RMP
OFFSITE CONSEQUENCE ANALYSIS
GUIDANCE
May 24, 1996
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This document guides the owner or operator of processes covered by the Risk Management Program
rule in the analysis of offsite consequences of accidental releases of substances regulated under section
112(r) of the Clean Air Act. This document does not substitute for EPA's regulations, nor is it a
regulation itself. Thus, it cannot impose legally binding requirements on EPA, States, or the
regulated community, and may not apply to a particular situation based upon the circumstances. EPA
may change this guidance in the future, as appropriate.
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TABLE OF CONTENTS
Roadmap to Consequence Analysis Guidance by Type of Chemical vii
1.0 Overview 1
2.0 Determining Worst-Case Scenario 2
2.1 Definition of Worst-Case Scenario 2
2.2 Determination of Quantity for the Worst-Case Scenario 4
2.3 Selecting Single Worst-Case Scenario 5
3.0 Release Rates for Toxic Substances 5
3.1 Release Rates for Toxic Gases ; 5
3.1.1 Unmitigated Releases of Gas 6
3.1.2 Releases of Gas in Enclosed Space 6
3.1.3 Releases of Liquefied Refrigerated Gas in Diked Area 7
3.2 Release Rates for Toxic Liquids 8
3.2.1 Releases of Liquids from Pipes 8
3.2.2 Unmitigated Releases of Liquids 9
3.2.3 Releases of Liquids with Passive Mitigation 10
3.2.4 Mixtures Containing Toxic Liquids 13
3.3 Release Rates for Common Water Solutions of Toxic Substances 15
4.0 Estimation of Distance to Toxic Endpoint 18
5.0 Estimation of Distance to Overpressure Endpoint for Flammable Substances 21
5.1 Flammable Substances Not in Mixtures 21
5.2 Flammable Mixtures 22
Reference Tables for Worst-Case Consequence Distances 24
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by
Endpoint, F Stability, Wind Speed 1.5 Meters per Second
1 10-Minute Release, Rural Conditions 24
2 60-Minute Release, Rural Conditions . 25
3 10-Minute Release, Urban Conditions 26
4 60-Minute Release, Urban Conditions 27
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TABLE OF CONTENTS
(Continued)
Page
Dense Gas Distances to Toxic Endpoint, F Stability, Wind Speed 1.5 Meters per
Second
5 10-Minute Release, Rural Conditions 28
6 60-Minute Release, Rural Conditions , 29
7 10-Minute Release, Urban Conditions . . . . . 30
8 60-Minute Release, Urban Conditions 31
Vapor Cloud Explosion Distances for Flammable Substances:
9 Distance to Overpressure of 1.0 psi for Vapor Cloud Explosions
of 10,000 - 500,000 Pounds of Regulated Flammable Substances . . 32
6.0 Determining Alternative Release Scenarios . , 35
7.0 Analysis of Alternative Scenarios for Toxic Substances 35
8.0 Estimation of Release Rates for Alternative Release Scenarios for Toxic Substances ... 36
8.1 Release Rates for Toxic Gases 36
8.1.1 Unmitigated Releases of Gases 36
8.1.2 Mitigated Releases of Gases 37
8.2 Release Rates for Toxic Liquids . 39
8.2.1 Liquid Release Rate and Quantity Released for Unmitigated Releases ... 39
8.2.2 Liquid Release Rate and Quantity Released for Mitigated Releases .... 41
8.2.3 Evaporation Rate from Liquid Pool 43
8.2.4 Common Water Solutions of Toxic Substances 44
9.0 Estimating Impact Distances for Alternative Release Scenarios for Toxic Substances ... 44
10.0 Analysis of Alternative Release Scenarios for Flammable Substances 47
11.0 Estimation of Release Rates for Alternative Release Scenarios for Flammable
Substances 48
11.1 Flammable Gases 48
11.2 Flammable Liquids . 49
12.0 Estimating Impact Distances for Alternative Release Scenarios for Flammable
Substances 49
12.1 Vapor Cloud Fires 49
12.2 Pool Fires 52
12.3 BLEVEs 53
12.4 Vapor Cloud Explosion 53
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TABLE OF CONTENTS
(Continued)
Page
Reference Tables for Distances for Alternative Scenarios 55
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by
Endpoint, D Stability, Wind Speed 3.0 Meters per Second:
10 10-Minute Release, Rural Conditions 55
11 60-Minute Release, Rural Conditions , 56
12 10-Minute Release, Urban Conditions '. 57
13 60-Minute Release, Urban Conditions 58
Dense Gas Distances to Toxic Endpoint, D Stability, Wind Speed 3.0 Meters per
Second:
14 10-Minute Release, Rural Conditions 59
15 60-Minute Release, Rural Conditions 60
16 10-Minute Release, Urban Conditions 61
17 60-Minute Release, Urban Conditions . 62
Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL) for Release
Rate Divided by LFL:
18 Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second ; 63
19 Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second 63
Dense Gas Distances to Lower Flammability Limit:
20 Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second 64
21 Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second 65
BLEVE Distances for Flammable Substances:
22 Distance to Radiant Heat Dose at Potential Second Degree Burn Threshold Assuming
Exposure for Duration of Fireball 66
13.0 Estimating Offsite Receptors 69
14.0 Submitting Offsite Consequence Analysis Information for Risk Management Plan 70
14.1 Documentation Required for Worst-Case Scenarios for Toxic Substances 70
14.2 Documentation Required for Alternative Scenarios for Toxic Substances 71
14.3 Documentation Required for Worst-Case Scenarios for Flammable Substances . . 71
14.4 Documentation Required for Alternative Scenarios for Flammable Substances ... 72
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TABLE OF CONTENTS
(Continued)
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APPENDICES
Appendix A: Publicly Available Models and References for Calculation Methods 73
Appendix B: Toxic Substances , 81
B.I Data for Toxic Substances . .....;.. .;.;,,. . , . . . . 82
B.2 Mixtures Containing Toxic Liquids 89
Appendix C: Flammable Substances 91
C.I Equation for Estimation of Distance to 1 psi Overpressure for Vapor Cloud
Explosions 92
C.2 Mixtures of Flammable Substances 92
C.3 Data for Flammable Substances 93
Appendix D: Technical Background 101
D.I Worst-Case Release Rate for Gases 102
D.I.I Unmitigated Release 102
D.1.2 Gaseous Release Inside Building 102
D.2 Worst-Case Release Rate for Liquids
102
D.3
D.2.1 Evaporation Rate Equation 102
D.2.2 Factors for Evaporation Rate Estimates 103
D.2.3 Common Water Solutions 104
D.2.4 Releases Inside Buildings 105
Toxic Endpoints 107
D.4 Reference Tables for Distances to Toxic and Flammable Endpoints
108
D.4.1 Neutrally Buoyant Gases 108
D.4.2 Dense Gases 109
0.4.3 Choice of Reference Table for Liquids and Solutions 110
D.5 Worst-Case Consequence Analysis for Flammable Substances 110
D.6 Alternative Scenario Analysis for Toxic Gases Ill
D.7 Alternative Scenario Analysis for Toxic Liquids 113
D.7.1 Releases from Holes in Tanks . 113
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TABLE OF CONTENTS
(Continued)
: •>,..-. Page
D.7.2 Releases from Pipes . 114
D.8 Vapor Cloud Fires ......: 115
D.9 Pool Fires 115
>: D.10 BLEVEs ........:.. :. . . - 118
D.ll Alternative Scenario Analysis for Vapor Cloud Explosions 120
Appendix E: Risk Management Program Rule 122
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VI
LIST OF EXHIBITS
Exhibit Page
1 Required Parameters for Modeling 3
2 Atmospheric Stability Classes 45
A-l Summary of Several Public Domain Models 75
A-2 Selected References for Information on Consequence Analysis Methods . 79
B-l Data for Toxic Gases 83
B-2 Data for Toxic Liquids 85
B-3 Data for Water Solutions of Toxic Substances and for Oleum 88
C-l Heats of Combustion for Flammable Substances 94
C-2 Data for Flammable Gases 97
C-3 Data for Flammable Liquids 100
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Roadmap to Consequence Analysis Guidance by Type of Chemical
Type of Chemical and Release Scenario
Applicable Sections and Appendices
Toxic Gas
Worst-Case Scenario
1) Define Worst Case
2) Select Scenario
3) Calculate Release Rates
Unmitigated
Passive Mitigation
Refrigerated
4) Find Toxic Endpoint
5) Determine Reference Table and Distance
Dense or Neutrally Buoyant Plume
Urban or Rural
Release Duration
Section 2.1
Sections 2.2 & 2.3
Section 3.1.1
Section 3.1.2
Section 3.1.3
Appendix B (Exhibit B-l)
Section 3,1.3, 3.2.3
Section 4 & Appendix B (Exhibit B-l)
Sections 2.1 & 4
Section 2.1
Alternative Scenario
1) Define Alternative Scenario
2) Select Scenario
3) Calculate Release Rates
Unmitigated (from tanks and pipes)
Active or Passive Mitigation
4) Find Toxic Endpoint
5) Determine Reference Table and Distance
Dense or Neutrally Buoyant Plume
Urban or Rural
Release Duration
Section 6
Section 7
Section 8.1.1
Section 8.1.2
Appendix B (Exhibit B-l)
Section 9 & Appendix B (Exhibit B-l)
Sections 2.1 & 9
Section 8.1.1
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Toxic Liquid
Worst-Case Scenario
1) Define Worst Case
2) Select Scenario
3) Calculate Release Rates
Releases from pipes
Unmitigated Pool Evaporation
Passive Mitigation (dikes, buildings)
Release at Ambient Temperature
Release at Elevated Temperature
Releases of Solutions
Releases of Mixtures
4) Find Toxic Endpoint
For Liquids/Mixtures
For Solutions
5) Determine Reference Table and Distance
Dense or Neutrally Buoyant Plume (liquids)
Dense or Neutrally Buoyant Plume (solutions)
Urban or Rural
Release Duration (liquids)
Release Duration (solutions)
Section 2.1
Sections 2.2 & 2.3
Section 3.2.1
Section 3.2.2
Section 3.2.3
Section 3.2.2
Section 3.2.2
Section 3.3 & Appendix B (Exhibit B-3)
Section 3.2.4 and Appendix B (Section B.2)
Appendix B (Exhibit B-2)
Appendix B (Exhibit B-3)
Section 4 and Appendix B (Exhibit B-2)
Section 4 and. Appendix B (Exhibit B-3)
Section 2.1 and 4, '.
Section 3.2.2
Section 4
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IX
Toxic Liquid
Alternative Scenario
1) Define Alternative Scenario
2) Select Scenario
3) Calculate Release Rates
Unmitigated (from tanks and pipes)
Active or Passive Mitigation
Release at ambient temperature
Release at elevated temperature
Release of solution
4) Find Toxic Endpoint
For liquids/mixtures
For solutions
5) Determine Reference Table and Distance
Dense or Neutrally Buoyant Plume (liquids/mixtures)
Dense or Neutrally Buoyant Plume (solutions)
Urban or Rural
Release Duration (liquids/mixtures)
Release Duration (liquids/mixtures)
Section 6
Section 7
Section 8.2
Section 8.2.1
Section 8.2.2
Section 8.2.3
Section 8.2.3
Sections 8.2.4 and 3.3 and Appendix B (Exhibit B-3)
Appendix B (Exhibit B-2)
Appendix B (Exhibit B-3)
Section 9 and Appendix B (Exhibit B-2)
Section 9 and Appendix B (Exhibit B-3)
Sections 2.1 and 9
Section 3.2.2
Section 9
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Flammable Substances
Worst-Case Scenario
1) Define Worst Case
2) Select Scenario
3) Determine Distance to Overpressure Endpoint
For Pure Flammable Substances
For Flammable Mixtures
Sections 5.1 and 2.1
Section 5.1 and 2.2 and 2.3
Section5.1
Section 5.2
Alternative Scenario
1) Define Alternative Scenario
2) Select Scenario
3) For Vapor Cloud Fires
Calculate Release Rates (gases)
Calculate Release Rates (liquids)
Find Lower Flammability Limit (gases)
Find Lower Flammability Limit (liquids)
Dense or Neutrally Buoyant (gases)
Dense or Neutrally Buoyant (liquids)
Urban or Rural
Release Duration
Determine Distance
4) For Pool Fires
5) For BLEVEs
6) For Vapor Cloud Explosions
Section 10
Section 10
Section 12.1 . .
Section 11.1 and Appendix C (Exhibit C-2)
Section 11.2
Appendix C (Exhibit C-2)
Appendix C (Exhibit C-3)
Appendix C (Exhibit C-2)
Appendix C (Exhibit C-3)
Section 2.1 and 9
Section 12.1
Section 9
Section 12.2 and Appendix C (Exhibit C-3)
Section 12.3
Section 12.4
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OFFSITE CONSEQUENCE ANALYSIS GUIDANCE
1.0 Overview
Under the accidental release provisions of the Clean Air Act, regulated sources are required
to conduct hazard assessments, including offsite consequence analyses. This guidance is intended to
assist sources to conduct such offsite consequence analyses for worst-case release scenarios involving
regulated substances and alternative release scenarios. The worst-case consequence analyses and the
analyses for alternative scenarios are to be reported in the risk management plan (RMP). Consult
Chapters 13 and 14 of this document for information on what you will need to report.
If your site has Program 1 processes, you must submit information on a worst-case release
scenario for each toxic and flammable substance held above the threshold quantity in a Program 1
process. If your site has Program 2 or Program 3 processes, you must provide information on one
worst-case release for all toxic regulated substances present above the threshold quantity and one
worst-case release scenario for all flammable regulated substances present above the threshold
quantity. You may need to submit an additional worst-case scenario if a worst-case release from
another process at the source would potentially affect public receptors different from those potentially
affected by the initial worst-case scenario(s) for flammable and toxic regulated substances.
In addition to a worst-case release scenario, sources with Program 2 and Program 3 processes
must also provide information on alternative release scenarios. Alternative release scenarios are
should be those that may result in concentrations, overpressures, or radiant heat that reach the
endpoints specified for these effects offsite. You must present information on one alternative release
scenario for each regulated toxic substance, including the substance used for the worst-case release,
held above the threshold quantity and one alternative release scenario to represent all flammable
substances held above the threshold quantity.
The rule for risk management programs for accidental release prevention can be found at the
end of this document as Appendix E. Consult the rule for details of the requirements' for regulated
sources.
This guidance provides simple methods and reference tables for determining consequence
distances for worst-case and alternative release scenarios. Results obtained using these methods are
expected to be conservative. Conservative assumptions have been introduced to compensate for high
levels of uncertainty. The methodology provided is optional. If you use this guidance to derive your
distances to endpoints, you will be considered to be in compliance with the requirements for offsite
consequence analyses. You may, however, use other air dispersion models or computation methods
provided that:
• They are publicly or commercially available or they are proprietary models
that you are willing to share with the implementing agency;
• They are appropriate for the chemicals and conditions being modeled;
• You use the applicable definitions of worst-case scenarios; and
• You use the applicable parameters specified in the rule.
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Exhibit 1 (next page) briefly presents the required parameters for modeling both worst-case
and alternative scenarios. If you do your own modeling, you may consider some site-specific
conditions for the worst-case analysis, as noted in the exhibit, and use site-specific conditions for the
alternative scenario analysis. For this guidance, a number of assumptions had to be made for broad
applicability and simplicity of use. These assumptions, which are noted in Exhibit 1 and in the text,
are built into and chemical-specific tables of data to be used in carrying out the release rate
calculations and the reference tables of distances. :
Appendix A of this guidance provides some information on public domain models and
references that may be consulted for other methods of analysis. You are not limited to the models
and references included in the appendix, but may use any applicable model or method, this appendix
does not include details on the capabilities of the models listed. You will find that modeling results
may sometimes vary greatly from model to model.
In addition to this generic guidance, EPA is providing specific guidance for several industry
sectors, including:
• Ammonia, refrigeration, Model Risk Management Program and Plan for
Ammonia Refrigeration (currently available); ...
• Propane distribution (currently in development); and
• Water treatment (currently in development).
2.0 Determining Worst-Case Scenario
2.1 Definition of Worst-Case Scenario .
EPA has defined a worst-case release as the release of the largest quantity of a regulated
substance from a vessel or process line failure that results in the greatest distance to a specified
endpoint. The largest quantity should be determined taking into account administrative controls.
Administrative controls are procedures that limit the quantity of a substance that can be stored or
processed in a vessel or pipe at any one time, or, alternatively, procedures that occasionally allow the
vessel or pipe to store larger than usual quantities (e.g., during shutdown/turnaround). For the worst-
case analysis, you do not need to consider the possible causes of the worst-case release or the
probability that such a release might occur; the release is simply assumed to take place. All releases
are assumed to take place at ground level for the worst-case analysis.
Meteorological conditions for the worst-case scenario are defined for this guidance as
atmospheric stability class F (stable atmosphere), wind speed of 1.5 meters per second (3.4 miles per
hour), and ambient air temperature of 25° C (77° F). ' ;
Two choices are provided for topography for the worst-case scenario. If your site is located
in an area with few buildings or other obstructions, you should assume open (rural) conditions. If
your site is in an urban location, or is in an area with many obstructions, you should assume urban
conditions.
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Exhibit 1
Required Parameters for Modeling
WORST CASE
ALTERNATIVE SCENARIO
Endpoints
Endpoints for toxic substances are specified in Appendix B.
For flammable substances, endpoint is overpressure of 1
pound per square inch (psi) for vapor cloud explosions.
'•'r,.;:v ;..••.' •-;•.. • '•' . .-.. : • .'-"•-
•'• ; ! '--.•'•••'• •.-.'••- • ;' " • \. • • .,
Endpoints for toxic substances are specified in Appendix B.
For flammable substances, endpoint is overpressure of 1 ps
for vapor cloud explosions, or
Radiant heat level of 5 kilowatts per square meter (kW/m2)
for 40 seconds for heat from fires (or equivalent dose), or
Lower flammability limit (LFL) as specified in NFPA
documents or other generally recognized sources.
Wind speed/stability
Use wind speed of 1.5 meters per second and F stability class
unless you can demonstrate that local meteorological data
applicable to the site show a higher minimum wind speed or
less stable atmosphere at all times during the previous three
years. If you can so demonstrate, these minimums may be
used. This guidance assumes 1 .5 meters per second and F
stability.
For site-specific modeling, use typical meteorological
conditions for your site. If you use this guidance, you
assume wind speed of 3 meters per second and D stability.
Ambient temperature/humidity
For toxic substances, use the highest daily maximum
temperature and average humidity for the site during the past
three years. If you are using this guidance, 25°C (77°F) and
50 percent humidity are assumed.
You may use average temperature/humidity data gathered a
the site or at a local meteorological station. If you are
using this guidance, 25 °C and 50 percent humidity are
assumed.
Height of release
For toxic substances, assume a ground level release.
Release height may be determined by the release scenario.
For this guidance, a ground-level release is assumed.
Topography
Use urban or rural topography, as appropriate.
Use urban or rural .topography, as appropriate.
Dense or neutrally buoyant gases
Tables or models used for dispersion of regulated toxic
substances must appropriately account for gas density. If you
use this guidance, see Tables 1-4 for buoyant gases and
Tables 5-8 for dense gases.
Tables or models used for dispersion must appropriately
account for gas density. If you use this guidance, see
Tables 10-13 for buoyant gases and Tables 14-17 for dense
gases.
Temperature of released substance
Consider liquids (other than gases liquefied by refrigeration)
to be released at the highest daily maximum temperature,
based on data for the previous three years, or at process
temperature, whichever is higher. Assume gases liquefied by
refrigeration at atmospheric pressure are released at their
boiling points. If you are using this guidance, 25 °C or the
boiling point of the released substance may be used.
Substances may be considered to be released at a process o
ambient temperature that is appropriate for the scenario.
If you are using this guidance, 25 °C or the boiling point of
the released substance may be used.
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Toxic gases. Toxic gases include all regulated toxic substances that are gases at ambient
temperature (temperature 25° C, 77° F), with the exception of gases liquefied by refrigeration under
atmospheric pressure. For the consequence analysis, a gaseous release of the total quantity is
assumed to occur in 10 minutes. Passive mitigation measures (e.g., enclosure) may be taken into
account in the analysis of the worst-case scenario. Gases liquefied by refrigeration alone and released
into diked areas may be modeled as liquids at their boiling points and assumed to be released from a
pool by evaporation.
The endpoint for air dispersion modeling to estimate the consequence distance for a release of
a toxic gas is presented for each regulated toxic gas in Exhibit B-l of Appendix B. The toxic
endpoint is, in order of preference: (1) the Emergency Response Planning Guideline 2 (ERPG-2),
developed by the American Industrial Hygiene Association (AIHA), or (2) the Level of Concern
(LOG) for extremely hazardous substances (EHSs) regulated under section 302 of the Emergency
Planning and Community Right-to-Know Act (EPCRA). This endpoint was chosen as the threshold
for serious injury from exposure to a toxic substance in the air. (See Appendix D, Section D.3, for
additional information on the toxic endpoint.)
Toxic liquids. For toxic liquids, the total quantity in a vessel is assumed to be spilled onto a
flat, non-absorbing surface. For toxic liquids carried in pipelines, the quantity that might be released
from the pipeline is assumed to form a pool. Passive mitigation systems (e.g., dikes) may be taken
into account in consequence analysis. The total quantity spilled is assumed to spread instantaneously
to a depth of 0.39 inch (one centimeter) in an undiked area or to cover a diked area instantaneously.
The release rate to air is estimated as the rate of evaporation from the pool. If liquids at your site
might be spilled onto a surface that could rapidly absorb the spilled liquid (e.g., porous soil), the
methods presented in this guidance may greatly overestimate the consequences of a release. Consider
using another method in such a case.
The endpoint for air dispersion modeling to estimate the consequence distance for a release of
a toxic liquid is presented for each regulated toxic liquid in Exhibit B-2 of Appendix B. The toxic
endpoint is, in order of preference: (1) the ERPG-2 or (2) the LOG for EHSs, as for toxic gases.
Flammable substances. For regulated flammable substances, including both flammable gases
and volatile flammable liquids, the worst-case release is assumed to result in a vapor cloud containing
the total quantity of the substance that could be released from a vessel or pipeline. The entire
quantity in the cloud is assumed to be between the upper and lower flammability limits of the
substance. For the worst-case consequence analysis, the vapor cloud is assumed to detonate.
The endpoint for the consequence analysis of a vapor cloud explosion of a regulated
flammable substance is an overpressure of 1 pound per square inch (psi). This endpoint was chosen
as the threshold for potential serious injuries to people as a result of property damage caused by an
explosion (e.g., injuries from flying glass from shattered windows or falling debris from damaged
houses). (See Appendix D, Section D.5 for additional information on this endpoint.)
2.2 Determination of Quantity for the Worst-Case Scenario
For the analysis of the worst-case scenario, you must consider the largest quantity of a
regulated substance handled on site in a single vessel at any one time, taking into account
administrative controls. For example, if you have written procedural restrictions that limit vessel
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inventories to less than the maximum, you would not consider the maximum possible vessel
inventory. If the vessel normally contains only a small quantity, but may contain a much greater
quantity under special circumstances, such as a turnaround, you must use the larger quantity for the
worst case. You also must consider the quantity that might be released if a pipeline were sheared.
2.3 Selecting Single Worst-Case Scenario
The hazard assessment requires a single offsite consequence analysis of the worst-case
scenario for substances in each hazard category (i.e., one for regulated toxic substances and one for
regulated flammable substances). Only the hazard for which the substance is listed needs to be
considered (i.e., substances on the list of regulated toxic substances that are also flammable should be
analyzed only for their toxic hazard; substances on the list of regulated flammable substances should
be considered only for flammability).
The substance chosen for the consequence analysis for each hazard should be the substance
that has the potential to cause the greatest offsite consequences. Choosing the toxic substance that
might lead to the greatest offsite consequences may require a screening analysis of the toxic
substances on site, because the potential consequences are dependent on a number of factors,
including quantity, toxicity, and volatility. Location (distance to the fenceline) and conditions of
processing or storage (e.g., a high temperature process) also should be considered.
For flammable substances, the consequences of a vapor cloud explosion must be considered in
the analysis. The severity of the consequences of a vapor cloud explosion depends on the quantity of
the released substance in the vapor cloud and its heat of combustion. In most cases, the analysis
probably should be based on the regulated flammable substance present in the greatest quantity;
however, a substance with a high heat of combustion may have a greater potential offsite impact than
a larger quantity of a substance with a lower heat of combustion. In some cases, a regulated
flammable substance that is close to the fenceline might have a greater potential offsite impact than a
larger quantity farther from the fenceline.
3.0 Release Rates for Toxic Substances
This section describes 3. simple method for estimating release rates for regulated toxic
substances for the worst-case scenario. The estimated release rates may be used to estimate
dispersion distances to the toxic endpoint for regulated toxic gases and liquids, as discussed in Section
4.
3.1 Release Rates for Toxic Gases
Regulated substances that are gases at ambient temperature (temperature 25° C, 77° F) should
be considered gases for consequence analysis, with the exception of gases liquefied by refrigeration at
atmospheric pressure. Gases liquefied under pressure should be treated as gases. Gases liquefied by
refrigeration alone and released into diked areas may be treated as liquids at their boiling points. You
may consider passive mitigation for gaseous releases and releases of gases liquefied by refrigeration.
For regulated toxic gases, you may estimate a release rate as described below. Sections 3.1.1 and
3.1.2 describe methods for estimating release rates for unmitigated and mitigated gaseous releases,
and Section 3.1.3 describes the estimation of the release rate of a refrigerated liquefied gas from a
diked pool.
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EPA is providing guidance, including guidance on offsite consequence analysis, specifically
for ammonia refrigeration facilities in Model Risk Management Program and Plan for Ammonia
Refrigeration. The ammonia-specific guidance takes into account the conditions encountered in
ammonia refrigeration; modeling results are somewhat less conservative than the results obtained
using this off-site consequence analysis guidance. If you are conducting a worst-case analysis for
ammonia used for refrigeration, you should consult the guidance for ammonia refrigeration facilities.
3.1.1 Unmitigated Releases of Gas •
If no passive mitigation system is in place, estimate the release rate for the release over a 10r
minute period of the largest quantity resulting from a pipe or vessel failure. For a release from/a
vessel, calculate the release rate as follows: •
QR--&
10
(1)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds) • ;
For a gas pipeline, assume the pipeline is sheared and use the usual flow rate through the pipe as the
release rate for the consequence analysis.
Example 1. Gas Release (Diborane)
You have a tank containing 2,500 pounds of diborane gas. Assuming the total quantity in the tank is
released over a 10-minute period, the release rate (QR), from .Equation 1, is:
QR = ,2,500 pounds/10 minutes = 250 pounds per minute
3.1.2 Releases of Gas in Enclosed Space
If a gas is released in an enclosure such as a building or shed, the release rate to the outside
air may be lessened considerably. The dynamics of this type of release are complex; however, you
may use the simplified method presented here to estimate an approximate release rate to the outside
air from a release in an enclosed space. The enclosed space is assumed to be in direct contact with
the outside air; i.e., this method does not apply to a release in a room that is enclosed within a
building. For the worst case, assume as before that the largest quantity resulting from a pipe or
vessel failure is released over a 10-minute period. Determine the unmitigated worst-case scenario
release rate of the gas as the quantity released divided by 10 (Equation 1). The release rate from the
building will be approximately 55 percent of the worst case scenario release rate (see Appendix D,
Section D.I.I for the derivation of this factor), as follows:
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QR = JcO.55
10
(2)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
0.55 = Mitigation factor (discussed in Appendix D, Section D.I.2)
Example 2. Gas Release in Enclosure (Diborane)
Suppose the diborane gas from Example 1 is released inside a building at the rate of 250 pounds per
minute. The mitigated release to the outside air from the building would be:
QR = 250 pounds/minute x 0.55 = 138 pounds per minute
3.1.3 Releases of Liquefied Refrigerated Gas in Diked Area
If you have a toxic gas that is liquefied by refrigeration alone, and it will be released into an
area where it will be contained by dikes to form a pool more than 0.033 feet (1 centimeter) in depth,
you can carry out the worst-case analysis assuming evaporation from a liquid pool. First compare the
diked area to the maximum area of the pool that could be formed. You can use Equation 6 in Section
3.2.3 to estimate the maximum size of the pool. Density factors (DF) for toxic gases at their boiling
points are listed in Exhibit B-l of Appendix B. If the pool formed by the released liquid would be
smaller than the diked area, assume a ten-minute gaseous release, and estimate the release rate as
described in Section 3.1.1. If the dikes prevent the liquid from spreading out, to form a pool of
maximum size (assuming a depth of 0.033 feet (one centimeter)), you may use the method described
in Section 3.2.3 for mitigated liquid releases to estimate a release rate from a pool at the boiling point
of the released substance. Use Equation 8 in Section 3.2.3 for the release rate. The Liquid Factor
Boiling (LFB) for each toxic gas is listed in Exhibit B-l of Appendix B.
After you have estimated the release rate, estimate the duration of the vapor release from the
pool by dividing the total quantity spilled by the release rate.
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-8-
Example 3. Mitigated Release of Gases Liquefied by Refrigeration (Chlorine)
You have a refrigerated tank containing 50,000 pounds of liquid chlorine. A diked area around the
chlorine tank of 275 square feet is sufficient to hold all of the spilled liquid chlorine. Once the liquid
spills into the dike, it is then assumed to evaporate at its boiling point (-29° F or 239 Kelvin). The
evaporation rate at the boiling point is determined from Equation 8. For the calculation, wind speed
is assumed to be 1.5 meters per second and the wind speed factor is 1.4, LFB for chlorine (from
Exhibit B-l) is 0.19, and A is 275 square feet. The release rate is:
QR = 1.4 x 0.19 x 275 = 73 pounds per minute
The duration of the release would be:
t = 50,000 pounds/73 pounds per minute = 685 minutes
3.2 Release Rates for Toxic Liquids
The release rate to air for toxic liquids is assumed to be the rate of evaporation from the pool
formed by the released liquid. Assume the total quantity in a vessel is released into the pool, or
estimate the quantity that might be released from a pipe as discussed in Section 3.2.1 below. Passive
mitigation measures (e.g., dikes) may be considered in determining the area of the pool and the
release rate. If the substance on site is always at ambient temperature, the evaporation rate may be
determined assuming the pool and surroundings are at 25° C (77° F); this guidance provides data for
this calculation. This guidance also provides data for estimating the evaporation rate at the boiling
point of the substance, for cases where the substance may be at elevated temperatures.
The calculation methods provided in this section apply only to substances that are liquids
under ambient conditions. For substances that are gases under ambient conditions, but are liquefied
under pressure or refrigeration, see Section 3.1 above.
3.2.1 Releases of Liquids from Pipes
To consider a liquid release from a broken pipe, estimate the maximum quantity that could be
released assuming that the pipe is full of liquid. To estimate the quantity in the pipe, you need to
know the length of the pipe (in feet) and cross-sectional area of the pipe (in square feet). Note also
that liquid may be released from both directions at a pipe shear (both in the direction of operational
flow and the reverse direction, depending on the location of the shear). Therefore, the length would
be the full length of pipe carrying the liquid on the facility grounds. Then, the volume of the liquid
in the pipe (in cubic feet) is the length of the pipe times the cross-sectional area. The quantity in the
pipe (in pounds) is the volume divided by the Density Factor (DF) times 0.033. (1/(DF times 0.033)
is equal to density in pounds per cubic foot). Assume the estimated quantity (in pounds) is released
into a pool and use the method and equations described below in Section 3.2.2 (unmitigated releases)
or 3.2.3 (releases with passive mitigation) to determine the evaporation rate of the liquid from the
pool.
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3.2.2 Unmitigated Releases of Liquids
If no passive mitigation measures are in place, the liquid is assumed to form a pool 0.39 inch
(one centimeter) deep instantaneously. You may calculate the release rate to air from the pool (the
evaporation rate) as discussed below for releases at ambient or elevated temperature.
Ambient temperature. If the liquid is always at ambient temperature, find the Liquid Factor
Ambient (LFA) and the Density Factor (DF) in Exhibit B-2 of Appendix B (see Appendix D, Section
D.2.2 for the derivation of these factors). Calculate the release rate of the liquid from the following
equation:
QR = QS x 1.4 x LFA x DF
(3)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
( 1.4 = Wind speed factor = 1.5°-78, where 1.5 meters per second (3.4 miles per hour) is the
wind speed for the worst case
LFA = Liquid Factor Ambient
DF = Density Factor
Example 4. Unmitigated Liquid Release at Ambient Temperature (Acrylonitrile)
You have a tank containing 20,000 pounds of acrylonitrile at ambient temperature. The total
quantity in the tank is spilled onto the ground in an undiked area, forming a pool. Assume the pool
spreads out to a depth of one centimeter. The release rate from the pool (QR) is calculated from
Equation 3. For the calculation, the wind speed is assumed to be 1.5 meters per second and the
wind speed factor is 1.4. From Exhibit B-2, Appendix B, LFA is for acrylonitrile is 0.018 and DF
is 0.61. Then:
QR = 20,000 x 1.4 x 0.018 x 0.61 = 307 pounds per minute
The duration of the release (from Equation 5) would be:
t = 20,000 pounds/307 pounds per minute = 65 minutes
Elevated temperature. If the liquid is at an elevated temperature (any temperature above 25°
C), find the Liquid Factor Boiling (LFB) and the Density Factor (DF) in Exhibit B-2 of Appendix B
(see Appendix D, Section D.2.2, for the derivation of these factors). Calculate the release rate of the
liquid from the following equation:
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-10-
QR = QS x 1.4 x LFB x DF
(4)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
1.4 = Wind speed factor = 1.5°-78, where 1.5 meters per second (3.4 miles per hour) is the
wind speed for the worst case
LFB = Liquid Factor Boiling
DF = Density Factor
Example 5. Unmitigated Release at Elevated Temperature (Acrylonitrile)
You have a tank containing 20,000 pounds of acrylonitrile at an elevated temperature. The total
quantity in the tank is spilled onto the ground in an undiked area, forming a pool. Assume the pool
spreads out to a depth of 0.033 feet (one centimeter). The release rate from the pool is calculated
from Equation 4. For the calculation, the wind speed factor for 1.5 meters per second is 1.4. From
Exhibit, B-2, Appendix B, LFB for acrylonitrile is 0.11 and DF is 0.61. Then:
QR = 20,000 x 1.4 x 0.11 x 0.61 = 1,880 pounds per minute
The duration of the release (from Equation 5) would be:
t = 20,000 pounds/1880 pounds per minute =11 minutes
Duration of Release. After you have estimated a release rate as described above, determine
the duration of the vapor release from the pool (the time it will take for-the liquid pool to evaporate
completely). To estimate the time in minutes, divide the total quantity released (in pounds) by the
release rate (in pounds per minute) as follows:
t =
QR
(5)
where': t = Duration of the release (minutes)
QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
You will use the duration of the vapor release from the pool to decide which table is appropriate for
estimating distance, as discussed in Section 4 below.
3.2.3 Releases of Liquids 'with Passive Mitigation
Diked Areas. If the toxic liquid will be released into an area where it will be contained by
dikes, compare the diked area to the maximum area of the pool that could be formed; the smaller of
the two areas should be used in determination of the evaporation rate. The maximum area of the pool
(assuming a depth of 0.033 feet (1 centimeter)) is:
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-11-
A := QS x DF
(6)
where: A = Area (square feet)
,, QS = Quantity released (pounds)
DF = Density Factor (listed in Exhibit B-2, Appendix B)
If the maximum area of the pool is smaller than the diked area, calculate the release rate as
described for "no mitigation" above. If the diked area is smaller, go to Exhibit B-2 in Appendix B to
find the Liquid Factor Ambient (LFA), if the liquid is at ambient temperature, or the Liquid Factor
Boiling (LFB), if the liquid is at a temperature above ambient: Calculate the release rate from the
diked area as follows:
QR = 1,4 x LFA x A
(7)
or
QR = 1.4 x LFB x A
(8)
where: QR = Release rate (pounds per minute)
1.4 = Wind speed factor = 1.5°-78, where 1.5 meters per second (3.4 miles per hour) is the
wind speed for the worst case
LFA = Liquid Factor Ambient (listed in Exhibit B-2, Appendix B)
, , LFB := Liquid Factor Boiling (listed in Exhibit B-2,. Appendix B) , , :
A = Diked area (square feet)
In case of a large liquid spill, you also need to consider whether the liquid could overflow the
diked area. Follow these steps:
• Determine the volume of the diked area in cubic feet from length times width times
depth (in feet).
• Determine the volume of liquid spilled in cubic feet from QS x DF x 0.033 (DF x
0.033 is equal to I/density in pounds per cubic foot).
*-',-, • ' ' •
• Compare the volume of the diked area to the volume of liquid spilled. If the volume
of liquid is greater than the volume of the diked area:
Subtract the volume of the diked area from the total volume spilled to
determine the volume that might overflow the diked area.
Estimate the maximum size of the pool formed by the overflowing liquid (in
square feet) by dividing the overflow volume (in cubic feet) by 0.033 (the
depth of the pool in feet). .
Add the surface area of the diked area and the area of the pool formed by the
overflow to estimate the total pool area (A).
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-12-
Estimate the evaporation rate from Equation 7 or 8 above.
After you have estimated the release rate, estimate the duration of the vapor release from the
pool by dividing the total quantity spilled by the release rate (Equation 5 above).
Example 6. Mitigated Liquid Release at Ambient Temperature (Bromine)
You have a tank containing 20,000 pounds of bromine at ambient temperature. Assume that the total
quantity in the tank is spilled into a diked area 10 feet by 10 feet (area 100 square feet). The area
(A) that would be covered to a depth of 0.033 feet (one centimeter) by the spilled liquid is given by
Equation 6 as the quantity released (QR) times the Density Factor (DF). From Exhibit B-2,
Appendix B, DF for bromine is 0.16. Then:
A = 20,000 x 0.16, or 3,200 square feet
The diked area is smaller than the maximum pool area; therefore, the diked area should be used to
determine the evaporation rate from Equation 7. For the calculation, wind speed is 1.5 meters per
second, the wind speed factor is 1.4, LFA for bromine (from Exhibit B-2) is 0.073, and A is 100
square feet. The release rate is:
QR = 1.4 x 0.073 x 100 = 10 pounds per minute
The duration of the release would be:
t = 20,000 pounds/10 pounds per minute = 2,000 minutes
Other containment. If the toxic liquid will be contained by other means (e.g., enclosed catch
basins or trenches), consider the total quantity that could be spilled and estimate the surface area of
the released liquid that potentially would be exposed to the air. Look at the dimensions of trenches or
other areas where spilled liquids would be exposed to the air to determine the surface area of pools
that could be formed. Use the instructions above to estimate a release rate from the total surface
area.
Releases Into Buildings. If the toxic liquid is released inside a building, compare the area of
the building floor to the maximum area of the pool that could be formed; the smaller of the two areas
should be used in determining the evaporation rate. The maximum area of the pool is determined as
described above in releases into diked areas, using Equation 6. The area of the building floor is:
A = Lx W
(9)
where: A = Area (square feet)
L = Length (feet)
W = Width (feet)
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-13-
The evaporation rate is then determined for a worst case scenario (i.e., wind speed is 1.5 meters per
second (3.4 miles per hour)). The maximum rate of evaporated liquid exiting the building is taken to
be 10 percent of the calculated worst case scenario evaporation rate (see Appendix D, Section D.2.4
for the derivation of this factor), as follows:
QRB = 0.1 x QR
(10)
where: QRB = Release rate from building
QR = Release rate from pool, estimated as discussed above
0.1 = Mitigation factor, discussed in Appendix D, Section D.2.4
Example 7. Liquid Release Inside Building (Bromine)
Suppose that your tank of bromine from Example 6 is contained inside a storage shed 10 feet by 10
feet (area 100 square feet). From Example 6, you see that the area covered by the bromine in an
unenclosed space would be 3,200 square feet. The building area is smaller than the maximum pool
area; therefore, the building area should be used to determine the evaporation rate from Equation 7.
For the calculation, first determine the worst case scenario evaporation rate:
QR = 1.4 x 0.073 x 100 = 10 pounds per minute
The release rate to the outside air of the evaporated liquid leaving the building would then be:
QRB = 0.1 X 10 pounds per minute = 1 pound per minute
3.2.4 Mixtures Containing Toxic Liquids
In case of a spill of a liquid mixture containing a regulated toxic substance (with the exception
of common water solutions, discussed in the next section), you have several options for estimating a
release rate:
• Carry out the analysis ai> described above in Sections 3.2.2 or 3.2.3 using the quantity
of the regulated substance in the mixture and the liquid factor (LFA or LFB) and
density factor for the regulated substance in pure form. This is a simple approach
that will likely give conservative results.
• If you know the partial pressure of the regulated substance in the mixture, you may
estimate a more realistic evaporation rate. An equation for the evaporation rate is
given at the end of Section B.2 in Appendix B.
