Evaporative Emission Regulations for
1978 Model Year Light Duty
Vehicles and Trucks
Analysis of Comments
Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
A	United States
Environmental Protection
June 1976

The Notice of Proposed Rulemaking for Evaporative Emission
Regulations was published on January 13, 1976. Fifteen motor
vehicle manufacturers, one environmental organization, the re-
search subsidiary of a petroleum company, the State of California,
a manufacturers' association, and an equipment manufacturer,
responded to the request for comments. The respondents are
listed in Table 1.
The responses were, in general, directed toward the areas of
concern identified in the Notice.
The consensus of the respondents was that the proposed change in
the test procedure is desirable; a six gram per test standard is
attainable; and implementation in 1978, while difficult, is possible.
Some manufacturers urged postponement until 1979.
Most of the respondents argued that a two gram per test standard
is unattainable, or at least not attainable by 1979 - esspecially if
vehicle background hydrocarbon emissions are included in the mea-
surement .
The analysis of comments resulted in no major changes to the test
The analysis of comments consists of the following items:
1.	A brief statement of each issue;
2.	A description of each respondent's position regarding
the issue;
3.	A discussion and analysis of the issue; and
4.	Recommendat ions.
This analysis of comments deals only with the 1978 procedure and
standards. The comments regarding the 1979 and later 2 g/test stan-
dard are discussed in a separate package.

Table 1
List of Respondents
1.	American Motors Corporation (AMC)
2.	Automotive Environmental Systems, Inc. (AESi)
3.	British Leyland
4.	California Air Resource Board (CARB)
5.	Chrysler Corporation (Chrysler)
6.	Exxon Research and Engineering Co. (Exxon)*
7.	Fiat
8.	Ford Motor Company (Ford)
9.	General Motors Corporation (GM)
10.	Honda Motor Co. (Honda)
11.	International Harvester (IH)
12.	Mercedes Benz
13.	Motor Vehicle Manufacturers Association (MVMA)
14.	Natural Resource Defense Council (NKDC)
15.	Niaaati Motor Co. (Nissan)
16.	Renault, Inc.
17.	Toyo Kogyo, Co.
18.	Toyota Motor Sales, U.S.A., Inc. (Toyota)
19.	Volkswagen
20.	Volvo
* Although Exxon Research and Engineering Co. responded on behalf
of its corporation, it should ^e noted that Exxon Research and
Engineering was a contractor to EPA to explore evaporative emission
control technology. The subsequent discussions differentiate be-
tween the contract study results and Exxon's corporate response
to the NPRM.

Analysis of Comments
(6 g Standard)
Description	Page
"Feasibility and Lead Time Requirements of a
6 g/test Standard 		1
"Cost of a 6 g/test Standard		5
"Evaporative Family Concept for Certification		7
"Durability and Evaporative System Deterioration 		14
"Need for Evaporative Regulations, 		
"Background Emissions		31
"Test Variability		41
"Vehicle Preconditioning 		45
"Amount of Fuel Used for Preconditioning		49
"Soak Time Between the Preconditioning Drive and the Start
of the Cold Start Exhaust Test		51
"Pressure Check of Fuel System		52
"Length of Enclosure Purge 		54
"Diurnal Test		55
"Ambient Temperature During the Diurnal Test 		60
"Use of Type "T" Thermocouples		61
"Time Between the Diurnal and Exhaust Emission Test Phases ...	63
"Heat Build Required Prior to Non-Evap Vehicle Exhaust Test. . .	64
"Determining the Need for a Running Loss Test		65
"Time Between the Exhaust and Hot Soak Test Phases		66
"Length of the Hot Soak Test		69
"Maximum Hot Soak Temperature		70
"Enclosure Specifications		73
"Air Circulation in the Enclosure		76
"Enclosure Calibration 		78
"Enclosure Background Measurements after Maintenance 		79
"Evaporative Emission Hydrocarbon Recording System 		80
"FID Fuel for Evaporative Emission Measurements		81
"Calculation of Evaporative Emissions		83
"Calibration Gases 		86
"Evaporative Testing at High Altitude		89
SI Units		92
"California Procedures 		93
"Miscellaneous Comments and Changes to Regulations 		94

Issue - "Feasibility and Lead Time Requirements of a 6 g/test Standard"
An evaporative emission standard of 6 g/test.is proposed for
the 1978 model year vehicles. This section deals with the technical
feasibility and time requirements for meeting this regulation.
A. Summary of Comments
AMC - "Carburetors for both our six cylinder and eight engines
will require venting changes to meet a 6 g/test standard. Lead time
requirements for incorporating these carburetor changes are approxi-
mately 40 weeks after satisfactory systems have been defined by our
various Engineering groups. At this time, we are confronted with a
very tight schedule if we are to meet SHED requirements for 1978
across our entire product line. Any unexpected problems could seriously
jeopardize our certification schedule and our ultimate production
British Leyland - "In our present development situation we are
not in a position to comment on the proposed 6 gram test standard
and it will be a little time yet before we shall have completed
tests which will enable us to make meaningful comment."
Chrysler - "In order to meet or approach the proposed evapor-
ative emission standard of 6 g/test, it has been estimated that
at least the following design changes would bei required to
Chrysler's present and planned engine offerings:
a.	Vent carburetor bowl to the charcoal canister
b.	Add two-way vent (mechanical or solenoid operation)
to carburetor."
Exxon - "We think that the proposed standard of 6 grams per
SHED test for the 1978 model year is a reasonable standard."
Fiat - "The Fiat certification process lasts, on the basis
of our experience of the previous certifications, from the
presentation of Part I application to the obtaining of the
certificate of conformity, about ten months. Fiat suggests that
the 6 g/test standard be postponed to the 1979 model year."
Ford - Ford has successfully developed evaporative emission
control systems that would allow emission data vehicles to meet
a 6 g/test standard, and there appears to be sufficient lead time
to produce these components for the 1978 model year. The systems
have been designed to function for 50,000 miles of operation
without deterioration. However, no durability testing has yet
been conducted, and due to the short time remaining, cannot be

conducted prior to the start of 1978 certification. Consequently,
Ford recommends that the proposed regulations for a 6 g/test
standard for 1978 be revised to delete deterioration factors.
If durability verification is required for evaporative
systems, Ford would like to be permitted to do this by appropriate
design verification tests. These would be done in lieu of 50,000
durability vehicle tests. If these tests showed deterioration of any
systems, those particular systems would then be subject to 50,000 mile
vehicle durability tests for the determination of a deterioration
GM - A 6 g/test evaporative emission standard is technically
feasible. If this were the only new regulation being promulgated
for the 1978 model year, GM might not consider it particularly
burdensome. However, the (exhaust) emission standards for the 1978
model year are yet unknown, fuel economy standards begin in 1978
and there are proposed new light duty and heavy duty truck standards
for the 1978 model year. The combination of these factors, along
with other emission regulations, becomes overwhelming.
"As for the lead-time factor, our normal tooling release date
will have passed by the time these regulations are promulgated.
Although possible, compression of this lead-time would create ad-
ditional expense and complication in the introduction of our 1978
There also has not been enough experience with the SHED pro-
cedure to establish measurement precision. Postponement of the
regulations for one year would provide experience with the procedure on
California vehicles. This would also minimize the risk involved in
introducing the new hardware by applying it to a limited number of
vehicles. GM strongly recommends that the regulation be postponed
until the 1979 model year.
IH - Preliminary investigations indicate that the present
California heavy duty evaporative system with revisions may be
capable of meeting the 6 g/test 1978 standard. Estimated changes
required to meet this standard are canister location and additional
vents and hoses.
Nissan - "It will be possible for us to install additional
controls to satisfy the 6 g/test requirement in time for 1978 model
year production. Baseline emission data indicates that the
electronic fuel injection vehicle will meet the standard with no
modification to the present vehicle. However, additional controls
are needed to some carbureted vehicles to meet the 6 g/test standard.
For these vehicles, the results from our experimental work tell us
that it will be possible to comply with the proposed 6 g/test
standard, applying a carburetor external vent connected with the

Toyo Kogyo - "We believe it would be difficult to comply with
the EPA proposed standard of 6 g/test for 1978, and would recommend
it be implemented for the 1979 model year due to the following
A.	Although we have purchased SHED equipment, we would
require more time to establish the measuring techniques
that would enable us to make accurate evaluations,
because we consider that the test result variations we
have experienced are due to the measuring method.
B.	Due to the time consuming measurement procedures, a
considerably longer period of time would be required
for us to develop appropriate control systems. We
consider the standard would require a considerable
degree of modification to the current evaporative
emission control systems, including reviewing basic
factors such as fuel system design, control of ambient
temperature around the carburetor, and various kinds
of sealings. Furthermore, the EPA proposal would have
a far-reaching effect on the reliability, product
acceptability, and productivity of the total systems
which we will have to confirm.11
Toyota - "As a result of our recent efforts, our new evapora-
tive emission control system has progressed to such a level that
we may be able to satisfy the proposed California and EPA evapora-
tive standard of 6 g/test in 1978. It is desirable that the evapora-
tive regulations based on the SHED method be implemented at the same
time that the exhaust emission standards are revised in order to
make the certification work efficient and to save certification
costs and testing time."
Volkswagen - "The time for development and certification is 2.5 years
after the law has been issued."
B. Discussion
The comments received generally indicate that a 6.0 g/test standard
is technically feasible and that, although the schedule will be rather
tight, it can be implemented for the 1978 model year. Three manu-
facturers (Fiat, GM, and Toyo Kogyo) recommend that the standard be
postponed until the 1979 model year, but do not say that the 1978
compliance date can't be met. Only Volkswagon, with the lead time
estimate of 2.5 years from issue of the regulation, indicates that they
cannot meet the 1978 date. Volkswagon gives no breakdown of the tasks
included in the 2.5 years lead-time requirement.

Ford states that there is not enough remaining time to conduct
durability testing before the start of 1978 certification, and recom-
mends deletion of deterioration factors for 1978. While some of
Ford's 1977 durability vehicles started mileage accumulation in
September 1975, others did not start until March, 1976. If the 1978
models follow a similar schedule, there are several months remaining
before mileage accumulation would begin on the durability vehicles.
So time is available for durability testing.
Ford also said that, if durability testing were required, it
would like to do this by design verification tests rather than 50,000
mile vehicle tests. It is EPA's judgment that it is very difficult to
incorporate in a laboratory test, all the conditions that will occur
in 50,000 miles of vehicle operation. It is essentially impossible to
predict all the conditions to which an emission control system will be
exposed in day-to-day vehicle operation. Since the emission control
systems which will be used for meeting the SHED test requirement are
of new (or at least modified) design, vehicle durability data is
essential. (See "Durability and Evaporative System Deterioration"
issue for additional detailed discussion).
GM's greatest concern with meeting the 6.0 g standard in 1978
appears to be the number of other regulations which may be implemented
in that same year. However, some of the regulations which GM listed
will not be implemented with the 1978 models. The heavy duty truck
standards are being proposed for the 1979 model year. As of this
analysis Congress is also considering amendments to the Clean Air Act
which might provide relief in either implementation dates and/or
emission standards for Light Duty Vehicles.
In regards to GM's comment on measurement precision, the most
recent data available to us are results of the EPA-MVMA SHED cross-
check study. This program consisted of multiple SHED tests on two
vehicles at the facilities of AMC, Chrysler, EPA, Ford, and GM. The
standard deviation of the means between facilities was 15% for one
vehicle and 7% for the other. This Is no greater than typical vari-
ation in exhaust emission tests between facilities.
C. Recommendation
The 6.0 g/test standard is technically feasible and there is
sufficient lead time to implement it for the 1978 model year. There-
fore, the 6.0 g/test standard should be promulgated for the 1978 model

Issue - "Cost of a 6 g/test Standard"
In the Environmental and Economic Impact Statement associated
with the "Proposed Evaporative Emission Regulations," the sales
weighted increase in vehicle retail price required to meet a 6
g/test standard was estimated at $7.30. The following comments
were received regarding the costs involved in meeting a 6 g/te9t
evaporative standard.
A. Summary of Comments
Chrysler - For the 1978 model year, the retail price increase
per light duty vehicle is estimated at $6.00 over the 1977 models
(1976 economics).
Ford - Ford's current estimate of control system costs to
meet a 6 g/test standard for 1978 is a retail price equivalent of
$15.00 per vehicle.
GM - It is estimated that the cost to the consumer for hard-
ware necessary to comply with the proposed 6 grams of hydrocarbon
evaporative emission test (SHED) will be in the area of $1 to $4
per car over the current 1976 models.
Nissan - Retail cost Increase from 1977 model is estimated
as follows:
A.	Carburetor vehicle (per vehicle)
Carburetor external vent (with solenoid valve) $4.20
Canister size up 	$1.80
Total	$6.00
B.	Electronic fuel injection vehicle: No cost increase.
Assumption: Current price level
1 U.S. dollar = 304 Yen
Toyota - The price per vehicle increase to meet a 6 g/test
standard on the 1978 model vehicle is expected to be approximately
IH - IH estimates the system cost to the customer at $32.00
per vehicle (in 1976 dollars).
B. Discussion
The range in vehicle price increase estimates supplied by
the manufacturers was greater than anticipated, especially among
the three largest U.S. automakers. GM estimated a range of $1 to

$4 and Ford estimated a cost of $15. Apparently the proposed control
systems to be used by these manufacturers may be quite different,
although the range in the evaporative emission levels of the 1976 model
vehicles from these two manufacturers is not substantially different.
The reasons for the substantially higher Ford estimate could not be
ascertained. However, this suggests either a low cost effectiveness for
the Ford system or that the Ford system was targeted for lower emission
Exxon Research and Engineering has recently conducted a test
program for EPA which investigated the cost of vehicle modifications to
reduce evaporative emissions. As part of this program, the evapor-
ative control systems of six production passenger cars were modified
using several different types of modifications in order to demonstrate
lower emission levels. At some point in the modification program, all
vehicles reached an evaporative emission level below 6 g/test. A sales
weighted average of the estimated increase in vehicle retail price for
these modifications was about $2. Although this cost estimate is based
on limited data, it is in agreement with the cost estimate of $1 to $4
which was supplied by General Motors. Thus, it would appear this
estimate of the cost of a system for compliance with a 6 g/test standard
seems reasonable.
Based on the cost estimate received from the manufacturers, the
sales weighted vehicle retail price increase required to meet a 6 g/test
standard (assuming $2.50 for GM vehicles) is $7.40. The sales data were
obtained from "Automotive News" for the 1974 model vehicles as listed in
the "Environmental and Economic Impact Statement" for this regulation.
This sales weighted price increase of $7.40 is in agreement with the
price increase estimate of $7.30 which was contained in the "Environ-
mental and Economic Impact Statement". The $7.40 estimate is higher
than the $2 estimate made by Exxon primarily due to the high $15 cost
given by Ford. For estimating the economic impact of a 6 g/test standard
it would seem most appropriate to use the manufacturer's sales weighted
average of $7.40. However, it is concluded that compliance with a 6
g/test standard is possible for a $3/vehicle average cost increase.
C. Recommendat ion
Some recent data indicate that the required increase in sales
weighted vehicle retail price may be as low as $2.00. It is recommended
that a cost increase of $7.30 be retained for cost-effective and eco-
nomic impact considerations because it agrees with the sales weighted
average of the manufacturer's estimates.
(1) Clarke, P.J., "Investigation and Assessment of Light Duty
Vehicle Evaporative Emission Sources and Control," Exxon Research
and Engineering, EPA Contract #68-03-2172, April 1976.

Issue - Evaporative Family Concept for Certification
The NPRM proposed a new certification scheme for determining
evaporative compliance in the interest of improved sampling of
manufacturers' product lines with respect to evaporative parameters
and in the interest of reducing the total evaporative testing
burden. Comments were requested on the proposal in terms of
potential savings and in terms of problems which may arise in
attempting to integrate the evaporative family concept into the
existing engine family concept of certification.
A. Summary of Comments
AMC - "We endorse the evaporative emission family concept,
however, its interpretation and possible application raises
questions, especially in the area of alternate suppliers for
items such as charcoal canisters. (We currently have three
sources). We request further definition of this vital concept,
especially in light of the recently proposed 1978 light-duty
truck regulations."
Chrysler - Chrysler comments that the definition of evaporative
emission families is not entirely clear to them. They ask several
specific questions about the limitations placed on the allowable
variation in components to be classed within the same evaporative
emission family. The final Chrysler comment on the issue is
"that the definition of evaporative emission families be more clearly
Fiat - "The introduction of criteria, which further dif-
ferentiate the various models within an engine family, may Involve
a greater number of vehicles to be tested for certification, with
consequent burden of cost and time both for the Manufacturers
and EPA." In Fiat's estimation, a particular problem exists
for manufacturers who use only one basic evaporative emission
systems for their whole product line, because the new criteria
force a subdivision of each engine family into different evaporative
"Fiat suggests therefore that the criteria for evaporative
families in the final rules be revised to take in due consider-
ation this situation."
Specific comments are:
1. A tolerance on design working capacity needs to be indicated
as a limitation for evaporative emission family criteria.

2.	Canister housing material has no Influence on evaporative
emissions and should be eliminated as an evaporative family criterion.
3.	Determination of evaporative families based on carburetor
model Is too restrictive, the word "model" must be deleted and
replaced by "type or configuration".
4.	Determination of evaporative families baaed on different
fuel filler cap retention mechanism will not minimize testing. The
criteria should be revised from "seal mechanism and retention
mechanism" to "sealed type or with ventilation valve".
Ford - Ford basically supports the evaporative emission "family
concept". However, Ford recommends that, because there is a general
lack of data regarding the effect of family determinators on the
DF, EPA specify family determinators more generally in the Federal
Register so that the MSAPC Advisory Circular system can be used to
modify family determinators on a much more timely basis as technical
input becomes available.
Specific areas on evaporative family determinants which Ford
recommends be revised are:
1.	Basic canister design - Parameters to be limited should
be an Advisory Circular topic rather than in the regulations.
2.	Carburetor type (IV vs. 2V vs. 4V) or fuel injection
type should be the family criteria not carburetor model or features
such as external carburetor bowl vent or purge control valves.
3.	Fuel tank and fuel filler cap parameters should be advisory
circular topics rather than in the regulations.
In discussion of the problems which might arise from in-
tegration of the evaporative family concept into the exhaust
emission family concept Ford points out the following:
1.	The relationship between exhaust and evaporative
emission "family" certification is not fully defined. It appears
that a test vehicle failing evaporative standards would not be
certified until it passed both exhaust and evaporative standards,
while a vehicle falling exhaust standards and passing the evapor-
ative standards would still be certified for evaporative emissions.
Ford recommends that the regulations permit the manufacturer to
demonstrate, where applicable, that the evaporative and exhaust
emission characteristics are not related, so they can be certified
2.	The proposed regulations indicate that after an evaporative
emission family has been certified, EPA may waive further evaporative
emission testing, currently conducted in conjunction with
certification of running changes.
These issues should be clarified in the promulgated regulations.

GM - "Creating additional engihe families on the basis of dif-
ferences in evaporative emission control systems cannot be justified.
Therefore, separate engine families for evaporative emission control
systems should not be required."
"We believe that SHED testing of exhaust emission certification
data vehicles would provide more than adequate demonstration of
compliance with evaporative emission standards. The addition of the
proposed Evaporative Emission Family is not needed".
Based on the 1977 product line, GM estimates that 25 durability
vehicles would be required solely to establish evaporative deteriora-
tion, (assuming the capability of exhaust emission data carryover
to meet 1978 exhaust standards). GM feels this represents a
considerable burden to both EPA and industry.
IH - The evaporative emissions family criteria as related to fuel
tanks does not address dual fuel tank3, fuel tank shape or location.
Clarifications in the regulations are needed.
The evaporative emission family criteria include such
items as canister housing material, basic fuel filler cap type etc.
IH fails to see the reason for such items to be included as family
criteria. Emission data vehicle testing would be sufficient to
evaluate optional designs in these areas. The same procedure
should be used for dual fuel tank approval.
Mercedes Benz - "DB asks that an advisory circular be
issued shortly after issuing the final evaporative emission
regulations in order to clarify under what conditions evaporative
control systems are considered to represent the same evaporative
control system family."
Nissan - The concept of Evaporative Emission Family is considered
quite reasonable. It will be very desirable and favorable for both
EPA and manufacturer, as mentioned in the proposed regulations,
if testing loads can be reduced by introducing this concept
into certification program.
Toyota - ..we feel that it should not be required that the
effects of a change in the canister working design be evaluated
by using the durability data vehicles because, if other conditions
of the system are the same, then a change in the working capacity
of the canister would have little effect on the deterioration
factor of the evaporative emission.11
"If our comments are not accepted as plausible, then some
reasonable tolerance for the canister working capacity should be
considered in the determination of the evaporative family."

B. Discussion
It is apparent from the comments that there may be a misunder-
standing of the evaporative emission family concept. Some manu-
facturers that do understand the concept do not support it because
they feel it does not represent a reduction in testing during MY
1978. These manufacturers do not understand the implications of
the regulations for evaporative testing for 1978 if the existing
"engine-system" concept remains unchanged.
The existing definition for "engine-system combination" is an
engine family-exhaust emission control system - fuel evaporative
control system combination. The requirements for certification
require that for each "engine-system combination a durability vehicle
generate deterioration factors for HC, CO, NOx and evaporative HC,
and at least one emission data vehicle generate 4000 mile emission
values for HC, CO, NOx and evaporative HC." A provision exists for use
of data from a previously certified vehicle to satisfy the require-
ments in lieu of a manufacturer actually testing durability and emis-
sion data vehicles. It is this provision that manufacturers argue
will allow them to use carryover exhaust emission data for 1978 if
the exhaust emission standards are not significantly different in
1978. They .view the testing required under the proposed evaporative
emission family regulations as a significant increase over little or
no testing (substantial or complete use of carryover). The fact that
both the test procedure and standard for evaporative emissions will
change for 1978 will require complete recertification under the cur-
rent certification requirements because no evaporative carryover can
be allowed for any engine-system combination as no previously certified
engine-system combination will have generated evaporative emission
data according to the 1978 procedures.
The proposed evaporative emission family concept should in
fact significantly reduce the evaporative emission testing that
would be required by the current certification scheme of engine-
system combination.
Two manufacturers apparently interpreted the evaporative emission
family concept incorrectly as a subgrouping within established engine
families with resultant testing required for each evaporative family
within each engine family. These manufacturers would not support the
evaporative family concept due to the apparent proliferation of test-
ing requirements. The concept of evaporative emission family is that
the product line is evaluated for its evaporative emission characteristics
independently of its engine family groupings, when vehicle configur-
ations are specified separately for both exhaust emission testing and
evaporative emission testing. At the point where the vehicle require-
ments for both standards are specified, then the product line is
examined to see if a single vehicle can satisfy both requirements. In
the case of a small manufacturer with a narrow product line and only
one evaporative emission control system (by the current definition

this is solely a function of vapor storage method; i.e., canister, air
cleaner, crankcase), the new evaporative emission family concept could
divide his single "control system" into more than one evaporative
emission family based on parameters which vary between the models of his
product line. If the new criteria created more evaporative emission
families than engine families, it would result in an increase in testing
requirements compared to the testing requirements under the current
A study of 1976 and 1977 light duty vehicle evaporative emission
control systems with respect to the proposed evaporative emission
family concept was conducted to determine to what extent a further
division of existing engine families might occur (rather than the
expected consolidation of existing engine families into fewer evapor-
ative families), only three cases occurred which a potential increase in
testing might have been realized. In each such case, the additional
testing would have been one durability and one emission data vehicle as
only one vehicle in the product line employed the unique system components.
The purpose of the evaporative emission family concept is to more adequately
evaluate the performance of the evaporative control system. A side
benefit of the concept was that it would involve less testing as most
manufacturers do not use very diverse evaporative emission control
systems. The principle of more accurately evaluating the performance of
the evaporative control system should not be compromised in the interest
of the few manufacturers who choose to proliferate their evaporative
controls. The performance of the controls must still be evaluated in
these cases.
Some manufacturers proposed revisions to the evaporative emission
family criteria, or the application of tolerances to those existing
criteria. In general, the manufacturers would prefer to have the
evaporative emission family criteria expressed in general terms in the
regulations and allow tolerances to be applied by the MSAPC Advisory
Circular system on a timely basis as technology changes. The concept is
commensurate with that currently employed for engine family and exhaust
emission control system definition. The method suggested by the manu-
facturers is the approach which should be followed in the final regula-
tions. Additional input on the values of tolerance which should be
applied and specific recommendations for revisions to the criteria for
evaporative emission family determinants would be useful in revising the
family and control system criteria in the proposal.
The criteria which will determine evaporative emission families
will be expressed in general terms in the regulations but this does not
eliminate EPA's concern that the parameters originally identified are
significant when evaluating the evaporative performance of a vehicle.
The canister parameters which are considered to be significant are the
vapor absorption capacity, the housing material and the general configuration
including vent and purge mechanism. Several manufacturers suggested
that tolerances might be applied to the canister working capacity.

