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Federal Motor Vehicle Safety Standards; Fuel System Integrity of Compressed Natural Gas Vehicles

American Government Special Collections Reference Desk

American Government Topics:  National Highway Traffic Safety Administration

Federal Motor Vehicle Safety Standards; Fuel System Integrity of Compressed Natural Gas Vehicles

Christopher A. Hart
Federal Register
April 25, 1994

[Federal Register: April 25, 1994]


=======================================================================
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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 93-02; Notice 4]
RIN 2127-AD48

 
Federal Motor Vehicle Safety Standards; Fuel System Integrity of 
Compressed Natural Gas Vehicles

AGENCY: National Highway Traffic Safety Administration (NHTSA), 
Department of Transportation (DOT).

ACTION: Final rule.

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SUMMARY: This rule establishes a new Federal motor vehicle safety 
standard, Standard No. 303, Fuel System Integrity of Compressed Natural 
Gas Vehicles, that specifies vehicle performance requirements for the 
fuel system of vehicles fueled by compressed natural gas (CNG). The 
Standard enhances the fuel system integrity of CNG vehicles by 
subjecting the vehicles to crash testing and placing a limit on the 
post-crash pressure drop in the fuel system. The Standard specifies 
frontal, rear, and lateral barrier crash tests for light vehicles and a 
moving contoured barrier crash test for school buses with a GVWR over 
10,000 pounds. The purpose of this new standard is to reduce deaths and 
injuries caused by fires resulting from fuel leakage during and after 
crashes involving vehicles fueled by CNG.
    This is the first final rule in the agency's comprehensive effort 
to regulate alternative fueled vehicles. In addition to this final 
rule, NHTSA anticipates issuing another final rule that will specify 
performance requirements addressing the strength, durability, and 
venting of CNG fuel containers. In addition, as a result of public 
comments on the CNG notice of proposed rulemaking (NPRM), the agency 
anticipates issuing a supplemental notice of proposed rulemaking 
(SNPRM) proposing performance requirements that would evaluate a CNG 
fuel container's internal corrosion, brittle fracture under low 
temperatures, external damage, and fragmentation.

DATES: Effective Date: The Standard becomes effective on September 1, 
1995.
    Petitions for Reconsideration: Any petition for reconsideration of 
this rule must be received by NHTSA no later than May 25, 1994.

ADDRESSES: Petitions for reconsideration of this rule should refer to 
Docket 93-02; Notice 3 and should be submitted to: Administrator, 
National Highway Traffic Safety Administration, 400 Seventh Street SW., 
Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Mr. Gary R. Woodford, NRM-01.01, 
Special Projects Staff, Office of Rulemaking, National Highway Traffic 
Safety Administration, 400 Seventh Street SW., Washington, DC 20590 
(202-366-4931).

SUPPLEMENTARY INFORMATION:

Outline

I. Background
    A. General Information
    B. Advance Notice of Proposed Rulemaking
    C. Notice of Proposed Rulemaking
II. Comments on the Proposal
III. Agency's Decision
    A. Overview
    B. Vehicles Subject to the Performance Requirements
    1. Gross Vehicle Weight Ratings
    2. Terminology
    C. Performance Requirements
    1. Allowable Pressure Drop
    a. Regulatory Background
    b. Problems with Measuring Small Pressure Drops
    c. Test Time
    d. Test Temperature
    e. Leakage from Fuel System Components
    f. Bi-Fuel and Dual Fuel Applicability
    D. Test Conditions
    1. Test Pressure
    2. Test Gas
    3. Electric Shutoff Valves
    E. Requirements Not Adopted
    1. Static Rollover
    2. Refueling connections
    3. Venting
    4. Leak detection
    5. Retention of Fuel Storage Containers
    F. Other Considerations
    1. Vehicles manufactured in more than one stage
    2. Benefits
    3. Costs
    4. Leadtime
VI. Rulemaking Analyses
    A. Executive Order 12688 and DOT Regulatory Policies and 
Procedures
    B. Regulatory Flexibility Act
    C. Executive Order 12612 (Federalism)
    D. National Environmental Policy Act
    E. Civil Justice Reform

I. Background

A. General Information

    At standard temperature and pressure, natural gas is a gas that is 
lighter than air.\1\ When used as a vehicle fuel, natural gas is 
typically stored on-board a vehicle in cylindrical containers at a 
pressure of approximately 20,684 kPa pressure (3,000 psi). Natural gas 
is kept in this compressed state to increase the amount that can be 
stored on-board the vehicle. This serves, in turn, to increase the 
vehicle's driving range. Since natural gas is flammable and is stored 
under high pressure when used as a vehicle fuel, it poses a potential 
risk to motor vehicle safety.
---------------------------------------------------------------------------

    \1\Standard temperature is 0 deg. Celsius or 32 deg. Fahrenheit 
and standard pressure is 101.4 kiloPascals (kPa) or 14.7 pounds per 
square inch (psi).
---------------------------------------------------------------------------

    Alternative fuel vehicles powered by CNG have not been numerous to 
date. The number of CNG vehicles in the United States has more than 
doubled from 10,300 in 1990 to 23,800 at the end of 1992. The number of 
CNG vehicles is projected to again double to an estimated 50,800 
vehicles in 1994.
    However, Federal legislation, as well as the need to meet 
environmental and energy security goals, will lead to increased 
production and use of these vehicles. Among the items of Federal 
legislation encouraging the use of alternative fuels in general are: 
(1) The Alternative Motor Fuels Act of 1988, (2) the Clean Air Act 
Amendments of 1990, and (3) the Energy Policy Act of 1992. The 
Alternative Motor Fuels Act of 1988 directs the Department of Energy to 
conduct demonstration programs to encourage the use of alternative 
motor fuels, including natural gas. As a further encouragement, this 
Act also specifies that new passenger automobiles will have their fuel 
economy calculated according to a special mileage enhancing procedure. 
The Clean Air Act Amendments of 1990 establish the clean fuel 
requirements that treat fuel type and content, along with vehicle 
technology, as a potential source of emission reductions. These 
Amendments call for programs that will substantially increase the 
number of low-polluting vehicle/fuel combinations in use. The Energy 
Policy Act of 1992 directs the Department of Transportation to issue 
safety standards applicable to vehicle conversions.
    Executive branch initiatives will also encourage the increased use 
of alternative fueled vehicles. Executive Order 12844 increased by 50 
percent the number of alternative fueled vehicles to be acquired by the 
Federal Government from 1993 through 1995. (April 21, 1993) In 
addition, in 1993, the President established the Federal Fleet 
Conversion Task Force to accelerate the commercialization and market 
acceptance of alternative fueled vehicles throughout the country.

