The rankings are the
same with or without a catalyst. The effect could be mitigated by the presence of a
thermal switch.
regulator failure.
Fuel filter or
injector
restriction.
engine and
Catalyst
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst. Any effect that the catalyst
might have on temperature level is offset by the expected improvements in air cooling
of the manifold system on Phase 3 products. If the change in temperature is
significant the effect could be mitigated by the presence of a thermal switch.
Injector wiring
connection
degraded. MAP,
ECM, or 02
sensor failure.
Catalyst overheats
and fails (substrate
cracks, washcoat
spalling, noble metal
sintering, alumina
phase change,
crystallite growth)
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
Attachment 9 P-2
-------
2. carburetor or fuel injection system
Item Selected: \
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Restriction in fuel
passages, wrong
jets in production,
or choke stuck
open, or
production
variability. Fuel
injection system
fuel pump or fuel
pressure
regulator failure.
Fuel filter or
injector
restriction.
Injector wiring
connection
degraded. MAP,
ECM, or 02
sensor failure.
leaner mixture
engine won't
start
inoperable and needs
repair
3_Performance
8
3
24
24
8
3
0
The rankings are the same with or without a catalyst.
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed, or
production
variability. Fuel
noise
4_0ther
3
4
12
9
3
3
3
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a properly designed catalyzed muffler system. That fact drives a reduction
in the Occurrence ranking.
richer mixture
backfire
Flame out of muffler
4_0ther
4
4
16
12
4
3
4
In this case it is expected that a momentary flame does not cause a safety issue.
EPA demonstrated that the backfire incidence was significantly reduced with the
addition of a properly designed catalyzed muffler system. That fact drives a reduction
in the Occurrence ranking.
injection fuel
system fuel
pressure
regulator failure.
Fuel injector
stuck open. MAP,
ECM, 02 sensor
failure.
fire or burn
1_Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can cause a fire or burn. Fp»
demonstrated that the backfire incidence was significantly reduced with the addition of
a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
Attachment 9 P-3
-------
2. carburetor or fuel injection system
Item Selected: \
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed, or
production
variability. Fuel
injection fuel
system fuel
pressure
regulator failure.
Fuel injector
stuck open. MAP,
ECM, 02 sensor
failure.
richer mixture
cooler exhaust
and catalyst
no effect
4_0ther
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed, or
production
variability. Fuel
injection fuel
system fuel
pressure
regulator failure.
Fuel injector
stuck open. MAP,
ECM, 02 sensor
failure.
richer mixture
engine power
loss
degraded
performance
3_Performance
5
4
20
20
5
4
0
The rankings are the same with or without a catalyst.
Attachment 9 P-4
-------
2. carburetor or fuel injection system
Item Selected: \
Item Function Selected: 1. mixes the air and fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Float breaks,
debris in float
needle, or wrong
jets in production,
choke stuck
closed, or
production
variability. Fuel
injection fuel
system fuel
pressure
regulator failure.
Fuel injector
stuck open. MAP,
ECM, 02 sensor
failure.
richer mixture
engine won't
start
inoperable and needs
repair
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
None
wear, wiring
short, age of
pump
fuel pump failure
inoperable and needs
repair
3_Performance
8
3
24
24
8
3
0
The rankings are the same with or without a catalyst.
Item Selected:
Item Function Selected: 2. throttles the air
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Throttle shaft
wear
butterfly /
linkage failure
lack of load
control
engine will only idle
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
Throttle shaft
wear
significant air
leak around
shaft
degraded load
control
degraded
performance
3_Performance
4
2
8
8
4
2
0
The rankings are the same with or without a catalyst.
Throttle shaft
wear
slight air leak
around shaft
leaner mixture
no effect
4_0ther
1
2
2
2
1
2
0
The rankings are the same with or without a catalyst.
Attachment 9 P-5
-------
2. carburetor or fuel injection system
Item Selected: I
Item Function Selected: 3. stores fuel
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
gasket failure, or
needle valve
stuck open, or
fuel
pump/ regulator
leak
leakage of
fuel to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
fuel ignites
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst because exposed muffler
temperatures are nominally equivalent. Fuel can be ignited by hot surfaces or the
ignition system.
gasket failure, or
needle valve
stuck open, or
fuel
pump/regulator
leak
leakage of
fuel to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
engine stalls
inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
gasket failure, or
needle valve
stuck open, or
fuel
pump/regulator
leak
leakage of
fuel to mower
deck, air filter
or elsewhere
(i.e. out of air
filter)
Fuel puddles
no effect
4_Other
1
3
3
3
1
3
0
The rankings are the same with or without a catalyst.
needs repair
3_Performance
5
3
15
15
5
3
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
3
30
30
10
3
0
The rankings are the same with or without a catalyst because exposed muffler
surfaces have been shown to be nominally equivalent in Phase 2 (no catalyst) and
Phase 3 (catalyzed) prototype systems.
ECM failure,
solenoid return
spring breakage
causes fuel cutoff
solenoid open
failure
fuel flow into
and from
engine
fuel puddles
needs repair
3_Performance
5
4
20
20
5
4
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst.
ECM failure,
solenoid return
spring breakage
causes fuel cutoff
solenoid open
failure
fuel flow into
and from
engine
floods engine
inoperable/ needs
repair
3_Performance
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
None
fuel cutoff
solenoid fails
closed during
operation
engine shuts off
inoperable/ needs
repair
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
Attachment 9 P-6
-------
Item Selected: ETTTWTTTTi
Item Function Selected: 1. controls engine speed and load
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
malfunctioning
governor
open governor
causes engine
overspeed
higher exhaust
temperatures
3_Performance
2
2
4
4
2
2
0
The rankings are the same with or without a catalyst. This is not a significant
overspeed condition.
engine failure (internal
component seizure,
broken valve or
spring, excess wear)
3_Performance
9
2
18
18
9
2
0
Engine failure caused by overspeed. The rankings are the same with or without a
catalyst.
catastrophic failure
(potential injury due to
flying parts)
1_Safety
10
2
20
20
10
2
0
Engine failure caused by overspeed. The rankings are the same with or without a
catalyst.
None
malfunctioning
governor
closed governor
prevents the
engine from
making power
equipment inoperable
and needs repair
3_Performance
8
3
24
24
8
3
0
Insufficient power available to perform the job. The rankings are the same with or
without a catalyst.
None
malfunctioning
governor
poor load control
degraded engine
performance
3_Performance
6
4
24
24
6
4
0
The rankings are the same with or without a catalyst.