Application of tolerances to the canister working capacity would allow
manufacturers to combine families which would otherwise be separated
because of different canister capacities. An examination of existing
product lines shows that an application of reasonable tolerances on
canister capacity would not group any families that would otherwise be
separated. None of the manufacturers who suggested that a tolerance be
applied suggested levels of tolerance which could be applied nor did
they explain the reasons for this request. The canister housing material
is considered since it has an influence on the life of the absorption
material and that the housing integrity has an influence on the retention
of the absorption material as well as the fuel vapors. The canister
configuration to the extent detailed in the NPRM has an influence on the
basic canister performance with respect to loading, breakthrough and
purge characteristics of one canister as compared to another configuration.
The fuel system parameters were probably the most misunderstood
parameters, particularly the carburetor related items. The specifica-
tion of carburetor model was an attempt to characterize the type of
significant differences in evaporative emission related parameters that
EPA considers necessary to evaluate. Some specific areas of concern
are: fuel bowl size and vent configuration, purge controls, location of
fuel bowl with respect to the carburetor mounting flanges (as a heat
source) and general throttle shaft and accelerator pump shaft configurations.
The areas that are to be isolated are of an evaporative related nature
and carburetor model seemed like a convenient manner in which to isolate
these areas. After an examination of the carburetor model designations
from those manufacturers' product lines who specifically commented on
the issue, it became apparent that some non-fuel evaporative parameters
(as well as some non-exhaust emission related parameters) may in fact
determine a different carburetor model for these manufacturers. For
this reason, the criteria listed in the regulations were made general
enough to alleviate the problem.
The basic fuel tank type was considered important due to its
obvious function to store the fuel and to maintain integrity against
vapor or liquid loss through vent design, vapor control baffles, bladder
like liner, etc. The consideration of material enters here from the
standpoint of tank integrity against fuel or vapor loss. The fuel
filler cap is also of significant concern due to EPA's experience with
caps on test vehicles failing to pass leak checks. The cap retention
mechanism and seal mechanism both contribute to the integrity of the
fuel cap-fuel tank interface, and the variations in design have to be
In summary, the same parameters which EPA felt important to evaluate
for evaporative emission characteristics are still going to contribute
to the sampling plan to be adopted for certification as no manufacturer
has submitted any data or arguments that would adequately support a
recommendation to the contrary.

Ford was the only manufacturer commenting on potential problems In
Integrating the evaporative emission family concept into the existing
engine family concept of certification. In addition to the areas
pointed out >by Ford, some other revisions are necessary to eliminate
problems in applying the new evaporative emission family system to the
existing certification scheme. The primary issue is .that of vehicle
representation; i.e., a vehicle selected and tested for exhaust emission
compliance only, represents those vehicles of the same engine family-
exhaust emission control system; a vehicle selected and tested for both
exhaust emission and evaporative emission compliance represents vehicles
of the same engine family-exhaust emission control system as well as all
vehicles of the same evaporative emission family-evaporative emission
control system. This is because a vehicle may be tested Tor exhaust
emission compliance without requiring an evaporative emission compliance
test. However, if the vehicle was selected for only evaporative emission
compliance determination, it would require both exhaust and evaporative
emission compliance testing. An issue related to vehicle representation
is that of options available to the manufacturer cshould a vehicle 'fail
to comply with either the exhaust emission standard, or the evaporative
emission standard or both. Revisions have been made to ithe .necessary
-sections of the regulations to clarify the procedures that will be
followed in the areas in question.
C. Recommendations
The proposal for evaporative emission 'families as a certification
scheme should be maintained. The evaporative emission "family criteria
should be modified *to provide good decriptions of .the xr'lteria.
The areas in the regulations which provide for integration .of the
evaporative emission family concept into the existing exhaust emission
family scheme should "be revised to provide clarity.

Issue - Durability and Evaporative System Deterioration
The certification method proposed in the NPRM for determining
evaporative emission compliance was patterned'after the existing certifi-
cation procedure.
Initially, each manufacturer's planned product line is divided
into major groups (evaporative families) based on similarities in
basic emission-related characteristics of the vehicles and their
evaporative control systems. Because It is believed that changes in
various fuel system and emission control system calibrations are
likely to have a significant effect only on absolute emission levels,
and not on changes in emission levels with use, separate evaluations
are made for emission deterioration characteristics and for low mileage
emission levels.
For each evaporative family, generally one prototype vehicle is
built and operated by the manufacturer over 50,000 miles of use.
Mileage accumulation is substantially accelerated over what would be
typical in actual use. Emission measurements are made on each vehicle
at 5,000 mile increments, ending with the 50,000 mile test. Generally
a single emission test is performed at each mileage point. Test
results for the 5,000 mile through 50,000 mile test points for each
vehicle are then used to estimate a linear emission deterioration rate
for each pollutant for each vehicle. Finally, deterioration factors,
which represent the difference between the 50,000 mile to 4,000 mile
values of the linear approximations, are calculated.
To evaluate the various different system calibrations that may be
used within a given family a somewhat larger number of prototypes
(generally two to six) are built and operated to 4,000 miles at which
point they are emission tested. These emission data vehicles are
selected based on the manufacturer's projected sales of different
designs within the evaporative family as well as on design character-
istics judged likely by EPA to lead to higher emissions than other
designs in the same family. A single emission test is performed on
each vehicle, although if a vehicle is judged to have failed a standard
(by a process to be described subsequently) the vehicle may, at the
manufacturer's option, be retested. In that case, the second set of
emission results is used.
Compliance of a vehicle with standards is determined by adding
the appropriate deterioration factor determined in the 50,000 mile
testing to each emission data vehicle's 4000 mile emission value. The
resulting value for each pollutant must be equal to, or less than, the
respective standard. For an evaporative family to be approved (certi-
fied) for sale, all emission data vehicles tested in that family must
comply with the standard. Systems represented by emission data vehicles
which fail must be redesigned and retested until they do comply, or
must be dropped from the planned product line. In the latter case,

additional vehicles may have to be tested to A,000 miles to make up
the full complement of test vehicles required for that evaporative
A. Summary of Comments
Chrysler - "The EPA has failed to demonstrate that evaporative
emission systems significantly deteriorate during the useful life of
the vehicle. Therefore, the inclusion of evaporative emission de-
terioration factors for certification purposes is inappropriate."
Chrysler states that, to date, experience (no data provided) shows
that significant evaporative system deterioration does not exist and
that EPA should prove that deterioration does exist prior to requiring
durability testing to certify evaporative control systems.
Chrysler also points to the statistical variability associated
with the test procedure and use of only a single vehicle to determine
deterioration factors as reasons against required durability testing.
Chrysler recommends "that deterioration factors be omitted from
the final rulemaking until a need and an objective method for the
inclusion of such a factor is demonstrated."
Ford - Ford's position regarding the proposal is as follows:
"Ford has successfully developed evaporative emission control
systems that would allow emission data vehicles to meet a 6 gin/test
standard when tested by the SHED procedure. However, no durability
testing has yet been conducted on these systems and, due to the short
time remaining, cannot be conducted prior to the start of 1978 certifi-
cation. Further, Ford believes that we can adequately demonstrate
that there is in fact no need to establish deterioration factors for
the Ford evaporative emission control system. Ford proposes that EPA
establish optional procedures that permit a manufacturer to show that
the evaporative emission control system would function adequately
during its lifetime by either of the following methods:
1. Verify the mechanical integrity of the evaporative control
system by demonstrating a high component lifetime reliability through
appropriate design verification testing. Such verification testing
would be in lieu of running a certification car for 50,000 miles and
periodically measuring evaporative emissions to establish a deterior-
ation factor. In effect, the verification tests would be required to
demonstrate that no deterioration of the system would occur.

2. Conduct 50,000 mile certification vehicle tests to
establish appropriate evaporative system deterioration factors
for those systems that do deteriorate.
With respect to option 2 above (deterioration factor testing!,
it must be noted that no data currently exists at Ford or to our
knowledge within the public domain, to show a 6 gm/test SHED
evaporative emission standard that includes system deterioration
as being technologically feasible.. Accordingly, Ford recommends
that the proposed regulations for a 6 gm/test SHED standard for
1978 be revised to delete deterioration factors."
GM - "We believe that sufficient data exist to demonstrate
that the GMEC System does not deteriorate with mileage accumula-
tion. Certification data, albeit obtained by the charcoal trap
method, show that the deterioration factors generated by the GMEC
System are equal to 0.00." The data GM presents is combined
evaporative emission deterioration factor data for various model
years (1973 through 1975). These data are carbon trap data and
are basically an average deterioration factor for vehicles tested
for the particular model year. The resultant D.F.'s were all
negative (lower high mileage emissions than low mileage).
The SHED data presented by GM, based on tests of 1972 certifi-
cation vehicles, shows a deterioration factor spread from -7.07
to +2.37, the average was -1.21.
"It seems clear to us that, this substantial history clearly
demonstrates that the GMEC System does not deteriorate with use,
and therefore no deterioration testing should be required.
Compliance with standards would be shown by SHED tests on data
cars only."
B. Discussion
Although their approaches differ, the three commenters on the
issue of evaporative system deterioration share the concept that
evaporative control systems do not deteriorate, Chrysler states that
experience shows that there is no deterioration of evaporative control
systems and that EPA should prove otherwise prior to requiring durability
testing. Ford has no deterioration information on their evaporative
control system when tested by the SHED procedure, and believe that no
data exist to support a 6 gram per test standard with evaporative
deterioration as technically feasible. Ford feels that some sort of
"design verification testing" could prove that certain systems do not
deteriorate. In some instances, however, Ford concedes that vehicle
durability testing may be required. General Motors supplies some data
to support their contention that their evaporative control system does
not deteriorate appreciably and that, therefore durability testing
should not be required.

The commenters' contention that evaporative emissions systems
do not show a deterioration is not supported by the information
supplied. The carbon trap data does not show significant deter-
ioration levels for the evaporative control systems certified
to date, but the carbon trap test does not measure all sources of
fuel evaporative losses. Some sources which will be measured by
the SHED technique, which were previously not measured by the
carbon trap technique, have a potential for significant deteriora-
tion. Some such sources are, carburetor throttle shafts, accelera-
tor pump shafts and bowl vent switches, all of which may provide
an increased evaporative loss due to wear. The fuel filler cap
has been the most significant single cause for leak down failure
in certification testing. The problem has been one of poor
sealing due to seal or retention mechanism deterioration. All of
these areas have a potential to significantly increase the fuel
evaporative losses with increased time and mileage.
The SHED data provided by General Motors which provided
average evaporative emission deterioration factors (average of
all deterioration factors) indicating a negative evaporative
deterioration is misleading for two reasons:
1.	The average evaporative emission deterioration may show
that for those GM vehicles tested, the average deterioration was
negative. The individual vehicle configurations and evaporative
emission system configurations represented, however, showed a
range in deterioration from -7.07 to +2.37. This indicates that
at least some systems did show a significant deterioration level.
The certification program does not address average deterioration
levels but specific deterioration levels for a distinct evaporative
system configuration; therefore, the information does show a need
to determine the system deterioration.
2.	The predominance of the negative deterioration factors
from the SHED data may not reflect actual evaporative fuel hydrocar-
bon deterioration due to the possibility of significant vehicle
non-fuel emissions (background) decay skewing the early test
points. GM did not indicate that any attempt had been made to
stabilize the non-fuel emissions levels from the test vehicles
included in the 1972 SHED sample. Decay of non-fuel emissions
could conceivably skew the measured SHED levels from a significant
portion of the durability testing.
The evaporative contribution of the vehicle over its life is
a combination of fuel evaporative losses and non-fuel evaporative
losses. The non-fuel evaporative losses exhibit a relatively
high level early in the vehicle's life, and then decay primarily
as a function of time. The fuel evaporative losses exhibit a
trend of increasing HC emissions primarily as a function of
mileage or cycles. The total evaporative contribution of the

vehicle is then relatively high when new, decreases with time to the
point where fuel HC losses become significant, and then begins to
increase with mileage towards the level of the new vehicle. Figure 1
exhibits this.
In summary, while previous carbon trap durability data indicated
little if any system deterioration, the new SHED test procedure provides
a method of measuring all fuel evaporative losses from a vehicle and
thereby enables an evaluation of the deterioration characteristics of
the total fuel system as well as the evaporative control system. The
limitations of the previously used test procedure did not allow an
evaluation of certain components that technical judgment indicates may
deteriorate significantly. The data presented by GM that was generated
by a SHED test procedure bears out that some evaporative control systems
do deteriorate significantly. Therefore this evaporative deterioration
should be quantified, if possible, to assess the evaporative performance
of the vehicle over its useful life.
The question that now arises is how can EPA evaluate the fuel
systems and evaporative control systems to be used on new vehicles to
determine 1) if a system deteriorates and if so, 2) how much does that
system deteriorate? A test procedure to evaluate system durability must
focus on the intended function of the system and on the evironment in
which it will operate to identify the possible failure modes, and then
establish criteria for acceptable performance in view of the failure
The purpose of the evaporative control system is to control the
loss of fuel vapor from the vehicle. The predominant control technology
currently used is that which stores the fuel vapors during non-operational
vehicle modes and then "purges" the storage mechanism and burns the
vapors during operational vehicle modes. The control and the sequencing
of the storage and purging operations is critical for some systems and
therefore some additional hardware is required to accomplish this control.
With the advent of the SHED test technique, particular attention must be
given to total fuel system integrity as well as the evaporative control
system, as any leakage may be a significant source of vapors. The
environment in which this system must function is that which is encountered
in typical consumer usage of the vehicle. The potential failure modes
of individual components are numerous and will be treated later. The
synergistic effects of fuel and evaporative system operation with respect
to all other vehicle systems must be evaluated. In any system, proper
operation depends on the function of all components as any single failure
may induce other component malfunctions, and in the case of the fuel
system and the evaporative control system, a failure in some related
vehicle system may adversely influence evaporative emissions levels.
For example, a failure in a carburetor air cleaner seal which allowed
the induction of excess air might reduce the "purging" of the fuel vapor
storage medium and thereby allow excess fuel vapors to escape. The same
failure may also allow carburetor fuel vapors to escape into the atmosphere.

Total Vehicle Evaporative Emissions
total vehicle
orative emissions
fuel evaporative
non-fuel evaporative
5 years
0 non-fuel evaporative emissions time scale
0 fuel evaporative emissions mileage scale ^- ^ . 50,000 miles
Figure 1

The criteria for acceptable performance of the systems are dictated
by the Clean Air Act where vehicles are required to meet emission standards
for their useful life (50,000 miles) and control system components are
required to be warranted by the manufacturer for the same period with
reasonable maintenance precautions. EPA, in the case of Evaporative
Emissions is then required to determine:
1.	That the evaporative emissions control systems are designed
to not exceed the standards for 50,000 miles and
2.	That maintenance of the control system is reasonable in
light of anticipated consumer usage.
Because of these criteria, any malfunction or failure, whether partial
or total, and any change in performance of a component must be quantified
in terms of how many grams of evaporative hydrocarbons does this represent,
both directly, and indirectly through synergistic influence on the
related evaporative or fuel system functions. In addition, maintenance
required as a result of, or to prevent component or system failure
must be evaluated in light of customer usage to determine its reasonable-
Ford has suggested that some systems could be "design verification
tested" through a serious of functional checks of individual components,
following some cyclic tests designed to simulate the intended component
function and its expected environment. The immediate inadequacies of
this proposal which become apparent in light of the past discussion
1.	Inability to account for synergistic influences on component
2.	Difficulty of adequately simulating actual component environment.
3.	Inability to quantify in forms of evaporative hydrocarbon
losses, the various failure modes or variations in component performance.
4.	Inability to quantify in terms of evaporative hydrocarbon losses,
the various synergistic influences component failure or performance
variations may induce.
These same inadequacies limit any "design verification" type test
where the acceptance criteria are actual "real world" performance
characteristics of a total system. Even if this sort of test program
were designed to provide adequate information on single components,
or even total systems, if EPA required testing of this type, the result-
ing individual test programs would be diverse considering the number of
manufacturers, systems and applications. That is not to say that this
sort of testing is not useful. It becomes extremely useful in comparing
the performance of a component with that of a similar component which
has previously demonstrated that it functions satisfactorily in a system
which has demonstrated that it meets "real world" performance criteria.

Data generated by this type of testing is currently used in the LDV
Certification program for consideration of exhaust emission related
running changes and durability data carryover. This type of test program
would be very useful in conjunction with other types of durability
The time factors and time related failure modes and a few failure
modes related to engine off cycle cannot be adequately evaluated by the
present method of 50,000 mile durability vehicle testing that is used
for the evaluation of exhaust emission control durability, as the 50,000
miles are accumulated by continuous driving in three to six months rather
than the 5 years and numerous engine off cycles associated with vehicle
useful life. Not enough information is currently available on the
potential time related failure modes to determine the extent to which
time can influence fuel and evaporative system performance, and EPA
intends to investigate these issues. The commenting manufacturers have
proposed other methods of durability information on these aspects of
the systems. The influence of fuel tank and line oxidation, rubber
seal ozone aging, plastic component embrittlement and other similar
issues need to be explored.
C. Evaluation of Key Specific Issues
The key questions brought out by the manufacturers with regard to
durability testing are:
1)	Do fuel and evaporative emission control systems deteriorate?
2)	If so, how can system deterioration best be evaluated?
The data that are currently available indicate that there is a
strc/ng probability that present fuel and evaporative control systems do
deteriorate. SHED test results from a 1972 Surveillance Program study
showed an average emission level of 24 g/test on in-use vehicles. These
vehicles represented a statistical cross section of in-use vehicles.
The 24 g/test emission level is substantially higher than the 9 g/test
emission level which the manufacturer's contend is representative of new
car levels. The 24 g/test value has received criticism from the manu-
facturers who contend that actual in-use levels are much lower. GM has
tested 20 1970-72 GM vehicles which showed emission levels ranging from
2.45g to 28.4g with an average of 8.73g. However, EPA has evaluated the
surveillance program data in detail and has found no reason to believe
these data are incorrect. Evaporative emission levels measured in 4
other program studies in 1971 through 1973 showed average emission
levels from controlled vehicles above 20 g/test. Again this is much
higher than the manufacturer's value for new cars.
The results of the 5 surveillance programs imply that either the
condition of the vehicles prior to testing was different than the condi-
tion of the vehicles tested in other studies (due to preconditioning or

vehicle handling differences) or that the vehicle systems deteriorated
while in-use. It should be noted that vehicle preconditioning or handling
prior to testing should not have affected hot soak levels and that hot
soak levels measured in the surveillance programs were still much higher
than the 9g level measured for both the diurnal and hot soak by the
manufacturers. Thus, there is at least a strong implication based on
the surveillance programs that fuel and/or evaporative control systems
do deteriorate.
The fuel system and evaporative control system would, from an engineer-
ing point of view, be expected to deteriorate. The failure mode analysis
indicated that such things as valves, pumps and other moving parts would
be expected to wear out as a result of use. Also, some materials used
in th^se systems could also be expected to deteriorate with age, or as a
resul^ of exposure to high temperatures, vibration or foreign material.
The contention that these systems will not deteriorate, does not seem
reasonable considering the many failure modes possible.
Based on the above discussion it is concluded that there is evidence
that fuyl and evaporative emission control systems probably deteriorate,
and thaj: this conclusion is supported by an engineering evaluation of
expectep deterioration of certain fuel system components.
The second question that requires answering is "How can evaporative
emissiop control system durability be evaluated?" There is no question
of the need for such an evaluation: Available data suggests that there
potentially is deterioration of evaporative emission control effective-
ness, and Section 206(a)(1) requires the EPA to determine whether emis-
sion control effectiveness will be sustained for the useful life of
the vehicle. Nevertheless, the EPA is currently unable to specify a
single test protocol that can be demonstrated to be a valid durability
test for all vehicles likely to be produced; in the absence of being
able to specify a test protocol for which such a demonstration can be
made, there is little sense in specifying some arbitrarily selected
test protol, even if that test protocol were to be the traditional
50,000 mile durability test.
Much more experience and data is needed before the EPA can reasonably
expect to be in a position to design and specify a single test protocol
for evaluating the durability of evaporative emission control systems.
One way of providing such experience and data is to require each manu-
facturer, for such number of model years as it may take EPA to develop
and promulgate a single test protocol, to design his own test protocol
and to report the results of his testing to EPA as a part of the certifica-
tion process. It is recognized that some manufacturers may use this
opportunity for establishing their own test protocols as an excuse for
doing no testing at all; but if they do so, that will become apparent
very quickly, and would become a basis for prompt Federal remedial action.
It is also possible that through this approach all manufacturers will do
a responsible job of evaluating the durability of their evaporative emis-
sion control systems, and that in that manner there may never be a need

for the promulgation of a standardized durability testing protocol. In
any case, this approach provides the only feasible way, at the present
time, for generating any valid data on the durability of evaporative
emission control systems, data that can in subsequent years be checked
against the results of surveillance testing of in-use vehicles to
identify the valid and the invalid durability evaluation procedures.
D. Recommendations
The recommended procedure for establishing the deterioration and
durability espects of the evaporative emission families is to require
the manufacturers to perform testing to establish a deterioration factor
for each evaporative emission family. This testing should^faesigned by
the manufacturer to provide him with the data that he judges necessary to
quantify the evaporative performance of his various fuel system and
evaporative control system designs.
The manufacturer should be required to file his test plans with EPA
in his Part I Application for Certification. The manufacturer would be
expected to pursue his test plans to completion, and would be required
to provide in the Part II Application the data from the test plans and
the resultant deterioration factor for each evaporative emission family,
to be used in determining the adjusted evaporative level of the 4000
mile emission data vehicles tested by EPA. The projected 50,000 mile
levels of the 4000 mile emission data vehicles would then be used to
determine compliance.
This procedure will provide the manufacturer with the flexibility
of designing his own test programs to quantify evaporative emissions
deterioration and system durability without imposing the restrictive
requirement of the existing 50,000 mile durability vehicle test procedure.
EPA hopes to gain information from the variety of test plans which are
anticipated, based on NPRM Comments, to aid in the development of an
optimum certification durability test program for evaporative emissions.