In this case, estimate a pool size for the entire quantity of the mixture, for an
unmitigated release. If you know the density of the mixture, you may use it
in estimating the pool size; otherwise, you may assume the density is the same
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-14-
as the pure regulated substance (in most cases, this assumption is unlikely to
have a large effect on the results).
You may estimate the partial pressure of the regulated substance in the mixture by the
method described in Section B.2 in Appendix B and use the equation presented there
to estimate an evaporation rate. As discussed above, use the pool size for the entire
quantity of the mixture for an unmitigated release.
Examples. Mixture Containing Toxic Liquid (Acrylonitrile)
You have a tank containing 50,000 pounds of a mixture of acrylonitrile (a regulated substance) and
N,N-dimethylformamide (not regulated). The weight of each of the components of the mixture is
known (acrylonitrile = 20,000 pounds; N,N-dimethylformamide = 30,000 pounds.) The molecular
weight of acrylonitrile, from Exhibit B-2, is 53.06, and the molecular weight of N,N-
dimethylformamide is 73.09. Using Equation B-3, Appendix B, calculate the mole fraction of
acrylonitrile in the solution as follows:
Xr =
(20.000/53.06")
(20,000/53.06) + (30,000/73.09)
Xr = 377 • .
377 + 410
Xr = 0.48
Estimate the partial vapor pressure of acrylonitrile using Equation B-4 as follows (using the vapor
pressure of acrylonitrile in pure form at 25°C, 108 mm Hg, from Exhibit B-2, Appendix B):
VPm = 0.48 x 108 = 51.8 mm Hg
Before calculating evaporation rate for acrylonitrile in the mixture, you must determine the surface
area of the pool formed by the entire quantity of the mixture, using Equation 6. The quantity
released is 50,000 pounds and the Density Factor for acrylonitrile is 0.61 in Exhibit B-2; therefore:
A = 50,000 x 0.61 = 30,500 square feet '
Now calculate the evaporation rate for acrylonitrile in the mixture from Equation B-5 using the VPm
and A calculated above:
QR = 0.0035 x 1.0 x (53.06)% x 30.500 x 51.8
298
QR = 262 pounds per minute
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-15-
'3*3 Release Rates for Common Water Solutions of Toxic Substances
This section presents a simple method of estimating the release rate from spills of water
solutions of several substances. Oleum (a solution of sulfur trioxide in sulfuric acid) also is discussed
in this section. " •"• ; •-•'•'* • '-
The vapor pressure and evaporation rate of a substance in solution depends on its
concentration in the solution. If a concentrated water solution containing a volatile toxic substance is
spilled, the toxic substance initially will evaporate more quickly than water from the spilled solution,
and the vapor pressure and evaporation rate will decrease as the concentration of the toxic substance
in the solution decreases. At much lower concentrations, water may evaporate more quickly than the
toxic substance. There is one concentration at which the!composition of the solution does not change
as,evaporation occurs. 'For most situations of interest, the concentration11 exceeds this concentration,
and the toxic substance evaporates more quickly than'water. ; "'" •' !
For estimating release rates from solutions, this guidance lists liquid factors (ambient) for
several common water solutions at several concentrations that take into account the decrease in
evaporation rate with decreasing concentration. Exhibit B-3 in Appendix B provides LFA and DF
values for several concentrations of ammonia, formaldehyde, hydrochloric acid, hydrofluoric acid,
and nitric acid in water solution. Factors for oleum are also included in the exhibit. These factors
may be used to estimate an average release rate for the listed substances from a pool formed by a spill
of solution. Liquid factors are provided for two different wind speeds, because the wind speed affects
the rate of evaporation.
For the worst case, the factor for a wind speed of 1.5 meter per second (3.4 miles per hour)
should be used. You need to consider only the first 10 minutes of the release for solutions under
ambient conditions in estimating the consequence distance, because the toxic component in a solution
evaporates fastest during the first few minutes of a spill, when its concentration is highest. Therefore,
you do not need to take the duration of the release into account. Estimate release rates as follows:
• . Unmitigated, If no passive mitigation measures are in place, and the solution is at
ambient temperature, find the LFA at 1.5 meters per,second (3.4 miles per hour) and
DF for the solution in Appendix B, Exhibit B-3. Follow the instructions for liquids
presented in Section 3.2.2 above to estimate the release rate of the listed substance in
solution. Use the total quantity of the solution as the quantity released (QS) in
carrying out the calculation of release rate. ., ,: . .-....:. ...
• Mitigated. If passive mitigation is in place, and the solution is at ambient
temperature, find the LFA at 1.5 meters per second (3.4 miles per hour) in Appendix
B, Exhibit B-3, and follow the instructions for liquids in Section 3.2.3 above. Use
the total quantity of the solution to estimate the maximum pool area for comparison
with the diked area.
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-16-
Example 9. Evaporation Rate for Water Solution at Ambient Temperature (Hydrochloric Acid)
You have a tank containing 50,000 pounds of 37 percent hydrochloric acid solution, at ambient
temperature. For the worst-case analysis, you assume the entire contents of the tank is released,
forming a pool. The release occurs in a diked area of 9,000 square feet.
From Exhibit B-3, Appendix B, the Density Factor (DF) for 37 percent hydrochloric acid is 0.42.
From Equation 6, the maximum area of the pool would be 50,000 times 0.42, or 21,000 square feet.
The diked area is smaller; therefore, the diked area should be used in the evaporation rate (release
rate) calculation, using Equation 7.
For the calculation using Equation 7, you need the pool area (9,000 square feet) and the Liquid
Factor Ambient (LFA) for 37 percent hydrochloric acid; you assume a wind speed of 1.5 meters per
second, so the wind speed factor is 1.4. From Exhibit B-3, Appendix B, the LFA is 0.0085. From
Equation 7, the release rate (QR) of hydrogen chloride from the pool is:
QR = 1.4 x 9,000 x 0.0085 = 107 pounds per minute
You do not need to consider the duration of the release, because only the first ten minutes are
considered.
Elevated temperature. If the solution is at an elevated temperature, the vapor pressure
of the regulated substance and its release rate from the solution will be much higher.
If you know the vapor pressure of the solution at the relevant temperature, you can
carry out the calculation of the release rate using the equations in Appendix D,
Sections D.2.1 and D.2.2. If you do not know the vapor pressure, as a conservative
approach for the worst case analysis, use the appropriate instructions, as follows:
Solutions containing substances that are gases under ambient conditions. The
list of regulated substances includes several substances that, in their pure
form, are gases under ambient conditions, but that may commonly be found in
water solutions. These substances include ammonia, formaldehyde, hydrogen
chloride, and hydrogen fluoride. For a release of a solution of ammonia,
formaldehyde, hydrochloric acid, or hydrofluoric acid above ambient
temperature, assume the quantity of the hydrogen chloride, hydrogen fluoride,
or ammonia in the solution is released as a gas over 10 minutes, as discussed
in Section 3.1 above. You may determine the amount of pure substance in the
solution from the concentration (e.g., a solution of 30 percent hydrochloric
acid by weight would contain a quantity of hydrogen chloride equal to 0.3
tunes the total weight of the solution).
-------
Example 10.
Acid)
-17-
Evaporation Rate for Water Solution at Elevated Temperature (Hydrochloric
You have 50,000 pounds of 37 percent hydrochloric acid solution in a high-temperature process. For
the worst-case analysis, you assume the entire contents of the process vessel is released. In this
case, because the solution is at an elevated temperature, you consider the release of gaseous
hydrogen chloride from the hot solution.
The solution would contain 50,000 x 0.37 pounds of hydrogen chloride, or 18,500 pounds. You
assume the entire 18,500 pounds is released over 10 minutes. From Equation 1, the release rate is
18,500 divided by 10, or 1,850 pounds per minute.
Liquids in solution. For a release of nitric acid solution at a temperature
above ambient, determine the quantity of pure nitric acid in the solution from
the concentration. Assume the quantity of pure nitric acid is released at an
elevated temperature and use the LFB to estimate a release rate as discussed in
Section 3.2 above. Similarly, for a release of oleum at an elevated
temperature, determine the quantity of free sulfur trioxide in the oleum from
the concentration and assume the sulfur trioxide is released at an elevated
temperature. Use the LFB to estimate a release rate as discussed in Section
3.2.
Example 11. Evaporation Rate for Liquids in Solution at Elevated Temperature (Nitric Acid)
You have 18,000 pounds of 90% nitric acid solution in a high temperature process. The solution
would contain 18,000 x 0.90 pounds of nitric acid, or 16,200 pounds. You assume 16,200 pounds
of pure nitric acid is released at an elevated temperature.
For the calculation using Equation 4, you need the quantity released (16,200); the Liquid Factor
Boiling (LFB) for nitric acid (0.12 found in Exhibit B-2); the Density Factor (DF) for nitric acid
(0.32 found in Exhibit B-2); and you assume a wind speed of 1.5 meter per second, so the wind
speed factor is 1.4. From Equation 4, the release rate (QR) of hot nitric .acid is:
QR = 16,200 x 1.4 x 0.12 x 0.32 = 870 pounds per minute
The duration of release (from Equation 5) would be:
t = 16,200 pounds/870 pounds per minute =19 minutes
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4.0 Estimation of Distance to Toxic Endpoint
This guidance.provides reference tables giving worst-case distances for neutrally buoyant
gases and vapors and for dense gases and vapors for both rural (open) and urban (congested) areas.
The tables were,developed assuming a wind speed of 1.5 meters per second (3.4 miles per hour) and
F stability. To use the reference tables, you need the worst-case release rates estimated as described
in the previous sections. For liquid pool evaporation, you also need the duration of the release. In
addition, you will need to determine the appropriate toxic endpoint and whether the gas or vapor is
neutrally buoyant or dense, using the exhibits in Appendix B. ,
Tables are provided for both,for 10-minute releases and for 6Q-minute releases. You should
use the tables for 10-minute releases if the duration of your release is 10 minutes or less; use the
tables for 60-minute releases if the duration of your release is more than 10 minutes. For the worst
case analysis, all releases of toxic gases are assumed to last for ;10 minutes; you need to consider the
estimated duration of the release (from Equation 5) for evaporation of pools of toxic liquids. For
evaporation of water solutions of toxic liquids, you should always use the tables for 10-minute
releases.
The tables for distances (Reference. Tables 1-8) are found at the end of Section 5. The
conditions for which each table is applicable are summarized below.
Reference Table
Number
1
2
3
4
5
6 "'
7
8
Applicable Conditions
Release Duration
.(minutes)
10
60
IP ... ' ,
60
10
60
10
60
Topography
Rural
Urban, ,
Rural
Urban
Gas, or .Vapor Density
Neutrally buoyant
Dense
To use the reference tables, follow these steps:
• Find the toxic endpoint for the substance .in Appendix B (Exhibit B-l for toxic gases
or Exhibit B-2 for toxic liquids). •
• Determine whether the table for neutrally buoyant or dense gases and vapors is
appropriate from Appendix B (Exhibit,B-l for toxic gases or Exhibit B-2 for toxic
liquids). . : ,
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-19-
• Determine whether the table for rural or urban conditions is appropriate.
Use the rural table if your site is in an open area with few obstructions.
Use the urban table if your site is in an urban or obstructed area
• Determine whether the 10-minute table or the 60-minute table is appropriate.
Always use the 10-minute table for worst-case releases of toxic gases.
— If you estimated the release duration for an evaporating toxic liquid pool to be
10 minutes or less, use the 10-minute table.
— If you estimated the release duration for an evaporating toxic liquid pool to be
more than 10 minutes, use the 60-minute table.
Neutrally Buoyant Gases or Vapors
• If Exhibit B-l or B-2 indicates the gas or vapor should be considered neutrally
buoyant, divide the estimated release rate (pounds per minute) by the toxic endpoint
(milligrams per liter).
• Find the range of release rate/toxic endpoint values that includes your calculated
release rate/toxic endpoint in the first column of the appropriate table (Reference
Table 1, 2, 3, or 4), then find the corresponding distance to the right.
Dense Gases or Vapors
• If Exhibit B-l or B-2 indicates the substance should be considered a dense gas or
vapor (heavier than air), find the distance in the appropriate table (Reference Table 5,
6, 7, or 8) as follows;
Find the toxic endpoint closest to that of the substance by reading across the
top of the table. If the endpoint of the substance is halfway between two
values on the table, choose the value on the table that is smaller (to the left).
Find the release rate closest to the release rate estimated for the substance at
the left of the table. If the calculated release rate is halfway between two
values on the table, choose the release rate that is larger (farther down on the
table).
Read across from the release rate and down from the endpoint to find the
distance corresponding to the toxic endpoint and release rate for your
substance.
The development of Reference Tables 1-8 is discussed in Appendix D, Section D.4. These
tables generally give conservative results. If you think the results of the method presented here
overstate the potential consequences of a worst-case release at your site, you may choose to use other
methods or models that take additional site-specific factors into account.
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Example 12. Gas Release (Diborane)
In Example 1, you estimated a release rate for diborane gas of 250 pounds per minute. From
Exhibit B-l, the toxic endpoint for diborane is 0.0011 mg/L; the appropriate reference table for
diborane is a neutrally buoyant gas table. Your facility and the surrounding area have many
buildings, pieces of equipment, and other obstructions; therefore, you assume urban conditions. The
appropriate reference table is Reference Table 3, for a 10-minute release of a neutrally buoyant gas
in an urban area.
The release rate divided by toxic endpoint for this example is 250/0.00.11 = 230,000.
From Reference Table 3, release rate divided by toxic endpoint falls between 221,000 and 264,000,
corresponding to about 8.1 miles.
Example 13. Gas Release (Ethylene Oxide)
You have a tank containing 10,000 pounds of ethylene oxide gas. Assuming the total quantity in the
tank is released over a 10-minute period, the release rate (QR) from Equation 1 is:
QR = 10,000 pounds/10 minutes = 1,000 pounds per minute
From Exhibit B-l, the toxic endpoint for ethylene oxide is 0.09 mg/L; the appropriate reference table
for ethylene oxide is the dense gas table. Your facility is in an open, rural area with few
obstructions; therefore, you use the table for rural areas.
Using Reference Table 5 for 10-minute releases of dense gases in rural areas, the toxic endpoint of
0.09 mg/L is closer to 0.1 than 0.075 mg/L. For a release rate of 1,000 pounds per minute, the
distance to Q.I mg/L is 3.6. miles.
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-21-
Example 14. Liquid Evaporation from Pool (Acrylonitrile)
You estimated an evaporation rate of 307 pounds per minute for acrylonitrile from a pool formed by
the release of 20,000 pounds into an undiked area (Example 4). You estimated the time for
evaporation of the pool as 65 minutes. From Exhibit B-2, the appropriate reference table for a
worst-case release of acrylonitrile is the dense gas table, and the toxic endpoint for acrylonitrile is
0.076 mg/L. Your facility is in an urban area. You use Reference Table 8 for 60-minute releases
of dense gases in Urban areas.
From Reference Table 8, the toxic endpoint closest to 0.076 mg/L is 0.075 mg/L, and the closest
release rate to 307 pounds per minute is 250 pounds per minute. Using these values, the table gives
a worst-case consequence distance of 2.9 miles.
5.0 Estimation of Distance to Overpressure Endpoint for Flammable Substances
5.1 Flammable Substances Not in Mixtures
For the worst-case scenario involving a release of flammable gases and volatile flammable
liquids, the total quantity of the flammable substance is assumed to form a vapor cloud within the
upper and lower flammability limits, and the cloud is assumed to detonate. As a conservative
assumption, 10 percent of the flammable vapor in the cloud is assumed to participate in the explosion.
You need to estimate the consequence distance to an overpressure level of 1 pound per square inch
(psi) from the explosion of the vapor cloud. An overpressure of 1 psi may cause partial demolition of
houses, which can result in serious injuries to people, and shattering of glass windows, which may
cause skin laceration from flying glass.
You may estimate the consequence distance for a given quantity of a regulated flammable
substances using Reference Table 9. This table provides distances to 1 psi overpressure for vapor
cloud explosions of quantities from 10,000 to 500,000 pounds. These distances were estimated from
Equation C-l in Appendix C, Section C.I, using data provided in Exhibit C-l, Appendix C. If you
prefer, you may calculate your worst-case consequence distance for flammable substances directly,
using Equation C-l.
-------
-22-
Example 15. Vapor Cloud Explosion (Propane)
You have a tank containing 50,000 pounds of propane. From Reference Table 9, the distance to 1
psi overpressure is 0.30 miles for 50,000 pounds of propane.
Alternatively, you can calculate the distance to 1 psi using Equation C-l from Appendix C:
D. = 17 x [ 0.1 x (50,000/2.2) x (46,333/4,680) ]%
D = 480 meters; converted to miles, 480 x 0.00062 = 0.30 miles
For the worst-case analysis of propane at propane distribution facilities, you should consult
the guidance developed specifically for this industry segment, when it becomes available.
The method presented here for analysis of vapor cloud explosions is based on a TNT-
equivalent model. Other methods are available for analysis of vapor cloud explosions, including
methods that consider site-specific conditions. You may use other methods for your worst-case
analysis if you so choose, provided you assume the total quantity of flammable substance is in the
cloud and the yield factor is 10 percent and use an endpoint of 1 psi. Appendix A includes references
to documents and journal articles on vapor cloud explosions that may be useful.
5.2 Flammable Mixtures
If you have more than 10,000 pounds of a mixture of flammable substances that meets the
criteria for listing under CAA section 112(f) (flash point below 22.8° C (73° F), boiling point below
37.8° C (100° F), National Fire Protection Association (NFPA) flammability hazard rating of 4), you
may need to carry out a worst-case consequence analysis for the mixture. For simplicity, you may
carry out the worst-case analysis based on the predominant flammable component of the mixture or a
major component of the mixture with the highest heat of combustion (see Exhibit C-l, Appendix C
for data on heat of combustion). Estimate the consequence distance from Reference Table 9 for the
major component with the highest heat of combustion, assuming that the quantity in the cloud is the
total quantity of the mixture.
-------
-23^
Example 16. Vapor Cloud Explosion of Flammable Mixture (Ethylene and Isobutane)
You have 10,000 pounds of a.mjxture of ethylene (the reactant) and isobutane (a catalyst carrier).
To carry out the worst-case analysis, assume the quantity in the cloud is the total quantity of the
mixture. Use data for ethylene because it is the component with the highest heat of combustion.
(Ethylene heat, of combustion; = 47, 145 kilojoules per kilogram; isobutane heat of combustion =
45,576, from Exhibit C-1, Appendix C). From Reference Table 9, the distance to 1 psi
overpressure is 0.18 miles, for 10,0,00 pounds of ethylene; this distance would also apply to the
10,000-pound mixture of ethylene and isobutane.
Calculating the worst-case consequence distance from Equation C-1, Appendix C:
D=' I? X[ .1 x (10000/22) x (47, 145/4,680)
••v%V-J£1^y'^is^.1^^^
''''' ''"' ""'"""•""" "••"•' '
D,= 283 meters; converted to miles, 283 x 0.00062 = 0.18 miles
Alternatively, you may estimate the heat of combustion of the mixture from the heats of
combustion of the components of the mixture using the method described in Appendix C, Section
C,2, and then use the Equation C-1 in Appendix-C to determine the vapor cloud explosion distance.
Example 17. Estimating Heat of Combustion of Mixture for Vapor Cloud Explosion Analysis
You have a mixture of 8,.QOQ pounds of ethylene (the reactant) and 2,000 pounds of isobutane (a
catalyst carrier).. To carry out the worst-case analysis, estimate the heat of combustion of the
mixture from the .heats of, combustion of the components of the mixture. (Ethylene, heat of
combustion =47,145 kilojoules per kilogram; isobutane heat of combustion = 45,576). Using
Equation C-2, Appendix C: .'.,',...; ...
HCm =
"
(8.000/2.2) x 47,145] + f (2.000/2.2) x 45,576]
' (10,000/2.2) (10,000/2.2)
HCm = (37,716) + (9,115)
HCm = 46,831 kilojoules per kilogram
Now use the calculated heat of combustion for the mixture in Equation C-1 to calculate the distance
to 1 psi overpressure for vapor cloud explosion.
D = 17 x [ 0.1 x (10,000/2.2) x (46,831/4,680) ]1/s>
D = 282 meters =0.18 miles
-------
-24-
Reference Table 1
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
10-Minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-4.4
4.4 - 37
37-97
97 - 180
180 - 340
340 - 530
530 - 760
760 - 1,000
1,000 - 1,500
1,500 - 1,900
1,900 - 2,400
2,400 - 2,900
2,900 - 3,500
3,500 - 4,400
4,400-5,100
5,100 - 5,900
5,900 - 6,800
6,800 - 7,700
7,700 - 9,000
9,000 - 10,000
10,000- 11,000
' 11,000-12,000
12,000 - 14,000
14,000 - 15,000
15,000 - 16,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2,8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
16,000 - 18,000
18,000 - 19,000
19,000 - 21,000
21,000-23,000
23,000 - 24,000
24,000-26,000
26,000 - 28,000
28,000 - 29,600
29,600-35,600
35,600 - 42,000
42,000 - 48,800
48,800 - 56,000
56,000 - 63,600
63,600-71,500
71,500-88,500
88,500 - 107,000
107,000- 126,000
126,000 - 147,000
147,000 - 169,000
169,000- 191,000
191,000-215,000
215,000 - 279,000
279,000 - 347,000
> 347,000
Distance to
Endpoint
(miles)
4.8
5,0
,5.2
5.4
5.6
5.8
6.0
6.2
6.8
7.5
8.1
8.7
9.3
9.9
11
12
14
15
16
1?
19
22
25
>25
-------
Reference Table 2
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
60-Mmute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-5.5
5.5 - 46
46 - 120
120 - 220
220 - 420
420 - 650
650 - 910
910 - 1,200
1,200- 1,600
1,600- 1,900
1,900-2,300
2,300 - 2,600
2,600 - 2,900
2,900 - 3,400
3,400 - 3,700
3,700-4,100
4,100-4,400
4,400 - 4,800
4,800 - 5,200
5,200 - 5,600
5,600 - 5,900
5,900 - 6,200
6,200 - 6,700
6,700 - 7,000
7,000 - 7,400
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
7,400 - 7,700
7,700-8,100
8,100-8,500
8,500 - 8,900
8,900 - 9,200
9,200 - 9,600
9,600 - 10,000
10,000 - 10,400
10,400- 11,700
11,700- 13,100
13,100-14,500
14,500 - 15,900
15,900 - 17,500
17,500 - 19,100
19,100-22,600
22,600 - 26,300
26,300 - 30,300
30,300 - 34,500
34,500 - 38,900
38,900 - 43,600
43,600 - 48,400
48,400-61,500
61,500 - 75,600
> 75, 600
Distance to
Endpoint
(miles)
4.8
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.8
7.5
8.1
8.7
9.3
9.9
11
12
14
15
16
17
19
22
25
>25
-------
-26-
Reference Table 3
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
10-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-21
21 - 170
170 - 420
420 - 760
760 - 1,400
1,400-2,100
2,100-3,100
3,100-4,200
4,200-6,100
6,100 - 7,800
7,800 - 9,700
9,700 - 12,000
12,000 - 14,000
14,000 - 18,000
18,000 - 22,000
22,000 - 25,000
25,000 - 29,000
29,000 - 33,000
33,000 - 39,000
39,000 - 44,000
44,000 - 49,000
49,000 - 55,000
55,000 - 63,000
63,000 - 69,000
69,000 - 76,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint ,
[(lbs/min)/(mg/L)]
76,000-83,000
83,000 - 90,000
90,000 - 100,000
100,000'- 110,000
110,000- 120,000
120,000 - 130,000
130,000 - 140,000
140,000 - 148,000
148,000 - 183,000
183,000-221,000
221,000-264,000
264,000 - 310,000
310,000-361,000
361,000 - 415,000
415,000 - 535,000
535,000 - 671,000
671,000-822,000
822,000-990,000
990,000 - 1,170,000
1,170,000- 1,370,000
1,370,000- 1,590,000
1,590,000-2,190,000
2,190,000-2,890,000
>2,890,000
Distance to
Endpoint
(miles)
'• 4.8
5.0
-. •• 5'.-2.
. ' • 5.4
''•" - 5.6
5.8
6.0
6.2
6.8 '
7.5
8.1
8.7
9.3
9,9
•'.;<•".*' 11.
••'•': 12 .
in ;
15
16
17
19
• - 22
' ' 25 •
••>• ' >25 ,
-------
-27-
Reference Table 4
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
60-Minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-26
26 - 210
210 - 530
530 - 940
940 - 1,700
1,700-2,600
2,600 - 3,700
3,700 - 4,800
4,800 - 6,400
6,400 - 7,700
7,700-9,100
9,100- 11,000
11,000- 12,000
12,000 - 14,000
14,000 - 16,000
16,000 - 17,000
17,000 - 19,000
19,000-21,000
21,000-23,000
23,000 - 24,000
24,000 - 26,000
26,000 - 28,000
28,000 - 30,000
30,000 - 32,000
32,000 - 34,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0:62
0.81
0.99
1,2
1.4 .-.
1.6
1.8
2.0
2.2 •..
2.4
2.6
2.8 ,
3.0 :
3.2
3.4
3.6
3.8 ,
4.0
•• 4.2 '
.4.4
4.6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
34,000 - 36,000
36,000 - 38,000
38,000-41,000
41,000-43,000
43,000 - 45,000 ,
45,000 - 47,000
47,000 - 50,000
50,000 - 52,200
52,200 - 60,200
60,200 - 68,900
68,900 - 78,300 ;
78,300 - 88,400
88,400 - 99,300
99,300- 111,000
111,000- 137,000
137,000 - 165,000
165,000 - 197,000
197,000 - 232,000
232,000-271,000
271,000-312,000
312,000-357,000
357,000 - 483,000
483,000 - 629,000
> 629,000
Distance to .
Endpoint
(miles)
4.8
5.0
5.2
5.4
5.6
: 5,:8
6.0
6.2
6.8
• . 7.5
• •" • 8:.l
8.7
9.3
9.9
11
12
. • 14 ,
15
16 ,
17
19
22
25
>25
-------
-28-
Reference Table 5
Dense Gas Distances to Toxic Endpoint
10-minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
0.0004
0.0007
Toxic Endpoint (mg/L)
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
2.2
3.0
4.8
6.8
11
14
19
24
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
1.7
2.4
3.7
5.0
8.7
11
15
18
22
>25
*
*
*
*
*
*
*
*
*
*
*
*
1.5
2.1
3.0
4.2
6.8
9.3
12
15
19
>25
*
... *
*
*
*
*
*
*
*
*
*
*
1.1
1.5
2.2
3.0
5.2
6.8
8.7
11
14
19
23
>25
*
*
*
*
*
*
*
*
*
*
0.81
1.1
1.7
2.4
3.9
5.0
•6.8
8.1
11
14
17
20
24
>25
•*
*
*
*
*
*
*
*
0.68
0.93
1.5
2.1
3.4
4.2
5.8
6.8
8.7
12
15
17
20
23
>25
*
*
*
*
*
*
*
0.53
0.74
1.2
1.7
2.8
3.5
4.8
5.7
7.4
9.9
12
14
16
19
20
23
>25
*
*
*
*
*
0.46
0.68
0.99
1.4
2.4
• 3.0
4.2
5.0
6.2
8.7
11
12
14
16
18
20
22
25
>25
*
• ' *
*
0.31
0.45
0.74
0.99
1.7
2.2
2.9
3.6
4.5
6.2
7.4
8.1
9.9
11
12
14
16
17
20
24
>25
*
0.23
0.33
0.53
0.74
1.3
1.7
2.2
2.7
3.4
4.7
5.5
6.2
7.4
8.7
9.3
9.9
11
13
15
17
20
23
0.19
0.27
0.43
0.62
1.1
1.4
1.9
2.3
2.8
3.8
4.5
5.2
6.2
6.8
8.1
8.7
9.3
11
12
14
17
19
0.15
0.21
0.34
0.50
0.87
1.1
1.6
1.9
2.3
3.1
3.7
4.2
5.0
'5.6
6:2
6.8
7.4
8.7
9.9
11
13
15
0.12
0.18
0.29
0.42
0.74
0.93
1.3
1.6
2.0
2.7
3.2
3.6
4.3
4.8
5.3
5.6
6.2
6.8
8.7
9.3
11
12
0.06
0.11
0.16
0.24
0.42
0.56
0.81
0.93
1.2
1.6
1.9
2.2
2.5
2.9
3.2
3.4
3.8
4.2
4.9
5.5
6.2
7.4
tt
<0.06
0.11
0.15
0.27
0.35
0.51
0.61
0.81
1.1
1.3
1.4
1.7
1.9
2.1
2.2
2.5
2.7
3.2
3.6
4.2
4.7
ff
<0.06
0.07
0.12
0.20
0.27
0.38
0.47
0.60
0.87
0.99
1.1
1.3
1.5
1.6
1.7
2.0
2.1
2.5
2.8
3.2
3.7
* > 25 miles
# <0.06 miles
-------
-29-
Reference Table 6
Dense Gas Distances to Toxic Endpoint
60-minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
Toxic Endpoint (mg/L)
0.0004
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
3.7
5.3
8.7
12
22
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*-
2.7
4.0
6.8
9.3
16
21
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
2.2
3.2
5.3
8.1
14
18
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
1.4
2.2
3.7
5.3
9.9
12
18
22
>25
*
*
*
#
*
*
*
*
*
*
*
*
*
0.99
1.6
2.7
4.0
7.4
9.3
13
17
22
>25
*
*
*
*
*
*
*
*
*
*
*
*
0.81
1.2
2.2
3.3
6.1
8.1
11
14
18
25
>25
*
*
*
*
*
*
*
*
*
*
*
0.62
0.99
1.7
2.7
4.9
6.2
9.3
11
14
20
25
>25
*
*
*
*
*
*
*
*
*
*
0.53
0.81
1.4
2.2
4.1
5.4
7.4
9.9
12
17
22
25
>25
*
*
*
*
*
*
*
*
*
0.34
0.53
0.93
1.4
2.9
3.8
5.5
6.8
8.7
12
15
17
20
24
>25
*
*
*
*
*
*
*
0.24
0.37
0.62
0.99
2.1
2.7
4.0
4.9
6.2
9.3
11
12
16
17
20
21
24
>25
*
*
*
*
0.19
0.29
0.51
0.81
1.6
2.2
3.2
4.0
5.2
7.4
9.3
11
12
14
16
17
20
22
>25
*
*
*
0.14
0.22
0.39
0.60
1.2
1.7
2.5
3.1
4.1
5.8
7.4
8.1
9.9
11
13
14
16
17
21
24
>25
*
0,12
0,18
0.32
0.50
0.99
1.4
2.1
2.7
3.5
5.0
6.1
6.8
8.7
9.9
11
12
14
15
18
20
24
>25
<0.06
0.09
0.17
0.26
0.52
0.74
1.1
1.4
1.9
2.9
3.5
4.0
5.0
5.7
6.2
6.8
8.1
8.7
11
12
14
16
tt -
<0.06
0.10
0.16
0.31
0.43
0.68
0.87
1.2
1.8
2.2
2.6
3.2
3.7
4.2
4.5
5.2
5.7
6.8
7.4
9.3
9.9
#
<0.06
0.07
0.11
0.22
0.31
0.48
0.61
0.87
1.3
1.7
2.0
2.5
2.9
3.2
3.5
4.0
4.4
5.2
6.0
6.8
8.1
* > 25 miles
# <0.06 miles
-------
-30-
Reference Table 7
Dense Gas Distances to Toxic Endpoint
10-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
0.0004
0.0007
0.001
0.002
Toxic Endpoint (mg/L)
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
Distance (Miles)
1.6
2.2
3.5
4.9
8.1
11
15
19
24
>25
*
*
*
*
*
*
*
*
*
*
*
*
1.2
1.7
2.7
3.8
6.2
8.1
11
14
18
>25
*
*
*
*
*
*
*
*
*
*
*
*
1.1
1.4
2.2
3.1
5.3
6.8
9.3
12
15
21
>25
*
*
*
*
*
*
*
*
*
*
*
0.74
1.1
1.6
2.2
3.7
4.8
6.8
8.1
11
15
18
21
>25
*
*
*
*
*
*
*
*
*
0.55
0.81
1.2
1.7
2.9
3.7
5.2
6.1
8.1
11
14
16
19
22
24
>25
*
*
*
*
*
*
0.45
0.62
0.99
1.4
2.4
3.1
4.2
5.2
6.8
9.3.
11
13
16
18
20
22
25
>25
*
*
*
*
0.36
0.50
0.81
1.2
2.0
2.5
3.5
4.3
5.4
7.4
9.3
11
12
15
16
18
20
23
>25
*
*
*
0.31
0.44
0.68
0.99
1.7
2.1
3.0
3.6
4.6
6.2
8.1
9.3
11
12
14
16
17
20
24
>25
*
*
0.21
0.29
0.48
0.68
1.2
1.5
2.1
2.5
3.3
4.5
5.5
6.2
7.4 •
8.7
9.9
11
12
14
16
19
22
>25
0.15
0.20
0.35
0.50
0.87
1.1
1.6
1.9
2.4
3.4
4.1
4.6
5.6
6.2
6.8
7.4
8.7
9.9
12
14
16
19
0.13
0.17
0.27
0.40
0.74
0.93
1.3
1.6
2.0
2.8
3.3
3.8
4.6
5.2
5.8
6.2
6.8
8.1
9.9
11
13
15
0.10
0.13
0.21
0.31
0.56
0.74
0.99
1.2
1.6
2.2
2.6
3.0
3.7
4.1
4.7
5.0
5.6
6.2
7.4
8.7
11
12
0.07
0.11
0.17
0.25
0.45
0.61
0.87
1.1
1.4
1.9
2.2
2.5
3.'0
3.5
3.8
4.2
4.8
5.3
6.2
7.4
8.7
9.9
0.25
tt
<0.06
0.10
0.14
0.24
0.33
0.47
0.58
0.74
1.1
1.3
1.5
1.7
2.0
2.2
2.4
2.7
3.0
3.6
4.1
4.9
5.5
0.5
tt
tt
<0.06
0.09
0.14
0.19
0.28
0.35
0.47
0.68
0.81
0.93
1.1
1.3
1.4
1.6
1.7
1.9
2.3
2.6
3.1
3.5
0.75
ff
tt
H
<0.06
0.11
0.14
0.20
0.25
0.33
0.48
0.60
0.68
0.81
0.93
1.1
1.2
1.3
1.4
1.7
2.0
2.3
2.7
* > 25 miles
# <0.06 miles
-------
-31-
Reference fable 8
Dense Gas Distances to Toxic Endpoint
60-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
Toxic Endpoint (mg/L)
0.0004
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
2.6
3.8
6.2
9.3
16
22
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
1.9
2.9
4.7
6.8
12
16
24
>25
*
*
*
*
*
*
*
*•
*
*
*
*
*
*
1.5
2.3
3.9
5.6
9.9
14
20
24
>25
*
*
*
*
*
*
*
*
*
*
*
*
*
1.1
1.5
2.6
3.9
7.4
9.3
14
17
22
>25
. *
*
*
*
*
*
*
*
*
*
* •
*
0.68
1.1
1.9
2.9
5.3
6.8
9.9
12
16
24 -
>25
* -
*
*
*
*
*
*
*
*
; ' *
*
0.55
0.87
1.5
2.3
4.3
5.7
8.1
11
14
19
24
>25
*
*
*
*
*
*
*
*
*
*
0.43
0.68
1.2
1.8
3.4
4.5
6.8
8.1
11
16
19
22
:>25
* •
* •
*
• *
*
*
*
*
*
0.35
0.55
0.93
1.5
2.9
3.8
5.7
6.8
9.3
- 13
16
19
. 24
>25
*
*
*
*
*
*
*
*
0.22
0.35
0.61
0.93
1.9
2.6
3.8
4.8
6.2
9.3
11
13
16
19
20
" 22
>25
*
*
*
*
*
0.16
0.24
0.42
0.68
1.3
1.8
2.7
3.5
4.5
6.8
8.1
• 9.3
12
13
15
16
19
21
>25
*
*
*
0.12
0.19
0.33
0.51
0.99
1.4
2.2
2.8
3.7
5.4
6.8
7.4
9.3 ;
11
12
13
16
17
20
24
>25
*
0.09
0.14
0.25
0.38
0.74
1.1
1.7
2.2
2.9
4.2
5.2
6:0
7.4
8.7
9.3
11
12
14
16
19
22
>25
0.07
0.11
0.20
0.31
0.62
0.87
1.4
1.8
2.4
3.5
' 4.3
5.0
6.2
7.4
8.1
8.7
9.9
11
14
16
19
21
#
<0.06
0.10
0.16
0.31
0.43
0.68
0.87
1.2
1.9
2.4
2.8
3.4
4.0
4^5
4.9
5.6
6.2
7.4
8.7
11
12
ff
tt
<0.06
0.09
0.17
0.24
0.38
0.49
0.68
1.1
1.4
1.6
2.1
2.5
2.8
3.0
3.5
4.0
4.8
5.5
6.8
7.4
#
#
#
<0.06
0.12
0.17
0.26
0.34
0.47
0.74
0.99
1.2
1.5
1.8
2.1
2.2
2.6
3.0
3.6
4.2
5.1
5.8
* > 25 miles
# <0.06 miles
-------
-32-
Reference Table 9
Distance to Overpressure of 1.0 psi for Vapor Cloud Explosions of 10,000 - 500,000 Pounds of Regulated Flammable Substances
Based on TNT Equivalent Method, 10 Percent Yield Factor
CAS No.
75-07-0
74-86-2
598-73-2
106-99-0
106-97-8
25167-67-3
590-18-1
624-64-6
106-98-9
107-01-7
463-58-1
7791-21-1
590-21-6
557-98-2
460-19-5
75-19-4
4109-96-0
75-37-6
124-40-3
463-82-1
74-84-0
Quantity in Cloud (pounds)
Chemical Name
Acetaldehyde
Acetylene
Bromotrifluoroethylene
1,3-Butadiene
Butane
Butene
2-Butene-cis
2-Butene-trans
1 -Butene
2-Butene
Carbon oxysulfide
Chlorine monoxide
1-Chloropropylene
2-Chloropropylene
Cyanogen
Cyclopropane
Dichlorosilane
Difluoroethane
Dimethylamine
2,2-Dimethylpropane
Ethane
10,000
20,000
30,000
50,000
100,000
150,000
200,000
300,000
500,000
Distance (Miles) to 1 psi Overpressure
0.14
0.18
0.061
0.17
0.17
0.17
0.17
0.17
0.17
0.17
0.10
0.049
0.14
0.14
0.13
0.17
0.10
0.11
0.16
0.17
0.18
0.18
0.22
0.077
0.22
0.22
0.22
0.22
0.22
0.22
0.22
0.13
0.061
0.17
0.17
0.17
0.22
0.12
0.14
0.20
0.22
0.22
0.20
0.25
0.088
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.15
0.070
0.20
0.20
0.19
0.25
0.14
0.16
0.23
0.25
0.25
0.24
0.30
0.10
0.29
0.30
0.30
0.30
0.30
0.30
0.30
0.17
0.083
0.24
0.24
0,23
0.30
0.17
0.19
0.27
0.30
0.30
0.31
0.38
0.13
0.37
0.37
0.37
0.37
0.37
0.37
0.37
0.22
0.10
0.30
0.30
0.29
0.38
0.21
0.24
0.34
0.37
0.38
0.35
0.44
0.15
0.42
" 0.43
0.43
0.43
0.43
0.43
0.43
0.25
0.12
0.34
0.34
0.33
0.43-
0.24
0.27
0.39
0.43
0.43
0.39
0.48
0.17
0.47
0.47
0,47
0.47
0.47
0.47
0.47
0.28
0.13
0.37
0.37
0.36
0.47
0.27
0.30
0.43
0.47
0.48
0.44
0.55
0.19
0.53
0.54
0.54
0.54
0.54
0.54
0.54
0.32
0.15
0.43
0.43
0.42
0.54
0.30
0.34
0.50
0.54
0.55
0.52
0.65
0.22
0.63
0.64
0.64
0.64
0.64
0.64
0.64
0.37
0.18
0.51
0.51
0.49
0.64
0.36
0.40
0.59
0.64
0.65
-------
-33-
Reference Table 9 (continued)
Quantity in Cloud (pounds)
CAS No.