Item Selected:
Item Function Selected: 1. Transfer the air/fuel mixture to the intake valve
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Crack or leak in
manifold
leaner mixture
engine, exhaust
system and
catalyst run
hotter
no effect
4_Other
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
muffler failure
3_Performance
6
4
24
24
6
4
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
engine failure
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
fire or burn
1_Safety
10
4
40
40
10
4
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
Catalyst failure
2_Regulatory
1
1
1
36
9
4
-35
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
Crack or leak in
manifold
leaner mixture
change power
degraded engine
performance
3_Performance
4
4
16
16
4
4
0
The rankings are the same with or without a catalyst.
Attachment 9 P-7
-------
4. intake manifold, port, valve and seals
Item Selected: \
Item Function Selected: 1. Transfer the air / fuel mixture to the intake valve
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Crack or leak in
manifold
leaner mixture
engine stalls
inoperable
3_Performance
8
4
32
32
8
4
0
The rankings are the same with or without a catalyst.
Crack or leak in
manifold
leaner mixture
engine failure
(internal
component
seizure, broken
valve or spring,
excess wear)
inoperable
3_Performance
8
3
24
24
8
3
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
Crack or leak in
manifold
leaner mixture
catalyst
overheats and
fails (substrate
cracks,
washcoat
spalling, noble
metal sintering,
alumina phase
change,
crystallite
growth)
loss of emission
control
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
None
damaged
valve
leaky intake
valve
power loss
3_Performance
5
4
20
15
5
3
5
The lower Phase 3 occurrence due to the Phase 3 definition of improved cooling and
fuel control, which could reduce cases of excessive temperature that could damage
valves.
leaky intake
manifold gasket
head gasket
failure
loss of
compression
degraded engine
performance
3_Performance
7
4
28
28
7
4
0
The rankings are the same with or without a catalyst.
Intake manifold
leak causes MAP
to read higher
pressure
richer mixture
backfire
noise
4_Other
3
3
9
9
3
3
0
The failure relates to fuel Injected engines. EPA demonstrated that the backfire
impact was reduced with the addition of a catalyst for Class I. However, since the
design quality of the Class II equipment mufflers is very good on Phase 2, the impact
of adding the catalyst is minimal.
Flame out of muffler
3_Performance
4
3
12
12
4
3
0
The failure relates to fuel Injected engines. EPA demonstrated that the backfire
impact was reduced with the addition of a catalyst for Class I. However, since the
design quality of the Class II equipment mufflers is very good on Phase 2, the impact
of adding the catalyst is minimal.
fire or burn
1_Safety
10
3
30
30
10
3
0
The failure relates to fuel Injected engines. EPA demonstrated that the backfire
impact was reduced with the addition of a catalyst for Class I. However, since the
quality of the Class II equipment mufflers is very good on Phase 2, the impact of
adding the catalyst is minimal.
Attachment 9 P-8
-------
4. intake manifold, port, valve and seals
Item Selected: \
Item Function Selected: 1. Transfer the air / fuel mixture to the intake valve
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Intake manifold
leak causes MAP
to read higher
pressure
richer mixture
cooler exhaust /
catalyst
no effect
4_Other
1
4
4
4
1
4
0
The rankings are the same with or without a catalyst.
Intake manifold
leak causes MAP
to read higher
pressure
richer mixture
power loss
degraded
performance
3_Performance
5
4
20
20
5
4
0
The rankings are the same with or without a catalyst.
Intake manifold
leak causes MAP
to read higher
pressure
richer mixture
won't start
inoperable
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
Item Selected: hWiiMyiiTwrJTTreTl
Item Function Selected: 1. Produces power
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Higher thermal
load
higher engine
temperatures
engine failure
(internal
component
seizure, broken
valve or spring,
excess wear)
inoperable
3_Performance
8
3
24
24
8
3
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
catastrophic failure
(potential injury due to
flying parts)
1_Safety
9
3
27
27
9
3
0
Engine failure caused by excessive temperatures. The rankings are the same with or
without a catalyst. The effect could be mitigated by the presence of a thermal switch.
fire or burn
1_Safety
10
3
30
30
10
3
0
Engine failure can result in contact with hot metal or fluids. The rankings are the same
with or without a catalyst. The effect could be mitigated by the presence of a thermal
switch.
None
ring, cylinder
or valve wear
or leakage
increased oil
consumption
catalyst poisoning
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
None
ring, cylinder
or valve wear
or leakage
increased oil
consumption
smoke
3_Performance
3
6
18
18
3
6
0
The rankings are the same with or without a catalyst.
no effect
4_Other
1
6
6
6
1
6
0
The rankings are the same with or without a catalyst.
Attachment 9 P-9
-------
6. exhaust valve and seal
Item Selected: [j
Item Function Selected: 1. seal combustion chamber
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Excessive engine
temperature or
wear
burned or
warped valve
valve leakage
higher exhaust and
catalyst temperature
3_Performance
4
3
12
12
4
3
0
The rankings are the same with or without a catalyst.
backfire
3_Performance
5
3
15
15
5
3
0
The rankings are the same with or without a catalyst.
lower power
3_Performance
5
3
15
15
5
3
0
The rankings are the same with or without a catalyst.
allow unburned fuel
and oil to reach the
catalyst
2_Regulatory
1
1
1
27
9
3
-26
The lower Phase 3 occurrence due to the Phase 3 improved cooling and fuel control
which would reduce cases of excessive temperature that would damage valves.
Burn or warped
valve
head warpage
engine damage
inoperable
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
7. exhaust manifold, muffler, muffler shroud and gaske
Item Selected: [
Item Function Selected: 1. seals exhaust and directs exhaust and muffles noise
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
cracked
muffler,
manifold or
failed gasket
exhaust leak
increased emissions
2_Regulatory
1
4
4
27
9
3
-23
The RPN difference is due to the regulatory requirement of Phase 3 and the increased
severity. Also, the lower occurrence for the Phase 3 is due to the Improved exhaust
system design.
noise
3_Performance
6
4
24
18
6
3
6
The lower occurrence for the Phase 3 is due to the improved design of the engine.
fire or burn
1_Safety
10
4
40
30
10
3
10
The lower Phase 3 occurrence is due to the Phase 3 definition of improved exhaust
system design.
heat surrounding
components reducing
their durability
3_Performance
4
4
16
12
4
3
4
The lower Phase 3 occurrence is due to the Phase 3 definition of improved exhaust
system design.
Debris
accumulation
reduction in
engine
cooling /
increased
muffler
temperatures
ignition of debris
adjacent to
muffler
Fire
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the improvement of the air ducting for
cooling and control of debris accumulation.
None
removal or
mechanical
failure
loss of muffler
shroud
fire or burn
1_Safety
10
3
30
20
10
2
10
The lower occurrence for the Phase 3 is due to the improvement of the air ducting
design for cooling and shroud design.