Issue - Need for Evaporative Regulations
A 1973 surveillance test program used the SAE recommended procedure
for measuring evaporative emissions in a sealed enclosure. The results
of those tests on in-use 1973 MY vehicles showed a 31 g/test (diurnal
plus hot soak) emission level, which was stated in the NPRM. Recently a
computation error has been found which resulted in a lower average value
than the reported 31 g/test value. The actual average was 26.5 g/test.
Based on this and other studies, however, the current "carbon trap"
evaporative emission test has been found to greatly underestimate
evaporative emissions.
The 1972 surveillance test program, which was similar to the 1973
program, showed evaporative emissions at a 24 g/test level. The urban
gram per mile equivalent of a 24 g/test level is 1.76 g/mile as compared
to the current Federal hydrocarbon exhaust emission standard of 1.5
g/mile and the statutory standard of 0.41 g/mile. The amount of control
over evaporative emissions thought to exist does not in fact exist.
A study of the cost effectiveness of reducing evaporative emissions
to a 6 g/test level from the 24 g/test level indicated it would cost
$50/ton of pollutant removed. The cost effectiveness of reducing exhaust
hydrocarbon emissions from the current standard of 1.5 g/mile to the
statutory 0.41 g/mile level is between $500 and $1400 per ton of hydrocarbon
removed. The urgency of the proposed evaporative emission regulations
is based on the fact that a sizable reduction (24 g/test to 6 g/test)
can be made initially, the cost effectiveness is better than other
control actions, and if action is not taken evaporative emissions would
exceed and possibly nullify exhaust emission improvements from the
In a letter fypm the Motor Vehicle Manufacturer's Association
(MVMA) to the EPA , the validity of the 31 g/test level reported for
the 1973 surveillance program results was questioned. The validity of
the results has been questioned due to a study by the California Air
Resources Board (CARB), which indicates that a leak in the fuel cap
could have resulted during the tests due to the insertion of a thermocouple
wire through a drilled hole in the cap. Also, the MVMA cites the results
of testing done by the manufacturers which show emission levels on 1975
vehicles to be at a 9 g/test level instead of 31 g/test. It is, therefore,
charged that the environmental impact and the cost effectiveness of the
proposed regulations is not as good as indicated in the environmental
and inflationary impact study, and therefore, the urgency of the proposal
has been over-emphasized.
A. Summary of Comments
AMC - We believe that the 31 g/test assessment of in-use vehicles
may overstate the situation by as much as 50 percent. It is recommended
that more recent data be used to arrive at a more realistic conclusion.
(1) Letter from Lou Duffing, MVMA, to Ron Kruse, EPA,
January 15, 1976.

Chrysler - By utilizing the 31 g/test level, EPA's cost effective-
ness analysis shows $56/ton of pollutant removed. The 31 g/test level
is erroneously high and should actually be 9.06 g/test as reported in
the letter by MVMA. If one assesses the cost effectiveness of a 6
g/test standard using the 9 g/test level and a $6.00 retail cost to
achieve the 6 g/test standard, the cost effectiveness is $181'/ton. The
cost effectiveness of achieving the 2 g/test standard could be $630/ton
based on a cost of $50 per vehicle. The cost effectiveness of going
from a 6 g/test to a 2 g/test level is $1,023/ton. This analysis indicates
the cost effectiveness of the proposed regulations is grossly overstated
by the EPA. The cost effectiveness of going to the 2 g/test requirement
must seriously be reconsidered.
Ford - It is Ford's understanding that the 31 g/test average cited
as representative of in-use vehicles has been determined to be abnormally
high because of fuel tank vapor leaks introduced with the installation
of a thermocouple through the fuel cap. Actual levels from in-use
vehicles have been reported to be at a 9 g/test level.
GM - "EPA has greatly over estimated the contribution of vehicle
evaporative emissions as an atmospheric hydrocarbon source and therefore
ascribed unnecessary urgency to imposition of the proposed rules."
Volkswagon - Tests by EPA and CARB show test results of 2 g/test
and 11.7 g/test respectively on similar fuel-injected Volkswagons. This
discrepancy indicates that the amount of hydrocarbons emitted from a
motor vehicle is highly influenced by the service condition of the test
vehicle. The reliability of the surveillance program results is felt to
be very poor.
The relationship between exhaust hydrocarbons and evaporative
hydrocarbon emissions is significantly different from the estimation
made by EPA, because the maximum part of the exhaust hydrocarbons must
be considered to be reactive while only 20% of the evaporative hydrocarbon
emissions are reactive. Based on our analysis the contribution of
reactive hydrocarbons from evaporative emissions is only 0.04 g/mile
from uncontrolled vehicles. An average of seven 1975 and 1976 VW vehicles
showed an average evaporative emission level of 8 g/test. The corresponding
contribution of reactive hdryocarbons from these controlled vehicles is
only 0.06 g/mile.
B. Discussion
The consensus of the U.S. manufacturers is that the regulations are
not as urgent as previously thought due to inaccurate baseline data.
The 31 g/test (actually 26.5 g/test) level for current vehicles is
thought to be too high and the actual level is thought to be 9.06 g/test.
Volkswagon commented that evaporative emissions were not as serious as
exhaust emissions due to the higher relative reactivity of exhaust

EPA has responded to the letter from MVMA* (see section D of this
issue). The response from EPA indicates that the alleged leaking gas
caps should not have been a problem because pressure checks were per-
formed prior to each test with the test gas cap in place. Also, other
considerations lead us to believe that the Surveillance test results are
representative of in-use vehicles, as discussed in the attached letter.
Therefore, the 26.5 g/test value should be valid. The reason for the
discrepancy between the results of that test program and the results of
tests by the manufacturers has not been determined.
It should be emphasized at this point that the cost effectiveness
of the proposed action was not based on the data from the 1973 sur-
veillance program. Instead, it was based on the results of the 1972
surveillance study which showed emissions to be at a 24 g/test level,
because the 1972 results are published in Supplement No. 5 for the
compilation of Air Pollution Emission Factors, AP-42. Publication in
AP-42 is a result of close review of the appropriate data. The 1973
results have not yet received this review and were, therefore, not used.
The comment concerning the relative reactivity of evaporative
emissions compared to exhaust emissions makes the point that exhaust
emissions are much more reactive than evaporative emissions. The data
supplied by Volkswagon, however, did not show the relative magnitude of
the reactivity of both evaporative and exhaust hydrocarbons. Only data
on the reactivity of evaporative emission was given. Therefore, a
definitive statement concerning the comparative reactivity cannot be
Further, the definition of reactivity has not yet been agreed upon.
Reports** indicate that, "The most important findings from recent chamber
experiments, and also from some field work, is that practically all
organic compounds can be photolyzed given enough time for reaction."
The reactivity data supplied by Volkswagon shows compounds as being non-
reactive. Because of the uncertainty of the exact definition of reactivity,
their evaluation of the relative reactivity of evaporative emissions
seems questionable.
C. Recommendation
Implement the regulations according to the originally proposed
* Letter from Mr. Ron Kruse to Mr. Lou Duffing, March 4, 1976. (See
Section D of this issue.)
** Memo from Mr. R. Strelow, EPA, to the Regional Administrators,
January 29, 1976.

D. Letter from Mr. Ron Kruse, EPA, to Mr. Lou Duffing, MVMA,
March 4, 1976.
Mr. Lewis E. Duffing
Environmental Engineering Division
Motor Vehicle Manufacturers Association
320 New Center Building
Detroit, Michigan 48202
Dear Mr. Duffing:
This letter is in response to your critique of the report by Ellsworth
entitled "Assessment of Light Duty Vehicle Evaporative Emission Control
Technology". In particular we would like to address your comments
concerning the validity of the Surveillance Program (SHED) test results.
We would also like to get additional information from you concerning
your experience with some of the ideas expressed in that report suggesting
possible evaporative emission control strategies and their cost.
We are aware of the discrepancies between the evaporative emission
levels measured during the 1971 through 1973 Surveillance test programs
and emission levels measured by the manufacturers. The possibility that
leaks could have occurred where the thermocouple was inserted in the gas
cap prompted us to investigate the procedures used during the surveillance
programs. During all of the surveillance programs, the fuel thermocouples
were inserted through a drilled hole in the gas cap. Therefore, if a
pressure check of the fuel system was not performed prior to testing
with the test cap in place, a possibility did exist that an undetected
leak was present. Discussion with the contractors involved in the
various test programs indicated the following:
1)	No pressure checks were conducted for tests conducted during
1971, 1972, and 1973 programs conducted by Automotive Testing
Laboratories (ATL).
2)	Automotive Environmental Systems, Inc., (AESi) did not conduct
pressure checks during the 1971 and 1972 test programs, but they
did conduct a pressure check of the fuel system prior to each
evaporative emission test with the test cap in place during the
1973 surveillance test program. This procedure was spelled out in
the test procedure flow chart used during each test and the procedure
was verified by the contractor. (See attached flow chart). One of
the gas caps with the hole for the thermocouple drilled in it was
supplied to EPA. Pressure checks indicated that this cap did not

Therefore, we are reasonably certain that for at least the AESi
1973 program, the modified gas caps did not leak. This is the program
cited in Ellsworth's paper. Since gas cap leaks did not contribute to
the 31.5 g/test level found in 1973, we doubt that gas cap leaks were a
significant factor in any of the other studies. Particularly since
results of the other studies were below 31.5 g/test.
Even if the gas caps did leak, the change in the effect upon air
quality would be relatively small. A leak in the gas cap should not
have had a sizeable effect on hot soak emissions measured, because most
of the hot soak losses would be from the carburetor bowl. The only
effect of a leaky gas cap would be to increase emissions due to increasing
tank temperatures forcing fuel vapors out of the hole in the gas cap.
Fuel temperatures during the surveillance testing did rise 1-2F during
the hot soaks.
A simplified approach for estimating the contribution from the fuel
tank to total hot soak losses would be to subtract the portion of the
diurnal loss value corresponding to a 2F temperature rise from the
measured hot soak levels. The diurnal losses measured during the 1973
AESi program were 15.1 grams. Thus, only 1.3 grams of the hot soak
would be attributed to a leaky gas cap (15.1 grams x 2F/24F). There-
fore, the 16.4 gram/hot soak test could have been made up of 1.3 grams
from the tank plus 15.1 grams from the carburetor bowl. While we still
don't believe there was a gas cap leak problem for the 1973 AESi data,
such a problem could not have been responsible for as large a difference
in test results as exists between those data and the manufacturer's data
which you cited. The estimated 15.1 grams from the carburetor bowl
alone is still much larger than the 9.06 g/test (diurnal + hot soak)
value cited.
Evaporative diurnal and hot soak emissions should be converted to a
gram per mile equivalent in order to evaluate the effect of evaporative
emissions on air quality. If one assumes that the diurnal results from
the 1973 AESi program were erroneous due to a leaky cap, such that the
actual levels were only 1.5 grams (the value measured on 1975 vehicles
in a CAKB study), then the gram per mile value obtained by combining
this value and the 15.1 g/hot soak test value is 1.75 g/mi.* This value
is roughly equivalent to the 1.76 g/mi. value used in the "Draft Environ-
mental and Economic Impact Statement" written in support of the "Pro-
posed Evaporative Emission Regulations". This value, which is the
lowest value possible even if a gas cap leak did occur, is still much
higher than the 0.9 g/mi. value associated with a 9.0 g/test level
(based on assumption of 1.5 g/diurnal test plus 7.5 g/hot soak test).
Therefore, even if there were a gas cap leak problem, the emissions that
did not result from the leak would have been large enough to pose a
serious problem.
*Based on 3.3 trips per day and 29.4 miles traveled per day model used in
"Supplement No. 5. For compilation of Air Pollutant Emission Factors - AP 42."

The differences between the in-use vehicle test data and the
manufacturer's data were not due to gas cap leaks. Therefore, other
possibilities should be considered. The discrepancy in teat results
could have been due to a better evaporative control system design
employed on 1975 model year vehicles than on the 1973 model year vehicles
tested in the 1973 AESi surveillance program. We are, however, not
aware of any control system changes capable of making such a difference
and we would appreciate any information on such changes if they do
If there were no differences in the control system design, then the
difference in emission results could have been due to a difference in
the test procedure or in the vehicles used for testing. One difference
in the test procedures used in the surveillance program and in testing
done by the manufacturers was the type of preconditioning done prior to
the evaporative emission test. During the surveillance testing, the
preconditioning consisted of driving the vehicle to the test facility.
Such a drive would have been somewhat indicative of normal driving.
Differences in diurnal losses could have been effected by the precon-
ditioning performed. The hot soak test on the other hand, should not
have been affected by the type of preconditioning and as stated before,
the hot soak emission levels alone were much higher than the combined
emission level cited in your critique.
The condition of the vehicles prior to testing could have had a
significant effect on the resulting emission levels. The vehicles used
during the surveillance programs were obtained from private owners,
inspected and then tested. No attempt to repair defects was made so
that the vehicles would be representative of "in-use" vehicles. It is
possible that the fuel system and evaporative control system of some
vehicles tested deteriorated in use. We would appreciate information
regarding the "in-use" condition of the vehicles tested by the manu-
facturers to determine if there were differences in the selection and
handling of test vehicles.
The critique of Mr. Ellsworth's paper also contends that running
losses should have been included in the emission levels for pre-controlled
vehicles, and that running losses have been eliminated entirely from
vehicles with present evaporative control systems. We would appreciate
any data from enclosure testing showing the running loss emission
levels from vehicles with and without evaporative emission controls to
verify this statement.
The assessment report was written in order to promote a discussion
of the various evaporative emission control strategies. The conceptual
approaches and actual hardware changes needed to implement those conceptual
approaches were presented. We are aware that some of the hardware which
is suggested may be undesirable, but we still feel that many of the
ideas presented hold considerable promise of reducing evaporative emis-
sions at a reasonable cost. As EPA does not have the experience with
the actual hardware that the industry must have, we will appreciate

receiving the information which you can share with us. Any additional
data showing the effectiveness or costliness of evaporative control
hardware would be much appreciated so that we can further analyse the
industries' capabilities in this area.
Ronald Kruse, Project Manager
Standards Development and Support Branch

Issue - Background Emissions
The proposed procedure does not distinguish fuel evaporative
emissions from other vehicle hydrocarbon evaporative emissions, nor does
It make any allowance for these non-fuel emissions whatsoever, even with
regards to a credit based upon sources or vehicle age.
A. Summary of Comments
AMC - No data have been shown that background emissions contribute
to air pollution or endangers the public.
Therefore, a subtractive allowance of 1 g/test should be stipulated
for the first year or until satisfactory technical analysis is completed
that resolves the unanswered questions.
Chrysler - The proposed regulations are unduly stringent, burdensome,
and disruptive because they evaluate evaporative vehicle emissions
regardless of source. Chrysler asserts background emissions are relatively
small when averaged out over the useful life of a vehicle, and have an
insignificant effect on ambient air quality and the public health and
welfare. Before inclusion into any evaporative emission regulation, EPA
must first make a finding that non-fuel background evaporative emissions
are harmful to the public health. Chrysler is convinced that the better
way to account for such emissions is to have a subtractive correction
factor of at least 1 g/test and that the manufacturer have the option of
testing the certification vehicle for background emissions and supplying
EPA a more accurate subtractive correction factor. Data on a 1975 Dodge
Coronet have shown that at the 6g level, background emissions can mean
the difference of passing or failing, and at the 2 g level, background
emissions alone could exceed the standard.
The majority (98% for 1976 certification) of the prototype vehicles
utilized by Chrysler in certification and running change programs are
fabricated with new components on new production models. Therefore the
brand new vehicle is not a "rare" occurrence as indicated in the NPKM.
EPA certification vehicle requirements do not occur until after sub-
mission of the Part I Application and this requirement cannot be antic-
ipated by the manufacturer, thus the proposed regulations would add 3 to
4 months to the length of the present certification program, which by
itself has added 10 months to the lead time requirements.
Ford - Vehicle background must not be disregarded since it contributes
significantly to a 6 g standard and overwhelmingly to a 2 g standard,
even after three months of vehicle aging. A means of accounting for
vehicle background hydrocarbon emissions must be developed in order to
implement a sensible SHED program. Sufficient time is not available to
do this for 1978; accordingly, Ford proposes that EPA develop a blanket
background factor to be used for 1978 only, based on available industry
Based on 43 vehicles in Ford's 1976 certification fleet, the
average age of the test vehicle from build to 4 K testing was 92 days.

Only 3 vehicles in this fleet were less than 30 days old and they ranged
from 26-30 days. Even at the 92-day average age, background emissions
continue to be a dominant portion of the 2 g standard. A comprehensive
test program is underway to determine the magnitude of background emissions
(non-fuel sources). Results thus far on a 12-vehicle fleet, representative
of new 1976 production vehicles, show that the initial mean level is
4.09 g/test and the 90 day (extrapolated) level is 0.75 g/test. It is
generally agreed that background levels diminish with age; however, the
background emission level continues to be a significant portion of the 2
g standard after three months of the vehicle build date. It is unreasonable
for EPA to propose a procedure that would include background levels
equaling or exceeding the evaporative level of the vehicle fuel system
and not take them into account. The very fact that background levels
are changing with time supports the fact that a large test error is
generated by including them.
Another factor to consider when vehicle background is not taken
into consideration is its effect on the evaporative emission deterioration
factor (DF). If the vehicles are aged any length of time prior to starting
mileage accumulation, the DF would be influenced greatly. The DF might
be more influenced by the relationship between vehicle age and the 5000
mile test point than actual system deterioration over mileage. It is
clear that there is a need to develop a technique for background subtrac-
tion, which goes beyond the actual testing of the vehicle for this
effect. One such method could allow substraction based upon vehicle
type and age, this would require that a family of background emissions
versus vehicle age curves be generated for the product line or possibly
for the industry as a whole. Assuming no change in assembly materials,
such curves could also be used for each certification year. These
curves could also be constructed to make allowances for the variability
found in background emission measurements.
In summary, vehicle background is a significant portion of a 6 g
standard and certainly a major portion of a 2 g standard. It is important
to develop a standard and procedure which includes consideration of
emissions which do not occur in "real life". Ford states very strongly
that background emissions should be accounted for in any SHED test
procedure, and if, for no other reason the 2 g standard be delayed until
this problem can be solved.
GM - Background emissions should not be counted as evaporative
emissions and a correction factor should be used. The 60-90 day car
background levels in the order of 1.0 g/test (as cited in the NPRM) are
not small from a 6 g/standard and are very large in the context of a 2 g
standard. The time required to insure that test vehicles are adequately
weathered would present unreasonable delays in the certification program.
Certification cars are built with new powertrains which are oil-coated
for corrosion protection. It is unrealistic to suggest that a manufacturer
can select test cars a year in advance to allow aging of body and
chassis components. Certification durability cars require 4 months to
complete necessary mileage accumulation, and completion of durability
testing for a given engine, primarily, is normally accomplished before a

significant amount of calibration work can begin on the 4000-mile data
cars. To anticipate the EPA selection and allow time for such test cars
to age is totally out of the question. The most serious problem is
where a replacement car has been built for replacement of a failed
(damaged or crashed) test car. In several instances a replacement has
been built for initiation of mileage accumulation within 4 days. With
the addition of approximately seven days to complete the 4000 mile
accumulation, the chronological age of such cars will likely be about
two weeks. Clearly the background emissions from such a car will be
An age dependent correction factor could be developed, so the
correction would not serve as a bonus. Regardless, provisions should be
made in the regulations to allow actual measurement of background emissions
on an individual test car. The added cost and complexity to the manu-
facturer to exercise such an option would be a strong deterrent.
IH - International Harvester purchases new vehicles to meet fleet
requirements. IH does not have a goodly supply of used chassis on hand
such that they "can usually be selected to be sufficiently aged to avoid
problems of non-fuel evaporative emissions". The 60-90 day aging time,
as noted by EPA to achieve a 1 g/test background, will add considerably
to a manufacturer's lead time requirements. IH urges EPA to adopt an
alternate of at least 1 g/test subtraction to account for background
emissions even in the case where aged vehicles must be used. EPA should
provide a method to measure background emissions.
EPA has failed to address the background emissions caused by road
materials (tars, oils, etc.) picked up during mileage accumulation.
IH's road route contains all types of roads from freeways to two-lane
rural roads. A method of cleaning vehicles needs to be developed which
in itself will not contribute to background emissions. IH believes that
the 1979 standard of 2 g/test, with the present state of the art, is
virtually unattainable on IH-vehicles with no background allowances.
Mercedes Benz - Mercedes Benz strongly objects to EPA's assumption
regarding the use of aged vehicles. It is not at all a "rare" occurrence
to use a brand new chassis. Daimler-Benz has always used and will
continue to use brand new cars for certification purposes. This procedure
guarantees that emission data vehicles are built-up in the assembly
plant according to the production vehicles which they represent. An
unjustified burden would be suffered if no subtractive factor was
allowed to reflect the vehicle's background emissions in this early
stage. It is recommended that a certain subtractive value be allowed
if the manufacturer can show that he is not using aged chassis and
drivetrains. A value of 0.5 g is reasonable in the case of a vehicle
tested within 2 to 3 months after its date of production. An additional
bonus of 0.5 g is requested since even under utmost precaution, single
fuel droplets may be scattered outside the fuel tank during fill-up.

MVMA - If EPA intends that vehicle manufacturers reduce background
emissions along with evaporative emissions, then they must first find
that such reductions are technologically achievable and that background
emissions in fact cause or contribute to, or are likely to cause or
contribute to, air pollution which endangers the public health or
welfare. No health or welfare finding has been made regarding the
transient background emissions and, in fact, MVMA knows of no data or
research which would support such a finding.
The available data concurs with the Administrator's indication,
that the background hydrocarbon emission from cars decrease with car age
at an exponential rate. The available experimental data confirms this
type of time-dependent relationship. This suggests that an experimentally
determined mean value as a function of car age would predict the background
of any given car with reasonable accuracy - beyond some minimum age as
10 to 20 days.
MVMA urges that the procedure be revised to properly take into
account non-fuel vehicular background emissions so that such emissions
are not counted in the calculations for determining compliance with the
standards. One possible method, which was suggested by MVMA to the
California Air Resources Board for effecting this result, would be to
provide for a constant subtractive correction factor to account for
background emissions. Another possible approach would be to establish a
variable correction factor based upon vehicle age. In addition the
procedure should be revised to afford the manufacturers the opportunity
to measure the actual background emissions of a particular test vehicle
following an accepted background measurement procedure or take other
corrective action, such as cleaning, when evidence of a typically high
background emissions exist.
Nissan - Electronic fuel injection vehicles have essentially no
evaporative sources in the fuel system, except for the fuel tank.
Emissions from fuel tanks are, of course, adsorbed into the canister
which is designed to have enough capacity for fuel tank emissions.
Nevertheless, 1.2 to 1.5 g/test of evaporative emissions are still
observed, which suggests that substantial amounts of emissions come from
non-fuel sources of the vehicle.
NRDC - National Resources Defense Council, Inc., supports the
decision to measure all evaporative emissions regardless of source,
including non-fuel hydrocarbon evaporative emissions. As the preamble
notes these vehicle background emissions are pollutant emissions and
should not be ignored. This is especially true when development of
procedure which would exclude measurement of these emissions would
produce a test which is both complex and subject to "test beating"
maneuvers by the manufacturers.