B. Advance Notice of Proposed Rulemaking

    On October 12, 1990, NHTSA published an advance notice of proposed 
rulemaking (ANPRM) to explore whether the agency should issue Federal 
motor vehicle safety standards (FMVSSs) to promote the fuel system 
integrity of motor vehicles using CNG or liquefied petroleum gas (LPG) 
as a motor fuel. (55 FR 41561) The ANPRM sought comment about the crash 
integrity of vehicle fuel systems, the integrity of fuel storage 
containers, and pressure relief for such containers.

C. Notice of Proposed Rulemaking

    On January 21, 1993, NHTSA published a notice of proposed 
rulemaking (NPRM) in which the agency proposed to establish a new FMVSS 
specifying performance requirements for vehicles fueled by CNG (58 FR 
5323). The proposal was based on comments received in response to the 
ANPRM and other available information. The NPRM was divided into two 
segments: (1) Vehicle requirements that addressed the integrity of the 
entire fuel system, and (2) equipment requirements that addressed the 
safety of the fuel containers themselves.
    NHTSA decided to model the proposed requirements for CNG fueled 
motor vehicles on Standard No. 301, Fuel System Integrity. Standard No. 
301 specifies performance requirements for vehicles that use fuel with 
a boiling point above 32  deg.F (i.e., liquid fuels under standard 
temperature and pressure). Both gasoline and diesel fuel have a boiling 
point above that temperature. Since CNG has a boiling point below 32 
deg.F, vehicles manufactured to use only CNG are not subject to 
Standard No. 301. Standard No. 301 limits the amount of fuel spillage 
from ``light vehicles''\2\ during and after frontal, rear, and lateral 
barrier crash tests and a static rollover test. The Standard also 
limits fuel spillage from school buses with a GVWR over 10,000 pounds 
after being impacted by a moving contoured barrier at any point and any 
angle. By adopting a CNG rule based on Standard No. 301, the agency 
would afford passengers of CNG vehicles a level of safety comparable to 
that provided passengers of vehicles fueled by gasoline or diesel fuel.
---------------------------------------------------------------------------

    \2\Light vehicles include passenger cars, multipurpose passenger 
vehicles (MPV's), trucks, and buses with a gross vehicle weight 
rating (GVWR) of 10,000 pounds or less.
---------------------------------------------------------------------------

    NHTSA proposed that the fuel system integrity requirements for CNG 
vehicles would include frontal, rear, and lateral barrier crash tests 
for light vehicles, and a moving contoured barrier crash test for large 
school buses. The agency proposed that fuel system integrity would be 
assessed by measuring the fuel system's post-crash pressure drop, 
instead of fuel spillage as under Standard No. 301, since CNG is a gas. 
The allowable pressure drop for CNG fueled vehicles would be 
equivalent, as measured by the energy content of fuel, to the allowable 
spillage of fuel during Standard No. 301 compliance testing.
    With respect to the ``equipment'' requirements applicable to CNG 
containers, NHTSA proposed a definition for ``CNG fuel tank'' and 
performance requirements for such fuel containers manufactured for 
motor vehicles, including aftermarket containers.\3\ The Agency 
proposed that the CNG containers would be subject to a pressure cycling 
test to evaluate durability and a pressure burst test to evaluate 
strength. In addition, the NPRM proposed equipment requirements to 
regulate how the container may ``vent'' its contents under specified 
conditions of elevated temperature and pressure.
---------------------------------------------------------------------------

    \3\Among the terms used to describe CNG fuel tanks are tanks, 
containers, cylinders, and high pressure vessels. The agency will 
refer to them as ``containers'' throughout this document.
---------------------------------------------------------------------------

II. Comments on the Proposal

    NHTSA received a large number of comments addressing the CNG 
proposal. The commenters included manufacturers of CNG containers, 
vehicle manufacturers, trade associations, other CNG-oriented 
businesses, research organizations, State and local governments, the 
United States Department of Energy, and energy companies. In addition, 
NHTSA met with the Compressed Gas Association (CGA) and the Natural Gas 
Vehicle Coalition (NGVC) and had telephone conversations and meetings 
with some of the commenters. A record of each of these contacts may be 
reviewed in the public docket.
    The commenters generally believed that a Federal safety standard 
regulating the integrity of CNG fuel systems and fuel containers was 
necessary and appropriate. In fact, some commenters, including the CGA, 
the NGVC, and CNG container manufacturers stated that NHTSA needs to 
issue a Federal standard as soon as possible to facilitate the safe and 
expeditious introduction of CNG fueled vehicles. The commenters 
generally agreed with most of the vehicle-oriented proposals including 
those related to the standard's applicability, the formula used to 
determine the allowable amount of CNG leakage, and the barrier crash 
tests. Nevertheless, commenters were concerned with the inability of 
commercially available measuring devices to measure what they viewed as 
the extremely small pressure drops allowed by the proposal.

III. Agency's Decision

A. Overview

    In today's final rule, NHTSA is issuing a new Federal motor vehicle 
safety standard, Standard No. 303, Fuel System Integrity of Compressed 
Natural Gas Vehicles. It specifies vehicle performance requirements 
applicable to the fuel system of a CNG fueled vehicle. As explained in 
the NPRM, and summarized above, the fuel system integrity requirements 
are comparable to those requirements in Standard No. 301. Like those 
requirements, the CNG requirements specify frontal, rear, and lateral 
barrier crash tests for light vehicles and a moving contoured barrier 
crash test for school buses with a GVWR over 10,000 pounds.
    There are, however, some differences between Standard No. 301 and 
Standard No. 303. For instance, as noted above, CNG fuel leakage is 
determined by the post-crash pressure drop in the fuel system instead 
of by fuel spillage. The amount of allowable pressure drop is to be 
based on the volume of the CNG leakage that either (1) is equivalent in 
energy content to the amount of gasoline leakage permitted by Standard 
No. 301, as calculated by the pressure drop formula\4\ or (2) 1062 kPa 
(154 psi), whichever volume is greater. Another difference with 
Standard No. 301 is that a static rollover provision has not been 
included in the CNG Standard because while such a procedure can affect 
the leakage of a liquid fuel, it has no affect on the leakage of a 
lighter-than-air gaseous fuel.
---------------------------------------------------------------------------

    \4\The formula is set forth in S5.2(a)(2) and discussed in the 
sections titled ``Problems with measuring small pressure drops,'' 
``Test temperatures,'' and ``Test pressures.''
---------------------------------------------------------------------------

