P.1 

OAR Box 1818 

Prepped by Ollie Stewart 

Document Number: 

5) ll-C-2 

Docket Number: 

A-87-11 

Printed 11/6/2008 3:12:41 PM Sheet 5 of 79 
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• m P)p ACT EPA-AA-SDSB-87-05 ^""B7-IC 

Technical Report 

''/()W 

Safety Implications of Onboard Refueling 

Vapor Recovery Systems 

March 1987 

DRAFT 

DO NOT QUOTE OR CITE 

Technical Reports do not necessarily represent final EPA 

decisions or positions. They are intended to present 

technical analysis of issues using data which are 

currently available. The purpose in the release of such 

reports is to facilitate the exchange of technical 

information and to inform the public of technical 

developments which may form the basis for a final EPA 

decision, position or regulatory action. 

Standards Development and Support Branch 

Emission Control Technology Division 

Office of Mobile Sources 

Office of Air and Radiation 

U. S. Environmental Protection Agency 
P.3 

Table of Contents 

Section Page 

I. Executive Summary 3 

II. Introduction 7 

III. Onboard Control System Description 9 

IV. Design Considerations for a Safe 

Onboard System 26 

V. In-Use Fuel System Safety 48 

VI. Cost and Leadtime Considerations 60 

VII. Heavy-Duty Gasoline Vehicle Requirements 73 

VIII. Conclusion 95 

IX. References 96 
P.4 

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I. Executive Summary 

The purpose of this technical report is to evaluate the 

safety implications of requiring onboard refueling vapor 

recovery systems on gasoline-powered passenger cars, light 

trucks and heavy-duty vehicles. In that light, special 

attention is given to the analysis of the design considerations 

for a safe onboard system and the other measures necessary to 

insure that the design considerations incorporated are capable 

of providing a high level of in-use fuel system integrity. 

Onboard refueling systems are in many ways similar to 

present fuel tank evaporative emission systems. The emissions 

emanate from the same location on the vehicle and the basic 

technology used to control the two types of emissions is quite 

similar. Many of the components are analagous, if not 

essentially identical, and the configuration/layout of the 

systems on the vehicle is also expected to be about the same. 

In fact, these two systems and system functions are so similar 

that many manufacturers will likely combine their onboard 

refueling and fuel tank evaporative emission systems into one 

integrated system which can serve both purposes. The fact that 

these systems are similar and will be integrated has two 

effects on the safety of onboard systems. First, many of the 

approaches and techniques used to safely implement evaporative 

emission control systems can also be applied to insure the safe 

implementation of an integrated onboard refueling/evaporative 

emission system. Second, any safety problems related to 

integrated onboard/evaporative systems should be evaluated 

incremental to present evaporative systems. Quite simply, 

there is no need to add a whole new system to the vehicle. 

Concerns over the potential safety implications of onboard 

systems have, however, been raised. These concerns can be 

grouped into four general areas. These include requirements to 

pass the National Highway Traffic Safety Administration (NHTSA) 

safety tests, the effects of tampering and system defects, 

refueling operations, and in-use fuel system safety. 

Concerns with the design requirements necessary to comply 

with the NHTSA safety tests focused on the need to integrate an 

onboard system into a vehicle in a manner which would provide 

the crashworthiness and rollover protection demanded by Federal 

Motor Vehicle Safety Standard (FMVSS) 301. EPA's analysis 

indicates that crashworthiness for the key vapor lines and 

other system components could be accomplished using many of the 

same approaches and techniques now applied successfully to 

evaporative emission systems. Further, the rollover protection 

now provided for the fuel tank through the use of a limiting 

orifice can be gained through the application of one of the 

several rollover valve designs now available. 
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Concerns have also been expressed that canister tampering 

and component defects could lead to in-use safety problems. 

While canister tampering is infrequent, the rate can be reduced 

and the potential safety effects eliminated through proper 

placement. Manufacturers are expected to consider the safety 

implications of tampering when evaluating canister location 

options on the vehicle as they do now with evaporative control 

system canisters. While the concern has been expressed that 

defects in onboard system components could have safety 

implications, no data or other bases have been found that 

suggest onboard systems would influence the nature or frequency 

of such occurrences as compared to those seen on current 

evaporative emission systems. In fact, given the experience 

gained by the manufacturers in safely implementing evaporative 

controls, it is likely that an integrated onboard/evaporative 

system could be implemented with no more (and perhaps less) 

problems than present evaporative emissions systems. 

Concerns over the safety of refueling operations are 

centered on the potential to overpressurize the fuel system. 

EPA's analysis finds that use of a liquid seal solves all 

overpressure problems, and that if a mechanical seal is used a 

simple pressure relief device can be used to eliminate any 

overpressure concerns. As discussed in the analysis, a few 

other less significant potential problems have very 

straightforward engineering solutions. 

Finally, while it is clear that onboard-equipped vehicles 

can be designed to comply with FMVSS 301 requirements, there 

has been concern expressed that fuel system integrity in-use 

may decrease by some nori-quantifiable amount because FMVSS 301 

can't cover all potential accident situations and an onboard 

system requires modifications and additions to the present 

evaporative emission system. While no test procedure can cover 

all potential situations, it does not necessarily follow that 

system modifications or additions will cause an increase in 

risk over present systems. 

Both vehicle and fuel system safety are evaluated as an 

integral part of the overall design and development process. 

This involves multiple trade-offs, balances, and compromises 

with other key design considerations. Given the need to 

consider all key design criteria, manufacturers accept or 

manage a certain amount of risk. Since the safety demands of 

Federal standards such as FMVSS 301 must be incorporated into 

vehicles/systems, these standards represent the minimum. In 

many cases the level of safety achieved in-use goes beyond that 

required by Federal standards, being driven by in-use liability 

concerns. 
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If a" manufacturer perceives that the added risk mentioned 

above may exist for one or more of its vehicle models, there 

are ways to respond through direct measures or through keeping 

the overall risk in-use at acceptable levels through other 

design flexibilities. EPA's analysis identifies and describes 

a number of these measures. Manufacturers can make vehicles 

safer than they are now; an onboard requirement does not 

increase the amount of risk a manufacturer need incur or 

accept. Manufacturers are expected to integrate onboard 

controls into their fuel systems without compromising safety 

iges which have been 

„>_ ..^v. ^ ^v..,^ ..V^_WXLO (e.g., changing from 

fill). Finally, if a manufacturer choses to use - „ c „ 

fuel bladder to control refueling emissions, this would 

eliminate all of the potential concerns raised relative to the 

canister based onboard system, and would provide improvements 

in safety over the present fuel system. 

Other key considerations include safety related costs and 

the leadtime needed to implement onboard controls safely. This 

analysis estimates that safety costs related to implementing 

onboard systems will range from $4.50-$9.00 per vehicle. While 

the cost estimates for the needed hardware, modifications and 

fuel consumption impacts are reasonably accurate, there is some 

uncertainty in the development and safety crash testing cost 

estimates. However, safety related onboard costs are quite 

insensitive to even large changes in the estimates for 

development and safety certification. 

In a general sense, EPA's estimates are supported by the 

fact that the modifications needed for present vehicles to 

insure fuel system safety in-use have been acquired relatively 

inexpensively, and vehicles with evaporative emission systems 

comply with FMVSS 301 today. Much of the groundwork needed to 

implement an integrated onboard refueling/evaporative emission 

control system safely has been completed and many of the same 
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techniques and approaches can be used. The fact that 

integrated systems will be used means that some costs incurred 

to implement evaporative emissions systems safely will not 

reoccur. EPA's analysis has adequately accounted for safety 

costs in its estimate of the total onboard system cost. Safety 

costs contribute about 25 percent of the $20 cost estimated for 

a passenger car onboard system. 

With regard to leadtime, given the magnitude of the task 

and past experience with implementing evaporative emission and 

fuel system integrity standards (FMVSS 301), this analysis 

indicates that 24 months leadtime is adequate. However, EPA is 

coamitted to providing the leadtime needed to implement onboard 

controls safely and effectively, and is open to considering a 

short phase-in of controls to assist manufacturers in dealing 

with problems on unique vehicle models. 

Finally, the onboard systems which would be installed on 

HDGVs are quite similar to those expected for passenger cars 

and light trucks, even though the safety test requirements are 

different for HDGVs. With the exception of school buses, the 

fuel system integrity testing centers more on evaluation of 

fuel tank integrity than vehicle crash testing. Nevertheless, 

many of the concerns raised and addressed above regarding 

onboard safety for lighter-weight vehicles also apply to HDGVs 

and support the judgment that onboard systems can be applied 

safely to this class of vehicles within the leadtime laid out 

above and for a reasonable cost. 
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II. Introduction 

EPA has received several comments from the Motor Vehicle 

Manufacturers Association, Automobile Importers of America (and 

their member companies), and the Insurance Institute for 

Highway Safety which have expressed various levels of concern 

about the potential safety implications of onboard vapor 

recovery systems.[1,2] Also, some preliminary comments 

regarding onboard safety have been received from NHTSA's 

technical staff. [3] The American Petroleum Institute (which 

has independently developed several onboard-equipped vehicles) 

and the Center for Auto Safety have expressed support for the 

implementation of onboard vapor recovery systems.[4,5] The 

purpose of this report is to discuss and analyze the safety 

related concerns raised regarding onboard vapor recovery 

systems. 

Motor vehicle manufacturers face many difficult technical 

decisions in the design and development of vehicle systems and 

the integration of these systems into new vehicle models. The 

difficulty of these decisions often arises from the fact that 

this design, development and integration process requires the 

simultaneous consideration of a number of key criteria. One of 

the most important of these criteria, safety, is normally given 

a high priority in the design and integration process. 

However, the process also includes careful and prudent 

consideration of the trade-offs necessary to deal with other 

important criteria such as performance, reliability, cost, 

styling, and regulatory requirements such as fuel economy and 

emissions. In each case, manufacturers must find the 

appropriate balance of all the important criteria. Since the 

design of emission control systems has the potential to affect 

the overall safety of vehicles, EPA views safety as a primary 

concern when evaluating the feasibility of an emission control 

device. 

EPA is presently evaluating the use of onboard vapor 

recovery systems "(onboard systems) as a means of controlling 

refueling emissions. The potential safety implications of such 

controls require special consideration, because implementing 

onboard systems will involve some minor modifications of the 

vehicle fuel system. While safety influences all aspects of 

vehicle design, fuel system safety and integrity is a key 

concern in the design and integration process. 

In evaluating the safety implications of requiring onboard 

controls, EPA has applied the philosophy that no increase in 

overall risk should be caused or accepted, beyond that now 

present with today's fuel/evaporative system. This applies to 

both compliance with the applicable Federal safety standards 
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and the in-use safety of vehicles equipped with onboard 

systems. The following analysis will show that straight 

forward engineering solutions are available for all of the 

potential safety problems which have been identified, and that 

while final choices regarding exact system designs lie with the 

manufacturers, safe fuel system designs are achievable by all. 

Further, as will be discussed below, this analysis indicates 

that it is quite possible that overall fuel system safety 

improvements could accompany the implementation of onboard 

controls. 

The importance of evaluating the safety of onboard systems 

is highlighted by the Clean Air Act (Section 202 (a)(6)) which 

directs EPA to consult with the Department of Transportation 

(DOT) before requiring the use of onboard vapor recovery 

systems. This requirement is intended to insure that all 

safety issues have been properly identified and addressed. 

This report will also help to assist in the fulfillment of this 

requirement. 

As outlined below, the remainder of this report is divided 

into five sections. The first section following this 

introduction (Section III), provides a general description of 

an onboard system to aid in the understanding of any related 

safety issues. Section IV summarizes and provides EPA's 

analysis of the comments received regarding the design of a 

safe onboard system, and Section V discusses onboard effects on 

in-use fuel system safety. Section VI discusses the effects 

safety considerations have on other important factors such as 

vehicle costs and leadtime. Heavy-duty gasoline-fueled 

vehicles (HDGV) pose similar yet distinct onboard control 

system safety issues, and Section VII addresses these 

similarities and differences. The final section provides 

conclusions. 
P.10 

III. Onboard Control System Description 

Before considering any safety issues, it is important to 

have a clear understanding of onboard refueling vapor recovery 

systems (onboard systems) and how they work. Likewise, before 

considering the characteristics of the control system, it is 

important to understand the nature of refueling emissions. The 

purpose of this section is to provide the reader with both a 

clear understanding of what refueling emissions are and how 

onboard systems operate to control these emissions. 

In many respects, onboard systems are similar to the 

evaporative emission control systems now in use on most 

gasoline-powered vehicles. In fact, it has been suggested that 

onboard systems are more an extension or modification of 

current evaporative emission systems than the implementation of 

a new control technology. An explanation of the differences 

and similarities between the two systems will provide a better 

understanding of the incremental nature of onboard systems 

relative to current evaporative systems, and will be useful in 

assessing the design, cost, and leadtime implications of 

implementing onboard controls safely, which are to be discussed 

later in the report. 

This section will first briefly describe evaporative 

emissions and how they are currently controlled. Next, 

refueling emissions will be discussed and similarities between 

onboard systems and current evaporative emission systems will 

be presented. The section will end with a discussion of the 

differences between the two control systems. 

A. Evaporative Emissions 

Evaporative emissions emanate from two basic sources: the 

fuel tank and the fuel metering system (either a carburetor or 

a fuel injector). Evaporative emissions arising from the fuel 

tank are primarily "diurnal" emissions while those from the 

fuel metering system are termed "hot soak" emissions.* This 

analysis is primarily concerned with fuel tank evaporative or 

diurnal emissions since these emissions are currently 

controlled using an approach similar to that envisioned for an 

onboard system. 

It should be noted that a small amount of hot soak 

emissions come from the fuel tank; the fuel tank 

evaporative control system would handle these as well as 

the diurnal emissions. 
P.11 

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Diurnal evaporative emissions consist of gaseous 

hydrocarbons that are displaced from the tank when fuel in the 

tank is heated. Fuel heating can result from changes in 

ambient temperature or during vehicle operation due to the 

vehicle exhaust system and/or recirculation of fuel heated by 

the engine. In either case, as fuel in the tank and vapor 

above the fuel heat up, more of the liquid fuel evaporates, and 

the vapor itself expands, thus causing hydrocarbon vapor to be 

released into the atmosphere (unless captured by a control 

system). Fuel volatility, size/ of the vapor space, initial 

tank temperature, and the degree to which the tank is heated 

can all impact the quantity of hydrocarbons emitted. Diurnal 

emissions occur on at least a daily basis, and a system 

designed to control these emissions must be capable of handling 

repeated evaporative emission loads. Since the early 1970's, 

most vehicles have come equipped with a control system to limit 

the amount of diurnal evaporative emissions. The next section 

discusses the type of control system typically used on today's 

vehicles. 

B. Evaporative Emission Control System 

Figure 1 depicts a fuel tank equipped with an evaporative 

emission control system.[6] As can be seen from this figure, 

the control system is relatively simple in design and requires 

very few components. The purpose of this section is to 

describe each of the system's components in terms of both 

physical appearance and function. 

In order to effectively prevent the escape of fuel tank 

vapors to the atmosphere, an evaporative control system must 

perform three basic functions. First, the system must limit 

the number of exits through which fuel tank vapors might 

escape. Second, the exit that does allow fuel tank vapors to 

escape must lead to a container where the vapors can be 

captured. Third, the system must eventually restore the 

capacity of the storage container by purging it of the trapped 

vapors. The discussion below describes how an evaporative 

emission system performs these three functions. 

The first function an evaporative emission system must 

perform is to limit the outlets through which vapors can 

escape. As can be seen in Figure 1, there are only three 

openings through which vapors can pass: 1) the fillpipe 

opening, 2) the external vapor vent line to the fillpipe top 

(about 1/2" diameter), and 3) the small limiting orifice 

(approximately 0.050-0.055 inch) in the top of the tank. The 

fuel tank cap is designed to form a tight seal with the 

fillneck so that once the cap is secured in place, vapors from 

the fillpipe opening and the external vent line are trapped 

within the system. Thus, only one outlet exists through which 

fuel tank vapors can escape. This single available outlet is 

the small limiting orifice in the top of the tank. 
PRESSURE/VACUUM 

RELIEF CAP 

EXTRENAL VENT 

LINE 

/ " 

Figure 1 

Typical Current Evaporative System 

-LIMITING ORIFICE 

-TLOAT/ROLLOVER 

VALVE 

L 3/8" DIA. 

8' LONG 

# 

PURGE VALVE 

TO PURGE 

INDUCTION 

POINT 

1 LITER 

CARBON 

CANISTER 

14 GALLON FUEL TANK 
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As the tank undergoes temperature changes, and hydrocarbon 

vapors are generated, pressure builds up in the tank (as long 

as the fuel tank cap is secure in place) . This pressure 

build-up is slowly relieved as gas tank vapors eventually force 

their way through the only available exit: the small limiting 

orifice in the top of the fuel tank which leads to the vapor 

storage device (charcoal canister) . By limiting the number of 

vapor escape passages and routing the evaporative hydrocarbons 

to a single point, the control system has successfully 

performed the first of its three basic functions. Before 

discussing the evaporative emission system's second function, 

it is important to understand why the orifice in the top of the 

tank is so limited in size. 

The orifice in the top of the tank is very small in size 

for three reasons. First, it allows pressure to build up in 

the tank when vapors are generated. This pressure build-up 

inhibits further evaporation and creates a pressure 

differential which eventually leads to hydrocarbon vapor being 

forced through the limiting orifice. Second, the limiting 

orifice acts as a liquid/vapor separator. If liquid gasoline 

were to splash up into the vent line leading to the evaporative 

emission control storage device (charcoal canister), damage 

could potentially occur to the storage media (charcoal). 

However, the orifice in the top of the tank is so small that 

liquid passes through it at only a very slow rate. Essentially 

only vapor is allowed to continue to the canister. This point 

leads to the final reason for limiting the size of the vent 

orifice to such an extent. Were the vehicle ever to be in a 

rollover accident, a very little amount of liquid fuel would be 

able to leak from the tank through such a small orifice. Thus, 

the limiting orifice is sized large enough to allow for 

adequate escape of evaporative emissions, but is small enough 

to permit only a slow leak from the fuel tank in the case of a 

vehicle rollover and thus provides the protection needed to 

comply with FMVSS 301. The cost for this is low. However, 

some manufacturers incorporate an additional valve for added 

protection; an example is shown in Figure 2.[7] 

Storing the evaporative hydrocarbons is the second basic 

function an evaporative emission system must perform. Once the 

vapors escape from the fuel tank through the small limiting 

orifice, they proceed through a vent line (usually about 

l/4"-3/8" inside diameter and made of some type of flexible 

rubber compound) that leads to a canister containing charcoal. 