Volvo - Although the experience with background emissions on Volvo
cars is limited, tests have been carried out on vehicles with different
ages. The test results indicate a rather constant level of non-fuel
evaporative emissions on vehicles with an age between 4 months and 3
years. Background levels have been 0.9 to 1,0 g/test. Separate measure-
ment of only non-fuel evaporative emissions involves complicated and
time consuming procedures. The manufacturers should be permitted to
utilize a correction factor that compensates for normal background
emissions. The consequence of a correction factor of 1 g/test would be
small compared to the current Federal hydrocarbon standard of 1.5
g/mile, but amounts to 50 percent of the 1979 proposed standard.
Instead of spending a lot of time and effort in reducing background
emissions on certification vehicles (which will not improve air quality),
the application of a correction factor would be a better alternative.
VW - Background emissions decrease continuously, but very slowly
during the lifetime of the vehicle. The rate of decrease differs from
one of our vehicles to another, and in the case of 4K mile certification
vehicles less than 25 days old, the background level can be between 0.5
and 1.2 g/test. By extrapolation it is evident that these emissions
will be zero long before the vehicle lifetime ends at 5 years or 50,000
miles. Therefore the application of a deterioration factor for the
evaluation of the emission data (4000 miles) vehicles is not at all
Summary of Manufacturers' Comments
All responding manufacturers state that non-fuel hydrocarbon evapo-
rative emissions should not be included in the evaporative emission
measurement. They further state that no sound basis has been established
which indicates that background emissions adversely affect public health
and welfare. They contend that usage of new vehicles for certification
is not a "rare" occurrence, and thus, background emissions should be
allowed for. The manufacturers generally indicated that to force the
use of "aged" vehicles is an undue hardship, and to provide "aged"
vehicles would require, in most cases, additional lead time for certi-
fication. The data submitted by the manufacturers indicate that, even
at best, the aged vehicle will have background emission levels of at
least 0.5 to 1.0 g/test.
The manufacturers recommend that a means be developed to account
for background emissions and that these emissions not be included in the
standards. They contend that sufficient time is not available to do
this for 1978 and recommended that a subtractive correction factor,
possibly based upon vehicle age, be established and that the manufac-
turers have the option of determining, through testing, a vehicle's
unique background level.

B. Discussion
Air Quality Impact of Non-Fuel Evaporative Emissions
There appears to be general agreement, including EPA, that non-fuel
evaporative emissions are, indeed, hydrocarbon emissions; however, the
manufacturers contend they should not be accountable for such emissions.
The formation of photochemical smog does not distinguish non-fuel related
hydrocarbons from fuel-related hydrocarbons. There is no reason to
consider that the effect on the public health and welfare is any less
from non-fuel related hydrocarbon than those evolved from fuel-related
sources. Although background emissions decay logarithmically, Volvo
points out that even after 3 years of vehicle aging, they still exist
and therefore they do occur as a "real-life" emission. Fuel-related
evaporative emissions are usually periodic in nature in the sense that
they are generated by ambient temperature excursion and vehicle operation.
Non-fuel related evaporative emissions, on the other hand, are evolving
continuously throughout the day and increase with vehicle operation (as
observed in hot background tests). Based upon the premise that all
hydrocarbon emissions are detrimental to the public health, the signi-
ficance of the background emissions can be estimated based upon data
submitted by Ford.
A conservative estimate of the overall contribution of background
hydrocarbon emissions can be extrapolated from the data obtained from a
fleet of six Ford Granadas (Ford comments Exhibit No. A, page 19).
From this we find that, on the average, background emissions for 5 years
are 1.38 g/day, and integrating over the first year only, exhibits 2.98
g daily. However, a study presently being conducted by Exxon Research
and Engineering Company for the EPA to assess the effectiveness of light
duty vehicle evaporative emission sources and control systems, showed
that, on a fleet of fifteen 1973 to 1975 model year vehicles, the cold
background emissions averaged, with the exception of one vehicle, 0.04
g/hour. By extrapolating the equation developed by Ford (above ref.), this
emission level would appear after 992 days (y 2.7 years). Therefore,
some agreement is shown by both data, although the Exxon data, as shown
in Table 1, indicate that the background levels "stabilize" sooner than
the Ford projections would indicate. In any case, to the extent that
stabilized non-fuel evaporative emissions are emitted, such emissions are
real and do have an effect on air quality, and should be included in the
evaporative hydrocarbon determination procedure.
Ability to Achieve Low, Stable Non-Fuel Evaporative Emissions
Information submitted by the manufacturers indicates that for
vehicles 60-90 days old the non-fuel evaporative emissions have already
decayed to levels of 0.5 to 1.0 g/test. Data generated by Exxon under
contract to EPA showed that, on a fleet of fifteen 1973 to 1975 model
year vehicles, the non-fuel evaporative emissions averaged 0.35 g/test.
The range of the background emissions was from 0.0 to 1.5 g/test as
shown in Table 1. These data indicate that low, stabilized non-fuel
evaporative emissions are achievable even when vehicles are "naturally"

It is EPA's intent to allow the manufacturers may^nm flexibility
in preparing a test vehicle with low stable background levels. In
addition to selecting naturally aged vehicles, manufacturers have
several courses of action available to them:
1.	Vehicles may be subjected to accelerated aging techniques.
These includes baking the vehicles in paint drying ovens or environ-
mental chambers for several hours, or operating the vehicles at
high speeds for extended periods.
2.	Hydrocarbon emitting materials (paint, sound proofing, vinyl
trim, etc.), may be removed from the vehicles. Where necessary
aged components, or components of other compositions may be sub-
3.	Older or used vehicles may be rebuilt to certification con-
figurations. EPA's requirements governing the rebuilding of used
vehicles for certification purposes are being reviewed and will be
eased in the near future, making this alternative even more attrac-
tive to the manufacturers.
These are viable alternatives. For example, accelerated aging has been
reasonably demonstrated by subjecting a 5 day old vehicle to a 130F
temperature for several hours. The background emissions were reduced by
more than 50%.* Alternatively, supplying especially prepared vehicles
has been common practice in the past for manufacturers. In order to
meet weight restrictions for example, vehicles have been supplied
without seats, bumpers, etc.
Table I
Exxon Vehicles, Background Levels

Background Emissions
















No background data for these cars due to gasoline spillage oa carpet.
A Evidence of gasoline spillage in Crunk prior to test would account
for high background (not included in average).
A Appears to be coming from external enamel paint.

Lead-Time Implications of Using Vehicles with Low,
Stabilized Non-Fuel Evaporative Emissions
To put the lead-time constraint in proper perspective, the basic
certification process is shown as a flow chart in Figure 1. Historically,
major domestic and foreign manufacturers take 14-16 months to complete
their certification program. However, assuming the manufacturer is
thoroughly prepared, both administratively and technically, it can be
seen that presently, the overall process can be accomplished in approxi-
mately 12 months.
The lead-time constraint faced by the manufacturer in providing a
test vehicle with typical, naturally stabilized background levels (e.g.,
60 to 90 days after production) is certainly understandable. This,
however, does not appear to be an insurmountable problem. The manu-
facturers' recommendation for a subtractive correction factor (1 g/test)
is based upon the assumption that non-fuel related hydrocarbons should
not be included in the standard. Ford indicated that the A3 vehicles in
its certification fleet had an average age of 92 days, from vehicle
build to the EPA official certification test point of 4000 miles. None
of these vehicles were less than 26 days old. The data submitted indicated
that background levels were generally in the order of 1.0 g/test on
vehicles 60-90 days old. Therefore, it must be assumed that, if a 1
g/test subtractive allowance were allowed, the manufacturers would
supply test vehicles that have aged 60-90 days.
Therefipre, there is no reason to believe that the same test vehicles
cannot be available when no subtractive allowance is made. Also, since
special vehicle preparation, even stripping of the car to obtain low
background levels is feasible and within the.capabilities of the manufacturer
to do, there is no reason to expect that such a procedure will not be
done regaprdless of whether or not a subtractive correction factor is
Alternative Methods of Handling Non-Fuel Evaporative Emissions
The most accurate means of determining the exact level of hydro-
carbon emissions resulting from fuel evaporation only, would be to
separately measure and subtract out the non-fuel evaporative emissions.
In some few cases, it may be more convenient for the manufacturer to
submit vehicles for testing that are less than 90 days old whose non-
fuel evaporative emissions are a substantial part of their total evapo-
rative emissions. This option would allow them to do so without risking
failing the evaporative standard due to high non-fuel evaporative emis-
sions. However, a separate measurement of non-fuel evaporative emissions
involves removing the fuel system and is complicated and costly to
perform (takes several times as long as the evaporative test itself),
*Reference EPA Technical Memorandum, "Background Test Evaluation at
Ford Motor Co.," dated April 9, 1976, from Gary Wilson, EPA to
Charles Gray, EPA.

Figure 1 -
Certification. Process
Manufacturer	EPA
2 wks
1-2 wks
2 wks
3 wks
2 wks
1-5 wks
2 wks
*Application for data vehicle nay be
made anytine during durability
mileage accumulation, early
application might, however, jeopardize
the final calibration.
Accumulate 4K Miles
Test & Ship
Conformatory Tests
Review All Program
Data & Issue Certificate
Review Update Part I,
Including Projected Sales
Data & Select Emission
Data Vehicle
Perform 5OK Mile
Durability Program &
Update Part I
Prepare Test Vehicle,
Perform "0" Mile Test
Prepare Calibration
Review Calibration Data
& Vehicle Description
Certification Complete
Review & Approve
Vehicle Test Data
Review Equipment &
Select Durability
Prepare Part I
Prepare Part II,
Including All Program
Build Emission
Data Vehicle & Perform "01
Mile Test

and would jeopardize the integrity and thus representativeness of the
certification vehicles. Also, for very new vehicles, the resultant
measured non-fuel background level could only be used for a short period
since the background level is changing rapidly. Subtracting total non-
fuel evaporative emissions would be ignoring the stabilized background
component of the vehicle evaporative emissions.
To provide an allowance (correction factor) for non-fuel evaporative
emissions such that a correction factor could be applied to results from
the enclosure test to account for non-fuel evaporative emissions (e.g.,
allow substraction of 1 g/test) has been considered. There could be a
single standard correction factor, or different correction factors for
different types of vehicles. In this way, the manufacturers would not
be penalized for non-fuel evaporative emissions. However, in actual
practice, a correction factor has serious disadvantages. It would be
difficult to specify a reasonably valid correction factor given the
variability and rapid change in non-fuel evaporative emission levels
from vehicles less than 90 days old. Also, if vehicles with low non-
fuel evaporative emissions were used, as is generally the case, the
correction factor would serve as a bonus towards meeting the evaporative
emission standard. It should be noted that even a 1 g/test allowance,
as recommended by many manufacturers, does not account for new, high
background vehicles. So even an allowance of one gram will not solve
the problem.
From a regulatory point of view, including the non-fuel evaporative
emissions as part of the evaporative emissions to be measured during the
certification process is the most straightforward method of handling the
non-fuel emissions. No complicated and costly measurements or dubious
correction factors are required.
C. Summary and Recommendation
Since stabilized non-fuel background emissions are real life hydro-
carbon emissions, there can be no justification in ignoring the effect
on the public health and welfare. To the extent that stabilized, non-
fuel evaporative emissions are emitted, such emissions should be included
in the evaporative hydrocarbon determination.
The available data show that the manufacturers can supply vehicles
with low, stable background emissions. It is reasonable to expect that
the manufacturers will do so, because it is to their advantage, regardless
of whether background emissions are included in the emission measurement.
It is therefore recommended that the evaporative emission standard .not
include an allowance for non-fuel evaporative emissions. For the certifi-
cation (emission data) vehicles, the manufacturer should be allowed to
conduct repeat testing to gain assurance that the evaporative 'emissions
have stabilized before bringing the vehicle to EPA for the certification

Issue - Test Variability
The test methodology developed for determining vehicle compliance
to emission regulations is influenced by variability of not only the
vehicle, but the test procedure and the associated measurement system.
The magnitude of such variability will have a significant effect on
the ability of a single test to represent the true value of the
vehicle emissions.
A. Summary of Comments
Chrysler - The lack of experience by both EPA and the industry
with the enclosure method and the inability to obtain test correlation
and repeatability between different laboratories and enclosure designs
with the various evaporative emission control systems presently being
manufactured, makes adopting the evaporative emission standards based
upon this technique entirely unobjective and premature at this time.
Replicate test data on two vehicles varies as much as 4.0 g/test and
1.	Test variability does not decrease as enclosure emission
levels are reduced.
2.	Extreme variability can be encountered with the enclosure
test even though the same test vehicle is utilized.
3.	Test variability alone could exceed the 2 g/test proposed
Lab-to-lab results on the same vehicle varied as much as 3.4
g/test. Chrysler agress with the Administrator's Decision Regarding
the Waiver of Federal Pre-exemption Regarding California's 1978
Evaporative Emission Requirements, when he stated, "no emission
standards has meaning unless it is stated in terms of a test procedure
by which the numbers in the standard can be measured in a repeatable
way." Because so many unresolved questions remain regarding the
proposed regulation, its test procedure and methods, and the accuracy
and objectivity of the test technique, Chrysler believes that EPA must
resolve these issues before any final rulemaking is enacted.
Ford - Since the emission systems componentry necessary to the 6
g/test standard has just been developed, test results on these systems
are limited. The test-to-test pooled standard deviation is 0.82 at an
average emission level of 3.23 g/test. Two vehicles tested back-to-
back for background emission had a mean level of 0.81 g/test with an
average test-to-test standard deviation of 0.26. An estimate of the
variability expected at the 2 g emission level can be made by plotting
the standard deviation versus the mean emission level (0.82, 3.23,
0.26, and 0.81). Based on this method the variability expected at the
2 g level is 0.54. This assumes that variability is dependent upon
emission level, which is a valid assumption based upon past experience
with exhaust emissions.

MVMA - Based upon the preliminary data from the member companies
and EPA cross-check program, SHED design, test procedure and testing
techniques are not sufficiently defined at the present time to produce
reliable, correlatable emission data between laboratories. On a 1975
Valient, emissions ranged from 5.3 to 8.7 g with a 7.0 g average
level. On a 1976 Vega, results ranged from 1.6 to 2.4 g with an
average level of 2.0 g. Although the program has not been completed
as of this writing, a comprehensive analysis of the test data will be
undertaken after completion to establish probable cause for lack of
correlation and to draft recommended changes to improve test precision
and repeatability between laboratories.
Volkswagen - Even if test parameters are maintained as constant
as possible, the measuring uncertainty of the procedure, calculated
using experimental data, can have values up to + 46% of the mean.
When influenced by the different parameters (e.g., preconditioning,
fuel variability, cooling during dynamometer run, thermal charac-
teristics of the enclosure material, background emissions and general
correlation problems) uncertainties of the test results up to 200% can
occur. To minimize the risk of failing the certification test, the
manufacturers have to allow a safety margin beyond the standards when
designing evaporative emission control devices. The measured un-
certainties lead to engineering goals of less than 1 g/test. The
spread of variability, which should be considered for certification
testing and standard setting, has to be determined by means of an
approved procedure for correlation testing. The margin of error
inherent in the proposed procedures leads to the conclusion that the
certification of an evaporative emission control device cannot be
based on single measurements on a small number of vehicles. Com-
pliance can only be determined by an averaging procedure from a
minimum of 5 tests per vehicle.
B. Discussion
It is true that test variability forces the manufacturers to
allow a safety margin and establish engineering goals below the es-
tablished standard (true of exhaust emission, also). One manufacturer
suggests establishing an averaging procedure using the results of at
least five tests per vehicle.
EPA recognizes that all tests developed to simulate a real-life
situation are subject to some variability and this variability exists
between test-to-test and lab-tolab testing. With regards to the
MVMA-EPA crosscheck program, it must be pointed out that test tech-
niques improve significantly once experience has been gained. The
1976 Vega used in the program, when tested at EPA, had a coefficient
of variation of 2.5% for a mean emission level of 2.01 g; whereas the
1975 Valient had coefficient variation of 6.3% for an 8.5 g level.
-42 -

EPA has recently completed an extensive test procedure evaluation
and refinement program to identify and reduce the sources of test pro-
cedure variability and to relax those tolerances which were difficult to
achieve (often causing void tests) when such tolerances did not signi-
ficanty influence variability. The resultant improvements (such as
tight time and temperature tolerances for the diurnal and hot soak
tests) which have been made to the test procedure are expected to
reduce variability significantly while providing a test procedure which
is less burdensome to conduct. The variability of the tests conducted
on the five 1975 model year test vehicles used in this program were:
12% for a Vega; 8% for a Camaro; 5% for a Matador; 51% for a New Yorker;
and 10% for a Volkswagen Beetle (with fuel injection). There were
between 6 and 10 tests conducted on each vehicle. The large variability
seen for the New Yorker was strongly influenced by one high value out of
the eight tests conducted.
The variability of the enclosure test method is similar to, if not
somewhat better than, the variability associated with exhaust emission
measurements. A study of exhaust emission variability done by an inde-
pendent consultant for the EPA* showed the variability of exhaust hydrocarbon
measurements to be 11-17%. The variability of CO measurements was 24-
41%, and the variability of NOx measurements was 6-14%. The study
looked at either 10 or 11 replicate tests on three test vehicles.
It is interesting to note that the manufacturers' concern with
variability is sometimes tempered by a concern over the difficulty of
conducting the test (voiding tests) which relates directly to the
"strictness" of the test procedure tolerances. Since the factors of
variability and test tolerances are usually at odds, some manufacturers
appear to be arguing both sides of the issue, i.e., test procedure is
too variable - test tolerances are too tight. For example, EPA proposed
tight time tolerances for both the diurnal and hot soak test phases to
reduce test variability. Yet, several manufacturers expressed the
opinion that these tolerances were too tight. Relaxing these tolerances
would, however, increase test variability.
It would be extremely difficult to allow variability in excess of
the standard as the magnitude of variability is subject to change with
changing procedures and vehicles. An established standard is considered
to be an absolute level of control such that any measurement that exceeds
such an absolute level of control would result in a failure. Test
variability is understood to inherently exist within the absolute value
of the standard. Recognition or "credit" of variability in excess of an
extablished standard would be tantamount to relaxation of the standard.
*"Emissions and Fuel Economy Test Methods and Procedures," Consultant
Report to the Committee on Motor Vehicle Emissions Commission on
Sociotechnical Systems National Research Council, September 1974.

Repeated testing, as suggested by Volkswagen, develops a confidence
level to Insure that such a failure is due to the vehicle and not to the
procedure and associated equipment. This repeated testing does represent
a reasonable and statistically valid methodology. However, major dis-
advantage of repeat testing is the increase in resources required. A
compliance technique that is based on averaging 5 tests per vehicle
would increase personnel and facility requirements by more than 5 times,
considering the normal occurrence of void tests. EPA already allows a
second test if the first test is above the standard, which is generally
accepted as a reasonable compromise.
C. Recommendations
Although not recommended to be incorporated into the procedures at
this time, it is recommended that EPA continue to investigate ways of
reducing test variability and the feasibility of establishing a more
statistical representation of vehicle compliance.

Issue - Vehicle Preconditioning
Current vehicle preconditioning consists of one hour of road
operation according to the durability mileage accumulation schedule, or
approved alternatives. This one hour of preconditioning is followed by
one UDDS. The proposal eliminates the one hour of road preconditioning
since EPA concludes that one UDDS provides sufficient preconditioning
for normal circumstances. For vehicles which have received abnormal
treatment (extended storage, etc.) additional UDDS's can be requested up
to three with one hour soaks between them. The proposed regulation also
discontinues the practice of using the test vehicle to set the dynamometer
horsepower prior to the UDDS.
A. Summary of Comments
British Leyland - Asks, "Is road preconditioning still to be al-
lowed on vehicles delivered to EPA for certification testing, and at
what stage will the specification test now be performed."
Chrysler - "The statement... that a gasoline fueled test vehicle may
not be used to set dynamometer horsepower presents severe constraints on
a manufacturer's testing operation that are not justiified."
Chrysler states that the limitation of only one UDDS to precondi-
tion the test vehicle is too extreme. This would place severe con-
straints on evaporative emission control system design and increase
markedly the problem of handling exhaust-evaporative interaction.
Chrysler says that additional preconditioning should be granted
routinely for vehicles which receive abnormal treatment and proposes
that we retain the alternate Emission Testing Vehicle Preconditioning
Procedure as outlined in MSAPC Advisory Circular No. 39, published
February 28, 1974. This would allow running of three consecutive runs
of the UDDS.
Exxon - States that the one hour preconditioning is a necessary
step in the test sequence because Exxon concludes that it is easy to
abnormally load the evaporative control system of a test vehicle which
has not been in normal use immediately before the test. In their
opinion, a one hour trip, would bring the level of the retained hydro-
carbons in the evaporative control system from an abnormally high level
to about the equilibrium level.
Fiat - Considers that the one hour of preconditioning is necessary
and useful for the repeatability of the tests. Fiat suggests that three
consecutive UDDS operations be run, as allowed in Advisory Circular No.
39, to represent normal urban driving.

Ford - Aggrees with the proposal provided that section 86.128-78
(3) which permits EPA to grant additional preconditioning for unusual
circumstances is retained.
GM - States that the restriction on the use of a test vehicle to
set the dynamometer horsepower is "undue". A mileage limit could be set
instead. GM strongly objects to the deletion of the one hour of mileage
accumulation driving, wants data to support that the practice is wasteful
and feels that the need should be established with future control systems.
GM claims that the durability mileage accumulation schedule does represent
actual vehicle operation since the average speed is about 30 mph. GM
proposes that one hour of vehicle operation be allowed on an optional
basis for vehicles which receive abnormal treatment.
Honda - States that vehicles which are transported by air or boat
should receive additional preconditioning. Feels that the durability
driving schedule should be used for the additional preconditioning.
IH - States that even three UDDS may not be enough for some unusual
Mercedes Benz - Comments that the provision "...where additional
preconditioning may be allowed..." should be retained in the final
Toyo Kogyo - Are concerned about insufficient time for purging
particularly in the case of a retest. They consider that one hour of
mileage accumulation would be effective for that purpose.
Toyota - One cycle of the UDDS does not purge the Toyota control
system. Three or four cycles of the UDDS should be run and the soak
between should be 30 minutes to save testing time.
B. Discussion
Some manufacturers are opposed to changing the current one hour of
mileage accumulation preconditioning. Ford and Mercedes Benz will agree
with the proposal of one preconditioning UDDS if provisions for additional
preconditioning under special circumstances are retained. The other
manufacturers would prefer three or four UDDS cycles for preconditioning.
Chrysler and GM want to continue the use of the test vehicle for setting
dynamometer horsepower.
The manufacturers are all concerned that their vehicles' evapor-
ative emission control system receive adequate purges. EPA is concerned
that the vehicle preconditioning be reasonably representative of typical
urban vehicle use.