    Each specific issue about the fuel system integrity requirements 
for CNG vehicles will be discussed later in this notice. These issues 
include the applicability of the vehicle requirements, the 
practicability of measuring small pressure drops, the test time, the 
test temperature, leakage from components in the fuel system, 
evaluating vehicles that have more than one fuel system, and the test 
conditions including the test pressure and test gas. The notice also 
discusses the agency's decision not to adopt requirements regarding 
certain matters, including static rollover, refueling connections, fuel 
storage retention, venting, leakage detection, and warning devices.
    This rule assures crash integrity of the vehicle which is 
comparable to that required in Standard No. 301. In addition, NHTSA 
recognizes that additional safety precautions may be required because 
of the unique concerns with high pressure fuel containers and the 
failure modes to which they may be subject. Thus, in addition to this 
final rule, NHTSA has issued a supplemental notice of proposed 
rulemaking (SNPRM) addressing the burst test for CNG containers (58 FR 
68846, December 29, 1993). Based on comments to that notice and 
comments to the January 1993 NPRM, the agency anticipates issuing 
another final rule in the near future that will specify requirements 
regulating a CNG container's strength, durability, and venting. 
Moreover, based on comments to the NPRM and other available 
information, the agency anticipates issuing a supplemental notice of 
proposed rulemaking (SNPRM) that would propose performance requirements 
addressing a CNG fuel container's internal corrosion, brittle fracture 
under low temperature conditions, external damage, and fragmentation.

B. Applicability of the Vehicle Requirements

1. Gross Vehicle Weight Ratings
    NHTSA proposed to apply the CNG Standard to passenger cars, 
multipurpose passenger vehicles, trucks, and buses with a GVWR of 
10,000 pounds or less, and to school buses, regardless of their GVWR. 
This applicability is identical to the applicability of Standard No. 
301. In the NPRM, the agency tentatively stated that it would be 
inappropriate to apply the fuel leakage limits to CNG vehicles that 
have a GVWR greater than 10,000 pounds other than school buses, because 
barrier crash tests are not currently required for liquid-powered 
vehicles that have a GVWR over 10,000 pounds other than school buses.
    Navistar, Amoco, Transportation Manufacturing Corporation (TMC), 
Chrysler, Thomas Built, and Flxible agreed with the agency's proposal 
to apply the CNG vehicle requirements to light vehicles and school 
buses. Washington State and Blue Bird commented that non-school buses 
should be treated the same as school buses and thus be subject to the 
new CNG Standard.
    After reviewing the comments, NHTSA has decided to apply Standard 
No. 303 to light vehicles and to all school buses. The agency's 
objective in regulating the fuel system integrity of CNG vehicles is to 
provide the same level of safety as that provided by Standard No. 301 
for liquid fueled vehicles. Accordingly, the agency has decided to 
specify the same applicability for CNG vehicles as Standard No. 301 
specifies for gasoline and diesel vehicles. The agency disagrees with 
comments favoring the application of the CNG standard to non-school 
buses with a GVWR over 10,000 pounds. As explained in the NPRM, NHTSA 
does not currently include any vehicle over 10,000 pounds, other than 
school buses, in its crash test requirements. NHTSA further notes that 
because the anticipated requirements for CNG fuel containers will apply 
to containers equipped on all vehicles regardless of GVWR, CNG-fueled 
heavy vehicles will be equipped with fuel containers that have been 
certified to comply with that equipment standard.
2. Terminology
    NHTSA proposed that the vehicle requirements be applicable to 
vehicles manufactured to operate on CNG-only (``dedicated'') vehicles 
and to vehicles manufactured to operate on two fuels, CNG and either 
gasoline or diesel fuel. The agency referred in the NPRM to this latter 
type of vehicle as a ``dual fuel'' CNG vehicle.
    The American Automobile Manufacturers Association (AAMA), Blue 
Bird, Oklahoma Gas, and the NGVC commented that the agency used the 
term ``dual fuel vehicle'' incorrectly. These commenters explained that 
the industry's generally understood meaning of ``dual fuel vehicle'' is 
a vehicle that uses a mixture of two fuels simultaneously, in this case 
CNG and another fuel such as gasoline or diesel. A vehicle that is 
capable of operating either on CNG and another fuel such as gasoline or 
diesel, but not a mixture of both, is referred to as a ``bi-fuel'' 
vehicle. A vehicle equipped with one fuel system and designed to 
operate on CNG is referred to as a ``dedicated CNG vehicle.''
    NHTSA has decided to adopt the generally accepted terminology used 
in the alternative fuel industry for vehicles that operate on more than 
one fuel. Accordingly, the final rule includes definitions for ``Bi-
fuel CNG vehicle,'' ``Dedicated CNG vehicle,'' and ``Dual-fuel CNG 
vehicle.'' The agency notes that these definitions are generally 
consistent with the statutory terms in the Energy Policy Act. Section 
403 of that Act amended certain provisions in Title V of the Motor 
Vehicle Information and Cost Savings Act, including definitions for 
``dedicated vehicle'' and ``dual fueled vehicles.'' The definitions of 
these terms in this notice are consistent with the statutory 
provisions. The one difference between the agency's definitions and the 
statutory definitions is that the agency's definition of ``bi-fuel'' 
vehicle also falls under the Act's definition of ``dual fueled 
automobile'' (i.e., ``an automobile which is capable of operating on an 
alternative fuel [such as CNG] and on gasoline or diesel)''. 
Nevertheless, the agency believes that it is necessary that its 
definition of ``bi-fuel'' vehicle include the greater specificity 
provided by the industry's definition of this term.