Attachment 9 P-10
-------
8. catalyst (monolith, matting)
Item Selected: fj
Item Function Selected: 1. reduce emissions (HC NOx CO)
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Manufacturing,
material problem
or vibration
catalyst mat
failure
mechanical
failure of
ceramic
monolith catalyst
increased emissions
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
change engine back
pressure
3_Performance
1
1
1
9
3
3
-8
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the catalyst being present.
Attachment 9 P-l 1
-------
8. catalyst (monolith, matting)
Item Selected: fj
Item Function Selected: 1. reduce emissions (HC NOx CO)
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
catalyst
overheats and
fails (substrate
cracks,
washcoat
spalling, noble
metal sintering,
alumina phase
change,
crystallite
growth)
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Lean mixture or
over speed, one
lean cylinder in
two cylinder
engine.
excessive
temperatures
change engine back
pressure
3_Performance
1
1
1
6
3
2
-5
The performance change is small. The failure mode could be mitigated by the
presence of a thermal switch.
Rich mixture
soot coats
catalyst
deactivates
catalyst
increased emissions
2_Regulatory
1
1
1
27
9
3
-26
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Engine wear
excessive
lubricant
consumption
poison
deactivation due
to lubricant
components
increased emissions
2_Regulatory
1
1
1
36
9
4
-35
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
Replicates failure modes from power cylinder rankings.
Manufacturing or
supplier problem
defective /
wrong catalyst
poor catalyst
performance
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
reduced emissions
3_Performance
1
1
1
2
1
2
-1
The performance change is small.
Manufacturing,
supplier or
installation
problem
incorrect or
improperly
installed
catalyst
increased
slightly higher
temperatures
3_Performance
1
1
1
2
1
2
-1
The performance change is small.
catalyst
performance
fire or burn
1_Safety
1
1
1
20
10
2
-19
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential safety impact. The effect could
be mitigated by the presence of a thermal switch.
Engine wear
engine debris
catalyst plugs
increased emissions
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance.
increase engine back
pressure
3_Performance
1
1
1
6
3
2
-5
The performance change is small.
Attachment 9 P-12
-------
8. catalyst (monolith, matting)
Item Selected: [j
Item Function Selected: 1. reduce emissions (HC NOx CO)
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
Fuel or ignition
system
malfunction
increased
thermal load
from catalyst
potential
damage to
engine, catalyst
or components
poor performance
3_Performance
1
1
1
12
6
2
-11
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the catalyst being present. The failure mode
could be mitigated by the presence of a thermal switch.
reduced durability
3_Performance
1
1
1
12
6
2
-11
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the catalyst being present. The failure mode
could be mitigated by the presence of a thermal switch.
engine failure
3_Performance
1
1
1
16
8
2
-15
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the catalyst being present. The failure mode
could be mitigated by the presence of a thermal switch.
Item Selected:
Item Function Selected: 1. Provides cooling air to engine and components
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
material
failure or
loose bolt
fan /flywheel
fails
engine stops
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst.
engine overheats and
stalls
3_Performance
7
2
14
14
7
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
burn risk
1_Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
None
cooling
system
shroud failed
loss of cooling
engine failure
3_Performance
8
2
16
16
8
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
hotter engine
3_Performance
1
2
2
2
1
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
higher muffler and/or
converter surface
temperatures
3_Performance
1
2
2
2
1
2
0
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch.
Attachment 9 P-13
-------
9. cooling system
Item Selected: [j
Item Function Selected: 1. Provides cooling air to engine and components
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
engine overheats and
stalls
3_Performance
5
4
20
15
5
3
5
By definition of the Phase 3 product, the improved design features for Phase 3 results
in a slight reduction in Occurrence. The effect could be mitigated by the presence of a
thermal switch.
plugging of
cooling
passages due
to debris
engine failure
3_Performance
8
4
32
24
8
3
8
By definition of the Phase 3 product, the improved design features are expected to
result in a slight reduction in Occurrence. The effect could be mitigated by the
presence of a thermal switch.
None
reduction of
engine cooling
hotter engine
3_Performance
1
4
4
3
1
3
1
By definition of the Phase 3 product, the improved design features for Phase 3 results
in a slight reduction in Occurrence. The effect could be mitigated by the presence of a
thermal switch.
higher muffler and/or
converter surface
temperatures
3_Performance
1
4
4
3
1
3
1
By definition of the Phase 3 product, the improved design features for Phase 3 results
in a slight reduction in Occurrence. The effect could be mitigated by the presence of a
thermal switch.
burn risk
1_Safety
9
4
36
27
9
3
9
The rankings are the same with or without a catalyst. The effect could be mitigated by
the presence of a thermal switch,
Item Selected:
Item Function Selected: 1. provides timed spark
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module failure
loss of spark
engine stalls and
unburned fuel pumped
through engine
resulting in high
catalyst temperatures
3_Performance
7
4
28
24
8
3
4
The lower occurrence for the Phase 3 is due to the improved ignition system for Phase
3 products.
engine stalls and won't
run
3_Performance
8
4
32
24
8
3
8
The lower occurrence for the Phase 3 is due to the improved ignition system for Phase
3 products.
Attachment 9 P-14
-------
Item Function Selected: 1. provides timed spark
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
ignition
module failure
spark timing
changes
engine stalls and won't
run
3_Performance
8
3
24
16
8
2
8
The lower occurrence for the Phase 3 is due to the improved ignition system for Phase
3 products.
Attachment 9 P-15
-------
10. ignition system
Item Selected: |
Item Function Selected: 1. provides timed spark
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
degraded engine
performance
3_Performance
6
4
24
18
6
3
6
The lower occurrence for the Phase 3 is due to the improved ignition system for Phase
3 products.
plug bad,
short in plug
wire, failed
coil, loose
flywheel,
magneto,
weak or
intermittent
spark, or loss of
ignition in one of
two cylinders
potentially higher
muffler / catalyst
temperatures
3_Performance
2
4
8
8
2
4
0
The rankings are the same with or without a catalyst.
None
engine stalls and won't
run
3_Performance
8
4
32
24
8
3
8
The lower occurrence for the Phase 3 is due to the improved ignition system for Phase
3 products.
ignition
module failure
(misfire)
excessive muffler or
catalyst temperatures
and increased burn
risk
1_Safety
9
3
27
27
9
3
0
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential safety impact. Excess air and
unburned fuel can cause high catalyst exotherm. The effect could be mitigated by the
presence of a thermal switch.