The canister itself is usually made of plastic and is generally 

a cylindrical or rectangular container. Once inside the 

canister, the hydrocarbons are adsorbed onto activated charcoal 

where they are stored temporarily. 
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Figur e 2 

STANDARD 

VERSIONS 

ORIFICE 

FLOAT 

SPRING 

HIGH FLOW 

FILTERED 

The tank mounted spring balanced float valve is a low cost unit designed for venting 

fuel tank vapor to the carbon canister. The device employs a float which remains open 

under normal conditions. Should the tank level reach a critical height, the float will 

close the canister vent line. In the event of extreme vehicle attitude or roll-over, the 

float will close the canister vent line. 

A filtered tank mounted spring balanced float valve is available that performs the 

same functions as the above sketches except the tank side of the part is filtered to 

prevent contaminates from entering the part which might effect float closing of the 

canister vent line. 

For high flow applications that require a large volume of vapor venting, such as fuel injection applications, a high flow valve has been developed that has more than twice 

the present flow capacity without loosing other critical performance parameters. 

FLOAT VALVE 

Borg-Warner Automotive, Inc. 

707 Southside Or, Decatur, Illinois 62525 

Phone 217/428-4631 

437 

SKETCH 

NUMBER 
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The working capacity of the charcoal, the quantity and 

frequency of the evaporative emissions, and the capability of 

the system to restore its working capacity all affect the 

amount of charcoal required. Current passenger car evaporative 

emission control systems typically utilize a 0.85-1.5 liter 

canister.[8] (This size is sufficient for both diurnal and hot 

soak evaporative emissions.) However, a finite amount of 

charcoal is used in the canister, so the storage capability of 

the canister is limited. Once the evaporative hydrocarbons 

have been adsorbed onto the charcoal in the storage canister, 

they will remain there until removed. The hydrocarbons must be 

stripped from the charcoal periodically in order to restore 

enough working capacity to adequately capture each successive 

evaporative emission load. 

While the vehicle is operated, the evaporative emission 

system performs its third basic function of restoring the 

storage capability of the charcoal canister. After the 

vehicle's engine is running, manifold vacuum is used to draw 

hydrocarbon-free air through the charcoal canister. 

Hydrocarbons stored in the canister are desorbed into the air 

stream which flows into the fuel metering system via a flexible 

rubber purge line of about 3/8" diameter. Once purged, the 

evaporative hydrocarbons are burned as fuel through normal 

combustion in the engine. This process "empties" the canister, 

thereby preparing it for the next evaporative emission load. 

One aspect of the purge process which needs to be 

mentioned but will not be explained in great detail is the fact 

that the canister is not continuously purged during vehicle 

operation.[8,9] A valve located between the canister and the 

fuel metering system is opened and closed at opportune times to 

control the purge process and limit disturbances which affect 

engine performance and exhaust emissions. 

To summarize, the current evaporative emission control 

system performs three basic functions: 1) it limits the exits 

through which fuel tank vapors can escape; 2) it traps the 

vapors in a storage device; and 3) it restores the capacity of 

the storage device to prepare it for the next evaporative 

emission load. 

Onboard systems are very similar to evaporative emission 

control systems because they must also effectively perform the 

same three basic functions to efficiently control refueling 

emissions. However, due to differences in the quantity of 

vapors and the rate of generation of evaporative and refueling 

emissions, equipping vehicles with onboard systems will require 

that some minor modifications be made to current fuel and 

evaporative emission control systems. 
P.16 

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The next section provides additional detail regarding 

refueling emissions to help explain the fuel and evaporative 

system modifications that would be required to equip vehicles 

with onboard systems. 

C. Refueling Emissions 

Three processes contribute to the release of hydrocarbons 

during a refueling operation. The first two are collectively 

termed displacement losses, the third spillage. First, the 

hydrocarbon vapor present in the tank is displaced from the 

fuel tank by liquid fuel entering through the fillpipe. If the 

vehicle fuel tank is equipped with an external vapor vent line 

(as shown in Figure 1), much of the fuel tank vapor escapes via 

the external vent line which is connected to the top of the 

fillpipe. However, if no such vapor passage exists, the vapor 

makes its way out through the fillpipe concurrent to the 

incoming liquid fuel. Hydrocarbons are also generated and 

released during refueling as a result of liquid fuel 

evaporating as it is dispensed into the tank. This second type 

of displacement loss is caused by the turbulence in the 

liquid/air interface during the refueling process and is 

enhanced by the higher volatility of the dispensed fuel 

relative to the fuel in the tank. A third source of 

hydrocarbon refueling emissions is the evaporation of any 

liquid fuel spilled during the refueling operation. Of the 

three refueling emission sources, the two displacement sources 

are generally the largest (by far), unless a large spill occurs. 

Because the bulk of refueling emission emanate from within 

the fuel system, refueling emissions are in many ways similar 

to diurnal evaporative emissions. Therefore, it follows that 

an effective onboard system can be designed which utilizes the 

same basic technology and approach utilized by current 

evaporative emission systems. In fact virtually all onboard 

systems considered by manufacturers in their comments 

incorporate this approach as do the prototype systems developed 

to date.[10,11,12,13,14,15] The similarities between onboard 

and evaporative emission systems are discussed below. 

D. Onboard Refueling Control Systems 

1. Similarities with Evaporative Emission Control 

Systems 

In order to control refueling emissions, onboard systems 

must perform the same three basic functions as described 

previously for diurnal evaporative emission systems. These 

include limiting the number of exits through which refueling 

vapors can escape, storing refueling emissions temporarily in a 
P.17 

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charcoal canister, and purging the charcoal canister of the 

stored refueling vapors to restore its capacity prior to the 

next refueling operation. Because these three functions are so 

similar to the three functions a diurnal evaporative emission 

control system must perform and the emissions arise from the 

same location, extrapolation of known technology leads to the 

conclusion that an onboard system would use the same approach 

and similar hardware to that which is currently used to control 

evaporative emissions. Figures 3 and 4 depict two 

representative onboard systems and a comparison with Figure 1 

shows that onboard controls are very similar in overall design 

to current diurnal evaporative emission control systems. 

However, while onboard systems do use many of the same basic 

components as evaporative systems, (i.e., charcoal canisters, 

flexible rubber tubing, purge control valve, etc.), the basic 

differences between refueling and evaporative emissions require 

a few additional components, and an enlargement of certain 

existing hardware is required for the onboard system. These 

are the key differences between the two systems. 

Before discussing the component additions and 

enlargements, an important aspect of the onboard refueling 

vapor recovery system must be introduced. 

Since both emissions emanate from the same location, a 

properly designed onboard system could control both refueling 

emissions and diurnal evaporative emissions. Thus, if an 

onboard refueling system were incorporated into a vehicle's 

fuel system, the current diurnal evaporative emission control 

system would no longer be needed. This aspect of onboard 

systems has several implications. First, it reduces the 

conceived degree of complexity the system adds to the vehicle's 

fuel system. An entirely new, larger, more complex system 

would not be needed in addition to that which currently 

exists. Rather, the current control system would be modified 

to be somewhat larger with a small increase in the number of 

components. Second, since onboard systems are basically 

modified evaporative emission systems, many of the safety 

design concerns associated with onboard systems have already 

been addressed in current evaporative emission control system 

designs. These approaches could also be used in the integrated 

system. One final effect a "dual function" control system has 

is it requires less "packaging" space and is less expensive to 

produce than two separate systems. 
Figure 3 

Integrated Evaporatiye/Refueling System 

Nozzle Actuated Valve 

Front Mounted Canister 

Mechanical Seal 

I— PRESSURE/VACUUM 

RELIEF CAP 

r\ 

NOZZLE ACTUATED 

ROLLOVER/VENT VALVE 

r 5/8" DIA. 

3' LONG liMECHANICAL 

SEAL 

05" DIA. LIMITING ORIFICE 

/ 

<TLOAT/ROLLOVER 

VALVE 

14 GALLON FUEL TANK 

PURGE 

VALVE I 

TO PURGE 

INDUCTION 

POINT 

3 LITER 

CARBON 

CANISTER 

00 
Figure 4 

Integrated Evaporative/Refueling System 

Tank Mounted Valves 

Rear Mounted Canister 

J-Tube Seal 

-NOZZLE ACTUATED 

ROLLOVER/VENT VALVE 5/8" DIA. 

3" LONG 

3/8" DIA. 

5' LONG 

3 LITER 

CARBON 

CANISTER 

PURGE 

I VVALV A E 

4 /==^<l 1-

TO PURGE 

INDUCTION 

POINT 

14 GALLON FUEL TANK 

CO 
P.20 

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2. Additions/Modifications to Evaporative Emission 

Control Systems. 

The differences between onboard systems and current 

diurnal evaporative emission control systems can be separated 

into two broad categories: 1) those related to the sealing of 

the system and 2) those related to the magnitude and frequency 

of the refueling emissions. Because of these differences, 

onboard systems require several additional components, and 

several components of the current evaporative system must be 

increased in size or slightly modified. 

a. Additions to the Present System 

Diurnal evaporative emission control systems limit 

the number of vapor exits by using a fuel tank cap to close off 

the fillneck. However, during a refueling operation, the fuel 

tank cap is not in place, and consequently, onboard systems 

must rely on some other type of sealing mechanism to prevent 

the escape of vapor through the fillneck opening. Currently, 

two types of fillneck seals are available for use on onboard 

systems -- liquid and mechanical. 

Liquid fillneck seals utilize modified fillpipe designs to 

route incoming gasoline in such a way that a column of gasoline 

is formed which prohibits the vapors in the fuel tank from 

escaping to the atmosphere via the fillneck. While this may 

sound somewhat complicated at first, the concept is fairly easy 

to understand with the help of a picture. Several liquid seal 

configurations have been developed, but one design which has 

been shown to be particularly attractive from both a design and 

cost perspective is the "J-tube" (shown in Figure 5).[16] As 

fuel is dispensed into the fillneck, it is forced to pass 

through the "U" shaped portion of the fillpipe. A liquid trap 

is formed in the "U" shaped portion of the fillpipe which 

prevents vapors from escaping via the fillneck. The "J-tube" 

extension could be made of metal, plastic or hard rubber. 

Another type of fillneck seal which has been shown to be 

effective is the mechanical type seal.[14,15] The mechanical 

type seal (see Figure 6) is basically an elastomeric device 

which forms a close connection with the inserted fuel nozzle 

and thereby eliminates any space in the fillneck opening 

through which vapor could escape. While both the liquid and 

mechanical type seals perform the same basic function of 

limiting the available vapor exits, the liquid type seal is 

inherently a simpler design. 
P.21 

-20-

Figur e 5 

J-Tube Liquid Seal 

J-TUBE 

TO CANISTER 
-21 -

Figur e 6 

Mechanical Seal 

P.22 

MOOOTCATIONS 

ROTARY SEAL 

ROTARY SEALTRAP DOOR 

LEAD RESTRICTOR 

FILL RPE MODIFfCATIONS 

ROTARY SEAL 

ROTAPY SEAL 

TRAPDOOR 

LEAD RESTRICTOR 
P.23 

-22-

If a mechanical type seal were used, excessive pressure 

could build in the fuel tank if the fuel nozzle automatic shut 

off mechanism failed, or if for some unusual reason the vapor 

line leading to the charcoal canister became blocked. To avoid 

the possibility of a fuel spitback which could be caused by 

this overpressure, a simple pressure relief device would be 

needed. More detail on this device will be provided in Section 

IV. 

Therefore, either type of sealing mechanism - liquid or 

mechanical - can be used to prevent the escape of refueling 

vapors to the atmosphere via the fillneck. 

b. Modifications to the Present System 

The differences in the frequency, magnitude, and rate of 

generation of refueling and diurnal evaporative emissions leads 

to the need for several modifications to the present 

evaporative system. Each of these is discussed below. 

(1) Charcoal Canister Size 

Generally speaking, on a per event basis, refueling 

emissions are produced less frequently but are larger in 

magnitude than diurnal evaporative emissions. Consequently, 

more hydrocarbon storage capacity (larger charcoal canister) is 

needed to control refueling emissions than is needed for 

evaporative emissions. 

The size of the canister needed for an integrated 

refueling/evaporative control system cannot be stated 

categorically since there are several variables which must be 

considered such as purge rate, charcoal working capacity, and 

canister geometry. However, on average it is expected that a 

canister for an integrated refueling/evaporative system would 

be approximately 3 times as large as the one used for the 

present evaporative system.[17] While the larger canister does 

not present any technical problems it may cause packaging 

problems on a few smaller vehicle models which could lead to 

canisters being placed in locations other than under the 

vehicle hood. While virtually all evaporative emission system 

canisters are now located under the vehicle hood there is 

nothing inherent in the design of an onboard system which 

requires that canisters for integrated systems also be located 

there. In fact, there may be some cost advantage to locating 

the canister near the fuel tank since the amount of larger 

vapor lines can be minimized. It is expected that 

manufacturers would place canisters in a location which 

provides the optimum mix of safety, cost, and performance 

characteristics. 
P.24 

-23-

(2) Refueling Vent Line Modifications 

Also, in order to accommodate the higher vapor flow rates 

associated with refueling emissions, a larger vent line between 

the fuel tank and charcoal canister is needed along with a 

larger opening in the top of the fuel tank to accommodate the 

larger vent line. The current vent line to the canister 

associated with the evaporative system is about 3/8 inch. The 

vent line with the integrated evaporative/refueling system 

would be approximately 1/2 - 5/8 inch in diameter.[ 16] The 

larger vent line (and larger opening in the top of the fuel 

tank) introduce a few added complexities. 

Unlike the limiting orifice used in evaporative emission 

systems, the larger opening required for an onboard system 

cannot provide liquid/vapor separation or rollover protection. 

Consequently, additional devices are required on an onboard 

system to meet these needs. The liquid/vapor separator, 

examples of which are shown in Figures 7 and 8, is simple in 

design and purpose.[14,18] It acts to remove gasoline droplets 

from the vapor stream and returns the liquid to the fuel tank 

to prevent liquid gasoline from entering the charcoal 

canister. Many design approaches are available in addition to 

those shown here. The separator itself may be a distinct 

component, or its function may be built into another component 

such as shown later in Figure 21. In terms of rollover 

protection, several simple devices are available which can 

prevent fuel spills during an accident, and also provide the 

benefits of a limiting orifice described above. These will be 

discussed in more detail in Section IV of this document since 

rollover and accident protection for the fuel system is 

primarily a safety issue. 

Aside from the differences discussed above, onboard and 

evaporative emission control systems are very similar in 

design. They both act to direct, trap, and consume hydrocarbon 

vapor. Onboard systems require only a few additional 

components, and because they could be integrated into vehicle 

fuel systems to handle both refueling and evaporative 

emissions, overall control system complexity is not increased 

significantly. Also, because of the integration of the 

refueling/evaporative emission control functions, it should be 

apparent that many of the safety concerns associated with 

onboard systems have already been considered in designs of the 

present evaporative emission systems. The experience and 

knowledge gained in implementing safe evaporative emission 

systems provides a substantial base of information to use in 

designing and developing safe integrated evaporative/refueling 

systems. 
P.25 

-24-

Figure 7 

VAPOR-LIQUI D SEPARATOR 

Mounting Holes 

^ z £ 

Float Weight 
Figure 8 

VAPOR OUT 

J-Un nriiii.intiiii 111 IJ 1111$ yi.i.i.if.i'n .•t.9l^.i,......'A 

ADHESIVE SEAL 

i—.7 5 HOSt TYR 

• - VAPOR/UOUJD IN 

T 

UQUJD/COfcDENSATE RETURN 

o 

10 

UCMD REUEF SLOT 

MOUNTING TABS (3) 

, — i.. u i 

r , •, . / 

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z.o 

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ro 

ui 

I 

AR OPtZH 6KU . fOA M 

AR 

W 

MESH FABRIC 

UPPER riOUSlMa 

LDVMCR H0U5IN 6 

MtCWPTNM 

NVLO M 

PLASTIC 

PLA6TIC 

•ATMAL 

VAPOR - LIQUID SEPARATOR 

U1LL1W A.«OCIATI> . WC UttMW . MP 

>»*>« n/tfl/ad *«**••• FU L L I I^Ui. 
P.27 

-26-

IV. Design Considerations for a Safe System 

As was discussed previously, several commenters have 

expressed concern regarding the potential safety implications 

of onboard systems. A review of these comments indicates that 

these concerns fall into two broad areas: the design of a safe 

onboard system and effects on in-use fuel system safety. 

Concerns in the first area will be addressed in this section. 

The section which follows (Section V) will address the later 

area of concern. 

Comments received regarding the design of a safe onboard 

system fall in three categories: 1) safety test design 

requirements, 2) safety effects of tampering and defects and 3) 

refueling operation safety. EPA's summary and analysis of the 

comments in each category is presented below. 

A. Safety Test Design Requirements 

1. Introduction 

Before analyzing the safety test design requirements it is 

interesting to look at fuel system safety from an in-use 

perspective for passenger cars meeting FMVSS 301. Presently, 

about 1.6 percent of all accidents involve a vehicle rollover 

of some type and about 0.5 percent of the rollover accidents 

result in a fire. [19] This results in a fire rate of 0.008 

percent. Thus, neither rollover accidents or subsequent fires 

are common. Similarly, 0.14 percent of all front and rear end 

collisions lead to a vehicle fire.[19] Thus, from an in-use 

perspective, vehicle crash fires are uncommon events. 

One of the most effective ways to protect against vehicle 

crash fires is to restrict fuel leakage during accidents by 

insuring the overall integrity of the vehicle's fuel system. 