C. Performance Requirements

1. Allowable Pressure Drop
    a. Regulatory background. In the ANPRM, NHTSA discussed the 
possibility of proposing a prohibition against any fuel leakage during 
the crash test and for up to 30 minutes after the vehicle's motion had 
ceased. A number of commenters to the ANPRM objected to a no-leakage 
requirement, claiming that any pressurized gaseous fuel system will 
produce a minimal amount of leakage from fittings and valves. Along 
with their concerns about practicability, commenters further stated 
that a no-leakage requirement would be overly restrictive in comparison 
to Standard No. 301. That standard permits a minimal amount of leakage.
    After considering the comments on the ANPRM, NHTSA decided that 
instead of proposing a no-leakage requirement, it would propose 
allowing not more than a minimal level of leakage for a specified time 
period. The allowable leakage provision was patterned after Standard 
No. 301 and was intended to avoid the practicability problems 
associated with a no-leakage requirement. The agency believed that the 
allowable amount of leakage is equivalent in energy content to the 
leakage allowed for gasoline in Standard No. 301.
    Under the proposal, CNG leakage from the vehicle's entire fuel 
system would have been measured for a 15-minute period following a 
barrier crash test. The proposal discussed two alternatives related to 
measuring the allowable leakage: (1) Leakage would be measured through 
incremental measurements from the time of impact until the vehicle 
ceased motion, for the subsequent five-minute period, and every minute 
in the next 10-minute period, or (2) the cumulative leakage would be 
measured only once, at the end of the 15-minute test period. With 
either measurement, the total gas permitted to leak at the end of the 
test period would have been the same. The agency requested comment on 
the feasibility and practicability of specifying gaseous leakage 
measurements at specific time intervals and about devices that are 
capable of measuring incremental pressure changes.
    NHTSA received many comments about the proposal to evaluate a CNG 
vehicle's fuel system integrity through an allowable pressure drop 
requirement. Among the issues addressed by commenters were (1) 
practicability problems with measuring small levels of pressure drop, 
(2) the appropriate length of time necessary to evaluate pressure drop, 
(3) the effect of temperature variations on pressure drop, (4) leakage 
from fuel system components, (5) and evaluating bi-fuel and dual fuel 
vehicles. Each of these issues will be addressed below, along with the 
agency's response to the comments.
    b. Problems with measuring small pressure drops. AAMA, Thomas, 
Navistar, TMC, NGVC, Minnesota Gas, and Flxible stated that the 
proposal about allowable pressure drop would result in manufacturers 
trying to measure amounts of gas leakage too small to be measured by 
existing technology. They stated that presently manufactured measuring 
devices known as pressure transducers do not have the capability to 
measure the proposed amounts of pressure drop, even if only one 
cumulative measurement is taken after 15 minutes. AAMA stated that a 
state-of-the-art capacitance type pressure transducer has an accuracy 
of 0.11 percent. Therefore, it believed that if this pressure 
transducer has a range of measurement of 0 to 20,685 kPa (0 to 3000 
psi), the error associated with any measurement would be 
22.8 kPa (3.3 psi). AAMA further stated that a 
variation in 5.6 deg. Celsius (10 deg. Fahrenheit) could result in 
errors of 41.4 kPa and 31.0 kPa 
(6.0 and 4.5 psi) from thermal zero shift and 
thermal coefficient sensitivity, respectively. Finally, AAMA stated 
that the conversion of analog data to digital form would introduce an 
error of 0.056 percent or 11.0 kPa (1.6 psi). 
Aggregating all these alleged measurement errors would result in a 
potential error of 106.1 kPa (15.4 psi). AAMA 
further stated that it is contrary to accepted engineering measurement 
practice to accurately measure data that are of the same order of 
magnitude as known transducer data system errors. Thus, it stated that 
the total measurement error should not exceed 10 percent of the value 
being measured and that given the above mentioned errors, pressure 
drops under 1062 kPa (154 psi) should not be measured with a 
capacitance type transducer. AAMA evaluated the error estimates for a 
less accurate type of pressure transducer than the capacitance 
transducer (the strain gage transducer) and obtained a maximum error of 
328.2 kPa (47.6 psi).
    Based on these comments about the accuracy and practicability of 
using measurement transducers, NHTSA has independently determined that 
current pressure transducers are not able to measure the relatively 
small pressure drops that would have been allowed to occur after 15 
minutes for a container with a 3000 psi service pressure. The agency 
found that most pressure transducers have an accuracy of approximately 
0.1 percent, and now concludes that it would have been impracticable to 
measure the proposed pressure drop levels.
    In view of the problems in measuring small pressure drops, NHTSA 
has modified the allowable pressure drop requirement so that the 
pressure drop of a CNG vehicle must not exceed the amount calculated by 
the pressure drop formula or a pressure drop level of 1062 kPa (154 
psi), whichever is greater. As noted above, 1062 kPa (154 psi) is the 
cumulative potential error (106.1 kPa (15.4 
psi)) of a capacitance type transducer, multiplied by 10 (i.e., 
22.8 kPa (3.3 psi) associated with measurement 
error, 72.4 (10.5 psi) associated with 
temperature variation, and 11.0 kPa (1.6 psi) 
associated with data conversion). Both a 22.8 kPa (3.3 psi) and a 72.4 
kPa (10.5 psi) range would result in a significant percentage of the 
allowable amount of leakage during a 15-minute period, particularly for 
vehicles with large fuel systems. The agency believes that by modifying 
the requirement to specify a floor under the amount of permissible 
pressure drop determined using the pressure drop formula, the agency 
will be able to regulate pressure loss from CNG vehicles to the extent 
permitted by existing pressure drop measurement technology.
    NHTSA notes that establishing a floor under the amount of 
permissible pressure drop is especially important for vehicles with 
large fuel systems, such as school buses, because they will experience 
extremely small pressure drops. This is so because in the formula for 
calculating the allowable pressure drop, pressure drop equals the 
ambient temperature divided by the volume of the fuel system. Since the 
fuel system volume is the denominator, the allowable pressure drop 
decreases as the vehicle's fuel system volume increases. Without the 
floor, the formula would yield pressure drops potentially too small to 
be measured.
    In response to Blue Bird's recommendation that the regulation allow 
a five percent drop after the barrier crash test, NHTSA is concerned 
that this approach would allow varying amounts of fuel leakage from 
different vehicles depending on the fuel system's size. Therefore, the 
agency has decided to reject Blue Bird's recommendation.
    c. Test time. NHTSA received nine comments addressing the 
appropriate test time for the pressure drop requirement. Of the nine 
commenters, Washington, NGV Systems, Navistar, and NGVC stated that a 
cumulative measurement should be taken after 15 minutes because the 
amount of gas leaking each minute would be too small to measure 
accurately. They believed that taking incremental measurements within 
the 15 minute period would not be acceptable. Other commenters, 
including AAMA, Thomas, TMC, and Blue Bird stated that even the 
cumulative leakage over 15 minutes would be too small to measure in 
some cases. Blue Bird stated that the proposed leakage limit was 
``totally unacceptable'' because it would be necessary to detect a 
pressure drop of 0.6 psi in a 3000 psi fuel system. AAMA stated that 
measurement of the pressure drop 60 minutes after impact would be 
reasonable and should be adopted by the agency based on the limitations 
of available measurement equipment, since the proposed leakage rate 
would result in a total pressure drop of 211 psi for a 3000 psi, 170 
liter (45 gallon) fuel system.
    Given the problems with measuring the proposed levels of allowable 
pressure drop, NHTSA has decided to change the pressure drop 
requirement to make it more measurable while keeping it as close to a 
no-leakage requirement as practicable. The agency considered two 
alternative changes to the proposal to ensure that the level of 
pressure drop was practicable to measure: (1) Increase the amount of 
CNG leakage allowed during the proposed 15 minute test period or (2) 
increase the test time period. The agency has decided to reject the 
option of increasing the level of allowable leakage to the point that 
even marginal violations of the leakage limit could be reliably 
measured at the end of a 15 minute period. Such an increase might be 
unsafe and would be inconsistent with the agency's goal of establishing 
a minimum leakage requirement that is as close to a no-leakage 
requirement as possible while still being readily measurable.
    Instead, to accomplish its goal of establishing a safe and 
practicable requirement, NHTSA has decided to increase the test time 
from 15 minutes to 60 minutes. The agency has determined that it is 
necessary to lengthen the test period to permit measurement of safe 
levels of leakage. To illustrate, a container with a service pressure 
of 3000 psi and an allowable pressure drop of approximately 50 psi 
after 15 minutes, would have an allowable pressure drop of 200 psi 
after 60 minutes. Since the agency has determined that it is not 
possible to reliably measure a pressure drop of less than 154 psi 
within a 10  deg.F temperature variation, then the agency's original 
goal of prohibiting a pressure drop of more than 50 psi in 15 minutes 
would not be practicable. Accordingly, the agency determined that it is 
necessary to lengthen the test period or else the only detectable 
violations would be gross violations of the pressure drop limit. Small 
violations of the limit would not be detectable. Moreover, while a 
pressure drop of 50 psi in 15 minutes could not be reliably measured, a 
pressure drop of 200 psi (4 x 50 psi=200 psi in 60 minutes (4 x 15 
minutes=60 minutes) is readily measurable. While those two pressure 
drops are equally stringent since the leakage rate is essentially 
constant for a marginal violation, only the 60 minute period would 
permit measurable results.
    By increasing the test time to 60 minutes, the agency believes that 
the requirement will allow only readily measurable and safe amounts of 
leakage. The agency believes that increasing the test time from 15 
minutes to 60 minutes will not result in an increase in leakage rate. 
As explained above, if the limit and the time are proportionately 
increased the same extent, the stringency is maintained. Increasing the 
test time will not increase the safety risk since the rate of CNG 
leakage is still equivalent, in terms of energy content, to that 
allowed of liquid fuels in Standard No. 301. In addition, the leakage 
rate is more critical than the total level of leakage over an extended 
period of time, since CNG dissipates rapidly because it is lighter than 
air.
    d. Test temperature. In the NPRM, NHTSA proposed a formula in which 
the volume of allowable CNG leakage would translate into certain 
allowable pressure drops in units of kPa for CNG fuel systems, as 
follows: 