107-00-6
75-04-7
75-00-3
74-85-1
60-29-7
75-08-1
109-95-5
1333-74-0
75-28-5
78-78-4
78-79-5
75-31-0
75-29-6
74-82-8
74-89-5
563-45-1
563-46-2
115-10-6
107-31-3
115-11-7
504-60-9
109-66-0
109-67-1
Chemical Name
Ethyl acetylene
Ethylamine
Ethyl chloride
Ethylene
Ethyl ether
Ethyl mercaptan
Ethyl nitrite
Hydrogen
Isobutane
Isopentane
Isoprene
Isopropylamine
Isopropyl chloride
Methane
Methylamine
3-Methyl-l-butene
2-Methyl-l-butene
Methyl ether
Methyl formate
2-MethyIpropene
1,3-Pentadiene
Pentane
1-Pentene
10,000
20,000
30,000
50,000
100,000
150,000
200,000
300,000
500,000
Distance (Miles) to 1 psi Overpressure
0.17
0.16
0.13
0.18
0.16
0.15
0.13
0.24
0.17
0.17
0.17
0.16
0.14
,0.18
0.15
0.17
0.17
0.15
0.12
0.17
0.17
0.17
0.17
0.22
0.20
0.17
0.22
0.20
0.19
0.16
0.30
0.22
0.22
0.22
0.20
0.18
0.23
0.19
0.22
0.22
0.19
0.15
0.22
0.22
0.22
0.22
0.25
0.23
0.19
0.25
0.23
0.21
0.18
0.35
0.25
0.25
0.25
0.23
0.20
0.26
0.22
0.25
0.25
0.21
0.17
0.25
0.25
0.25
0.25
0.30
0.27
0.23
0.30
0.27
0.25
0.22
0.41
0.30
0.30
0.29
0.28
0.24
0.31
0.26
0.29
0.29
0.25
0.21
0.30
0.29
0.29
0.29
0.37
0.34
0.28
0.38
0.34
0.32
0.27
0.52
0.37
0.37
0.37
0.35
0.30
0.39
0.33
0.37
0.37
0.32
0.26
0.37
0.37
• 0.37
0.37
0.43
0.39
0.32
0.43
0.39
0.36
0.31
0.59
0.43
- 0.43
0.42
0.40
0.34
0.44
0.38
0.42
0.42
0.37
0.30
0.43
0.42
0.42
0.42
0.47
0.43
0.36
0.48
0.43
0.40
0.35
0.65
0.47
0.47
0.46
0.44
0.38
0.49
0.42
0.47
0.47
0.40
0.33
0.47
0.46
0.47
0.47
0.54
0.49
0.41
0.55
0.49
0.46
0.40
0.74
0.54
0.54
0.53
0.50
0.43
0.56
0.48
0.53
0.53
0.46
0.37
0.54
0.53
0.54
0.54
0.64
0.59
0.48
0.65
0.58
0.54
0.47
0.88
0.64
0.64
0.63
0.59
0.51
0.66
0.56
0.63
0.63
'0.55
0.44
0.64
0.63
0.63
0.63
-------
-34-
Reference Table 9 (continued)
CAS No.
646-04-8
627-20-3
46349-0
74-98-6
115-07-1
74-99-7
7803-62-5
116-14-3
75-76-3
10025-78-2
79-38-9
75-50-3
689-97-4
75-01-4
109-92-2
75-02-5
75-35-4
75-38-7
107-25-5
Quantity in Cloud (pounds)
Chemical Name
2-Pentene, (E)-
2-Pentene, (Z)-
Propadiene
Propane
Propylene
Propyne
Silane
Tetrafluoroethylene
Tetramethylsilane
Trichlorosilane
Trifluorochloroethylene
Trimethylamine
Vinyl acetylene
Vinyl chloride
Vinyl ethyl edier
Vinyl fluoride
Vinylidene chloride
Vinylidene fluoride
Vinyl methyl ether
10,000
20,000
30,000
50,000
100,000
150,000
200,000
Distance (Miles) to 1 psi Overpressure
0.17
0.17
. 0.17
0.17
0.17
0.17
0.17
0.053
0.17
0.075
0.059
0.16
0.17
0.13
0.16
0.063
0.11
0.11
0.15
0.22
0.22
0.22
0.22
0.22
0.22
0.22
0.066
0.21
0.10
0.075
0.21
0.22
0.16
0.20
0.079
•0.13
0.14
0.19
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.076
0.24
0.11
i 0.086
0.24
0.25
0.19
0.22
0.091
0.15
0.15
0.22
0.29
0.29
0.30
0.30
0.30
0.30
0.29
0.090
0.29
0.13 -
0.10 :
0.28
0.30
0.22
0.27
0.11
0.18
0.18
0.26
0.37
0.37
0.38
0.38
0.37
0.38
0.37
0.11
0.36
0.16
0.13
0.35
0.37
0.28
0.34
0.14
0.23
0.23
0.33
0.42
0.42
0.43
' 0.43
0.43
0.43
0.42 .
0.13
0.42
0.19
0.15
0.40
0.43
0.32
0.38
0.16
0.26
0.26
0.37
0.47
0.47
0.47
0.47
0.47
,0.47
0.47 -
0.14
' 0.46
0.20
0.16
0.44
0.47
0.35
0.42
0.17
0.29
0.29
0.41
300,000
0.53
0.53
0.54
0.54
0.54
0.54
0.53
0.16
0.52
0.23
0.18
0.51
0.54
0.40
0.48
0.20
0.33
0.33
0.47
500,000
0.63
0.63
0.64
0.64
0.64
0.64
0.63
0.19
0.62
0.28
0.22
0.60
0.64
0.48
0.57
0.23
0.39
0.40
0.56
-------
-35-
6.0 Determining Alternative Release Scenarios
You are required to analyze at least one alternative release scenario for each listed toxic
substance you have in a Program 2 or Program 3 process above its threshold quantity. You also are
required to analyze one alternative release scenario for flammable substances in Program 2 or 3
processes as a class. You do not need to analyze an alternative scenario for each flammable
substance. For example, if you have five listed substances - chlorine, ammonia, hydrogen chloride,
propane, and acetylene - above the threshold in Program 2 or 3 processes, you will need to analyze
one alternative scenario each for chlorine, ammonia, and hydrogen chloride and a single alternative
scenario to cover propane and acetylene (listed flammable substances). Even if you have a substance
above the threshold in several processes or locations, you need only analyze one alternative scenario
for it.
Alternative release scenarios for toxic substances should be those that lead to concentrations
above the toxic endpoint beyond your fenceline. Scenarios for flammable substances should have the
potential to cause substantial damage, including on-site damage. Those releases that have the
potential to reach the public are of the greatest concern.
For alternative release scenarios, you are allowed to consider active mitigation systems, such
as interlocks, shutdown systems, pressure relieving devices, flares, emergency isolation systems, and
fire water and deluge systems, as well as passive mitigation systems, as described in Sections 3.1.2
and 3.2.3.
For alternative release scenarios for ammonia used for refrigeration, consult EPA's Model
Risk Management Program and Plan for Ammonia Refrigeration. For toxic substances at water
treatment facilities, see the guidance for this industry segment.
7.0 Analysis of Alternative Scenarios for Toxic Substances
You have a number of options for selecting release scenarios for toxic substances.
• You may use your worst-case release scenario and apply your active mitigation system
to limit the quantity released and the duration of the release.
• You may use information from your process hazards analysis, if you have conducted
one, to select a scenario.
• You may review your accident history and choose an actual event as the basis of your
scenario.
• If you have not conducted a process hazards analysis, you may review your operations
and identify possible events and failures.
Whichever approach you select, the key information you need to define is the quantity to be
released and the time over which it will be released; together, these allow you to estimate the release
rate and use essentially the same methods you used for the worst-case analysis.
-------
-36-
Section 8 below provides detailed information on calculating release rates for alternative
release scenarios. If you can estimate release rates for the toxic gases and liquids you have on site
based on readily available information, you may skip Section 8 and go to Section 9. Section 9
describes how to estimate distances to the toxic endpoint for alternative scenarios for toxic substances.
8.0 Estimation of Release Rates for Alternative Release Scenarios for Toxic Substances
8.1 Release Rates for Toxic Gases
8.1.1 Unmitigated Releases of Gases
Gaseous Release from Tank. Instead of assuming release of the entire contents of a vessel
containing a toxic gas, you may decide to consider a release from a hole in a vessel or pipe. To
estimate a hole size you might assume, for example, the hole size that would result from shearing off
a valve or pipe from a vessel containing a regulated substance. If you have a gas leak from a tank,
you may use the following simplified equation to estimate a release rate based on hole size, tank
pressure, and the properties of the gas. (See Appendix D, Section D.6 for the derivation of this
equation.)
QR = HA x Pt x — x GF
FT
V1*
(11)
where: QR = Release rate (pounds per minute)
HA = Hole or puncture area (square inches) (from hazard evaluation or best estimate)
Pt = Tank pressure (pounds per square inch - absolute (psia)) (from process information)
Tt = Tank temperature (K)
GF = Gas Factor, incorporating discharge coefficient, ratio of specific heats, molecular
weight, and conversion factors (listed for each regulated toxic gas in Exhibit B-l,
Appendix B)
This equation will give an estimate of the initial release rate. It will overestimate the overall
release rate, because it does not take into account the decrease in the release rate as the pressure in
the tank decreases. You may use a computer model or another calculation method if you want a
more realistic estimate of the release rate.
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Example 18. Release of Toxic Gas from Tank (Diborane)
You have a tank that contains diborane gas at a pressure of 30 pounds per square inch - absolute
(psia). The temperature of the tank and its contents is 298 K (25 °C). A valve on the side of the
tank shears off, leaving a hole in the tank wall 5 square inches. From Exhibit B-l, the Gas Factor
for diborane is 17. Therefore, the release rate is:
QR = 5 x 30 x l/(298)'/2 x 17 = 148 pounds per minute
Gaseous Release from Pipe. If shearing of a pipe may be an alternative scenario for a toxic
gas at your site, you could use the usual flow rate through the pipe as the release rate and carry out
the estimation of distance as discussed in Section 9.
If you want to consider a release of toxic gas through a hole in a pipe as an alternative
scenario, you may use the method described above for a gas release from a hole in a tank. This
method neglects the effects of friction along the pipe and, therefore, provides a conservative estimate
of the release rate.
Duration of Release. The duration of the release is used in choosing the appropriate reference
table for distances (Section 9 below). You may calculate the maximum duration by dividing the
quantity in the tank or the quantity that may be released from pipes by your calculated release rate.
You may use 60 minutes as a default value for maximum release duration. If you know how long it
is likely to take to stop the leak, you may use that time as the release duration.
If a gaseous release from a hole in a tank or pipe is likely to be stopped very quickly (e.g.,
by a block valve), resulting in a puff of toxic gas that forms a vapor cloud rather than a plume, you
may want to consider other methods for determining a consequence distance. The behavior of a cloud
of toxic gas resulting from a puff release will not exhibit the same behavior as a plume resulting from
a longer release (e.g., a release over 10 minutes).
Gases Liquefied Under Pressure. Gases stored under pressure as liquids may be released very
rapidly in case of tank or pipe damage or failure. Such releases may involve rapid vaporization of a
fraction of the liquified gas and possibly aerosolization. The methods presented in this guidance are
not appropriate for this type of release. If you think release of a liquefied gas under pressure is a
potential release scenario at your site, you may want to consider other models or methods to carry out
a consequence analysis.
8.1.2 Mitigated Releases of Gases
For gases, passive mitigation may include enclosed spaces, as discussed in Section 3.1.2.
Active mitigation for gases, which may be considered in analyzing alternative release scenarios, may
include an assortment of techniques including automatic shutoff valves, rapid transfer systems
(emergency deinventory), and water/chemical sprays. These mitigation techniques have the effect of
reducing either the release rate or the duration of the release, or both.
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Active Mitigation to Reduce Release Duration. An example of a mitigation technique to
reduce the release duration is automatic shutoff valves. If you have an estimate of the rate at which
the gas will be released and the time it will take to shut off the release, you may estimate the quantity
potentially released (release fate times time). If the release will take place over a period of 10
minutes or more, you may use the release rate to estimate the distance to the toxic endpoint, as
discussed in Section 9. For releases stopped in less than 10 minutes, multiply the initial release rate
by the duration of release to estimate the quantity released, then divide the new quantity by 10
minutes to estimate a mitigated release rate that you may apply to the reference tables in Section 9 to
estimate the consequence distance. If the release would be stopped very quickly, you might want to
consider other methods that will estimate consequence distances for a puff release.
Active Mitigation to Directly Reduce Release Rate to Air. Examples of mitigation techniques
to directly reduce the release rate include scrubbers and flares. Use test data, manufacturer design
specifications, or past experience to determine the fractional reduction of the release rate by the
mitigation technique. Apply this fraction to the release rate that would have occurred without the
mitigation technique. The initial release rate, without mitigation, may be the release rate for the
alternative scenario (e.g., a release rate estimated from the equations presented earlier in this section)
or the worst-case release rate. The mitigated release rate is: ;
QRR = (1 - PR) x QR
where: QRR = Reduced release rate (pounds per minute)
FR = Fractional reduction resulting from mitigation
QR = Release rate without mitigation (pounds per minute)
(12)
Example 19. Water Spray Mitigation (Hydrogen Fluoride)
A bleeder valve on a hydrogen fluoride (HF) tank opens, releasing 660 pounds per minute of HF.
Water sprays are applied almost immediately. Experimental field and laboratory test data indicate
that HF vapors could be reduced by 90 percent. The reduced release rate is:
QRR = (1 - 0.9) x (660 pounds per minute)
= 66 pounds per minute
Passive Mitigation. The same simplified method used for worst-case releases may be used for
alternative release scenarios to estimate the release rate to the outside air from a release in an
enclosed space. For alternative scenarios, you may use a modified release quantity, if appropriate.
Use the equations presented in Section 3.1.2 to estimate the release rate to the outside air.
Duration of Release. You should estimate the duration of the release either from your
knowledge of the length of time it may take to stop the release or by dividing the quantity that may be
released by your estimated release rate.
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8.2 Release Rates for Toxic Liquids
This section describes methods for estimating liquid release rates from tanks and pipes. The
released liquid is assumed to form a pool, and the evaporation rate from the pool is estimated as for
the worst-case scenario. For the alternative scenario, you may assume the average wind speed in
your area in the calculation of evaporation rate, instead of a wind speed of 1.5 meters per second (3.4
miles per hour). For the reference tables in this guidance, the wind speed,for alternative scenarios is
assumed to be 3.0 meters per second (6.7 miles per hour).
If you have sufficient information to estimate the quantity of liquid that might be released to
an undiked area under an alternative scenario, you may go directly to Section 8.2.3 to estimate the the
evaporation rate from the pool and the release duration. After ypu have estimated the evaporation
rate and release duration, go to Section 9 for instructions on estimating distance to the toxic endpoint.
8.2.1 Liquid Release Rate and Quantity Released for Unmitigated Releases
Liquid Release from Tank under Atmospheric Pressure. If you have a liquid stored in a tank
at atmospheric pressure, you may use the following simple equation to estimate the liquid release rate
from a hole in the tank below the liquid level. (See Appendix D, Section D.7.1, for the derivation of
this equation.)
QRL = HA x x LLF
(13)
where: QRL ==
HA =
LH =
LLF =
Liquid release rate (pounds per minute)
Hole or puncture area (square inches) (from hazard evaluation or best
estimate)
Height of liquid column above hole (inches) (from hazard evaluation or best
estimate) ">
Liquid Leak Factor incorporating discharge coefficient and liquid density
(listed for each toxic liquid in Exhibit B-2, Appendix B).
This equation will give an overestimate of the release rate, because it does not take into
account the decrease in the release rate as the height of the liquid above the hole decreases. You may
use a computer model or another calculation method if you want a more realistic estimate of the
liquid release rate.
You may estimate the quantity that might be released by multiplying the liquid release rate
from the above equation by the time (in minutes) that likely would be needed to stop the release.
Alternatively, you may assume the release would stop when the level of liquid in the tank drops to the
level of the hole. You may estimate the quantity of liquid above that level in the tank from the
dimensions of the tank, the liquid level at the start of the leak, and the level of the hole. Assume the
estimated quantity is released into a pool and use the method and equations in Section 8.2.3 below to
determine the evaporation rate of the liquid from the pool and the duration of the release.
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Example 20. Liquid Release from Atmospheric Tank (Acrylonitrile)
You have a tank that contains 20,000 pounds of acrylonitrile at ambient temperature and pressure. A
valve on the side of the tank shears, leaving a hole in the tank wall 5 square inches in area. The
liquid column is 23 inches above the hole in the tank. From Exhibit B-2, the Liquid Leak Factor for
acrylonitrile is 39. Therefore, the release rate is:
QR = 5 x (23)1/4 x 39 = 936 pounds per minute . • .
It takes 10 minutes to stop the release so that 10 minutes x 936 pounds per minute = 9,360 pounds
of acrylonitrile is released. From Exhibit B-2, the Density Factor for acrylonitrile is 0.61, and the
Liquid Factor Ambient is 0.018. Assuming that the liquid is not released into a diked area or inside
a building, the evaporation rate from the pool of acrylonitrile, from Equation 3, using a wind speed
factor of 2.4 for wind speed 3 meters per second, is:
QR = 9,360 x 2.4 x 0.018 x 0.61 = 247 pounds per minute
Release from Pressurized Tank. If you have a liquid stored in a tank under pressure, you
may estimate a release rate using the equations presented in Appendix D, Section D.7.1.
Release from Pipe. To consider a liquid release from a broken pipe, you may use the
equations below (see Appendix D, Section D.7.2 for more information on these equations.) First
estimate the initial operational flow velocity of the substance through the pipe using the initial
operational flow rate as follows:
FRx DF x 0.033
(14)
where: Va = Initial operational flow velocity (feet per minute)
FR = Initial operational flow rate (pounds per minute)
DF = Density Factor (from Exhibit B-2, Appendix B)
A- = Cross-sectional area of pipe (square feet)
The release velocity is then calculated based on the initial operational flow, any gravitational
acceleration or deceleration effects, and the pressure difference between the hole/shear and tank using
a form of the Bernoulli equation:
_
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(77,500 x Pa -.7.85-* 109)
D
+ (77,460 * g x Z) + Va-
(15)
where: Vb = Release velocity (feet per minute)
Pa •= Operational pipe pressure (Pascals)
Z = Change in pipe elevation, inlet to outlet (meters)
g = Gravitational acceleration (9.8 meters per second2)
Va = Operational velocity (feet per minute)
D = Density of liquid (kilograms per cubic meter)
Please note that if the height of the pipe at the release point is higher than the initial pipe height, then
Z is negative and the release rate is actually lower than the operational rate.
The release velocity can then be used to calculate a release rate as follows:
DF x 0.033
(16)
where: QRL = Release rate (pounds per minute)
Vb = Release velocity (feet per minute)
DF = Density Factor
A- = Cross-sectional area of pipe (square feet)
You may estimate the quantity released into a pool from the broken pipe by multiplying the
liquid release rate (QR^ from the equation above by the time (in minutes) that likely would be
needed to stop the release. Assume the estimated quantity is released into a pool and use the method
and equations described in Section 8.2.3 below to determine the evaporation rate of the liquid from
the pool.
In the case of very long pipes, estimated release rates from a sheer or hole will be lower due
pipe roughness and frictional head loss. If this effect is deemed considerable, an established method
for calculating frictional head loss such as the Darcy formula may be used.
8.2.2 Liquid Release Rate and Quantity Released for Mitigated Releases
For alternative release scenarios, you are permitted to take credit for both passive and active
mitigation systems, or a combination if both are in place. For liquids, passive mitigation may include
techniques already discussed in Section 3.2.3 such as dikes and trenches. Active mitigation for
liquids may include an assortment of techniques including automatic shutoff valves, emergency
deinventory, foam, or tarp coverings, and water or chemical sprays. These mitigation techniques have
the effect of reducing either the quantity released into the pool or the evaporation rate from the pool.
Some methods of accounting for active mitigation are discussed below.
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Active Mitigation to Reduce Quantity Released. Examples of mitigation techniques to reduce
the quantity released into the pool include automatic shutoff valves and emergency deinventory. You
may use the equations in Section 8.2.1 above for calculating liquid release rate, if applicable.
Estimate the approximate time needed to stop the release by the mitigation technique. Multiply the
release rate times the duration of release to estimate quantity released. Assume the estimated quantity
is released into a pool and use the method and equations described in Section 8.2.3 below to
determine the evaporation rate of the liquid from the pool. You should also consider mitigation of
evaporation from the pool, if applicable; see the discussion of active mitigation below or passive
mitigation in Section 3.2.3.
Example 21. Mitigated Liquid Release
A bromine injection system suffers a hose failure; the greatly lowered system pressure triggers an
automatic shutoff valve within 30 seconds of the release. The flow rate out of the ruptured hose is
approximately 330 pounds per minute. Because the release occurred for only 30 seconds (0.5
minutes), the total quantity spilled was 330 x 0.5, or 165 pounds.
Active Mitigation to Reduce Evaporation Rate. Examples of active mitigation techniques to
reduce the evaporation rate from the pool include water sprays and foam or tarp covering. Use test
data, manufacturer design specifications, or past experience to determine the fractional reduction of
the release rate by the mitigation technique. Apply this fraction to the release rate (evaporation rate
from the pool) that would have occurred without the mitigation technique, as follows:
QRRV = (1-FR) x QR
(17)
where: QR&V = Reduced evaporation rate from pool or release rate to air (pounds per minute)
FR = Fractional reduction resulting from mitigation
QR = Evaporation rate from pool without mitigation (pounds per minute)
Releases Into Buildings. If a toxic liquid is released inside a building, compare the area of
the building floor to the maximum area of the pool that could be formed; the smaller of the two areas
should be used in determining the evaporation rate, as for the worst case scenario. The maximum
area of the pool is determined from Equation 6 in Section 3.2.3 for releases into diked areas. The
area of the building floor is the length times width of the floor (in feet) (Equation 9).
If the floor area is smaller than the maximum pool size, estimate the outdoor evaporation rate
from a pool the size of the floor area from Equation 20 in the next section (Section 8.2.3). If the
maximum pool area is smaller, estimate the outdoor evaporation rate from a pool of maximum size
from Equation 18 in the next section. Estimate the rate of release of the toxic vapor from the
building as five percent of the calculated outdoor evaporation rate (multiply your evaporation rate by
0.05). See Appendix D, Section D.2.4 for more information on releases into buildings.
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8.2.3 Evaporation Rate from Liquid Pool
Ambient temperature. For pools with no mitigation, if the liquid is always at ambient
temperature, find the Liquid Factor Ambient (LFA) and the Density Factor (DF) in Exhibit B-2 of
Appendix B (see Appendix D, Section D.2.2 for the derivation of these factors). Calculate the
release rate of the liquid from the following equation:
QR = QS x 2.4 x LFA x DF
(18)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
"J 2.4 = Wind speed factor = 3.0°-7?, where 3.0 meters per second (6.7 miles per hour) is the
wind speed for the alternative scenario for purposes of this guidance
LFA = Liquid Factor Ambient
'•'! DF = Density Factor
Elevated temperature. For pools with no mitigation/if the liquid is at an elevated temperature
(any temperature above 25° C), find the Liquid Factor Boiling (LFB) and the Density Factor (DF) in
Exhibit B-2 of Appendix B (see Appendix D, Section D.2.2, for the derivation of these factors).
Calculate the release rate of the liquid from the following equation:
QR = QS x 2.4 x LFB x DF
(19)
where: QR = Release rate (pounds per minute)
QS = Quantity released (pounds)
2.4 = Wind speed factor = 3.0°-78, where 3.0 meters per second (6.7 miles per hour) is the
wind speed for the alternative scenario for purposes of this guidance
LFB = Liquid Factor Boiling
DF = Density Factor
Diked Areas. If the toxic liquid will be released into an area where it will be contained by
dikes, compare the diked area to the maximum area of the pool that could be formed, as described in
Section 3.2.3 (see Equation 6). The smaller of the two areas should be used in determination of the
evaporation rate. If the maximum area of the pool is smaller than the diked area, calculate the release
rate as described for pools with no mitigation (above). If the diked area is smaller, go to Exhibit B-2
in Appendix B to find the Liquid Factor Ambient (LFA), if the liquid is at ambient temperature, or
the Liquid Factor Boiling (LFB), if the liquid is at a temperature above ambient. Calculate the
release rate from the diked area as follows:
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QR = 2.4 xLFAxA
(20)
or
QR = 2.4 x LFB x A
(21)
where: QR = Release rate (pounds per minute)
2.4 = Wind speed factor = 3.0°-78, where 3.0 meters per second (6.7 miles per hour) is the
wind speed for the alternative scenario for purposes of this guidance
LFA = Liquid Factor Ambient (listed in Exhibit B-2, Appendix B)
LFB = Liquid Factor Boiling (listed in Exhibit B-2, Appendix B)
A = Diked area (square feet)
Duration of Release. After you have estimated a release rate as described above, determine
the duration of the vapor release from the pool (the time it will take for the liquid pool to evaporate
completely). To estimate the time in minutes, divide the total quantity released (in pounds) by the
release rate (in pounds per minute) (see Equation 5 in Section 3.2.2).
8.2.4 Common Water Solutions of Toxic Substances
You may use the methods described above for pure liquids to estimate the quantity of a
solution of a toxic substance that may be spilled into a pool. LFA arid DF values for several
concentrations of ammonia, formaldehyde, hydrochloric acid, hydrofluoric acid, and nitric acid in
water solution and for oleum are listed in Appendix B, Exhibit B-3. The LFA for a wind speed of
3.0 meters per second (6.7 miles per hour) should be used in the release rate calculations for
alternative scenarios for pools of solutions at ambient temperature. For unmitigated releases or
releases with passive mitigation, follow the instructions in Section 8.2.3. If active mitigation
measures are in place, you may estimate a reduced release rate from the instructions in 8.2.2 above.
Use the total quantity of the solution as the quantity released from the vessel or pipeline (QS) in
carrying out the calculation of the release rate to the atmosphere. If the solution is at an elevated
temperature, you may treat the substance in solution as a pure substance and follow the instructions in
Section 3.3, or use a method that accounts for increased volatilization of the toxic regulated
substance.
9.0 Estimating Impact Distances for Alternative Release Scenarios for Toxic Substances
If you do your own modeling for analysis of alternative release scenarios, you should consider
typical weather conditions at your site. If you do not keep weather data for your site (most sources
do not), you may call another nearby source, such as an airport, or a compiler, such as the National
Weather Service, to determine the average wind speed for your area. Atmospheric stability classes
are described in Exhibit 2. Select one that describes your typical weather. Your airport or other
source will be able to tell you average percent of cloud cover.
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Exhibit 2. Atmospheric Stability Classes
Surface Wind Speed at 10
Meters
Meters per
second
<2
2-3
3-5
5-6
>6
Miles per
hour
<4.5 .
4.5-5
5-11
11-13
>13
Day
Incoming Solar Radiation
Strong*
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
D
Slight**
B
C
C
D
D
Night
Thinly Overcast
or >4/S low
cloud
E
D
D
D
<.3/8
Cloud
F
E
D
D
Class A is the most unstable, class D is neutral, class F is the most stable.
The neutral class, D, should be assumed for overcast conditions during day or night.
* Sun high in the sky with no clouds. Solar radiation would be reduced to moderate with
broken middle clouds (5/8 to 7/8 cloud cover) and to slight with broken low clouds.
Sun low in the sky with no clouds.
Source: D. Bruce Turner, Workbook of Atmospheric Dispersion Estimates, U.S. Department of
Health, Education and Welfare. Cincinnati: 1970.
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For estimating distances for toxic substances, this guidance provides four reference tables for
neutrally buoyant plumes and four for dense gases. These tables were developed assuming D stability
and a wind speed of 3.0 meters per second (6.7 miles per hour) as representative of likely conditions
for many sites. Many wind speed and atmospheric stability combinations may be possible at different
times in different parts of the country. If D stability and 3.0 meters per second are not reasonable
conditions for your site, you may want to use other methods to estimate distances.
To use the reference tables, you need to consider the release rates estimated for gases and
evaporation from liquid pools and the duration of the release. For the alternative scenarios, the
duration of toxic gas releases may be longer than the 10 minutes assumed for the worst-case analysis
for gases. You need to determine the appropriate toxic endpoint and whether the gas or vapor is ;
neutrally buoyant or dense, using the tables in Appendix B. '
The reference tables for distances (Reference Tables 10-17) are found at the end of Section
12. The tables and the conditions for which each table is applicable are:
Reference Table
Number
10
11
12
13
14
15
16
17
Applicable Conditions
Release Duration
(minutes)
10
60
10
60
10
60
10
60
Topography
Rural
Urban
Rural
Urban ,;;
Gas or Vapor Density
Neutrally buoyant
Dense
For releases lasting 10 minutes or less, use the 10-minute tables. For releases lasting more
than 10 minutes, use the 60-minute'tables. You should always use the 10-minute tables for releases
of water solutions of toxic substances. Follow the instructions in Section 4 to estimate distances to
the toxic endpoint for toxic gases and liquids.
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Example 22. Gas Release of Chlorine
Assume that you calculated a release rate of 500 pounds per minute of chlorine from a tank. From
Exhibit B-l, Appendix B, the toxic endpoint for chlorine is 0.0087 mg/L, and chlorine is listed as a
dense gas. Based on emergency response systems available, you have estimated that the release will
last for 6 minutes. At a release rate of 500 pounds per minute, 3,000 pounds of chlorine would be
released in 6 minutes. To derive a release rate applicable to the reference tables, you calculate a 10-
minute release rate as 3,000 pounds/10 minutes, or 300 pounds per minute. The 10-minute reference
tables are appropriate for estimating the distance. The topography of your site is urban. For a 10-
minute release of a dense gas under average meteorology (D stability and 3 meters per second wind
speed) and urban topography, Reference Table 16 is appropriate. The toxic, endpoint of O.OQ87
mg/L is approximately halfway between 0.0075 and 0.01; you go to the lower endpoint of 0.0075
mg/L. The estimated release rate of 300 pounds per minute is closer to 250 pounds per minute pn
the table than to 500 pounds per minute, so you use 250 pounds per minute. Then the consequence
distance for the alternative scenario is 2.0 miles.
10.0 Analysis of Alternative Release Scenarios for Flammable Substances
Alternative release scenarios for flammable substances are somewhat more complicated than
for toxic substances because the consequences of a release and the endpoint of concern may vary.
For the worst case, the consequence of concern is a vapor cloud explosion, with an overpressure
endpoint. For alternative scenarios (e.g., fires), other endpoints (e.g., heat radiation) may need to be
considered.
Possible scenarios involving flammable substances include:
• Vapor cloud fires (flash fires) may result from dispersion of a cloud of flammable
vapor and ignition of the cloud following dispersion. Such a fire could flash back and
could represent a severe heat radiation hazard to anyone in the area of the cloud.
This guidance provides methods to estimate distances to a concentration equal to the
lower flammability limit (LFL) for this type of fire. (See Sections 11 and 12.1.)
• A pool fire, with potential radiant heat effects, may result from a spill of a flammable
liquid. This guidance provides a simple method for estimating the distance from a
pool fire to a radiant heat level that could cause second degree burns from a 40-
second exposure. (See Section 12.2).
• A boiling liquid, expanding vapor explosion (BLEVE), leading to a fireball that may
produce intense heat, may occur if a vessel containing flammable material ruptures
explosively as a result of exposure to fire. Heat radiation from the fireball is the
primary hazard; vessel fragments and overpressure from the explosion also can result.
BLEVEs are generally considered unlikely events; however, if you think a BLEVE is
possible at your site, this guidance provides a method to estimate the distance at
which radiant heat effects might lead to second degree burns. (See Section 12.3.)
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You also may want to consider models or calculation methods to estimate effects of
vessel fragmentation. ,
• For a vapor cloud explosion to occur, rapid release of a large quantity, turbulent
conditions (caused by a turbulent release or congested conditions in the area of the
release, or both), and other factors are generally necessary. Vapor cloud explosions
generally are considered unlikely events; however, if conditions at your site are
conducive to vapor cloud explosions, you may want to consider a vapor cloud
explosion as an alternative scenario. This guidance provides methods you may use to
estimate the distance to 1 psi overpressure for a vapor cloud detonation, based on less
conservative assumptions than the worst-case analysis. (See Section 12.4.) A vapor
cloud deflagration, involving lower flame speeds than a detonation and resulting in
less damaging blast effects, is more likely than a detonation. This guidance does not
provide methods for estimating the effects of a deflagration, but you may use other
methods of analysis if you want to consider such events.
• A jet fire may result from the puncture or rupture of a tank or pipeline containing a
compressed or liquefied gas under pressure. The gas discharging from the hole can
form a jet that "blows" into the air in the direction of the hole; the jet then may
ignite. Jet fires could contribute to BLEVEs and fireballs if they impinge on tanks of
flammable substances. A large horizontal jet fire may have the potential to pose an
offsite hazard. This guidance does not include a method for estimating consequence
distances for jet fires. If you want to consider a jet fire as an alternative scenario,
you should consider other models or methods for the consequence analysis.
11.0 Estimation of Release Rates for Alternative Release Scenarios for Flammable Substances
This section describes methods to estimate a release rate that may be used in determination of
dispersion distance to the LFL for a vapor cloud fire (Section 12.1).
11.1 Flammable Gases
An alternative scenario for a release of a flammable gas may involve a leak from a vessel or
piping. To estimate a release rate for flammable gases from hole size and storage conditions, you
may use the method described above in Section 8.1 for toxic gases. This release rate may be used to
determine the dispersion distance to the lower flammability limit (LFL), as described in Section 12.1.
Exhibit C-2 in Appendix C includes Gas Factors (GF) that may be used in carrying out the
calculations for each of the regulated flammable gases.
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Example 23. Release Rate of Flammable Gas from Hole in Tank
A pipe tears off a tank containing acetylene. The release rate from the hole can be estimated from
Equation 11 in Section 8.1. You estimate that the pipe would leave a hole with an area (HA) of 5
square inches. The temperature inside the tank (Tt) is 282 K, 9°C, and the square root of the
temperature is 16.8. The pressure in the tank (Pt) is approximately 481 psia. From Exhibit C-2,
Appendix C, the gas factor (GF) for acetylene is 17. From Equation 11, the release rate (QR) is:
QR = 5 X 481 x (1/16.8) X 17 = 2,400 pounds per minute
11.2 Flammable Liquids
You may estimate a release rate for flammable liquids by estimating the evaporation rate from
a pool. You first need to estimate the quantity in the pool.
You may use the method discussed in Section 8.2 to estimate a rate of liquid release for
flammable liquids into a pool from a hole in a tank or from a pipe shear. Exhibit C-3 in Appendix C
includes liquid leak factors (LLF) for calculating release rate from a hole. Note that the LLF is
appropriate only for atmospheric tanks.
Once you have an estimate of the quantity of flammable liquid in a pool, you may use the
methods presented in Section 3.2 to estimate the evaporation rate from the pool. Liquid factors at
ambient and boiling temperature (LFA and LFB) for the calculation are listed in Exhibit C-3 in
Appendix C. Assume a wind speed of 3.0 meters per second and use a value of 2.4 for the wind
speed factor for the evaporation rate calculations. Both passive mitigation (discussed in Section 3.2.3)
and active mitigation measures (discussed in Section 8.2.2) may be taken into account. You do not
need to estimate the duration of the release, because this information is not used to estimate distance
to the LFL, as discussed in the next section.
12.0 Estimating Impact Distances for Alternative Release Scenarios for Flammable Substances
12.1 Vapor Cloud Fires
The distance to the LFL represents the maximum distance at which the radiant heat effects of
a vapor cloud fire might have serious consequences. Exhibit C-2, Appendix C, provides LFL data
(in volume percent and milligrams per liter) for listed flammable gases; Exhibit C-3 provides these
data for flammable liquids. To determine the distance to the LFL, find the LFL in milligrams per
liter and identify the appropriate reference table (neutrally buoyant or dense gas) from Exhibit C-2 or
C-3, Appendix C. Follow the steps described in Section 9 and Section 4 for toxic substances to find
the distance to the LFL from the release rate, using the appropriate reference table for flammable
substances, as discussed below. >
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-50-
Because LFL values are generally much larger than toxic endpoints for regulated toxic
substances, and because vapor cloud fires are instantaneous events (in contrast to releases of toxic
substances, where the duration of exposure to the toxic cloud is an important factor), the reference
tables of distances for toxic substances are not applicable to vapor cloud fires. Therefore, additional
reference tables for the alternative scenario .conditions (D stability and wind speed 3.0 meters per
second) are provided for estimating the distance to the LFL. Release duration does not need to be
considered for estimating vapor cloud fire distances; the reference tables for flammable substances
apply to both 10-minute and 60-minute releases. The reference tables for flammable substances
(Reference Tables 18-21 at the end of-Section 12) are:
Reference Table
Number
18
19
20
21
Applicable Conditions
Release Duration
(minutes)
10-60
10-60
10-60
10-60
Topography
Rural
Urban
Rural
Urban
Gas or Vapor Density
Neutrally buoyant
Dense
The development of these tables is discussed in Appendix D, Section D.4.
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-51-
Example 24. Vapor Cloud Fire from Evaporating Pool of Flammable Liquid
You have a tank containing 20,000 pounds of ethyl ether. A likely scenario for a release might be
shearing of a pipe from the tank, with the released liquid forming a pool. You want to estimate the
consequences of a vapor cloud fire that might result from evaporation of the pool and ignition of the
vapor.
You first need to estimate the rate of release of the liquid from the tank. You can do this using
Equation 13, Section 8.2.1. For this calculation, you need the area of the hole that would result
from shearing the pipe (HA), the height of the liquid in the tank above the hole (LH), and the liquid
leak factor (LLF) for ethyl ether, from Exhibit C-3 in Appendix C. The pipe diameter is 2 inches,
so the cross sectional area of the hole would be 3.1 square inches. You estimate that the pipe is 2
feet, or 24 inches, below the level of the liquid when the tank is full. The square root of LH (24
inches) is 4.9. LLF for ethyl ether is 34. From Equation 13, the rate of release of the liquid from
the hole is calculated as:
QRL = 3,1 x 4.9x34
= 520 pounds per minute
You estimate that the release of the liquid could be stopped in about 10 minutes. In 10 minutes, 10
x 520, or 5,200 pounds, would be released.
The liquid would be released into an area without dikes. To estimate the evaporation rate from the
pool formed by the released liquid, you use Equation 3 from Section 3.2.2. To carry out the
calculation, you need the Liquid Factor Ambient (LFA) and the Density Factor (DF) for ethyl ether.
From Exhibit C-3, Appendix C, LFA for ethyl ether is 0.11 and DF is 0.69. Wind speed (U) is
assumed to be 3.0 meters per second; 3 to the 0.78 power is 2.4. The release rate to air is:
QR = 5,200 x 2.4 x 0.11 x 0.69
= 950 pounds per minute
To estimate the maximum distance at. which people in the area of the vapor cloud could suffer
serious injury, you use the estimated release rate and the lower flammability limit (LFL) (in
milligrams per liter) for ethyl ether, and find the distance on the appropriate reference table. From
Exhibit C-3, Appendix C, LFL for ethyl ether is 57 mg/L, and the appropriate reference table is a
dense gas table. Your site is in a rural area with few obstructions, so you use Reference Table 20.
From Reference Table 20, the closest LFL is 60 mg/L. The lowest release rate on the table is 1,500
pounds per minute, which is higher than the evaporation rate estimated for the pool of ethyl ether.
For a release rate less than 1,500 pounds per minute, the distance to the LFL is less than 0.06 miles.
-------
-52-
Example 25. Flammable GaS Release (Acetylene)
In Example 23, you estimated a release rate for acetylene from a hole in a tank of 2,400 pounds per
minute. You want to estimate the distance to the LFL for a' vapor cloud fire resulting from this
release.
Froni Exhibit C-2, Appendix C, the LFL for acetylene is 27 irig/L, and the appropriate table for
distance estimation is a neutrally buoyant gas table for flammable substances. Your site is in a rural
area, so you would use Reference Table 18.
To use the neutrally buoyant gas tables, you need to calculate release rate/endpoint. In this case,
release rate/LFL = 2,400/27 or 89. 6n Reference Table 18, 89 falls in the range of release
rate/LFL values corresponding to 0.20 miles.
12.2 PoolFirfe
A "Pool Fire Factor" (PFF) has been derived for each of the regulated flammable substances
to aid in the consequence analysis. This factor, listed in Appendix C, Exhibits C-2 and C-3 for each
regulated flammable substance, may be used to estimate a distance frdni the center of a pool fire
where people could potentially receive second degree burns from a 40-second exposure. The heat
radiation endpoint for this analysis is 5 kilowatts per square meter (kW/m2). Ambient temperature is
assumed to be 25° C (77° F) for calculation of the PFF for flammable liquids.
To estimate a distance using the PFF, you first need to estimate the size of the pool, in square
feet, that might b'e formed by the release of a flammable substance. You may use the methods
described above for toxic liquids to estimate pool size (density factors (DF) for the estimation of pool
size in undiked areas may be found for flammable liquids in Exhibit C-3 of Appendix C). Distances
may be estimated from the PFF and the pool area as follows:
d = PFF x
(22)
where: d = Distance (feet)
PFF = Pool Fire Factor (listed for each flammable substance in Appendix C, Exhibits C-2
and C-3)
A = Pool area (square feet)
The derivation of these factors is discussed in Appendix D, Section D.9.