To insure fuel system integrity during a crash, all currently 

manufactured passenger cars and light-duty truck's with a Gross 

Vehicle Weight Rating (GVWR) of 10,000 lbs or less, must comply 

with Federal Motor Vehicle Safety Standard (FMVSS) 301.[20] 

Basically, FMVSS 301 requires a vehicle to restrict fuel 

leakage to less than one ounce per minute when subjected to a 

rollover test following front and rear collisions at 30 miles 

per hour (mph), and side collision(s) at 20 rnph. In a rollover 

test, a vehicle is turned on each of its sides and completely 

upside down and held in each of these three positions for a 

period of five minutes. Onboard system designs must take into 

account and protect against fuel leakage or other fire hazards 

which could occur in FMVSS 301 testing. 
P.28 

-27-

Along these lines, two issues exist regarding the design 

of an onboard system capable of passing FMVSS 301. These 

include rollover protection and the crashworthiness of key 

onboard system components and connections. As was discussed 

previously, onboard systems require the use of a somewhat 

larger vent line (about l/2"-5/8" diameter as compared to 

l/4"-3/8" on current vehicles) between the fuel tank and 

charcoal canister, and a similar sized orifice would exist in 

the fuel tank. While the external vent line used on some 

current fuel tanks also requires a 1/2" orifice, manufacturer's 

onboard system designs may incorporate a rollover protection 

device to protect against fuel leakage during an FMVSS 301 

rollover test even though present designs do not. Also, 

vehicle crashes present the possibility of direct or indirect 

damage to fuel system components. In some cases this damage 

could lead to a fuel leak or increase the potential for a 

vehicle fire in some other portion of the fuel system. Thus a 

properly designed onboard system must not compromise the 

crashworthiness of the system and key components. 

2 . Rollover Protection 

A rollover protection device is basically a valve that 

would close off the refueling vent line whenever the risk of 

fuel leakage existed. Several rollover protection designs have 

been proposed by auto manufacturers and other interests which 

could adequately perform this safety function. Several of 

these are discussed below. 

One design which has been proposed by several sources can 

be termed the nozzle actuated valve. The valve is integral to 

the fillpipe and is located near the top of the fillpipe, 

perhaps near the leaded fuel restrictor. During refueling, the 

valve is opened by the insertion of a fuel nozzle. With the 

valve open, a clear passage through the vent line is available 

to allow for the routing of refueling vapors to the charcoal 

canister. Other than during refueling, the valve remains 

closed and effectively eliminates the potential for fuel 

leakage through the refueling vent line during a rollover 

accident. Figures 9 thorough 15 show five different nozzle 

actuated valve assemblies capable of performing the rollover 

protection function.[13,15,18,21] Figures 9 through 13 also 

demonstrate how nozzle insertion would open the valve to 

provide a large orifice for the venting of fuel tank vapors 

during refueling and when the nozzle is removed the vent line 

would be closed. 
Figure 9 

SEALED FILLER NECK SYSTEM 

TANK VENT VALVE ASSEMBLY 

IDURING NORMAL VEHICLE OPERATIONI 

TO CANISTER -

yr- LIQUID STOP 

kill -LS) 

SHUT-OFF %*LVE HS 

-"—' "~^*-^ \. ^ 

\ J ' V (^^^X. ^rm 2/^r 

s / / SCAL 

/ ^ 1— LEADED FUEL 

\ . JT DEFLECTOR 

-GA S CAP 

RELIEF UALVE 

, 

-28-
Figure 10 

SEALED FILLER NECK SYSTEM 

TANK VENT VALVE ASSEMBLY 

(DURING REFUEUNG EVENT) 

TO CANISTER -

VAPOR 

FROM 

TANK 

LIQUID STOP 

LEADED FUEL 

OEFLECTOR 

VO 

I 

OVERFILL 

RELIEF VALVE 

SEAL 

FUEL NOZZLE 
Figure 11 

LIQUID SEAL SYSTEM 

TANK VENT VALVE ASSEMBLY 

(DURING NORMAL VEHICLE OPERATIONI 

TO CANISTER -

SHUT OFF VALVE 

LEADED FUEL 

DEFLECTOR 

i 

OJ 

o I 

GAS CAP 

P 
Figure 12 

LIQUID SEAL SYSTEM 

TANK VENT VALVE ASSEMBLY 

(DURING REFUEUNG EVENT) 

TO CANISTER -

VAPOR 

FROM TANK 

SHUT-OFF 

VALVE 

LEADED FUEL 

OEFLECTOR 

FUEL NOZZLE 

i 

OJ 
Figure 13 

NOZZLE-ACTUATED REFUEUNG EMISSIONS VAPOR VENT VALVE 

Vapor to 

Canister 

Vapor from 

Vapor/Liquid Separator 

i 

OJ 

to 

I 
P.34 

r-\ CU •H &4 

-33-

u I 

t. 

I 

o 

r 

if? 

I 

a\ 

UJ 

z UJ U. UJ OC 
P.35 

-34-

Figure 15 

"Toyota Concept" 

Rubber Seal 

to Canister 

from Fuel \. 

Tank

 v ' 

/ / 

to Fuel Tank 

Refueling 

Nozzle 
P.36 

-35-

Also, while a rollover protection device might be 

necessary, it is interesting to note that many current 

production passenger car and light truck models (mostly side 

fill) employ an external vapor vent line of about 1/2" diameter 

that connects the fuel tank to the top of the fillpipe (see 

Figure 1). This external vent line is approaching the size 

needed for a refueling vent line, and yet manufacturers have 

included these external vent lines without any rollover 

protection device. As will be discussed below, adding a 

rollover protection system to these vehicles may actually 

enhance safety over current designs. 

This analysis has presented several basic rollover valve 

designs capable of providing the protection required by FMVSS 

301 tests. Manufacturers could choose to implement one of 

these approaches, or could develop another. The approach 

ultimately selected will be that which provides cost efficient 

protection, is compatible with the other components of the 

manufacturers onboard system, and can be integrated effectively 

into the vehicle design from both safety and operational 

perspectives. 

3. Component/System Crashworthiness 

The second issue regarding safety test design requirements 

involves the crashworthiness of the key components of an 

onboard system. This includes those components most 

susceptible to damage in an accident (nozzle actuated rollover 

valve, canister) and the structural integrity of the vapor line 

(and connections) which may exist between the top of the fuel 

tank and the rollover valve. A problem in one of these three 

areas could cause a vehicle to fail FMVSS 301 tests and must be 

addressed in proper system design. Each of these concerns is 

discussed below. 

However, before beginning these discussions, it should be 

noted that component/system crashworthiness is not at all a new 

concern. Manufacturers must address these same concerns in the 

design of the current evaporative emission systems. Given the 

similarity of onboard refueling and evaporative controls, and 

that many systems will be integrated, there should be no new or 

unique problems in this area. 

a. Rollover Valve 

First, the crashworthiness of the rollover protection 

device is a design consideration for nozzle actuated valves, 

since they would be located near the exterior shell of the 

vehicle. Integration of nozzle actuated valves into the 

overall vehicle design would have to include a consideration of 

the potential to sustain damage if struck in a collision. 
-36-

However, this design consideration is straightforward, and 

it is reasonable to expect that manufacturers can and will 

integrate rollover valves into their fillpipe designs without 

decreasing the structural integrity of the fillpipe while 

providing crashworthiness for the valve. For example, it is 

worth noting that vehicle manufacturers have dealt with similar 

problems in their designs of fillpipes, external vapor vent 

lines, and gas caps, and in fact, one would not expect the 

nozzle actuated rollover valve to be any more susceptible to 

damage than these components. As was mentioned previously, the 

1/2" external vent line lies in this same area on the vehicle, 

and yet manufacturers have included such vent lines without a 

rollover protection device. 

b. Vapor Line 

Similarly, manufacturers will have to be cognizant of the 

structural integrity of the vapor line and vapor line 

connections, if any, between the fuel tank and the rollover 

valve. These would have to be designed to withstand the 

stresses which might occur in a crash in order to maintain fuel 

system integrity. However, there is no significant engineering 

challenge to accomplishing this objective. 

The integrity of this portion of the vehicle's vapor line 

can be assured through use of a vapor line material of proper 

strength, flexibility, and durability. A number of vapor lines 

of different material, wall thickness, and construction are 

currently available. In addition, routing of this portion of 

vapor line is another design parameter available to 

manufacturers. As a matter of course, manufacturers are 

expected to insure that the line is protected from abrasion and 

normal wear and that it is not in a vulnerable location in the 

event of a collision. This is considered straightforward given 

that on integrated systems the refueling vapor line now 

replaces that used for control of diurnal evaporative 

emissions. Similar routings would be expected. Vapor line 

integrity and connections in current vehicles must meet similar 

requirements, and it is reasonable to expect that similar 

materials and connecting approaches would be used. 

Finally with regard to vapor line integrity and 

connections, it is worth noting that some vehicle models now 

use a flexible insert between the fillpipe and fuel tank to 

enhance the fuel system safety in-use (see Figure 16).[15] 

Similarly, in many vehicle models the external vent line 

actually incorporates a flexible vapor line which connects the 

metal portions of the external vent line from the top of the 

fuel fillpipe and the fuel tank (see Figure 16). These 
Figure 16 

BUICK CENTURY FUEL TANK AND FILLPIPE 

PRODUCTION CONFIGURATION 

Fuel Sending Unit 

and Vent Orifice 

Nozzle 

Spout 

12%" 

i 

Ul 

I 
P.39 

-38-

connectiohs are subject to the same performance requirements as 

would be needed for onboard system vapor lines and in some 

cases are even more critical and demanding. Evidence is that 

these have been incorporated safely. The manufacturers' 

experience with current vehicle evaporative and fuel systems 

described above demonstrates that vapor line and vapor line 

connections can be made to withstand the stresses which occur 

in a vehicle accident. 

c. Charcoal Canister 

Concerns regarding the crashworthiness of the charcoal 

canister center on the possibility that a canister ruptured in 

an accident could present a fire hazard if an ignition source 

exists nearby. 

Even if the rupture of the integrated refueling/ 

evaporative canister occurred in some cases, the potential 

hazard should not be overstated. While the refueling load to 

the canister is larger than the evaporative load, after the 

first few miles of driving the canister would be purged such 

that the amount of vapor remaining in the canister is 

essentially the same as that present in current evaporative 

emission canisters alone.* Thus it could be argued that the 

real hazard, if any, is not significantly different than that 

now found on present systems. Thus, it is hard to perceive any 

added risk from the use of a larger charcoal canister. 

Nevertheless, if a manufacturer believed that the canister 

posed too great of a potential risk, the risk could be 

eliminated through placement of the canister in a protected 

area such as the rear of the engine compartment or in some 

underbody area as has been suggested by some 

manufacturers.[12,13] In most cases it is expected that 

manufacturers would simply place the integrated 

refueling/evaporative canister where the present canister is 

now located; in these cases no new design issues really exist. 

Due to the nature of the charcoal used to trap hydrocarbon 

vapors, and strict certification test requirements, 

hydrocarbons would be quickly stripped from the charcoal 

early in the purge process. Therefore, during most of the 

operation of the vehicle (90 percent), the charcoal 

canister does not contain enough hydrocarbon vapor to 

present any safety risks.[9] 
P.40 

-39-

d. Summary 

In summary, current fuel and evaporative emission systems 

must meet the same FMVSS 301 requirements and much of the 

experience gained in designing and building current systems can 

be directly extrapolated to implementing an onboard system. 

The analysis presented above leads to the conclusion that 

straightforward, viable engineering solutions exist to address 

any potential safety design concerns, and that onboard systems 

can be incorporated into the vehicle's fuel/evaporative system 

without compromising fuel system integrity or reducing the 

vehicle's ability to pass FMVSS 301 requirements. 

While an onboard system can be designed to provide fuel 

system integrity both in FMVSS 301 testing and in-use, it is 

prudent to consider the possibility of tampering, 

malmaintenance and defects with these systems, and means to 

address any potential problems which may exist. These issues 

will be addressed next. 

B. Tampering, Malmaintenance, and Defects 

Even if a system is designed properly and functions safely 

under "normal" and "extreme" in-use conditions, some question 

remains as to the potential effects of tampering, 

malmaintenance, and defects on onboard system safety. 

Tampering involves the intentional disablement (partial or 

total) or removal of a component within the system. 

Malmaintenance is the incorrect application of a prescribed 

maintenance procedure, and defects involve the improper 

operation of a prescribed system or system component caused by 

design, manufacturing or assembly errors. 

An onboard system is expected to be essentially 

maintenance free (no scheduled maintenance) as are current 

evaporative emission systems. Thus th^ focus of safety 

concerns turns more toward the effects of defects and 

tampering. Although both defects and tampering are uncommon, 

they are possible and some thought must be given to designing 

systems which minimize the likelihood of these events and the 

safety effects if they do occur. 

1. Defects 

First, with regard to defects, the primary safety related 

concern deals with the possibility that defects in the 

operation of one or more components of the onboard system 

in-use might lead to safety problems for the vehicle. This 

includes possible problems with components such as the 

liquid/vapor separator, purge valve, charcoal canister and 

rollover valve. 
P.41 

-40-

Since onboard system components such as the liquid/vapor 

separator, purge valve, and charcoal canister are very similar 

to those used in evaporative systems, one method to assess the 

potential safety effects of defects is to review the experience 

seen with evaporative systems. In an effort to quantify the 

potential for defect problems regarding onboard systems, three 

different computer files provided by NHTSA were reviewed for 

evidence as to defects pertaining to the evaporative emission 

system which could impact vehicle safety in-use.[22] The files 

reviewed covered recalls, service bulletin reports, and owner 

complaints current as of November, 1986 for all three vehicle 

classes (passenger car, light truck, and heavy-duty gasoline). 

A review of the recall files revealed only 12 cases that could 

be even remotely linked to the evaporative emission system out 

of an estimated 3,000 families certified with evaporative 

emission systems. Service bulletin reports for dealers added 

an additional 21 cases for a total of 33 possible problems out 

of over 3000 families. None of these were identified as having 

caused an accident; the vast majority were more emission system 

performance than safety defects. Finally, a review of the 

owner complaints indicated only about 100 problems out of over 

180 million vehicles sold with evaporative emission controls. 

In only a few of the owner complaints did safety problems 

actually occur, and no significant damage was reported. On a 

percentage basis these potential problems are very small. 

Two other valuable observations can be drawn from a review 

of these files. Problems/complaints have diminished with newer 

model year vehicles with evaporative controls, which 

demonstrates that gaining experience leads to product 

improvement. Given the similarity between onboard refueling 

and evaporative emission controls, and the fact that the two 

systems will be integrated in most cases, much of this 

experience will be directly transferable to onboard systems and 

thus improve in-use performance. Second, the review of the 

owner complaints files indicated no trends other than those 

related to improvements in newer model year vehicles; thus no 

systematic problems in components or systems were evident. 

Further, it is important to note that the very mechanisms 

used to generate the files for this survey would actually act 

to help eliminate any potential in-use safety effects of 

onboard systems defects. Dealer service bulletin reports are 

effective in dealing with problems raised at the dealerships, 

and owner complaints assist the manufacturers and NHTSA in 

assessing the need to conduct voluntary or mandatory recalls. 

Finally, to place the potential for defect problems from 

onboard systems in context, it should be noted that the onboard 

risk is essentially incremental to that now seen for 

evaporative systems, since in most cases the refueling and 

evaporative systems would be integrated. On an incremental 

basis, the frequency of defects would likely be unaffected. 
P.42 

-41-

Finaily, since a rollover valve could be used on some 

onboard system designs specifically to enhance safety and they 

are not used on current vehicles, it is worth discussing the 

possibility of valve defects. First, it should be noted that 

defects in these valves should be rare. Manufacturing 

engineering techniques permit the development and production of 

highly reliable valves and statistical quality control 

techniques are available to insure that production valves meet 

design standards. In fact, if a rollover valve is defective at 

the vehicle assembly point, the vehicle will probably not be 

able to accept the fuel provided at the end of the assembly 

line, and repairs will be needed even before the vehicle leaves 

the plant. Second, to insure in-use protection, rollover 

valves must be designed to fail in the closed position. This 

would be considered "safe" because a closed position valve 

failure would never cease providing rollover protection and it 

would effectively block the refueling vent line and make 

refueling the vehicle extremely difficult. This difficulty 

would provide incentive for the vehicle operator to identify 

and repair the failure. Also, rollover valve failure might be 

one component of an onboard system which could be incorporated 

into onboard vehicle diagnostics and thus allow the operator 

notice of the problem when it occurs and provide an opportunity 

for repair before the fuel level becomes critical. Fail safe 

designs would be effective in achieving both protection and 

repair, and that the other measures discussed above would 

assist in eliminating or addressing any in-use defects. 

2. Tampering 

A second area of potential safety problems involves the 

effects of possible system tampering. While several types of 

tampering occur with evaporative emission systems (see Table 

1 ), past in-use experience with these systems shows that only 

one type, disconnection and/or removal of the charcoal 

canister, might be a safety problem for onboard systems. This 

type of tampering poses a possible safety hazard because during 

the refueling operation it would lead to a flow of gasoline 

vapor into the atmosphere at the point where the missing 

canister had been located. While the gasoline vapor mixture 

reaching the canister location in this situation would be well 

above the upper flammability limit, it would briefly be 

flammable as the vapor dissipates and at the air/vapor 

transition zones. If a spark or other ignition source were 

present, the mixture could briefly burn. While this situation 

is likely to be rare, the possible safety effects of such an 

occurrence must be considered in the onboard system design. 
P.43 

-42-

Table 1 

Types of Tampering Problems 

And Typical Rates of Occurrence 

Rate of 

Problem Occurrence (%) 

Gas Cap Removed 1.2% 

Canister Vacuum Disconnected 1.7 

Cap Removed & Canister Vacuum Disconnected 0.1 

Canister Removed 0.3 

Non-vacuum Canister Disconnection 0.2 

Total Disablements 3.5% 

Tampering rates calculated from the combined data from the 

EPA Tampering surveys performed in 1982, 1983 and 1984. 

(9,142 vehicles) 
P.44 

-43-

There are several points which need to be made relative to 

canister tampering. First, this is not unique to onboard 

systems - similar potential problems now exist with evaporative 

emission canisters but a safety concern regarding tampering 

with evaporative emission system canisters has not surfaced. 

Second, using current evaporative emission canisters as an 

indicator, this situation is likely to be rare for integrated 

onboard refueling/evaporative canisters. As is shown in Table 

2, current average canister tampering is only about 3 percent 

of all vehicles, and similar rate would be expected for 

integrated refueling/evaporative emissions canisters. Third, 

if the canister were located in an area which would be 

difficult to access, tampering could be further discouraged. 