None
weak or
intermittent
spark
excessive
catalyst
temperatures
catalyst overheats and
fails (substrate cracks,
wash coat spalling,
noble metal sintering,
alumina phase
change, crystallite
growth)
2_Regulatory
1
1
1
18
9
2
-17
The Phase 2 ranking is low by definition, since Phase 2 does not have a catalyst. For
Phase 3, the severity ranks high due to the potential regulatory non-compliance. The
effect could be mitigated by the presence of a thermal switch.
noise
3_Performance
3
4
12
9
3
3
3
EPA demonstrated that the backfire impact was significantly reduced with the addition
of a catalyst. That fact drives a reduction in the Occurrence ranking.
bad plug, short in
plug wire, failed
coil, loose
flywheel,
magneto
loss of spark
backfire (misfire)
Flame out of muffler
3_Performance
4
4
16
12
4
3
4
In this scenario a momentary flame does not cause a safety issue. Fp»
demonstrated that the backfire impact was significantly reduced with the addition of a
catalyst. That fact drives a reduction in the Occurrence ranking.
fire or burn
1_Safety
10
4
40
30
10
3
10
In this scenario, the backfire is of such intensity that it can cause a fire or burn. Fp»
demonstrated that the backfire incidence was significantly reduced with the addition of
a properly designed catalyzed muffler system. That fact drives a reduction in the
Occurrence ranking.
Attachment 9 P-16
-------
Item Selected:
Item Function Selected: 1. Contains fuel and conveys to engine
Potential Cause
(Contributing)
Potential
Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification
of Effect
Sev
Ph2
Occur
Ph 2
RPN
Ph 2
RPN
Ph 3
Sev
Ph 3
Occur
Ph 3
RPN Delta
(Ph 2 vs Ph 3)
Note
None
leak of tank or
line
fuel puddles, or
sprays
needs repair
3_Performance
5
3
15
10
5
2
5
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
operator fuel exposure
1_Safety
9
3
27
18
9
2
9
The rankings are the same with or without a catalyst.
Equipment tip
over, material
failure,
component
failure
leak of tank or
line
fuel contacts hot
component
needs repair
3_Performance
5
3
15
10
5
2
5
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
fire or burn
1_Safety
10
3
30
20
10
2
10
By definition of the Phase 3 product, the improved design features for Phase 3 is
expected to result in a slight reduction in Occurrence. The evaporative emission
controls will reduce leak occurrence
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel puddles or
sprays
needs repair
3_Performance
5
2
10
10
5
2
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
operator fuel exposure
1_Safety
9
2
18
18
9
2
0
The rankings are the same with or without a catalyst.
High muffler or
catalyst
temperatures
near fuel tank
fuel tank or
line melted
fuel contacts hot
component
needs repair
3_Performance
5
2
10
10
5
2
0
The rankings are the same with or without a catalyst.
fire or burn
1_Safety
10
2
20
20
10
2
0
The rankings are the same with or without a catalyst.
Attachment 9 P-17
-------
ATTACHMENT 10
PROCESS FMEA REPORT - REFUELING PROCESS FOR
CLASS I AND CLASS II, PHASE 2 AND PHASE 3 EQUIPMENT
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
1. Shut off engine
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
1
Shut off engine
failed to shut
engine off
engine running
risk of refueling while
engine running and a
potential of a fire or burn
1_Safety
9
2
18
No difference between Phase 2
and Phase 3 expected. Thermal
images indicate that at idle
operation the maximum surface
temperatures are comparable for
Phase 2 and Phase 3 designs.
Selected Process Function:
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
2
Get fuel can
no fuel
empty can
no refueling
3_Performance
1
6
6
No difference between Phase 2
and Phase 3 expected
3
Get fuel can
mislabeled
gas can,
operator
behavior
wrong fuel
engine won't run after
refueling (E-85)
3_Performance
8
3
24
No difference between Phase 2
and Phase 3 expected
4
Get fuel can
mislabeled
gas can,
operator
behavior
will run, but smoky after
refueling (2-cycle fuel)
3_Performance
6
3
18
No difference between Phase 2
and Phase 3 expected
Attachment 10P-1
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
5
Open mower cap
overpressure
of fuel tank
spillage (hot
fuel, full tank,
pressurized
tank - i.e. vent
blocked)
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and
Phase 3 expected. (Phase 3 tank
venting could be a slight
improvement)
6
Open mower cap
overpressure
of fuel tank
spillage onto deck
4_Other
3
2
6
No significant difference between
Phase 2 and Phase 3 expected.
(Phase 3 tank venting could be a
slight improvement)
7
Open mower cap
overpressure
of fuel tank
spillage onto ground
4_Other
3
2
6
No significant difference between
Phase 2 and Phase 3 expected.
(Phase 3 tank venting could be a
slight improvement)
8
Open mower cap
overpressure
of fuel tank
spillage onto hot
surfaces and a potential
of a fire or burn
1_Safety
9
2
18
A safety concern, but no significant
difference between Phase 2 and
Phase 3 expected. (Phase 3 tank
venting could be a slight
improvement)
9
Open mower cap
overpressure
of fuel tank
fire
1_Safety
10
2
20
A safety concern, but no significant
difference between Phase 2 and
Phase 3 expected. (Phase 3 tank
venting could be a slight
improvement)
Selected Process Function:
4. Remove and replace fuel can cap and vent
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
10
Remove fuel can
cap
operator
behavior
Fail to remove
cap and vent
no refueling
3_Performance
1
2
2
No difference between Phase 2
and Phase 3 expected.
11
Remove fuel can
cap
operator
behavior
Fail to open
vent
fuel spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
12
Remove fuel can
cap
operator
behavior
no effect
4_Other
1
4
4
None
Attachment 10 P-2
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
4. Remove and replace fuel can cap and vent
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
13
Remove fuel can
cap
hot fuel and
high
pressure(high
temperature
storage,
heating from
sunlight)
fuel spray upon
opening
cap/vent
operator contact w/ fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
14
Remove fuel can
cap
hot fuel and
high
pressure(high
temperature
storage,
heating from
sunlight)
spillage
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
15
Remove fuel can
cap
hot fuel and
high
pressure(high
temperature
storage,
heating from
sunlight)
pressure is relieved
4_Other
1
2
2
None
16
Remove fuel can
cap
operator
behavior
fail to recap the
can
no effect
4_Other
1
4
4
None
17
Remove fuel can
cap
operator
behavior
spillage
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
18
Remove fuel can
cap
operator
behavior
vapor released from can
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
Attachment 10 P-3
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
5. Pick up can and tilt to pour in to the mower fuel tank fill tube
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
19
pick up can and
pour
fuel spill
fuel puddle on
equipment
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
20
pick up can and
pour
fuel spill
no effect
4_Other
1
4
4
None
21
pick up can and
pour
fuel spill
fuel spill into
fan inlet
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
22
pick up can and
pour
fuel spill
no effect
4_Other
1
4
4
None
23
pick up can and
pour
fuel spill
fuel over the
cowling and
makes contact
with a hot
exhaust system
component
fuel fire
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
24
pick up can and
pour
fuel spill
no effect
4_Other
1
4
4
None
25
pick up can and
pour
fuel spill
spill on
operator and/or
bystander
fuel exposure
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
26
pick up can and
pour
fuel spill
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
27
pick up can and
pour
fuel spill
spillage on
surrounding
areas
fuel fire and burn
1_Safety
10
4
40
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
28
pick up can and
pour
fuel spill
creates combustible
material
1_Safety
9
4
36
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
29
pick up can and
pour
fuel spill
no effect
4_Other
1
4
4
None
30
pick up can and
pour
material
failure
gas can cracks
fuel spill and potential of
fire or burn
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
31
pick up can and
pour
material
failure
debris in fuel
tank
fuel control problem
3_Performance
6
3
18
No difference between Phase 2
and Phase 3 expected.