1 2
EPA has conducted several studies ' to evaluate the relationship
between preconditioning and emissions, both evaporative and exhaust.
These tests were conducted with vehicles of current configuration.
The general relationships developed from the experiments are:
1. For vehicles in normal use, one hour of road preconditioning,
whether it is conducted or not, prior to the first fuel drain and fill
and dynamometer preconditioning has no effect upon subsequent evaporative
or exhaust emission levels.
2. The type of preconditioning conducted during the dynamometer
operation does have an effect upon subsequent evaporative and exhaust
emission levels.
The conclusion, then, is that the road run preceeding the dyna-
mometer preconditioning is unnecessary and that the dynamometer operation
must be carefully defined.
The UDDS is the method for representing urban driving with respect
to emissions and fuel economy. It has an average speed of about 20 mph,
a distance of 7.5 miles and a duration of about 23 minutes. The durability
mileage accumulation schedule may do a reasonable job of representing,
for mileage accumulation purposes, combined urban and rural driving.
Its average speed of 30 mph is about right for that and it is run con-
tinuously. For preconditioning, it is run for one hour and a distance
of 30 miles. As stated abov^, the average urban trip is 7.5 miles and
many trips are much shorter. Since the emission measurement-test
procedure measures urban emissions, the preconditioning must represent
urban operations. Therefore, the preconditioning drive must be a HDDS.
Most frequently the need for additional preconditioning will occur
for vehicles shipped to or stored at the EPA test facility. For vehicles
tested at the manufacturers' facilities and vehicles driven to the EPA
facility and promptly tested, the proposed preconditioning is adequate.
Most vehicles tested at the EPA laboratory are driven to the laboratory.
. Vehicles shipped to EPA and vehicles stored at EPA for extended
periods may be given additional preconditioning. In keeping with the
concept of normal urban operation, the preconditioning should consist of
one, two, or three UDDS drives. Each UDDS should be followed by a one
hour soak. Usually, one additional UDDS drive will be enough to con-
dition the evaporative emission system.
1.	"EPA In-House Test Program Report No.	1 - Vehicle Preconditioning:
AMA + LA-4 vs. LA-4", Report No. EVAP 75-1, June 1975.
2.	"EPA In-House Test Program Report No.	2 - Vehicle Preconditioning:
LA-4 vs. HFET", Report No. EVAP 75-5,	November 1975.
3.	"A Survey of Average Driving Patterns in Six Urban Areas of the
United States: Summary Report - System Development Corporation",
January 29, 1971, NTIS PB202-192.

In the past, EPA had allowed the test vehicle to be used to set
dynamometer horsepower prior to running the UDDS preconditioning. This
practice provides additional evaporative system purging which is certainly
not representative of urban driving.
Certification dynamometers can be operated in an automatic mode and
need not be set by use of a vehicle. EPA will use the automatic mode of
dynamometer operation. Thus, at EPA the test vehicle will not be used
to set the dynamometer. To minimize test variability, a uniform practice,
of not using the test vehicle to set dynamometer power, must be established.
C. Recommendations
1.	Retain the wording of the notice of proposed rulemaking.
2.	Modify Advisory Circulars 39 and 50 (and any others which are
relevant) to reflect the new preconditioning.
3.	Encourage manufacturers to use the automatic method of dyna-
mometer setting.
4.	Allow idle settings to be measured according to the manu-
facturers' recommendations to the vehicle owners any time prior to the
preconditioning fuel drain and fill.

Issue - Amount of Fuel Used for Preconditioning
The proposed regulations require the fuel tank to be drained
and filled with approximately 2 gallons of the specified test fuel prior
to the UDDS preconditioning drive. For instances where additional
preconditioning is to be performed, the fuel tank may be filled up to
the prescribed "tank fuel volume." The prescribed "tank fuel volume" is
40% of the nominal fuel tank capacity.
A.	Summary of Comments
Chrysler - It is recommended that the tank be filled with approxi-
mately 8 gallons of the specified test fuel prior to preconditioning.
Preconditioning shall consist of four consecutive UDDS's.
Exxon - Stated that a 2 gallon fuel level represents an unrealistic
and uncommon practice. If the fuel tank only contains 2 gallons of
fuel, the vapor space will be uncommonly large and the fuel may be
elevated to unrealistically high temperatures. This, in turn, could
generate excessive running losses from the tank during the precondition-
ing drive so that a representative purge and operation of the evaporative
control system would not be possible.
GM - Tank emissions increase with increasing vapor space and
temperature excursion. Although the deletion of a temperature speci-
fication and the small test fuel quantity for preconditiong represent
test conveniencies and economies, they unrealistically aggravate loading
of a vapor storage system.
Honda - The 2 gallon value prescribed for use in preconditioning is
much smaller than that expected in the field. Fuel evaporative emissions
vary very much with the ratio of fuel volume to the tank volume. It is
recommended that the prescribed fuel volume be the same as that prescribed
for the diurnal breathing loss test.
Togo Kogyo - We,desire that the amount of fuel used for precondition-
ing be amended from two gallons to the prescribed "tank fuel volume"
(40% of the nominal tank capacity). An amount of fuel as small as two
gallons becomes sensitive to the temperatures encountered during the hot
soak which occurs after the preconditioning drive. This can cause a
significant variation in evaporative emission data.
B.	Discussion
The consensus of opinion among the respondents is that a 2 gallon
fuel fill for the preconditioning drive can cause abnormal evaporative
emission results. This is due to the fact that the loading of the
evaporative control system is sensitive to the size of the vapor space

and to the temperature excursion of the fuel. The small amount of fuel
can result In a larger than normal vapor volume, and a larger than
normal fuel temperature rise during preconditioning. It is generally
recommended that an increased amount of fuel be added for preconditioning
(preferably 40% of the nominal tank capacity). Also, it is recommended
that the fuel be at room temperature.
The purpose of the 2 gallon fuel fill was to conserve teat fuel.
The comments regarding the sensitivity of emissions to the percent fuel
fill has been substantiated by testing done at the MVEL laboratory.*
Testing indicated that the emissions from the fuel tank are signifi-
cantly affected by both the amount of fuel in the tank and the tempera-
ture excursion of the fuel.
C. Recommendations
Require the fuel tank to be filled to the prescribed fuel volume
(40% of the nominal tank capacity). The fuel should be not warmer than
* "In-House Test Program Report No. 4, Part II - Typical Vehicle Diurnal,"
Report No. EVAP 76-3, March 1976.

Issue - Soak Time between the Preconditioning Drive and the
Start of the Cold Start Exhaust Teat
The current regulations specify a minimum soak time of 12 hours
between the preconditioning drive and the start of the cold start
exhaust test. No maximum time specification is made. The proposed
regulations specify a minimum 12 hour and maximum 36 hour soak time.
The maximum time limit of 36 hours is an attempt to limit test vari-
ability by limiting the length of the soak while allowing adequate
test scheduling flexibility.
A. Summary of Comments
GM - Twenty-four hours should allow reasonable test scheduling
flexibility and prevent the possibility of an additional "tank diurnal"
which could be forced into a vapor storage system if the vehicle is
allowed to soak for up to 36 hours.
B. Discussion
Testing facilities normally attempt to operate at one set temper-
ature (within the 68-86F range) during the day. This temperature
will not remain constant, but will generally only fluctuate a few
degrees. Therefore, even though the allowable soak temperature range
is relatively large, the temperature fluctuations should be relatively
small. The vehicle's vapor storage system should not be abnormally
loaded when the vehicle is soaked under such conditions. Limiting the
soak time to 24 hours instead of 36 hours should not decrease the load-
ing on the vapor storage device significantly, but it would limit
testing flexibility considerably.
A 24 hour maximum time limit would greatly reduce testing
flexibility. A vehicle preconditioned early in the morning would have
to be tested early the following morning if a maximum 24 hour soak was
specified. A 36 hour soak time allows a test to be performed at any
time during the day even when the vehicle was preconditioned early the
previous morning. In actual practice the length of the soak will
rarely be as long as 36 hours. If testing is being conducted during a
single 8-hour shift work day, the maximum time for the soak would be roughly
30 hours due to the time required to run the emissions test.
C. Recommendations
Retain the 36 hour maximum soak time limit.

Issue - Pressure Check of Fuel System
The current evaporative emission regulations for the "carbon
trap" test procedure allows for an inspection of the fuel system prior
to the certification test. This inspection may be a pressure check
(not specified) of the fuel system. If such an inspection indicates
leaks to the atmosphere of liquid or vapor fuel, corrective action may
be taken under the provisions for unscheduled maintenance. Unscheduled
maintenance may be approved by the Administrator if the repair of a
part or system malfunction doesn't render a vehicle unrepresentative
of in-use vehicles. If the pressure check indicated a leak in the
fuel system due to a malfunction that may be representative of in-use
vehicles, the source of the leak was trapped and included as an emis-
sion source. Since the enclosure measurement method measures evapor-
ative emissions regardless of source, there no longer exists the need
to perform a pressure check to identify system leaks representative of
in-use vehicles. The proposed regulations, therefore, do not in-
corporate fuel system inspection using a pressure check as an integral
part of the test procedure.
A. Summary of Comments
Chrysler  A pressure leak check of the fuel tank system must be
permitted after installation of the fuel tank thermocouples to insure
that no leakage is occuring through the thermocoupled sensing unit.
Ford - Certification vehicles are invariably built with some
prototype parts. Also, the treatment of test vehicles during certifi-
cation is atypical of the treatment the vehicle gets in the hands of
the public (i.e., fuel systems are drained, tanks heated, thermo-
couples installed etc.). Without a pressure check, leaks which the
manufacturer should be allowed to fix won't be detected since overt
indications of such leaks are generally not evident. Because of
undetected fuel system leaks, deterioration factors may be adversely
affected due to a malfunction related to the test procedure and
totally unrepresentative of actual system deterioration. It is pro-
posed that a pressure check be allowed and leaks not representative of
in-use vehicles be repaired prior to each emission test. In addition,
if SHED test results show an atypical number, the manufacturer should
be permitted to investigate for the cause of the atypical result.
Again, if the result is due to factors which do not represent in-use
vehicles, corrective action should be allowed, the test voided and
GM - "A pressure check to insure the integrity of the (fuel)
system should be mandatory." This is essential to insuring that
various test pieces such as the tank drain and fuel tank thermocouples
are still sealing.
m ~ A pressure check should be allowed when the thermocouple is
initially installed and at each test point to develop a history for
justification of unscheduled maintenance.

B. Discussion
The consensus of those commenting is that a pressure check is
needed to determine if leaks of the fuel system not representative of
in-use vehicles are present. Past experience at EPA indicates that
leaks of this nature are uncommon. Allowing pressure checks at each
test point is, therefore, an unnecessary and time consuming practice.
The fuel system should be initially checked when thermocouples and
fuel drains are installed. If diagnostic work indicates that an
abnormally high test result is due to a leak unrepresentative of in-
use vehicles, the regulations allow corrective action to be performed
and the test rerun.
C. Recommendations
Retain the proposed wording.

Issue - Length of Enclosure Purge
The evaporative enclosure Is required to purge for several
minutes prior to the diurnal and hot soak test phases.
A. Summary of Comments
British Leyland - "Could a more positive definition of the phrase
'for several minutes' be provided."
B. Discussion
The length of the purge should not affect the emission results,
since the initial hydrocarbon concentration in the enclosure is
subtracted from the final concentration. Purging for several minutes
is good engineering practice and will prevent excessive buildup of
hydrocarbon levels. A particular amount of purging should not be
specified in the regulations as it would only serve to complicate the
test procedure.
C. Recommendation
Retain the currently proposed wording.

Issue - The Diurnal Test
The proposed test sequence for the diurnal test is as follows:
1.)	Drain fuel from the fuel tanks;
2.)	Fill the fuel tank with the prescribed amount of fuel. The
fuel shall be between 50 and 60F;
3.)	The test vehicle shall be moved into the evaporative emis-
sion enclosure, and the windows and luggage compartment
4.)	The fuel tank temperature sensor shall be connected to the
recording system and the heat source properly positioned
with respect to the fuel tank(s);
5.)	The enclosure doors shall be closed and sealed;
6.)	The temperature recording system started;
7.)	When the fuel temperature reaches 60 + 1F, the diurnal test
is initiated.
3.) The test length shall be 60 + 2 minutes long and the final
fuel temperature shall be 84 + 1F.
9.) At any time (t) during the heat build the fuel temperature
must be within + 2F of (F) as determined by the following
F = 60 + 0.4 t
F = fuel temperature, F
t = time from the beginning of the
test, min.
The ideal heat build is from 60 to 84F in 60 minutes.
A. Summary of Comments
Chrysler - Final rulemaking should include a requirement that
the vehicle tank should not be capped prior to the diurnal test until
the fuel temperature reaches 60 + 1F. Capping the fuel tank prior
to this point is improper, because the vapors generated due to the
fuel being heated from as low as 50F to 60 + 1F will load the vapor
storage device. The enclosure should not be closed and sealed until
the fuel temperature reaches 60 + 1F. At that time, the fuel tank
should be sealed, the enclosure sealed and the initial hydrocarbon
concentration recorded.

Vapor losses from a fuel tank are determined by the temperature
excursion and not the heating rate. The proposed temperature control
limits are unduly stringent and should be relaxed to + 3F to avoid
invalidating a test for a minor temperature excursion from the
specified heating rate. Relaxing this requirement should not influence
diurnal emissions.
The + 2 minute tolerance for the 60 minute diurnal heat build is
too tight. Fuel tank vapors are generated by the temperature excursion
and not the heating rate. The length of the diurnal should be
specified as 60+4 minutes. This action will lessen the number of
voided tests due to the inability to meet the proposed strict time
temperature tolerances.
Ford - There exists a possibility of up to a 10F temperature rise
after the fuel fill and prior to the start of the diurnal test. This
temperature rise could result in significant differences in the initial
canister loading. It is recommended that the fuel cap be left off
until the fuel temperature reaches 60 + 1F. This could be done either
outside the SHED or inside the SHED with the purge blower on and the
SHED door open.
"Ford feels that we cannot reach the starting temperature of 60 +
1F naturally on dual tank vehicles." In most cases the tanks heat at
different rates and it is extremely difficult to get both tanks to the
prescribed 84 + 1F within a 60 + 2 minute time limit. For some
vehicles with single tanks (particularly with tanks installed vertically
in confined areas), it is difficult to stay within the 60+2 minute
time constraints. It is recommended that artificial means of heating
the tank fuel be allowed to heat the fuel up to the prescribed starting
temperature. Also, the time tolerance for the test should be widened
to + 10 minutes.
GM - In order to prevent abnormally loading the evaporative control
system as the fuel temperature comes up to 60F, the fuel cap should be
left off until the fuel temperature reaches 58F. The vehicle should
be fueled and pushed to the enclosure, the heat source and other test
equipment connected, and the windows and trunk opened. The heat source
may be used to bring the fuel up to test temperature. When the fuel
reaches 58F, install the test cap, push the vehicle into the enclosure
and seal the enclosure door.
IH - Installing the fuel filler cap immediately after the fuel is
added prior to the diurnal test is objectionable. Test to test vari-
ability will increase due to a 10F allowable variation in starting
fuel temperatures. It is recommended that the vehicle fuel cap be
left off until the fuel temperature reaches 60F + 1F.

Mercedes Benz - They recommend that the requirement of 60 + 1F be
changed to 60 + 2F. A tolerance of + 1F is more or Isbs a laboratory
type tolerance. For practical use, + 2F can-be achieved with a far
lower probability of error than a + 1F temperature tolerance.
B. Discussion
The consensus of the respondents is that the fuel cap not be
installed until the fuel temperature reaches either 58 or 59F. This is
due to the possibility of an abnormal loading of the vapor storage
device as the fuel heats up from 50 to 60F. Also, it is claimed that
the + 2F temperature control limit for the diurnal heat build is too
tight. It has been recommended that this tolerance be relaxed up to +
3F. The +2.0 minute time tolerance for the length of the test is
generally stated to be too tight and it has been recommended that this
be widened up to + 10 minutes.
A recent EPA study* looked at the test variables during the diurnal
test. It was determined that the controlling parameter was the vapor
temperature in the tank, which is in agreement with an earlier study by
Wade**. Temperature data from the EPA study showed that the vapor
temperature in the fuel tank was roughly 68F at the start of the
diurnal test (i.e., liquid fuel temperature at 60F). The vapor tem-
perature went through a 14F temperature rise and was at 82F at the end
of the diurnal test (i.e., after the liquid fuel had gone through a 24F
temperature excursion and was at 84F). During a real life diurnal
these two excursions would be roughly the same.
The current diurnal test procedure has no specification for vapor
temperatures. The minimum vapor temperature could be affected by the
initial fuel temperature, the ambient temperature, or the method used to
bring the liquid fuel up to the prescribed starting temperature (i.e.,
natural vs. forced heating). Since the emission levels are dependent on
the vapor temperature excursion, test variability could be reduced by
specifying the tank vapor temperature when the fuel tank is capped.
Ideally, this minimum vapor temperature should be 60F. However, achieving
this temperature would probably require lower initial fuel temperatures
than currently specified (50-60F) and a tighter control on the ambient
temperature during fueling. Due to the need to explore the practical
problems associated with an initial tank vapor temperature specification
of 60F, such a specification should be delayed and be implemented in
conjunction with promulgation of future evaporative emission standards.
For the regulations to become effective in 1978, it is recommended
that the tank be capped when the liquid fuel reaches at least 58F as
suggested in the comments, and that capping take place in the enclosure
with the purge blowers running.
* "In-House Test Program Report No. 4 - Part I; Typical Vehicle Diurnal,"
Report No. EVAp 76-3, April 1976.
** D. T. WadeT "Factors Influencing Vehicle Evaporative Emissions,"
SAE Paper No. 670126.

To shorten the length of the test, It is recommended to allow
forced heating of the fuel to bring the temperature up to at least 58F.
Also, it is recommended that a temperature rise of 24 + 1F be specified
instead of specifying the initial and final temperatures. This allows
for a broader tolerance on the initial fuel temperature and still maintains
a close tolerance on the fuel heat rise. Also, it allows the use of
Type "J" thermocouples instead of Type "T", as Type "J" thermocouples
should be able to measure a temperature rise as accurately as Type "T"
Preliminary results of testing done at the EPA facility show that
time may be an important parameter. Widening the time tolerance to + 10
minutes could result in increased variability. Therefore, it is recom-
mended that the proposed + 2 minute tolerance be maintained.
The control limits on the heat build are an attempt to define the
degree of linearity of the heat build. Analysis of heat build fuel
temperature data for tests conducted at EPA indicate that a + 2F
control limits would result in an undesirable number of voided tests, as
suggested by Chrysler. Experience indicates that a + 3F tolerance
should virtually eliminate the possibility of a void test. It is,
therefore, recommended that the control limits be broadened to + 3F.
C. Recommendations
In order to address the problems with the diurnal test brought up
by those commenting and to maintain an accurate, repeatable test, the
following test sequence is recommended for testing during the 1978 model
1.)	Drain the fuel from the fuel tanks and leave the fuel cap off;
2.)	Fill the fuel tank with the prescribed amount of fuel. The
fuel shall be between 50 and 60F;
3.)	The test vehicle shall be moved into the evaporative
emission enclosure, and the windows and luggage compartment
opened. The purge blowers shall be operating;
4.)	The fuel tank temperature sensor shall be connected to the
recording system and the heat source properly positioned with
respect to the fuel tank(s);
5.)	Start the temperature recording system;
6.)	When the fuel temperature reaches at least 58F, the fuel
tank(s) shall be capped, the purge blowers turned off,and
the enclosure doors shall be closed and sealed. Artificial
means to bring the fuel up to 60 + 2 may be used;

7.) The start of the test shall take place when the fuel
temperature is 60 + 2F;
8.)	The test length shall be 60 + 2 minutes long and the
final fuel temperature shall be 24 + 1F above the
initial fuel temperature. For vehicles equipped with
dual tanks, the heat build will be governed by the
larger tank, fuel temperature. The smaller tank fuel
temperature must be within + 3F of the larger tank
temperature at any time.
9.)	At any time (t) during the heat build, the fuel temper-
ature must be within + 3F of the prescribed fuel temper-
ature (F) as determined by the following equation:
F = To + 0.4t
F = fuel temperature, F
To = initial fuel temperature, F
t = time from the beginning of the
test, min.
It is further recommended that, in the future, tighter control of
tank vapor temperatures be specified.

Issue - Ambient Temperature During the Diurnal Test
The proposed regulations specify the ambient temperature during
the diurnal test phase to be 68-86F.
A. Summary of Comments
NRDC - The ambient temperature during the diurnal test should
reflect the average hot summer day average temperature in the hotter
portions of the United States. A temperature of 68F is undoubtedly
lower than this average temperature. A lower temperature than the
average temperature of a hot summer day should not be permitted unless
it can be shown that the use of lower ambient temperatures has no
appreciable effect on the total evaporative emissions generated during
this test phase.
B. Discussion
An evaluation of ambient temperatures for 31 major urban centers
of the United States for the months of July and August showed that the
average minimum and maximum temperatures were 64F and 84F respec-
tively.* Thus, the average temperature on a summer day is 74F. The
specification of a 68-86F ambient temperature range allows needed
flexibility to the control of ambient test conditions at test facilities.
The ambient temperature is normally kept at a level somewhere between
the allowable limits. Thus, the ambient temperature during the diurnal
may very well be kept near the 74F average temperature. In addition,
diurnal emissions are primarily generated in the fuel tank. The fuel
tank is subjected to a diurnal heat build during the diurnal test.
The condition of the fuel tank is the important factor and not the
ambient temperature surrounding the test vehicle.
C. Recommendations
Retain the proposed 68-86F ambient temperature limits for the
diurnal phase of the test.
*"ln-House Test Program Report No. 4, Part I - Typical Vehicle Diurnal",
Report No. EVAP 76-3, March, 1976.

Issue - Use of Type "T" Thermocouples
The current evaporative emission regulations specify use of iron-
constantan (Type J) thermocouples and specifies a temperature record-
ing accuracy of + 1F. Current industry practice is to use standard
grade Type J thermocouples which have an accuracy of + 4F. Premium
grade Type J thermocouples are only accurate to + 2F. Recorder error
may contribute another + 0.5F inaccuracy. Therefore, the equipment
currently used cannot meet the requirements of the current regulations.
The proposed evaporative emissions regulations have specified the use
of type T (copper-constantan) thermocouples which have an accuracy of
+ 1.5"F or + 0.75F for standard or premium grade wire respectively.
The proposed regulations also changed the required accuracy from + 1F
to + 2F. These proposals allow for adequate accuracy and specify the
equipment required to meet that accuracy.
A. Summary of Comments
AMC - The switch from Type "J" to Type "T" thermocouples is un-
warranted and impractical. Calculation of mass emissions is dependent
on the absolute temperature ( F + 460) and, therefore, a + 2F error
is comparatively small. Also, the emissions are more dependent on the
temperature difference than on the accuracy of the individual temper-
ature measurements. Type "J" thermocouples also have the advantage of
giving slightly better resolution over the test range than Type "T"
thermocouples. It is recommended that the specification of Type "T"
thermocouples be removed or made optional.
Chrysler - Type "J" thermocouples can provide the desired ac-
curacy for fuel tank temperature measurement. Also, automatic temper-
ature controllers will have more difficulty "tracking" the specified
heat rate due to the decreased resolution (millivolt change per  F)
of the Type "T" thermocouple. There also exists greater likelihood
for incorrect temperature measurement due to the possibility of in-
correct hookups of Type "T" and Type "J" temperature measuring and
recording equipment. The proposed change from Type "J" to Type "T" is
costly and unjustified. It is therefore recommended to specify use of
Type "J" thermocouple wire.
GM - The cost effectiveness of changing thermocouple specific-
ations should be carefully examined. A changeover will require con-
siderable time and money. Further, the confusion that could result
when running changes for 1977 are being processed through the test
procedure will be significant.
Mercedes Benz - It is recommended that the type of thermocouple
used be left up to the manufacturer as long as the accuracy require-
ments are met. We currently use Ni Cr Ni - thermocouples which are
manufactured with the same accuracy performance as the Type "T" thermo-
couples specified in the proposal.