-------
-53-
Example 26. Pool Fire of Flammable Liquid
For the tank containing 20,000 pounds of ethyl ether, discussed in Example 24, you want to estimate
the consequences of a pool fire, for comparison with the vapor cloud fire results.
In Example 25, you estimated that 15,000 pounds would be released into an area without dikes,
forming a pool. Assuming the liquid spreads to a depth of 1 centimeter (0.39 inches), you estimate
the area of the pool formed from Equation 6, Section 3.2.3. For this calculation, you need die
density factor (DF) for ethyl ether; from Exhibit C-3, Appendix C, DF for ediyl edier is 0.69.
From Equation 6, die area of the pool is:
A = 15,000 x 0.69 = 10,400 square feet
You can use Equation 18 to estimate the distance from die center of the burning pool where the heat
radiation level would reach 5 kW/m2. For die calculation, you need die square root of the pool area
(A) and the pool fire factor (PFF) for ethyl ether. The square root of A, 10,400 square feet, is 102
feet. From Exhibit C-3, Appendix C, PFF for ethyl edier is 4.3. From Equation 18, the distance
(d) to 5 kW/m2 is:
d = 4.3 x 102 = 440 feet (about 0.08 miles)
12.3 BLEVEs
If a fireball from a BLEVE is a potential release scenario at your site, you may use Reference
Table 22 to estimate the distance to a potentially harmful radiant heat level. The table shows
distances for a range of quantities to the radiant heat level that potentially could cause second degree
burns to a person exposed for the duration of the fire. The quantity you use should be the total
quantity in a tank that might be involved in a BLEVE. The equations used to derive this table of
distances are presented in Appendix D, Section D.10. If you prefer, you may use the equations to
estimate a distance for BLEVEs, or you may use a different calculation method or model.
12.4 Vapor Cloud Explosion
If you have the potential at your site for the rapid release of a large quantity of a flammable
vapor, particularly into a congested area, a vapor cloud explosion may be an appropriate alternative
release scenario. For the consequence analysis, you may use the same methods as for the worst case
to estimate consequence distances to an overpressure endpoint of 1 psi (see Section 5.1 and the
equation in Appendix C). Instead of assuming the total quantity of flammable substance released is in
the vapor cloud, you may estimate a smaller quantity in the cloud. You could base your estimate of
the quantity in the cloud on the release rate estimated as described above for gases and liquids
multiplied by the time required to stop the release.
To estimate the quantity in the cloud for a gas liquefied under pressure (not refrigerated), you
may use the following equation, incorporating a "flash fraction factor" (FFF), listed in Appendix C,
Exhibit C-2 for regulated flammable gases, to estimate the quantity that could be immediately flashed
-------
-54-
into vapor upon release plus the quantity that might be carried along as spray or aerosol (see
Appendix D, Section D.ll for the derivation of this equation):
QF = FFF x QS x 2
(23)
where: QF = Quantity flashed into vapor plus aerosol (pounds) (cannot be larger than QS)
QS = Quantity spilled (pounds)
FFF = Flash fraction factor (unitless) (listed in Appendix C, Exhibit C-2)
2 = Factor to account for spray and aerosol
For derivation of the FFF, the temperature of the stored gas was assumed to be 25° C (77°
F). You may estimate the flash fraction under other conditions using the equation presented in
Appendix D, Section D.ll.
You may estimate the distance to 1 psi for a vapor cloud explosion from the quantity in the
cloud using Reference Table 9 (at the end of the worst-case analysis discussion) or from Equation C-1
in Appendix C. For the alternative scenario analysis, you may use a yield factor of 3 percent, instead
of the yield factor of 10 percent used in the worst-case analysis. If you use the equation in Appendix
C, use 0.03 instead of 0.1 in the calculation. If you use Reference Table 9, you can incorporate the
lower yield factor by multiplying the distance you read from Reference Table 9 by 0.67.
Example 27. Vapor Cloud Explosion (Propane)
You have a tank containing 50,000 pounds of propane liquefied under pressure at ambient
temperature. You want to estimate the consequence distance for a vapor cloud explosion resulting
from rupture of the tank.
You use Equation 19 to estimate the quantity that might be released to form a cloud. You base the
calculation on the entire contents of the tank (QS = 50,000 pounds). From Exhibit C-2 of Appendix
C, the Flash Fraction Factor (FFF) for propane is 0.38. From Equation 19, the quantity flashed into
vapor, plus the quantity that might be carried along as aerosol, (QF) is:
QF = 0.38 x 50,000 x 2 = 38,000 pounds
You assume 38,000 pounds of propane is in the flammable part of the vapor cloud. This quantity
falls between 30,000 pounds and 50,000 pounds in Reference Table 9; 30,000 pounds is the quantity
closest to your quantity. From die table, the distance to 1 psi overpressure is 0.33 miles for 30,000
pounds of propane for a 10 percent yield factor. To change the yield factor to 3 percent, you
multiply this distances by 0.67; then the distance becomes 0.22 miles.
-------
-55-
Reference Table 10
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
10-Minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(Ibs/min)/(mg/L)]
0-64
64 - 510
510 - 1,300
1,300-2,300
2,300-4,100
. 4,100 - 6,300
6,300 - 8,800
8,800-12,000
12,000 - 16,000
16,000 - 19,000
19,000 - 22,000
22,000 - 26,000
26,000 - 30,000
30,000 - 36,000
36,000-42,000 '
42,000 - 47,000
47,000 - 54,000
54,000 - 60,000
60,000 - 70,000
70,000 - 78,000
78,000 - 87,000
87,000 - 97,000
97,000- 110,000
110,000- 120,000
120,000 - 130,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
130,000-140,000 :
140,000 - 160,000,
160,000 - 180,000
180,000 - 190,000
190,000 - 210,000
210,000-220,000
220,000-240,000
240,000-261,000 ,
261,000-325,000
325,000 - 397,000
397,000 - 477,000
477,000 - 566,000
. 566,000,, 663,000
663,000 - 769,000-
769,000 - 1,010,000
1,010,000-1,280,000
1,280,000-1,600,000
.1,600,000 - 1,950,000
1,950,000 - 2,340,000
2,340,000-2,770,000
2,770,000 - 3,240,000
3,240,000 - 4,590,000
4,590,000 - 6, 190,000
> 6, 190,000
Distance to
Endpoint
(miles)
4.8
5.0
5.2
5.4
' 5.6
5,8
6.0
6.2
6.8
7.5
8.1
8.7
9.3
9.9
11
12
14
15
16
17
• 19
22
25
>25
-------
-56-
Reference Table 11
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
60-Minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-79
79 - 630
630- 1,600
1,600 - 2,800
2,800 - 5,200
5,200 - 7,900
7,900- 11,000
11,000- 14,000
14,000 - 19,000
19,000 - 23,000
23,000 - 27,000
27,000 - 32,000
32,000 - 36,000
36,000 - 42,000
42,000 - 47,000
47,000 - 52,000
52,000 - 57,000
57,000 - 61,000
61,000-68,000
68,000 - 73,000
73,000 - 79,000
•79,000-84,000
84,000 - 91,000
91,000 - 97,000
97,000 - 100,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
100,000- 110,000
110,000- 110,000
1 10,000 - 120,000
120,000 - 130,000
130,000 - 130,000
130,000 - 140,000
140,000 - 150,000
150,000- 151,000
151,000- 171,000
171,000- 191,000
191,000-212,000
212,000 - 233,000
233,000 - 256,000
256,000 - 280,000
280,000 - 332,000
332,000 - 390,000
390,000 - 456,000
456,000 - 529,000
529,000 - 610,000
610,000 - 699,000
699,000 - 796,000
796,000- 1,080,000
1,080,000- 1,410,000
> 1,410,000
Distance to
Endpoint
(miles)
4.8
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.8
7.5
8.1
8.7
9.3
9.9
11
12
14
15
16
17
19
22
25
>25
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-57-
Reference Table 12
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
10-Minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-160
160 - 1,400
1,400 - 3,600
3,600 - 6,900
6,900 - 13,000
13,000 - 22,000
22,000-31,000
31,000-42,000
42,000 - 59,000
59,000 - 73,000
73,000 - 88,000
88,000 - 100,000
100,000 - 120,000
120,000 - 150,000
150,000 - 170,000
170,000 - 200,000
200,000 - 230,000
230,000 - 260,000
260,000 - 310,000
310,000 - 340,000
340,000 - 390,000
390,000-430,000
430,000 - 490,000
490,000 - 540,000
540,000 - 600,000
Distance to
Endpoint
(miles)
0.06
0.19
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Release Rate/Endpoint ,
[(lbs/min)/(mg/L)]
600,000 - 660,000
660,000 - 720,000
720,000 - 810,000
810,000 - 880,000
880,000 - 950,000
950,000- 1,000,000
1,000,000- 1,100,000
1,100,000.- 1,220,000
1,220,000- 1,530,000
1,530,000- 1,880,000
1,880,000-2,280,000
2,280,000 - 2,710,000
2,710,000 - 3,200,000
3,200,000 - 3,730,000
3,730,000 - 4,920,000
4,920,000 - 6,310,000
6,310,000-7,890,000
7,890;000 - 9,660,000
9,660,000- 11,600,000
11,600,000- 13,800,000
13,800,000 - 16,200,000
16,200,000-23,100,000
23,100,000-31,300,000
> 3 1,300,000
Distance to
Endpoint
(miles)
4.8
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.8
7.5
8.1
8.7
9.3
9.9
11
12
14
15
16
17
19
22
25
>25
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-58-
Reference Table 13
Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint
60-Minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-200
200 - 1,700
1,700-4,500
4,500 - 8,600
8,600 - 17,000
17,000 - 27,000
27,000 - 39,000
39,000 - 53,000
53,000 - 73,000
73,000 - 90,000
90,000-110,000
110,000- 130,000
130,000 - 150,000
150,000 - 170,000
170,000 - 200,000
200,000 - 220,000
220,000 - 240,000
240,000 - 270,000
270,000-300,000
300,000 - 320,000
320,000 - 350,000
350,000 - 370,000
370,000 - 410,000
410,000 - 430,000
430,000 - 460,000
Distance to
Endpoint
(miles)
0.06
0.19 „ . ,
0.31
0.43
0.62
0.81
0.99
1.2
1.4
1.6
1.8
2.0
. 2.2 .
' 2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4,6
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
460,000 - 490;000
490;000 - 520,000
520^000-550,000
550,000-580,000
580,000-610,000
610,000-640,000
640,000-680,000
680,000-705,000
705,000 - 804,000
804,000 - 905,000
905,000- 1,010,000
1,010,000- 1,120,000
1,120,000- 1,230,000
1,230,000-1,350,000
1,350,000- 1,620,000
1,620,000- 1,920,000
1,920,000-2,250,000
2,250,000 - 2,620,000
2,620,000 - 3,030,000
3,030,000-3,490,000
3,490,000 - 3,980,000
3,980,000 - 5,410,000
5,410,000-7,120,000
> 7, 120,000
Distance to
Endpoint
(miles)
4.8
5.0
5.2
5.4
5.6
5.8
,6.0
6.2
6.8
7.5
8.1
8.7
9,3
9.9
11
12
14
15
16
17
19
22
25
>25
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-59-
Reference Table 14
Dense Gas Distances to Toxic Endpoint
10-minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
Toxic Endpoint (mg/L)
0.0004
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
0.60
0.87
1.4
2.0
3.7
5.0
7.4
8.7
12
17
22
>25
*
*
*
*
*
*
*
*
*
*
0.44
0.62
1.1
1.5
2.7
3.7
5.3
6.8
8.7
13
16
19
23
>25
*
*
*
*
*
*
*
*
0.36
0.50
0.87
1.2
2.2
3.0
4.3
5.5
7.4
11
13
16
19
22
25
>25
*
*
*
*
*
*
0.24
0.37
0.60
'0.87
1.5
2.1
3.0
3.8
5.0
7.4
9.3
11
13
15
17
19
22
>25
*
*
*
*
0.17
0.26
0.44
0.62
1.1
1-9
2.3
2.8
3.7
5.3
6.8
8.1
9.9
12
13
14
17
19
24
>25
*
*
0.14
0.22
0.36
0.54
0.93
1.2
1.7
2.3
3.0
4.5
5.6
6.8
8.1
9.3
11
12
14
16
19
22
>25
*
0.11
0.17
0.29
0.43
0.74
0.99
1.4
1.9
2.4
3.6
4.5
5.2
6.8
7.4
8.7
9.3
11
12
16
18
22
>25
0.09
0.14
0.24
0.36
0.68
0.87
1.2
1.6
2.1
3.0
3.8
4.5
5.6
6.8
7.4
8.1
9.3
11
13
16
19
22
<0.06
0.09
0.17
0.25
0.47
0.62
0.87
1.1
1.4
2.1
2.7
3.1
3.9
4.5
5.2
5.7
6.8
7.4
9.3
11
13
16
<0.06
0.07
0.12
0.18
0.34
0.45
0.62
0.81
1.1
1.6
1.9
2.3
2.9
3.4
3.8
4.2
4.9
5.6
6.8
8.1
9.9
11
tt
<0.06
0.09
0.14
0.28
0.37
0.56
0.68
0.87
1.3
1.6
2.2
2.4
2.7
3.2
3.5
4.1
4.7
5.8
6.8
8.1
9.3
tt
<0.06
0.07
0.11
0.22
0.30
0.43
0.56
0.74
1.1
1.3
1.5
1.9
2.2
2.5
2.8
3.3
3.7
4.7
5.3
6.8
7.4
#
#
<0.06
0.09
0.19
0.25
0.37
0.47
0.51
0.87
1.1
1.3
1.6
1.9
2.1
2.4
2.8
3.1
4.0
4.6
5.7
6.8
tt
it
tt
<0.06
0.11
0.15
0.23
0.29
0.38
0.56
0.68
0.81
0.99
1.2
1.3
1.4
1.7
2.1
2.4
2.8
3.5
4.0
tt
tt
tt
<0.06
0.07
0.10
0.15
0.19
0.26
0.37
0.47
0.56
0.68
0.81
0.87
0.99
1.1
1.3
1.6
1.9
2.4
2.8
tt
tt
tt
tt
<0.06
0.08
0.12
0.15
0.20
0.30
0.37
0.44
0.55
0.62
0.74
0.81
0.93
1.1
1.3
1.5
1.9
2.2
* > 25 miles
<0.06 miles
-------
-60-
Reference Table 15
Dense Gas Distances to Toxic Endpoint
60-minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
Toxic Endpoint (mg/L)
0.0004
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
0.53
0.81
1.6
2.0
4.0
5.5
8.7
12
17
>25
*
*
*
*
*
*
*
*
*
*
*
*
0.39
0.57
0.99
1.4
2.8
3.9
6.1
8.1
11
19
25
>25
*
*
*
*
*
- *
*
*
*
*
0.32
0.47
0.81
1.2
2.2
3.1
4.8
6.2
8.7
14
19
24
>25
*
*
*
*
*
*
*
*
*
0.22
0.32
0.54
0.81
1.5
2.1
3.2
4.1
5.6
9.3
12
15
20
24
>25
*
*
*
*
*
*
*
0.16
0.23
0.39
0.58
1.1
1.5
2.2
2.9
4.0
6.2
8.7
11
14
17
19
22
>25
*
*
*
*
*
0.13
0.19
0.32
0.47
0.87
1.2
1.8
2.3
3.2
5.0
6.8
8.1 .
11
13
15
17
21
25
>25
*
*
*
0.10
0.15
0.25
0.38
0.68
0.99
1.4
1.8
2.5
3.9
5.1
6.1
8.1
9.9
12
13
16
19
25
>25
*
*
0.09
0.13
0.22
0.32
0.61
0.81
1.2
1.6
2.1
3.3
4.2
5.2
6.8
8.1
9.3
11
14
16
20
25
>25
*
<0.06
0.09
0.15
0.22
0.42
0.56
0.81
1.1
1.4
2.2
2.8
3.4
4.3
5.2
6.0
6.8
8.7
9.9
13
16
21
25
9
<0.06
0.11
0.16
0.30
0.41
0.61
0.74
1.1
1.6
2.0
2.4
3.0
3.7
4.3
4.8
5.8
6.8
9.3
11
14
17
8
<0.06
0.09
0.13
0.25
0.34
0.50
0.62
0:87
1.3
1.6
1.9
2.5
2.9
3.4
3.8
4.7
5.3
6.8
8.7
11
14
tt
<0.06
0.07
0.11
0.20
0.27
0.40
0.51
0.68
0.99
1.3
1.5
1,9
2.3
2.7
3.0
3.6
4-1
5.4
6.8
8.7
11
it
a
<0.06
0.09
0.17
0.23
0.34
0.43
0.57
0.87
1.1
1.3
1.7
1.9
2.2
2.5
3.0
3.5
4.5
5.4
7.4
8.7
it
a
tt
<0.06
0.10
0.14
0.20
0.26
0.35
0.51
0.62
0.74
0.99
1.2
1.3
1.5
1.7
2.0
2.6
3.1
4.0
4.8
It
ft
tt
<0.06
0.07
0.09
0.14
0.18
0.24
0.35
0.44.
0.52
0.68
0.74
0.87
0.99
1.2
1.4
1.7
2.1
2.6
3.1
S
tt
It
tt
<0.06
0.07
O.ii
0.14
0.19
0.28
0.35
0.42
0.52
0.61
0.68
0.81
0.93
1.1
1.4
1.6
2.1
2.5
* > 25 miles
# <0.06 miles
-------
-61-
Reference Table 16
Dense Gas Distances to Toxic Endpoint
10-minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
Toxic Endpoint (mg/L)
0.0004
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
0.49
"0.68
1.1
2.1
3.0
4.1
5.8
7.4
9.9
14
17
20
>25
*
*
*
*
*
*
*
*
*
0.34
0.50
0.81
1.2
2.2
.3.0
4.3
5.5
7.4
11
13
15
19
22
24
>25
*
*
*
*
*
*
0.24
0.43
0.62
0.99
1.9
. 2.5
3.5
4.5
5.8
8.7
11
12
16
18
20
22
>25
*
*
*
*
*
0.19
0.28
0.47
0.68
1.2
1.6
'2.7
3.1
4.1
5.9
7.4
8.7
11
12
14
16
18
20
>25
*
*
*
0.12
0.22
0.33
0.50
0.93
1.2
1.8
2.2
3.0
4.3
5.5
6.2
8.1
9.3
11
11
14
15
19
22
>25
*
0.11
0.17
0.28
0.42
0.81
0.99
1.4
1.9
2.5
3.6
4.5
5.3
6.2
7.4
8.7
9.3
11
12
16
18
22
>25
0.08
0.12
0.21
0.31
0.62
0.81
1.2
1.4
2.0
2.9
3.6
4.3
5.2
6.2
6.8
7.4
8.7
9.9
12
14
18
20
0.06
0.11
0.19
0.28
0.56
0.68
0.99
1.2
1.7
2.5
3.1
3.5
4.5
5.2
6.0
6.8
7.4
8.7
11
12
16
18
<0.06
0.07
0.12
0.19
0.37
0.50
0.74
0.87
1.1
1.7
2.1
2.5
3.0
3.7
3.8
4.5
5.3
5,8
7.4
8.7
11
12
#
<0.06
0.09
0.13
0.27
0.30
0.56
0.68
0.87
1.2
1.6
1.8
2.2
2.7
3.0
3.3
4.0
4.4
5.5
6.2
8.1
9.3
8
<0.06
' 0.07
0.11
0.22
0.29
0.45
0.56
0.68
0.99
•1-2.
1.5
1.8
2.2
2.2
2.7
3.2
3.6
4.5
5.2
6.8
7.4
#
tt
<0.06
0.08
0.17
0.23
0.36
0.44
0.58
0.81
0.99
1.2
1.5
1.7
1.9
2.1
2.6
2.9
3.6
4.2
5.2
6.0
tt
tt
<0.06
0.06
0.14
0.19
0.29
0.37
0.50
0.68
0.87
0.99
1.2
1.4
1.7
1.9
2.1
2.4
3.0
3.6
4.4
5.2
H
tt
tt
<0.06
0.08
0.11
0.17
0.22
0.29
0.45
0.54
0.62
0.74
0.87
0.99
1.1
1.2
1.4
1.8
2.1
2.6
3.0
#
a
it
tt
<0.06
0.07
0.11
0.17
0.19
0.28
0.35
0.42
0.52
0.60
0.68
0.74
0.87
0.93
1.2
1.4
1.7
2.0
• 8
it
tt
tt
a
<0.06
0.08
0.11
0.14
0.21
0.27
0.32
0.40
. 0.47
0.55
0.57
0.68
0.74
0.93
1.1
1.3
1.6
* > 25 miles
# <0.06 miles
-------
-62-
Reference Table 17
Dense Gas Distances to Toxic Endpoint
60-minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
1
2
5
10
30
50
100
150
250
500
750
1000
1500
2000
2500
3000
4000
5000
7500
10000
15000
20000
0.0004
Toxic Endpoint (mg/L)
0.0007
0.001
0.002
0.0035
0.005
0.0075
0.01
0.02
0.035
0.05
0.075
0.1
0.25
0.5
0.75
Distance (Miles)
0.43
0.68
1.1
1.7
3.3
4.7
7.4
9.9
14
22
>25
*
*
*
*
*
*
*
*
*
*
*
0.31
0.47
0.81
1.2
2.4
3.3
5.2
6.8
9.3
16
20
24
>25
*
*
*
*
*
*
*
*
*
0.25
0.38
0.68
0.99
1.9
2.6
4.1
5.3
7.4
12-
16
19
>25
>25
>25
*
*
*
*
*
*
*
0.17
0.25
0.43
0.68
1.3
1.7
2.7
3.4
4.7
7.4
9.9
12
16
19
23
>25
>25
*
*
*
*
*
0.12
0.18
0.32
0.47
0.93
1.2
1.9
2.4
3.4
5.2
6.8
8.1
11
14
16
18
22
>25
*
*
*
*
0.09
0.15
0.25
0.38
0.74
0.99
1.5
1.9
2.7
4.2
5.4
6.8
8.7
11
12
14
17
20
25
>25
*
*
0.07
0.11
0.20
0.30
0.58
0.81
1.2
1.5
2.1
3.2
4.2
5.0
6.8
8.1
9.3
11
13
16
20
24
>25
*
<0.06
0.09
0.17
0.26
0.50
0.68
0.99
1.3
1.7
2.7
3.5
4.2
5.5
6.8
7.4
8.7
11
12
17
20
>25
>25
tt
<0.06
0.11
0.17
0.33
0.45
0.68
0.87
1.1
1.7
2.2
2.7
3.5
4.2
4.9
5.5
6.8
8.1
11
13
17
20
ff
<0.06
0.08
0.12
0.24
0.33
0.48
0.61
0.81
1.2
1.6
1.8
1.9
3.0
3.4
3.8
4.7
5.3
6.8
8.7
11
14
tt
It
<0.06
0.10
0.19
0.27
0.40
0.50
0.68
0.99
1.3
1.6
2.0
2.2
2.7
3.0
3.1
4.3
5.6
6.8
8.7
11
it
tt
<0.06
0.07
0.16
0.21
0.32
0.40
0.53
0.81
0.99
1.2
1.6
1.9
2.1
2.4
2.8
3.3
4.3
5.2
6.8
8.1
tt
tt
<0.06
0.06
0.13
0.17
0.27
0.33
0.45
0.68
0.87
0.99
1.3
1.6
1.7
2.0
2.4
2.7
3.5
4.3
5.6
6.8
tt
ff
It
<0.06
0.07
0.10
0.16
0.19
0.26
0.38
0.49
0.58
0.74
0.87
0.99
1.1
1.3
1.5
2.0
2.4
3.0
3.6
tt
tt
tt
tt
<0.06
0.06
0.10
0.13
0.17
0.25
0.32
0.38
0.48
0.56
0.62
0.74
0.87
0.99
1.2
1.5
1.9
2.3
tt
tt
tt
tt
tt
<0.06
0.07
0.10
0.13
0.20
0.27
0.30
0.37
0.44
0.50
0.56
0.68
0.74
0.93
1.1
1.5
1.7
* > 25 miles
# <0.06 miles
-------
-63-
Reference Table 18
Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL)
For Release Rate Divided by LFL
Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-28
28 -40
40-60
60 - 220
220 - 530
530 - 860
860 - 1,300
1,300- 1,700
1,700-2,200
2,200 - 2,700
Distance to
Endpoint
(miles)
0.06
0.08
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
2,700 - 3,300
3,300 - 3,900
3,900-4,500
4,500-5,200
5,200. -5,800
5,800 - 6,800
6,800,- 8,200
8,200 - 9,700
9,700-11,000 ,
11,000- 13,000
Distance to
Endpoint
(miles)
0.90
1.0
1.1
1.2
1.3
1.4
1.6
1.8
2.0
2.2
Reference Table 19
Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL)
For Release Rate Divided by LFL
Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release Rate/Endpoint
[(lbs/min)/(mg/L)]
0-68
68 - 100
100 - 150
150 - 710
710-1,500
1,500-2,600
2,600 - 4,000
4,000 - 5,500
Distance to
Endpoint
(miles)
0.06
0.08
0.10
0.20
0.30
0.40
0.50
0.60
Release Rate/Endpoint
[Obs/min)/(mg/L)]
5,500 - 7,300
7,300 - 9,200
9,200-11,000
11,000- 14,000
14,000 - 18,000
18,000 - 26,000
26,000 - 31,000
31,000-38,000
Distance to
Endpoint
(miles)
0.70
0.80
0.90
1.0
1.2
1.4
1.6
1.8
-------
-64-
Reference Table 20
Dense Gas Distances to Lower Flammability Limit
Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
<1500
1500
2000
2500
3000
4000
5000
7500
10000
Lower Flammability Limit (mg/L)
27
30
35
40
45
50
60
70
100
>100
Distance (Miles)
#
<0.06
0.07
0.08
0.09
0.11
0.12
0.15
0.17
#
<0.06
0.06
0.07
0.08
0.10
0.11
0.14
0.16
#
#
<0.06
0.07
0.07
0.09
0.10
0.12
0.14
#
#
ft
<0.06
0.07
0.08
0.09
0.11
0.13
#
#
#
#
<0.06
0.07
0.08
0.11
0.12
#
#
#
#
<0.06
0.07
0.07
0.10
0.11
#
#
#
#
#
<0.06
0.07
0.09
0.10
#
#
#
#
#
#
<0.06
0.07
0.09
#
#
#
'#
#
#
#
<0.06
0.07
#
#
#
#
#
#
#
#
<0.06
# < 0.06 mile
-------
-65-
Reference Table 21
Dense Gas Distances to Lower Flammability Limit
Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
Release
Rate
(Ibs/min)
<5000
5000
7500
10000
Lower Flammability Limit (mg/L)
27
30
35
40
>40
Distance (Miles)
#
<0.06
0.07
0.09
#
<0.06
0.06
0.07
#
#
<0.06
0.07
#
#
.#
<0.06
#
#
#
#
# < 0.06 miles
-------
-66-
Rcference Table 22
Distance to Radiant Heat Dose at Potential Second Degree Burn Threshold Assuming Exposure for Duration of Fireball
(Dose = [5 kW/m2]4'3 x Exposure Time)
Quantity in Fireball (pounds)
Duration of Fireball (seconds)
CAS No.
75-07-0
74-86-2
598-73-2
106-99-0
106-97-8
106-98-9
107-01-7
25167-67-3
590-18-1
624-64-6
463-58-1
7791-21-1
557-98-2
590-21-6
460-19-5
75-194
4109-96-0
75-37-6
124-40-3
463-82-1
74-84-0
Chemical Name
Acetaldehyde
Acetylene
Bromotrifluoroethylene
1,3-Butadiene
Butane
1-Butene
2-Butene
Butene
2-Butene-cis
2-Butene-trans
Carbon oxysulfide
Chlorine monoxide
2-Chloropropylene
1-Chloropropylene
Cyanogen
Cyclopropane
Dichlorosilane
Difluoroethane
Dimethylamine
2,2-Dimethylpropane
Ethane
1,000
3.5
5,000
5.9
10,000
7.5
20,000
9.4
30,000
10.8
50,000
12.7
75,000
14.8
100,000
15.5
200,000
17.4
300,000
18.7
500,000
20.3
Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Burns
0.036
0.050
o.oio'
0.048
0.049
0.049
0.049
0.048
0.048
0.048
0.022
0.007
0.035
0.035
0.033
0.049
0.021
0.024
0.043
0.048
0.050
0.076
0.11
0.021
0.10
0.10
0.10
0.10
0,10
0.10
0.10
0.046
0.015
0.073
0.073
0.069
0.10
0.043
0.051
0.091
0.10
0.10
0.10
0.14
0.029
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.063
0.021
0.10
0.10
0.10
0.14
0.060
0.071
0.12
0.14
0.14
0.14
0.20
0.040
0.19
0.19
0.19
0.19
0.19
0.19
0.19
0.086
0.029
0.14
0.14
0.13
0.20
0.082
0.10
0.17
0.19
0.20
0.17
0.24
0.048
0.23
0.23
0.23
0.23
0.23 :
0.23
0.23 '
0.10
0.035
0.17
0.17
0.16
0.24
0.10
0.12
0.21
0.23
0.24
0.22
0.30
0.061
0.29
0.29
0.29
0.29
0.29
0.29
0.29
0.13
0.044
0.21
0.21
0.20
0.30
0.13
0.15
0.26
0.29
0.30
0.26
;0.37
0.074
0.35
'0.36
0.36
0.36
0.36
0.36
0.35
0.16
0.053
0.25
0.25
0.24
0.36
0.15
0.18
0.32
0.35
0.36
0.30
0.41
0.083
0.40
0.40
0.40
0.40
0.40
0.40
0.40
0.18
0.060
0.28
0.28
0.27
0.40
0.17
0.20
0.35
0.40
0.41
0.39
0.54
0.11
0.52
0.53
0.53
0.53
0.52
0.52
0.52
0.24
0.078
0.37
0.37
0.36
0.53
0.22
0.26
0.47
0.52
0.54
0.46
0.64
0.13
0.61
0.62
0.62
0.62
0.62
0.62
0.62
0.28
0.092
0.44
0.44
0.42
0.63
0.26
0.31
0.55
0.62
0.63
0.56
0.78
0.16
0.75
0.76
0.76
0.76
0.76
0.76
0.75
0.34
0.11
0.54
0.54
0.52
0.77
0.32
0.38
0.67
0.75
0.77
-------
-67-
Reference Table 22 (continued)
Quantity in Fireball (pounds)
Duration of Fireball (seconds)
CAS No.
107-00-6
75-04-7
75-00-3
74-85-1
60-29-7
75-08-1
109-95-5
1333-74-0
75-28-5
78-78-4
78-79-5
75-31-0
75-29-6
74-82-8
74-89-5
563-45-1
563-46-2
115-10-6
107-31-3
115-11-7
504-60-9
109-66-0
109-67-1
Chemical Name
Ethyl acetylene
Ethylamine
Ethyl chloride
Ethylene
Ethyl ether
Ethyl mercaptan
Ethyl nitrite
Hydrogen
Isobutane
Isopentane
Isoprene
Isopropylamine
Isopropyl chloride
Methane
Methylamine
3-Methyl-l-butene
2-Methyl-l-butene
Methyl ether
Methyl formate
2-Methylpropene
1,3-Pentadiene
Pentane
1-Pentene
1,000
3.5
5,000
5.9
10,000
7.5
20,000
9.4
30,000
10.8
50,000
12.7
75,000
14.8
100,000
15.5
200,000
17.4
300,000
18.7
500,000
20.3
Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Burns
0.049
0.043
0.032
0.050
0.042
0.038
0.031
0.079
0.049
0.048
0.048
0.044
0.035
0.051
0.040
0.048
0.048
0.039
0.028
0.048
0.048
0.048
0.048
0.10
0.090
0.068
0.10
0.088
0.080
0.064
0.17
0.10
0.10
0.10
0.091
0.074
0.11
0.085
0.10
0.10
0.081
0.059
0.10
0.10
0.10
0.10
0.14
0.12
0.093
0.14
0.12
0.11
0.088
0.23
0.14
0.14
0.14
0.13
0.10
0.15
0.12
0.14
0.14
0.11
0.081
0.14
0.14
0.14
0.14
0.19
0.17
0.13
0.20
0.17
0.15
0.12
0.31
0.19
0.19
0.19
0.17
0.14
0.20
0.16
0.19
0.19
0.15
0.11
0.19
0.19
0.19
0.19
0.23
0.20
0.15
0.24
0.20
0.18
0.15
0.38
0.23
0.23
0.23
0.21
0.17
0.24
0.19
0.23
0.23
0.19
0.14
0.23
0.23
0.23
0.23
0.29
0.26
0.19
0.30
0.25
0.23
0.19
: 0.48
0.29
0.29
0.29
0.26
0.21
0.31
0.24
0.29
0.29
0.23
0.17
0.29
0.29
0.29
0.29
0.36
0.31
0.24
0.36
0.31
0.28
0.22
0.58
0.36
0.35
0.35
0.32
0.26
0.37
0.30
0.35
0.35
0.28
0.21
0.35
0.35
0.35
0.35
0.40
0.35
0.26
0.41
0.34
0.31
0.25
0.65
0.40
0.40
0.39
0.36
0.29
0.42
0.33
0.40
0.39
0.32
0.23
0.40
0.39
0.40
0.40
0.53
0.46
0.35
0.54
0.45
0.41
0.33
0.85
0.53
0.52
0.52
0.47
0.38
0.55
0.44
0.52
0.52
0.42
0.31
0.52
0.51
0.52
0.52
0.62
0.54
0.41
0.63
0.53
0.48
0.39
1.0
0.62
0.61
0.61
0.55
0.45
0.65
0.51
0.61
0.61
0.49
0.36
0.62
0.60
0.61
0.61
0.76
0.67
0.50
0.77
0.65
0.59
0.48
1.2
0.76
0.75
0.74
0.68
0.55
0.79
0.63
0.75
0.75
0.60
0.44
0.75
0.74
0.75
0.75
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-68-
Reference Table 22 (continued)
Quantity in Fireball (pounds)
Duration of Fireball (seconds)
CAS No.
646-04-8
627-20-3
463-49-0
74-98-6
115-07-1
74-99-7
7803-62-5
116-14-3
75-76-3
10025-78-2
79-38-9
75-50-3
689-97-4
75-01-4
109-92-2
75-02-5
75-35-4
75-38-7
107-25-5
Chemical Name
2-Pentene, (E)-
2-Pentene, (Z)-
Propadiene
Propane
Propylene
Propyne
Silane
Tetrafluoroethylene
Tetramethylsilane
Trichlorosilane
Trifluorochloroethylene
Trimethylamine
Vinyl acetylene
Vinyl chloride
Vinyl ethyl ether
Vinyl fluoride
Vinylidene chloride
Vinylidene fluoride
Vinyl methyl ether
1,000
3.5
5,000
5.9
10,000
7.5
20,000
9.4
30,000
10.8
50,000
12.7
75,000
14.8
100,000
15.5
200,000
17.4
300,000
18.7
500,000
20.3
Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Burns
0.048
0.048
0.049
0.049
0.049
0.049
0.048
0.008
0.047
0.014.
0.010
0.044
0.049
0.031
0.041
0.011
0.023
0.024
0.040
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.017
0.098
0.029
0.020
0.093
0.10
0.066
0.087
0.022
0.049
0.050
0.084
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.024
0.13
0.040
0.028
0.13
0.14
0.090
0.12
0.031
0.067
0.068
0.11
0.19
0.19
0.19
0.19
0.19
0.19
0.19
0.032
0.18
0.055
0.039
0.18
0.19
0.12
0.16
0.042
0.092
0.094
0.16
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.039
0.22
0.067
0.047
0.21
0.23
0.15
0.20
0.051
0.11
0.11
0.19
0.29
0.29
0.30
0.30
0.30
0.30
0.29
0.049
0.28
0.085
0.059
0.27
0.29
0.19
0.25
0.065
0.14
0.14
0.24
0.35
0.35
0.36
0.36
0.36
0.36
0.35
0.060
0.34
0.10
0.072
0.33
0.36
0.23
0.30
0.078
0.17
0.17
0.29
0.40
0.40
0.40
0.40
0.40
0.40
0.39
0.067
0:38
0.11
0.080
0.37
0.40
0.26
0.34
0.088
0.19
0.19
0.33
0.52
0.52
0.53
0.53
0.53
0.53
0.52
0.088
0.50
0.15
0.11
0.48
0.53
0.34
0.45
0.12
0.25
0.26
0.43
0.61
0.61
0.62
0.62
0.62
0.62
0.61
0.10
0.59
0.18
0.12
0.57
0.62
0.40
0.53
0.14
0.30
0.30
0.51
0.75
0.75
0.76
0.76
0.76
0.76
0.75
0.13
0.73
0.22
0.15
0.69
0.76
0.49
0.64
0.17
0.36
0.37
0.62
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-69-
13.0 Estimating Offsite Receptors
The rule requires that you estimate residential populations within the circle of your worst-case
and alternative release scenarios. In addition, you must report in the RMP whether types of public
receptors and environmental receptors are within the circles.
To estimate residential populations, you may use the most recent Census data or any other
source of data that you believe is mote accurate. You are not required to update Census data or
conduct any surveys to develop your estimates. Census data are available in public libraries and in
the LAND VIEW system, which is available on CD-ROM. The rule requires that you estimate
populations to two-significant digits. For example, if there are 1,260 people within the circle, you
may report 1,300 people.
Census data are presented by Census tract. If your circle covers only a portion of the tract,
you should develop an estimate for that portion. The easiest way to do this is to determine the
population density per square mile (total population of the Census tract divided by the number of
square miles in the tract) and apply that density figure to the number of square miles within your
circle. Because there is likely to be considerable variation in actual densities within a Census tract,
this number will be approximate. The rule, however, does not require you to correct the number.
Other public receptors must be noted in the RMP. If there are any schools, residences,
hospitals, prisons, public recreational areas or arenas, or major commercial or industrial areas within
the circle, you must report that. You are not required to develop a list of all institutions and areas;
you must simply checkoff that one or more such areas are within the circle. Most of these institutions
or areas can be identified from local street maps. Recreational areas include public swimming pools,
public parks, and other areas that are used on a regular basis for recreational activities (e.g., baseball
fields). Commercial and industrial areas include shopping malls, strip malls, downtown business
areas, industrial parks, etc.
Environmental receptors are defined as national or state parks, forests, or monuments;
officially designated wildlife sanctuaries, preserves, or refuges; and Federal wilderness areas. All of
these can be identified on local U.S. Geological Survey maps. You are not required to locate each of
these specifically. You are only required to checkoff in the RMP that these specific types of areas are
within the circle. If any part of one of these receptors is within your circles, you must note that in
the RMP.
The rule does not require you to assess the likelihood, type, or severity of potential impacts
on either public or environmental receptors. Identifying them as within the circle indicates that they
could be adversely affected by the release.
-------
-70-
14.0 Submitting Offsite Consequence Analysis Information for Risk Management Plan
For the offsite consequence analysis (OCA) component of the RMP you must provide
information on your worst-case and alternative release scenario(s) for toxic and flammable regulated
chemicals held above the threshold quantity. The requirements for what information you must submit
differs if your source has Program 1, Program 2, or Program 3 processes.
If your source has Program 1 processes, you must submit information on a worst-case release
scenario for each toxic and flammable substance held above the threshold quantity in a Program 1
process. If your source has Program 2 or Program 3 processes, you must provide information on one
worst-case release for all toxic regulated substances present above the threshold quantity and one
worst-case release scenario for all flammable regulated substances present above the threshold
quantity. You may need to submit an additional worst-case scenario if a worst-case release from
another process at the source would potentially affect public receptors different from those potentially
affected by the initial worst-case scenario(s) for flammable and toxic regulated substances.
In addition to a worst-case release scenario, sources with Program 2 and Program 3 processes
must also provide information on alternative release scenarios. Alternative releases are releases that
could occur, other than the worst-case, that may result in concentrations, overpressures, or radiant
heat that reach endpoints offsite. You must present information on one alternative release scenario
for each regulated toxic substance, including the substance used for the worst-case release, held above
the threshold quantity and one alternative release scenario to represent all flammable substances held
above the threshold quantity. The format of the information will be provided by EPA in general
guidance to the Risk Management Program. The types of documentation to submit are presented
below for worst-case scenarios involving toxic substances, alternative scenarios involving toxic
substances, worst-case scenarios involving flammable substances, and alternative scenarios involving
flammable toxic substances.
14.1 Documentation Required iFor Worst-Case Scenarios for Toxic Substances
For worst-case scenarios involving toxic substances, you will have to submit the following
information. See the Risk Management Plan Data Elements Guide for complete instructions.