Further, the potential problem could be reduced through 

proper placement of the canister in a location distant from any 

ignition sources. Possible locations include the rear of the 

engine compartment (as is done with some evaporative canisters) 

or in some underbody area as has been suggested by some 

manufacturers for packaging reasons. Placing the canister in 

an underbody area would also reduce the potential for tampering 

by making it less accessible to the owner as mentioned above. 

While canister tampering is infrequent, and means exist to 

discourage such actions even further, good engineering judgment 

dictates that canisters not be placed in a location where 

tampering could create a safety hazard. It is expected that 

manufacturers will take all reasonable steps necessary to 

reduce tampering, and that refueling canisters would not be 

placed in locations where their removal could create a safety 

risk. 

3. Summary 

In summary, neither component defects or tampering need 

create the potential for in-use safety risks. There is no 

evidence to indicate that possible defects in other onboard 

system components would lead to safety problems. There are 

very few defects' with present evaporative emission systems, and 

since it is likely that refueling and evaporative emission 

systems would be integrated, the overall defect rate is likely 

to be no different than that seen in present vehicles. 

Further, methods are available to assure that reliable rollover 

valves are installed in vehicles and to insure rollover 

protection in the unlikely event of a valve failure. 

While canister tampering effects must be considered, it 

should be noted that it presently is uncommon, and this low 

rate is expected to continue for onboard systems. Also, 

tampering could actually decrease through judicious canister 
P.45 

-44-

Table 2 

Canister Tampering Survey Results 

By Year* 

Passenger Car and Light Truck** 

Year % Tampered 

1978 3 

1979 2 

1980 No Report 

1981 2 

1982 2 

1983 5 

1984 3 

1985 4 

Avg 

* Motor Vehicle Tampering Survey - 1985, US EPA, OAR, OMS, 

FOSD, November 1986. 

** Since HDGVs did not require evaporative controls until 

1985, survey data is currently not available for these 

vehicles. 
P.46 

-45-

placement on the vehicle. Nevertheless, prudent design 

practices dictate that manufacturers not place canisters in a 

location where tampering could lead to a safety problem, and it 

is expected that this approach would be followed. 

An onboard system design must also include consideration 

of potential effects on the safety of refueling operations. 

This is discussed in the next section. 

C. Refueling Operation Safety 

1. Fuel Tank Overpressure During Refueling 

The first potential safety issue involves the possibility 

of pressure build-up in the fuel tank during the refueling of a 

vehicle equipped with an onboard system. Whenever a system is 

designed to be "sealed" from its environment, some forethought 

must be exercised to evaluate the possibility and consequences 

of an overpressure within the system. 

Although an onboard system does not completely seal off a 

vehicle's fuel tank, it is designed to allow for only one 

opening, the refueling vapor vent line. If for some unusual 

reason, the vent line were to become fully or partially blocked 

or the nozzle automatic shut-off mechanism failed during a full 

refill, excess pressure could build in the fuel tank. This 

concern is only associated with an onboard system utilizing a 

mechanical seal as illustrated in Figure 3. With a liquid seal 

system (see Figure 4), excess pressure cannot build up in the 

tank during refueling because fuel would simply flow out the 

fillneck opening (the same way it currently does) and the 

nozzle operator could then stop the fuel flow. Liquid seal 

systems would function in the same manner as current fuel 

systems. From the nozzle operator's viewpoint, the refueling 

operation remains the same. 

If a manufacturer elects the mechanical seal design, he 

must incorporate a simple pressure relief device capable of 

relieving fuel tank pressure. In the event of a nozzle failure 

or vent line blockage, this device would eliminate potential 

tank overpressurization by opening an "emergency" passage to 

the atmosphere through which pressurized vapor and any gasoline 

would spill onto the pavement or some other location noticeable 

to the nozzle operator. This spillage would make the fuel pump 

operator aware of the problem and fuel flow could be stopped 

without causing damage to the fuel system or causing fuel to 

spitback on to the operator. 
P.47 

-46-

There have been several different designs suggested for 

such pressure relief devices. A sample design is shown in 

Figure 17 which would be incorporated directly into the design 

of the fillpipe so that the condition would be noticeable by 

the operator.[18] The operator would then be prompted to 

repair any problems in order to resume normal refueling 

actions. (The need for prompt repair would have positive 

safety and air quality complications.) As was shown in Figure 

9, it might also be possible to incorporate the pressure relief 

function into some other component of the system such as the 

rollover valve. Any overpressure concerns can be eliminated 

through a simple pressure relief device such as these. 

2. Pre-Refueling Overpressure Effects 

Another potential safety issue raised relating to 

refueling operations has to do with the "U" bend in the 

"J-tube" fillneck seal. If the tank vent became blocked, and 

pressure built up substantially in the tank, upon removal of 

the fuel cap, the liquid gasoline which was left standing in 

the "U" bend could be spit back out the fillpipe. 

This concern can be easily addressed by drilling a small 

hole in the bottom of the "U" bend (see Figure 4), which would 

allow any fuel left standing in the fillpipe subsequent to a 

refueling event to drain out into the fuel tank. Given the 

range of fuel dispensing rates seen in-use, this hole can be 

sized to quickly provide drain capacity and still provide the 

seal needed during refueling. By evacuating the column of fuel 

left standing in the fillpipe, the potential for spitback to 

occur upon removal of the fuel tank cap would be eliminated. 

3. Summary 

The analysis presented above demonstrates that simple, 

straightforward engineering solutions exist for the specific 

concerns raised by the commenters. In all cases, manufacturers 

have a number of design options available to address any 

specific concerns. 
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P.49 

-48-

V. In-Use Fuel System Safety 

1. Summary of Concerns 

Some concern has been expressed that any time a system 

increases in size or complexity, the potential for a failure 

within the system also increases. Applying this line of 

thinking to vehicle emission control systems, it has been 

suggested that onboard systems would inherently decrease 

overall fuel system safety because several components are 

larger and a few more components are needed than for current 

evaporative emission systems. In-use vehicles are subject to 

innumerable accident situations, and some concern exists as to 

whether or not an increase in component size/number could lead 

to safety problems. 

Further, it has been stated that even if a vehicle fuel 

system is safe enough to pass FMVSS 301, it does not insure 

that it is free of all safety risks in-use as evidenced by the 

number of vehicle crash fires that occur each year. It has 

been argued that vehicles equipped with an onboard system could 

pass all FMVSS 301 tests and yet directionally increase risk 

in-use by some unquantifiable (presumably small) amount. Thus, 

it follows that because some in-use situations differ from 

FMVSS 301 tests, onboard systems must not only be designed to 

be capable of passing Federal safety standards, but these 

systems must also be designed so as not to increase in-use risk 

for fuel system related hazards. 

2. Analysis of Issues 

Fundamentally, EPA believes that overall risk in-use 

should not increase. And, while it is true that FMVSS 301 

cannot protect against every conceivable in-use situation, 

manufacturers are motivated to consider fuel system safety 

implications for reasons other than insuring that their 

vehicles pass Federal safety standards. Manufacturers must 

determine what they consider to be an appropriate level of 

safety and in-use risk, and then design their vehicles to meet 

this level. Often this leads to different overall levels of 

safety in different vehicle models. Before discussing how to 

address this issue, it is valuable to discuss how safety 

concerns are integrated into the overall vehicle design and 

development process. 

First, safety is an integral part of the design process 

and is normally not considered incrementally. However, 

managing risk involves a series of trade-offs, balances, and 

compromises with other key design criteria. Manufacturers 

choose not to make their vehicles free of all risk because of 

other valid design considerations such as performance, styling, 

weight, cost, and other factors. It is generally accepted that 
P.50 

-49-

no technological constraints exist which would prevent the 

production of a nearly "fire-proof" vehicle, and certainly 

vehicles could be made safer than they currently are as 

evidenced by numerous "safety car" designs.[23] However, cost 

and other considerations are valid and they prevent "zero" risk 

(or a perfectly safe vehicle) from being considered 

appropriate. One analyst has stated, "It is definitely not 

reasonable to expect manufacturers to produce 'Sherman Tanks' 

... as such vehicles would neither serve the needs of societal 

safety, mobility, or economy."[24] 

This same logic and risk management process applies to 

fuel system safety. Factoring safety into fuel system design 

is a complicated process that involves numerous tradeoffs and 

compromises as above. Fuel system designs are not all alike, 

and fuel system safety considerations vary from one design to 

another. For example, fuel tank size and location on the 

vehicle have a substantial impact on a vehicle's safety during 

a collision. Rear fill tanks are in a more accident prone 

location than side fill tanks, and are usually located closer 

to the exterior shell of vehicle. Side fill tanks are 

generally considered safer than rear fill tanks, and 

consequently, rear fill fuel tanks are gradually being phased 

out of vehicle designs. However, it should be noted that this 

change over has not occurred immediately due to other design 

considerations such as cost and conflicting interaction with 

other aspects of the total vehicle design. A similar set of 

arguments can be made with plastic versus metal fuel tanks. 

These simple examples demonstrate how risks are managed 

relative to other considerations. Even current fuel systems 

could be safer but some risk is accepted. 

Another interesting example lies in the area of fuel 

system external plumbing such as emission control vapor lines 

or external vent lines along the fillpipe. At one time added 

piping connections similar to the external vapor vent lines 

that appear on some of today's vehicles were characterized as 

an unacceptable added safety risk by General Motors.[25] 

However, today that same manufacturer incorporates an external 

vapor vent line into many of its vehicle's fuel systems. 

This particular design change illustrates a very 

significant aspect of fuel system safety. Even though concern 

existed over the potential safety aspects of additional fuel 

system plumbing, the mere fact that these additional lines 

appear on today's vehicles confirms that safety concerns can be 

technically addressed if desired. Any perceived in-use risk 

can be managed. Safety does not have to be an obstacle to fuel 

system improvements or modifications. The technology to reduce 

safety risks is currently available, and the degree to which it 

is utilized depends on how much risk a manufacturer is willing 

to accept. 
P.51 

-50-

As illustrated in the discussions above, manufacturers 

accept or manage varying amounts of risk in order to strike a 

balance or compromise with all of the important design 

criteria. Clearly safer vehicles could be made, and the amount 

of in-use risk reduced. As considerations change, the amount 

of risk accepted may also change. Often the level of 

acceptable risk may be more constrained by in-use liability 

concerns than government safety tests. For example, crash 

testing results recently released by the Insurance Institute 

for Highway Safety show a wide range of performance on vehicles 

designed to meet the NHTSA bumper standards. A number of 

vehicles performed better than required by the standards and 

performance varied by vehicle model.[26] Some manufacturers 

chose to incorporate safer designs on some models for liability 

and perhaps marketability reasons. 

Similarly, the safety of an onboard system on in-use 

vehicles will depend on the design decisions made by the 

manufacturers. Onboard systems would increase the size and 

number of fuel system emission control components, and some 

concern has been expressed that the safety of these components 

in FMVSS 301 testing may not necessarily be indicative of 

in-use performance. However, adding these systems does not 

need to affect the level of risk a manufacturer is willing to 

or can afford to accept. As with any other system change, 

manufacturers would integrate onboard systems into their 

vehicles' fuel systems without increasing overall system risk, 

and clearly, there are no inherent technical constraints 

prohibiting them from doing so. 

Further, there is little merit to the assertion that an 

onboard system must be inherently less safe than an evaporative 

emission system because it is more "complicated". Adding a few 

components and enlarging a couple of others presents no risk 

which cannot be managed to levels now deemed acceptable. As a 

matter of fact, many of the improvements recently implemented 

on passenger cars and light trucks have resulted in 

vehicles/systems which are increased in both safety and 

complexity. Consider for example advances made in 

vehicle/engine control systems. Electronic engine controls 

have increased vehicle engine complexity tremendously over 

previous systems, yet there is no evidence that these system 

"complications" have jeopardized safety. In fact, 

manufacturers are now considering computer controls for other 

vehicle systems such as the suspension and handling, with the 

direct purpose of improving vehicle safety.[27] A more 

complicated system does not imply a less safe one if given 

proper consideration during design. 
P.52 

-51-

As discussed in detail earlier, manufacturers have many 

options available in the design of an onboard system which can 

manage or eliminate any perceived increase in in-use risk. 

However, for manufacturers with special concerns regarding 

in-use safety there are even more design options available. 

Fail safe, redundant, or breakaway rollover valves could be 

used. The integrity of the critical portion of vapor line 

between the fuel tank and rollover valve could be assured 

through the use of steel braid covered rubber hose in key areas 

or steel tubing.[28] Both rubber and steel vapor line have 

been used on past vehicle models. If chafing of this critical 

portion of vapor line is a concern, the affected areas could be 

wrapped in a spiral spring for protection. Also, slack could 

be provided in this critical portion of vapor line to minimize 

the possibility of separation or rupture in an accident. 

Improved or additional fittings, adhesives, or clamps could be 

used to increase the strength of key vapor line connections 

between the fuel tank and the rollover valve. Concerns related 

to the charcoal canister can be addressed by using a reinforced 

canister shell or a protective barrier. While these may be 

somewhat extraordinary, this brief listing demonstrates that 

further design options are available which if used could 

improve safety over current vehicles. 

In summary, manufacturers can manage their in-use risk and 

can choose to make an onboard system as safe as they deem 

appropriate. Onboard systems present no safety concerns which 

cannot be eliminated through proper design, and each 

manufacturer will develop the fuel system design which 

represents the best balance for each particular vehicle model, 

with full consideration of the safety risks and all other key 

factors. 

3. Opportunities for Improvement 

Implementing onboard controls could actually result in a 

net improvement in overall fuel system safety. Since 

manufacturers would need to redesign some aspects of their 

vehicles' fuel systems to incorporate onboard systems, the 

opportunity would be provided to reexamine other aspects of 

fuel system safety as well. Some of the potential fuel system 

improvements that could result from this reexamination include 

an acceleration of the transition from rear fill to side fill, 

integration of the current external vapor vent line inside the 

fillpipe, better placement of the fuel tank, or even 

improvement in the fuel tank integrity itself. Also, any number 

of other minor modifications or improvements in the fuel or 

emission control systems could be made which could enhance 

safety and performance and perhaps reduce cost. These include 

areas such as tank venting, purge valve operation, and 

eliminating many problems identified through owner complaints 

and other similar survey measures. 
P.53 

-52-

Also, it is likely that an onboard refueling control 

requirement would lead to a decrease in the amount of fuel 

spilled in-use and thus improve the overall safety of refueling 

events. In the certification refueling test, vehicles would 

have to be designed to accommodate a refueling dispensing rate 

at the high end of the present range of in-use values (8-10 

gallons per minute) without any spillage or spitbacks. This is 

because any fuel spilled during the test is considered as part 

of the test results. Since one tablespoon of gasoline 

evaporates to a substantial amount of vapor (about 10 grams), 

almost any spillage that occurred during the certification test 

would result in a failure. Thus, the test procedure 

requirements will insure that manufacturers' fuel system 

fillpipe designs are capable of handling dispensed fuel at flow 

rates up to 10 gallons/minute without allowing any spitback. 

The use of these fillpipe designs are predicted to lead to a 

reduction in the amount of fuel spilled in-use. This is 

compared to some current vehicle fillpipe designs which have 

difficulty accepting fuel at the lower end of the in-use range 

(8-10 gpm) without spitback. To assure this benefit accrues in 

the long term, EPA is considering an in-use dispensing rate 

limit of 10 gallons per minute along with any onboard 

requirement. 

Also, from the analysis presented above, it is evident 

that implementing onboard controls would provide at least three 

other direct safety benefits over present systems. First, 

adding a rollover protection device will improve the safety of 

present fuel tank systems which use a 1/2" external vent line 

without rollover protection. Second, adding a rollover valve 

will enhance the safety for those vehicles which now use a 

limiting orifice for rollover protection, since a rollover 

valve will provide a positive seal in lieu of the "controlled 

leak" approach provided by the limiting orifice. Last of all, 

it should be noted that refueling vapors are currently vented 

to an area which poses somewhat of a safety hazard. This is 

because the potential exists for refueling vapors to ignite 

inadvertently as they escape from the fillneck opening. 

However, as onboard controls are phased in, and more and more 

vehicles route refueling vapors away from the fuel pump 

operator to a safer point (the charcoal canister) the overall 

risk involved in refueling a vehicle will be reduced. 

Finally, to address any special concerns regarding onboard 

system crashworthiness and to perhaps improve crashworthiness 

over current vehicles, there is an alternative onboard system 

design available which manufacturers may elect. As is shown in 

Figure 18, this system is similar to Figure 4, except all the 

needed valves (rollover, vent, liquid/vapor separator) are 

built into the top of the fuel tank, instead of externally. 
. PRESSUT^AACULM' 

RELIEF CAP 

Figure 18 

ALTERNATIVE INTEGRATED EVAPORATIVE/REFUELING SYSTEM 

TANK MOUNTED VALVES 

REAR MOUNTED CANISTER 

J-TUBE SEAL 

MECHANICAL OR SOLENOID 

ACTUATED VENT/ROLLOVER 

VALVE, LIMITING ORIFICE 

& LIQUID/VAPOR SEPARATOR 

5/8" DIA. 

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14 GALLON FUEL TANK 
-54-

A solenoid activated rollover valve could be used (Figure 

19) which is located on top of or inside the fuel tank. [29] 

This valve would normally be closed except during refueling 

when it would normally be closed except during refueling when 

it would be electronically opened by a switch located near the 

opening of the fillpipe. The switch could be activated either 

by the opening of the door over the fuel cap or removal of the 

fuel cap itself (see Figure 20). 

Yet another approach is a mechanical ball valve. This 

device would normally remain open to provide a clear vapor 

passage. However, in the event of a rollover accident gravity 

causes a metal ball to roll into a fitted seat and seal off the 

vent line. One variation on this design (see Figure 21) would 

be simple mechanical ball valve built in combination with other 

needed valves.[15] 

As is shown in Figure 18, this onboard system design may 

need a fill limiter to allow for normal refueling operations 

(i.e., automatic shut-off) and to prevent overfilling the tank 

during full refills. A sample design is shown in Figure 

22. [29] The operation of the fill limiter is quite simple. 

When the tank is full the float rises in the fill limiter and 

closes off the refueling vent line. This causes pressure to 

rise in the tank, subsequently fuel runs up the fillpipe and 

activates the nozzle automatic shut off mechanism. While 

incorporation of a fill limiter is quite simple from an 

engineering perspective, the design would have to incorporate a 

"soft close" to avoid back pressure "spikes" and possible 

spills at the end of a full refill. 