B. Discussion
The response to the change from Type "J" to Type "T" thermo-
couples has been uniformly negative. It has been recommended to
either specify Type "J" or to leave the choice of thermocouple to the
discretion of the individual manufacturer. The necessity of Type "T"
thermocouples is questioned based on its reduced resolution capa-
bilities, the relative insensitivity of the emissions results to an
absolute temperature inaccuracy of + 2F, and the fact that Type "J"
wire can give sufficient accuracy.
The discussion of the temperature specifications for the diurnal
test indicated that Type "J" thermocouple wires would be adequate if
the diurnal temperature requirements were changed. It is therefore
recommended that type "J" thermocouples be specified.
C. Recommendations
It is recommended that the specification of Type "T" thermo-
couples be changed to Type "J".

Issue - Time Between the Diurnal and Exhaust Emission Test Phases
The proposed regulations require that the exhaust emission test
start within one hour after the end of the diurnal heat build test.
Prior to these regulations, the time between the end of the diurnal
test and the start of the cold start exhaust test was not specified.
A. Summary of Comments
Chrysler - It is recommended that the cold start exhaust test be
started within 15 minutes after the end of the diurnal test. Allowing
for up to an hour between test phases is unsatisfactory, because it
would allow time for the fuel tank to cool down and then heat up again
before the start of the exhaust test. This would, in effect, expose
the vehicle to a second diurnal vapor loading of the vapor storage
device. Also, care should be taken to avoid heating the test fuel
beyond 84 + 1F.
B.	Discussion
The fuel tank at the end of the diurnal should be at or near
8AF. During the time of up to one hour before the exhaust test, the
fuel tank may cool down somewhat due to cooler surrounding temper-
atures. The fuel tank should not, however, heat up again during the
one hour period as the soak temperature should be relatively constant.
A 15 minute maximum time limit between test phases would significantly
reduce the flexibility in scheduling tests. A one hour time limit
should adequately prevent abnormal loading of the vapor storage
device, while maintaining enough flexibility in the overall test.
C.	Recommendations
Retain the current one hour maximum time limit between the
diurnal and cold start test phases.

Issue - Heat Build Required Prior to Non-Evap Vehicle Exhaust
The evaporative emission family concept will result in some
vehicles only undergoing the exhaust emission test. Those vehicles
must undergo a diurnal heat build (not necessarily in the enclosure)
prior to the exhaust emission test.
A.	Summary of Comments
IH - For the small effect, if any, of the evaporative system upon
total exhaust emission results, the proposed requirement of conducting
a diurnal test prior to the exhaust emission test adds unnecessary
time to the program.
B.	Discussion
There exists a possibility of interactive effects between exhaust
emissions and evaporative emissions depending on specific design
characteristics of either system. The diurnal heat build prior to the
exhaust test will load the evaporative emission storage device. These
stored vapors are purged into the engine during the exhaust test and
burned. The loading of the canister by a diurnal heat build should
therefore take place prior to every exhaust test, regardless of
whether evaporative emissions are being measured.
C.	Recommendations
Retain the proposed requirement of a heat build prior to every
exhaust test.

Issue - Determining the Heed for a Running Loss Test
The proposed regulations require a running loss test only if an
engineering analysis indicates the possibility of evaporative emis-
sions during vehicle operation.
A. Summary of Comments
NRDC - The proposed regulations do not indicate procedures for
determining the possibility of evaporative emissions during vehicle
operation. If there are certain design or engineering features as-
sociated with future vehicles which make running loss emissions un-
likely they should be identified. Vehicles with those features could
be considered exempted from the running loss test.
B.	Discussion
Hardware employed for the control of hot soak and diurnal evapor-
ative emissions should control running loss emissions. An engineering
analysis of specific system designs is required to determine whether
the possiblity of running loss emissions exists. There exists no set
criteria for determining the possiblity of running loss emissions.
C.	Recommendations
Retain the current wording.

Issue - Time Between the Exhaust and Hot Soak Test Phases
The current evaporative emission regulations do not specify the
time tolerance for the period between the exhaust and hot soak test
phases. The proposed regulations specify 1.0 minute between engine
shut-down and the start of the hot soak test, and a total of 5.0
minutes between the end of the exhaust test and the start of the hot
soak test. During the time that the engine is idling, the vehicle
must be prepared to leave the dynamometer, then driven off the dyna-
mometer to within 10 feet of the enclosure. Also, during this period
of engine idling the vehicle's windows and trunk may be opened.
After the engine is shut-down, the vehicle must be pushed into
the enclosure, the enclosure doors closed and sealed. When sealing is
complete the initial hydrocarbon and temperature readings are recorded.
This marks the start of the test.
A. Summary of Comments
AMC - Due to the physical location of the SHED with respect to
the chassis dynamometers, and the number of tasks that must be per-
formed in moving the vehicle into the SHED, it is felt that the 1.0
minute time limit from engine-off to the start of the hot soak test is
overly constrictive. It is recommended that a 2.0 minute specific-
ation be adopted for the time from engine shut-down to the start of
the hot soak test. In our judgment, a 2.0 minute time limit would not
detract from test integrity.
Chrysler - Allowing the vehicle to coast into the enclosure with
the engine shut off should be made an optional procedure. This op-
tional procedure can shorten considerably the time between engine
shut-off and the start of the hot soak test.
Ford - It is recommended that the time from engine shut-down to
the start of the hot soak test be limited to 2.0 minutes instead of
1.0 minute. Further, it is recommended that the overall time from the
end of the exhaust test to the start of the hot soak test be a maximum
of 7.0 minutes. California Air Resources Board (CARB) has accepted
these recommendations and, to our knowledge, has provided a seven
minute maximum specification in their latest procedure draft. Test
data (with the time from engine-off to the start of the hot soak held
constant at 2.0 minutes) indicate that evaporative emissions are not
affected by the total time from the end of the exhaust test to the
start of the hot soak test.
GM - A maximum distance requirement of 10 feet from the enclosure
at engine shut-down is unnecessary due to adequate specifications of
transit, key-off, and test start times. It may cause operational dif-
ficulties due to facility layout. It is preferred that the specific-
ation be dropped so that the manufacturer has the option of leaving
the vehicle further away.

The portion of the procedure dealing with engine shut-down is un-
desirable in that the engine is required to run up to four (4) min-
utes. Rewording to allow engine shut down after leaving the dyna-
mometer is suggested. Also, the requirement that the enclosure doors
be closed and sealed within one minute of engine shut-down is unduly
restrictive. The recording of this time will have to be accurate to
within one second. The effect on actual emissions is questionable.
Further, many facilities have enclosure doors that take up to 30
seconds to close. It is suggested that no time limit be placed on the
time from engine shutdown to the start of the hot soak test, and the
time from the end of the exhaust test to the start of the hot soak
test be limited to 5 minutes.
Mercedes Benz - Four minutes may be a too stringent requirement
for the time Interval between the end of the exhaust test and engine-
off due to relative location of the chassis dynamometer and the en-
closure. \Je ask that the intervals be changed to 10 minutes between
the end of the exhaust test and the beginning of the hot soak test.
Also, the time from engine shut-down to the start of the hot soak test
should be allowed to be 5 minutes.
Toyo Kogyo - We support the 5 minute upper limit from the end of
the exhaust test to the start of the hot soak test. It is recommended
that a minimum time of 4.5 minutes be specified to limit test vari-
B. Discussion
The consensus of the comments on this subject is that the pro-
posed time tolerances are too strict. The recommendations for the
tolerance on idle time vary from agreement with the proposed time
limit to a 5 minute time limit. The recommendations for the time from
engine shut-down to the start of the hot soak vary from agreement with
the proposal to a recommendation of "no specification". The most
frequent recommendation was a 2.0 minute tolerance for the time be-
tween engine shut-down and the start of the hot soak. It was also
suggested that the distance requirement of 10 ft. be eliminated and
that the vehicle be allowed to coast into the enclosure.
The effect of the time between engine shut-down and the start of
the hot soak was also evaluated in the EPA study. The results indic-
ated that the length of this time period can affect emission levels.
By limiting this time period as much as is practical, test variability
can be reduced. However, putting too tight a tolerance on this time
could result in an excessive number of void tests. The 1.0 minute
time tolerance is a desirable goal to achieve during testing, but it
may result in an excessive number of void tests. Therefore, it is
recommended that this tolerance be extended to 2.0 minutes in the
final rulemaking.

A recent study done at EPA* supports the conclusion which Ford
drew from its study of the effect of idle time on emission levels. The
studies showed that hot soak emissions were unaffected by idle times of
up to 8 minutes duration. Therefore, since a 5 minute upper time limit
has been recommended by several of the commentors, and since it will
have little effect on emission levels, it is recommended that up to a
5.0 minute idle time be specified in the final rulemaking.
The requirement that the vehicle stop within 10 feet of the en-
closure prior to engine shutdown was proposed so that the vehicle
could be pushed into the enclosure in the allotted time. Allowing the
engine to be shut-down while the vehicle coasts into the enclosure
would be somewhat desirable as long as the engine stops prior to
entering the enclosure. It is recommended, therefore, to require the
engine to stop prior to any part of the vehicle entering the enclo-
C. Recommendations
Specify the time from engine stopped to the start of the hot soak
to be no greater than 2.0 minutes. Specify the overall time from the
end of the exhaust test to the start of the hot soak test to be no
greater than 7.0 minutes. Specify that the engine be stopped before
any part of the vehicle enters the enclosure.
*In-House Test Program Report No. 5 - Hot Soak Time Constraints,
Report No. EVAP 76-2, March 1976.

Issue - Length of the Hot Soak Test
The proposed regulations specify the length of the hot soak test to
be 60 + .5 min.
A. Summary of Comments
British Leyland - "The very tight tolerance placed on the 60 minute
period, could lead to unnecessary voiding of tests. Does it have to be
as tight as + 0.5 minutes to retain the required degree of accuracy."
Mercedes-Benz - The time tolerance of + 0. 5 min. for the length of
the hot soak test is unnecessarily stringent and complicates the pro-
cedure. We recommend a + 2 min. tolerance as allowed for the diurnal
B. Discussion
The time tolerance of + 0.5 min. will reduce test to test vari-
ability and should be an easy specification to meet. A + 2 min. tol-
erance could result in variability in the hydrocarbon measurement of
up to + 5% during the hot soak.
C. Recommendation
Retain the +0.5 min. tolerance for the length of the hot soak

Issue - Maximum Hot Soak Temperature
The proposed regulations require that the ambient temperature in
the evaporative enclosure be maintained between 68 and 86F for the
hot soak portion of the test. This temperature range is consistent
with the ambient temperature range specified for the other phases of
the exhaust and evaporative emission test. The upper limit of 86F is
4F lower than the 90F upper limit currently recommended by the SAE
for the hot soak test using the evaporative enclosure technique. The
86F maximum was specified so that the vehicle would not be subjected
to an abnormal ambient condition.
A. Summary of Comments
AMC - The setting of an 86F maximum temperature (instead of 90F)
is desirable because it would more closely approximate the conditions of
a "hot soak" on an actual vehicle. However, the requirement is dif-
ficult to accommodate due to the requirement for additional cooling. It
is suggested that this requirement will create a greater lead time than
the current time table allows.
AESi - The proposed setting of a uniform ambient temperature
tolerance of 68-86F for all test phases is a desirable and practical
step to refine and simplify the test procedure. It is felt, however,
that the location for the temperature measurement in the enclosure and
in the entire soak area needs to be more specific. Due to the temper-
ature stratification with height in the enclosure and in the soak area,
it is recommended that the height of the temperature measurement be
specified as 1.0+0.1 meters above the floor upon which the vehicle is
located. It is felt that this specification would reduce test to test
errors between laboratories.
Practical experience with enclosure testing indicates that tem-
peratures in the enclosure during a hot soak test with a hot, average
sized vehicle in an enclosure constructed of excellent heat transfer
materials will exceed 86F, if the ambient temperature in the soak area
is 80F. Therefore, some form of cooling is required. It is recom-
mended that an allowance for cooling be made, provided the cooling
surface temperature remain above 68F. Also, due to temperature strat-
ification, requiring the ambient temperature measurement to be made 6-
12" from the ceiling surface makes an 86F maximum temperature even more
difficult to achieve.
Chrysler - "The ambient temperature in the test area external to
the SHED should be held to 68-72F during the hot soak portion of the
SHED test sequence to prevent the heat buildup in the SHED from ex-
ceeding 86F." If external wall cooling is permitted, cooling methods
should be defined with the provision that internal SHED surfaces should
not be cooled below 65F.

NRDC - Widening the ambient temperature range from 76-86F
(current temperature range for hot soak certification tests) to 68-
86F could allow ambient temperatures to be as low as 68F. A just-
ification for the statement that a 76-86F temperature range is too
restrictive has not been Justified. Unrealistically low ambient
temperatures such as 68F may result in lower emissions than would be
present in the "real" world. It is believed that the ambient temper-
ature should be representative of maximum temperatures on hot summer
days. The minimum allowable hot soak ambient temperature should be
90F or higher.
B. Discussion
With the exception of the Natural Resource Defense Council
(NRDC), the proposed 68-86F temperature range was considered desir-
able as it was typical of "real" world conditions. NRDC felt that the
temperature range was too large and that the ambient temperature
should represent maximum temperatures on hot summer days. Other
comments received related to the short lead time involved to implement
cooling methods.
A recent EPA study*, examined the effect of hot soak temperatures
on emissions. It was concluded that a higher allowable ambient
temperature (such as 90F) could potentially result in significantly
higher (10%) emission levels. It was recommended that the maximum
temperature be specified as 86F.
The current evaporative emission test procedure requires hot soak
temperatures to be between 76 and 86F. The temperature rise in the
enclosure, however, may be larger than 10F. Therefore, the lower end
of the temperature range was lowered to 68F to account for the large
temperature rise in the enclosure. The temperature range of 68-86F
that was proposed is, therefore, still believed to be an appropriate
and practical specification.
NRDC expressed the belief that ambient hot soak temperatures
should represent the maximum daily temperature for the hotter regions
of the U.S. on the hottest days of the year. Such a requirement would
be inappropriate and much too severe. All hot soaks do not occur
during the hottest hour of the day, but will take place throughout the
day. Therefore, the average ambient temperature during the hot summer
months would be a more appropriate ambient soak temperature. Another
study done by EPA**, indicates that the average temperature variation
during the months of July and August for 31 major U.S. urban areas is
64-84F. Thus, the average temperature would be 74F. An ambient
temperature between 68 and 86F would, therefore, be more represent-
ative than the temperatures above 90F as suggested by NRDC.
* "In-House Test Program Report No. 5 - Hot Soak Temperature
Constraints", Report No. EVAP 76-1, March, 1976.
** "In-House Test Program Report No. 4, Part I - Typical Vehicle
Diurnal", Report No. EVAP 76-3, March, 1976.

The study of hot soak temperatures done by EPA includes a discus-
sion of ways to maintain an 86"F maximum temperature. There are
several ways of achieving cooling, and no one could be considered the
"correct" way. The method of cooling was, therefore, left unspec-
ified. Reducing soak area ambient temperatures, blowing air on the
inner and outer enclosure wall surfaces, building the enclosure out of
materials such as aluminum and use of cooling fins to increase surface
area are techniques which can be employed to limit the heat rise
within the enclosure. Other techniques such as water cooling or air
conditioning can be employed for even more cooling, but use of the
above mentioned simpler techniques should be sufficient for most
It is recognized that the lead-time for procuring equipment and
preparing for testing is short. However, obtaining the capability for
cooling should not require any more lead time than the lead time
necessary for obtaining other enclosure testing related equipment.
The suggestion by AESi that the temperature sensor in the enclo-
sure be placed 1.0 +0.1 meters above the floor is a desirable change
to the proposal. It will help to standardize the height of the
temperature measurement and will make it somewhat easier to achieve an
86F maximum temperature. This should be specified in english units
(3.0 + <0-.3^ ft.) for consistency, however.
The 68-86F temperature range was intended to
surfaces of the enclosure. It is recommended that
enclosure wall surface temperature be specified as
C. Recommendations
1.	Retain the proposed 68-86F ambient temperature requirement
for the hot soak phase in the final rulemaking.
2.	Specify that the, temperature sensor for measuring the
ambient temperature in the, enclosure be placed 3.0 +0.5 feet above
the floor of the enclosure.
3.	Specify a 68F minimum inner wall surface temperature.
include the inner
the minimum inner
68F to emphasize

Issue - Enclosure Specifications
The enclosure was first described in the Federal Register (32 FR
2448) in 1967 as an airtight, readily sealable enclosure, rectangular in
shape with an internal volume no greater than six times the external
volume of the vehicle (vehicle volume = 1/2 x height x width x length).
Since then, the enclosure was more definitively defined by the Society
of Automotive Engineers as a recommended practice for measuring evapor-
ative emissions (SAE J171a). The proposed regulations have attempted
not to describe a unique enclosure with ancillary equipment, but rather
to describe the performance requirements of such. Performance spec-
ifications allow the manufacturers to uniquely describe the enclosure
and equipment design and placement that best fit their own facility
arrangement needs and requirements.
A. Summary of Comments
AESi - The possibility of increasing lab-to-lab variability is
increased by not specifying the placement of the enclosure temperature
sensor. Although the proposed regulation states that the temperature
probe be 6-12 inches below the ceiling, no height of the ceiling is
specified. Additionally, no position of the temperature sensor is
specified for recording the ambient cold soak temperature where signi-
ficant temperature stratification may take place. AESi recommends that
ambient temperature be uniformly measured at a height of 1.0 + 0.1
meters above the floor. This height is also recommended for the en-
closure temperature probe. Since the ceiling of the enclosure will
normally be a few degrees warmer than other areas of the enclosure at
the height of the vehicle, a one meter height on either side of the
vehicle can help meet the 86F maximum enclosure temperature. Practical
experience indicates that with a hot average size vehicle, at a room
ambient temperature of 80F, the enclosure temperature would exceed 86F
within the one hour test. This can be overcome with relocating the
temperature probe and by allowing cooling of the enclosure by external
or internal means. Cooling can be economically accomplished with little
or no hydrocarbon condensation or absorption by specifying a minimum
cooling surface temperature of 68F. Further, this would minimize the
potential pressure build up within the enclosure, due to a rising
temperature, if the expandable section could not handle a 3.41% increase
in volume (assuming an enclosure volume of 1500 ft ).
Although the specifications indicate the enclosure should be "gas
tight", this is very subjective. AESi recommends adoption of a pres-
sure/volume expansion specification stating a minimum pressure require-
ment of 0.5 inches 1^0 and shall withstand a pressure increase or shall
expand in volume by not less than 0.2% per F temperature rise.
Chrysler - To decrease test-to-test and lab-to-lab variability in
determining enclosure emissions, certain construction parameters require
better definition. Internal enclosure dimensions are a critical para-
meter during the hot soak portion of the test sequence. The volume and

shape of the enclosure should be fixed. Recommended dimensions are 10
fc. wide x 22 ft. long x 8.5 ft. high. Any vehicle larger than this can
be certified by design. Another critical parameter is the ambient
temperature in the cold soak area. The range recommended is 68-72F.
If the surrounding temperature is held to a 72 F maximum, then the
enclosure interior temperature can be adequately controlled with little
or no cooling. External wall cooling should be permitted* and a re-
quirement that enclosure surfaces not be cooled below 65F should be
specified. Condensation on interior walls has been observed when wall
temperatures were cooled below 65CF.
GM - Provisions should be allowed for an internally located heat
exchanger and blower. In addition, a more definitive statement regard-
ing homogeneity of the mixture within the enclosure is required along
with blower size and location. General Motors is currently studying the
mixing within the enclosure and may be able to provide a better state-
ment after the completion of the study. In absence of mixing criteria,
and considering the wide variety of enclosures that may be performing
these critical test3, the location and length of the FID sampling probe
should be specified. Uniformity in components only partially ensures
low variability in testing. General Motors recommends that the sampling
prqbe be located within a 6 inch radius of the temperature sensor and
that the FID sampling system include a path for returning FID bypass
flow to the enclosure. The bypass return is especially important in
facilities that continuously monitor the concentrations in the enclo-
B. Discussion
The generalization associated with describing the enclosure in
terms of performance specifications has not been totally accepted.
Manufacturers claim the variability of the test supports the need for
not only more definitive enclosure specifications, but the dimensional
placement of the sample probe and temperature sensor. Further comments
regarding the ability of the enclosure to maintain a maximum internal
temperature of 86F suggest the ability to artificially maintain cooling
of the enclosure.
EPA has attempted to provide the manufacturer with greater flex-
ibility in defining equipment requirements. To uniquely describe such
equipment presents limitations on incentive and innovation. Several of
the comments on placement of equipment can be accommodated with no loss
to the fundamental approach of performance specifications. Indeed, test
variability i3 a basic problem with all test procedures; however, in a
homogeneous mixture, the placement of the FID sample probe should not
have any effect on this. The return of the FID bypass cannot have a
substantial effect when it is realized that the normal flow rate into
the analytical system is ^ess than 10 CFH. In an enclosure with a
nominal volume of 1500 ft , this represents a change in volume of 0.01%
per minute, or 0.67%/hr. This is an unmeasurable effect. Conversely,
however, there is no basis for restricting this practice if the manu-
facturer desires to monitor enclosure concentrations continuously. The

ability to artificially cool the enclosure represents added expense
and additional test data to be recorded. The design of an enclosure
with maximum surface cooling can accommodate the increasing temper-
atures of the hot soak, phase if the initial ambient temperature is
maintained at the lower portion of the temperature specification
range. Since there is an extreme possibility that some vehicles with
large displacement engines can present a marginal situation and that
forced cooling may be desirable, external cooling should be allowed,
provided that the specified ambient temperature range (68-86F) is not
C. Re commendation
It is recommended that specific placement of the temperature
sensor be specified and that no restriction be placed upon returning
the FID bypass flow to the enclosure.
To accommodate the concern for high ambient temperatures during
the hot soak phase, external cooling should be allowed, provided that
no enclosure interior surface temperatures are lower than 68F.