• Chemical name;
• Physical state of the chemical released (gas, liquid, refrigerated gas, refrigerated
liquid);
• Basis of results (OCA reference tables or modeling; name of the model used);
• Scenario (toxic gas release or liquid spill and vaporization);
• Quantity released (pounds);
• Release rate (pounds per minute);
• Duration of release (minutes) (10 minutes for gases; if you used OCA guidance for
liquids, indicate either 10 or 60 minutes);
• Wind speed (meters per second) and stability class (1.5 meters per second and F
stability unless you can show higher minimum wind speed or less stable atmosphere at
all times during the last three years);
• Topography (rural or urban);
• Distance to endpoint (miles);
• Population within distance (residential population rounded to two significant digits);
-------
-71-
• Public receptors within the distance (schools, residences, hospitals, prisons, public
recreation areas or arenas, major commercial or industrial areas);
• Environmental receptors within the distance (national or state parks, forests, or
, monuments; officially designated wildlife sanctuaries, preserves, or refuges; Federal
wilderness areas); and
• Passive mitigation measures considered (dikes, enclosures, berms, drains, sumps,
other).
14.2 Documentation Required for Alternative Scenarios for Toxic Substances
For alternative scenarios involving toxic substances held above the threshold quantity in a
Program 2.or Program 3 process, you will have to submit the following information. See the Risk
Management Plan Data Elements Guide for complete instructions.
• Chemical name;
• Physical state of the chemical released (gas, liquid, refrigerated gas, refrigerated
liquid);
• Basis of results (OCA reference tables or modeling; name of model used);
• Scenario (transfer hose failure, pipe leak, vessel leak, overfilling, rupture disk/relief
valve, excess flow valve, other);
• Quantity released (pounds);
• Release rate (pounds per minute);
• Duration of release (minutes) (if you used OCA guidance, indicate either 10 or 60
minutes);
• Wind speed (meters per second) and stability class (3.0 meters per second and D
stability if you use OCA guidance, otherwise use typical meteorological conditions at
your site);
• Topography (rural or urban);
• Distance to endpoint (miles);
• Population within distance (residential population rounded to two significant digits);
• Public receptors within the distance (schools, residences, hospitals, prisons, public
recreation areas or arenas, major commercial or industrial areas);
• Environmental receptors within the distance (national or state parks, forests, or
monuments; officially designated wildlife sanctuaries, preserves, or refuges; Federal
wilderness areas);
• Passive mitigation measures considered (dikes, enclosures, berms; drains, sumps,
other); and
•• Active mitigation measures considered (sprinkler system, deluge system, water
curtain, neutralization, excess flow valve, flares, scrubbers, emergency shutdown
system, other).
14.3 Documentation Required for Worst-Case Scenarios for Flammable Substances
For worst-case scenarios involving flammable substances, you will have to submit the
following information. See the Risk Management Plan Data Elements Guide for complete
instructions.
-------
-72-
Chemical name;
Basis of results (OCA reference tables or modeling; name of model used);
Scenario (vapor cloud explosion; BLEVE if it produces worst-case consequences);
Quantity released (pounds);
Endpoint used (for vapor cloud explosions use 1 psi, for BLEVE use 5 kw/m2 for 40
seconds (or thermal dose equivalent to receive second degree burns));
Distance to endpoint (miles);
Population within distance (residential population rounded to two significant digits);
Public receptors within the distance (schools, residences, hospitals, prisons, public
recreation areas, major commercial or industrial areas);
• Environmental receptors within the distance (national or state parks, forests, or
monuments, officially designated wildlife sanctuaries, preserves, or refuges, Federal
wilderness areas); and
• Passive mitigation measures considered (dikes, fire walls, blast walls, enclosures,
other).
14.4 Documentation Required for Alternative Scenarios for Flammable Substances
For alternative scenarios involving flammable substances held above the threshold quantity in
a Program 2 or Program 3 process, you will have to submit the following information. See the Risk
Management Plan Data Elements Guide for complete instructions.
Chemical name;
Basis of results (OCA reference tables or modeling; name of the model used);
Scenario (vapor cloud explosion, vapor cloud fire, BLEVE, pool fire, jet fire, other);
Quantity released (pounds);
Release rate (pounds per minute) (only for vapor cloud fires);
Wind speed (meters per second) and stability class (only for vapor cloud fires; 3.0
meters per second and D stability if you use OCA guidance, otherwise use typical
meteorological conditions at your site);
Topography (rural, urban) (only for vapor cloud fires);
Endpoint used (for vapor cloud explosions use 1 psi; for BLEVE, jet fire, pool fire,
use 5 kw/m2 for 40 seconds (or thermal dose equivalent to receive second degree
burns); for vapor cloud fire use lower flammability limit);
Distance to endpoint (miles);
Population within distance (residential population rounded to two significant digits);
Public receptors within the distance (schools, residences, hospitals, prisons, public
recreation areas, major commercial or industrial areas);
Environmental receptors within the distance (national or state parks, forests, or
monuments, officially designated wildlife sanctuaries, preserves, or refuges, Federal
wilderness areas);
Passive mitigation measures considered (e.g., dikes, fire walls, blast walls,
enclosures, other); and
Active mitigation measures considered (e.g., sprinkler system, deluge system, water
curtain, neutralization, excess flow valve, flares, scrubbers, emergency shutdown
system, other).
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-73-
APPENDIX A
PUBLICLY AVAILABLE MODELS AND REFERENCES FOR CALCULATION METHODS
-------
-74-
This appendix provides information on some models that could be used for the offsite
consequence analyses required under CAA section 112(r) and lists references that may provide useful
information for modeling or calculation methods that could be used in the offsite consequence
analyses. Exhibit A-l summarizes information on some publicly available models. Exhibit A-2 lists
references that provide information on consequence analysis methods. Neither of these exhibits is
intended to be a complete listing of models or references that may be used in the consequence
analysis; any appropriate model or method may be used.
-------
-75-
Exhibit A-l
Summary of Several Public Domain Models
Identification
Description
Information on Acquiring Software
AIRTOX Modeling System
Developed by ENSR
AIRTOX calculates concentrations of toxic or
flammable chemicals for steady, instantaneous, or time-
varying releases of volatile liquids or gases. A number
of accompanying spreadsheet-based models are available
for calculation of specific release profiles. AIRTOX
has algorithms that address releases from various source
configurations, including buoyant and heavier-than-air
sources, jets, liquid pools, fires, and explosions. The
model has been applied to offsite consequence
assessments, response planning, and accident
investigations.
Address:
ENSR
35 Nagog Park
Acton, MA 01720
Phone:
1-508-635-9500, ext. 3150
Cost:
Dependent upon the modeling package selected;
contact ENSR for information
ALOHA
(Areal Locations of Hazardous
Atmospheres)
Developed by the National Oceanic
and Atmospheric Administration
(NOAA) and the Environmental
Protection Agency (EPA)
ALOHA is an emergency response model, intended
primarily for rapid deployment by responders as well as
for use in emergency pre-planning. It incorporates
source strength as well as Gaussian and heavy gas
dispersion models and an extensive chemical library.
Model output data is in both text and graphic form and
includes a "footprint" plot of the area downwind of a
release where concentrations may exceed a user-set
threshold level. ALOHA can accept weather data
transmitted from portable monitoring stations and can
plot footprints on electronic maps displayed in a
companion mapping application, MARPLOT™.
ALOHA runs on a Macintosh or in Microsoft Windows.
Address:
National Safety Council
P.O. Box 558
Itasca, IL 60611
Phone: 1-800-621-7619
Fax: 1-708-285-0797 '
Cost:
ALOHA: $215/Govt. & Non-profit
$610/Commercial
CAMEO MAC/ALOHA: $375/Govt. & Non-profit,
$1050/Commercial ,
-------
-76-
Exhibit A-l (continued)
Identification
Description
Information on Acquiring Software
ARCHIE
(Automated Resource for Chemical
Hazard Incident Evaluation)
Prepared for the Federal
Emergency Management Agency
(FEMA), Department of
Transportation (DOT), and
Environmental Protection Agency
(EPA)
ARCHIE estimates downwind dispersion of a chemical
release to provide emergency planning personnel with
the tools necessary to evaluate the nature and magnitude
of chemical release threats at potentially hazardous
sites. Includes methods to estimate the discharge rate
and duration of a gas or liquid release from a tank or
pipeline, the size of a liquid pool, the rate at which a
liquid pool will evaporate or boil, the overpressure and
heat generated from explosions and fires, and the
downwind chemical concentration and hazard zones.
Contact/Address:
William Dorsey
ARCHIE
(DHM-15/Room 8104)
U.S. Dept. of Transportation
400 7th St., SW
Washington, DC 20590
Phone: (202)366-4900
Cost: Free
BP CIRRUS
Developed by the Corporate Safety
Services of British Petroleum,
International
BP CIRRUS is a package of models to forecast the
effects of a release of hydrocarbon or other chemical
liquid or vapor. It is used for consequence modeling in
relation to the design of new facilities, in risk
assessment studies, and in developing emergency plans
for currently operating facilities.
HELPLINE
Address:
Corporate Safety Services
BP International Ltd.
London
Phone: (044) 71 920 3157
Fax: (044) 71 628 2709
DEGADIS
(Dense Gas Dispersion)
Developed by the United States
Coast Guard
DEGADIS predicts contaminant movement for heavier-
than-air gases for instantaneous and continuous ground
level releases. It is used for emergency response
planning and vulnerability analysis.
Address:
National Technical Information Service (NTIS)
5285 Port Royal Rd.
Springfield, VA 22161
Phone: (703)487-4600
Cost: $90 (Version 2.1)
The FORTRAN source code for operation on a
VAX or PC can be downloaded through the Support
Center for Regulatory Air Models (SCRAM)
Bulletin Board System, (919)541-5742.
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-77-
Exhibit A-l (continued)
Identification
Description
Information on Acquiring Software
HGSYSTEM
Developed by the Industry
Cooperative HF Mitigation /
Assessment Program (20 companies
from the chemical and petroleum
industries)
HGSYSTEM is a package of models for predicting the
transient and steady-state release and dispersion
behavior of hydrogen fluoride or ideal gases;
incorporates the thermodynamic and cloud aerosol
effects of hydrogen fluoride.
Address:
Energy, Science & Technology Software Center
P.O. Box 1020
Oak Ridge, TN 37831-1020
Phone: (615)576-2606
Cost: $510
SAFER System - TRACE and
SAFER Real-Time System
Developed by DuPont"
TRACE can model ground level and elevated releases
of dense, neutral, or buoyant gases and predict
downwind chemical concentrations and impact on
receptors. Methods are included to estimate the
discharge rate and duration of releases from tanks or
pipelines and size and evaporation rate of liquid pools.
A high momentum jet model, special algorithms to
model hydrogen fluoride and titanium tetrachloride, and
models for a variety of fire and explosion scenarios are
included. Output is presented in text and graphical
forms. An optional enhancement allows in-depth
evaluation of impact on population.
SAFER Real-Time System is based on the same
modeling algorithms as the TRACE model, but is
designed for emergency preparedness and response
•activities. The model uses real-time meteorological data
for modeling, has optional complex terrain modeling
capabilities, and can interface with toxic gas sensors.
Address:
DuPont SAFER Systems, Inc.
4165 E. Thousand Oaks Blvd., Suite 350
Westlake Village, CA 91362
Phone: (805)446-2450
FAX: (805)446-2470
Cost:
TRACE (including Fire and Explosion models):
$15,000
SAFER Real-Time System: $ 18,400
-------
-78-
Exhibit A-l (continued)
Identification
Description
Information on Acquiring Software
SLAB
Developed by the Lawrence
Livermore National Laboratory
SLAB is a dense gas model for various types of releases
including a ground-level evaporating pool, an elevated
horizontal jet, a stack or elevated vertical jet, and an
instantaneous volume source; solves conservation
equations of mass, momentum, energy, and species for
continuous, finite duration, and instantaneous releases.
Contact/Address:
BOWMAN Environmental Engineering, Inc.
P.O. Box 59916
Dallas, TX 75229
Phone: (214)233-5463
FORTRAN version available on EPA Bulletin Board
at no cost / (919)541-5742 „"
TSCREEN
Developed for EPA by Pacific
Environmental Services, Inc.
TSCREEN is a model for screening toxic _air pollutants
to assist state and local agencies in analyzing toxic
emissions and their subsequent dispersion from one of
many different types of possible releases from
Superfund sites. SCREEN, RVD, and PUFF are three
air toxics dispersion screening models imbedded within
TSCREEN that are used to simulate the release and to
calculate the dispersion characteristics and pollutant
concentrations of the resulting plume.
Contact/Address:
Jawad Touma
USEPA, OAQPS
Maildrop 14
Research Triangle Park, NC 27711 ,
Phone: (919)541-5381
TSCREEN can be acquired through the EPA
Electronic Bulletin Board at no cost by means of a
modem or via the Internet / (919)541-5742
WHAZANH
(World Bank Hazard Analysis')
Developed by DNV Technica Ltd.
and the World Bank
WHAZAN is a series of models to predict the
consequences of accidental releases of toxic and
flammable gases or liquids. The models provide
information about outflow, behavior immediately after
release, dispersion, and fires and explosion. WHAZAN
includes a database containing the values of relevant
properties for twenty hazardous chemicals.
Contact/Address:
Mike Johnson
DNV Technica Ltd.
40925 County Center Drive
Suite 200
Temechula, CA 92591
Phone: (909)694-5790
Cost: $2500
-------
-79-
ExhibitA-2
Selected References for Information on Consequence Analysis Methods
Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for
Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs. New
York: AIChE, 1994.
Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for
Use of Vapor Cloud Dispersion Models. New York: AIChE, 1987.
Center for Process Safety of the American Institute of Chemical Engineers (AIChE). International
Conference and Workshop on Modeling and Mitigating the Consequences of Accidental
Releases of Hazardous Materials, September 26-29, ,1995. New York: AIChE, 1995.
Federal Emergency Management Agency, U.S. Department of Transportation, U.S. Environmental
'• Protection Agency. Handbook of Chemical Hazard Analysis Procedures. 1989.
Madsen, Warren W. and Robert C. Wagner. "An Accurate Methodology for Modeling, the
Characteristics of Explosion Effects." Process Safety Progress, 13 (July 1994), 171-175.
Mercx, W.P.M., D.M. Johnson, and J. Puttock. "Validation of Scaling Techniques for Experimental
Vapor Cloud Explosion Investigations." Process Safety Progress, 14 (April 1995), 120.
Mercx, W.P.M., R.M.M. van Wees, and G. Opschoor. "Current Research at TNO on Vapor Cloud
; Explosion Modelling." Process Safety Progress, 12 (October 1993), 222.
Prugh, Richard W: "Quantitative Evaluation of Fireball Hazards." Process Safety Progress, 13
(April 1994), 83-91.
Scheuermann, Klaus P. "Studies About the Influence of Turbulence on the Course of Explosions."
Process Safety Progress, 13 (October 1994), 219. ,
TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research.
Methods for the Calculation of the Physical Effects of the Escape of Dangerous Material
(Liquids and Gases). Voorburg, the Netherlands: TNO (Commissioned by Directorate-
General of Labour), 1980.
TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research.
Methods for the Determination of Possible Damage to People and Objects Resulting from
Releases of Hazardous Materials. Rijswijk, the Netherlands: TNO (Commissioned by
Directorate-General of Labour), 1992.
Touma, Jawad S., et al. "Performance Evaluation of Dense Gas Dispersion Models." Journal of
Applied Meteorology, 34 (March 1995), 603-615.
-------
-80-
U.S. Environmental Protection Agency, Federal Emergency Management Agency, U.S. Department
of Transportation. Technical Guidance for Hazards Analysis, Emergency Planning for
Extremely Hazardous Substances. December 1987.
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. Workbook of
Screening Techniques for Assessing Impacts of Toxic Air Pollutants. EPA-450/4-88-009.
September 1988.
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. Guidance on
the Application of Refined Dispersion Models for Hazardous/Toxic Air Release. EPA-454/R-
93-002. May 1993.
U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxic Substances.
Flammable Gases and Liquids and Their Hazards. EPA 744-R-94-002. February 1994.
-------
-81-
APPENDIX B
TOXIC SUBSTANCES
-------
-82-
B.l Data for Toxic Substances
The exhibits in this section of Appendix B provide the data needed to carry out the
calculations for regulated toxic substances using the methods presented in the text of this guidance.
Exhibit B-1 presents data for tpxic gases, Exhibit B-2 presents data for toxic gases, and Exhibit B-3
presents data for several toxic substances commonly found in water solution and for oleum.
-------
-83-
Exhibit B-l
Data for Toxic Gases
CAS Number
7664-41-7
778442-1
10294-34-5
7637-07-2
7782-50-5
10049-04-4
506-77-4
19287-45-7
75-21-8
7782-41-4
50-00-0
74-90-8
7647-01-0
7664-39-3
7783-07-5
7783-06-4
74-87-3
74-93-1
10102-43-9
Chemical Name
Ammonia (anhydrous)*
Arsine
Boron trichloride
Boron trifluoride
Chlorine
Chlorine dioxide
Cyanogen chloride
Diborane
Ethylene oxide
Fluorine
Formaldehyde (anhydrous)*
Hydrocyanic acid
Hydrogen chloride
(anhydrous)*
Hydrogen fluoride
(anhydrous)*
Hydrogen selenide
Hydrogen sulfide
Methyl chloride
Methyl mercaptan
Nitric oxide
Molecular
Weight
17.03
77.95
117.17
67.81
70.91
67.45
61.47
27.67
44.05
38.00
30.03
27.03
36.46
20.01
80.98
34.08
50.49
48.11
30.01
Ratio of
Specific
Heats
1.31
1.28
1.15
1.20
1.32
1.25
1.22
1.17
1.21
1.36
1.31
1.30
1.40
1.40
1.32
1.32
1.26
1.20
1.38
Toxic Endpoint
Level (mg/L)
0.14
0.0019
0.010
0.028
0.0087
0.0028
0.030
0.0011
0.090
0.0039
0.012
0.011
0.030
0.016
0.00066
0.042
0.82
0.049
0.031
Basis
ERPG-2
EHS-LOC (IDLH)
EHS-LOC (Tox">
EHS-LOC (IDLH)
ERPG-2
EHS-LOC equivalent
(IDLH)f
EHS-LOC equivalent
(Tox)*
ERPG-2
ERPG-2
EHS-LOC (IDLH)
ERPG-2
ERPG-2
ERPG-2
ERPG-2
EHS-LOC (IDLH)
ERPG-2
ERPG-2
ERPG-2
EHS-LOC (TLV#)
Liquid Factor
Boiling
(LFB)
0.073
0.23
0.22
0.25
0.19
0.15
0.14
0.13
0.12
0.35
0.10
0.079
0.15
0.066
0.21
0.13
0.14
0.12
0.21
Density
Factor
(Boiling)
0.71
0.30
0.36
0.31
0.31
0.30
0.41
1.13
0.55
0.32
0.59
0.72
0.41
0.51
0.25
0.51
0.48
0.55
0.38
Gas
Factor
(GF)
14
30
36
28. .
29
28
26
17
22
22
19
18
21
16
31
20
24
23
19
Reference
Table
(See Notes)
Buoyant
Dense
Dense
Dense
Dense
Dense
Dense
Buoyant
Dense
Dense
Dense
Buoyant
Dense
Buoyant
Dense
Dense
Dense
Dense
Dense
-------
-84-
Exhibit B-l (continued)
CAS Number
75-44-5
7803-51-2
7446-09-5
7783-60-0
Chemical Name
Phosgene
Phosphine
Sulfur dioxide (anhydrous)
Sulfur tetrafluoride
Molecular
Weight
98.92
34.00
64.07
108.06
Ratio of
Specific
Heats
1.17
1.29
1.26
1.30
Toxic Endpoint
Level (mg/L)
0.00081
0.0035
0.0078
0.0092
Basis
ERPG-2
ERPG-2
ERPG-2
EHS-LOC (Tox**)
Liquid Factor
Boiling
(LFB)
0.20
0.15
0.16
0.25
Density
Factor
(Boiling)
0.35
0.65
0.33
0.25
(at -73°C)
Gas
Factor
(GF)
33
20
27
36
Reference
Table
(See Notes)
Dense
Dense
Dense
Dense
Notes:
"Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense gases and
vapors. See Appendix D, Section D.4.3, for more information on the choice of reference tables.
* See Exhibit B-3 of this appendix for data on water solutions.
** LOC is based on the IDLH-equivalent level estimated from toxicity data.
t Not an EHS; LOC-equivalent value was estimated from one-tenth of the IDLH.
* Not an EHS; LOC-equivalent value was estimated from one-tenth of the IDLH-equivalent level estimated from toxicity data.
* LOC based on Threshold Limit Value (TLV) - Time-weighted average (TWA) developed by the American Conference of Governmental Industrial
Hygienists (ACGIH).
-------
-85-
Exhibit B-2
Data for Toxic Liquids
CAS
Number
107-02-8
107-13-1
814-68-6
107-18-6
107-11-9
7784-34-1
353-42-4
7726-95-6
75-15-0
67-66-3
542-88-1
107-30-2
4170-30-3
123-73-9
108-91-8
75-78-5
57-14-7
106-89-8
107-15-3
151-56-4
110-00-9
302-01-2
Chemical Name
Acrolein
Acrylonitrile
Acrylyl chloride
Allyl alcohol
Allylamine
Arsenous trichloride
Boron trifluoride compound
with methyl ether (1:1)
Bromine
Carbon disulfide
Chloroform
Chloromethyl ether
Chloromethyl methyl ether
Crotonaldehyde
Crotonaldehyde, (E)-
Cyclohexylamine
Dimethyldichlorosilane
1 , 1-Dimethylhydrazine
Epichlorohydrin
Ethylenediamine
Ethyleneimine
Furan
Hydrazine
Molecular
Weight
56.06
53.06
90.51
58.08
57.10
181.28
113.89
159.81
76.14
119.38
114.96
80.51
70.09
70.09
99.18
129.06
60.10
92.53
60.10
43.07
68.08
32.05
Vapor
Pressure
at 25° C
(mmHg)
274
108
110
26.1
242
10
11
212
359
196
29.4
199
30.8
30.8
10.1
141
157
16.5
12.2
211
600
14.4
Toxic Endpoint
Level
(mg/L)
0.0011
0.076
0.00090
0.036
0.0032
0.01
0.023
0.0065
0.16
0.49
0.00025
0.0018
0.029
0.029
0.16
0.026
0.012
0.076
0.49
0.018
0.0012
0.011
Basis
ERPG-2
ERPO-2
EHS-LOC (Tox1)
EHS-LOC (IDLH)
EHS-LOC (Tox1)
EHS-LOC (Toxf)
EHS-LOC (Tox*)
ERPG-2
ERPG-2
EHS-LOC (IDLH)
EHS-LOC (Toxf>
EHS-LOC (Toxf)
ERPG-2
ERPG-2
EHS-LOC (Toxf)
ERPG-2
EHS-LOC (IDLH)
ERPG-2
EHS-LOC (IDLH)
EHS-LOC (IDLH)
EHS-LOC (Tox1)
EHS-LOC (IDLH)
Liquid Factors
Ambient
(LFA)
0.047
0.018
0.026
0.0046
0.042
0.0037
0.0030
0.073
0.075
0.055
0.0080
0.043
0.0061
0.0061
0.0025
0.042
0.028
0.0039
0.0022
0.030
0.12
0.0017
Boiling
(LFB)
0.12
0.11
0.15
0.11
0.12
0.21
0.16
0.23
0.15
0.19
0.17
0.15
0.12
0.12
0.14
0.20
0.12
0.14
0.13
0.10
0.14
0.069
Density
Factor
(DF)
0.58
0.61
0.44
0.58
0.64
0.23
0.49
0.16
0.39
0.33
0.37
0.46
0.57
0.57
0.56
0.46
0.62
0.41
0.54
0.58
0.52
0.48
Liquid
Leak
Factor
(LLF)
40
39
54
41
36
100
48
150
60
71
63
51
41
41
41
51
38
56
43
40
45
48
Reference Table
(See Notes)
Worst
Case
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Buoyant*
Alternative
Case
Dense
Dense
Dense
Buoyant*
Dense
Buoyant*
Buoyant*
Dense
Dense
Dense
Dense
Dense
Buoyant*
Buoyant*
Buoyant*
Dense
Dense
Buoyant
Buoyant*
Dense
Dense
Buoyant*
-------
-86-
Exhibit B-2 (continued)
CAS
Number
13463-40-6
78-82-0
108-23-6
126-98-7
79-22-1 ,
60-34-4
624-83-9
556-64-9
75-79-6
13463-39-3
7697-37-2
79-21-0
594-42-3
10025-87-3
7719-12-2
110-89-4
107-12-0
109-61-5
75-55-8
75-56-9
7446-11-9
75-74-1
509-14-8
7550-45-0
Chemical Name
Iron, pentacarbonyl-
Isobutyronitrile
Isopropyl chloroformate
Methacrylonitrile
Methyl chloroformate
Methyl hydrazine
Methyl isocyanate
Methyl thiocyanate
Methyltrichlorosilane
Nickel carbonyl
Nitric acid (100%)**
Peracetic acid
Perchloromethylmercaptan
Phosphorus oxychloride
Phosphorus trichloride
Piperidine
Propionitrile
Propyl chloroformate
Propyleneimine
Propylene oxide
Sulfur trioxide
Tetramethyllead
Tetranitromethane
Titanium tetrachloride
Molecular
Weight
195.90
69.11
122.55
67.09
94.50
46.07
57.05
73.12
149.48
170.73
63.01
76.05
185.87
153.33
137.33
85.15
55.08
122.56
57.10
58.08
80.06
267.33
196.04
189.69
Vapor
Pressure
at25°C
(mmHg)
40
32.7
28
71.2
108
49.6
457
10
173
400
63.0
14.4
6
35.8
120
32.1
47.3
20.0
533
187
263
22.5
13
12.4
Toxic Endpoint
Level
(mg/L)
0.00044
0.14
0.10
0.0027
0.0019
0.0094
0.0012
0.085
0.018
0.00067
0.026
0.0045
0.0076
0.0030
0.028
0.022
0.0037
0.010
0.12
0.59
0.010
0.0040
0.0040
0.020
Basis
EHS-LOC (Toxf)
ERPG-2
EHS-LOC (Toxt)
EHS-LOC (TLV#)
EHS-LOC (Tox*)
EHS-LOC (IDLH)
ERPG-2
EHS-LOC (Tox1)
ERPG-2
EHS-LOC (Toxf)
EHS-LOC (IDLH)
EHS-LOC (Tox1)
EHS-LOC (IDLH)
EHS-LOC (Tox1)
EHS-LOC (IDLH)
EHS-LOC (Tox1)
EHS-LOC (Tox*)
EHS-LOC (Toxt
EHS-LOC (IDLH)
ERPG-2
ERPG-2
EHS-LOC (IDLH)
EHS-LOC (IDLH)
ERPG-2
Liquid Factors
Ambient
(LFA)
0.016
0.064
0.080
0.014
0.026
0.0074
0.079
0.0020
0.057
0.14
0.012
0.0030
0.0023
0.012
0.037
0.072
0.080
0.0058
0.032
0.093
0.057
0.011
0.051
0.0048
Boiling
(LFB)
0.24
0.12
0.17
0.12
0.16
0.094
0.13
0.11
0.22
0.26
0.12
0.12
0.20
0.20
0.20
0.13
0.10
0.17
0.12
0.13
0.15
0.29
0.22
0.21
Density
Factor
(DF)
0.33
• 0.63
0.45
0.61
0.40
0.56
0.52
0.45
0.38
0.37
0.32
0.42
0.29
0.29
0.31
0.57
0.63
0.45
0.61
0.59
0.26
0.24
0.30
0.28
Liquid
Leak
Factor
(LLF)
70
37
52
38
58
42
45
51
61
63
73
55
81
80
75
41
37
52
39
40
91
96
78
82
Reference Table
(See Notes)
Worst
Case
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Alternative
Case
Dense
Buoyant*
Dense
Dense
Dense
Buoyant
Dense
Buoyant*
Dense
Dense
Dense
Buoyant*
Buoyant*
Dense
Dense
Buoyant*
Buoyant*
Buoyant*
Dense
Dense
Dense
Dense
Buoyant*
Buoyant*
-------
-87-
Exhibit B-2 (continued)
LAo
Number
584-84-9
91-08-7
26471-62-5
75-77-4
108-05-4
Chemical Name
Toluene 2,4-diisocyanate
Toluene 2,6-diisocyanate
Toluene diisocyanate
(unspecified isomer)
Trimethylchlorosilane
Vinyl acetate monomer
Molecular
Weight
174.16
174.16
174.16
108.64
86.09
Vapor
Pressure
at 25° C
(nun Hg)
0.013
0.05
0.013
231
114
Toxic Endpoint
Level
(mg/L)
0.0070
0.0070
0.0070
0.050
0.26
Basis
EHS-LOC (IDLH)
EHS-LOC (IDLH*)
EHS-LOC
equivalent (IDLH+)
EHS-LOC (Tox1)
ERPG-2
Liquid Factors
Ambient
(LFA)
0.000005
0.000018
0,000005
0.061
0.026
Boiling
(LFB)
0.16
0.16
0.16
0.18
0.15
Density
Factor
(DF)
0.40
0.40
0.40
0.57
0.52
Liquid
Leak
Factor
(LLF)
59
59
59
41
45
Reference Table
(See Notes)
Worst
Case
Buoyant*
Buoyant*
Buoyant*
Dense
Dense
Alternative
Case
Buoyant*
Buoyant*
Buoyant*
Dense
Dense
Notes:
"Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense gases and vapors. See Appendix
D, Section D.4.3, for more information on the choice of reference tables.
•f;
Use dense gas table if substance is at an elevated temperature.
See Exhibit B-3 of this appendix for data on water solutions.
t LOG is based on IDLH-equivalent level estimated from toxicity data.
* LOG for this isomer is based on IDLH for toluene 2,4-diisocyanate.
+ Not an EHS; LOC-equivalent value is based on IDLH for toluene 2,4-diisocyanate.
LOG based on Threshold Limit Value (TLV) - Time-weighted average (TWA) developed by the American Conference of Governmental Industrial Hygienists
(ACGIH).
-------
Exhibit B-3
Data for Water Solutions of Toxic Substances and for Oleum
Average Vapor Pressure and Liquid Factors Over 10 Minutes for
Wind Speeds of 1.5 and 3.0 Meters per Second (mis)
CAS
Number
7664-41-7
50-00-0
7647-01-0
7664-39-3
7697-37-2
8014-95-7
Regulated
Substance
in Solution
Ammonia
Formaldehyde
Hydrochloric acid
Hydrofluoric acid
Nitric acid
Oleum - based on
sulfur trioxide (S03)
Molecular
Weight
17.03
30.027
36.46
20.01
63.01
80.06
(S03)
Toxic Endpoint
Level
(mg/L)
0.14
0.012
0.030
0.016
0.026
0.010
Basis
ERPG-2
ERPG-2
ERPG-2
ERPG-2
EHS-LOC
(IDLH)
ERPG-2
Initial
Concentration
(Wt%)
30
24
20
37
38
37
36
34
30
70
50
90
85
80
30 (SO3)
10-minute Average Vapor
Pressure (mm Hg)
Wind Speed
1.5 m/sec
332
241
290
1.5
78
67
56
38
13
124
16
25
17
10.2
3.5 (SO3)
Wind Speed
3.0 m/s
248
184
148
1.4
55
48
42
29
12
107
15
22
16
10
3.4 (S03)
Liquid Factor at 25° C
(LFA)
Wind Speed
1.5 m/sec
0.026
0.019
0.015
0.0002
0.010
0.0085
0.0072
0.0048
0.0016
0.011
0.0014
0.0046
0.0032
0.0019
0.0008
Wind Speed
3.0 m/s
0.019
0.014
0.011
0.0002
0.0070
0.0062
0.0053
0.0037
0.0015
0.010
0.0013
0.0040
0.0029
0.0018
0.0007
Density
Factor
(DF)
0.55
0.54
0.53
0.44
0.41
0.42
0.42
0.42
0.42
0.39
0.41
0.33
0.33
0.33
0.25
Reference Table
(See Notes)
Worst
Case
Buoyant
Buoyant
Buoyant
Buoyant
Dense
Dense
Dense
Dense
Buoyant
Buoyant
Buoyant
Dense
Dense
Dense
Buoyant
Alternative
Case
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Buoyant
Notes:
"Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense gases and vapors. See Appendix
D, Section D.4.3, for more information on the choice of reference tables.
-------
-89-
B.2. Mixtures Containing Toxic Liquids
In case of a spill of a liquid mixture containing a regulated toxic substance (with the exception
of common water solutions, discussed in Section 3.3 in the text), the area of the pool formed by the
entire liquid spill is determined as described in Section 3.2.2 or 3.2.3. For the area determination, if
the density of the mixture is unknown, the density of the regulated substance in the mixture may be
assumed as the density of the entire mixture.
If the partial vapor pressure of the regulated substance in the mixture is known, that vapor
pressure may be used to derive a release rate using the equations in Section 3.2. If the partial vapor
pressure of the regulated toxic substance in the mixture is unknown, it may be estimated from the
vapor pressure of the pure substance (listed in Exhibit B-2, Appendix B) and the concentration in the
mixture, if you assume the mixture is an ideal solution (an ideal solution is one in which there is
complete uniformity of cohesive forces). Use the following steps, based on Raoult's Law for ideal
solutions:
• Determine the mole fraction of the regulated substance in the mixture.
The mole fraction of the regulated substance in the mixture is the number of
moles of the regulated substance in the mixture divided by the total number of
moles of all substances in the mixture.
If the molar concentration (moles per liter) of each component of the mixture
is known, the mole fraction may be determined as follows:
xr =
OM)
or
x =
(B-2)
where: Xr
Mr
Vt
Mx
M
Mole fraction of the regulated substance in the mixture
(unitless)
Molar concentration of the regulated substance in the mixture
(moles per liter)
Total volume of mixture (liters)
Molar concentration of second component of the mixture
(moles per liter)
Molar concentration of any other components of the mixture
(moles per liter)
If the weight of each of the components of the mixture is known, the mole
fraction of the regulated substance in the mixture may be calculated as
follows:
-------
-90-
where: X
MWr =
MWX =
Wn -
MWn =
MW
W.
(B-3)
MWr) (MWxj (MWn)
Mole fraction of the regulated substance
Weight of the regulated substance
Molecular weight of the regulated substance
Weight of the second component of the mixture
Molecular weight of the second component of the mixture
Weight of any other component of the mixture
Molecular weight of any other component of the mixture
(Weights can be in any consistent units)
Estimate the partial vapor pressure of the regulated substance in the mixture as
follows:
VPm =
(B-4)
where: VPm =
m
X
Partial vapor pressure of the regulated substance in the
mixture (millimeters of mercury (mm Hg)) '
Mole fraction of the regulated substance (unitless)
Vapor pressure of the regulated substance in pure form at the
same temperature as the mixture (mm Hg) (vapor pressure at
25° C is given in Exhibit B-l, Appendix B)
The evaporation rate for the regulated substance in the mixture is determined as for pure
substances, with VPm as the vapor pressure. If the mixture contains more than one regulated toxic
substance, carry out the analysis individually for each of the regulated components. The release rate
equation is:
0.0035 x J7°-78 MW213 xAxVP
(B-5)
where: QR
U
MW
A
VP
T
Evaporation rate (pounds per minute)
Wind speed (meters per second)
Molecular weight (given in Exhibit B-2, Appendix B)
Surface area of pool formed by the entire quantity of the mixture (square feet)
(determined as described in 3.2.2)
Vapor pressure (mm Hg) (VPm from Equation B-4 above)
Temperature (Kelvin (K); temperature in ° C plus 273, or 298 for 25° C)
Worst-case consequence distances to the toxic endpoint may be estimated from the release rate
using the tables and instructions presented in Section 4.
-------
-91-
APPENDIX C
FLAMMABLE SUBSTANCES
-------
-92-
C.l Equation for Estimation of Distance to 1 psi Overpressure for Vapor Cloud Explosions
For a worst-case release of flammable gases and volatile flammable liquids, the release rate is
not considered. The total quantity of the flammable substance is assumed to form a vapor cloud.
The entire contents of the cloud is assumed to be within the flammability limits, and the cloud is
assumed to explode. For the worst-case, analysis, 10 percent of the flammable vapor in the cloud is
assumed to participate in the explosion (i.e., the yield factor is 0.10). Consequence distances to an
overpressure level of 1 pound per square inch (psi) may be determined using the following equation,
which is based on the TNT-equivalency method:
D = 17 x 0.1 x Wx
/3
(C-l)
where: D
Wf
HCf
HCTNT-
Distance to overpressure of 1 psi (meters)
Weight of flammable substance (kilograms or pounds/2.2)
Heat of combustion of flammable substance (kilojoules per kilogram) (listed in
Appendix C)
Heat of combustion of trinitrotoluene (TNT) (4,680 kilojoules per kilogram)
The factor 17 is a constant for damages associated with 1.0 psi overpressures. The factor 0.1
represents an explosion efficiency of 10 percent. To convert distances from meters to miles,
multiply by 0.00062.
C.2 Mixtures of Flammable Substances
For a mixture of flammable substances, you may estimate the heat of combustion of the
mixture from the heats of combustion of the components of the mixture using the equation below and
then use the equation given in the previous section of this appendix to determine the vapor cloud
explosion distance. The heat of combustion of the mixture may be estimated as follows:
HC =
m
— £
w
x HC + —L x HC
* w
(C-2)
where: HCm =
HCX =
Wy
HCy
Heat of combustion of mixture (kilojoules per kilogram)
Weight of component "X" in mixture (kilograms or pounds/2.2)'
Total weight of mixture (kilograms or pounds/2.2)
Heat of combustion of component "X" (kilojoules per kilogram)
Weight of component "Y" in mixture (kilograms or pounds/2.2)
Heat of combustion of component "Y" (kilojoules per kilogram)
Heats of combustion for regulated flammable substances are listed in Exhibit B-l in
Exhibit C-l in the next section (Section C.3) of this appendix.
-------
-93-
C.3 Data for Flammable Substances
The exhibits in this section of Appendix C provide the data needed to carry out the
calculations for regulated flammable substances using the methods presented in the text of this
guidance. Exhibit C-l presents heat of combustion data for all regulated flammable substances,
Exhibit C-2 presents additional data for flammable gases, and Exhibit C-3 presents additional data for
flammable liquids.
-------
-94-
Exhibit C-l
Heats of Combustion for Flammable Substances
CAS No.
75-07-0
74-86-2
598-73-2
106-99-0
106-97-8
25167-67-3
590-18-1
624-64-6
106-98-9
107-01-7
463-58-1
7791-21-1
590-21-6
557-98-2
460-19-5
75-19-4
4109-96-0
75-37-6
124-40-3
463-82-1
74-84-0
107-00-6
75-04-7
75-00-3
74-85-1
60-29-7
Chemical Name
Acetaldehyde
Acetylene [Ethyne]
Bromotrifluoroethylene [Ethene, bromotrifluoro-] -
1,3-Butadiene
Butane
Butene
2-Butene-cis
2-Butene-trans [2-Butene, (E)]
1 -Butene
2-Butene
Carbon oxysulfide [Carbon oxide sulfide (COS)]
Chlorine monoxide [Chlorine oxide]
1-Chloropropylene [1-Propene, 1-chloro-]
2-Chloropropylene [1-Propene, 2-chloro-]
Cyanogen [Ethanedinitrile]
Cyclopropane
Dichlorosilane [Silane, dichloro-]
Difluoroethane [Ethane, 1,1-difluoro-]
Dimethylamine [Methanamine, N-methyl-]
2,2-Dimethylpropane [Propane, 2,2-dimethyl-]
Ethane
Ethyl acetylene [1-Butyne]
Ethylamine [Ethanamine]
Ethyl chloride [Ethane, chloro-]
Ethylene [Ethene]
Ethyl ether [Ethane, l.l'-oxybis-]
Physical State
at 25° C
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Liquid
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Liquid
Heat of
Combustion
(kjoule/kg)
25,072
48,222
1,967
44,548
45,719
45,200*
45,171
45,069
45,292
45,100*
9,126
1,011*
23,000*
22,999
21,064
46,560
8,225
11,484
35,813
45,051
47,509
45,565
35,210
19,917
47,145
33,775
-------
-95-
Exhibit C-1 (continued)
CAS No. ..'
75-08-1
109-95-5
1333-74-0
75-28-5
78-78-4
78-79-5
', 75-31-0
75-29-6
74-82-8
74-89-5
; 563-45-1
563-46-2
: 115-10-6
107-31-3
115-11-7
, 504-60-9
109-66-0
109-67-1
646-04-8
627-20-3
463-49-0
74-98-6
115-07-1
74-99-7
7803-62-5
116-14-3
75-76-3
Chemical Name
•Ethyl mercaptan [Ethanethiol]
Ethyl nitrite [Nitrous acid, ethyl ester]
Hydrogen
Isobutane [Propane, 2-methyl] • '
Isopehtane [Butane, 2-methyl-]
Isoprene [1,3-Butadiene, 2-methyl-]
Isopropylamine [2-Propanamine]
Isopropyl chloride [Propane, 2-chloro-]
Methane
Methylamine [Methanamine]
3-Methyl-l-butene
2-Methyl-l-butene
Methyl ether [Methane, oxybis-]
Methyl formate [Formic acid, methyl ester]
2-Methylpropene [1-Propene, 2-methyl-]
1,3-Pentadiene
Pentane
1-Pentene .