From a safety perspective this alternative is attractive 

because all the external components are either removed or 

mounted in a more protected location. The external vent line 

(Figure 1) can be eliminated and the other system valves and 

vapor lines are move'1, away from the vehicle shell to a more 

protected area within the vehicle body. Also, no vapor line 

exists between the fuel tank and the rollover valve, so vapor 

line integrity and connections are less critical. 

Finally, depending on how high a priority a manufacturer 

assigns to safety or if significant in-use risk is perceived, a 

collapsible bladder tank design could be used to meet the 

onboard requirement. Bladder tanks could lead to a substantial 

improvement in fuel system safety by providing an additional 

shell of protection to help reduce fuel spillage in case of an 

accident. Also, a bladder tank could eliminate essentially all 

of the safety concerns raised regarding control of refueling 

emissions. This is because a vapor space would not be present 

in a bladder tank, and without a vapor space, refueling 

emissions would not occur. Thus neither a refueling emissions 
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P.58 

-57-

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P.60 

-59-

canister, external plumbing, or a rollover valve would be 

needed. It might even be possible to eliminate the present 

evaporative system and enhance safety even more. Also, 

bladders should be an attractive option for those who claim 

high costs or packaging problems with canister-based onboard 

systems. EPA is quite interested in collapsible bladder tanks 

as an option to canister-based onboard systems, and plans to 

further explore the cost and technological feasibility of this 

approach as well as the safety and emission benefits. 

In conclusion, the information and rationale presented 

above refute the assertion that adding an onboard system would 

directionally increase in-use risk, even if only by some 

unquantifiable (presumably small) amount. Any perceived risk 

is manageable, and furthermore, it appears that the net effect 

of an onboard refueling control requirement could be a 

potential increase in fuel system safety. As discussed above, 

and in Section IV there are numerous design alternatives to 

address the safety concerns raised. To varying degrees all 

options have the potential to improve the safety of fuel 

systems in-use. 
P.61 

-60-

VI. Cost and Leadtime Considerations 

The comments received regarding onboard vapor recovery 

systems also addressed the cost and leadtime implications of 

implementing such controls. More specifically, several of the 

comments addressed onboard safety costs in some form (usually 

addressing hardware costs), and several commenters expressed 

some concern over EPA's leadtime estimate. An analysis of the 

costs and leadtime necessary to implement onboard controls 

safely is an integral part of the overall evaluation of the 

feasibility of this control approach. As was mentioned above, 

cost is one of the other key considerations which is often 

balanced carefully against safety concerns, and the costs 

needed to implement onboard systems safely must be reasonable 

relative to other safety costs and the overall costs of onboard 

systems. Further, the analysis must carefully consider the 

manufacturer leadtime needed to implement onboard controls on 

their production vehicles. This includes the time needed to 

identify, evaluate, and address all safety concerns and to 

comply with the test requirements prescribed in FMVSS 301. 

The first portion of this section addresses onboard safety 

costs; the second discusses leadtime and describes the basis 

for EPA's leadtime estimate. Some of the cost figures cited in 

the safety cost analysis are drawn from a broader EPA analysis 

which develops total onboard system costs in 1984 dollars.[17] 

A. Safety Costs 

As is evident from the discussion presented in Section IV, 

the costs needed to implement onboard controls safely fall in 

several areas. R&D type costs will be incurred, some new or 

modified components will be needed which may slightly affect 

vehicle operating costs, and safety certification testing will 

be necessary. However before beginning a discussion of these 

costs, it is valuable to discuss how the FMVSS 301 standards 

and EPA's evaporative emission control requirements impact 

onboard safety costs. 

The control of refueling emissions through an onboard 

system would not be the first Federal regulation to require an 

investment to improve fuel system safety. The first fuel 

system integrity standards (FMVSS 301) were implemented by 

NHTSA for 1968 vehicles, and since then there have been 2 major 

additions to these requirements. Each of these new 

requirements has caused a small cost increase, but each has 

also led to an improvement in fuel system safety on in-use 

vehicles. In the mid 1970's, FMVSS 301 was substantially 

upgraded to extend the coverage of impact types to include 

rollover events and, rear end and side collisions. A 1983 
P.62 

-61-

NHTSA Technical Report[19] describes the nature of the 

modifications made in response to the upgrading of the standard 

and estimates the costs incurred by vehicle manufacturers in 

order to meet the revised standard and provide a higher level 

of in-use assurance. 

Table 3 describes modifications that were made to 1977 

model year vehicle fuel systems in response to the increased 

requirements of FMVSS 301. These modifications ranged from 

minor changes such as the slight revision of mounting bolts or 

clips to more major ones such as recontouring the fuel tank. 

Based on information submitted to NHTSA by vehicle 

manufacturers, the average (sales-weighted) cost increase 

required to make these modifications was $4.60 per vehicle.* 

These modifications were also estimated to increase vehicle 

weight slightly (an average of three pounds per vehicle), which 

would tend to marginally increase the amount of fuel consumed 

over the life of the vehicle (about 3 gallons of fuel). When 

these two costs are added, NHTSA estimated the total safety 

cost resulting from the 1977 revisions to FMVSS 301 averaged 

about $8.50 per vehicle (1982 dollars). 

Based on an evaluation of in-use accident information for 

1977 and later model year vehicles, NHTSA's 1983 Technical 

Report also estimated that the upgrading of FMVSS 301 would in 

the long term annually prevent 400 fatalities, 630 injuries, 

and 6500 post crash fires. This indicates that FMVSS 301 has 

been effective in substantially improving many aspects of 

overall fuel system safety and that these improvements were 

purchased relatively inexpensively. 

The second area of interest is the effect of current 

evaporative emission systems on potential onboard system safety 

costs. As was described in Section III of the report, an 

onboard system is in many ways an extrapolation of current 

evaporative emission control technology and the two systems are 

quite similar. Many of the control techniques and basic system 

components used would be similar, and the same system and 

vehicle assembly approaches could be used. In fact, many 

manufacturers will likely integrate their refueling and fuel 

tank evaporative control systems. All current vehicle fuel 

systems incorporate fairly sophisticated evaporative emission 

control systems. Since these fuel systems have all been 

A Bureau of Labor Statistics analysis estimated that 

vehicle costs incurred to meet the 1977 revision to FMVSS 

301 were $4.70 and costs to meet the 1976 revision to the 

standard (added rollover test) cost $2.10.[30,31] 
P.63 

-62-

Table 3 

Summary of Vehicle 

Modifications in Response to 301-77 

Vehicle Components 

Fuel System 

Components 

Fuel Tank 

Fuel Gauge Sensor 

Fuel Lines 

Fuel Vapor Lines 

Fuel Pump 

Modification(s) to 

Improve Crashworthiness 

- Increase gauge of tank material 

- Add protective shield 

- Recontour to minimize 

contact/puncture by other adjacent 

vehicle components. 

- Strengthen/shield filler neck 

- Increase strength of solder/weld 

seams 

- Strengthen mounting by adding 

brackets, revising mounting bolts, 

increasing torque of mounting 

straps 

- Strengthen filler cap seal, 

improve impact resistance 

- Strengthen mounting 

- Recontour 

- Recontour, revise, revise clamps 

- Provide shield 

Other Vehicle Components Changed to Improve Fuel System Integrity 

Rear Floor Pan/Support 

Rails/Wheel Housing 

Rear Suspension (Springs, 

Shock Absorbers) 

Rear Axle Assembly 

Rear Axle Assembly 

Seat Belt Brackets 

Engine Mount 

Power Steering Pump Bracket 

- Revise, add supports 

- Change support brackets, revise 

mounting bolts, revise mounting 

procedure, and shield 

- Minor changes in contour of lines, 

screw heads, mounting clips, 

recontour vent cover 

- Revise hinge assembly 

- Revise anchorage 

- Slight revision 

- Slight revision 
P.64 

-63-

designed to meet the most recent and most stringent version of 

FMVSS 301 and also provide a high level of in-use safety 

performance, it follows that a thorough evaluation of the 

potential safety implications of evaporative control systems 

has already been conducted. Since onboard systems are 

basically extensions of evaporative emission systems, clearly 

many of the safety design considerations associated with 

onboard systems related to passing FMVSS 301 or providing 

in-use assurance have already been resolved or at least 

addressed in evaporative emission system designs. 

Consequently, much of the "ground work" required to insure 

onboard safety has already been performed. Therefore, it is 

important to keep the magnitude of the onboard safety design 

process in perspective, because clearly much of the safety 

technology needed for onboard is simply an extension of that 

which already exists. 

Remembering the relatively inexpensive and yet effective 

nature of current fuel system integrity measures and the 

"incremental" nature of onboard safety in terms of the 

magnitude of the task and actual cost relative to evaporative 

systems, it is now possible to describe the components which 

factor into onboard safety costs. Basically, the integration 

of safety into a fuel system incorporating an onboard controls 

involves four types of costs. These four costs are for 1) 

design and development (R&D), 2) specific hardware, 3) safety 

testing, and 4) weight penalty (or added fuel consumption). 

The paragraphs that follow describe how each of the cost 

components are affected by onboard safety. 

To begin with, some research and development will have to 

be performed to safely integrate onboard controls into vehicle 

fuel systems. EPA has estimated that the total design and 

development cost required to incorporate onboard systems in 

vehicle fuel systems is about $112,000 per family or in the 

range of $0.35 to $0.55 per vehicle (passenger car and light 

truck) . This cost is for any development effort involved in 

combining the components of an onboard system with the rest of 

the vehicle to form a unit that interacts safely and 

effectively. Because safety is evaluated inherently in the 

design and development process and yet is only one part of the 

total effort, only a fraction of the total cost should be 

directly allocated to safety. Also, because much of the safety 

related system development work has already been completed it 

is not unreasonable to expect that onboard safety development 

costs would only be a small fraction of the total cost in this 

area. In addition, because of the incremental nature of the 

onboard system, much of the research and development that went 

into making evaporative control systems safe can be applied 

directly to onboard controls. 
P.65 

-64-

Given that manufacturers are designing an onboard system 

in the context of many requirements and certain design features 

serve multiple functions, it is very difficult to isolate the 

level of expenditures directly attributable to safety. For 

this analysis it was assumed that about 20 percent of R&D 

expenditures relate to safety, which translates to about $0.10 

per vehicle. However, total onboard cost is quite insensitive 

to this assumption, even if the safety related development 

costs were tripled, per vehicle costs would increase by only 

one percent. 

The second component of onboard safety costs relates to 

specific hardware that may be required to insure fuel system 

safety. EPA has estimated costs for three specific items which 

have been identified as potential components to be included as 

part of the onboard system design explicitly for safety 

reasons. These three items are 1) a rollover valve, 2) a 

pressure relief mechanism, and 3) fuel system\ modifications 

necessary to safely incorporate a rollover valve, pressure 

relief mechanism, or other onboard hardware. EPA has estimated 

the cost of a solenoid rollover valve (like the one shown in 

Figures 19 and 20) to be $4.60. [17] This price included the 

cost of the valve, an actuator located at the fillcap, and the 

necessary wiring and connectors. Manufacturers estimate the 

cost of a valve assembly similar to that described by EPA's 

cost estimate would be in the range of $5.00 to $6.00. It 

should be noted that these estimates are for the most complex 

rollover valve type, and that the cost of a simpler valve 

assembly such as the fillneck mounted type (see Figures 9-15) 

is estimated to be more in the $3.00 to $4.00 range. The 

available information indicates that an appropriate rollover 

valve cost falls into a range of $3.00 to $6.00. 

The second safety hardware cost is for a pressure relief 

mechanism. This mechanism would only be needed for onboard 

systems incorporating a mechanical fillneck seal, and 

consequently not all vehicles would require its use. However, 

for those systems that would require a pressure relief 

mechanism, EPA has estimated that this device would increase 

system costs by approximately $0.50. This estimate is based on 

pressure relief mechanisms currently used in automotive 

applications which perform the same basic function and are 

similar in complexity.[32] 

The final onboard safety hardware cost accounts for any 

fuel system modifications that would be necessary in order to 

safely accommodate any onboard control hardware. For example, 

a vehicle's fuel tank or fillpipe might have to be re-shaped or 

modified in order to accept a rollover valve. Also, for safety 

reasons, some slight re-routing of the fuel system's vapor 
P.66 

-65-

lines may be required. EPA has estimated a total modification 

cost to be $0.50 per vehicle. Only part of this total cost 

would be required for safety purposes. However, because safety 

inherently enters into the decision to make any modifications, 

it is difficult to access what part of the total modification 

cost should be allocated to safety; perhaps half or more ($0.25 

to $0.30 per vehicle) could be considered as driven by safety 

related concerns. 

Summing up the three individual safety hardware costs 

yields a total estimated figure in the range of $3.25 to 

$6.80. However, this cost estimate does not include 

manufacturer overhead and profit. In order to obtain the 

retail price equivalent cost, these estimates must be 

multiplied by a markup factor. Presently, a markup factor 

value of 1.26 appears representative.[33] Therefore, after 

inclusion of the markup factor, a total retail price equivalent 

safety-related hardware cost falls within the range of $4.10 to 

$8.60. 

The third component of safety costs accounts for any 

safety crash testing that would be necessary. EPA has 

estimated the cost of crash testing to assure fuel system 

integrity for onboard systems to be about $34,000 per 

bodyline/style or about $0.12 per vehicle.[34] This estimate 

is based on four tests required per body line/style with two 

vehicles required for each sequence of four tests. Clearly 

safety crash test costs are very minimal in the long term and 

do not pose an obstacle to the adoption of onboard controls. 

Even if total costs were double the estimate, the overall per 

vehicle cost would rise by less than one percent. 

The fourth component of safety costs is the estimate of 

the added fuel consumed over the life of the vehicle due to the 

increase in vehicle weight resulting from added safety 

hardware. The amount of weight added to a vehicle for a 

rollover valve and pressure relief mechanism is very small (0.4 

lbs), and EPA estimates that only about $0.:5 in added fuel 

costs will result from their inclusion into the onboard 

system.[17] 

A total onboard safety cost is calculated by summing all 

four individual component costs. Total capital costs per 

family average about $56,000. The per vehicle safety-related 

costs range from $4.50 to $9.00, or about 25 percent of EPA's 

estimate of the total cost, depending on the type of rollover 

valve used. 
P.67 

-66-

One final point needs to be made with regard to these 

safety cost estimates. To the degree that manufacturers take 

the opportunity introduced by an onboard requirement to further 

reduce in-use risk beyond that now accepted with present 

systems, some additional costs might be involved which have not 

been identified or quantified. On a fleetwide basis these 

would be quite small. Also, it should be noted that the added 

benefits of these measures have not been included either. 

EPA estimates safety related onboard costs to be 

$4.50-9.00 per vehicle. While there is some uncertainty in the 

development cost portion of the estimate, the total range shown 

here is quite insensitive to any error. These costs are quite 

similar to those previously incurred by manufacturers to insure 

fuel system safety. Many of the potential problems related to 

implementing onboard systems safely have already been 

considered in the design and development of present evaporative 

systems. The manufacturers previous experience in implementing 

evaporative systems safely and the incremental nature of 

onboard systems reduces costs and the level of potential 

problems. This analysis demonstrates that high levels of 

in-use fuel system safety can be achieved at low cost, and 

there is no need for a manufacturer to "cut corners" on onboard 

safety. 

B. Leadtime 

If EPA were to implement an onboard requirement, it would 

be necessary to allow a sufficient period of leadtime between 

the date the rule is promulgated and the model year the systems 

are to be required on production vehicles. This leadtime is 

provided so that manufacturers will be able to adequately 

prepare for the requirement through system design, development, 

testing, tooling, certification, and safety evaluation. Some 

of the tasks involved in the preparation process could be 

worked on simultaneously, while some tasks cannot begin before 

others are complete. While EPA estimates that none of the 

individual leadtime tasks require more than twelve months to 

complete, due to the sequential nature of some of the tasks, a 

period of approximately 24 months will be the total amount of 

leadtime required by manufacturers. 

Figure 23 shows how the individual leadtime components 

result in a total estimate of 24 months. First, four to six 

months are included for manufacturers to develop and optimize 

working prototype systems applicable to all of their different 

vehicle models. This is not at all unreasonable given the fact 

that working prototypes already exist and many manufacturers 

have evaluated these or their own prototype to some degree. 

Once the prototype development is complete, initial durability 

testing of the prototype could be conducted under laboratory 

conditions. This laboratory testing is not expected to last 

more than two months. 
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FIGURE 23 ONBOARD LEADTIME 

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P.69 

-68-

Following laboratory testing, three separate actions can 

begin simultaneously. These three tasks are 1) in-vehicle 

testing, 2) tooling, and 3) safety optimization and prove out 

of the overall control system through efficiency and durability 

verification. Similar in-vehicle testing programs have 

required four to six months for completion. Tooling could also 

begin once laboratory testing is complete. Figure 23 shows 

EPA's estimate that tooling could require as little as three 

months and as much as 12 months depending on the magnitude of 

the task. However, even if 12 months are required for tooling 

or tooling decisions are delayed, this task would still be 

complete well within the total 24-month leadtime period. 

Safety evaluation is the third task which could begin 

subsequent to the completion of the prototype laboratory 

testing. Safety evaluation would involve the use of computer 

crash simulation models and vehicle crash testing (four tests 

per body line/style) to verify the crashworthiness of the 

vehicle's modified fuel system. Because this evaluation could 

begin immediately after the completion of laboratory testing, a 

full 14 months of leadtime would be available to manufacturers 

if needed to perform this task. Based on a discussion with 

NHTSA, it appears this amount of time would be more than 

adequate to perform the necessary safety evaluation.[35] 

The only other process which requires completion within 

the 24-month leadtime period is emissions certification. EPA 

has found from past experience that a manufacturer normally 

requires between 10 to 12 months to certify its product 

line.[36] This estimate is based on a 10 month engine family 

certification schedule which allows time for durability, 

emission data, fuel economy, and confirmatory testing. Because 

certification cannot begin prior to the completion of 

in-vehicle testing, EPA estimates a total leadtime period of 24 

months will be needed overall. 