------------------------------------------------------------------------
       Volume of CNG leakage               Allowable pressure drop      
------------------------------------------------------------------------
39.8 liters CNG....................  13.72 (T/VFS).                     
199.0 liters CNG...................  68.6 (T/VFS).                      
------------------------------------------------------------------------


where
    T=Temperature of the test gas in degrees Kelvin, stabilized to 
ambient temperature prior to testing.
    VFS=The internal volume in liters of the fuel system from 
which CNG is leaked.

    In the NPRM, NHTSA also considered but decided not to propose 
specifying an ambient temperature. The agency believed that not 
specifying an ambient temperature would not affect a vehicle's 
compliance with the standard and would facilitate the combining of 
tests for various standards. The agency requested comments about its 
tentative decision not to specify an ambient temperature.
    Several commenters, including AAMA, NGVC, Navistar, Blue Bird, 
Minnesota Gas, Flxible, and Thomas, addressed the issue of ambient 
temperature variability. NGVC, Minnesota Gas, Thomas, and Blue Bird 
agreed with the agency that no ambient temperature should be specified. 
Nevertheless, all the commenters, except for Thomas, stated that 
temperature variations should be compensated for when conducting the 
crash test. AAMA stated that temperature variations that occur over the 
course of the testing would change the pressure of the test gas. It 
stated that a 5.6  deg.C (10  deg.F) variance in the test temperature 
would result in a 413.7 kPa (60 psi) change in the pressure of the test 
gas in a 170 liter (45 gallon) fuel container. AAMA stated that a 
pressure change due to a temperature change could mask or intensify the 
actual pressure drop measurement. However, AAMA did not suggest any 
method to correct for the temperature.
    After reviewing the comments, NHTSA continues to believe that no 
ambient temperature should be specified for the reasons set forth in 
the NPRM. However, the agency also believes that the test procedure and 
formula should control for temperature variations. Without such 
control, a large change in temperature could artificially affect the 
test results. NHTSA has decided to specify that the maximum ambient 
temperature variation over the 60-minute test period cannot exceed
5.6  deg.C (10  deg.F). A temperature variation exceeding this amount 
will invalidate the test results. The agency believes that this test 
condition will minimize changes in test gas temperature and 
instrumentation accuracy during the 60-minute period, without placing 
an unreasonable burden on those performing the test.
    In addition, NHTSA has decided to include in the pressure drop 
formula a provision to calculate the average ambient temperature by 
measuring the ambient temperature at the test's start and then every 15 
minutes until 60 minutes has elapsed. The sum of these temperatures is 
then divided by five (the number of measurements taken) to yield the 
average ambient temperature. This calculation will be used for the 
term, ``T,'' in the agency's pressure drop formula. NHTSA believes that 
including a calculation for the average ambient temperature in the 
formula will directly control for fluctuations in pressure due to 
temperature variations, because pressure and temperature are linearly 
related in the formula (i.e., pressure equals temperature multiplied by 
a constant, where the constant includes the volume of the system and 
the compressibility factor).
    AAMA recommended that testing be conducted between 60 deg. and 70 
deg.F. Blue Bird commented that the test conditions specify a 
permissible temperature range of between 0  deg.C and 32  deg.C 
(32 deg. to 90  deg.F) to eliminate testing at unusually low or high 
temperatures. It believed that controlling such temperature extremes 
could reduce variables that affect vehicle and fuel system reactions to 
crash tests.
    After reviewing the comments and other available information, NHTSA 
has decided that prohibiting ambient temperature variation by more than 
10  deg.F during the 60-minute period after testing will be sufficient 
to minimize pressure drop variability due to temperature change. 
However, the agency has decided not to specify a minimum or maximum 
temperature for the 60-minute period after testing. This will 
facilitate the combining of tests for various standards. In addition, 
specifying a range like the one recommended by AAMA would be 
inappropriate for those vehicle manufacturers that conduct their 
compliance crash testing outdoors throughout the year.
    e. Leakage from fuel system components. In the NPRM, NHTSA 
discussed two alternatives regarding measurement of CNG leakage after a 
barrier crash test. Under the first alternative, the allowable CNG 
leakage level would apply to the vehicle's entire fuel system, instead 
of the fuel storage containers only. The agency proposed that the term 
``fuel system'' be defined as ``all components used to store or supply 
CNG to the vehicle's engine.'' This approach would have required a 
manufacturer to measure the internal volume of the vehicle's entire 
fuel system, including the lines, components, and fuel storage 
containers as the basis for evaluating allowable leakage. Under the 
second alternative, the allowable CNG leakage would only apply to the 
CNG fuel container or containers. This approach would have required a 
manufacturer to measure the volume of the fuel storage containers only. 
The agency tentatively preferred the first alternative, believing that 
it would more closely reflect a real world crash. The agency was 
concerned that the second alternative would permit unlimited leakage 
from the vehicle's plumbing system including fuel lines and other 
components downstream from the fuel containers during a crash test.
    Nine commenters addressed the issue of what components of a fuel 
system should be evaluated for leakage. Navistar, NGV Systems, Flxible, 
CNG Pittsburgh, Washington, and Amoco supported measuring leakage from 