2-Pentene, (E)- ;•'" •
2-Pentene, (Z)- : :' •
Propadiene [1,2-Propadiene] ' ' '
Propane '•'
Propylene [1-Propene]
Propyne [1-Propyne]
Silane
Tetrafluoroethylene [Ethene, tetrafluoro-]
Tetramethylsilane [Silane, tetramethyl-]
Physical State
at 25° C
Liquid
Gas
Gas
Gas
Liquid
Liquid
Liquid
Liquid
Gas
Gas
Gas
Liquid
Gas •
Liquid
Gas
Gas
Liquid
Liquid
Liquid
Liquid
Gas
Gas
Gas
Gas
Gas
Gas
Liquid
Heat of
Combustion
(kjoule/kg)
27,948
18,000
119,950
45,576
44,911
43,809
36,484
23,720
50,029
31,396
44,559
44,414
28,835
15,335
44,985
43,510*
44,697
44,625
44,458
44,520
46,332
46,333
45,762
46,165
44,307
1,280
41,712
-------
-96-
Exhibit C-l (continued)
CAS No.
10025-78-2
79-38-9
75-50-3
689-97-4
75-01-4
109-92-2
75-02-5
75-35-4
75-38-7
107-25-5
Chemical Name
Trichlorosilane [Silane, trichloro-]
Trifluorochloroethylene [Ethene, chlorotrifluoro-j
Trimethylamine [Methanamine, N,N-dimethyl-]
Vinyl acetylene [l-Buten-3-yne]
Vinyl chloride [Ethene, chloro-]
Vinyl ethyl ether [Ethene, ethoxy-]
Vinyl fluoride [Ethene, fluoro-]
Vinylidene chloride [Ethene, 1,1 -dichloro-]
Vinylidene fluoride [Ethene, 1,1-difluoro-]
Vinyl methyl ether' [Ethene, raethoxy-]
Physical State
at 25° C
Liquid
Gas
Gas
Gas
Gas
Liquid
Gas
Liquid
Gas
Gas
Heat of
Combustion
(kjoule/kg)
3,754
1,837
37,978
45,357
18,848
32,909
2,194
10,354
10,807
30,549
* Estimated heat of combustion
-------
-97-
Exhibit C-2
Data for Flammable Gases
CAS Number
75-07-0
74-86-2
598-73-2
106-99-0
106-97-8
25167-67-3
590-18-1
624-64-6
106-98-9
107-01-7
463-58-1
7791-21-1
557-98-2
460-19-5
75-194
4109-96-0
75-37-6
124-40-3
463-82-1
74-84-0
107-00-6
Chemical Name
Acetaldehyde
Acetylene
Bromotrifluoroethylene
1,3-Butadiene
Butane
Butene
2-Butene-cis
2-Butene-trans
1 -Butene
2-Butene
Carbon oxysulfide
Chlorine monoxide
2-Chloropropylene
Cyanogen
Cyclopropane
Dichlorosilane
Difluoroethane
Dimethylamine
2,2-Dimethylpropane
Ethane
Ethyl acetylene
Molecular
Weight
44.05
26.04
160.92
54.09
58.12
56.11
56.11
56.11
56.11
56.11
60.08
86.91
76.53
52.04
42.08
101.01
66.05
45.08
72.15
30.07
54.09
Ratio of
Specific
Heats
1.18
1.23
1.11
1.12
1.09
1.10
1.12
1.11
1.11
1.10
1.25
1.21
1.12
1.17
1.18
1.16
1.14
1.14
1.07
1.19
1.11
Flammability Limits (Vol %)
Lower
(LFL)
4.0
2.5
*
2.0
1.5
1.7
1.6
1.8
1.6
1.7
12.0
23.5
4.5
6.0
2.4
4.0
3.7
2.8
1.4
2.9
2.0
Upper (UFL)
60.0
80.0
37.0
11.5
9.0
9.5
9.7
9.7
9.3
9.7
29.0
NA
16.0
32.0
10.4
96.0
18.0
14.4
7.5
13.0
32.9
LFL (mg/L)
72
27
*
44
36
39
37
41
37
39
290
830
140
130
41
160
100
52
41
36
44
Gas Factor
(GF)
22
17
41*
. 24 .
25
24
24
24
24
24
26
31
29
24
22
33
27
22
27
18
24
Reference
Table
(See Notes)
Dense
Buoyant
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Pool Fire
Factor
(PFF)
2.7
4.8
0.42
5.5
5.9
5.6
5.6
5.6
5.7
5.6
1.3
0.15
3.3
2.5
5.4
1.3
1.6
3.7
6.4
5.4
5.4
Flash
Fraction
Factor
(FFF)*
0.018
0.23
0.15
0.15
0.15
0.14
0.11
0.12
0.17
0.12
0.29
NA
0.011
0.40
0.21
0.084
0.23
0.089
0.11
0.75
0.091
-------
-98-
Exhibit C-2 (continued)
CAS Number
75-04-7
75-00-3
74-85-1
109-95-5
1333-74-0
75-28-5
74-82-8 .
74-89-5
563-45-1
115-10-6
115-11-7
504-60-9
463-49-0
74-98-6
115-07-1
74-99-7
7803-62-5
116-14-3
79-38-9
75-50-3
689-97-4
75-01-4
Chemical Name
Ethylamine
Ethyl chloride
Ethylene
Ethyl nitrite
Hydrogen
Isobutane
Methane
Methylamine
3-Methyl-l-butene
Methyl ether
2-Methylpropene
1 ,3-Pentadiene
Propadiene
Propane
Propylene
Propyne
Silane
Tetrafluoroethylene
Trifluorochloroethylene
Trimethylamine
Vinyl acetylene
Vinyl chloride
Molecular
Weight
45.08
64.51
28.05
75.07
2.02
58.12
16.04
31.06
70.13
46.07
56.11
68.12
40.07
44.10
42.08
40.07
32.12
100.02
116.47
59.11
52.08
62.50
Ratio of
Specific
Heats
1.13
1.15
1.24
1.30
1.41
1.09
1.30
1.19
1.08
, ,1-15.
1.10
1.30
1.16
1.13
1.15
1.16
1.24
1.12
1.11
1.10
1.13
1.18
Flammabilily Limits (Vol %)
Lower
(LFL)
3.5
3.8
2.7
4.0
4.0
1.8
5.0 ••'
4.9
1.5
3.3
1.8
2.0
2.1
2.0
2.0
1.7
*
11.0
8.4
;' 2.0 '
2.2
3.6
Upper (UFL)
14.0
15.4
36.0
50.0
75.0
8.4
15.0
20.7
9.1
27.3
8.8
NA
2.1
9.5
11.0
39.9
*
60.0
38.7
11.6
31.7
33.0
LFL (mg/L)
64
100
31
120
3.3
43
33
62
43
64
41
56
34
36
34
28
*
450
400
48
47
92
Gas Factor
(GF)
22
27
18
30
5.0
25
14
19
26
22
24
28
21
22
21
21
19"
33
35
25
24
26
Reference
Table
(See Notes)
Dense
Dense
Buoyant
Dense
**
Dense
Buoyant
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Pool Fire
Factor
(PFF)
3.6
2.6
5.4
2.0
t
6.0
5.6
2.7
6.0
3.4
5.7
NA
5.2
5.7 :
5.5
4.9
5.7
: 0.25
0.34
4.8
5.4
2.4
Flash
Fraction
Factor
(FFF)*
0.040
0.053
0.63
NA
NA
0.23
0.87
0.12
0.030
0.22
0.18
NA
0.20
0.38
0.35
0.18
0.41
0.55
0.27
0.12
0.086
0.14
-------
-99-
Exhibit C-2 (continued)
CAS Number
75-02-5
75-38-7
107-25-5
Chemical Name
Vinyl fluoride
Vinylidene fluoride
Vinyl methyl ether
Molecular
Weight
46.04
64.04
58.08
Ratio of
Specific
Heats
1.20
1.16
1.12
Flammability Limits (Vol %)
Lower
(LFL)
2.6
5.5
2.6
Upper (UFL)
21.7
21.3
39.0
LFL (mg/L)
49
140
62
Gas Factor
(GF)
23
27
25
Reference
Table
(See Notes)
Dense
Dense
Dense
Pool Fire
Factor
(PFF)
0.28
1.8
3.7
Flash
Fraction
Factor
(FFF)*
0.41
0.50
0.093
Notes
"Buoyant" in the Reference Table column refers to the tables for neutrally-buoyant gases and vapors; "Dense" refers to the tables for dense gases and vapors. See Appendix
D, Section D.4.3, for more information on the choice of reference tables. '
NA: Data not available
Reported to be spontaneously combustible; estimation of dispersion distance to LFL not appropriate.
Much lighter than air; table of distances for neutrally buoyant gases not appropriate.
t Pool fire unlikely.
Calculated at 298 K (25° C) with the following exceptions:
Acetylene factor at 250 K as reported in TNO, Methods for the Calculation of the Physical Effects of the Escape of Dangerous Material (1980).
Ethylene factor calculated at critical temperature, 282 K.
Methane factor calculated at critical temperature, 191 K.
Silane factor calculated at critical temperature, 270 K.
*
-------
-100-
Exhibit C-3
Data for Flammable Liquids
CAS Number
590-21-6
60-29-7
75-08-1
78-78-4
78-79-5
75-31-0
75-29-6
563-46-2
107-31-3
109-66-0
109-67-1
646-04-8
627-20-3
75-76-3
10025-78-2
109-92-2
75-35-4
Chemical Name
1-Chloropropylene
Ethyl ether
Ethyl mercaptan
Isopentane
Isoprene
Isopropylamine
Isopropyl chloride
2-Methyl-l-butene
Methyl formate
Pentane
1-Pentene
2-Pentene, (E)-
2-Pentene, (Z)-
Tetramethylsilane
Trichlorosilane
Vinyl ethyl ether
Vinylidene chloride
Molecular
Weight
76.53
74.12
62.14
72.15
68.12
59.11
78.54
70.13
60.05
72.15
70.13
70.13
70.13
88.23
135.45
72.11
96.94
Flammabffily Limit (Vol%)
Lower
(LFL)
4.5
1.9
2.8
1.4
2.0
2.0
2.8
1.4
5.9
1.3
1.5
1.4
1.4
1.5
1.2
1.7
7.3
Upper
(UFL)
16.0
48.0
18.0
7.6
9.0
10.4
10.7
9.6
20.0
8.0
8.7
10.6
10.6
NA
90.5
28.0
NA
LFL
(mg/L)
140
57
71
41
56
48
90
40
140
38
43
40
40
54
66
50
290
Liquid Factors
Ambient
(LFA)
0.17
0.11
0.10
0.14
0.11
0.10
0.11
0.12
0.10
0.10
0.13
0.10
0.10
0.17
0.18
0.10
0.15
Boiling
(LFB)
0.15
0.15
0.13
0.15
0.14
0.13
0.16
0.15
0.13
0.15
0.15
0.15
0.15
0.17
0.23
0.15
0.18
Density
Factor
0.52
0.69
0.58
0.79
0.72
0.71
0.57
0.75
0.50
0.78
0.77
0.76
0.75
0.59
0.37
0.65
0.44
Liquid Leak
Factor
(LLF)
45
34
40
30
32
33
41
31
46
30
31
31
31
40
64
36
54
Reference
Table
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Dense
Pool Fire
Factor
(PFF)
3.2
4.3
3.3
6.1
5.5
4.1
3.1
5.8
1.8
5.8
5.8
5.6
5.6
6.3
0.68
4.2
1.6
NA: Data not available
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APPENDIX D
TECHNICAL BACKGROUND
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D.l Worst-Case Release Rate for Gases
D.I.I Unmitigated Release
The assumption that the total quantity of gas is released in 10 minutes is the same assumption
used in EPA's Technical Guidance for Hazards Analysis (1987).
D.I.2 Gaseous Release Inside Building
The mitigation factor for gaseous release inside a building is based on a document entitled
"Risk Mitigation in Land Use Planning: Indoor Releases of Toxic Gases" by S.R. Porter. This paper
presented three release scenarios and discussed the mitigating effects that would occur in a building
with a volume of 1,000 cubic meters at three different building air exchange rates. There is a
concern that a building may not be able to withstand the pressures of a very large release. However,
this paper indicated that release rates of at least 2,000 pounds per minute could be withstood by a
building.
Analyzing the data in this paper several ways, the value of 55 percent emerged as
representing the mitigation that could occur for a release scenario into a building. Data are provided
on the maximum release rate in a building and the maximum release rate from a building. Making
this direct comparison at the lower maximum release rate (3.36 kg/s) gave a release rate from the
building of 55 percent of the release rate into the building. Using information provided on another
maximum release rate (10.9 kg/min) and accounting for the time for the release to accumulate in the
building, approximately 55 percent emerged again.
The choice of building ventilation rates affects the results. The paper presented mitigation for
three different ventilation rates, 0.5, 3, and 10 air changes per hour. A ventilation rate of 0.5
changes per hour is typical for buildings designed to house toxic gases; therefore, EPA decided that
this ventilation rate was appropriate for this analysis. A release factor of 55 percent serves as a
conservative value to use in the event of a gaseous release which does not destroy the building into
which it is released.
D.2 Worst-Case Release Rate for Liquids
D.2.1 Evaporation Rate Equation
The equation for estimating the evaporation rate of a liquid from a pool is from the Technical
Guidance for Hazards Analysis, Appendix G. The same assumptions are made for determination of
maximum pool area (i.e., the pool is assumed to be 1 centimeter (0.033 feet) deep). The
evaporation rate equation has been modified to include a different mass transfer coefficient for water,
the reference compound. For this document, a value of 0.67 centimeters per second is used as the
mass transfer coefficient, instead of the value of 0.24 cited in the Technical Guidance for Hazards
Analysis. The value of 0.67 is based on Donald MacKay and Ronald S. Matsugu, "Evaporation Rates
of Liquid Hydrocarbon Spills on Land and Water," Canadian Journal of Chemical Engineering,
August 1973, p. 434. The evaporation equation becomes:
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QR =
0.284 x U°'78 x MW3 xAxVP
82.05 x T
(D-l)
where: QR
U
MW
A
VP
T
Evaporation rate (pounds per minute)
Wind speed (meters per second)
Molecular weight (given in Exhibit B-2, Appendix B)
Surface area of pool formed by the entire quantity of the mixture (square feet)
(determined as described in 3.2.2)
Vapor pressure (mm Hg) (VPm from Equation B-4 above)
Temperature (Kelvin (K); temperature in ° C plus 273, or 298 for 25° C)
D.2.2 Factors for Evaporation Rate Estimates
Liquid Factors. The liquid factors, Liquid Factor Ambient (LFA) and Liquid Factor Boiling
(LFB) used to estimate the evaporation rate from a liquid pool (see Section 3.2 of this guidance
document), are derived as described in the Technical Guidance for Hazards Analysis, Appendix G,
with the following differences:
• The mass transfer coefficient of water is assumed to be 0.67, as discussed above; the
value of the factor that includes conversion factors, the mass transfer coefficient for
water, and the molecular weight of water to the one-third power, given as 0.106 in
the Technical Guidance is 0.284 in this guidance.
• Density of all substances was assumed to be the density of water in the Technical
Guidance; the density was included in the liquid factors. For this guidance document,
density is not included in the LFA and LFB values presented in the tables; instead, a
separate Density Factor (DF) (discussed below) is provided to be used in the
evaporation rate estimation.
With these modifications, the LFA is:
LFA =
0.284 x MW3 x VP
82.05 x 298
(D-2)
where: MW = Molecular weight
VP = Vapor pressure at ambient temperature in millimeters of mercury
298 K (25° C) = Ambient temperature
LFB is:
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LFB =
0.284 x MW3 x 760
82.05 x BP
(D-3)
where: MW = Molecular weight
760 = Vapor pressure at boiling temperature (millimeters of mercury (mm Hg))
BP = Boiling point (K)
Density Factor. Because some of the regulated liquids have densities very different from that
of water, the density of each substance was used to develop a Density Factor (DF) for the
determination of maximum pool area for the evaporation rate estimation. The density factor is:
DF =
1
d x 0.033
(D-4)
where: DF = Density factor (l/(lbs/ft2)
d = Density of the substance in pounds per cubic foot
0.033 = Depth of pool for maximum area (feet)
D.2.3 Common Water Solutions
Water solutions of regulated toxic substances must be analyzed somewhat differently from
pure toxic liquids. Except for solutions of relatively low concentration, the evaporation rate varies
with the concentration of the solution. At one specific concentration, the composition of the liquid
does not change as evaporation occurs. For concentrated solutions of volatile substances, the
evaporation rate from a pool may decrease, very rapidly in some cases, as the toxic substance
volatilizes and its concentration in the pool decreases. Using a the ALOHA model with an additional
feature (not available in the public version), changes in the release rate could be incorporated and the
effects of these changes on the consequence distance analyzed. The distance results obtained using
this model for various solutions were compared with the results from various time averages to
examine the sensitivity of the results. An averaging time of 10 minutes was found to give reasonable
agreement with the step-function model for most substances at various concentrations.
NOAA developed a computerized calculation method to estimate partial vapor pressures and
release rates for regulated toxic substance in solution as a function of concentration, based on vapor
pressure data from Perry's Engineers' Handbook and other sources. -Using this method, EPA
estimated partial vapor pressures and evaporation rates at one-minute intervals over 10 minutes for
solutions of various concentrations. The 10-minute time period was chosen based on the ALOHA
results. For each one-minute interval, EPA estimated the concentration of the solution based on the
quantity evaporated in the previous interval, and estimated the partial vapor pressure based on the
concentration. These estimated vapor pressures were used to calculate an average vapor pressure
over the 10-minute period; this average vapor pressure was used to derive Liquid Factor Ambient
(LFA) values, as described above for liquids. Use of these factors is intended to give an evaporation
rate that accounts for the decrease in evaporation rate expected to take place as the solution
evaporates.
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Density Factors (DF) were developed for solutions of various concentrations from data in
Perry's Engineers' Handbook and other sources, as discussed above for liquids.
Because solutions do not have defined boiling points, EPA did not develop Liquid Factor
Boiling (LFB) values for solutions. As a simple and conservative approach, the quantity of a
regulated substance in a solution at an elevated temperatures is treated as a pure substance. This
approach will likely give an overestimate of the consequence distance.
D.2.4 Releases Inside Buildings
If a toxic liquid is released inside a building, its release to the outside air will be mitigated in
two ways'. First, the evaporation rate of the liquid may be much lower inside a building than outside.
This is due to wind speed, which directly affects the evaporation rate. The second mitigating factor is
that the building provides resistance to discharge of contaminated air to the outdoors.
In this method, a conservative wind speed, U, of 0.1 m/s was assumed in the building. (See
end of text for a justification of this wind speed.) For a release outdoors in a worst-case scenario, U
is set to 1.5 m/s, and for an alternative scenario, U is set to 3 m/s. The evaporation rate equation is:
QR =
x (LFA, LFB) x A
(D-5)
where: QR = Release rate (pounds per minute)
U = Wind speed (meters per second)
LFA = Liquid Factor Ambient
LFB = Liquid Factor Boiling
A = Area of pool (square feet).
As can be seen, if U inside a building is only 0.1, then the evaporation rate inside a building will be
much lower than a corresponding evaporation rate outside (assuming the temperature is the same).
The rate will only be (0.1/1.5)0-78, about 12 percent of the rate for a worst case, and (0. l/3)°-78,
about seven percent of the rate for an alternative case.
The evaporated liquid mixes with and contaminates the air in the building. What EPA is
ultimately interested in is the rate at which this contaminated air exits the building. 'In order to
calculate the release of contaminated air outside the building, EPA adapted a method from an UK
Health and Safety Executive paper entitled, Risk Mitigation in Land Use Planning: Indoor Releases of
Toxic Gases, by S.R. Porter. EPA assumed that the time for complete evaporation of the liquid pool
was one hour. The rate at which contaminated air was released from the building during liquid
evaporation (based on the paper) was assumed to be equal to the evaporation rate plus the building
ventilation rate (no pressure buildup in building). The building ventilation rate was set equal to 0.5
air changes per hour, which is a typical ventilation rate for a building used to store toxic liquids and
gases. EPA used a typical storage building with a volume of 1000 m3 and a floor area of 200 m2
(2152 ft2), and assumed that the liquid pool would cover the entire building floor, representing a
conservative scenario.
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To provide a conservative estimate, EPA calculated the evaporation rate for a spill of a
volatile liquid, carbon disulfide, under ambient conditions inside the building:
QR = O.I0-78 x 0.075 x 2152 = 26.8 Ibs/min.
Next, this evaporation rate was converted to m3/min using the ideal gas law:
26.8 Ibs/min x 454 g/lb x 1 mol CS2/76.1 g x 0.0224 m3/mol = 3.58 m3/min.
The ventilation rate of the building is 0.5 changes per hour, which equals 500 m3 per hour, or
8.33 m3/min. Therefore, during evaporation, contaminated air is leaving the building at a rate of
8.33 + 3.58, or 11.9 m3/min.
EPA used an iterative calculation for carbon disulfide leaving a building using the above
calculated parameters. During the first minute of evaporation, 26.8 Ibs of pure carbon disulfide
evaporates, and EPA assumed this evenly disperses through the building so that the concentration of
CS2 in the building air is 0.0268 lbs/m3 (assuming 1000 m3 volume in the building). Contaminated
air is exiting the building at a rate of 11.9 m3/min, so EPA deduced that 11.9 x 0.0268 = 0.319 Ibs
of carbon disulfide exit the building in the first minute, leaving 26.5 Ibs still evenly dispersed inside.
Since this release occurs over one minute, the release rate of the carbon disulfide to the outside is
0.319 Ibs/min. During the second minute, another 26.8 Ibs of pure carbon disulfide evaporates and
disperses, so that the building now contains 26.8 + 26.5 = 53.3 Ibs of carbon disulfide, or 0.0533
lbs/m3. Contaminated air is still exiting the building at a rate of 11.9 m3/min, so 11.9 x 0.05328 =
0.634 Ibs of carbon disulfide are released, leaving 52.6 Ibs inside. Again, this release occurs over
one minute so that the rate of carbon disulfide exiting the building in terms of contaminated air is
0.634 Ibs/min. EPA continued to perform this estimation over a period of one hour. The rate of
release of carbon disulfide exiting the building in the contaminated air at the sixty minute mark is
13.7 Ibs/min. This represents the maximum rate of carbon disulfide leaving the building. After all of
the carbon disulfide is evaporated, there is a drop in the concentration of carbon disulfide in the
contaminated air leaving the building because the evaporation of carbon disulfide no longer
contributes to the overall contamination of the air.
Note that if the same size pool of carbon disulfide formed outside, the release rate for a worst
case scenario would be:
QR = 1.5°-78 x 0.075 x 2152 = 221 Ibs/min.
and for an alternative case:
QR = 30.78 x 0 075 x 2152 = 380 Ibs/min.
The maximum release rate of carbon disulfide in the contaminated building air, assuming a
1,000 m3 building with a building exchange rate of 0.5 air changes per hour, was only about 6
percent (13.7-^-221 Ibs/min x 100) of the worst case scenario rate, and only about 3.6 percent
(13.7-=-380 Ibs/min x 100) of the alternative scenario rate. EPA set an overall building mitigation
factor equal to 10 percent and five percent, respectively, in order to be conservative. Please note that
(at a constant ventilation rate of 0.5 changes per hour) as the size of the building increases, the
maximum rate of contaminated air leaving the building will decrease, although only slightly due to the
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balancing effect of building volume and ventilation rate. Obviously, a higher ventilation rate will
yield a higher maximum release rate of contaminated air from the building, but most buildings used to
store a toxic chemical should have ventilation rates close to 0.5 changes per hour.
For a release inside a building, EPA assumed a building air velocity of 0.1 m/s. This
conservative value was derived by setting the size of the ventilation fan equal to 1.0 m2. This fan is
exchanging air from the building with the outside at a rate of 0.5 changes per hour. For a 1000 m3
building, this value becomes 500 m3/hour, or 0.14 m3/s. Dividing 0.14 m3/s by the area of the fan
yields a velocity of 0.14 m/s, which was rounded down to 0.1 m/s.
D.3 Toxic Endpoints
The toxic endpoints found in Appendix B, Exhibits B-l, B-2, and B-3, were chosen as
follows, in order of preference:
(1) Emergency Response Planning Guideline 2 (ERPG-2), developed by the American
Industrial Hygiene Association, if available;
(2) Level of Concern (LOG) derived for extremely hazardous substances (EHSs) regulated
under section 302 of the Emergency Planning and Community Right-to-Know Act
(EPCRA) (see the Technical Guidance for Hazards Analysis for more information on
LOCs); the LOG for EHSs is based on:
One-tenth of the Immediately Dangerous to Life and Health .(IDLH) level,
developed by the National Institute of Occupational Safety and Health
(NIOSH), using IDLH values developed before 1994,
or, if no IDLH value is available,
One-tenth of an estimated IDLH derived from toxicity data; the IDLH is
estimated as described in Appendix D of the Technical Guidance for Hazards
Analysis.
ERPG-2 is defined as the maximum airborne concentration below which it is believed nearly
all individuals could be exposed for up to one hour without experiencing or developing irreversible or
other serious health effects or symptoms that could impair an individual's ability to take protective
action.
IDLH is defined in the NIOSH Pocket Guide to Chemical Hazards (1994) as a condition that
poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or
immediate or delayed adverse health effects or prevent escape from such an environment. The IDLHs
are intended to ensure that workers can escape from a given contaminated environment in the event of
failure of the respiratory protection equipment.
The estimated IDLH is derived from animal toxicity data, in order of preferred data, as
follows:
• From median lethal concentration (LC50) (inhalation): 0.1 x LC50
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• From lowest lethal concentration (LCLO) (inhalation): 1 x LCLO
• From median lethal dose (LD50) (oral): 0.01 x LD50
• From lowest lethal dose (LDLO) (oral): 0.1xLDLO
The toxic endpoints based on LOCs for EHSs presented in the tables in Appendix B are, in
some cases, different from the LOCs listed in the Technical Guidance for Hazards Analysis, because
some of the LOCs were updated based on IDLHs that were published after the development of the
LOCs (and before 1994) or on new or revised toxicity data.
D.4 Reference Tables for Distances to Toxic and Flammable Endpoints
D.4.1 Neutrally Buoyant Gases
Toxic Substances. Reference tables for distances to toxic endpoints for neutrally buoyant
gases and vapors were derived from the Gaussian model using the longitudinal dispersion coefficients
based on work by Beals (Guide to Local Diffusion of Air Pollutants. Technical Report 214. Scott Air
Force Base, Illinois: U.S. Air Force, Air Weather Service, 1971). The reasons for using the Beals
dispersion coefficients are discussed below.
Longitudinal dispersion (dispersion in the along-wind direction) is generated mostly by
vertical wind shear. Wind shear results from the tendency of the wind speed to assume a wind
profile—the speed is lowest next to the ground and increases with height until it reaches an asymptotic
value at approximately a few hundred feet above the surface. To account for shear-driven dispersion,
any air dispersion model intended for modeling short-duration releases must include either (a) a
formulation .that accounts, either implicitly or explicitly, for the height-dependence of wind speed or
(b) some type of parameterization that converts shear effect into ax, the standard deviation function in
the along-wind direction.
Because the standard Gaussian formula does not incorporate crx (it includes only ay and az, the
crosswind and horizontal functions), very few alternate ways to formulate crx have been proposed.
The simplest method was proposed by Turner (Workbook of Atmospheric Dispersion Estimates.
Report PB-191 482. Research Triangle Park, North Carolina: Office of Air Programs, U.S.
Environmental Protection Agency. 1970), who suggested simply setting ax equal to cy Textbooks
such as that by Pasquill and Smith (Atmospheric Diffusion. 3rd ed. New York: Halstead Press. 1983)
describe a well-known analytic model. However, this model is more complex than a Gaussian model
because according to it, dispersion depends on wind shear and the vertical variation of the vertical
diffusion coefficient. Wilson (Along-wind Diffusion of Source Transients, Atmospheric Environment
15:489-495. 1981) proposed another method in which CTX is determined as a function of wind shear,
but in a form that can then be used in a Gaussian model. However, it is now believed that Wilson's
formulation gives
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Averaging time is the time interval over which the instantaneous concentration of the ,
hazardous material in the vapor cloud is averaged to assess the health effects of the exposure.
Averaging time should generally be equal to or shorter than either the release duration or cloud
duration and if possible, should reflect the exposure time associated with the toxic exposure guideline
of interest. In this regulation, the exposure time associated with the toxic endpoints include 30
minutes for the Immediately Dangerous to Life and Health (IDLH) level and 60 minutes for the
Emergency Response Planning Guideline (ERPG). For the neutrally buoyant tables, the 10-minute
release scenario was modeled using a 10-minute averaging time. The 60-mihute release scenario was
modeled using a 30-minute averaging time to be consistent with the 30-minute exposure time
associated with the IDLH. A 60-minute averaging time may have underpredicted consequence
distances.
Cloud dispersion from a release of finite duration (10 and 60-minute releases) is calculated
using an equation specified in the NOAA publication ALOHA™ 5.6 Theoretical Description,
Technical Memorandum NOS ORCA 65, August 1992.
Flammable Substances. The reference tables of distances for neutrally buoyant flammable
substances were derived using the same model as for toxic substances, as described above. The
endpoint for modeling was the lower flammability limit (LFL). For flammable substances, an
averaging time of 0.1 minute (six seconds) was used, because fires are considered to be nearly
instantaneous events.
Distances of interest for flammable substances are generally much shorter than for toxic
substance, because the LFL concentrations are much larger than the toxic endpoints. For the short
distances found in modeling the flammable substances, modeling results were found to be the same
for 10-minute and 30-minute releases; therefore, one table of distances for rural conditions and one
table for urban conditions, applicable for both 10-minute and 30-minute releases, were developed for
flammable substances.
D.4.2 Dense Gases
Toxic Substances. The reference tables for dense gases were developed using the widely
accepted SLAB model, developed by Lawrence Livermore National Laboratory. SLAB solves
conservation equations of mass, momentum, energy, and species for continuous, finite duration, and
instantaneous releases. The reference tables were based on the evaporating pool algorithm and on
releases of hydrogen chloride (HCI). A SLAB modeling analysis of releases of dense CAA gases or
vapors with different molecular weights revealed that releases of HCI generally provided conservative
results under a variety of stability/wind speed combinations, release rates, and toxic endpoints.
Similar to the modeling of neutrally buoyant plumes, the 10-minute release scenario of toxic
chemicals was modeled using a 10-minute averaging time. The 60-minute release scenario was
modeled using a 30-minute averaging time to be consistent with the 30 minute exposure time
associated with the IDLH.
For all dense gas tables, the reference height for the wind speed was 10 meters. Relative
humidity was assumed to be 50 percent, and the ambient temperature was 25 °C. The source area
was the smallest value that still enabled the model to run for all release rates. The surface roughness
factor was one meter for urban scenarios and three centimeters for rural scenarios.
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Flammable Substances. The reference tables for dispersion of dense flammable gases, the
same model was used as for toxic substances, as described above, and the same assumptions were
made. For the dispersion of flammable chemicals, averaging time should be very small (i.e., no
more than a few seconds) since flammable vapors need only be exposed to an ignition source for a
short period of time to initiate the combustion process. Thus, both the 10-minute and 60-minute
reference tables for flammable substances use an averaging time of 10 seconds. The 10-minute and
60-minute tables were combined for flammable substances because the modeling results were found to
be the same.
D.4.3 Choice of Reference Table for Liquids and Solutions
The methodology presented in this guidance for consequence analysis for liquids and solutions
assumes evaporation from a pool. All of the toxic liquids regulated under CAA section 112(r) have
molecular weights greater than the molecular weight of air; therefore, their vapor would be heavier
than air. However, because the vapor from a pool will mix with air as it evaporates, the initial
density of the vapor with respect to air may not in all cases indicate whether the vapor released from
a pool should be modeled as a dense gas or a neutrally buoyant gas. If the rate of release from the
pool is relatively low, the vapor-air mixture that is generated may be neutrally buoyant even if the
vapor is denser than air. ,
To identify substances with molecular weight greater than air that might behave as neutrally
buoyant gases when evaporating from a pool, EPA used the ALOHA model for pool evaporation of a.
number of substances with a range of molecular weights and vapor pressures. Modeling was carried
out for F stability and wind speed 1.0 meter per second and for D stability and wind speed 3.0 meters
per second. Pool spread to a depth of one centimeter was assumed. EPA noted the molecular
weights and vapor pressures in cases where ALOHA used the model for neutrally buoyant gases. The
molecular weight-vapor pressure combinations at which ALOHA used the neutrally buoyant gas
model for the two stability and wind speed combinations were used to develop the reference table
choices given in Exhibit B-2 (for liquids) and B-3 (for solutions) in Appendix B. The neutrally
buoyant tables are to be used at ambient conditions when indicated, for the liquids; at elevated
temperatures, evaporation rates will be greater, and the dense gas tables should be used. When use of
the neutrally buoyant tables is indicated, these tables should generally give reasonable results for pool
evaporation under ambient conditions; however, the reference table choices shown in Exhibit B-2 are
not intended to predict the behavior of the substances when evaporating under all conditions. The
analysis did not take into account all factors (e.g., pool size) that may affect the degree of mixing of
the vapor with air.
D.5 Worst-Case Consequence Analysis for Flammable Substances
The equation used for the vapor cloud explosion analysis for the worst case involving
flammable substances is given in Appendix C. This equation is based on the TNT-equivalency
method of the UK Health and Safety Executive, as presented in the publication of the Center for
Chemical Process Safety of the American Institute of Chemical Engineers (AIChE), Guidelines for
Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs (1994). The
assumption was made for the worst case that the total quantity of the released substance is in the
flammable part of the cloud. The AIChE document lists this assumption as one of a number that have
been used for vapor cloud explosion blast prediction; it was chosen as a conservative assumption for
the worst-case analysis. The yield factor of 10 percent was a conservative worst-case assumption,
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based on information presented in the AIChE document. According to the AIChE document, reported
values for TNT equivalency for vapor cloud explosions range from a fraction of one percent to tens
of percent; for most major vapor cloud explosions, the range is one to ten percent.
The endpoint for the vapor cloud explosion analysis, 1 psi, is reported to cause damage such
as shattering of glass windows and partial demolition of houses. Skin laceration from flying glass
also is reported. This endpoint was chosen for the consequence analysis because of the potential for
serious injuries to people from the property damage that might result from an explosion.
The TNT equivalent model was chosen as the basis for the consequence analysis because of
its simplicity and wide use. This model does not take into account site-specific factors and many
chemical-specific factors that may affect the results of a vapor cloud explosion. Other methods are
available for vapor cloud explosion modeling; see the list of references in Appendix A for some
publications that include information on other vapor cloud explosion modeling methods.
D.6 Alternative Scenario Analysis for Toxic Gases
The equation for estimating release rate of a gas from a hole in a tank is based on the
equations for gas discharge rate presented in the Handbook of Chemical Hazard Analysis Procedures
by the Federal Emergency Management Agency (FEMA), DOT, and EPA, and equations in EPA's
Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants. The equation for an
instantaneous discharge under non-choked flow conditions is:
m =
0>-6)
where: m = Discharge rate, kg/s ',
Cd =. Discharge coefficient
Ah = Opening area, m2 :
7 — Ratio of specific heats
p0 = Tank pressure, Pascals
Pl = Ambient pressure, Pascals
P0 = Density, kg/m?
Under choked flow conditions (maximum flow rate), the equation becomes:
m =
(D-7)
For development of the equation and gas factors presented in this guidance, density (p) was
rewritten as a function of pressure and molecular weight, based on the ideal gas law:
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p =
-112-
POMW
RT.
(D-8)
where: MW = Molecular weight (kilograms per kilomole)
R = Gas constant (8314 Joules per degree-kilomole)
Tt = Tank temperature (K)
The choked flow equation can be rewritten:
m = C
MW
8314
(D-9)
To derive the equation presented in the guidance, all the chemical-specific properties,
constants, and appropriate conversion factors were combined into the "Gas Factor" (GF). The
discharge coefficient was assumed to have a value of 0.8, based on the screening value recommended
in EPA's Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants. The GF
was derived as follows:
GF = 132.2 x 0.6895 x 104 x 6.4516 x 10'4 x 0.8
(D-10)
where: 132.2 = Conversion factor for kg/s to Ibs/min
0.6895 x 104 = Conversion factor for Pascals to psi
6.4516 x 10"4 = Conversion factor for square meters to square inches
GF values were calculated for all gases regulated under CAA section 112(r) and are listed in
Appendix B, Exhibit B-l, for toxic gases and Appendix C, Exhibit C-2, for flammable gases.
From the equation for choked flow above and the equation for the GF above, the initial
release rate for a gas from a hole in a tank can be written as:
Qr = HA x Pt x — x GF
(D-ll)
where: QR = Release rate (pounds per minute)
HA = Hole area (square inches)
Pt = Tank pressure (psia)
Tt = Tank temperature (K)
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D.7 Alternative Scenario Analysis for Toxic Liquids
\
D.7.1 Releases from Holes in Tanks
The equation for estimating release rate of a liquid from a hole in a tank is based on the
equations for liquid release rate presented in the Handbook of Chemical Hazard Analysis Procedures
by FEMA, DOT, and EPA and EPA's Workbook of Screening Techniques for Assessing Impacts of
Toxic Air Pollutants. The equation for the instantaneous release rate:
(Ht
(P0 - Pa)]
(D-12)
where: m = Discharge rate (kilograms per second)
Ah = Opening area (square meters)
Cd = Discharge coefficient (unitless)
g = Gravitational constant (9.8 meters per second squared)
PI = Liquid density (kilograms per cubic meter)
P0 = Storage pressure (Pascals)
Pa = Ambient pressure (Pascals)
HL = Liquid height above bottom of container (meters)
Hh = Height of opening (meters)
If the liquid is stored at ambient pressure, the equation becomes:
m = AHCd9l fig (HL -Hh)
(D-13)
To derive the equation presented in the guidance, all the chemical-specific properties,
constants, and conversion factors were combined into the "Liquid Leak Factor" (LLF). The
discharge coefficient was assumed to have a value of 0.8, based on the screening value recommended
in EPA's Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants. The LLF
was derived as follows:
LLF = 132.2 x 6.4516 x IQ~4 x 0.1594 x Q.8 x
(D-14)
where: LLF = Liquid Leak Factor (pounds per minute-inches2-5)
132.2 = Conversion factor for kilograms per second to pounds per minute
6.4516 x 10"4 = Conversion factor for square meters to square inches
0.1594 = Conversion factor for square root of meters to square root of inches
0.8 = Discharge coefficient (0.8),
9.8 = Gravitational constant (meters per second squared)
Pl = Liquid density (kilograms per cubic meter)
LLF values were calculated for all liquids regulated under CAA section 112(r) and are listed
in Appendix B, Exhibit B-2, for toxic liquids and Appendix C, Exhibit C-3, for flammable liquids.
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From the equation for liquid release rate from a hole in a tank at ambient pressure and the
equation for the LLF, the initial release rate for a liquid from a tank under atmospheric pressure can
be written as: ' ,
(D-15)
QRL = HA x JLH x LLF
where: QRL = Liquid release rate (pounds per minute)
HA = Hole area (square inches)
LH = Height of liquid above hole (inches)
D.7.2 Releases from Pipes
The equation used to estimate releases of liquids from pipes is the Bernoulli equation. It
assumes that the density of the liquid is constant and does not account for losses in velocity due to
wall friction. The equation follows:
8
(D-16)
Sc
where: Pa = Pressure at pipe inlet (Pascals)
Pb = Pressure at pipe outlet (Pascals)
Za = Height above datum plane at pipe inlet (meters)
Zb = Height above datum plane at pipe release (meters)
g = Gravitational acceleration (9.8 meters per second2)
gc = Newton's law proportionality factor (1.0)
Va = Operational velocity (meters per second)
Vb = Release velocity (meters per second)
D = Density of liquid (kilograms per cubic meter)
Isolating Vb yields:
'
2 x 8c x (Pa -
D
2 x
(Za -
(D-17)
Adjusting Vb in feet per minute yields:
(77,500 x Pa - 7.85 x 109)
+ (77,460 x g x Z) + Va'•
0-18)
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where: Pa ,= Operational pipe pressure (Pascals)
Z = Change in pipe elevation, inlet to outlet (meters)
g = Gravitational acceleration (9.8 meters per second2)
Va = Operational velocity (feet per minute)
Vb = Release velocity (feet per minute)
D = Density of liquid (kilograms per cubic meter)
D.8 Vapor Cloud Fires
Factors for leaks from tanks for flammable substances were derived as described for toxic
substances (see above).