Twenty-four months of leadtime is quite reasonable, 

especially since most of the fundamental development work is 

already complete. Onboard system prototypes are presently 

available, and many aspects of the system's performance have 

already been tested and proven to be effective. Also, because 

onboard control technology is incremental in nature to 

evaporative emission controls, there is no need to design and 

develop entirely new systems. As a matter of fact, many of the 

critical onboard design issues have already been incorporated 

into current fuel system designs with the inclusion of 

evaporative emission control systems. For example, evaporative 

emission control systems have already added the following to 

fuel systems: vapor vent lines, vapor storage device, canister 

purge capability, and corresponding safety provisions 

associated with each of these additions. Since much of the 

development work is already complete, implementing onboard 

systems should be no more of a problem to vehicle manufacturers 

than was implementing evaporative emission control systems. 
P.70 

-69-

EPA's 24-month leadtime estimate is supported by past 

experience with three previous evaporative emission 

rulemakings. These rulemakings included the original 1978 6.0 

g/test LDV/LDT evaporative emission standard which was 

implemented with just 12 months of leadtime, the 1981 2.0 

g/test LDV/LDT evaporative emission standard which was 

implemented with 24 months of leadtime, and the 1985 HDGV 

evaporative standard which was implemented with 24 months of 

leadtime. In each of these three rulemakings, manufacturers 

faced leadtime factors identical to the ones that would 

accompany an onboard requirement, including safety. Since 

manufacturers were able to safely and effectively integrate 

evaporative emission controls into their vehicles' fuel systems 

with 24 months of leadtime, and since the magnitude of the 

onboard implementation task is similar, manufacturers should 

also be able to safely and effectively integrate onboard into 

vehicle fuel systems with 24 months of leadtime. 

As far as safety development and evaluation is concerned, 

EPA's leadtime estimate is also supported by the past 

experience of NHTSA in implementing the various versions of 

FMVSS 301. Table 4 shows the chronological history of FMVSS 

301. The original 1968 FMVSS 301 applicable to passenger cars 

was implemented with less than 12 months of leadtime. When the 

standard was revised for 1976 model year passenger cars, 

seventeen months of leadtime was provided. For 1977 model year 

passenger cars, manufacturers had to contend with the most 

substantial upgrade to the standard, and this was accomplished 

with only 29 months of leadtime, and only 12 months between new 

requirements. Also, beginning in the 1977 model year, FMVSS 

301 was extended to include light trucks. This extension 

involved a 29-month leadtime period with further crash 

requirements in effect 12 months later, thus requiring 

recertification. Finally, in 1977, FMVSS 301 was extended to 

include school buses (with a GVWR greater than 10,000 lbs), and 

this requirement was implemented with 17 months of leadtime. 

This experience indicates that 24 months of leadtime allows 

manufacturers sufficient time to factor in safety. 

Based on the information provided above, 24 months is 

adequate time to implement onboard controls, with full 

consideration of all safety concerns. Because safety 

evaluation can proceed in parallel to three other tasks, more 

than a year is available for computer simulation and actual 

safety crash testing. This allows adequate leadtime to 

properly integrate safety into onboard systems especially since 

manufacturers can utilize and expand safety technology used in 

current evaporative emission control systems to develop 

effective onboard systems. Also, much of the safety 
-70-

P.71 

Table 4 

Chronology of FMVSS 301 Requirements 

Model Year 

Requirement 

1968[1] 

1976[2] 

1977[2] 

1977[2] 

1978[2] 

1977[2] 

1978[2] 

1977[3] 

Vehicle 

Type 

PC 

PC 

PC 

Class 1 LDT 

Class 1 LDT 

Class 2 LDT 

Class 2 LDT 

School Buses 

Promulgation 

Date 

2-3-67 

3-21-74 

3-21-74 

3-21-74 

3-21-74 

3-21-74 

3-21-74 

10-15-75 

Effective 

Date 

1-1-68 

9-1-75 

9-1-76 

9-1-76 

9-1-77 

9-1-76 

9-1-77 

4-1-77 

Leadtime 

(Months) 

11 

17 

29 

29 

41 

29 

41 

17 

Time Since 

Last Requirements 

7 2/3 yrs. 

12 mos. 

12 mos. 

12 mos. 

[1] Motor Vehicle Safety Standard No. 301, Fuel Tanks, Fuel 

Tank Filler Pipes, and Fuel Tank Connections - Passenger 

Cars; 32 FR 2416, February 3, 1967, Part 571; S 301-1. 

[2] Federal Motor Vehicle Safety Standard No. 301, Fuel System 

Integrity, 39 FR 10588, March 21, 1974. 

[3] Federal Motor Vehicle Safety Standard No. 301, Fuel System 

Integrity, 40 FR 48352, October 15 1975. 
P.72 

-71-

developmeht which would be required has already taken place 

with the identification and resolution of such potential safety 

issues as rollover protection and fuel tank pressure relief. 

Consequently, a 24-month leadtime period would provide 

manufacturers with sufficient opportunity to develop safe and 

effective onboard systems. 

While this analysis indicates that the current leadtime 

estimate of 24 months is reasonable for virtually all vehicle 

models, EPA is sensitive to manufacturers concerns regarding 

leadtime requirements. Public comments regarding EPA's 

24-month leadtime estimate were submitted as part of comments 

on EPA's original Gasoline Marketing Study (July 1984).[37] 

While most commenters did not object to the 24-month leadtime 

estimate presented in the Gasoline Marketing Study, auto 

manufacturers felt that a 24-month leadtime was insufficient to 

implement onboard controls. The leadtime periods suggested by 

these commenters ranged from three to six years. Those 

commenters suggesting that four or more years would be 

necessary also suggested that onboard controls should be 

phased-in gradually as normal vehicle model redesign and 

turnover occurs. Using this approach, implementing onboard 

controls would be less burdensome and would allow extra time to 

deal with implementation or packaging problems on unique 

vehicles. However, it is worth noting that comments received 

from the manufacturers suggesting the need for a longer 

leadtime were not supported with any compelling arguments which 

would substantiate the insufficiency of a 24-month leadtime. 

EPA is committed to providing manufacturers the leadtime 

necessary to implement onboard controls safely and 

effectively. Consequently, EPA is open to considering a twoor perhaps three-model year phase-in period for onboard 

controls. Such a phase-in period would provide manufacturers 

with additional time to solve any onboard system packaging and 

testing problems for unique vehicle models. Also, if a 

manufacturer had unique safety concerns on one or two body 

lines/styles, this approach would offer a manufacturer more 

leadtime to properly address them. In addition, it could 

improve the cost efficiency of controls by allowing 

manufacturers to forego development of onboard systems for 

vehicle models scheduled for retirement or permit manufacturers 

other flexibilities with new models being planned and those now 

in production. 

It is also important to note that if onboard controls are 

required, the date of promulgation of the final rule may be 

such that more than 24-months leadtime is actually available. 

The model year generally begins in September or October. If 

the publication of the final rule is much beyond that period, 
P.73 

-72-

the manufacturers would have the remainder of that model year 

in addition to the 24 months discussed previously. Therefore, 

in actuality manufacturers could have substantially more than 

24 months, but EPA's analysis indicates that only 24 months is 

needed. 

In conclusion, given the magnitude of the task, this 

analysis indicates that 24 months of leadtime is adequate to 

allow manufacturers to safely and effectively implement onboard 

controls. This estimate is supported by EPA's experience with 

implementing evaporative emission standards and NHTSA's 

experience with implementing the various versions of 

FMVSS 301. However, EPA is committed to providing the leadtime 

necessary to implement onboard controls both safely and 

effectively. Thus EPA is open to considering a short phase-in 

period or other approaches which are pertinent. 

Up to this point, this report has addressed onboard safety 

issues from primarily a passenger car and light truck point of 

view. It should be noted however that just as evaporative 

emission control technology was extended to heavy-duty gasoline 

fueled vehicles (HDGVs), onboard control technology could also 

be applied to HDGVs. While many of the safety issues discussed 

thus far would be identical in an HDGV application, some 

aspects of HDGV onboard safety would be distinct from 

light-duty issues. The next section in this report has been 

included to address the similarities and differences between 

heavy-duty and light-duty onboard safety issues. 
P.74 

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VII. Heavy-Duty Gasoline Vehicle Requirements 

Since an EPA onboard refueling control requirement would 

cover heavy-duty gasoline vehicles (HDGVs), in addition to 

passenger cars and light trucks, it is important to evaluate 

any potential HDGV onboard system safety considerations as well 

as those encountered in light-duty applications. While none of 

the comments received regarding the safety implications of 

onboard specifically addressed HDGVs, overall light-duty 

concerns discussed earlier are expected to apply. However, it 

is important to note that HDGV fuel system configurations 

differ somewhat from those found on passenger cars and light 

trucks, and the fuel system safety requirements also differ. 

This section of the report identifies distinct HDGV 

onboard safety issues and discusses the implications these 

distinctions could have on manufacturers fuel system safety 

designs. It begins with a brief description of some of the 

more common HDGV configurations. Following these descriptions, 

a discussion of the HDGV fuel system safety standards will be 

presented, and differences between light- and heavy-duty 

vehicle onboard systems due to fuel system configurations and 

safety test requirements will be discussed. Next, HDGV onboard 

safety issues will be introduced and analyzed. Finally, this 

section will end with a brief segment concerning the effect of 

HDGV onboard safety on costs and leadtime. 

Before beginning this analysis one key clarification is 

needed. FMVSS 301 covers all vehicles with a gross vehicle 

weight rating (GVWR) of 10,000 lbs or less (plus school buses 

over 10,000 lbs GVWR). For emission control purposes EPA 

classifies all gasoline-powered vehicles with a GVWR of 8,501 

lbs or more as HDGVs. Out of EPA's HDGV category only 90,000 

vehicles (or approximately 25%) have a GVWR greater than 10,000 

lbs. Thus most (or approximately 75%) of EPA's HDGV class 

(those vehicles with a GVWR between 8,501 and 10,000 lbs-Class 

lib) is covered by the LDT requirements in FMVSS 301. Since 

the fuel systems on Class lib HDGVs are essentially identical 

to those on lighter weight LDTs, and FMVSS covers all LDTs up 

to 10,000 lbs GVWR, the previous portion of this analysis 

applies to the Class lib HDGVs. The remainder of this analysis 

will focus on gasoline-powered vehicles whose GVWR exceeds 

10,000 lbs. 

A. HDGV Fuel System Configurations 

Just as there are chassis and drivetrain differences 

between heavy and light-duty vehicles, there are also some 

differences in their fuel system configurations. Fuel tanks 

are generally of a heavier construction and are larger in 
P.75 

-74-

volume; dual fuel tanks are also more common. Fuel tank shapes 

vary somewhat as does the location of the tanks on the 

vehicle. Also, it is often the case that the fillpipe is 

integral with the fuel tank, or has a very limited length as 

compared to lighter weight vehicles. 

As a part of a recent contract study, EPA surveyed the 

characteristics of the fuel/vapor handling systems of HDGVs 

over 10,000 lbs GVWR. [38] The key results of the survey 

portion of that report are summarized in Table 5, which will 

serve as the basis for the remainder of this discussion. 

First, as can be seen in Table 5, there are only two 

manufacturers which market HDGVs. Between them they offer only 

about 10 different chassis models to which any number of 

different bodies or payloads can be attached (tanks, dumps, 

cargo boxes, motor homes, school buses, flat beds, etc). 

The second area of interest is the fuel tanks. 

Essentially three different tanks shapes are used: standard 

rectangular, step rectangular, and D-shape. Examples of these 

tanks are shown in Figure 24. The tank volumes range from 20 

gallons to 60 gallons, with an average in the range of 35 to 40 

gallons for single tank HDGVs and 75 gallons for dual-tank 

HDGVs. EPA estimates that about 15 percent of HDGVs use dual 

tanks, with most of those being in heavier weight trucks 

(>20,000 lbs GVWR).[17] Most passenger car and light truck 

fuel tanks are located under the vehicle body and this is also 

the case for some HDGV configurations (e.g., school buses). 

However, on some HDGV configurations, the fuel tanks are 

mounted on the outer side of the vehicle frame (right or left 

hand side for single tanks, both sides for dual tanks) and are 

exposed to the road rather than shielded by the vehicle body. 

As was alluded to above, most HDGV tanks have only a limited 

fillpipe length (<8") and some have essentially none at all, 

with the fuel cap being integral to the tank. 

Finally, with regard to the HDGV evaporative emission 

systems two observations are important. (See Figure 25 for an 

example of a HDGV evaporative system.) First, for the same 

reasons as described for passenger cars and light trucks, HDGVs 

use a limiting orifice in the evaporative emission system. 

Second, the total evaporative emission canister capacity on an 

HDGV is more than twice the average on passenger cars and LDTs 

(2.8-4.0 liters). However, on HDGVs diurnal emissions from the 

fuel tank and hot soak emissions from the fuel metering system 

are routed to different canisters. Hot soak emissions are 

somewhat more of a concern on HDGVs because most are carbureted 

rather than fuel injected. To the degree that HDGV engines 
Selected Characteristics of Heavy-Duty 

Manufacturer 

GM 

FORD 

Model or 

Series 

P4T042 

P6T042 

C5D042 

C6D042 

C7D042 

C7D064 

B6P042 

F-Series 

B-Series 

C-Series 

Fuel Tank 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

Rectangular 

D-Type 

Shape 

and 

Step 

and 

Step 

Table 5 

Gasoline Vehicle Fuel/Vapor 

Fuel Tank Location 

30 gal. Mount On Right 

Hand Frame 

30 and 60 gal. Mounted 

on Left Hand Frame 

20 gal. Mounted Right 

Hand Frame 

50 gal. Step Mounted 

Right or Left Hand Frame 

20 gal. Mounted Right 

Hand Frame 

50 gal. Step Mounted 

Right or Left Hand Frame 

Dual 50 gal. Step 

Mounted Left and Right 

Hand Frame 

30 gal. Mounted Right 

Hand Frame 

60 gal. Mounted Right 

Hand Frame 

35 gal. Right Hand 

Side Frame Mounted 

30 gal. Right Hand 

Side Frame Mounted 

50 gal. Right Hand 

Side Frame Mounted 

Handlj .nq 

Number of 

Canisters 

2 

2 

2 

2 

2 

2 

2 

2 

Systems by Vehicl 

Size of 

Canisters 

1500 and 

2500 cc 

1500 and 

2500 cc 

1500 and 

2500 cc 

1500 and 

2500 cc 

1500 and 

2500 cc 

1400 ml. 

1400 ml. 

1400 ml. 

ea. 

ea. 

ea. 

< 

s Model/Series 

Diameter 

of Vent 

Lines 

0.312 in. 

0.312 in. 

0.312 in. 

0.312 in. 

0.312 in. 

3/8 in. 

3/8 in. 

3/8 in. 

Diameter 

of Purge 

Lines 

0.375 in. 

0.375 in. 

0.375 in. 

0.375 in. 

-j 

Ul 

0.375 in. 

3/8 in. 

3/8 in. 

3/8 in. 
P.77 

-76-

Figure 24 

HDGV Fuel Tanks 

D-Shape 

Standard Rectangular 

Step Rectangular 
Figure 25 

TYPICAL HDGV EVAPORATIVE SYSTEM 

"BALL CHECK VALVE 

TANK RESTRICTOR 

PRESSURE/VACUUM 

RELIEF 

SEALED A 

GAS CAP-* 

L 3/16 " DIA 

-13 ' LONG 

IfPURGE 

VALVE 

Uc :€><* 

-3/8 " DIA 

~ 3 ' LONG 

* TO PURGE 

INDUCTION 

POINT 

2.5 LITER 

CANISTER 

I 

I 

30 GALLON FUEL TANK 

oo 
P.79 

-78-

fuel systems are converted from carbureted to fuel injected as 

is now projected, concerns over hot soak emissions may diminish 

and allow the elimination of the second canister on those 

vehicles.[39,40] 

With this brief background on HDGV fuel/evaporative 

systems we turn now to a discussion of the fuel system safety 

standards which apply to HDGVs over 10,000 lbs GVWR. 

B. HDGV Fuel System Safety Standards 

Fuel system safety regulations differ according to vehicle 

and fuel system configuration. The Department of 

Transportation/Bureau of Motor Carrier Safety (BMCS) has 

requirements which apply to all HDGVs over 10,000 lbs GVWR. In 

addition, school buses must meet the requirements prescribed 

specifically in FMVSS 301. The BMCS and FMVSS 301 requirements 

are summarized below. 

1. Bureau of Motor Carrier Safety Requirements 

BMCS safety regulations include both specific design 

requirements and actual fuel tank safety tests.[41] The design 

requirements contain rules . governing the location, 

installation, and construction of fuel tanks used on HDGVs. 

Also, fuel lines, fittings, and fillpipes must conform to 

certain requirements. 

The actual testing requirements depend on whether a fuel 

tank is side-mounted or non-side mounted. To paraphrase the 

definition, a truck fuel tank is considered side mounted if it 

extends beyond the outboard side of a front tire positioned in 

the straight ahead position. This is shown pictorially in 

Figure 26. Any fuel tank which does not have this 

characteristic is considered non-side mounted, and in this 

analysis will be referred to as frame mounted. The testing 

requirements for frame-mounted tanks will be discussed first. 

A frame mounted HDGV fuel tank has to be able to pass two 

fuel tank safety tests. The first of these two tests, the 

safety venting system test, involves applying an enveloping 

flame to an inverted fuel tank to insure that the fuel tank's 

safety venting system activates prior to the tank's internal 

pressure exceeding fifty pounds per square inch. The second 

fuel tank safety test is a leakage test which involves filling 

the tank to capacity and rotating the tank through an angle of 

150° in any direction from its normal position to insure that 

neither the tank nor any fitting leak more than one ounce of 

fuel per minute in any position the tank assumes during the 

test. 
P.80 

-79-

Figure 26 

Pictorial Definition of Side-Mounted Fuel Tank. 

If "the tank extends to the left of line A or to 

the right of line B, then the tank is side-mounted. 

Lines A and B are tangent to the outer sides of 

the front tires. 
P.81 

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HDGVs with side mounted fuel tanks must pass two other 

tests which involve dropping the fuel tank to test impact 

resistance. The first test, termed the drop test, involves 

dropping a fully loaded (equivalent weight of water) tank from 

30 feet onto an unyielding surface, so that it lands squarely 

on one corner. A second similar test (termed the fillpipe 

test) requires that a fully loaded tank be dropped from 10 feet 

onto an unyielding surface, so that it lands squarely on its 

fillpipe. In neither case, may the tank nor any fitting leak 

more than one ounce per minute. 