the entire fuel system. AAMA, Thomas, and Minnesota Gas stated that 
leakage should be measured from the fuel containers to the first 
pressure regulator, an area which is known as the high pressure side of 
the fuel system. Minnesota Gas stated that, while the fuel lines, 
connections, and valves may be the most vulnerable part of a fuel 
system, the volume of gas in these parts is small when compared to the 
gas volume stored in the fuel containers. Thomas stated that the volume 
of the gas in the fuel lines and valves between the containers and 
engine is negligible. AAMA stated that adding pressure transducers to 
points in the fuel lines solely for purposes of conducting the test 
would produce points of potential leakage that would not exist on a 
non-test vehicle. This would make the test vehicles potentially 
unrepresentative of the vehicle population. AAMA recommended that to 
minimize the potential leakage points, one pressure check point be used 
immediately upstream from the high pressure regulator, or at a location 
specified by the manufacturer.
    After reviewing the comments and other information, NHTSA has 
decided to measure leakage only from the high pressure portion of the 
fuel system. By ``high pressure portion'' of a CNG fuel system, the 
agency means all the components from and including the CNG fuel 
container or containers up to, but not including, the first pressure 
regulator. The agency notes that as CNG flows from the vehicle fuel 
containers to the engine, it passes through one or two pressure 
regulators that reduce the pressure of the gas before it enters the 
engine. On a carbureted type vehicle, there may be one or two pressure 
regulators. For systems with two pressure regulators, the first 
pressure regulator typically reduces service fuel line pressure from 
3000 psi to approximately 300 psi, while the second regulator reduces 
pressure from this level to approximately ambient pressure.
    When the agency proposed to regulate leakage from the entire fuel 
system, it was not aware of the significant difficulty involved in 
accurately measuring small amounts of leakage. In addition, the volume 
of gas in the fuel lines and valves is very small when compared to the 
volume of the fuel containers. For instance, Thomas stated that a 
school bus with six CNG fuel containers has 822 liters of CNG (137 
liters per container x 6). By comparison, the volume of that bus' 
plumbing system (e.g., fuel lines, valves, etc.) is 0.62 liters. Thus, 
the volume of CNG in the plumbing system is approximately 0.075 percent 
of the entire fuel system. Therefore, possible leakage from the 
plumbing system would be minimal and therefore not a significant safety 
concern. Thus, contrary to the agency's belief in the NPRM, measuring 
the entire fuel system would not be much more representative of real 
world crashes than measuring the fuel system's high pressure portion. 
Another reason that the agency decided not to measure leakage from the 
entire fuel system is that using additional transducers would have 
resulted in the test vehicles having more points of potential leakage 
than non-test vehicles, as pointed out by AAMA.
    f. Bi-fuel and dual fuel applicability. In the ANPRM, NHTSA 
discussed whether dual-fuel vehicles should be treated differently than 
dedicated CNG vehicles. Some commenters recommended that dual-fuel 
vehicles have separate fuel system integrity tests based on each of the 
fuels used in the particular vehicle. Under this approach, dual-fuel 
vehicles would be tested twice: once under current Standard No. 301 as 
though they operated only on gasoline or diesel fuel and a second time 
under the proposed CNG standard as though they operated only on CNG.
    In the NPRM, NHTSA proposed that the energy equivalency of the 
allowable fuel leakage from dual-fuel vehicles be the same as that for 
dedicated vehicles. The agency disagreed with commenters to the ANPRM 
that recommended running two separate tests. The agency believed that 
approach would result in an allowable level of total fuel leakage for 
dual-fuel vehicles that is twice what is currently permitted under 
Standard No. 301 or what the agency proposed to establish for CNG 
vehicles. In the NPRM, the agency explained that since a real world 
crash could cause both fuel systems to leak, safety concerns associated 
with dual-fuel vehicles would be best addressed by establishing a 
single, overall fuel leakage limit applicable to the combined energy 
equivalency of the amount of both types of fuel leaked in a single 
crash test.
    Six commenters addressed the most appropriate way to regulate the 
safety of dual-fuel and bi-fuel vehicles. While NFPA, CNG Pittsburgh, 
and NYCFD agreed with the proposal to require that dual-fuel vehicles 
comply with a single overall fuel leakage limit based on the combined 
energy level of both fuel types, AAMA, Blue Bird, and Brunswick 
disagreed. AAMA, Blue Bird, and Brunswick theoretically agreed with the 
concept of establishing a combined energy level. However, they stated 
that because the allowable leakage would be cut in half if the agency 
adopted the proposal, applying this criterion would make both CNG and 
liquid fuel leakage unmeasurable.
    After reviewing the comments, NHTSA has decided to require only one 
test on dual-fuel and bi-fuel vehicles that permits the amount of 
gaseous leakage specified in the CNG standard plus the amount of liquid 
leakage specified in Standard No. 301. Ideally, the agency would have 
preferred to adopt the proposed approach that would have kept the 
combined energy equivalency at an amount consistent with dedicated 
vehicles. However, as discussed in an earlier section, the 
practicability problems with measuring low levels of CNG leakage using 
current technology makes that approach impracticable. Along with being 
practicable, the requirement, as adopted, will reduce the test costs 
incurred by manufacturers since only one test will have to be run. In 
addition, NHTSA notes that the allowable leakage levels for liquid 
fuels under Standard No. 301 and CNG each approximate a ``no leakage'' 
condition.