The endpoint for estimating impact distances for vapor cloud fires of flammable substances,
the lower flammability limit (LFL), was chosen as a reasonable, but not very conservative, estimation
of the possible extent of a vapor cloud fire.
D.9 Pool Fires
Factors for estimating the distances to a heat radiation level that could cause second degree
burns from a 40-second exposure was developed based on equations presented in the AIChE
document, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and
BLEVEs and in the Netherlands TNO document, Methods for the Determination of Possible Damage
to People and Objects Resulting from Releases of Hazardous Materials (1992). The AIChE and TNO
documents present a point-source model that assumes that a selected fraction of the heat of
combustion is emitted as radiation in all directions. The radiation per unit area received by a target at
some distance from the point source is given by:
(D-19)
where: q = Radiation per unit area received by the receptor (Watts per square meter)
m = Rate of combustion (kilograms per second)
ra = Atmospheric transmissivity
Hc = Heat of combustion (Joules per kilogram)
f = Fraction of heat of combustion radiated
x = Distance from point source to receptor (meters)
The fraction of combustion energy dissipated as thermal radiation (f in the equation above) is
reported to range from 0.1 to 0.4. To develop factors for estimating distances for pool fires, this .
fraction was assumed to be 0.4 for all the regulated flammable substances. The heat radiation level
(q) was assumed to be 5,000 Watts per square meter. This level is reported to cause second degree
burns from a 40-second exposure. It was assumed that exposed people would be able to escape from
the heat in 40 seconds. The atmospheric transmissivity (ra) was assumed equal to one.
For a pool fire of a flammable substance with a boiling point above the ambient temperature,
the combustion rate can be estimated by the following empirical equation:
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tit =
O.OOlO Hc A
, + Cp (Tb - Ta)
(D-20)
where: m = Rate of combustion (kilograms per second)
Hc = Heat of combustion (Joules per kilogram)
Hv = Heat of vaporization (Joules per kilogram)
Cp = Liquid heat capacity (Joules per kilogram-degree K)
A = Pool area (square meters)
Tb = Boiling temperature (K)
Ta = Ambient temperature (K)
0.0010 = Constant
Combining the two equations given above, and assuming a heat radiation level of 5,000 Watts
per square meter, gives the following equation for liquid pools of substances with boiling points
above ambient temperature:
X ™
0.0010 A
(D-21)
or
X = W —
cv,l
0.0001 A
,000* (H
(D-22)
where: x = Distance from point source to receptor (meters)
q = Radiation per unit area received by the receptor = 5,000 Watts per square meter
Hc = Heat of combustion (Joules per kilogram)
f = Fraction of heat of combustion radiated = 0.4
Hv = Heat of vaporization (Joules per kilogram)
Cp = Liquid heat capacity (Joules per kilogram-degree K)
A = Pool area (square meters)
Tb = Boiling temperature (K)
Ta = Ambient temperature (K)
0.0010 = Constant
For a pool fire of a flammable substance with a boiling point below the ambient temperature
(i.e., liquefied gases) the combustion rate can be estimated by the following equation, based on the
TNO document:
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m =
O.OQIO Hc A
H..
(D-23)
where: m = Rate of combustion (kilograms per second)
Hv — Heat of vaporization (Joules per kilogram)
Hc = Heat of combustion (Joules per kilogram)
A = Pool area (square meters)
0.0010 = Constant
Then the equation for distance at which the radiation received equals 5,000 Watts per square meter
becomes:
x = H.
0.0001 A
5,0007i: Hv
(D-24)
where: x = Distance from point source to receptor (meters)
Radiation per unit area received by the receptor = 5,000 Watts per square meter
Hc = Heat of combustion (Joules per kilogram)
Hv = Heat of vaporization (Joules per kilogram)
A = Pool area (square meters)
0.0001 = Derived constant (see equations D-20 and D-21)
A "Pool Fire Factor" (PFF) was calculated for each regulated flammable liquid and gas to
allow estimation of the distance to the heat radiation level that would lead to second degree burns.
For the derivation of this factor, ambient temperature was assumed to be 298 K (25° C). Other
factors are discussed above. The PFF for liquids with boiling points above ambient temperature was
derived as follows:
PFF =
0.0001
5,0007t (H
Cp(Th - 298))
(D-25)
where: 5,000 = Radiation per unit area received by the receptor (Watts per square meter)
Hc = Heat of combustion (Joules per kilogram)
Hv = Heat of vaporization (Joules per kilogram)
Cp = Liquid heat capacity (Joules per kilogram-degree K)
Tb = Boiling temperature (K)
298 = Assumed ambient temperature (K)
0.0001 = Derived constant (see above)
0.0929 = Conversion factor for square meters to square feet
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For liquids with boiling points below ambient temperature^ .the PFF is derived as follows:
°-0001
c 5,000 * Hv
(D-26)
where: 5,000 = Radiation per unit area received by the receptor (Watts per square meter)
Hc = Heat of combustion (Joules per kilogram)
Hv = Heat of vaporization (Joules per kilogram)
0.0001 = Derived constant (see above)
0.0929 = Conversion factor for square meters to square feet
Distances where exposed people could potentially suffer second degree burns can be estimated
as the PFF multiplied by the square root of the pool area (in square feet), as discussed in the text.
D.10 BLEVEs
Reference Table 22, the table of distances for BLEVEs, was developed based on equations
presented in the AIChE document, Guidelines for Evaluating the Characteristics of Vapor Cloud
Explosions, Flash Fires, and BLEVEs. The Hymes point-source model for a fireball, as cited in the
AIChE document, uses the following equation for the radiation received by a receptor:
2.2 Ta R Hc
47tL2
(D-27)
where: q = Radiation received by the receptor (W/m2)
mf = Mass of fuel in the fireball (kg)
ra = Atmospheric transmissivity
Hc = Heat of combustion (J/kg)
R = Radiative fraction of heat of combustion
L = Distance from fireball' center to receptor (meters)
•K = 3.14
Hymes (as cited by AIChE) suggests the following values for R:
R = 0.3 for vessels bursting below relief valve pressure
R = 0.4 for vessels bursting at or above relief valve pressure
For development of the table in Exhibit 16, the following conservative assumptions were made:
R = 0.4
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The effects of radiant heat on an exposed person depend on both the intensity of the radiation
and the duration of the exposure. For development of the table of distances for BLEVEs, it was
assumed that the time of exposure would equal the duration of the fireball. The AIChE document
gives the following equations for duration of a fireball:
tc = 0.45 m/ for mf < 30,000 kg
(D-28)
and
tc, =. 2.6-rnf. for mf> 30,OQO kg
(D-29)
where: nif = Mass of fuel (kg)
tc = Combustion duration (seconds)
According to several sources (e.g., Eisenberg, et al,, Vulnerability Model, A Simulation^ . ',
System for Assessing Damage Resulting from Marine Spills; Mudah, Thermal Radiation Hazards from
Hydrocarbon Pool Fires (citing K. Buettner)), the effects of thermal radiation are generally
proportional to radiation intensity to the four-thirds power times time of exposure. Thus, a thermal
"dose" can be estimated using the following equation:
Dose = t q
(D-30)
where: t = Duration of exposure (seconds) : < ;
q = Radiation intensity (Watts/m2) . '
The thermal "dose" that could cause second-degree burns was estimated assuming 40-seconds
as the duration of exposure and 5,000 Watts/m2 as the radiation intensity. The corresponding dose is
3,420,000 (Watts/m2)4/3-s.
For estimating the distance from a fireball at which a receptor; might receive enough thermal
radiation to cause second degree burns, the dose estimated above was substituted into the equation for
radiation received from a fireball: • . , ;
q = 13,420,00014
3.
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[3,420,000l| _2.2vaRHc
.0.67
(D-32)
L =
2.2 ra R Hc m™7
471
[3,420,000
3
4
(D-33)
where: L = Distance from fireball center to receptor (meters)
q = Radiation received by the receptor (W/m2)
mf = Mass of fuel in the fireball (kg)
ra = Atmospheric, transmissivity (assumed to be 1)
Hc = Heat of combustion (J/kg)
R = Radiative fraction of heat of combustion (assumed to be 0.4)
t = Duration of the fireball (seconds) (estimated from the equations above); assumed to be
duration of exposure
D.ll Alternative Scenario Analysis for Vapor Cloud Explosions
For consideration of vapor cloud explosion as a potential alternative scenario, the guidance
provides a method to estimate the quantity in the cloud from the fraction flashed into vapor plus the
quantity that might be carried along as aerosol. The recommendation to use twice the quantity flashed
into vapor as the quantity flashed plus aerosol for determination of consequence distance is based on
the method recommended by the UK Health and Safety Executive (HSE), as cited in the AIChE
document, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and
BLEVEs. In addition, according to T.A. Kletz, in "Unconfmed Vapor Cloud Explosions" (Eleventh
Loss Prevention Symposium, sponsored by AIChE, 1977), unconfmed vapor cloud explosions almost
always result from the release of flashing liquids.
The equation for the flash fraction, for possible use in for the alternative scenario analysis, is
based on the Netherlands TNO document, Methods for the Calculation of the Physical Effects of the
Escape of Dangerous Material (1980), Chapter 4, "Spray Release." The following equation is
provided:
(D-34)
where: Xvap>a = Weight fraction of vapor after expansion
xvap'b = Weight fraction of vapor before expansion (assumed to be 0 for calculation of the
flash fraction)
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Tb = Boiling temperature of gas compressed to liquid (K)
T! = Temperature of stored gas compressed to liquid (K)
Ci = Specific heat of gas compressed to liquid (Joules/kilogram-K)
hv = Heat of evaporation of gas compressed to liquid (Joules/kilogram)
To develop a Flash Fraction Factor (FFF) for use in consequence analysis, compressed gases
were assumed to be stored at 25°C (298 K) (except in cases where the gas could not be liquefied at
that temperature). The equation for FFF is:
FFF =
^taf)
(D-35)
where: Tb = Boiling temperature of gas compressed to liquid (K)
C] = Specific heat of gas compressed to liquid (Joules/kilogram-K)
hv = Heat of evaporation of gas compressed to liquid (Joules/kilogram)
298 = Temperature of stored gas compressed to liquid (K)
The recommendation to use a yield factor of 0.03 for the alternative scenario analysis for
vapor cloud explosions also is based on the UK HSE method cited by AIChE.
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APPENDIXE
RISK MANAGEMENT PROGRAM RULE
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1. Part 68 is amended by redesignating Subpart C as Subpart F as follows:
Subpart F Regulated Substances for Accidental Release Prevention
2. The table of contents of Part 68 is revised to read as follows:
Part 68 — ACCIDENTAL RELEASE PREVENTION PROVISIONS
Subpart A General
68.1 Scope.
68.3 Definitions.
68.10 Applicability.
68.12 General requirements.
68.15 Management.
Subpart B Hazard Assessment
68.20 Applicability.
68.22 Offsite consequence analysis parameters.
68.25 Worst-case release scenario analysis.
68.28 Alternative release scenario analysis.
68.30 Defining offsite impacts — population.
68.33 Defining offsite impacts — environment.
68.36 Review and update.
68.39 Documentation.
68.42 Five-year accident history.
Subpart C Program 2 Prevention Program
68.48 Safety information.
68.50 Hazard review.
68.52 Operating procedures.
68.54 Training.
68.56 Maintenance.
68.58 Compliance audits.
68.60 Incident investigation.
Subpart D Program 3 Prevention Program
68.65 Process safety information.
68.67 Process hazard analysis.
68.69 Operating procedures.
68.71 Training.
68.73 Mechanical integrity.
68.75 Management of change.
68.77 Pre-startup review.
68.79 Compliance audits.
68.81 Incident investigation.
68.83 Employee participation.
68.85 Hot work permit.
68.87 Contractors.
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Subpart E Emergency Response
68.90 Applicability.
68.95 Emergency response program.
Subpart F Regulated Substances for Accidental Release Prevention
68.100 Purpose.
68.115 Threshold determination.
68.120 Petition process.
68.125 Exemptions.
68.130 List of substances.
Subpart G Risk Management Plan
68.150 Submission.
68.155 Executive summary.
68.160 Registration.
68.165 Offsite consequence analysis.
68.168 Five-year accident history.
68.170 Prevention program/program 2.
68.175 Prevention program/program 3.
68.180 Emergency response program.
68.185 Certification.
68.190 Updates.
Subpart H Other Requirements
68.200 Recordkeeping.
68.210 Availability of information to the public.
68.215 Permit content and air permitting authority or designated agency requirements.
68.220 Audits.
APPENDIX A Table of Toxic Endpoints
3. The authority citation is revised to read as follows:
Authority: 42 U.S.C. 7412(r), 7601(a)(l), 7661-7661f.
4. Section 68.3 is amended to add the following definitions:
68.3 Definitions
Act means the Clean Air Act as amended (42 U.S.C. 7401 et seq.)
Administrative controls mean written procedural mechanisms used for hazard control.
AIChE/CCPS means the American Institute of Chemical Engineers/Center for Chemical
Process Safety.
API means the American Petroleum Institute.
ASME means the American Society of Mechanical Engineers.
Catastrophic release means a major uncontrolled emission, fire, or explosion, involving one
or more regulated substances that presents imminent and substantial endangerment to public health
and the environment.
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Classifled information means "classified information" as defined in the Classified Information
Procedures Act, 18 U.S.C. App. 3, section l(a) as "any information or material that has been
determined by the United States Government pursuant to an executive order, statute, or regulation, to
require protection againsf unauthorized disclosure for reasons of national security."
Covered process means a process that has a regulated substance present in more than a
threshold quantity as determined under § 68.115 of this part.
Designated agency means the state, local, or Federal agency designated by the state under the
provisions of § 68.215(d) of this part.
Environmental receptor means natural areas such as national or state parks, forests, or
monuments; officially designated wildlife sanctuaries, preserves, refuges, or areas; and Federal
wilderness areas, that could be exposed at any time to toxic concentrations, radiant heat, or
overpressure greater than or equal to the endpoints provided in § 68.22(a) of this part, as a result of
an accidental release and that can be identified on local U. S. Geological Survey maps.
Hot work means work involving electric or gas welding, cutting, brazing, or similar flame or
spark-producing operations.
Implementing agency means the state or local agency that obtains delegation for an accidental
release prevention program under subpart E, 40 CFR part 63. The implementing agency may, but is
not required to, be the state or local air permitting agency. If no state or local agency is granted
delegation, EPA will be the implementing agency for that state.
Injury means any effect on a human that results either from direct exposure to toxic
concentrations; radiant heat; or overpressures from accidental releases or from the direct
consequences of a vapor cloud explosion (such as flying glass, debris, and other projectiles) from an
accidental release and that requires medical treatment or hospitalization.
Major change means introduction of a new process, process equipment, or regulated
substance, an alteration of process chemistry that results in any change to safe operating limits, or
other alteration that introduces a new hazard.
Mechanical integrity means the process of ensuring that process equipment is fabricated from
the proper materials of construction and is properly installed, maintained, and replaced to prevent
failures and accidental releases.
Medical treatment means treatment, other than first aid, administered by a physician or
registered professional personnel under standing orders from a physician.
Mitigation or mitigation system means specific activities, technologies, or equipment designed
or deployed to capture or control substances upon loss of containment to minimize exposure of the
public or the environment. Passive mitigation means equipment, devices, or technologies that
function without human, mechanical, or other energy input. Active mitigation means equipment,
devices, or technologies that need human, mechanical, or other energy input to function,
NFPA means the National Fire Protection Association.
Offsite means areas beyond the property boundary of the stationary source, and areas within
the property boundary to which the public has routine and unrestricted access during or outside
business hours.
OSHA means the U.S. Occupational Safety and Health Administration.
Owner or operator means any person who owns, leases, operates, controls, or supervises a
stationary source.
Population means the public.
Public means any person except employees or contractors at the stationary source.
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Public receptor, means offsite residences, institutions (e.g., schools, hospitals), industrial,
commercial, and offic§ buildings, parks, or recreational areas inhabited or occupied by the public at
any time without restriction by the stationary source where members of the public could be exposed
to toxic concentrations, radiant heat, or overpressure, as a result of an accidental release.
Replacement in kind means a replacement that satisfies the design specifications.
RMP means the risk management plan required under subpart G of this part.
SIC means Standard Industrial Classification.
Typical meteorological conditions means the temperature, wind speed, cloud cover, and
atmospheric stability class, prevailing at the site based on data gathered at or near the site or from a
local meteorological station.
Worst-case release means the release of the largest quantity of a regulated substance from a
vessel or process line failure that results in the greatest distance to an endpoint defined in § 68.22(a)
of this part.
5. Section 68.10 is added to read as follows:
68.10 Applicability.
(a) An owner or operator of a stationary source that has more than a threshold quantity of a
regulated substance in a process, as determined under § 68.115 of this part, shall comply with the
requirements of this part no later than the latest of the following dates:
(1) [insert date 3 years after the date of publication in the FEDERAL REGISTER!:
(2) Three years after the date on which a regulated substance is first listed under § 68.130 of
this part; or
(3) The date on which a regulated substance is first present above a threshold quantity in a
process.
(b) Program 1 eligibility requirements. A covered process is eligible for Program 1
requirements as provided in § 68.12(b) of this part if it meets all of the following requirements:
(1) For the five years prior to the submission of an RMP, the process has not had an
accidental release of a regulated substance where exposure to the substance, its reaction products,
overpressure generated by an explosion involving the substance, or radiant heat generated by a fire
involving the substance led to any of the following offsite:
(i) Death;
(ii) Injury; or
(iii) Response or restoration activities for an exposure of an environmental receptor;
(2) The distance to a toxic or flammable endpoint for a worst-case release assessment
conducted under Subpart B and § 68.25 of this part is less than the distance to any public receptor, as
defined in § 68.30 of this part; and
(3) Emergency response procedures have been coordinated between the stationary source and
local emergency planning and response organizations.
(c) Program 2 eligibility requirements. A covered process is subject to Program 2 ,
requirements if it does not meet the eligibility requirements of either paragraph (b) or paragraph (d)
of this section.
(d) Program 3 eligibility requirements. A covered process is subject to Program 3 if the
process does not meet the requirements of paragraph (b) of this section, and if either of the following
conditions is met:
(1) The process is in SIC code 2611, 2812, 2819, 2821, 2865, 2869, 2873, 2879, or 2911;
or
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(2) The process is subject to the OSHA process safety management standard, 29 CFR
1910,119, . :
(e) If at any time a covered process no longer meets the eligibility criteria of its Programv; v
level, the owner or operator shall comply with the requirements of the new Program level that applies
to the process and update the RMP as provided in § 68.190 of this part.
6. Section 68.12 is added to read as follows: ;,
68.12 General requirements. , - • '
(a) General requirements. The owner or operator of a stationary source subject to this part
shall submit a single RMP, as provided in §§ 68.150 to 68.185. of this part. The RMP shall include a
registration that reflects all covered processes. . ;: .
(b) Program 1 requirements. In addition to meeting the requirements of paragraph (a) of this
section, the owner or operator of a stationary source with a process eligible for Program 1, as
provided in § 68.10(b) of this part, shall:
(1) Analyze the worst-case release scenario for the process(es), as provided in § 68.25 of this
part; document that the nearest public receptor is beyond the distance to a toxic or flammable
endpoint defined in § 68.22(a) of this part; and submit in. the:RMP the worstTcase release scenario as
provided in § 68.165 of this part; : •
(2) Complete the five-year accident history for the process as provided in § 68.42 of this part
and submit it in the RMP as provided in § 68.168 of this part; ;. •
(3) Ensure that response actions have been coordinated with local emergency planning and
response agencies; and
(4) Certify in the RMP the following: "Based on the criteria in 40 CFR 68.10, the distance
to the specified endpoint for the worst-case accidental release scenario for the following process(es) is
less than the distance to the nearest public receptor: [list process(es)]. Within the past five years, the
process(es) has (have) had no accidental release that caused offsite impacts provided in the risk
management program rule (40 CFR 68.10(b)(l)). No additional measures are necessary to prevent
offsite impacts from accidental releases. In the event of fire, explosion, or a release of a regulated
substance from the process(es), entry within the distance to the specified endpoints may pose a danger
to public emergency responders. Therefore, public emergency responders should not enter this area
except as arranged with the emergency contact indicated in the RMP. The undersigned certifies that,
to the best of my knowledge, information, and belief, formed after reasonable inquiry, the
information submitted is true, accurate, and complete. [Signature, title, date signed]."
(c) Program 2 requirements. In addition to meeting the requirements of paragraph (a) of this
section, the owner or operator of a stationary source with,a process subject to Program 2, as provided
in § 68.10(c) of this part, shall:
(1) Develop and implement a management system as provided in § .68-15 of this part;
(2) Conduct a hazard assessment as provided in §§ 68.20 through 68.42 of this part;
(3) Implement the Program 2 prevention steps provided,in §§ 68.48 through 68.60 of this
part or implement the Program 3 prevention steps provided in §§ 68.65 through 68.87 of this part;
(4) Develop and implement an emergency response program as provided in §§ 68.90 to
68.95 of this part; and . -
(5) Submit as part of the RMP the data on prevention program elements for Program 2
processes as provided in § 68.170 of this part.
(d) Program 3 requirements. In addition to meeting the requirements of paragraph (a) of this
section, the owner or operator of a stationary source with a process subject to Program 3, as provided
in § 68.10(d) of this part shall:
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(1) Develop and implement a management system as provided in § 68.15 of this part;
(2) Conduct a hazard assessment as provided in §§ 68.20 through 68.42 of this part;
(3) Implement the prevention requirements of §§ 68.65 through 68.87 of this part;
(4) Develop and implement an emergency response program as provided in §§ 68.90 to
68.95 of this part; and
(5) Submit as part of the RMP the data on prevention program elements for Program 3
processes as provided in § 68.175 of this part.
7. Section 68.15 is added to read as follows:
6S.15 Management.
(a) The owner or operator of a stationary source with processes subject to Program 2 or
Program 3 shall develop a management system to oversee the implementation of the risk management
program elements.
(b) The owner or operator shall assign a qualified person or position that has the overall
responsibility for the development, implementation, and integration of the risk management program
elements.
(c) When responsibility for implementing individual requirements of this part is assigned to
persons other than the person identified under paragraph (b) of this section, the names or positions of
these people shall be documented and the lines of authority defined through an organization chart or
similar document.
8. Subpart B is added to read as follows:
Subpart B Hazard Assessment
68.20 Applicability.
68.22 Offsite consequence analysis parameters.
68.25 Worst-case release scenario analysis.
68.28 Alternative release scenario analysis.
68.30 Defining offsite impacts — population.
68.33 Defining offsite impacts — environment.
68.36 Review and update.
68.39 Documentation.
68.42 Five-year accident history.
68.20 Applicability. The owner or operator of a stationary source subject to this part shall prepare
a worst-case release scenario analysis as provided in § 68.25 of this part and complete the five-year
accident history as provided in § 68.42 of this part. The owner or operator of a Program 2 and 3
process must comply with all sections in this subpart for these processes.
68.22 Offsite consequence analysis parameters.
(a) Endpoints. For analyses of offsite consequences, the following endpoints shall be used:
(1) Toxics. The toxic endpoints provided in Appendix A of this part.
(2) Flammables. The endpoints for flammables vary according to the scenarios studied:
(i) Explosion. An overpressure of 1 psi.
(ii) Radiant heat/exposure time. A radiant heat of 5 kw/m2 for 40 seconds.
(iii) Lower flammability limit. A lower flammability limit as provided in NFPA documents
or other generally recognized sources.
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(b) Wind speed/atmospheric stability class. For the worst-case release analysis, the owner or
operator shall use a wind speed of 1.5 meters per second and F atmospheric stability class. If the
owner or operator can demonstrate that local meteorological data applicable to the stationary source
show a higher minimum wind speed or less stable atmosphere at all times during the previous three
years, these minimums may be used. For analysis of alternative scenarios, the owner or operator
may use the typical meteorological conditions for the stationary source.
(c) Ambient temperature/humidity. For worst-case release analysis of a regulated toxic
substance, the owner or operator shall use the highest daily maximum temperature in the previous
three years and average humidity for the site, based on temperature/humidity data gathered at the
stationary source or at a local meteorological station; an owner or operator using the RMP Offsite
Consequence Analysis Guidance may use 25°C and 50 percent humidity as values for these variables.
For analysis of alternative scenarios, the owner or operator may use typical temperature/humidity data
gathered at the stationary source or at a local meteorological station.
(d) Height of release. The worst-case release of a regulated toxic substance shall be analyzed
assuming a ground level (0 feet) release. For an alternative scenario analysis of a regulated toxic
substance, release height may be determined by the release scenario.
(e) Surface roughness. The owner or operator shall use either urban or rural topography, as
appropriate. Urban means that there are many obstacles in the immediate area; obstacles include
buildings or trees. Rural means there are no buildings in the immediate area and the terrain is
generally flat and unobstructed.
(f) Dense or neutrally buoyant gases. The owner or operator shall ensure that tables or
models used for dispersion analysis of regulated toxic substances appropriately account for gas
density.
(g) Temperature of released substance. For worst case, liquids other than gases liquified by
refrigeration only shall be considered to be released at the highest daily maximum temperature, based
on data for the previous three years appropriate for the stationary source, or at process temperature,
whichever is higher. For alternative scenarios, substances may be considered to be released at a
process or ambient temperature that is appropriate for the scenario.
68.25 Worst-case release scenario analysis.
(a) The owner or operator shall analyze and report in the RMP:
(1) For Program 1 processes, one worst-case release scenario for each Program 1 process;
(2) For Program 2 and 3 processes:
(i) One worst-case release scenario that is estimated to create the greatest distance in any
direction to an endpoint provided in Appendix A of this part resulting from an accidental release of
regulated toxic substances from covered processes under worst-case conditions defined in § 68.22 of
this part;
(ii) One worst-case release scenario that is estimated to create the greatest distance in any
direction to an endpoint defined in § 68.22(a) of this part resulting from an accidental release of
regulated flammable substances from covered processes under worst-case conditions defined in
§ 68.22 of this part; and
(iii) Additional worst-case release scenarios for a hazard class if a worst-case release from
another covered process at the stationary source potentially affects public receptors different from
those potentially affected by the worst-case release scenario developed under paragraphs (a)(2)(i) or
(a)(2)(ii) of this section.
(b) Determination of worst-case release quantity. The worst-case release quantity shall be the
greater of the following:
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(1) For substances in a vessel, the greatest amount held in a single vessel, taking into account
administrative controls that limit the maximum quantity; or
(2) For substances in pipes, the greatest amount in a pipe, taking into account administrative
controls that limit the maximum quantity. ••-.-•
(c) Worst-case release scenario— toxic gases.
(1) For regulated toxic substances that are normally gases at ambient temperature and
handled as a gas or as a liquid under pressure, the owner or operator shall assume that the quantity in
the vessel or pipe, as determined under paragraph (b) of this section, is released as a gas over 10
minutes. The release rate shall be assumed to be the total quantity divided by 10 unless passive
mitigation systems are in place. •
(2) For gases handled as refrigerated liquids at ambient pressure:
(i) If the released substance is hot contained by passive mitigation systems or if the contained
pool would have a depth of 1 cm of less, the owner or operator shall assume that the substance is
released as a gas in 10 minutes;
(ii) If the released substance is contained by passive mitigation systems in a pool with a depth
greater than 1 cm, the owner or operator may assume that the quantity in the vessel or pipe, as
determined under paragraph (b) of this section, is spilled instantaneously to form a liquid pool. The
volatilization rate (release 'rate) shall be calculated at the boiling point of the substance and at the
conditions specified in paragraph (d) of this section'.
(d) Worst-case release scenario — toxic liquids.
(1) For regulated toxic substances that are normally liquids at ambient temperature, the
owner or operator shall assume that the quantity in the vessel or pipe, as determined under paragraph
(b) of this section, is spilled instantaneously to form a liquid pool.
(i) The surface area of the pool shall be determined by assuming that the liquid spreads to 1
centimeter deep unless passive mitigation systems are in place that serve to contain the spill and limit
the surface area. Where passive mitigation is in place, the surface area of the contained liquid shall
be used to calculate the volatilization rate.
(ii) If the release would occur onto a surface that is not paved or smooth, the owner or •••••
operator may take into account the actual surface characteristics.
(2) The volatilization rate shall account for the highest daily maximum temperature occurring
in the past three years, the temperature of the substance in the vessel, and the concentration of the
substance if the liquid spilled is a mixture or solution.
(3) The rate of release to air shall be determined from the volatilization rate of the liquid
pool. The owner or operator may use the methodology in the RMP Offsite Consequence Analysis
Guidance or any other publicly available techniques that account for the modeling conditions and are
recognized by industry as applicable as part of current practices. Proprietary models that account for
the modeling conditions may be used provided the owner or operator allows the implementing agency
access to the model and describes model features and differences from publicly available models to
local emergency planners upon request. .
(e) Worst-case release scenario - flammables; The owner or operator shall assume that the
quantity of the substance, as determined under paragraph (b) of this section, vaporizes resulting in a
vapor cloud explosion. A yield factor of 10 percent of the available energy released in the explosion
shall be used to determine the distance to the explosion endpoint if the model used is based on TNT-
equivalent methods.
(f) Parameters to be applied. The owner or operator shall use the parameters defined in
§ 68.22 of this part to determine distance to the endpoints. The owner or operator may use the
methodology provided in the RMP Offsite Consequence Analysis Guidance or any commercially or
publicly available air dispersion modeling techniques, provided the techniques account for the
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modeling conditions and are recognized by industry as applicable as part of current practices.
Proprietary models that account for the modeling conditions may be used provided the owner or
operator allows the implementing agency access to the model and describes model features and
differences from publicly available models to local emergency planners upon request.
(g) Consideration of passive mitigation. Passive mitigation systems may be considered for
the analysis of worst case provided that the mitigation system is capable of withstanding the release
event triggering the scenario and would still function as intended.
(h) Factors in selecting a worst-case scenario. Notwithstanding the provisions of paragraph
(b) of this section, the owner or operator shall select as the worst case for flammable regulated
substances or the worst case for regulated toxic substances, a scenario based on the following factors
if such a scenario would result in a greater distance to an endpoint defined in § 68.22(a) of this part
beyond the stationary source boundary than the scenario provided under paragraph (b) of this section:
(1) Smaller quantities handled at higher process temperature or pressure; and
(2) Proximity to the boundary of the stationary source.
6S.28 Alternative release scenario analysis.
(a) The number of scenarios. The owner or operator shall identify and analyze at least one
alternative release scenario for each regulated toxic substance held in a covered process(es) and at
least one alternative release scenario to represent all flammable substances held in covered processes.
(b) Scenarios to consider. (1) For each scenario required under paragraph (a) of this
section, the owner or operator shall select a scenario:
(i) That is more likely to occur than the worst-case release scenario under § 68.25 of this
part; and ,
(ii) That will reach an endpoint offsite, unless no such scenario exists.
(2) Release scenarios considered should include, but are not limited to, the following, where
applicable:
(i) Transfer hose releases due to splits or sudden hose uncoupling;
(ii) Process piping releases from failures at flanges, joints, welds, valves and valve seals, and
drains or bleeds; ; .
(iii) Process vessel or pump releases due to cracks, seal failure, or drain, bleed, or plug
failure;
(iv) Vessel overfilling and spill, or overpressurization and venting through relief valves or
rupture disks; and
(v) Shipping container mishandling and breakage or puncturing leading to a spill.
(c) Parameters to be applied. The owner or operator shall use the appropriate parameters
defined in § 68.22 of this part to determine distance to the endpoints. The owner or operator may
use either the methodology provided in the RMP Offsite Consequence Analysis Guidance or any
commercially or publicly available air dispersion modeling techniques, provided the techniques
account for the specified modeling conditions and are recognized by industry as applicable as part of
current practices. Proprietary models that account for the modeling conditions may be used provided
the owner or operator allows the implementing agency access to the model and describes model
features and differences from publicly available models to local emergency planners upon request.
(d) Consideration of mitigation. Active and passive mitigation systems may be considered
provided they are capable of withstanding the event that triggered the release and would still be
functional.
(e) Factors in selecting scenarios. The owner or operator shall consider the following in
selecting alternative release scenarios:
(1) The five-year accident history provided in § 68.42 of this part; and
(2) Failure scenarios identified under §§ 68.50 or 68.67 of this part.
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68.30 Defining offsite impacts — population.
(a) The owner or operator shall estimate in the RMP the population within a circle with its
center at the point of the release and a radius determined by the distance to the endpoint defined in
§ 68.22(a) of this part.
(b) Population to be defined. Population shall include residential population. The presence
of institutions (schools, hospitals, prisons), parks and recreational areas, and major commercial,
office, and industrial buildings shall be noted in the RMP.
(c) Data sources acceptable. The owner or operator may use the most recent Census data, or
other updated information, to estimate the population potentially affected.
(d) Level of accuracy. Population shall be estimated to two significant digits.
68.33 Defining offsite impacts — environment.
(a) The owner or operator shall list in the RMP environmental receptors within a circle with
its center at the point of the release and a radius determined by the distance to the endpoint defined in
§ 68.22(a) of this part.
(b) Data sources acceptable. The owner or operator may rely on information provided on
local U.S. Geological Survey maps or on any data source containing U.S.G.S. data to identify
environmental receptors.
68.36 Review and update.
(a) The owner or operator shall review and update the offsite consequence analyses at least
once every five years.
(b) If changes in processes, quantities stored or handled, or any other aspect of the stationary
source might reasonably be expected to increase or decrease the distance to the endpoint by a factor
of two or more, the owner or operator shall complete a revised analysis within six months of the
change and submit a revised risk management plan as provided in § 68.190 of this part.
68.39 Documentation. The owner or operator shall maintain the following records on the offsite
consequence analyses:
(a) For worst-case scenarios, a description of the vessel or pipeline and substance selected as
worst case, assumptions and parameters used, and the rationale for selection; assumptions shall
include use of any administrative controls arid any passive mitigation that were assumed to limit the
quantity that could be released. Documentation shall include the anticipated effect of the controls and
mitigation on the release quantity and rate.
(b) For alternative release scenarios, a description of the scenarios identified, assumptions
and parameters used, and the rationale for the selection of specific scenarios; assumptions shall
include use of any administrative controls and any mitigation that were assumed to limit the quantity
that could be released. Documentation shall include the effect of the controls and mitigation on the
release quantity and rate.
(c) Documentation of estimated quantity released, release rate, and duration of release.
(d) Methodology used to determine distance to endpoints.
(e) Data used to estimate population and environmental receptors potentially affected.
68.42 Five-year accident history.
(a) The owner or operator shall include in the five-year accident history all accidental
releases from covered processes that resulted in deaths, injuries, or significant property damage on
site, or known offsite deaths, injuries, evacuations, sheltering in place, property damage, or
environmental damage.
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(b) Data required. For each accidental release included, the owner or operator shall report
the following information:
(1) Date, time, and approximate duration of the release;
(2) Chemical(s) released;
(3) Estimated quantity released in pounds;
(4) The type of release event and its source;
(5) Weather conditions, if known;
(6) On-site impacts;
(7) Known offsite impacts;
(8) Initiating event and contributing factors if known;
(9) Whether offsite responders were notified if known; and
(10) Operational or process changes that resulted from investigation of the release.
(c) Level of accuracy. Numerical estimates may be provided to two significant digits.
9. Subpart C is added to read as follows:
Subpart C Program 2 Prevention Program
68.48 Safety information.
68.50 Hazard review.
68.52 Operating procedures.
68.54 Training.
68.56 Maintenance.
68.58 Compliance audits.
68.60 Incident investigation.
68.48 Safety information.
(a) The owner or operator shall compile and maintain the following up-to-date safety
information related to the regulated substances, processes, and equipment:
(1) Material Safety Data Sheets that meet the requirements of 29 CFR 1910.1200(g);
(2) Maximum intended inventory of equipment in which the regulated substances are stored
or processed;
(3) Safe upper and lower temperatures, pressures, flows, and compositions;
(4) Equipment specifications; and
(5) Codes and standards used to design, build, and operate the process.
(b) The owner or operator shall ensure that the process is designed in compliance with
recognized and generally accepted good engineering practices. Compliance with Federal or state
regulations that address industry-specific safe design or with industry-specific design codes and
standards may be used to demonstrate compliance with this paragraph.
(c) The owner or operator shall update the safety information if a major change occurs that
makes the information inaccurate.
68.50 Hazard review
(a) The owner or operator shall conduct a review of the hazards associated with the regulated
substances, process, and procedures. The review shall identify the following:
(1) The hazards associated with the process and regulated substances;
(2) Opportunities for equipment malfunctions or human errors that could cause an accidental
release;
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(3) The safeguards used or needed to control the hazards or prevent equipment malfunction
or human error; and
(4) Any steps used or needed to detect or monitor releases.
(b) The owner or operator may use checklists developed by persons or organizations
knowledgeable about the process and equipment as a guide to conducting the review. For processes
designed to meet industry standards or Federal or state design rules, the hazard review shall, by
inspecting all equipment, determine whether the process is designed, fabricated, and operated in
accordance with the applicable standards or rules.
(c) The owner or operator shall document the results of the review and ensure that problems
identified are resolved in a timely manner.
(d) The review shall be updated at least once every five years. The owner or operator shall
also conduct reviews whenever a major change in the process occurs; all issues identified in the
review shall be resolved before startup of the changed process.
68.52 Operating procedures.
(a) The owner or operator shall prepare written operating procedures that provide clear
instructions or steps for safely conducting activities associated with each covered process consistent
with the safety information for that process. Operating procedures or instructions provided by
equipment manufacturers or developed by persons or organizations knowledgeable about the process
and equipment may be used as a basis for a stationary source's operating procedures.
(b) The procedures shall address the following:
(1) Initial startup;
(2) Normal operations;
(3) Temporary operations;
(4) Emergency shutdown and operations;
(5) Normal shutdown;
(6) Startup following a normal or emergency shutdown or a major change that requires a
hazard review;
(7) Consequences of deviations and steps required to correct or avoid deviations; and
(8) Equipment inspections.
(c) The owner or operator shall ensure that the operating procedures are updated, if
necessary, whenever a major change occurs and prior to startup of the changed process.
68.54 Training.
(a) The owner or operator shall ensure that each employee presently operating a process, and
each employee newly assigned to a covered process have been trained or tested competent in the
operating procedures provided in § 68.52 of this part that pertain to their duties. For those
employees already operating a process on [insert date 3 years after the date of publication in the
FEDERAL REGISTER], the owner or operator may certify in writing that the employee has the
required knowledge, skills, and abilities to safely carry out the duties and responsibilities as provided
in the operating procedures.
(b) Refresher training. Refresher training shall be provided at least every three years, and
more often if necessary, to each employee operating a process to ensure that the employee
understands and adheres to the current operating procedures of the process. The owner or operator,
in consultation with the employees operating the process, shall determine the appropriate frequency of
refresher training.
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(c) The owner or operator may use training conducted under Federal or state regulations or
under industry-specific standards or codes or training conducted by covered process equipment
vendors to demonstrate compliance with this section to the extent that the training meets the
requirements of this section.
(d) The owner or operator shall ensure that operators are trained in any updated or new
procedures prior to startup of a process after a major change.
68.56 Maintenance.
(a) The owner or operator shall prepare and implement procedures to maintain the on-going
mechanical integrity of the process equipment. The owner or operator may use procedures or
instructions provided by covered process equipment vendors or procedures in Federal or state
regulations or industry codes as the basis for stationary source maintenance procedures.
(b) The owner or operator shall train or cause to be trained each employee involved in
maintaining the on-going mechanical integrity of the process. To ensure that the employee can
perform the job tasks in a safe manner, each such employee shall be trained in the hazards of the
process, in how to avoid or correct unsafe conditions, and in the procedures applicable to the
employee's job tasks.
(c) Any maintenance contractor shall ensure that each contract maintenance employee is
trained to perform the maintenance procedures developed under paragraph (a) of this section.
(d) The owner or operator shall perform or cause to be performed inspections and tests on
process equipment. Inspection and testing procedures shall follow recognized and generally accepted
good engineering practices. The frequency of inspections and tests of process equipment shall be
consistent with applicable manufacturers' recommendations, industry standards or codes, good
engineering practices, and prior operating experience.
68.58 Compliance audits.
(a) The owner or operator shall certify that they have evaluated compliance with the
provisions of this subpart at least every three years to verify that the procedures and practices
developed under the rule are adequate and are being followed.
(b) The compliance audit shall be conducted by at least one person knowledgeable in the
process.
(c) The owner or operator shall develop a report of the audit findings.
(d) The owner or operator shall promptly determine and document an appropriate response to
each of the findings of the compliance audit and document that deficiencies have been corrected.
(e) The owner or operator shall retain the two (2) most recent compliance audit reports. This
requirement does not apply to any compliance audit report that is more than five years old.
68.60 Incident investigation.
(a) The owner or operator shall investigate each incident which resulted in, or could
reasonably have resulted in a catastrophic release.
(b) An incident investigation shall be initiated as promptly as possible, but not later than 48
hours following the incident.