Based on conversations with the two HDGV manufacturers, 

the vast majority of HDGV fuel tanks are frame mounted 

(non-side mounted). No side mounted tanks are offered as 

standard equipment, and only one is offered as an 

option.[42][43] Thus, this analysis will focus primarily on 

the safety venting and leakage test requirements which apply to 

frame mounted tanks. However, the drop tests for side mounted 

tanks will also be considered. 

2 . School Bus Requirements 

In addition to the BMCS requirements for frame-mounted 

tanks, outlined above, school buses are required to meet 

specific FMVSS 301 standards. However, this coverage does not 

include all of the test requirements as prescribed for 

passenger cars and light trucks. School buses must pass only a 

single moving barrier test (30 mph) which does not include a 

rollover test. In this test, the barrier impacts the school 

bus at the location of the fuel tank, and the fuel system must 

be designed so as not to leak more than one ounce of fuel per 

minute.[44] 

This briefly summarizes the Federal safety standards 

applicable to fuel systems on HDGVs over 10,000 GVWR. With 

this background information we are now prepared to discuss how 

the differences in vehicle/fuel system configurations and the 

Federal safety standards may affect the design of an onboard 

system for an HDGV relative to the design for passenger cars 

and light trucks. 

C. Distinctions in HDGV Onboard Systems 

Just as the evaporative emission control systems used on 

HDGVs are very similar to those used on passenger cars and 

light trucks, it is also expected that an HDGV onboard system 

would be very similar in design and approach to that conceived 

for lighter-weight vehicles (a possible HDGV onboard system is 

shown in Figure 27). However, some minor variations would 

exist due to differences in HDGV fuel system configurations and 
Figure 27 

POSSIBLE HDGV INTEGRATED EVAPORATIVE/REFUELING SYSlfcM 

• PRESSURE/VACUUM 

.RELIEF 

MECHANICAL OR SOLENOID 

ACTUATED VENT/ROLLOVER 

VALVE, LIMITING ORIFICE 

s£ LIQUID/VAPOR SEPERATOR 

l 

oo 

5/8" DIA 

~13' LONG 

# 

X' 

SEALEDGAS CAP 

MECHANICAL -* 

SEAL 

i. 

PURGE 

VALVE 

£X}= ^ — 

3/8" DIA 

~ 3' LONG 

TO PURGE 

INDUCTION 

POINT 

7.5 LITER 

CANISTER 

30 GALLON HDGV FUEL TANK 

oo 
-82-

the requirements levied by the applicable Federal safety 

standards. Before beginning a discussion of these minor 

variations, it is valuable to reiterate a few key points raised 

previously with regard to the magnitude of the task of 

implementing onboard controls. 

First, like passenger cars and light trucks, all HDGVs now 

incorporate evaporative emission control systems (see Figure 

25) and their fuel systems must meet the present Federal fuel 

system integrity standards (BMCS and NHTSA). Thus, as before 

with the lighter weight vehicles, the application of onboard 

systems is best evaluated incrementally to the measures already 

taken to incorporate evaporative emission controls and meet 

safety standards. Much of the ground work has already been 

completed, the needed modifications made and components added. 

In many cases no changes to present fuel system safety 

assurance or evaporative emission control measures will be 

needed. Second, it is important to note that HDGV onboard 

refueling and fuel tank evaporative emission control systems 

will likely be integrated as with lighter weight vehicles. 

This is quite easy to accomplish on HDGVs, since they now have 

separate canisters and control systems for fuel tank and fuel 

metering evaporative emissions. Thus a whole new system will 

not be added to control HDGV refueling emissions; instead the 

refueling and fuel tank evaporative emission control systems 

will be integrated into one (compare Figure 25 with Figure 

27) . Thus many of the primary design considerations which 

applied for the evaluation of onboard systems to passenger cars 

and light trucks also apply to HDGVs. 

Remembering the expected similarities between light and 

heavy-duty vehicle onboard systems and that the factors 

affecting the implementation are also the same, the expected 

minor variations in HDGV onboard systems can now be discussed. 

For sake of presentation, discussion will begin at the fillpipe 

and follow along the system to the canister. The analysis will 

assume an integrated onboard refueling/fuel tank evaporative 

control system as discussed above. 

To begin with, because the fillpipes on HDGV fuel tanks 

are either relatively short or integral with the tank, liquid 

fillneck seals which require an appreciable fill height may not 

be a practical approach in some configurations. Due to this 

lack of fill height, HDGV manufacturers might elect to utilize 

a mechanical seal approach and thus would need to incorporate 

some type of pressure relief device such as was described 

previously. HDGV fuel tanks now use a pressure-vacuum relief 

valve, and it is conceivable manufacturers will simply modify 

that valve for this application. However, under the proper 

backpressure conditions, it might be possible to use a liquid 

fillneck seal by extending the fillpipe horizontally in the 

tank as has been demonstrated in a prototype light-duty 

program.[15] 
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A second potential difference lies in the diameter of the 

refueling vapor line and related fuel tank vent. From a design 

perspective, the tank vent and refueling vapor line size 

(diameter) could be affected by the fuel dispensing rate. As 

part of the refueling emissions test procedure, EPA is 

proposing that HDGV fuel systems be designed for refueling at a 

maximum rate of 10 gallons per minute, the same rate as 

prescribed for other vehicles.* This 10 gallon per minute 

dispensing rate results in an increase in the current orifice 

and evaporative vapor line diameter from about 3/8 inch to 

about 5/8 inch for an HDGV onboard system. 

However, to minimize spillage during refueling, the BMCS 

has requirements that any liquid fuel tank over 25 gallons in 

capacity must be able to accept fuel at a rate of 20 gallons 

per minute.[45] For an onboard system this requirement could 

lead to a increase in the diameter of the tank vent outlet and 

refueling vapor line. It should be noted however, that while 

this requirement applies to all heavy-duty liquid fuel tanks 

(both diesel and gasoline), fundamentally it is aimed more at 

diesel fuel tanks. It is not uncommon to encounter an in-use 

diesel fuel dispensing rate of 20 gpm or more to reduce the 

time needed to fill a diesel tank since these tanks are 

typically much larger than gasoline tanks and dual diesel tanks 

are also more common.[46] In-use gasoline dispensing rates on 

the other hand normally do not exceed 10 gpm. Since in-use 

gasoline dispensing rates usually do not exceed 10 gpm, and 

EPA's refueling certification test would involve a 10 gpm 

maximum dispensing rate, BMCS's requirement in this area may 

not be needed. EPA has discussed this matter with DOT/BMCS, 

and they have expressed a willingness to consider changing this 

requirment to apply only to diesel fuel tanks.[46] 

Nevertheless, because HDGV fuel tanks do not use long 

fillnecks, fuel dispensing operations would not be as sensitive 

to higher backpressure as they would be in light-duty. Even if 

the refueling vent orifice/line were sized for a 10 gallon per 

minute dispensing rate, fuel could dispensed at a greater rate 

without premature shutoffs. Thus it may not be necessary to 

size the refueling orifice/vent line to match the dispensing 

rate requirements. However, in optimizing system designs with 

regard to fuel tank pressure, manufacturers may choose to use a 

slightly larger refueling vent orifice than seen on light-duty 

applications. 

Discussions with gasoline marketing interests and nozzle 

manufacturers indicate that gasoline available to 

passenger cars, light trucks, and HDGVs (either at retail 

or private pumps) is not dispensed at rates greater than 

10 gpm. 
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One final manner in which HDGV onboard systems might 

differ from those on lighter weight vehicles is in the design 

of the rollover protection device. The solenoid activated 

rollover valve (Figure 19) or the combination valve (Figure 21) 

could be applied to HDGV fuel tanks in their present 

configurations. One manufacturer's fuel tank design now 

incorporates a ball type check valve similar in principle to 

the combination valve.[38] Also, the nozzle actuated valves 

shown in Figures 9-15 could also be used on HDGV fuel tanks 

which have a fillpipe length of 6 inches or more. However, 

nozzle actuated valve designs would have to be modified 

slightly to perform on fuel tanks whose fillneck is essentially 

integral with the tank. Nonetheless, the basic approach and 

operation would be the same. 

Any of the three rollover valve designs mentioned above 

could be used on HDGV fuel tanks. However the best choice for 

any tank would depend on the fillpipe length or other 

trade-offs relative to cost, packaging etc. With proper design 

and integration any of these valve designs could provide 

roll 'er protection in-use. 

With this background on HDGV fuel system configurations, 

safety requirements, and HDGV onboard system characteristics, 

it is now possible to address some of the unique safety 

concerns related to HDGV onboard. The next segment of this 

report discusses and addresses potential impacts of HDGV 

onboard on fuel system safety considerations. 

D. HDGV Onboard Safety Issues 

1. Introduction 

While none of the comments received regarding the safety 

implications of onboard controls specifically addressed HDGVs, 

it is reasonable to expect that overall concerns would be 

similar because of the expected close resemblance between light 

and heavy-duty vehicle onboard systems. To avoid repeating 

much of what has previously been discussed, this segment will 

primarily focus on unique HDGV onboard safety considerations. 

The analysis presented in Section IV regarding tampering and 

defects and refueling operation safety apply equally to HDGVs 

and will not be repeated here. The potential problems are 

similar and the same basic straightforward engineering 

solutions can be used. Also, the extensive analysis in Section 

V regarding in-use fuel system safety also applies to HDGVs. 

As before, manufacturers are expected to manage risk 

appropriately; there is no reason that adding an onboard system 

would directionaly increase in-use risk over that now accepted 

with present HDGV fuel/evaporative emission systems. 
-85-

However, as was discussed above the fuel system 

configurations and the safety test requirements for HDGV fuel 

tanks are somewhat different from light-duty, so some 

discussion of distinct safety test design requirement issues is 

appropriate. 

2. Safety Test Design Requirements 

As mentioned above, there are two separate areas of safety 

test design considerations for HDGV fuel systems. The Bureau 

of Motor Carrier Safety (BMCS) has fuel system safety 

regulations which apply to all HDGVs, and NHTSA has additional 

requirements for school buses. This segment begins with a 

summary and analysis of safety design considerations related to 

BMCS requirements. Following this is a discussion of the 

effects of NHTSA's crash test requirements. 

a. BMCS Requirements/Considerations 

BMCS has established fuel system requirements for HDGVs to 

insure their structural and in-use integrity. As part of these 

requirements, HDGV fuel tanks must be capable of passing the 

the safety venting system and the leakage tests described 

previously. Currently HDGV fuel tanks employ a ball check 

valve and pressure vacuum relief valve to pass these two 

tests. Since the refueling vent orifice would be somewhat 

larger with an onboard system (5/8") the ball check valve would 

have to be upgraded to provide the necessary protection. 

Little or no change to the pressure vacuum relief valve would 

be needed. 

For an HDGV onboard system, the protection now supplied by 

the ball check valve could be supplied by the rollover valve 

designs described previously. The same three general types of 

rollover protection devices that were discussed for use in 

light-duty applications (nozzle actuated, solenoid, and 

mechanically activated valves) would all be feasible in various 

heavy-duty applications as well. However, for tanks with 

little or no fillpipe (<6") the nozzle actuated valve design 

would probably have to be modified slightly and mounted in the 

tank instead of on the fillneck. A solenoid or mechanical 

rollover (ball) valve design could essentially be used as shown 

earlier. 

HDGV and light-duty onboard systems would be functionally 

identical and would be very similar in design and configuration 

except for canister size and vapor line length. Of course , to 

meet safety requirements and to provide in use protection, 

manufacturers will have to consider the structural integrity 

and the materials used in key system components just as they do 
P.87 

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now with other components of the fuel/evaporative system. 

Thus, some components of the HDGV onboard system (notably the 

rollover valve) may need to be constructed of metal to provide 

impact resistance and the flammability protection demanded in 

the safety venting test. 

Also, with regard to impact resistance, the one optional 

side-mounted tank model, would be subject to two additional 

safety tests (drop tests) designed to evaluate the tank's 

impact resistance. A side-mounted fuel tank would likely 

utilize a rollover valve mounted integral to or within the tank 

to insure its integrity during the drop tests. While this 

would not be difficult to design (many current fuel tanks 

contain interior components), it would represent an additional 

design consideration for side-mounted fuel tanks. From an 

in-use safety perspective, the impact resistance and overall 

integrity of rollover valves on frame mounted tanks would be 

enhanced if they were mounted integral or internal to the 

tank. Thus, this approach would be attractive for all HDGV 

fuel tanks. 

b. NHTSA Requirements/Considerations 

In addition to BMCS requirements, all school buses over 

10,000 lbs. GVWR must also meet specific requirements of 

NHTSA's FMVSS 301. As described earlier, this coverage 

involves a single moving barrier test (30 mph) which does not 

include a rollover test. In this test, the barrier impacts the 

school bus at the location of the fuel tank, and the fuel 

system must be designed so as not to leak more than one ounce 

of fuel per minute. As was true of BMCS requirements, an 

acceptable school bus onboard system is one which does not 

impair the fuel tank's ability to meet this requirement. 

As in the light-duty test, the crashworthiness of all the 

onboard system components (rollover valve, charcoal canister, 

critical vapor line and vapor line connections between the top 

of the fuel tank and the rollover valve) would all be evaluated 

in the test. Design measures similar to those described for 

passenger cars and light trucks would have to be taken to 

assure the integrity of these three key components. 
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The crashworthiness discussion in Section IV-A and the 

further options discussed in Section V addressed specific 

safety design approaches for these components which could also 

be applied to school buses, so this will not be addressed 

further. As before with light-duty applications, evaporative 

emission systems provide directly relevant techniques and 

experience to assist in proper design, and specific engineering 

measures have been suggested to deal with potential concerns. 

In conclusion, HDGV onboard systems do not introduce any 

new or significant problems to manufacturers' attempts to 

design safe fuel systems capable of meeting NHTSA and BMCS 

safety requirements. Straightforward, viable engineering 

solutions are available to address all problems that have been 

identified. Therefore, onboard systems are expected to be 

integrated into HDGV fuel systems without reducing the system's 

ability to meet all applicable Federal safety requirements. 

3. Summary 

As was mentioned in the light-duty section of this report, 

EPA's philosophy in evaluating the safety implications of 

requiring onboard controls (including those for HDGVs), is 

that no increase in overall risk should be caused or accepted, 

beyond that now present with today's fuel/evaporative system. 

This applies to both compliance with the applicable Federal 

Safety standards and the in-use safety of vehicles equipped 

with onboard systems. This portion of the analysis has 

addressed the safety test design requirements related to 

implementing HDGV onboard systems, and as was the case for 

light-duty it concludes that straightforward engineering 

solutions are available for all of the potential safety 

problems which have been identified, and safe fuel system 

designs are achievable by all. 

E. Cost and Leadtime Considerations 

EPA has received no comments which directly address 

specific HDGV onboard safety cost and leadtime implications. 

However, an analysis of the costs and leadtime necessary to 

implement HDGV onboard controls safely is an integral part of 

the overall evaluation of the feasibility of this control 

approach. The first portion of this section addresses HDGV 

onboard safety costs; the second discusses HDGV leadtime 

requirements and describes the basis for EPA's leadtime 

estimates. Some of the cost figures cited in the safety cost 

analysis are drawn from a broader EPA analysis which develops 

total HDGV onboard system costs in 1984 dollars.[17] 
P.89 

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1. ' Safety Costs 

As was true of light-duty onboard safety costs, the costs 

needed to implement HDGV onboard controls fall in several 

areas. R&D type costs will be incurred, some new or modified 

components will be needed which may slightly affect vehicle 

operating costs, and safety certification testing will be 

necessary. However, before beginning a discussion of these 

costs, it is valuable to discuss how EPA's HDGV evaporative 

emission control requirements impact onboard safety costs. 

As was described in the light-duty section of the report, 

an onboard system (even those for HDGVs) is in many ways an 

extrapolation of current evaporative emission control 

technology and the two systems are quite similar. Since 

onboard systems are basically extensions of evaporative 

emission systems, clearly many of the safety design 

considerations associated with onboard systems related to 

meeting BMCS/NHTSA requirements or providing in-use assurance 

have already been addressed in evaporative emission system 

designs. Consequently, much of the ground work required to 

insure onboard safety has already been performed. It is 

important to keep the magnitude of the HDGV onboard safety 

design process in perspective, because much of the safety 

technology needed is simply an extension of that which already 

exists. Noting the "incremental" nature of onboard safety in 

terms of the magnitude of the task and actual cost relative to 

evaporative systems, it is now possible to describe the 

components which factor into onboard safety costs. 

Basically, the integration of safety into a fuel system 

incorporating an onboard system involves four types of costs. 

These four costs are for 1) design and development (R&D), 2) 

specific hardware, 3) safety testing, and 4) weight penalty (or 

added fuel consumption). The paragraphs that follow describe 

how each of the cost components are affected by onboard safety. 

To begin with, some research and development will have to 

be performed to safely integrate onboard controls into HDGV 

fuel systems. EPA has estimated that the total design and 

development cost required to incorporate onboard systems in 

HDGV fuel systems is about $34,200 per family or $1.50 per 

vehicle (over 10,000 lbs GVWR). This cost is for any 

development effort involved in combining the components of an 

onboard system with the rest of the vehicle to form a unit that 

interacts safely and effectively. Because safety is evaluated 

inherently in the design and development process and yet is 

only one part of the total effort, only a fraction of the total 

cost should be directly allocated to safety. The light-duty 

cost section explained why this fraction is likely to be 
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small. The same reasoning is also applicable for heavy-duty 

applications, and therefore it was assumed that about 20 

percent of R&D expenditures relate to safety, which translates 

to about $0.30 per vehicle. 

The second component of HDGV onboard safety costs relates 

to specific hardware that may be required to insure fuel system 

safety. EPA has estimated costs for three specific items which 

have been identified as potential components to be included as 

part of the onboard system design explicitly for safety 

reasons. These three items are 1) a rollover valve, 2) a 

pressure relief mechanism, and 3) fuel system modifications 

necessary to safely incorporate a rollover valve, pressure 

relief mechanism, or other onboard hardware. HDGV rollover 

valves should not differ in cost from light-duty valves since 

they would essentially be the same. Therefore, the light-duty 

estimate of $3.00 ti $6.00 will also be used here. 