D. Test Conditions

1. Test Pressure
    In the NPRM, NHTSA proposed that CNG fuel storage containers be 
tested at 100 percent of service pressure. The agency believed that 
this test condition would be consistent with Transport Canada's fuel 
system integrity standard for CNG vehicles. In addition, this is the 
pressure at which the container is designed to operate when filled with 
the gaseous fuel at 20  deg.C (68  deg.F).
    The proposal to specify 100 percent of service pressure level 
departed from the requirement in Standard No. 301 specifying that 
gasoline fueled vehicles be tested at a level of between 90 to 95 
percent of capacity. In the proposal, the agency noted that unlike 
gaseous fuels, gravity and vehicle attitude play important roles in 
determining the amount of leakage experienced by a liquid fuel. The 
fuel fill level is not as critical a test condition for liquid fuels. 
In contrast, while leakage of gaseous fuels is influenced by the level 
of pressure inside a ruptured fuel system, it is not influenced by the 
vehicle's attitude or gravity. Based on these considerations, NHTSA 
decided to propose that the containers be tested at the maximum fill 
level (i.e., 100 percent of service pressure) to simulate a worst case 
accident situation for CNG vehicles.
    Six commenters addressed the appropriate service pressure at which 
the CNG containers would be tested. Minnesota Gas, CNG Pittsburgh, and 
Washington agreed with the agency's proposal to test at 100 percent of 
service pressure. Minnesota Gas agreed with the proposal because it 
would be consistent with Transport Canada. AAMA, Navistar, and Thomas 
stated that some tolerance should be allowed, given practicability 
concerns. Thomas recommended that a tolerance range of about three 
percent should be allowed (i.e., 90 psi on a container with 
a 3000 psi service pressure.) AAMA recommended a range for fill level 
between 95 percent to 100 percent, because it believed that temperature 
in a CNG container may rise significantly as it is filled and that some 
time would be required for pressure and temperature to stabilize.
    NHTSA has decided to specify the fill level to be at 100 percent of 
the service pressure. After reviewing the comments, the agency 
considered allowing a fill level of between 95 percent to 100 percent 
of service pressure. However, allowing a fill level of 95 percent of 
the service pressure (i.e., 2850 psi for a 3000 psi container) would 
result in a less stringent condition before the crash test. Thus, the 
agency would no longer be testing a worst case situation. The agency 
acknowledges that a container will need additional time to stabilize 
when achieving a 100 percent fill condition. However, the agency 
believes that it is necessary to allow for this additional time since 
including a testing tolerance would affect the requirement's 
stringency. The agency further notes that including a 100 percent fill 
condition is consistent with Transport Canada's standard for fuel 
system integrity.
2. Test Gas
    In the NPRM, NHTSA proposed to specify nitrogen (N2) as the 
test gas. In determining the appropriate test gas, NHTSA sought one 
that adequately represents CNG, is safe during crash tests and provides 
a common baseline from which to derive all leakage measurements. The 
agency decided to propose using nitrogen as the test gas because both 
nitrogen and CNG are lighter than air and thus would disperse upward 
into the air through any rupture in the fuel system instead of pooling 
in cavities of the fuel system or falling to the ground. The agency 
believed that a volume of nitrogen that is leaked as a test gas would 
be equal to the same volume of CNG that leaks. In addition, nitrogen is 
readily available and is safer than CNG for crash tests because it is 
neither flammable nor toxic.
    Seven commenters addressed the issue of test gas. Of those 
commenters, six agreed with the agency's proposal to specify nitrogen 
as a test gas. Thomas Built requested that dry air be used as a test 
gas but offered no rationale. NGV Systems stated that the vehicles 
should be tested with the fuel with which it will operate.
    After reviewing the comments and other available information, NHTSA 
has decided to specify that nitrogen be the test gas during crash tests 
of CNG vehicles. Notwithstanding Thomas Built's request to allow dry 
air, the agency has decided not to specify dry air as an alternative 
test gas, even though it has properties similar to nitrogen. The agency 
believes that the test results will be more consistent and enforcement 
will be facilitated by permitting only one test gas. As indicated by 
the majority of commenters addressing this issue, NHTSA believes that 
nitrogen is stable and readily available and therefore should be 
specified in the Standard. This decision is consistent with Standard 
No. 301 which specifies the use of Stoddard Solvent as the single test 
liquid, and Transport Canada's standard for CNG fuel system integrity 
which specifies the use of nitrogen as a test gas.
    The type of test gas is relevant to calculating the allowable 
pressure drop, since the compressibility factor, ``Z,'' is included in 
the formula. In the NPRM, NHTSA estimated that the compressibility of 
nitrogen is 1.00. However, AAMA commented that a compressibility of 
1.05 is more accurate for the conditions the test gas will be under 
when tested in the fuel containers (approximately 20,685 kPa (3,000 
psi) and 21.1 deg.C (70 deg.F)). Upon further review, NHTSA agrees with 
AAMA that the appropriate compressibility factor is 1.05.
3. Electric Shutoff Valves
    In the NPRM, NHTSA proposed that ``if the vehicle has an 
electrically driven fuel pump that normally runs when the vehicle's 
electrical system is activated, it is operated at the time of the 
barrier crash.'' The agency also proposed that ``Any shutoff valve at 
the fuel tank is in the open position.'' In this latter statement, the 
agency was referring to manual shutoff valves, and not those which may 
be electrically operated.
    AAMA commented that requiring the crash test to be conducted with 
shutoff valves held open would be incompatible with the vehicle's 
normal operation during a crash sequence and with the intent of the 
standard. AAMA stated that vehicles equipped with manual shutoff valves 
at each fuel tank should have these valves in the fully open position 
during vehicle testing. However, electric shutoff valves should be 
handled in a manner consistent with other electrical devices such as an 
electric fuel pump.
    After reviewing the comment, NHTSA concurs and believes that if the 
vehicle has electrically operated shutoff valves that are normally open 
when the electrical system is activated, then they must be open at the 
time of the crash test. The agency believes that the vehicle test 
conditions should simulate, to the extent practicable, the conditions 
present in a real world crash. This is the same rationale used in 
having electrically activated fuel pumps in operation, before the crash 
test in Standard No. 301.