Attachment 10 P-4
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
5. Pick up can and tilt to pour in to the mower fuel tank fill tube
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
32
pick up can and
pour
engine
running
refuel while
running
spill fuel
1_Safety
9
2
18
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
33
pick up can and
pour
engine
running
fuel vapor ignites
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
34
pick up can and
pour
engine
running
engine refueled
4_Other
1
2
2
None
35
pick up can and
pour
static charge
spark
fire or explosion
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
36
pick up can and
pour
static charge
no effect
4_Other
1
2
2
None
37
pick up can and
pour
gas cap on
can is not
secure
spillage on
surrounding
areas
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
38
pick up can and
pour
gas cap on
can is not
secure
no effects
4_Other
1
2
2
None
Selected Process Function:
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
39
Recap the Mower
Tank
failure to
recap mower
tank
fuel spillage or
vapor release
onto equipment
or operator
during
operation
fire
1_Safety
10
3
30
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
40
Recap the Mower
Tank
failure to
recap mower
tank
fuel exposure
1_Safety
9
3
27
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
42
Recap the Mower
Tank
failure to
recap mower
tank
no effect
4_Other
1
3
3
None
Attachment 10 P-5
-------
Class I and Class 2 Refueling Process FMEA
Selected Process Function:
Ref. No.
Process Function
Potential
Cause
(Primary)
Potential
Failure Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
42
Restart
fuel on the
equipment
ignition
component
failure
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
43
Restart
fuel or debris
left on the
equipment
hot surfaces
ignites
fire or burn
1_Safety
10
2
20
A safety concern, but no difference
between Phase 2 and Phase 3
expected.
Attachment 10 P-6
-------
ATTACHMENT 11
PROCESS FMEA REPORT - SHUTDOWN AND EQUIPMENT
STORAGE PROCESS FOR CLASS I AND CLASS II, PHASE 2
AND PHASE 3 EQUIPMENT
-------
Class I and Class 2 Shutdown and Storage Process FMEA
Selected Process Function:
1. Engine Shut Down
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s)
of Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
1
Engine Shut
Down
ignition cut off and
engine brake fail (and
engine does not shut
off)
engine left
running, and
operator may pull
plug wire to stop
high surface
temperatures,
and risk of fuel
ignition from high
voltage spark and
risk of shock
1_Safety
9
2
18
No difference between Phase 2
and Phase 3 expected
2
Engine Shut
Down
engine won't stop and
operator goes for help
unattended
operation
runs out of fuel
3_Performance
1
2
2
No difference between Phase 2
and Phase 3 expected
3
Engine Shut
Down
engine won't stop and
operator goes for help
bystander gets
injured by burn
1_Safety
10
2
20
No difference between Phase 2
and Phase 3 expected
4
Engine Shut
Down
engine won't stop and
operator goes for help
debris fire
1_Safety
10
2
20
No difference between Phase 2
and Phase 3 expected
5
Engine Shut
Down
engine won't stop and
operator pulls plug wire
risk of fuel
ignition due to
high voltage
spark
fire or burn
1_Safety
10
2
20
No difference between Phase 2
and Phase 3 expected
6
Engine Shut
Down
engine won't stop and
operator pulls plug wire
engine stops
3_Performance
1
2
2
No difference between Phase 2
and Phase 3 expected
7
Engine Shut
Down
engine won't stop and
operator pulls plug wire
operator contacts
hot component
burn
1_Safety
10
2
20
No difference between Phase 2
and Phase 3 expected
Selected Process Function:
2. Equipment Storage
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s)
of Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
8
Equipment
Storage
cover with plastic tarp
while engine hot
plastic tarp melts
equipment mess
3_Performance
4
2
8
Tarp melts, but no resultant fire.
No impact due to addition of a
catalyst.
9
Equipment
Storage
cover with tarp while
engine hot (any
material)
tarp ignites
fire ignites
adjacent
materials
1_Safety
10
2
20
Tarp ignites and fire could spread.
No impact due to addition of a
catalyst.
10
Equipment
Storage
cover with tarp while
engine hot (any
material)
fire damages
equipment
1_Safety
10
2
20
Tarp ignites and fire could spread.
No impact due to addition of a
catalyst.
11
Equipment
Storage
cover with tarp while
engine hot (any
material)
tarp gets hot
no effect
4_Other
1
2
2
No impact due to addition of a
catalyst.
Attachment 11 P-l
-------
Class I and Class 2 Shutdown and Storage Process FMEA
Selected Process Function:
2. Equipment Storage
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s)
of Failure
Classification
of Effect
Sev
Occur
R.P.N.
Notes
12
Equipment
Storage
store in or near garage
or shed when engine
hot
equipment ignites
combustible
material
structural fire
1_Safety
10
1
10
Surrounding material could ignite.
No impact due to addition of a
catalyst. Data available does not
support a higher occurrence
ranking.
13
Equipment
Storage
store in or near garage
or shed when engine
hot
water heater pilot
light ignites gas
vapor
structural fire
1_Safety
10
1
10
Gas vapor could ignite. No impact
due to addition of a catalyst. Data
available does not support a higher
occurrence ranking.
14
Equipment
Storage
store in or near garage
or shed when engine
hot
debris on mower
deck ignites
structural fire
1_Safety
10
1
10
Debris on the mower deck could
ignite. No impact due to addition
of a catalyst. Data available does
not support a higher occurrence
ranking.
15
Equipment
Storage
store in or near garage
or shed when engine
hot
operator and/or
bystander
contacts hot
component
burn
1_Safety
10
2
20
No impact due to addition of a
catalyst.
16
Equipment
Storage
park equipment on
combustible debris
debris ignites
debris fire
1_Safety
10
2
20
Surrounding material could ignite.
No impact due to addition of a
catalyst.
17
Equipment
Storage
park equipment on
combustible debris
structural fire
1_Safety
10
2
20
Surrounding material could ignite.
No impact due to addition of a
catalyst.