Issue - Air Circulation in the Enclosure
The air inside the enclosure used for evaporative emission mea-
surement must be mixed thoroughly so that the hydrocarbon concentra-
tion is uniform throughout the enclosure. The proposed regulations
state that "Maintenance of uniform concentrations throughout the
enclosure is important to the accuracy of the test." Mixing is
normally accomplished by the use of one or more small blowers or fans.
The proposed regulations do not specify limits on mixing or how uni-
form mixing is to be determined. This is left up to good engineering
A. Summary of Comments
Chrysler - The total flow range of the mixing blowers or fans
should be specified to prevent undercooling or overcooling of the
vehicle through improper air circulation. An upper limit of 300 cfm
is recommended. Also, the airflow from the fan(s) should not be
directed onto the surface of the test vehicle.
GM - We are currently studying mixing within the enclosure as it
relates to blower size and location. A more definitive statement
concerning homogeneity of the enclosure air as related to blower size
may be possible after the study is complete.
Volkswagon - The air flow velocity in the enclosure has been
determined to influence the level of evaporative emissions especially
during the hot soak. The air flow velocity in the enclosure has to be
specified as well as measuring points and tolerances.
Since the windows and luggage compartments of the test vehicle
are open during the test, adequate mixing within the vehicle must be
achieved to assure homogeneity. Certain vehicles due to their geo-
metry may not receive adequate internal mixing. Therefore, either the
windows and doors should be opened or a blower should be positioned
into the test vehicle.
B. Discussion
The recommendations of those commenting on this issue are to
place upper limits on the air flow rate and air velocity of the mixing
air, to specify measuring points and tolerances for measurement of the
air velocity, to allow vehicles to receive extra cooling in their
interiors, and to insure that air not be directed at the test vehicle.
Air circulation is used to achieve uniform concentrations
throughout the enclosure and also may be used to increase heat
transfer across the enclosure wall. If the air flow rate is to be
specified, it should include a minimum value that will insure adequ-
ate mixing and a maximum value which will allow for adequate cooling.

Experience gained during testing at EPA indicates that a range of 200-
1000 cfm should adequately meet the above criteria. In addition, the
recommendation by Chrysler that air not be directed onto the surface of
the test vehicle should be adopted.
In reference to the comments from Volkswagon concerning the need
for internal mixing, it is EPA's judgment that flow rates of up to 1000
cfm should provide adequate mixing throughout the enclosure including
the internal vehicle volume for most vehicle geometries. However, if a
manufacturer can substantiate that his vehicle is not susceptible to
satisfactory testing by the specified test procedure, special test
procedures may be specified by the Administrator (see 85.075-8).
C. Recommendations
1.	Specify an allowable air flow rate range of 200-1000 cfm.
2.	State that the air flow may not be directed at the test

Issue - Enclosure Calibration
The enclosure is calibrated by
propane into the enclosure and then
proposed regulations do not specify
injecting a measured quantity of
analyzing the enclosure air. The
the quantity of propane to be
A. Summary of Comments
Chrysler - "Since it is good practice to calibrate at levels you
are going to measure, it is recommended that 6.0 + 0.5 grams of pro-
pane be injected into the SHED."
Toyota - Section 86.115-78 describes the procedures to determine
the enclosure leak rate. It specifies that the allowable enclosure
leak rate is less than 0.4 grams for the 4 hours. However, this leak
rate depends on the injection volume of propane, which is used to
determine the leak rate. Considering this, as shown in SAE-J-171(A),
the injection volume of the propane should be specified in the regul-
ations .
B.	Discussion
The amount of propane to be injected should generally be left to
engineering judgment. Factors such as SHED volume, instrument ranges
and expected hydrocarbon levels should dictate the optimum propane
mass to be used for these tests. In order to give general guidelines,
however, it is recommended that a nominal propane mass of 4 grams is
a convenient quantity.
Also, the criteria for an acceptable retention check should be
changed in the final regulations, to specify the change over the 4 hour
test as a percentage of the amount injected rather than an absolute
C.	Recommendations
Specify a nominal 4 grams of propane as a convenient quantity for the
enclosure calibration and retention tests. Also, specify that the amount
of propane measured at the end of 4 hours not differ by more than 4%
of the amount injected for the retention test.

Issue - Enclosure Background Measurements after Maintenance
The proposed regulations require enclosure background measure-
ments to be performed yearly or after any maintenance.
A.	Summary of Comments
GM - It is recommended that the background measurement only be
required after maintenance that would alter background emission
levels. Maintenance on the door raising mechanism, for example, would
hardly affect background emissions.
B.	Discussion
The intent of the proposed requirement for background measure-
ments after maintenance was to insure that sealing compounds or other
materials used for maintenance were not hydrocarbon emitters them-
selves. It is recognized, however, that some maintenance on the SHED
should have no impact on background emissions. Therefore, background
emission measurements should only be necessary after maintenance that
might alter background emissions.
C.	Recommendations
Require background emission measurements of the evaporative
emission enclosure only after maintenance which could alter background
emission levels.

Issue - The Evaporative Emission Hydrocarbon Recording System
The proposed regulations state that the recording of the hydro-
carbon concentration in the enclosure may be done "by means of a strip
chart potentiometric recorder, by use of an on-line computer system or
other suitable means...". Also, the recording system must provide a
positive indication of the initiation and completion of the evapor-
ative emission test phase.
A.	Summary of Comments
GM - It is assumed that the phrase "strip chart potentiometric
recorder" implies that continuous recording of the FID output is
acceptable. Continuous monitoring simplifies automation of the test.
Also, a change is required which would allow manual marking of the
recorder rather than requiring a "smart" recorder to automatically
indicate initiation and completion of the test.
B.	Discussion
A continuous recording of the FID output is acceptable. It is
agreed that manual marking of the recorder should be allowed.
C.	Recommendations
Alter the wording in the final regulations to allow manual
marking of the FID recorder.

Issue - FID fuel for evaporative emission measurements
EPA proposed use of hydrcgen/helium fuel for the FID analyzer
used for evaporative measurements. Hydrogen/nitrogen fuel is used to
measure gasoline-fueled light duty vehicle exhaust emissions.
A. Summary of Comments
British Leyland - Since helium is not required in the gas blend
for the measurement of exhaust emissions, where the greater syner-
gistic effects might be expected. Why is it required here?
Ford - A recent engineering study concludes that I^He fuel for
FID analysis of exhaust gas results in a 3 percent increase in hydro-
carbon readings when compared to the historically used hydrogen/nitro-
gen FID fuel. More recent preliminary data (Exhibit 6) indicates that
this 3 percent relationship also holds for the SHED FID readings.
This 3 percent increase reflects directly on the design task to
meet a standard. Historically, EPA has used a hydrogen/nitrogen
burner fuel for the FID analyzer. If helium fuel now must be used,
EPA should publish the rationale for its use and the standard should
be adjusted by the increase over a hydrogen/nitrogen fuel. Ford
recommends that the hydrogen/nitrogen fuel be retained (same as for
exhaust measuring FIDs) until such time as corrections are provided
for the impact of the proposed change on overall measurement.
GM - Recommend the following rewording and additions to 86.112-
78(a)(4). "Fuel for the...be a blend of 40 + 2% hydrogen with the
balance being helium. The mixture shall contain less than 1 ppm
equivalent carbon response. The heated FID fuel shall use the same
fuel as the analyzer used for evaporative measurements. Fuel for the
HC analyzer used for bag analysis shall be a blend of hydrogen (40 +
2%) and the balance nitrogen".
Mercedes Benz - For safety reasons all FID instruments at DB are
operated on Hg gas produced by generators. The new requirement
(60% He/40% H) would require costly modification of these instruments
without gaining better results.
VW - Investigations show that there is no necessity to apply a
special burner gas for the FID analysis of the evaporative emissions.
No systematic error of the results has been detected if a pure hydro-
gen fuel was used in a FID having oxygen compensation. The require-
ment of using a mixture of 60% He and 40% H adds useless safety
problems to an unsafe procedure. The danger of producing explosive
mixtures in the test cells can be decreased by the application of
hydrogen generators. This important advantage will be eliminated by
the requirement of the He/H^ gas.

B. Discussion.
Witt' the exception of General Motors, the response to the proposed
use of H^/H fuel was negative. Resultant higher emission levels and
safety were the two objections raised. EPA was asked to substantiate
the need for a new FID fuel.
The use of a H^/H blend for the FID fuel does give higher results
than a gas blend of	However, the results obtained with a
blend are more accurate, and thus, more technically correct.
The discussion of the safety aspects of this requirement is not
considered an issue, because the requirements don't specify how the
is to be obtained. The H_/H mixture can be obtained by using a
generator and precision blending the H-/H mixture instead of using
bottled gases. Thus, the regulations 3o not exclude the use of H?
generators. It should be noted that gas blends obtained in this fashion
must still meet the requirements for analytical gases (86.114-78).
In the past the manufacturers have been allowed the use of analyzers
designed to use pure	It is recommended that this still be allowable
as accurate results can be obtained from these instruments. However, if
gas analyzers are designed to use a mixture of H and a diluent, the
diluent must be H . Thus, if a manufacturer wants to use a generator
he may use instrumentation designed for use with pure ^ (witn advanced
approved of the Administrator) or precision blend the H with H .
Z	e
C. Recommendations
As proposed, H/H fuel should be required for evaporative HC
emission measurements fecause of the increased accuracy of such measure-
ments. Instruments designed to use pure H should be allowed with
advanced approval of the Administrator. Tne composition tolerance suggested
by GM should be adopted.

Issue - Calculation of Evaporative Emissions
The proposed method for calculating evaporative emissions and for
calculating the mass of propane used in the enclosure calibration is
as follows:
= K Vn x 10
"HCf Bf
= hydrocarbon mass, g.
C = hydrocarbon concentration, ppm carbon.
3 3
= net enclosure volume ft (ijj ) as determined by
subtracting 50 ft (1-42 m ) (volume of vehicle
with trunk and windows open) from the enclosure
volume. For the enclosure calibration the net
enclosure volume is the measured enclosure volume.
= barometric pressure, in. Hg (kPa).
T = enclosure ambient temperature, R(K).
k =	2.98 (17.2) for diurnal emissions
k =	2.95 (17.0) for hot soak emissions
k =	3.05 (17.6) for propane
i =	initial reading
f =	final reading
The above equation is derived from the ideal gas law.
A. Summary of Comments
GM - "Provisions should be made to allow the manufacturers to
determined and subtract the actual vehicle volume or the volume of a
representative vehicle (instead of using a nominal vehicle volume of
50 ft J.-
Volkswagen - "The given formula contains the hypothesis that
propane can be treated like an ideal gas. Due to the Van-der-Waals-
forces the real gases differ from the ideal gas law." The density of
propane theoretically calculated is more than 2% smaller than the
experimentally measured value. In order to accurately calculate the
hydrocarbon mass, the following equation is suggested:

V 10
J5ij To
J o

RHO = density of hydrocarbon,
To = Temperature which corresponds to the hydrocarbon
density used.
P = Pressure which corresponds to the hydrocarbon density
The experimentally determined value of propane is 2.0096 g/1 at
273K and 101.325 kPa.
The average density of diurnal and hot soak emissions using average
hydrogen to carbon ratios of 2.33 and 2.2 are erroneous because analyses
show that the major portion of hydrocarbons evaporated from the fuel
consists of lower boiling substances which have hydrogen to carbon
ratios of 2.4 and higher. Also, the vaporized fuel portions do not
follow the ideal gas law, and thus, the average density of evaporative
emissions should be experimentally determined. It is recommended that
the suggested formula be used to calculate hydrocarbon emissions.
B. Discussion
It has been recommended that the proposed formula for calculating
evaporative emissions be altered to allow the use of the measured
density of the hydrocarbon(s) and to allow the u|e of the measured
vehicle volume instead of using a standard 50 ft .
The comment concerning the fact that pure propane and the pure
hydrocarbons found in evaporative emission do not behave as ideal gases
is essentially correct. However, the degree to which real gases behave
as ideal gases depends on the concentration of the gas. The hydrocarbon
concentration of propane or evaporative hydrocarbon emissions is very
low in the enclosure. The lower the concentration, of a gas the less the
importance of the Van-der-Waals forces due to the physical separation of the
gas molecules. Thus, for the low concentrations seen in the enclosure,
the gases act essentially as ideal gases.
The hydrogen-carbon ratios used for calculating evaporative emissions
are 2.33 and 2.2 for diurnal and hot soak emissions respectively. These
ratios were originally determined by analysis of evaporated fuel vapors.
There exists no current evidence that these ratios would have changed
substantially since the original determination was made.
The use of 50 ft as a nominal vehicle volume is specified in the
SAE J171a recommended practice for evaporative emission measurements.
This simplifies the test procedure by not requiring the vehicle volume to
be measured for each test vehicle. No standard, acceptable measurement
technique has yet been developed. Also, the errors inherent In using

a nominal value are small, due t(j the relatively large volume of the
enclosure (approximately 1500 ft ) as compared with the relatively
small expected deviance from the nominal value (probably no larger
than 25 ft ). For these Teasons, the use of a set nominal value is a
desirable practice.
If measurement of the vehicle volume is made optional for each
vehicle, the option could conceiveably be abused (i.e., opting to
measure vehicle volume when the actual vehicle volume is greater than
50 ft ^nd opting to use ^he nominal value of 50 ft when the vehicle
volume is less than 50 ft ). However, in order to accommodate the
problem raised, it is recommended that the option of measuring the
actual vehicle volume by a method approved in advance by the Admin-
istrator be allowed on a manufacturer by manufacturer basis; i.e.,
if a manufacturer requests the option of measuring actual vehicle
volume, he would then measure the actual volume of all of his
certification vehicles.
C. Recommendations
The current method of calculating evaporative emissions is tech-
nically correct with respect to the density of hydrocarbons. There-
fore, it is recommended that the current equation be retained.
It is also recommended that measurement of the actual vehicle
volume, for use in calculating evaporative emissions be allowed on a
manufacturer by manufacturer basis, provided the measurement technique
is approved in advance by the Administrator.

Issue - Calibration Gases
The concentration of calibration gas was required to be known to
within 2% of the true value. To clarify and establish a "true" value
it was specified that a true value be defined as a standard gas established
by NBS, EPA., or other approved standard. Further that calibration gas
should be traceable to within 1% of such true concentrations. Span
gas tolerances remained the same as + 2% of true concentration.
The number of calibration gases required to generate a curve for
the carbon dioxide and carbon monoxide analyzers was reduced from
eight to six. This accommodated "actual practice" procedures and did
not significantly impact curve generation. Curve generation was based
upon "best judgment" criteria. If a best-fit straight line could not
be fitted within 2% or less of the value at each data point, then a
best-fit non-linear equation is to be used which represents the data
to within 2% of each data point.
A. Summary of Comments
British Leyland - Questions whether the change in calibration of
analytical gases makes the use of analyzers exclusively for labelling
purposes mandatory.
Chrysler - Suggests that calibration gases be traceable to only
one set of standards.
Fiat - The requirement that gases be traceable to NBS standards
within 1% is too restrictive because the same NBS gases are furnished
with a tolerance of + 1%. Further, EPA should specify the procedures
which the manufacturers have to follow to obtain approval by the
Administrator in having gases traceable to "other approved gas stan-
dards." It is suggested that EPA be available for the calibration of
the gases by the manufacturers. Further, on the basis of Fiat's
experience 6 data points are not sufficient in order to generate a
calibration curve. A minimum of 10 data points is deemed necessary.
Ford - By eliminating the restriction of "single" blend calibra-
tion gases, manufacturers have the option to use flow blending. Flow
blending should remain as an option because of the difficulties of
obtaining and storing stable low range gas concentrations.
GM - EPA should specify a method by which manufacturers will have
to be required to demonstrate compliance with the requirements. Since
this is the first time such requirements have been instituted such
approval is critical to the start of 1978 certification. The lead
time to obtain such approval is significant. Further the and 2%
gas tolerance requirements should include confidence limit statements.
Significant investment of time is required to ascertain these con-
fidence levels and to insure that the gases meet the requirements

stated. General Motors suggests that this set of requirements be
deleted at this time, but through a joint EPA-Industry effort, be
included as a technical amendments at a later date- Further, trace-
ability to an NBS standard should be adopted. There should not be
three yardsticks (NBS, EPA, other) to establish gas traceability to
the NBS standards only.
IH - It is difficult to determine with any confidence that a
given calibration gas would be within 1% of the true concentration.
It is suggested that calibration gas accuracy be determined in ac-
cordance with good laboratory practice.
Volkswagon - No true method has been established which can pro-
vide true or absolute composition of the gases. Results of cross-
check programs including "approved" gases have shown higher vari-
ability than the required tolerance. Even two gas bottles containing
NBS standards did not fullfill this requirement. Such procedures have
to be developed and until such a time, the gases should be prepared
using best engineering practices. According to a report by the HAS
Committee and Motor Vehicle Emissions, investigations have shown that
in the present state of exhaust regulations, the overall uncertainty
of the test results cannot be lessened substantially even by improving
the gas accuracy by a richer degree.
Volvo - Considering that the new specifications require that the
generated curves be within 2% of point and that commercially available
instruments are normally accurate to within 1% of full-scale, the
requirement that 1% calibration gases be used will probably not
improve the accuracy of the end results as lessen the test-to-test
variability. Volvo presently obtains calibration test points with a
gas mixing pump with an absolute accuracy of 0.03%. The improvements
due to using the 1% calibration gases will be negligible and the
cost/benefit relation will be very unfavorable due to the high extra
cost of purchasing and storing calibration gases of an accuracy of 1%.
B, Discussion
With the exception of Volkswagen all comments regarding the
source of traceability for calibration gases recommended a single
entity such as 1SBS. The implementation of this requirement was
considered to be extremely difficult for 1978 and further analysis of
the recommendation was considered necessary, particularly with respect
to establishing confidence limits around the 1% traceability require-
ment. In fact a few suggested no change in the gas tolerance because
minimal benefits would be derived. One manufacturer considered six
calibration test points as too few and others were concerned that the
words "single blends", when referring to gases, eliminated the pos-
sibility of flow blending.

The traceability of all gases to a known standard is a step in
the direction of improving not only accuracy within a facility, but
also in minimizing lab-to-lab test variability. The comments regard-
ing more than one standard is understandable and does tend to negate
the general intent. The possibility does exist that different standard
sources, (i.e., NBS, EPA, other) could introduce a potential 2%
difference if each source is only adaptable of a + 1% analysis. The
capability of each manufacturer demonstrating compliance is a pro-
cedure that may indeed be difficult to accomplish in the short time-
frame remaining for 1978 certification. However, this does not
detract from the purpose and need for establishing reliable trace-
ability requirements.
Six is a reasonable number of calibration points for the es-
tablishment of a calibration curve. No data or information is
available to suggest that this number is inaccurate. However, this is
not to say that six points are a maximum.
The ability to flow blend gases appears to be desirable to some
manufacturers and the indication of a "single blend" gas is not to
inhibit the use of such equipment. The responsibility of accurate
blends and traceability, however, cannot be omitted. The capability
of calibrating or checking the flow blending apparatus must still
depend on a separate gas standard. It would be remiss if it was
assumed that flow blending is a substitute for the eliminating of such
quality control procedures.
C. Recommendations
1.	Traceability to NBS (only) standards should be established
commencing with the 1979 certification. This should include the gas
tolerance specifications also.
2.	The word "single" will be omitted when describing gas blends
and a "minimum" of six calibration gases should now be required for
calibration of the infrared analyzers.

Issue - "Evaporative Testing at High Altitude"
Starting with the 1977 model year, EPA is certifying vehicles
which are sold at high altitude {> 4000 feet) locations. These
certification tests are being conducted at Automotive Testing Labor-
atories, Inc., where the elevation is 5490 feet. The specifications
for the gasoline to be used for these tests are identical to the
current Indolene test fuel, except fui. j.he RVP and D-86 IBP specific-
ations. The RVP and IBP specifications .for the current Indolene test
fuel are 8.7 - 9.2 psi and 75-85F respectively. The RVP and IBP
specifications for the high altitude test-fuel are 7.9 - 9.2 nni nn^
75~105F respectively.
A. Summary of Comments
Chrysler - SHED evaporative emission testing at altitude should
employ fuels with volatility characteristics similar to typical summer
fuel from the Denver area. The high altitude emission test gasoline
specifications for RVP and IBP should be 7.5 - 8.4 psi and 90-lQ5F
Ford - With respect to the requirement for testing evaporative
emission systems at altitude, no data have been generated to show the
feasibility of controlling evaporative emissions to a 6 gram standard
at altitude. As such, this requirement should be deleted from the
regulations until such time as feasibility has been demonstrated.
Missan - "We have all the test facilities at low altitude and,
consequently, ail of our development activities and certification
tests are being done at low altitude. Therefore, in order to conduct
enclosure tests under the high altitude condition, we will have to
make a modification to a soak room so that atmospheric pressure can be
adjusted. Vast costs and time are needed. It is our thought that
enclosure tests under high altitude condition is not reasonable in
terms of cost-benefit and, therefore, should not be required."
Toyo Kogyo - "We consider that the evaporative emissions control
at high altitudes should be treated separately, or that the EPA
should prescribe a test procedure that would allow us to substitute
the tests at high altitudes with those at low altitudes. Reasons:
1.	We do not yet have enough knowledge about what the
evaporative emissions at high altitudes would be like on our
systems as compared with those at low altitudes.
2.	Depending upon the degree of severity in technology that the
evaporative emission control for the high altitudes would
require, it would become necessary for us to construct special
testing facilities, as well as to establish the control
techniques necessary to meet the stringent requirements.
This would of course require a considerable amount of time
and cost."

B. Discussion
One comment received suggested that the test fuel at high altitudes
should have volatility characteristics similar to typical summer fuel
from the Denver area. This manufacturer supplied data from the 1972-
73 MVMA fuel survey which showed high altitude commercial gasoline to
have average RVP and D-86 IBP values of about 8.0 psi and 95F.
However, an analysis of the 1975 MVMA summer gasoline survey shows
that the average RVP for the 13 samples taken above 4000 feet (Albuquerque
and Salt Lake City) was 9.7 psi for unleaded, and 9.0 for regular
grades. Similarly, the average IBP of these samples was 90oF for
unleaded and 92F for regular grade.
To better define the current volatility of commercial gasoline in
high altitude areas, the data which Ethyl Corporation supplied the
Energy Research and Development Administration (ERDA) for their 1975
summer survey were analyzed. Twenty-four (24) samples of unleaded
gasoline from locations above 4000 feet (Albuquerque, Denver, and Salt
Lake City) were inspected. The average RVP and IBP of these samples
were 8.8 psi and 92F respectively.
One manufacturer commented that since the technical feasibility
of meeting a 6 g standard at high altitudes has not been demonstrated,
t^ie high altitude testing requirement should be deleted. Another
manufacturer thought that SHED testing at high altitudes would not be
desirable based on cost-benefit considerations. However, neither
commenter supplied information showing evaporative emission test
results at high altitudes, the relationship between evaporative
emissions at low and high altitudes, or the cost of systems required
for high altitude.
Theoretical considerations do predict higher evaporative emis-
sions as elevation increases. For a non-evaporative controlled vehicle,
the estimated increase in evaporative emission between sea level and
5200 feet is about 30%. However, the difference in evaporative emis-
sions for a controlled vehicle is much more difficult to predict. This
is because the particular type and capacity of the control system will
determine the amount of additional vapor loss as elevation increases.
A system which is marginal at low altitude may show a percentage
increase which is considerably higher than an uncontrolled vehicle.
On the other hand, a vehicle which has reserve capacity at low alti-
tude, might show essentially no increase.
Because of the expected large variation in difference between
evaporative emissions at low and high altitudes on evaporative con-
trolled vehicles, it would be difficult to conduct high altitude
certification tests at low altitudes and apply a correction factor.
Test programs would be required to determine the correction factor for
particular types of vehicle-emission control system combinations.
This would likely require more effort than conducting certification
tests at high altitudes.

C. Recommendat ions
1.	No change should be made to the current proposed regulations
in regard to high altitude testing.
2.	The current test fuel being used in Ann Arbor should also be
used at high altitude.