(c) A summary shall be prepared at the conclusion of the investigation which includes at a
minimum:
(1) Date of incident;
(2) Date investigation began;
(3) A description of the incident;
(4) The factors that contributed to the incident; and,
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(5) Any recommendations resulting from the investigation.
(d) The owner or operator shall promptly address and resolve the investigation findings and
recommendations. Resolutions and corrective actions shall be documented.
(e) The findings shall be reviewed with all affected personnel whose job tasks are affected by
the findings.
(f) Investigation summaries shall be retained for five years.
10. Subpart D is added to read as follows:
Subpart D Program 3 Prevention Program
68.65 Process safety information.
68,67 Process hazard analysis.
68.69 Operating procedures.
68.71 Training.
68.73 Mechanical integrity.
68.75 Management of change.
68.77 Pre-startup review.
68.79 Compliance audits.
68.81 Incident investigation.
68.83 Employee participation.
68.85 Hot work permit.
68.87 Contractors.
68.65 Process safety information.
(a) In accordance with the schedule set forth in § 68.67 of this part, the owner or operator
shall complete a compilation of written process safety information before conducting any process
hazard analysis required by the rule. The compilation of written process safety information is to
enable the owner or operator and the employees involved in operating the process to identify and
understand the hazards posed by those processes involving regulated substances. This process safety
information shall include information pertaining to the hazards of the regulated substances used or
produced by the process, information pertaining to the technology of the process, and information
pertaining to the equipment in the process.
(b) Information pertaining to the hazards of the regulated substances in the process. This
information shall consist of at least the following:
(1) Toxicity information;
(2) Permissible exposure limits; .
(3) Physical data;
(4) Reactivity data:
(5) Corrosivity data;
(6) Thermal and chemical stability data; and
(7) Hazardous effects of inadvertent mixing of different materials that could foreseeably
occur.
Note: Material Safety Data Sheets meeting the requirements of 29 CFR 19l0.1200(g) may be
used to comply with this requirement to the extent they contain the information required by this
subparagraph.
(c) Information pertaining to the technology of the process.
(1) Information concerning the technology of the process shall include at least the following:
(i) A block flow diagram or simplified process flow diagram;
(ii) Process chemistry;
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(iii) Maximum intended inventory;
(iv) Safe upper and lower limits for such items as temperatures, pressures, flows or
compositions; and,
(v) An evaluation of the consequences of deviations.
(2) Where the original technical information no longer exists, such information may be
developed in conjunction with the process hazard analysis in sufficient detail to support the analysis.
(d) Information pertaining to the equipment in the process.
(1) Information pertaining to the equipment in the process shall include:
(i) Materials of construction;
(ii) Piping and instrument diagrams (P&ID's);
(iii) Electrical classification;
(iv) Relief system design and design basis;
(v) Ventilation system design;
(vi) Design codes and standards employed;
(vii) Material and energy balances for processes built after [insert date 3 years after the date
of publication in the FEDERAL REGISTER!: and
(viii) Safety systems (e.g. interlocks, detection or suppression systems).
(2) The owner or operator shall document that equipment complies with recognized and
generally accepted good engineering practices.
(3) For existing equipment designed and constructed in accordance with codes, standards, or
practices that are no longer in general use, the owner or operator shall determine and document that
the equipment is designed, maintained, inspected, tested, and operating in a safe manner.
68.67 Process hazard analysis.
(a) The owner or operator shall perform an initial process hazard analysis (hazard evaluation)
on processes covered by this part. The process hazard analysis shall be appropriate to the complexity
of the process and shall identify, evaluate, and control the hazards involved in the process. The
owner or operator shall determine and document the priority order for conducting process hazard
analyses based on a rationale which includes such considerations as extent of the process hazards,
number of potentially affected employees, age of the process, and operating history of the process.
The process hazard analysis shall be conducted as soon as possible, but not later than [insert date 3
years after the date of publication in the FEDERAL REGISTER]. Process hazards analyses
completed to comply with 29 CFR 1910.119(e) are acceptable as initial process hazards analyses.
These process hazard analyses shall be updated and revalidated, based on their completion date.
(b) The owner or operator shall use one or more of the" following methodologies that are
appropriate to determine and evaluate the hazards of the process being analyzed.
(1) What-If;
(2) Checklist;
(3) What-If/Checklist;
(4) Hazard and Operability Study (HAZOP);
(5) Failure Mode and Effects Analysis (FMEA);
(6) Fault Tree Analysis; or
(7) An appropriate equivalent methodology.
(c) The process hazard analysis shall address:
(1) The hazards of the process;
(2) The identification of any previous incident which had a likely potential for catastrophic
consequences.
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(3) Engineering and administrative controls applicable to the hazards and their
interrelationships such as appropriate application of detection methodologies to provide early warning
of releases. (Acceptable detection methods might include process monitoring and control
instrumentation with alarms, and detection hardware such as hydrocarbon sensors.);
(4) Consequences of failure of engineering and administrative controls;
(5) Stationary source siting;
(6) Human factors; and
(7) A qualitative evaluation of a range of the possible safety and health effects of failure of
controls.
(d) The process hazard analysis shall be performed by a team with expertise in engineering
and process operations, and the team shall include at least one employee who has experience and
knowledge specific to the process being evaluated. Also, one member of the team must be
knowledgeable in the specific process hazard analysis methodology being used.
(e) The owner or operator shall establish a system to promptly address the team's findings
and recommendations; assure that the recommendations are resolved in a timely manner and that the
resolution is documented; document what actions are to be taken; complete actions as soon as
possible; develop a written schedule of when these actions are to be completed; communicate the
actions to operating, maintenance and other employees whose work assignments are in the process
and who may be affected by the recommendations or actions.
(f) At least every five (5) years after the completion of the initial process hazard analysis, the
process hazard analysis shall be updated and revalidated by a team meeting the requirements in
paragraph (d) of this section, to assure that the process hazard analysis is consistent with the current
process. Updated and revalidated process hazard analyses completed to comply with 29 CFR
1910.119(e) are acceptable to meet the requirements of this paragraph.
(g) The owner or operator shall retain process hazards analyses and updates or revalidations
for each process covered by this section, as well as the documented resolution of recommendations
described in paragraph (e) of this section for the life of the process.
68.69 Operating procedures.
(a) The owner or operator shall develop and implement written operating procedures that
provide clear instructions for safely conducting activities involved in each covered process consistent
with the process safety information and shall address at least the following elements.
(1) Steps for each operating phase:
(i) Initial startup;
(ii) Normal operations;
(iii) Temporary operations;
(iv) Emergency shutdown including the conditions under which emergency shutdown is
required, and the assignment of shutdown responsibility to qualified operators to ensure that
emergency shutdown is executed in a safe and timely manner.
(v) Emergency operations;
(vi) Normal shutdown; and,
(vii) Startup following a turnaround, or after an emergency shutdown.
(2) Operating limits:
(i) Consequences of deviation; and
(ii) Steps required to correct or avoid deviation.
(3) Safety and health considerations:
(i) Properties of, and hazards presented by, the chemicals used in the process;
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(ii) Precautions necessary to prevent exposure, including engineering controls, administrative
controls, and personal protective equipment;
(iii) Control measures to be taken if physical contact or airborne exposure occurs;
(iv) Quality control for raw materials and control of hazardous chemical inventory levels;
and,
(v) Any special or unique hazards.
(4) Safety systems and their functions.
(b) Operating procedures shall be readily accessible to employees who work in or maintain a
process.
(c) The operating procedures shall be reviewed as often as necessary to assure that they
reflect current operating practice, including changes that result from changes in process chemicals,
technology, and equipment, and changes to stationary sources. The owner or operator shall certify
annually that these operating procedures are current and accurate.
(d) The owner or operator shall develop and implement safe work practices to provide for the
control of hazards during operations such as lockout/tagout; confined space entry; opening process
equipment or piping; and control over entrance into a stationary source by maintenance, contractor,
laboratory, or other support personnel. These safe work practices shall apply to employees and
contractor employees.
68.71 Training.
(a) Initial training. (1) Each employee presently involved in operating a process, and each
employee before being involved in operating a newly assigned process, shall be trained in an
overview of the process and in the operating procedures as specified in § 68.69 of this part. The
training shall include emphasis on the specific safety and health hazards, emergency operations
including shutdown, and safe work practices applicable to the employee's job tasks.
(2) In lieu of initial training for those employees already involved in operating a process on
Hnsert date 3 years after the date of publication in the FEDERAL REGISTER] an owner or operator
may certify in writing that the employee has the required knowledge, skills, and abilities to safely
carry out the duties and responsibilities as specified in the operating procedures.
(b) Refresher training. Refresher training shall be provided at least every three years, and
more often if necessary, to each employee involved in operating a process to assure that the employee
understands and adheres to the current operating procedures of the process. The owner or operator,
in consultation with the employees involved in operating the process, shall determine the appropriate
frequency of refresher training.
(c) Training documentation. The owner or operator shall ascertain that each employee
involved in operating a process has received and understood the training required by this paragraph.
The owner or operator shall prepare a record which contains the identity of the employee, the date of
training, and the means used to verify that the employee understood the training.
68.73 Mechanical integrity.
(a) Application. Paragraphs (b) through (f) of this section apply to the following process
equipment:
(1) Pressure vessels and storage tanks;
(2) Piping systems (including piping components such as valves);
(3) Relief and vent systems and devices;
(4) Emergency shutdown systems;
(5) Controls (including monitoring devices and sensors, alarms, and interlocks) and,
(6) Pumps.
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(b) Written procedures. The owner or operator shall establish and implement written
procedures to maintain the on-going integrity of process equipment.
(c) Training for process maintenance activities. The owner or operator shall train each
employee involved in maintaining the on-going integrity of process equipment in an overview of that
process and its hazards and in the procedures applicable to the employee's job tasks to assure that the
employee can perform the job tasks in a safe manner.
(d) Inspection and testing. (1) Inspections and tests shall be performed on process
equipment.
(2) Inspection and testing procedures shall follow recognized and generally accepted good
engineering practices.
(3) The frequency of inspections and tests of process equipment shall be consistent with
applicable manufacturers' recommendations and good engineering practices, and more frequently if
determined to be necessary by prior operating experience.
(4) The owner or operator shall document each inspection and test that has been performed
on process equipment. The documentation shall identify the date of the inspection or test, the name
of the person who performed the inspection or test, the serial number or other identifier of the
equipment on which the inspection or test was performed, a description of the inspection or test
performed, and the results of the inspection or test.
(e) Equipment deficiencies. The owner or operator shall correct deficiencies in equipment
that are outside acceptable limits (defined by the process safety information in § 68.65 of this part)
before further use or in a safe and timely manner when necessary means are taken to assure safe
operation.
(f) Quality assurance. (1) In the construction of new plants and equipment, the owner or
operator shall assure that equipment as it is fabricated is suitable for the process application for which
they will be used.
(2) Appropriate checks and inspections shall be performed to assure that equipment is
installed properly and consistent with design specifications and the manufacturer's instructions.
(3) The owner or operator shall assure that maintenance materials, spare parts and equipment
are suitable for the process application for which they will be used.
68.75 Management of change.
(a) The owner or operator shall establish and implement written procedures to manage
changes (except for "replacements in kind") to process chemicals, technology, equipment, and
procedures; and, changes to stationary sources that affect a covered process.
(b) The procedures shall assure that the following considerations are addressed prior to any
change:
(1) The technical basis for the proposed change;
(2) Impact of change on safety and health;
(3) Modifications to operating procedures;
(4) Necessary time period for the change; and,
(5) Authorization requirements for the proposed change.
(c) Employees involved in operating a process and maintenance and contract employees
whose job tasks will be affected by a change in the process shall be informed of, arid trained in, the
change prior to start-up of the process or affected part of the process.
(d) If a change covered by this paragraph results in a change in the process safety
information required by § 68.65 of this part, such information shall be updated accordingly.
(e) If a change covered by this paragraph results in a change in the operating procedures or
practices required by § 68.69 of this part, such procedures or practices shall be updated accordingly.
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68.77 Pre-startup review.
(a) The owner or operator shall perform a pre-startup safety review for new stationary
sources and for modified stationary sources when the modification is significant enough to require a
change in the process safety information.
(b) The pre-startup safety review shall confirm that prior to the introduction of regulated
substances to a process:
(1) Construction and equipment is in accordance with design specificatipns;
(2) Safety, operating, maintenance, and emergency procedures are in place and are adequate;
(3) For new stationary sources, a process hazard analysis has been performed and
recommendations have been resolved or implemented before startup; and modified stationary sources
meet the requirements contained in management of change, § 68.75 of this part.
(4) Training of each employee involved in operating a process has been completed.
68.79 Compliance audits.
(a) The owner or operator shall certify that they have evaluated compliance with the
provisions of this section at least every three years to verify that the procedures and practices
developed under the standard are adequate and are being followed.
(b) The compliance audit shall be conducted by at least one person knowledgeable in the
process.
(c) A report of the findings of the audit shall be developed.
(d) The owner or operator shall promptly determine and document an appropriate response to
each of the findings of the compliance audit, and document that deficiencies have been corrected.
(e) The owner or operator shall retain the two (2) most recent compliance audit reports.
68.81 Incident investigation.
(a) The owner or operator shall investigate each incident which resulted in, or could
reasonably have resulted in a catastrophic release of a regulated substance.
(b) An incident investigation shall be initiated as promptly as possible, but not later than 48
hours following the incident.
(c) An incident investigation team shall be established and consist of at least one person
knowledgeable in the process involved, including a contract employee if the incident involved work of
the contractor, and other persons with appropriate knowledge and experience to thoroughly investigate
and analyze the incident.
(d) A report shall be prepared at the conclusion of the investigation which includes at a
minimum:
(1) Date of incident;
(2) Date investigation began;
(3) A description of the incident;
(4) The factors that contributed to the incident; and,
(5) Any recommendations resulting from the investigation.
(e) The owner or operator shall establish a system to promptly address and resolve the
incident report findings and recommendations. Resolutions and corrective actions shall be
documented.
(f) The report shall be reviewed with all affected personnel whose job tasks are relevant to
the incident findings including contract employees where applicable.
(g) Incident investigation reports shall be retained for five years.
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68.83 Employee participation.
(a) The owner or operator shall develop a written plan of action regarding the implementation
of the employee participation required by this section.
(b) The owner or operator shall consult with employees and their representatives on the
conduct and development of process hazards analyses and on the development of the other elements of
process safety management in this rule.
(c) The owner or operator shall provide to employees and their representatives access to
process hazard analyses and to all other information required to be developed under this rule.
68.85 Hot work permit.
(a) The owner or operator shall issue a hot work permit for hot work operations conducted
on or near a covered process. '
(b) The permit shall document that the fire prevention and protection requirements in 29 CFR
1910.252(a) have been implemented prior to beginning the hot work operations; it shall indicate the
date(s) authorized for hot work; and identify the object on which hot work is to be performed. The
permit shall be kept on file until completion of the hot work operations.
68.87 Contractors.'
(a) Application. This section applies to contractors performing maintenance or repair,
turnaround, major renovation, or specialty work on or adjacent to a covered process. It does not
apply to contractors providing incidental services which do not influence process safety, such as
janitorial work, food and drink services, laundry, delivery or other supply services.
(b) Owner or operator responsibilities. (1) The owner or operator, when selecting a
contractor, shall obtain and evaluate information regarding the contract owner or operator's safety
performance and programs.
(2) The owner or operator shall inform contract owner or operator of the known potential
fire, explosion, or toxic release hazards related to the contractor's work and the process.
(3) The owner or operator shall explain to the contract owner or operator the applicable
provisions of subpart E of this part.
(4) The owner or operator shall develop and implement safe work practices consistent with
§ 68.69(d) of this part, to control the entrance, presence, and exit of the contract owner or operator
and contract employees in covered process areas.
(5) The owner or operator shall periodically evaluate the performance of the contract owner
or operator in fulfilling their obligations as specified in paragraph (c) of this section.
(c) Contract owner or operator responsibilities. (1) The contract owner or operator shall
assure that each contract employee is trained in the work practices necessary to safely perform his/her
job.
(2) The contract owner or operator shall assure that each .contract employee is instructed in
the known potential fire, explosion, or toxic release hazards related to his/her job and the process,
and the applicable provisions of the emergency action plan.
(3) The contract owner or operator shall document that each contract employee has received
and understood the training required by this section. The contract owner or operator shall prepare a
record which contains the identity of the contract employee, the date of training, and the means used
to verify that the employee understood the training.
(4) The contract owner or operator shall assure that each contract employee follows the
safety rules of the stationary source including the safe work practices required by § 68.69(d) of this
part.
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(5) The contract owner or operator shall advise the owner or operator of any unique hazards
presented by the contract owner or operator's work,:or, of any hazards found by the contract owner or
operator's work. v
11. Subpart E is added to read as follows:
Subpart E Emergency Response
68.90 Applicability.
68.95 Emergency Response Program.
68.90 Applicability.
(a) Except as provided in paragraph (b) of this section, the owner or operator of a stationary
source with Program 2 and Program 3 processes shall comply with the requirements of § 68.95 of
this part.
(b) The owner or operator of stationary source whpse employees will not respond to
accidental releases of regulated substances need not comply with § 68.95 of this part provided that
they meet the following:
(1) For stationary sources with any regulated toxic substance held in a process above the
threshold quantity, the stationary source is included in the community emergency response plan
developed under 42 U.S.C. 11003;
(2) For stationary sources with only regulated flammable substances held in a process above
the threshold quantity, the owner or operator has coordinated response actions with the local fire
department; and
(3) Appropriate mechanisms are in place to notify emergency responders when there is a
need for a response.
68.95 Emergency response program •
(a) The owner or operator shall develop and implement an emergency response program for
the purpose of protecting public health and the environment. Such program shall include the
following elements:
(1) An emergency response plan, which shall be maintained at the stationary source and
contain at least the following elements: ,
(i) Procedures for informing the public and local emergency response agencies about
accidental releases; .-..•.-,
(ii) Documentation of proper first-aid and emergency medical treatment necessary to treat
accidental human exposures; and
(iii) Procedures and measures for emergency response after an accidental release of a
regulated substance;
(2) Procedures for the use of emergency response equipment and for its inspection, testing, ,
and maintenance;
(3) Training for all employees in relevant procedures; and
(4) Procedures to review and update, as appropriate, the emergency response plan to reflect
changes at the stationary source and ensure that employees are informed of changes.
(b) A written plan that complies with other Federal contingency plan regulations or is
consistent with the approach in the National Response Team's Integrated Contingency Plan Guidance
("One Plan") and that, among other matters, includes the elements provided in paragraph (a) of this
section, shall satisfy the requirements of this section if the owner or operator also complies with
paragraph (c) of this section.
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(c) The emergency response plan developed under paragraph (a)(l) of this section shall be
coordinated with the community emergency response plan developed under 42 U.S.C. 11003. Upon
request of the local emergency planning committee or emergency response officials, the owner or
operator shall promptly provide to the local emergency response officials information necessary for
developing and implementing the community emergency response plan.
12. Subpart G is added to read as follows:
Subpart G Risk management plan
68.150 Submission.
68.155 Executive summary.
68.160 Registration.
68.165 Offsite consequence analysis.
68.168 Five-year accident history.
68.170 Prevention program/program 2.
68.175 Prevention program/program 3.
68.180 Emergency response program.
68.185 Certification.
68.190 Updates.
68.150 Submission.
(a) The owner or operator shall submit a single RMP that includes the information required
by §§ 68.155 through 68.185 of this part for all covered processes. The RMP shall be submitted in a
method and format to a central point as specified by EPA prior to rinsert date 3 years after the date of
publication in the FEDERAL REGISTER].
(b) The owner or operator shall submit the first RMP no later than the latest of the following
dates:
(1) [insert date 3 years after the date of publication in the FEDERAL REGISTER!:
(2) Three years after the date on which a regulated substance is first listed under § 68.130 of
this part; or
(3) The date on which a regulated substance is first present above a threshold quantity in a
process.
(c) Subsequent submissions of RMPs shall be in accordance with § 68.190 of this part.
(d) Notwithstanding the provisions of §§ 68.155 to 68.190 of this part, the RMP shall
exclude classified information. Subject to appropriate procedures to protect such information from
public disclosure, classified data or information excluded from the RMP may be made available in a
classified annex to the RMP for review by Federal and state representatives who have received the
appropriate security clearances.
68.155 Executive summary.
The owner or operator shall provide in the RMP an executive summary that includes a brief
description of the following elements:
(a) The accidental release prevention and emergency response policies at the stationary
source;
(b) The stationary source and regulated substances handled;
(c) The worst-case release scenario(s) and the alternative release scenario(s), including
administrative controls and mitigation measures to limit the distances for each reported scenario;
(d) The general accidental release prevention program and chemical-specific prevention steps;
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(e) The five-year accident history;
(f) The emergency response program; and
(g) Planned changes to improve safety.
68.160 Registration.
(a) The owner or operator shall complete a single registration form and include it in the
RMP. The form shall cover all regulated substances handled in covered processes.
(b) The registration shall include the following data:
(1) Stationary source name, street, city, county, state, zip code, latitude, and longitude;
(2) The stationary source Dun and Bradstreet number;
(3) Name and Dun and Bradstreet number of the corporate parent company;
(4) The name, telephone number, and mailing address of the owner or operator;
(5) The name and title of the person or position with overall responsibility for RMP elements
and implementation;
(6) The name, title, telephone number, and 24-hour telephone number of the emergency
contact;
(7) For each covered process, the name and CAS number of each regulated substance held
above the threshold quantity in the process, the maximum quantity of each regulated substance or
mixture in the process (in pounds) to two significant digits, the SIC code, and the Program level of
the process;
(8) The stationary source EPA identifier;
(9) The number of full-time employees at the stationary source;
(10) Whether the stationary source is subject to 29 CFR 1910.119;
(11) Whether the stationary source is subject to 40 CFR part 355;
(12) Whether the stationary source has a CAA Title V operating permit; and
(13) The date of the last safety inspection of the stationary source by a Federal, state, or
local government agency and the identity of the inspecting entity.
68.165 Offsite consequence analysis.
(a) The owner or operator shall submit in the RMP information:
(1) One worst-case release scenario for each Program 1 process; and
(2) For Program 2 and 3 processes, one worst-case release scenario to represent all regulated
toxic substances held above the threshold quantity and one worst-case release scenario to represent all
regulated flammable substances held above the threshold quantity. If additional worst-case scenarios
for toxics or flammables are required by § 68.25(a)(2)(iii) of this part, the owner or operator shall
submit the same information on the additional scenario(s). Th& owner or operator of Program 2 and
3 processes shall also submit information on one alternative release scenario for each regulated toxic
substance held above the threshold quantity and one alternative release scenario to represent all
regulated flammable substances held above the threshold quantity.
(b) The owner or operator shall submit the following data:
(1) Chemical name;
(2) Physical state (toxics only);
(3) Basis of results (give model name if used);
(4) Scenario (explosion, fire, toxic gas release, or liquid spill and vaporization);
(5) Quantity released in pounds;
(6) Release rate;
(7) Release duration;
(8) Wind speed and atmospheric stability class (toxics only);
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(9) Topography (toxics only);
(10) Distance to endpoint;
(11) Public and environmental receptors within the distance;
(12) Passive mitigation considered; and
(13) Active mitigation considered (alternative releases only);
68.168 Five-year accident history. The owner or operator shall submit in the RMP the information
provided in § 68.42(b) of this part on each accident covered by § 68.42(a) of this part.
68.170 Prevention program/Program 2.
(a) For each Program 2 process, the owner or operator shall provide in the RMP the
information indicated in paragraphs (b) through (k) of this section. If the same information applies to
more than one covered process, the owner or operator may provide the information only once, but
shall indicate to which processes.the information applies.
(b) The SIC code for the process.
(c) The name(s) of the chemical(s) covered.
(d) The date of the most recent review or revision of the safety information and a list of
Federal or state regulations or industry-specific design codes and standards used to demonstrate
compliance with the safety information requirement.
(e) The date of completion of the most recent hazard review or update.
(1) The expected date of completion of any changes resulting from the hazard review;
(2) Major hazards identified;
(3) Process controls in use;
(4) Mitigation systems in use;
(5) Monitoring and detection systems in use; and
(6) Changes since the last hazard review.
(f) The date of the most recent review or revision of operating procedures.
(g) The date of the most recent review or revision of training programs;
(1) The type of training provided — classroom, classroom plus on the job, on the job; and
(2) The type of competency testing used.
(h) The date of the most recent review or revision of maintenance procedures and the date of
the most recent equipment inspection or test and the equipment inspected or tested.
(i) The date of the most recent compliance audit and the expected date of completion of any
changes resulting from the compliance audit.
(j) The date of the most recent incident investigation and the expected date of completion of
any changes resulting from the investigation.
(k) The date of the most recent change that triggered a review or revision of safety
information, the hazard review, operating or maintenance procedures, or training.
68.175 Prevention program/Program 3.
(a) For each Program 3 process, the owner or operator shall provide the information
indicated in paragraphs (b) through (p) of this section. If the same information applies to more than
one covered process, the owner or operator may provide the information only once, but shall indicate
to which processes the information applies.
(b) The SIC code for the process.
(c) The name(s) of the substance(s) covered.
(d) The date on which the safety information was last reviewed or revised.
(e) The date of completion of the most recent PHA or update and the technique used.
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(1) The expected date of completion of any changes resulting from the PHA;
(2) Major hazards identified; .
(3) Process controls in use; ..-',- . ;
(4) Mitigation systems in use;
(5) Monitoring and detection systems in use; and
(6) Changes since the last PHA.
(f) The date of the most recent review or revision of operating procedures.
(g) The date of the most recent review or revision of training programs;
(1) The type of training provided — classroom, classroom plus on the job, on the job; and
(2) The type of competency testing used. '
(h) The date of the most recent review or revision of maintenance procedures and the date of
the most recent equipment inspection or test and the equipment inspected or tested.
(i) The date of the most recent change that triggered management of change procedures and
the date of the most recent review or revision of management of change procedures.
(j) The date of the most recent pre-startup review.
(k) The date of the most recent compliance audit and the expected date of completion of any
changes resulting from the compliance audit; ,
(1) The date of the most recent incident investigation and the expected date of completion of
any changes resulting from the investigation;
(m) The date of the most recent review or revision of employee participation plans;
(n) The date of the most recent review or revision of hot work permit procedures;
(o) The date of the most recent review or revision of contractor safety procedures; and
(p) The date of the most recent evaluation of contractor safety performance.
68.180 Emergency response program.
(a) The owner or operator shall provide in the RMP the following information:
(1) Do you have a written emergency response plan?
(2) Does the plan include specific actions to be taken in response to an accidental releases of
a regulated substance?
(3) Does the plan include procedures for informing the public and local agencies responsible
for responding to accidental releases?
(4) Does the plan include information qn emergency health care?
(5) The date of the most recent review or update of the emergency response plan;
(6) The date of the most recent emergency response training for employees.
(b) The owner or operator shall provide the name and telephone number of the local agency
with which the plan is coordinated. ,
(c) The owner or operator shall list other Federal or state emergency plan requirements to
which the stationary source is subject.
68.185 Certification.
(a) For Program 1 processes, the owner or operator shall submit in the RMP the certification
statement provided in § 68.12(b)(4) of this part.
(b) For all other covered processes, the owner or operator shall submit in the RMP a single
certification that, to the best of the signer's knowledge, information, and belief formed after
reasonable inquiry, the information submitted is true, accurate, and complete.
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68.190 Updates.
(a) The owner or operator shall review and update the RMP as specified in paragraph (b) of
this section and submit it in a method and format to a central point specified by EPA prior to [insert
date 3 years after the date of publication in the FEDERAL REGISTER].
(b) The owner or operator of a stationary source shall revise and update the RMP submitted
under § 68.150 as follows:
(1) Within five years of its initial submission or most recent update required by paragraphs
(b)(2)-(b)(7) of this section, whichever is later.
(2) No later than three years after a newly regulated substance is first listed by EPA;
(3) No later than the date on which a new regulated substance is first present in an already
covered process above a threshold quantity;
(4) No later than the date on which a regulated substance is first present above a threshold
quantity in a new process;
(5) Within six months of a change that requires a revised PHA or hazard review;
(6) Within six months of a change that requires a revised offsite consequence analysis as
provided in § 68.36 of this part; and
(7) Within six months of a change that alters the Program level that applied to any covered
process.
(c) If a stationary source is no longer subject to this part, the owner or operator shall submit
a revised registration to EPA within six months indicating that the stationary source is no longer
covered.
13. Subpart H is added to read as follows:
Subpart H Other Requirements
68.200 Recordkeeping.
68.210 Availability of information to the public.
68.215 Permit content and air permitting authority or designated agency requirements.
68.220 Audits.
68.200 Recordkeeping.
The owner or operator shall maintain records supporting the implementation of this part for
five years unless otherwise provided in Subpart D of this part.
68.210 Availability of information to the public.
(a) The RMP required under subpart G of this part shall be available to the public under 42
U.S.C. 7414(c).
(b) The disclosure of classified information by the Department of Defense or other Federal
agencies or contractors of such agencies shall be controlled by applicable laws, regulations, or
executive orders concerning the release of classified information.
68.215 Permit content and air permitting authority or designated agency requirements.
(a) These requirements apply to any stationary source subject to part 68 and parts 70 or 71 of
this Chapter. The 40 CFR part 70 or part 71 permit for the stationary source shall contain:
(1) A statement listing this part as an applicable requirement;
(2) Conditions that require the source owner or operator to submit:
(i) A compliance schedule for meeting the requirements of this part by the date provided in
§68.10(a)of this part or;
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(ii) As part of the compliance certification submitted under 40 CFR 70.6(c)(5), a certification
statement that the source is in compliance with all requirements of this part, including the registration
and submission of the RMP.
(b) The owner or operator shall submit any additional relevant information requested by the
air permitting authority or designated agency.
(c) For 40 CFR part 70 or part 71 permits issued prior to the deadline for registering and
submitting the RMP and which do not contain permit conditions described in paragraph (a) of this
section, the owner or operator or air permitting authority shall initiate permit revision or reopening
according to the procedures of 40 CFR 70,7 or 71.7 to incorporate the terms and conditions
consistent with paragraph (a) of this section.
(d) The state may delegate the authority to implement and enforce the requirements of
paragraph (e) of this section to a state or local agency or agencies other than the air permitting
authority. An up-to-date copy of any delegation instrument shall be maintained by the air permitting
authority. The state may enter a written agreement with the Administrator under which EPA will
implement and enforce the requirements of paragraph (e) of this section.
(e) The air permitting authority or the agency designated by delegation or agreement under
paragraph (d) of this section shall, at a minimum:
(1) Verify that the source owner or operator has registered and submitted an RMP or a
revised plan when required by this part;
(2) Verify that the source owner or operator has submitted a source certification or in its
absence has submitted a compliance schedule consistent with paragraph (a)(2) of this section;
(3) For some or ail of the sources subject to this section, use one or more mechanisms, such
as, but not limited to, a completeness check, source audits, record reviews, or facility inspections to
ensure that permitted sources are in compliance with the requirements of this part; and
(4) Initiate enforcement action based on paragraphs (e)(l) and (e)(2) of this section as
appropriate.
68.220 Audits.
(a) In addition to inspections for the purpose of regulatory development and enforcement of
the Act, the implementing agency shall periodically audit RMPs submitted under subpart G of this
part to review the adequacy of such RMPs and require revisions of RMPs when necessary to ensure
compliance with subpart G of this part.
(b) The implementing agency shall select stationary sources for audits based on any of the
following criteria:
(1) Accident history of the stationary source;
Accident history of other stationary sources in the same industry;
Quantity of regulated substances present at the stationary source;
Location of the stationary source and its proximity to the public and environmental
(2)
(3)
(4)
receptors;
(5)
(6)
(7)
The presence of specific regulated substances;
The hazards identified in the RMP; and
A plan providing for neutral, random oversight.
(c) Exemption from audits. A stationary source with a Star or Merit ranking under OSHA's
voluntary protection program shall be exempt from audits under paragraph (b)(2) and (b)(7) of this
section.
(d) The implementing agency shall have access to the stationary source, supporting
documentation, and any area where an accidental release could occur.
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(e) Based on the audit, the implementing agency may issue the owner or operator of a
stationary source a written preliminary determination of necessary revisions to the stationary source's
RMP to ensure that the RMP meets the criteria of subpart G of this part. The preliminary
determination shall include an explanation for the basis for the revisions, reflecting industry standards
and guidelines (such as AIChE/CCPS guidelines and ASME and API standards) to the extent that
such standards and guidelines are applicable, and shall include a timetable for their implementation.
(f) Written response to a preliminary determination.
(1) The owner or operator shall respond in writing to a preliminary determination made in
accordance with paragraph (e) of this section. The response shall state the owner or operator will
implement the revisions contained in the preliminary determination in accordance with the timetable
included in the preliminary determination or shall state that the owner or operator rejects the revisions
in whole or in part. For each rejected revision, the owner or operator shall explain the basis for
rejecting such revision. Such explanation may include substitute revisions.
(2) The written response under paragraph (f)(l) of this section shall be received by the
implementing agency within 90 days of the issue of the preliminary determination or a shorter period
of time as the implementing agency specifies in the preliminary determination as necessary to protect
public health and the environment. Prior to the written response being due and upon written request
from the owner or operator, the implementing agency may provide in writing additional time for the
response to be received.
(g) After providing the owner or operator an opportunity to respond under paragraph (f) of
this section, the implementing agency may issue the owner or operator a written final determination
of necessary revisions to the stationary source's RMP. The final determination may adopt or modify
the revisions contained in the preliminary determination under paragraph (e) of this section or may
adopt or modify the substitute revisions provided in the response under paragraph (f) of this section.
A final determination that adopts a revision rejected by the owner or operator shall include an
explanation of the basis for the revision. A final determination that fails to adopt a substitute revision
provided under paragraph (f) of this section shall include an explanation of the basis for finding such
substitute revision unreasonable.
(h) Thirty days after completion of the actions detailed in the implementation schedule set in
the final determination under paragraph (g) of this section, the owner or operator shall be in violation
of subpart G of this part and this section unless the owner or operator revises the RMP prepared
under subpart G of this part as required by the final determination, and submits the revised RMP as
required under § 68.150 of this part.
(i) The public shall have access to the preliminary determinations, responses, and final
determinations under this section in a manner consistent with § 68.210 of this part.
(j) Nothing in this section shall preclude, limit, or interfere in any way with the authority of
EPA or the state to exercise its enforcement, investigatory, and information gathering authorities
concerning this part under the Act.
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14. Part 68 Appendix A is added to read as follows:
APPENDIX A
TABLE OF TOXIC ENDPOINTS
(as defined in § 68.22 of this part)
CAS No.
.- 107r02-8
107-13-1
814-68-6
107-18-6
107-11-9
7664-41-7
7664-41-7
7784-34-1
7784-42-1
10294-34-5
7637-07-2
353-42-4
7726-95-6
75-15-0
7782-50-5
10049-04-4
67-66-3
542-88-1
107-30-2
4170-30-3
123-73-9
506-77-4
108-91-8
19287-45-7
75-78-5
57-14-7
Chemical Name
Acrolein [2-Propenal]
Acrylonitrile [2-Propenenitrile]
Acrylyl chloride [2-Propenoyl chloride]
Allyl alcohol [2-Propen-l-ol]
Allylamine [2-Propen-l-amine]
Ammonia (anhydrous)
Ammonia (cone 20% or greater)
Arsenous trichloride
Arsine
Boron trichloride [Borane, trichloro-]
Boron trifluoride [Borane, trifluoro-]
Boron trifluoride compound with methyl ether (1:1) [Boron, trifluoro[oxybis[methane]]-, T-4
Bromine
Carbon disulfide •
Chlorine
Chlorine dioxide [Chlorine oxide (C1O2)]
Chloroform [Methane, trichloro-]
Chloromethyl ether [Methane, oxybis[chloro-]
Chloromethyl methyl ether [Methane, chloromethoxy-]
Crotonaldehyde [2-Butenal]
Crotonaldehyde, (E)- [2-Butenal, (E)-]
Cyanogen chloride
Cyclohexylamine [Cyclohexanamine]
Diborane
Dimethyldichlorosilane [Silane, dichlorodimethyl-]
1 , 1 -Dimethylhydrazine [Hydrazine ,1,1 -dimethyl-]
Toxic
Endpoint
(mg/L)
0.0011
0.076
0.00090
0.036
0.0032
0.14
0.14
0.010
0.0019
0.010
0.028
0.023
0.0065
0.16
0.0087
0.0028
0.49
0.00025
0.0018
0.029
0.029
0.030
0.16
0.0011
0.026
0.012
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CAS No.
10(3-89-8
107-15-3
151-56-4
75-21-8
7782-41-4
50-00-0
1
110-00-9
302-01-2
7647-01-0
74-90-8
7647-01-0
7664-39-3
7783-07-5
7783-06-4
13463-40-6
78-82-0
108-23-6
126-98-7
74-87-3
79-22-1
60-34-4
624-83-9
74-93-1
55,6-64-9
75-79-6
13463-39-3
7697-37-2
10102-43-9
8014-95-7
79-21-0
Chemical Name
Epichlorohydrin [Oxirane, (chloromethyl)-]
Ethylenediamine [1 ,2-Ethanediamine]
Ethyleneimine [Aziridine]
Ethylene oxide [Oxirane]
Fluorine
Formaldehyde (solution;
Furan
Hydrazine
Hydrochloric acid (cone 30% or greater)
Hydrocyanic acid . ,
Hydrogen chloride (anhydrous) [Hydrochloric acid]
Hydrogen fluoride/Hydrofluoric acid (cone 50% or greater) [Hydrofluoric acid]
Hydrogen selenide
Hydrogen sulfide
Iron, pentacarbonyl- [Iron carbonyl (Fe(CO)5), (TB-5-11)]
Isobutyronitrile [Propanenitrile, 2-methyl-]
Isopropyl chloroformate [Carbonochloridic acid, l-methylethyi ester]
Methacrylonitrile [2-Propenenitrile, 2-methyl-]
Methyl chloride [Methane, chloro-]
Methyl chloroformate [Carbonochloridic acid, methylester]
Methyl hydrazine [Hydrazine, methyl-]
Methyl isocyanate [Methane, isocyanato-]
Methyl mercaptan [Methanethiol]
Methyl thiocyanate [Thiocyanic acid, methyl ester]
Methyltrichlorosilane [Silane, trichloromethyl-]
Nickel carbonyl
Nitric acid (cone 80% or greater)
Nitric oxide [Nitrogen oxide (NO)]
Oleum (Fuming Sulfuric acid) [Sulfuric acid, mixture with sulfur trioxide]
Peracetic acid [Ethaneperoxoic acid]
Toxic
Endpoint
(mg/L)
0.076
0.49
0.018
0.090
0.0039
0.012
0.0012
0.011
0.030
0.011
0.030
0.016
0.00066
0.042
0.00044
0.14
0.10
0.0027
0.82
0.0019
0.0094
0.0012
0.049
0.085
0.018
0.00067
0.026
0.031
0.010
0.0045
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-153-
CAS No.
594-42-3
75-44-5
7803-51-2
10025-87-3
7719-12-2
110-89-4
107-12-0
109-61-5
75-55-8
, 75-56-9
7446-09-5
7783-60-0
7446-11-9
75-74-1
509-14-8
7550-45-0
584-84-9
91-08-7
26471-62-5
75-77-4
108-05-4
Chemical Name
Perchloromethylmercaptan [Methanesulfenyl chloride, trichloro-]
Phosgene [Carbonic dichloride]
Phosphine ......
Phosphorus oxychloride [Phosphoryl chloride]
Phosphorus trichloride [Phosphorous trichloride]
Piperidine
Propionitrile [Propanenitrile]
Propyl chloroformate [Carbonochloridic acid, propylester]
Propyleneimine [Aziridine, 2-methyl-]
Propylene oxide [Oxirane, methyl-]
Sulfur dioxide (anhydrous)
Sulfur tetrafluoride [Sulfur fluoride (SF4), (T-4)-]
Sulfur trioxide
Tetramethyllead [Plumbane, tetramethyl-]
Tetranitromethane [Methane, tetranitro-]
Titanium tetrachloride [Titanium chloride (TiC14) (T-4)-]
Toluene 2,4-diisocyanate [Benzene, 2,4-diisocyanato-l-methyl-]
Toluene 2,6-diisocyanate [Benzene, 1 ,3-diisocyanato-2-methyl-]
Toluene diisocyanate (unspecified isomer) [Benzene, 1 ,3-diisocyanatomethyl-]
Trimethylchlorosilane [Silane, chlorotrimethyl-]
Vinyl acetate monomer [Acetic acid ethenyl ester]
Toxic
Endpoint
(mg/L)
0.0076
0.00081
0.0035
0.0030
0.028
. 0.022
0.0037
0.010
0.12
0.59
0.0078
0.0092
0.010
0.0040
0.0040
0.020
0.0070
0.0070
0.0070
0.050
0.26
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