18
Equipment
Storage
park equipment on
combustible debris
bystander gets
injured by burn
1_Safety
10
2
20
No impact due to addition of a
catalyst.
19
Equipment
Storage
park equipment on
combustible debris
fire damages
equipment
1_Safety
10
2
20
Surrounding material could ignite.
No impact due to addition of a
catalyst.
Attachment 11 P-2
-------
ATTACHMENT 12
PROCESS FMEA REPORT - EQUIPMENT AND ENGINE
MAINTENANCE FOR CLASS I AND CLASS II, PHASE 2 AND
PHASE 3 EQUIPMENT
-------
Class I and Class 2 Equipment/Engine Maintenance Process FMEA
Selected Process Function:
1. Cleaning equipment
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
1
Cleaning
Equipment
Spray water into fuel
tank while cleaning
Engine will not
run
Engine inoperable
3_Performance
8
3
24
No difference between Phase 2
and Phase 3 expected
2
Cleaning
Equipment
Spray water into
engine intake
Engine will not
run
Engine inoperable
3_Performance
8
3
24
No difference between Phase 2
and Phase 3 expected
3
Cleaning
Equipment
Tip equipment to clean
underneath
spill fuel or oil
Fuel or oil spill
4_Other
4
8
32
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 28.
4
Cleaning
Equipment
Tip equipment to clean
underneath
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
5
Cleaning
Equipment
Tip equipment to clean
underneath
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
6
Cleaning
Equipment
Tip equipment to clean
underneath
damage engine or
equipment
3_Performance
7
8
56
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 49.
7
Cleaning
Equipment
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
Selected Process Function:
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
8
Change Oil /
Filter
Improper maintenance
wrong fluid fill
can't start
3_Performance
8
5
40
No difference between Phase 2
and Phase 3 expected
9
Change Oil /
Filter
Improper maintenance
premature wear
3_Performance
6
5
30
No difference between Phase 2
and Phase 3 expected
10
Change Oil /
Filter
Improper maintenance
no oil
engine failure
3_Performance
9
4
36
No difference between Phase 2
and Phase 3 expected
11
Change Oil /
Filter
Improper maintenance
left drain plug or
filter off
spilled on oil on
ground
4_Other
4
5
20
No difference between Phase 2
and Phase 3 expected
12
Change Oil /
Filter
Improper maintenance
over fill
loss of power
3_Performance
6
6
36
No difference between Phase 2
and Phase 3 expected
Attachment 12 P -1
-------
Class I and Class 2 Equipment/Engine Maintenance Process FMEA
Selected Process Function:
2. Change oil and filter
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
13
Change Oil /
Filter
Improper maintenance
spill
4_Other
4
6
24
No difference between Phase 2
and Phase 3 expected
14
Change Oil /
Filter
Improper maintenance
blow out seals
3_Performance
7
6
42
No difference between Phase 2
and Phase 3 expected
15
Change Oil /
Filter
Improper maintenance
spill oil
pollution
2_Regulatory
4
9
36
No difference between Phase 2
and Phase 3 expected
16
Change Oil /
Filter
Improper maintenance
operator exposure to
oil
1_Safety
9
9
81
No difference between Phase 2
and Phase 3 expected
17
Change Oil /
Filter
Improper maintenance
wrong filter
(Class II only)
leak
3_Performance
4
5
20
No difference between Phase 2
and Phase 3 expected
18
Change Oil /
Filter
Improper maintenance
engine damage
3_Performance
7
5
35
No difference between Phase 2
and Phase 3 expected
19
Change Oil /
Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
20
Change Oil /
Filter
Tip equipment for
maintenance
spill fuel or oil
Fuel or oil spill
4_Other
4
8
32
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 28.
21
Change Oil /
Filter
Tip equipment for
maintenance
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
22
Change Oil /
Filter
Tip equipment for
maintenance
operator exposure to
fuel or oil
1_Safety
9
8
72
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 63.
23
Change Oil /
Filter
Tip equipment for
maintenance
damage engine or
equipment
3_Performance
7
8
56
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 49.
Attachment 12 P -2
-------
Class I and Class 2 Equipment/Engine Maintenance Process FMEA
Selected Process Function:
3. Change air filte
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
24
Change Air Filter
improper maintenance
installed wrong
or incorrectly
prepared pre-
oiled filter
may affect engine
operation
3_Performance
3
5
15
No difference between Phase 2
and Phase 3 expected. These
failure modes were also
addressed in the design FMEAs.
25
Change Air Filter
improper maintenance
failed to change
or clean filter
may affect engine
operation
3_Performance
3
7
21
No difference between Phase 2
and Phase 3 expected
26
Change Air Filter
improper maintenance
failure to reinstall
filter
may affect engine
operation
3_Performance
3
5
15
No difference between Phase 2
and Phase 3 expected
27
Change Air Filter
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
Selected Process Function:
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
28
Change Spark
Plug
improper maintenance
failure to change
spark plug
may affect engine
operation
3_Performance
4
7
28
No difference between Phase 2
and Phase 3 expected
29
Change Spark
Plug
improper maintenance
installed wrong /
defective /
improperly
gapped spark
plug
may affect engine
operation
3_Performance
4
6
24
No difference between Phase 2
and Phase 3 expected
30
Change Spark
Plug
improper maintenance
failed to tighten
spark plug
may affect engine
operation
3_Performance
4
6
24
No difference between Phase 2
and Phase 3 expected
31
Change Spark
Plug
improper maintenance
failed to connect
plug wire
engine won't run
3_Performance
8
6
48
No difference between Phase 2
and Phase 3 expected
32
Change Spark
Plug
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
33
Change Spark
Plug
testing for spark
spark ignites fuel
fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
34
Change Spark
Plug
testing for spark
flash flame
3_Performance
5
3
15
In this case, a momentary flame
does not cause a safety issue.
No impact due to addition of a
catalyst.
Attachment 12 P -3
-------
Class I and Class 2 Equipment/Engine Maintenance Process FMEA
Selected Process Function:
5. Sharpen blade
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
35
Sharpen Blade
improper maintenance
improper
sharpening
blade fails
3_Performance
9
7
63
No difference between Phase 2
and Phase 3 expected
36
Sharpen Blade
improper maintenance
poor cutting
performance
3_Performance
5
7
35
No difference between Phase 2
and Phase 3 expected
37
Sharpen Blade
improper maintenance
imbalance
3_Performance
7
7
49
No difference between Phase 2
and Phase 3 expected
38
Sharpen Blade
tipping equipment for
blade access
equipment falls
personnel injury
1_Safety
10
5
50
No difference between Phase 2
and Phase 3 expected
39
Sharpen Blade
tipping equipment for
blade access
no effect
4_Other
1
5
5
No difference between Phase 2
and Phase 3 expected
40
Sharpen Blade
tipping equipment for
blade access
spill fuel or oil
fire
1_Safety
10
8
80
Vapor control requirements will
reduce occurrence with Phase 3
product to 7 and the RPN to 70.