The second safety hardware cost is for a pressure relief 

mechanism. Since this mechanism would be needed for onboard 

systems incorporating a mechanical fillneck seal, nearly all 

HDGVs would require its use. EPA's analysis prices this device 

at $2.50.[13] At this point, this estimate is considered to be 

very conservative, since the possibility exits that the present 

pressure relief device can be modified to perform this function. 

The final onboard safety hardware cost accounts for any 

fuel system modifications that would be necessary in order to 

safely accommodate any onboard control hardware. For example, 

a HDGV fuel tank or fillpipe might have to be re-shaped or 

modified in order to accept a rollover valve. Also, some 

slight re-routing of the fuel system's vapor lines may be 

required. EPA has estimated a total modification cost to be 

$0.50 per fuel tank. Only part of this total cost would be 

required for safety purposes. However, because safety 

inherently enters into the decision to make any modifications, 

it is difficult to access what part of the total modification 

cost should be allocated to safety; perhaps half ($0.25 per 

fuel tank) could be considered as driven by safety related 

concerns. 

Summing up the three individual safety hardware costs 

yields a total estimated figure in the range of $5.75 to 

$8.75. However, this cost estimate does not include 

manufacturer overhead and profit. Consequently, in order to 

obtain the retail price equivalent cost, these estimates must 

be multiplied by a markup factor. Presently, a markup factor 

value of 1.27 appears representative.[33] Therefore, after 

integration of the markup factor, a total retail price 

equivalent HDGV safety-related hardware cost falls within the 

range of $7.30 to $11.10. 
P.91 

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The third component of safety costs is for any safety 

testing that would be necessary. Unlike light-duty test costs, 

EPA has not thoroughly investigated HDGV safety test costs. 

However, safety test costs were estimated in an attempt to 

determine the approximate magnitude of the per vehicle HDGV 

safety test cost. Table 6 shows that even when fairly liberal 

safety test costs are assumed, the resulting cost/vehicle of 

$0.25 is very minimal in the long term. 

The fourth component of safety costs is the estimate of 

the added fuel consumed over the life of the vehicle due to the 

increase in vehicle weight resulting from added safety 

hardware. The amount of weight added to vehicle from a 

rollover valve or pressure relief mechanism is very small (0.4 

lbs), and because HDGVs are less sensitive to weight changes 

than lighter weight vehicles, less than $0.25 in added fuel 

costs will result from their inclusion into the HDGV onboard 

system.[21] 

A total onboard safety cost is calculated by summing all 

four individual component costs. Total capital costs per 

family average about $230,000, and the per vehicle costs range 

from $8.10 to $11.90 or about 20-25 percent of the total cost 

depending on the type of rollover valve used. 

2. Leadtime 

If EPA were to implement an HDGV onboard requirement, it 

would be necessary to allow manufacturers enough leadtime to 

adequately prepare for the requirement. The HDGV preparation 

process would involve the same individual tasks that would 

enter into the light-duty process: system design, development, 

testing, tooling, certification, and safety evaluation. 

Although two of these leadtime tasks (certification and safety 

evaluation) would involve somewhat different procedures for 

HDGVs, they will essentially require the same amount of time 

and would factor into the total process in the same manner as 

in light-duty. Therefore, it is estimated that 24 months would 

be the total amount of leadtime required by HDGV manufacturers, 

and Figure 25 which shows the parallel/sequential progression 

of the individual leadtime components would be essentially the 

same for HDGVs. 

Of the various leadtime components shown in Figure 25, all 

but two would be essentially the same for HDGVs as they would 

for light-duty applications. These two are certification and 

safety evaluation. In both cases, the HDGV processes appear as 

though they would take less time to complete than their 

light-duty counterparts because these tasks would be likely to 

be less difficult to perform. For example, in some cases, 
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Table 6 

HDGV Fuel Tank Safety Test Costs Estimate 

1. BMCS Requirements: 

2 tests per HDGV fuel system configuration 

(Safety Vent Test and Leakage Test) 

Conservative Cost/Test Estimate: $2,000 

7 HDGV Fuel Tank Configurations 

Total BMCS Safety Test Cost: $28,000 

2. NHTSA Requirements: 

1 test per HDGV fuel system configuration 

(30 mph moving barrier) 

Conservative Cost/Test Estimate: $30,000 

2 School Bus Configurations (2 manufacturers, 

1 config./manufacturer) 

Total NHTSA Safety Test Cost: $60,000 

3. Total HDGV Fuel Tank Safety Test Cost: $88,000 

4. Cost/Vehicle (Amortized at 10 percent over 5 years of 

vehicle sales*): $0.25 

* Vehicle sales were estimated at 90,000/year 
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durability assessments for certification of HDGVs does not 

require any actual vehicle testing; bench evaluations can be 

substituted based on the manufacturers engineering judgment. 

This could save considerable time. 

As far as safety evaluation goes, HDGV fuel tank tests 

performed to meet BMCS requirements would be much simpler to 

perform than NHTSA's safety crash tests for passenger cars and 

light trucks. Also, when NHTSA requirements do apply (as in 

the case of school buses) they only involve a single crash test 

with no rollover. (This is minor in comparison to tests which 

involve multiple crashes with rollover.) Therefore, the amount 

of time allowed for light-duty certification (10-12 months) and 

safety evaluation (>12 months) should also be sufficient for 

HDGVs since the heavy-duty processes are less involved. 

Overall, 24 months of leadtime for HDGV onboard is quite 

reasonable. This is especially true when one considers the 

development work already completed and the "incremental" nature 

of onboard in relation to current evaporative emission systems. 

EPA's 24-month leadtime estimate is supported by past 

experience with previous HDGV evaporative emission 

rulemakings. These rulemakings include the California Air 

Resources Board original 1978 6.0 g/test HDGV evaporative 

emission standard which was implemented with just 21 months of 

leadtime.[48] The stringency of this standard was increased 

for 1980 model year HDGVs allowing only 2 g/test. [49] While 

this stricter standard was promulgated with 37 months of 

leadtime, manufacturers had to meet the 1978 standard first, 

which effectively limited the leadtime for the 1980 standard to 

about 24 months. One final evaporative emission standard which 

was implemented with 24 months of leadtime was EPA's 1985 HDGV 

standard. In each of these three rulemakings, manufacturers 

faced leadtime factors identical to the ones that would 

accompany an onboard requirement, including safety. Since 

manufacturers were able to safely and effectively integrate 

evaporative emission controls into their vehicle's fuel systems 

with 24 months of leadtime, and since the magnitude of the 

onboard implementation task is similar, manufacturers should 

also be able to safely and effectively integrate onboard into 

vehicle fuel systems with 24 months leadtime. 

As far as safety development and evaluation is concerned, 

EPA's HDGV leadtime estimate is also supported by the past 

experience of BMCS and NHTSA in implementing various HDGV fuel 

system requirements. In 1973, BMCS extended its safety test 

requirements to include previously unaffected non-side-mounted 

(frame-mounted) HDGV fuel tanks. This requirement was 

implemented with just 18 months of leadtime.[50] Also in 1977, 

FMVSS 301 was extended to include school buses, and this 
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requiremeht was implemented with 17 months of leadtime.[51] 

This experience indicates that 24 months of leadtime allows 

manufacturers sufficient time to factor in safety. 

Based on the information provided above, it appears that 

24 months is adequate time to implement HDGV onboard controls, 

with full consideration of all safety concerns. Because safety 

evaluation can proceed in parallel to three other tasks, more 

than a year is available for actual fuel tank safety tests, 

school bus crash testing, or any desired computer simulation. 

This allows adequate leadtime to properly integrate safety into 

HDGV onboard systems especially since manufacturers can utilize 

and expand safety technology used in current evaporative 

emission control systems to develop effective onboard systems. 

Also, much of the safety development which would be required 

has already taken place with the identification and resolution 

of such potential safety issues as rollover protection and fuel 

tank pressure relief. Consequently, a 24-month leadtime period 

would provide manufacturers with sufficient opportunity to 

develop safe and effective onboard systems. 

While the current leadtime estimate of 24 months is 

reasonable for all vehicle models including HDGVs, EPA is 

sensitive to manufacturers concerns regarding leadtime 

requirements. EPA is committed to providing manufacturers the 

leadtime necessary to implement onboard controls safely and 

effectively. Consequently, EPA would include HDGVs as part of 

any overall consideration of a short phase-in period for 

onboard controls. 

F. Summary/Conclusion 

The purpose of this section was to identify and address 

the potential effects onboard controls could have on a HDGV 

manufacturer's fuel system safety designs. After analyzing the 

potential safety concerns related to implementing HDGV onboard 

systems, EPA has found that like passenger cars and light 

trucks, heavy-duty onboard systems are extensions of current 

evaporative systems and corresponding safety considerations are 

similar in nature to those discussed for light-duty 

applications. While a few unique considerations do exist (in 

part because of differences in testing requirements, tank 

designs/locations, structural integrity, size etc.), no 

increase in overall risk should be caused or accepted, beyond 

that now present with today's HDGV fuel/evaporative system. 

This applies to both compliance with the applicable Federal 

safety standards and the in-use safety of HDGVs equipped with 

onboard systems. As was the case for light-duty, 

straightforward engineering solutions are available for all of 

the potential safety problems which have been identified, and 
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that while final choices regarding exact system designs lie 

with the manufacturers, safe fuel system designs are achievable 

by all. EPA estimates that HDGV safety costs contribute about 

20-25 percent of the total HDGV onboard system cost and should 

fall within the range of $8.10 to $11.90. With regard to 

leadtime, EPA's analysis indicates that 24 months should 

provide HDGV manufacturers with adequate time to prepare for 

the safe and effective implementation of onboard controls. 
-95-

VIII. Conclusion 

EPA has investigated and analyzed each of the potential 

onboard system safety issues raised by the commenters. After 

carefully considering all of the potential impacts an onboard 

system could have on the overall safety of a vehicle's fuel 

system, it is concluded that straightforward, reliable, 

relatively inexpensive engineering solutions exist for each of 

the potential problems identified. Furthermore, no increase in 

risk need occur or be accepted because of the presence of an 

onboard system. Onboard equipped vehicles can be designed to 

pass FMVSS 301 and provide a level of in-use fuel system 

integrity equal to or better than that achieved on present 

vehicles which incorporate evaporative emission control 

systems. Of course final choices regarding exact onboard 

system designs lie with the manufacturers, and each 

manufacturer will choose the approach/system which provides the 

best balance of cost, safety, and other key factors. EPA would 

not adopt an onboard requirement unless it was clear that safe 

fuel system designs were available. This report demonstrates 

this to be the case. Safe fuel system designs are achievable 

by all manufacturers. 

Furthermore, it it is quite possible that overall fuel 

system improvements could accompany the implementation of 

onboard controls and lead to a net improvement in the level of 

fuel system safety on in-use vehicles. For example, 

collapsible bladder tanks are one design option that could 

control refueling emissions, reduce evaporative emissions and 

at the same time improve fuel system safety. 

Manufacturers can and are expected to design and implement 

onboard systems in a manner which provides at least the same 

level of fuel system safety as achieved on present vehicles. 

In addition, a number of design options and other measures are 

available with onboard systems, which suggest that fuel system 

safety in-use can be improved along with the incorporation of 

onboard control systems. 
P.97 

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IX. References 

1. Letter, Thomas Hanna MVMA and George Nield AIA to 

Lee Thomas US EPA, December 22, 1986. 

2. Letter, Brian O'Neil, IIHS to Lee Thomas, US EPA, 

September 23, 1986. 

3. Letter, Ralph Hitchcock NHTSA to Charles L. Gray, 

Jr., US EPA, November 13, 1986. 

4. American Petroleum Institute Comments on US EPA 

Gasoline Marketing Study, November 8, 1984, docket A-84-07. 

5. Letter, Clarence Ditlow, Center for Auto Safety 

to US EPA, March , 1987. 

6. "Survey of Evaporative Emission Systems Condition of 

In-Use, High Mileage Automobiles", API Publication 4393, 

February, 1985. 

7. Borg Warner Control Systems Catalog, February 1986. 

8. "Study of Gasoline Volatility and Hydrocarbon 

Emissions from Motor Vehicles", US EPA, AA-SDSB-85-5, November 

1985. 

9. "Summary and Analysis of Comments on the Recommended 

Practice for the Measurement of Refueling Emission", US EPA 

AA-SDSB-87, March 1987. 

10. Letter, T.M. Fisher, General Motors to James B. 

Weigold US EPA, November 8, 1984, Docket A-84-07. 

11. Ford Motor Company Comments on Evaluation of Air 

Pollution Regulatory Strategies for the Gasoline Marketing 

Industry November 8, 1984, Docket A-84-07. 

12. Chrysler Corporation comments on Evaluation of Air 

Pollution Regulatory Sraegies for the Gasoline Marketing 

Industry, November 5, 1984; Docket A-84-07. 

13. "Toyota Information on Refueling Vapor Recovery", 

presentation to US EPA, March 19, 1986. 

14. "Onboard Control of Vehicle Refueling Emissions 

Demonstration of Feasibility", API Publication 4306, Oct 1978. 

15. "Vehicle Onboard Refueling Control", API Publication 

4424, March 1986. 
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16. "Evaluation of the Feasibility of Liquid Fillneck 

Seals," US EPA AA-SDSB-86-003, December 1986. 

17. Evaluation of Air Pollution Regulatory Strategies 

for Gasoline Marketing Industry - Response to Public Comments, 

March 1987. 

18. "Onboard Refueling Vapor Recovery Cost Study," 

Mueller Associates Inc., December 1986. 

19. "Evaluation of Federal Motor Vehicle Safety Standard 

301-75, Fuel System Integrity: Passenger Cars," DOT HS-806-335, 

January 1983. 

20. Motor Vehicle Safety Standard No. 301-75, Fuel 

System Integrity: 39 FR 10588, March 21, 1974, PART 571; S 

301-75-5.1, 5.2, 5.3, and 40 FR 48352, October 15, 1975, PART 

571: S 301-75-5.1, 5.2, 5.3, 5.4. 

21. Letter, David E. Martin, GM to Barry Felrice, NHTSA, 

March 24, 1986. 

22. Note from Bob Williams, NHTSA, to Glenn Passavant, 

US EPA including 3 computer file printouts, November 13, 1986. 

23. "Design of a Fire Proof Vehicle," Chan, C.Y.K./Chi, 

L.L., California University, Berkeley, Fire Research Group., 

Report No. UCB-FRG-75-18, July, 1975. 

24. "A Perspective on Automobile Crash Fires", SAE 

850092, C. Warner, M. James, R. Wooley. 

25. "Supplement to General Motors Commentary to the 

Environmental Protection Agency Relative to Onboard Control of 

Vehicle Refueling Emissions," June 1978. 

26. IIHS Press Release, February 25, 1987. 

27. Ann Arbor News, "'Smart' Suspension System Includes 

Sensors; Computers," Ann Arbor News, Newhouse News Service, 

March 1, 1987. 

28. "Spilled Fuel Ignition Sources and Countermeasures," 

Johnson, N., DOT Contract No. HS-4-00872, Report No. 

2310-75-118, September, 1975. 

29. "Costs of Onboard Vapor Recovery Hardware", Jack 

Faucett and Mueller Associates, February 1985. 
P.99 

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30. "Report on Quality Changes for 1977 Model Passenger 

Cars" USDL-76-1376, BLS November 1976. 

31. "Report on Quality Changes for 1976 Model Passenger 

Cars," USDL-75-626, BLS November 1975. 

32. "Cost Estimations for Emission Control Related 

Components/Systems and Cost Methodology Description," 

EPA-460/3-78-002, March 1978. 

33. "Update of EPA's Motor Vehicle Emission Control 

Equipment Retail Price Equivalent Calculation Formula," Jack 

Faucett Associates for U.S. EPA, September 4, 1985. 

34. "Cost of Crash Testing to Assure Fuel System 

Integrity for Onboard Systems," EPA Memorandum, Robert Johnson 

to the Record, U.S. EPA, OAR, OMS, ECTD, SDSB, September 2, 

1986. 

35. Conversation with R. Hitchcock, NHTSA, March 28, 

1986. 

36. "Trap Oxidizer Feasibility Study", U.S. EPA, OANR, 

OMSAPC, ECTD, SDSB, March 1982. 

37. "Characterization of Fuel/Vapor Handling Systems of 

Heavy-Duty Gasoline Vehicles over 10,000 Pound GVW", Jack 

Faucett Associates, September 1985. 

38. "Evaluation of Air Pollution Regulatory Strategies 

for the Gasoline Marketing Industry", US EPA, OAR, 

EPA-450/3-84-012a, July 1984. 

39. Memorandum to File, Review of General Motors Heavy 

Duty Engine/Valued Certification Procedures, Team IV 

Certification Branch, August 4, 1986. 

40. Memorandum to File, Review of Ford HDE Certification 

Procedures, Team IV Certification Branch, August 5, 1986. 

41. 49 CFR Part 393.65 to 393.67. 

42. Conversation with Jim Feiten, GM, March 16, 1987. 

43. Conversation with Bob Bisaro, Ford, March 16, 1987. 

44. Motor Vehicle Safety Standard NO. 301-75, Fuel 

System Integrity: 40 FR 48352, October 15, 1975, PART 571: S 

301-75-5.4 and 41 FR 36026, August 26, 1976, PART 571: S 

301-75-5.4 
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45. " 49 CFR 393.67 (c)(7)(ii). 

46. Based on a WP of 10 psi for Emco Wheaton Model 

A6000 and OPW Model 7H diesel fuel nozzles. 

47. Conversation with Jim Brittell, DOT/BMCS, February 

18, 1987. 

48. Public Hearing to Consider Amendments to California 

Fuel Evaporative Emission Test Procedures for 1978 and 

Subsequent Model Gasoline-Powered Vehicles, Resolution No. 

76-15, March 31, 1976. 

49. Public Hearing on Proposed Changes to Regulations 

Regarding Vehicle Evaporative Emission Standards for 1980 and 

Subsequent Model Motor Vehicles, Resolution No. 76-45, November 

23, 1976. 

50. BMCS Regulations, Part 393-Parts and Accessories 

Necessary for Safe Operations (Fuel Systems): 36 FR 15444, 

August 14, 1971, and 37 FR 4340, March 2, 1972. 

51. FMVSS 301, 40 FR 48352, October 15, 1975.