Issue - SI Units
The proposed regulations incorporated many SI conversions to aid
the user.
A.	Summary of Comments
Volkswagen - The orderly transition to the metric system will
help to facilitate the work, of the engineers and will improve the
information. The presentation of Sl-units in the sections of the
proposal should aid this task.
But this goal cannot be obtained if there are given only the
arithmetically translated values in Sl-units. The conversion of the
numbers should pay regard to the allowable ranges, to the equipment
tolerances, and to the importance of the given values. Furthermore
all derived units should be included. The numbers should be rounded
to set practicable values. Approximate values in US-units should be
approximate in Sl-units too.
B.	Discussion/Recommendation
Incorporating metric conversions is a difficult problem due to
rounding errors. A test procedure is written in one set of units with
the other included as a conversion, solely for the convenience of the
user- In order to insure that both units give the same physical
quantity the metric number generally has more significant figures or
is not an even quantity. For example 100 yards in the regulations
would be expressed as 100 yds (91.44 meters). Any simpler metric
expression would not give the same physical quantity.

Issue - California Procedures
A. Summary of Comments
Chrysler - One of the key elements to be included in any new
evaporative emission regulation is to insure that the final test
procedures, equipment and methods are consistent, compatible and for
all practical purposes identical with that required in California. As
noted in the Senate Report regarding the California preemption pro-
vision, "It is essential that the Federal Government and the State of
California cooperate closely in the development of enforcement pro-
cedures so that industry, when confronted with different standards,
need not be faced with different methods of obtaining certification."
The EPA has recognized this requirement in prior rulemaking and
Chrysler believes that the agency should take the steps necessary to
make sure that the new Federal and California evaporative test pro-
cedures for certification are identical.
B. Recommendations
The California waiver should be revoked when these regulations
are promulgated. The standard proposed is the same and no purpose
will be served by having two separate procedures.

Issue - Miscellaneous Comments and Changes to Regulations
Many manufacturers commented or offered suggested wording changes
on various minor points in the regulations. These will be presented
in the same order as the regulations with EPA response to each point.
86.078-26 Mileage and service accumulation; emission measurements.
A.	Summary of Comments
Fiat - The reference 86.078-24(c) is not appropriate because
this paragraph regards the "durability data vehicles".
Toyota - Section 86.078-26(A)(3)(i) specifies emission data
vehicles. This section requires that the vehicles selected for the
durability test perform the complete exhaust emission and evaporative
emssion tests at 4,000 miles. This, we feel, is quite an unreasonable
requirement. Durability data vehicles should be subject to Section
B.	Discussion/Recommendations
The commentors are correct, the reference is wrong and should be
changed in the final regulation.

86.078-26 Mileage and service accumulation; emission measurements.
A. Summary of Comments
Fiat - The reference 86.078-24(c) is not appropriate because
this paragraph regards the "durability data vehicles".
To>ota - Section 86.078-26(A)(3)(i) specifies emission data
vehicles. This section requires that the vehicles selected for the
durability test perform the complete exhaust emission and evaporative
emssion tests at 4,000 miles. This, we feel, is quite an unreasonable
requirement. Durability data vehicles should be subject to Section
86.078-26(a)(4) (i).
B. Discussion/Recommendations
The commentors are correct, the reference is wrong and should be
changed in the final regulation.

86.107-78 Sampling and analytical system, evaporative emissions.
A. Summary of comments
Chrysler - IE external wall cooling is permitted, cooling methods
should be defined with provision that internal SHED surfaces should
not be cooled below 65T to prevent condensation. To further improve
repeatability, SHED materials, their thermal gradients, and major
details of construction should be specified.
The minimum full scale measuring sensitivity (range) of the
SHED FID should be increased from 5 to 10 ppm propane. NBS gases
below 5 ppm propane are not available with + 1% accuracy.
Also, it would be difficult to provide enough ranges that
any reading would fall within the upper 80% of the range in use.
It is suggested that statement should be changed to the upper 50%.
GM - The sample system to be used by EPA should be described.
For example, the sampling system may include a path for returning
FID bypass flow to the enclosure. This is of particular importance
in facilities that continuously monitor the concentrations in the
enclosure. A statement that the enclosure design must pass all
performance tests as specified in 86.115-78 is needed. Such a
statement would obviate the necessity for much verbiage. Provision
for allowing alternate techniques such as an internally located
heat exchanger and blower to assist in maintaining enclosure
temperature should be included. The requirement that the enclosure
accommodate the largest vehicle to be tested is trivial.
It is recommended that selection of ranges be left up to the
discretion of the laboratory, that will select ranges based on
their ability to meet certain required performance specifications.
It is desirable to express these performance specifications as a
function of the emission standard for which the analyzer is to
measure. It is suggested that 86.107-78(a)(2) be changed to read
as follows:
Evaporative emission hydrocarbon analyzer. A hydrocarbon
analyzer utilizing the hydrogen flame ionization principle
(FID) shall be used to monitor the atmosphere within the
enclosure. The FID shall be capable of meeting certain
performance requirements for the measurement of blends of
zero air and propane in air. Some of these requirements
are expressed as a function of C j, which is that level
of enclosure hydrocarbons corresponding to an emission
level equal to the evaporative emission standard.

(1)	Stability of the analyzer shall be better than 0.01
C , ppm at both zero and C , + 5 ppm over a 15-minute
std j ,,	, std -
period on all ranges used.
(2)	Repeatability of the analyzer, expressed as one stan-
dard deviation., shall be better than 0.005 C ^ ppm at
both zero and C ^ + 5 ppm on all ranges use!.
(3)	Speed of response of the analyzer to 90% of final
reading shall be less than 1.5 s when the analyzer
is connected to span gas as prescribed in paragraph
B. Discussion/Recommendations
The revised section shown above under GM's comments should be
adopted. It has addressed the manufacturers comments as follows:
1.	The language is simplified to eliminate redundancy.
2.	Continuous recording of hydrocarbons, manual marking of the test
record and additional cooling (68F/20C minimum) are all specifically
3.	FID analyzer performance specifications have been substituted for
the range and accuracy requirements previously used.
4.	Chrysler's comment on the number of FID ranges appears to be
confused. The NPRM required readings to "fall within the upper 80%";
Chrysler suggested 50% as a looser but adequate tolerance. To clarify,
the proposed language is revised to permit readings "between 20 and
100% of full scale".

86.109-78 Exhaust gas sampling system.
A.	Summary of Comments
Chrysler - The CFV-CVS component description. Figure B78-2, does
not show the exhaust gas sampling system for diesel HC analysis. This
should be included in Figure B78-2.
Ford - Temperature variations for the critical flow venturi (CFV)
should be limited to + 20F (11.1 C). The + 10F gas mixture varia-
tion specified in 86.109-78 (b)(2) for a positive displacement pump
(PDP) will produce the same magnitude of variation that a + 20F
variation produces in a critical flow venturi (CFV). In a positive
displacement CVS pump, the mass flow rate is a first order power
function of the absolute temperature, whereas, in a critical flow
venturi CVS, the mass flow rate is a function of the square root of
the absolute temperature. Because the allowance temperature range of
a CFV is twice that of a PDP, there is no reason to specify a temper-
ature response time for a CFV temperature sensor and not specify a
response time for a PDP temperature sensor.
GM - The critical flow venturi system is not a constant volume
sampler since sonic velocity varies with temperature and pressure and
those characteristics of the bulk stream are not controlled. Temperature
and pressure must be continuously monitored and used to continuously
calculate flaw which is summed or integrated over the test period to
be correct. This designation (CFV-CVS) should be amended throughout
the NPRM.
Pressure and temperature instrumentation which meets the accuracy
and precision requirements as stated (+ 2F; + 3mm Hg) is expensive
and of questionable reliability. EPA should provide data to show the
basis for requiring this quality of instrumentation.
The lack of equipment for testing diesel powered vehicles in
Figure 2 implies that the CFV system is not approved for diesel test-
ing. The NPRM should so state specifically if that is the case.
B.	Discussion/Recommendation
The systems identified in this section are ones which have been
used by EPA. (as specifically stated in paragraph (a)(3), other
systems yielding equivalent results may be used by manufacturers if
approved by EPA)). All specifications and equipment arrangements in
the NPRM were taken from EPA practice.
Essentially, both the venturi and pump are metering devices. If
fed air at a constant pressure and temperature, a constant mass will
flow through them. These devices operate at close to atmospheric
pressure so pressure variations are not a problem. However, even if

the dilution air is held to a constant temperature, the vehicle
exhaust temperature and volume varies during the driving cycle. In
the depicted systems, this problem is handled in two ways. The PDP
uses a heat exchanger to maintain constant temperature while the CFV
has electronic circuits to calculate flow temperature (and pressure)
GM's comment that the CFV is not strictly a constant volume
sampler is technically correct. Any change in temperature causes a
change in the sonic velocity which changes flow. However, this is
also true for the PDP and no objection is made to the term in that
case. True, a heat exchanger is used ahead of the pump, but some
variations do occur. In the CFV system used by EPA, these variations
are compensated for by the electronic system. Although neither system
is perfectly constant, the term is fairly descriptive of the system^s
Diesel testing is slightly more complex than for gasoline fueled
vehicles. Due to the nature of the fuel exhaust, hydrocarbons must be
measured continuously using a heated detector with sample pick-up
close to the tailpipe inlet. The heated detector has its own sample
pump. With a CFV, it is possible to have a varying flow through the
main venturi, but a constant flow for hydrocarbon analysis. The
hydrocarbon measurement would not be strictly proportional to the
dilute exhaust stream. (Other pollutants are sampled with a smaller
venturi and flow integrated into a sample bag. That is a proportional
sample). Possibly, natural temperature fluctuations would be within
tolerances to give an essentially proportional sample. Or, the CFV
could be used for testing diesels if it was equipped with a heat ex-
The section has been slightly revised to include the theory of
operation. Examples of acceptable alternate systems are given. Diesel
sampling has been specifically addressed.

86.110-78 Exhaust gas analytical system.
A.	Summary of Comments
GM - The inclusion of diesel test instrumentation with the
description of the analytical system for gasoline-powered vehicles
implies that the Administrator might test both types of vehicles with
the same sampling system. General Motors objects to having its
gasoline-powered vehicles tested using the same sampling and ana-
lytical system as used for diesels. The potential for hang-up and
contamination has not been fully determined. The following wording is
suggested to define the heated FID response time: "The response time
of this instrument shall be less than 1.5 seconds for 90% of full
scale response to a span gas as prescribed in paragraph 86.112-78(c).
B.	Discussion/Recommendation
EPA has not investigated possible hang-up problems from diesels,
a preliminary test on two-cycle motorcycles did not reveal any pro-
blems. It is expected that diesel LDVs and LDTs will not cause dif-
ficulties since their emissions are much lower than two-cycle motor-
GM's second point is somewhat confusing. The original language
that GM objected to is almost identical: "The response time of this
instrument shall be less than 1.5 seconds for 90 percent of full-scale
response." The only difference is that response time must be measured
using a span (as opposed to a calibration) gas. Certainly use of a
span gas is acceptable and intended. The original language permits
what GM requests, no change is necessary.
It is recommended that no changes be made in response to these

86.112-78 Analytical gases.
A.	Summary of Comments
GM - The paragraph dealing with NOx analyzer gases requires
clarification: "86.112-78(a)(3) Gases for NOx analyzer shall be
single blends of NO named as NOx with a maximum concentration of 5
percent of the nominal value using nitrogen as the diluent." General
Motors suggests that the wording be as follows: "Gases for the NOx .
. . be single blends of NO, named as NO and NOx with . . . diluent."
Rewording will avoid confusion since paragraph 86.120-78(b)(3) re-
quires NO in N for calibration while clearly indicating that the
allowable maximum concentration of N0 is not exceeded.
B.	Discussion/Recommendation
The gas mixture referred to in 86.120-78(b)(3) need not be a
calibration or a span gas, since it is only used to determine the
conversion efficiency of the NO^ to NO converter. There is no
purpose in naming the calibration gases as NO as well as NOx, and
therefore, it is recommended to retain the proposed language.

86.114-78 Calibrations, frequency and overview.
A. Summary of Comments
Fiat - On the basis of its experience, Fiat deems that it is suf-
ficent to check monthly the oxides of nitrogen converter efficiency
and to perform monthly the CVS system verification.
B. Discussion/Recommendation
EPA disagrees with Fiat's statement that monthly NOx efficiency
checks and CVS verifications are sufficient. With the lower levels of
emissions from late model cars, it is necessary that these items be
checked at least weekly; a month is too long to let any problem go

b6.116-78 Dynamometer calibration.
A.	Summary of Comments
Ford - Paragraph (a) as proposed could be deemed to be contra-
dictory. The middle of the paragraph states that other calibration
methods that yield equivalent results may be used, but the last
sentence states that, "These procedures shall be followed." The
inertia of the free (rear) roll, rather than the difference in coast-
down time between the free (rear) roll and the drive (front) roll, is
the parameter which is actually neglected. The regulations should
reflect this.
Paragraph (b) is too restrictive. Manufacturer should be allowed
to make more than one check.
GM - General Motors feels strongly that a monthly calibration
should be required. Addition of a weekly performance check is desir-
able, but several inertias and horsepower settings should be required.
We suggest rewording paragraph (a) as follows: "The dynamometer ahall
be calibrated at least once each month and performance verified at
least once each week ... If the load observed during the performance
verification is not within + 0.5 hp of the specified value, the dyna-
mometer should be recalibrated." General Motors suggests rewording of
paragraph (b) as follows: "The performance check consists of con-
ducting a dynamometer coast down at inertia weights and horsepower
settings that cover all basic inertia weights ..." While it is
recognized that these rules establish a minimum requirement and that
manufacturers may do more than what is required, the comments on (a)
and (b) are intended to increase the attention paid by all labor-
atories to the critical calibration of dynamometers.
B.	Discussion/Recommendation
The language should be revised as suggested by Ford. This pro-
cedure reflects current EPA practice and is deemed to be sufficient
at this time.

86.117-78 CVS calibration.
A. Summary of Comments
Chrysler - The calibration data measurements itemized in (a)(4)
include the parameter "Air temperature into LFE" with a tolerance of +
.IF. Equipment normally used to measure this parameter cannot meet
this tolerance. It is suggested that the tolerance can be relaxed to +
. 5F without losing accuracy.
Fiat - Measurements of the CVS pump pressure differentials made
with two pressure taps mounted at the top center and bottom center of
the pump drive headplate, are meaningful only if they are carried out
simultaneously. In the proposed procedure, the two pressure values are
measured at different times: therefore, because measurements are not
carried out simultaneously, it is not assured that the differential of
the two pressure measurements be truly the pressure differential in the
pump cavity. In addition, having to use a damper, due to the different
modulation of the pressure depression wave form there is the risk of
carrying out wrong measurements. On the basis of Fiat experience six
data points do not constitute a minimum sufficient for the calibration.
A minimum of ten data points is deemed necessary for a correct calibr-
ation. The second phrase, 86.117-78 (a)(8), beginning "The calibration
curves generated ..." should be deleted because it is meaningless. In
fact, if the A P pressure differential is zero, all "Do" points should
coincide and correspond with the geometrical displacement of the pump.
GM - General Motors suggests that EPA engage in exchange of tech-
nical information on "CVS calibration" techniques and equipment.
Calibration standards, equipment specifications, and traceability are of
major concern.
VW - The same difficulty with propane densities discussed under
SHED calibration occurs with CVS verification.
B. Discussion/Background
As suggested by Chrysler, the temperature tolerance for LFE inlet
air during calibration can be broadened. However, the tolerance permit-
ted is + 0.25UF, not the + 0.5F requested.
Volkswagon's comment is rejected for the same reasons given in the
discussion of SHED calibration.
EPA has used the described calibration procedures for a number of
years without difficulty. They are essentially the same procedures as
outlined in the Appendix to Part 85. Changes desired by Fiat are not
deemed necessary. However, if desired for their particular equipment,
Fiat can request to use alternate methods. Of course, any manufacturer
is permitted to use more than the specified number of data points in a
calibration. The regulations state this explicitly.

8b.118-78 Hydrocarbon analyzer calibration.
A. Summary of Comments
British Leyland - Current practice is to draw the straight line
between zero and the top point. Is this still current practice, or do
we now use the least squares best fit method? The latter is preferred.
Fiat - For what gasoline fueled light duty vehicles and trucks are
concerned, requirements of points (3) and (4) are not justified.
Considering the prescribed dilution values of the CVS, the 0 concentra-
tion in the three sample bags is never below 10-15 percent.
Ford - The hydrocarbon detector should be optimized monthly.
Alternate methods yielding equivalent results should be permitted.
GM - Annual optimization of the FID is not acceptable. General
Motors recommends the optimization be done after any maintenance of
capillaries or the burner occurs. In addition, semi-annual optimization
should be required. The method described for peaking or optimizing
analyzer response is outdated. General Motors suggests that an altern-
ate procedure be allowed if approved in advance. The alternate pro-
cedure that General Motors would propose is based on the FID section of
SAE J254 which is currently being revised to adopt state-of-the-art
knowledge of the FID.
General Motors would appreciate the opportunity to work with EPA to
develop a short diagnostic test to check oxygen response of the FID
analyzers on a regular basis, perhaps as a part of monthly calibration
checks on the analyzers.
General Motors feels that 86.118-78(b) is too demanding. The FID
hydrocarbon analyzers should be checked for oxygen response only in the
range of oxygen content of the gas mixture being measured. The only FID
which measures gas mixtures containing a wide range of oxygen is that
used for diesel testing. The FID analyzers used for the evaporative
measurements are sampling a mixture of HC and air. Oxygen response is
obviously of no concern. Gas mixtures found in bags collected from the
exhaust of gasoline fueled vehicles contain oxygen levels such that
insignificant errors occur, particularly if the excellent FID practices
described in the previously referenced revisions to SAE J254 are ob-
B. Discussion/Recommendation
No curve fitting method is specified. This has been addressed in
the fuel economy regulations.

EPA agrees that it is not necessary to measure oxygen inter-
ference over various oxygen concentrations. This requirement
should be deleted.
Equivalent alternate methods of FID calibration should be per-

86.119-78 Carbon monoxide analyzer calibration.
A.	Summary of Comments
British Leyland - Since all ND1R analyzers are substantially
non-linear, we need a ruling in the number of inflection points
allowable in the use of an "nth" order polynomial curve fitting
Fiat - To our experience, the use of techniques like "best-
fit line" or "best-fit non-linear equation" is cause of complica-
tions. Results obtained with the "best-fit non-linear equation"
do not appear so reliable as those obtained with the "best judgment"
method. In consideration of the importance of the question, in
our opinion, EPA should exemplify the methods followed for the
calibration of its instruments; in addition, EPA should also
allow the Manufacturers to continue using the "best judgment"
GM - General Motors recommends the following wording for
paragraph (a)(1): Adjust the analyzer to optimize performance on
the most sensitive range to be used. Paragraph (b)(3) changes
the number of required calibration gases from those required to
test to 1977 regulations. Since running changes overlap into the
following certification year, some provision should be made to
make these requirements for 1978 supersede the 1977 regulation at
some point in time. As a general comment, there are several
areas of the NPRM where the point at which regulations cease to
apply and new ones take over should be clarified. Each instance
should be considered on its own merits rather than apply a
blanket ruling.
B.	Discussion/Recommendation
The regulations give the manufacturer some latitude in
selecting calibration curves. At this time it is not necessary
to be more specific than to require good engineering judgment.
The reduced number of calibration gases will not have any
significant impact on test results. The transition period will
be addressed in an Advisory Circular.

86.122-78 Calibration of other equipment.
A.	Summary of Comments
GM - General Motors recommends that monthly calibration of
the barometric pressure measuring system and the humidity measur-
ing system be required. Further, all temperature measuring
equipment should receive monthly calibration checks.
B.	Discussion/Recommendation
Calibration of other equipment must be done according to the
manufacturer's recommendations. This is sufficient.

86.131-78 Dynamometer procedure.
A.	Summary of Comments
Flat - The procedure specifies the cooling conditions of the
test vehicles during the dynamometer operation. These conditions
are not realistic, because the operation on the dynamometer does
not reproduce exactly the ventilation conditions met by the
vehicles on the road. In fact, Manufacturers are allowed by EPA
to use additional fans. However, in our opinion, the procedure
prescribed to obtain this permission is very complicated. In
fact, in order to use additional fans, Manufacturers are requested
to be able to show that during field operation the vehicle
receives additional cooling. This means that for any model of
their product line, Manufacturers have to measure the real cooling
conditions, reproduce these conditions on dynamometer in order to
define the additional fans types which are needed to provide a
representative test. The request of additional fans must be made
already during the phase of the definition of the emission control
systems, because the Manufacturers have to know apriori if EPA
approves the additional cooling. In consideration of the complexity
of the procedure, Fiat deems, therefore, that a revision of the
rule on this matter is needed.
GM - Reword to include measurement of carbon dioxide dilution
air levels.
VW - A manufacturer may be allowed to apply "additional
vehicle cooling during the dynamometer operation" if he "can show
that" it will be "necessary". This provision will charge solely
the manufacturer with the burden to demonstrate the faultiness of
the test procedure again for each type of evaporative control
device. This situation is felt to be not acceptable from a legal
point of view. To simulate road conditions, a specification of
the maximum allowable temperature difference between road measure-
ments and dynamometer run is necessary. An approved procedure to
determine the reference temperatures has to be established by co-
operation of both the EPA and the manufacturers.
B.	Discussion/Recommendation
The regulations should include a requirement that dilution
air CO- be measured. This was apparently an oversight in previous
The requirements to obtain additional cooling are unchanged
from previous regulations. No change is necessary at this time.
EPA is currently evaluating road load. A revised procedure
will appear in the fuel economy package.

86.133-78 Dynamometer test runs.
A. Summary of Comments
Fiat - It is not clear the meaning of "the standby position".
We suppose that it is from "dump position".
B. Discussion/Recommendation
Fiat is correct. The term was changed to promote clarity.

86.135-78 Exhaust sample analysis.
A. Summary of Comments
GM - Span gases having concentrations between 75% and 100%
should be allowed.
B. Discussion/Recommendation
This is a good recommendation and the regulations should
reflect it.

86.138-78 Calculations, exhaust emissions.
A. Summary of Comments
Ford - The following technical changes are needed in paragraph
(c)(3) and (5):
(3) Where
CO = (1 - 0.01925 CO- - 0.000323R) CO
e	2e	em
The above equation is to be used only if the CO analyzer
used in performing the analysis is equipped with condition-
ing columns. Other conditions require direct substitution
of CO for CO .
em	e
(5) Where
Tp = Average temperature of dilute exhaust entering
positive displacement pump or critical flow
venturi during test, R(K).
GM - The emission equation should be modified to show distance
traveled during the test, not a constant 7.5 miles. Distance
traveled should be calculated using the front roll circumference
and number of revolutions of the front roll observed during the
test. In paragraph (c), the following changes should be made:
should be specified as the average pressure depression
^ should be specified as the average temperature
This paragraph should also include a method for determining V
for the CFV system. Continuous or instantaneous values shoulcf e
computed and the results averaged to a final value.
VW - The formulas for NOx correction factor in Si-units
should be corrected:
Using the conversion factors:
1 grain = 0.0648 g
1 pound = 0.4536 kg
the formulas will read:

^ " 1-0.0329 (H-10.71)
H =
6.211 * Ra * Pd
PB - (Pd
B. Discussion/Recommendation
The rewordings suggested are not necessary and should not be
Instituted. Actual distance measurement is being proposed in the
fuel economy regulations. VW's recommended NOx correction
factor is correct and should be used.