41
Sharpen Blade
tipping equipment for
blade access
no effect
4_Other
1
8
8
No difference between Phase 2
and Phase 3 expected
42
Sharpen Blade
Improper reassembly
blade imbalance,
failure or
separation
no effect
4_Other
1
1
1
No difference between Phase 2
and Phase 3 expected
43
Sharpen Blade
Improper reassembly
personnel injury
1_Safety
10
1
10
No difference between Phase 2
and Phase 3 expected
44
Sharpen Blade
Improper reassembly
engine damage
3_Performance
6
1
6
No difference between Phase 2
and Phase 3 expected
Selected Process Function:
6. Replace drive belt
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
45
Replace Drive
Belt
wrong belt installed
belt slips or does
not engage
poor or no
performance
3_Performance
7
4
28
No difference between Phase 2
and Phase 3 expected
46
Replace Drive
Belt
wrong belt installed
belt fire / debris fire
1_Safety
10
4
40
No difference between Phase 2
and Phase 3 expected
46
Replace Drive
Belt
belt installed
incorrectly
belt slips or does
not engage
poor or no
performance
3_Performance
7
3
21
No difference between Phase 2
and Phase 3 expected
Attachment 12 P -4
-------
Class I and Class 2 Equipment/Engine Maintenance Process FMEA
Selected Process Function:
6. Replace drive belt
Ref. No.
Process Function
Potential Cause
(Primary)
Potential Failure
Modes
Potential Effect(s) of
Failure
Classification of
Effect
Sev
Occur
R.P.N.
Notes
41
Replace Drive
Belt
belt installed
incorrectly
belt fire / debris fire
1_Safety
10
3
30
No difference between Phase 2
and Phase 3 expected
42
Replace Drive
Belt
maintenance or
cleaning while the
equipment is hot
contact with hot
part
burn
1_Safety
10
6
60
No difference between Phase 2
and Phase 3 expected
Attachment 12 P -5
-------
ATTACHMENT 13
IGNITION PROPERTY DATA OF VARIOUS MATERIALS
AND HUMAN SKIN DAMAGE AT ELEVATED
TEMPERATURE/RADIANT HEAT EXPOSURE DATA
-------
Ignition Property Data of Various Materials and Human Skin Damage at Elevated
Temperature/Radiant Heat Exposure Data
Tables 13-1 through 13-9 provides ignition data for various materials that are reasonably
expected to be in areas a lawn mower or other small residential application motor with hot
surfaces would be stored. Also provided are data related to contact burn temperatures and
thermal radiation exposure effects on human skin.
The types of materials considered are both solids and liquids. Ignition can occur in the
solid phase, known as smoldering ignition, and the gas phase, known as flaming ignition. For
flaming combustion to occur the solid or liquid must gasify. Liquids, such as gasoline, can exert
a vapor pressure at ambient conditions producing a flammable mixture. Unlike liquids, solid
combustibles do not exert a significant vapor pressure under ambient conditions and have to be
heated to gasify. The gasification of solids is a thermally induced decomposition of complex
molecules in a process known as pyrolysis. A solid can be heated to pyrolysis when exposed to a
heat flux source that is radiative, convective, conductive, or a combination. Whether or not a
solid material will reach a temperature sufficient to cause pyrolysis and how quickly it can reach
that temperature depends on factors such as the intensity of heat flux; material properties such as
thickness, density, specific heat, thermal conductivity, and emissivity.
Once a solid or liquid produces a combustible mixture of gases, flaming ignition can
occur as piloted ignition or unpiloted ignition. Unpiloted ignition is also known as auto-ignition.
A piloted ignition initiates from a small flame or a hot spark located in the combustible gases.
Auto-ignition initiates from a hot surface that heats the combustible gases to the auto-ignition
temperature.
Smoldering ignition occurs in the solid phase and is observed more frequently with
porous and cellulosic materials. Smoldering ignition occurs when a material is heated for long
durations under low heat flux conditions. The heat flux is not sufficient to produce adequate
pyrolysis for flaming combustion, but a high enough heat flux applied for a sufficient duration
causes an exothermic reaction at the surface that can become self-accelerating. This type of
ignition is observed as a glowing on the surface of the solid and can lead to flaming ignition if
the heat losses are low and the exothermic reaction is allowed to accelerate.
In addition to ignition of materials reasonably expected to be in areas of motor storage,
ignition of materials expected in areas of use, specifically vegetation, is also a concern. Ignition
temperatures of vegetation have been measured by numerous researchers with widely varying
values. The ignition temperature of vegetation varies based on moisture content, density,
thickness, species, etc. Ignition of vegetation by motors can occur by heat flux from hot surfaces
and ejection of hot material from the exhaust. Ignitability tests [1] of forest fuels showed that dry
vegetation ignites within a few seconds at 550°C and for long durations of exposure ignites at
350-400°C. However, due to the variability of vegetation ignition properties, Babrauskas [1]
recommends using ignition temperatures of solid wood.
Attachment 13 P -1
-------
The data provided in Table A13-10 is for the effects of thermal radiation levels on human
skin. Figure A13-1 provides data on reversible human skin injury and cell death as a function of
contact skin temperature versus exposure time. From Figure A13-1, a contact temperature of
approximately 70 °C for less than 1 second will cause cell death. Reversible injury, as defined in
ASTM C 1055 [2], occurs for an exposure time of less than 1 second at a temperature of
approximately 64 °C. As the exposure time increases, the temperature to cause cell injury and
the temperature to cause reversible injury approach each other.
For a more detailed discussion on ignition, material properties, and human burn hazards,
please refer to the references provided.
TABLE A13-1. IGNITION TEMPERATURES OF VARIOUS MATERIALS [3]
Material
Aircraft panel epoxy Fiberite
Asphalt shingle
Carpet #2 (wool, stock)
Carpet #2 (wool, treated)
Carpet #2 (wool, untreated)
Carpet (acrylic)
Carpet (nylon wool blend)
Chipboard (S118M)
Douglas fir particle board (1.27 cm)
Fiber insulation board
Fiberboard, low density (S119M)
Fiberglass shingle
Foam, flexible (2.54 cm)
Foam, rigid (2.54 cm)
Glass reinforced plastic (1.14 mm)
Glass reinforced plastic (2.24 mm)
Gypsum board, (common) (1.27
mm)
Gypsum board, fire retardant (1.27
cm)
Gypsum board, Wallpaper (S142M)
Hardboard (3.175 mm)
Hardboard (6.35 mm)
Hardboard (gloss paint) (3.4 mm)
Hardboard (nitrocellulose paint)
Hardboard (S159M)
Mineral wool, textile paper (S160M)
Particle board (1.27 cm stock)
Plywood, fire retardant (1.27 mm)
Plywood, plain (0.635 cm)
Plywood, plain (1.27 cm)
Polycarbonate (1.52 mm)
505
378
465
455
435
300
412
390
382
355
330
445
390
435
400
390
510
412
365
298
400
400
372
400
412
620
390
390
528
565
Attachment 13 P -2
-------
Polyisocyanurate (5.08 cm) 445
Polymethylmethacrylate polycast
(1.59 mm) 278
Polymethylmethacrylate type g
(1.27 cm) 378
Polystyrene (5.08 cm) 630
Polyurethane (S353M) 280
Wood panel (S178M) 385
TABLE A13-2. TYPICAL VALUES OF THE MINIMUM AUTO-IGNITION
TEMPERATURE FOR FLAMMABLE GASES AND VAPORS [4]
Minimum auto-
Material ignition
temperature (°C)
Hydrogen 400
Carbon disulphide 90
Carbon monoxide 609
Methane 601
Propane 450
n-Butane 288a
iso-Butane 460a
n-Octane 206a
iso-Octane (2,2,4-trimethylpentane) 415a
Ethene 450
Acetylene (ethyne) 305
Methanol 385
Ethanol 363
Acetone 465
Benzene 560
a Note that branched alkanes have much higher auto-ignition temperatures
than their straight-chain isomers.
TABLE A13-3. PILOTED IGNITION TEMPERATURES OF VARIOUS WOODS [1]
L, . t, -r Plateau .
Wood species 2X g temD 9
species (kw/mZ) (°C) temp. (s)
W
Western red cedar 15.4 450 366 583
(280 kg/m3) 10 7 431 37g 216
24.0 365 - 57
28.7 346 - 30
Attachment 13 P -3
-------
31.7
354
-
23
15.4
497
359
684
obeche
(350 kg/m3)
19.7
24.0
28.7
442
364
344
361
176
60
39
31.7
340
-
29
15.4
446
354
1094
white pine
(360 kg/m3)
19.7
24.0
28.7
411
397
387
380
257
95
48
31.7
375
-
32
15.4
465
365
850
mahogany
(540 kg/m3)
19.7
24.0
28.7
427
364
360
385
324
90
60
31.7
353
-
38
TABLE A13-4. TUBE FURNACE TESTS FOR THE AUTO-IGNITION
TEMPERATURE OF CELLULOSE FILTER PAPER [5]
Furnace
temperature (°C)
Heating
time (h)
Ignition
228
70
no
230
45
no
232
7-9
yes
246
3
yes
253
2
yes
280
0.5
yes
TABLE A13-5. AUTO-IGNITION OF FILTER PAPER FROM
HOT-AIR BLOWER [5]
Distance from outlet Hot air Ignition
(mm) temp. (°C) time (s)
25
876
3.8
51
849
3.7
76
705
5.3
102
545
10.5
127
413
N.I.
Attachment 13 P -4
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TABLE A13-6. HOTPLATE IGNITION TEMPERATURE OF SOME FABRICS [5]
Ignition
Fabric temperature
rc)
cotton 400
acetate 525
nylon 6 530
triacetate 540
acrylic 560
polypropylene 570
wool 600
modacrylic (Teklan - polyacrylonitrile / polyvinylidene Rqn
chloride, 50/50)
TABLE A13-7. AUTO-IGNITION OF COTTON FABRIC
FROM A HOT-AIR BLOWER [5]
Distance from outlet Hot air Ignition
(mm) temp. (°C) time (s)
25 876 3.1
51 849 3.5
76 705 5.0
102 545 17.0
114 470 N.I.
TABLE A13-8. HOT SURFACE IGNITION TEMPERATURES FOR CARPETS [5]
Ignition
Material temperature
(°C)
acrylic 710
nylon 6 660
polypropylene 735
viscose rayon 660
wool 760
Attachment 13 P -5
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TABLE A13-9. FLAMMABILITY LIMITS, QUENCHING DISTANCES, AND
MINIMUM IGNITION ENERGIES FOR VARIOUS FUELS [3 51
Flammability Limits
Spontaneous Equivalence Equivalence . , . . .
t i t- r-/x- ^ Stoichiometric
lBA Ignition Ratio®™ Ratio Omax MassAir.Fue|
( C) Temperature (Lean or Lower (Rich or Upper Do+i„„
(°C) Limit) Limit)
Acetylene
-83.9
305
0.19
00
13.3
Carbon
monoxide
-190.0
608.9
0.34
6.76
2.5
n-Decane
174.0
231.7
0.36
3.92
15.0
Ethane
-88.9
472.2
0.5
2.72
16.0
Ethylene
10.6
428.9
0.41
>6.1
14.8
Gasoline
155.0
298.9
-
-
-
Hydrogen
-252.7
571.1
0.14
2.54
34.5
Methane
-161.7
632.2
0.46
1.64
17.2
Methanol
64.5
470
0.48
4.08
6.5
n-Octane
125.6
240
0.51
4.25
15.1
Propane
-42.2
504.4
0.51
2.83
15.6
TABLE A13-10. EFFECTS OF THERMAL RADIATION [4]
Radiant heat
flux (kW/m2)
Observed effect
0.67
Summer sunshine
1.0
Maximum for indefinite skin exposure
6.4
Pain after 8-s skin exposure
10.4
Pain after 3-s skin exposure
16.0
Blistering of skin after a 5-s exposure
Attachment 13 P -6
-------
'Threshold A - Complete Transepidermal Necrosis (Cell Death)
'Threshold B - Reversible Epidermal Injury
= 60
100
Exposure Time - Seconds (Log Scale)
1000
10000
100000
FIGURE A13-1. TEMPERATURE-TIME RELATIONSHIP FOR BURNS [2]
References:
1. Babrauskas, V., Ignition Handbook. 2003, Issaquah, WA: Fire Science Publishers.
2. ASTM C 1055-03 Standard Guide for Heated System Surface Conditions that Produce
Contact Burn Injuries. 2003, ASTM International: West Conshohocken, PA.
3. The SFPE Handbook of Fire Protection Engineering. 3rd ed, ed. P. DiNenno, et al. 2002,
Quincy, Massachusetts: National Fire Protection Association.
4. Drysdale, D., An Introduction to Fire Dynamics. Second Edition ed. 1998, Southern
Gate, Chichester, West Sussex, England: John Wiley & Sons, Ltd.
5. Turns, S., An Introduction to Combustion: Concepts and Applications. 2nd ed. 2000:
McGraw-Hill Higher Education.
Attachment 13 P -7
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