E. Requirements Not Adopted

1. Static Rollover
    In the NPRM, NHTSA decided not to propose a static vehicle rollover 
test for dedicated CNG vehicles. The agency explained that a rollover 
requirement is only needed for liquid fuel vehicles (including dual-
fuel and bi-fuel vehicles) because leakage is a function of gravity and 
the location of the rupture relative to the fuel. Without a rollover 
test, a rupture in the fuel system above the level of the liquid fuel 
would not be detected. In contrast, CNG is pressurized and would 
quickly escape upon rupture of the fuel system. Thus, for a CNG fuel 
system, any leakage would be unaffected by vehicle attitude or gravity.
    NHTSA received three comments addressing whether to include a 
static vehicle rollover requirement. Navistar and Washington State 
agreed with the agency's proposal that such a test was not needed. The 
New York City Fire Department (NYFD) believed that a rollover 
requirement was necessary since some CNG containers may be mounted on 
the vehicle's roof.
    NHTSA continues to believe that a static rollover test is not 
needed for the reasons set forth in the NPRM. The agency notes that 
NYFD may have misinterpreted the rollover requirement that was under 
consideration. The agency was considering a static rollover requirement 
like the one in Standard No. 301 in which after crash testing, the 
vehicle is rotated on its axis to determine leakage. The agency was not 
considering a dynamic rollover test in the context of the CNG 
rulemaking.
2. Refueling Connections
    In the NPRM, NHTSA decided not to propose requirements regarding 
the standardization of refueling connections, notwithstanding comments 
to the ANPRM advocating such an approach. These commenters believed 
that specifying certain connector sizes would prevent over-
pressurization during refueling. NHTSA believed that it was not 
necessary to regulate this area because the potential safety risks 
associated with over-pressurization of the fuel storage containers are 
addressed through the proposed container venting requirements (bonfire 
test) discussed above. NHTSA further believed that voluntary actions by 
industry will address most, if not all, of the problems raised by 
commenters. The agency also believed that the issues raised by 
commenters to the ANPRM, with the exception of overfilling the fuel 
storage containers, did not present significant safety concerns.
    NHTSA received 12 comments addressing the need to standardize the 
refueling connections. EDO, Flxible, and Tecogen agreed with the 
agency's rationale for not including requirements for refueling 
connections. Nine commenters believed that NHTSA should adopt a 
requirement for refueling connections. AAMA, NGVC, and several natural 
gas companies believed that NHTSA should adopt NGV-1. NGV-1 is a 
voluntary standard being developed by the American National Standards 
Institute (ANSI)/Canadian Gas Association Standard for Compressed 
Natural Gas Vehicle Fueling Connection Devices. Ontario recommended 
that the agency should specify the universal use of a single maximum 
filling pressure of 20,685 kPa (3000 psi). It believed that such 
standardization would reduce the safety risk and promote international 
harmonization.
    After reviewing the comments, NHTSA continues to believe that 
Federal regulation is not needed with respect to the refueling 
connection devices. As explained in the NPRM, the agency continues to 
believe that problems associated with filling fuel containers do not 
present significant safety concerns. Moreover, the agency continues to 
believe that the proposed bonfire test, which the agency is considering 
for CNG containers, addresses potential safety risks associated with 
over-pressurization. In addition, the agency believes that refueling 
connections present an issue that is peripheral to the agency's focus 
of fuel system integrity as determined by crashes. Notwithstanding this 
decision, the agency will continue to monitor the safety of refueling 
connections to determine if future agency action is needed.
3. Venting
    In the ANPRM, the agency discussed requiring that all pressure 
relief mechanisms be vented to the outside of the vehicle, away from 
the passenger, luggage, or other compartments that could expose vehicle 
occupants to the gaseous fuel. However, after considering comments to 
the ANPRM, NHTSA decided not to propose a venting requirement. The 
agency believed that such a requirement would be unnecessarily design 
restrictive in view of the wide variations among vehicle designs and 
models. In addition, the agency noted that CNG used in motor fuel 
applications would have an odor that would warn vehicle occupants of 
the presence of escaping gas.
    NHTSA received comments from the California Highway Patrol (CHP) 
and Washington State about venting requirements. CHP stated that 
venting is necessary to ensure safety, but did not elaborate. 
Washington State stated that gaseous fuels could accumulate when a 
school bus is parked or when air circulation is inadequate. While it 
believed that such accumulation could be explosive, the commenter 
provided no data to indicate the extent of the alleged safety problem.
    After reviewing the comments, NHTSA continues to believe that it is 
not necessary or appropriate to specify venting requirements in the CNG 
vehicle standard. The agency notes that there are no data to verify 
that gases accumulate under vehicles or otherwise pose a safety problem 
that could be alleviated if a venting requirement were adopted. In 
addition, the agency believes that exposure to an ignition source would 
be unlikely for a parked vehicle.
4. Leak Detection
    In the NPRM, NHTSA requested comments about whether to require a 
sensing device to detect unacceptable levels of gaseous leakage from 
the fuel system and to provide a warning to vehicle occupants. The 
notice posed questions about the need for and types of warning devices, 
the amount of fuel in the air that would activate a warning device, and 
the availability, cost, and reliability of such a device.
    NHTSA received 11 comments about warning or leakage detection 
devices. EDO, CNG Pittsburgh, Oklahoma Gas, Minnesota Gas, Navistar, 
Thomas, Brooklyn Union Gas, Flxible, and NGVC stated that no 
requirement was necessary. Several commenters stated that a detection 
device was not needed because CNG is odorized and thus readily detected 
by the human nose. Therefore, according to these commenters, a 
vehicle's occupants or bystanders would be able to detect any CNG 
leakage. Two commenters, Washington State and the Metropolitan Suburban 
Bus Authority (MSBA), favored a requirement for the detection and 
warning of fuel leakage. However, neither commenter elaborated about 
the need for such a requirement.
    After reviewing the comments, NHTSA has determined that a 
requirement applicable to detecting or warning about fuel leakage is 
not necessary. The agency agrees with those commenters who noted that 
CNG is odorized and thus is readily detectable.
5. Retention of Fuel Storage Containers
    In the NPRM, NHTSA decided not to propose a specific requirement 
for container retention. This decision was based on the agency's belief 
that manufacturers would need to design container retention 
characteristics in order for their CNG vehicles to meet the allowable 
leakage limits specified for the crash tests.
    Nine commenters addressed whether the agency should specify a 
container retention requirement. Of the commenters, AAMA, Navistar, and 
NGV Systems agreed with the agency's decision not to include a 
container retention requirement. Manchester commented that such a 
requirement would pose problems. Five commenters, the General Services 
Commission (GSC), the National Fire Protection Association (NFPA), 
Flxible, NGVC, and CNG Pittsburgh, disagreed with the agency's decision 
not to include a container retention requirement. GSC stated that CNG 
fuel containers should be surrounded by a strong metal cage to prevent 
the container from breaking loose. Alternatively, GSC recommended that 
the agency require an internal excess-flow shutoff valve that would 
prevent loss of fuel if the external valving ruptured. Several 
commenters stated that container detachment was important and could be 
prevented by adopting NFPA 52.\5\ NFPA further stated that fuel 
container breakaway could occur without fuel leakage if an excess flow 
valve or an automatic shutoff valve were actuated during a crash. The 
container could then cause injury to the occupants or damage the 
vehicle.
---------------------------------------------------------------------------

    \5\NFPA 52 is a voluntary standard issued by the National Fire 
Protection Association that applies to the design and installation 
of CNG engine fuel systems including aftermarket and OEMs and their 
associated fueling systems.
---------------------------------------------------------------------------

    After reviewing the comments, NHTSA has decided not to adopt a 
requirement regulating the retention of fuel storage containers. The 
agency believes that fuel container retention does not pose a safety 
problem, as long as a manufacturer produces its vehicles to comply with 
the standard's leakage requirements. If a CNG fuel container did break 
away from the vehicle, NHTSA believes that it is highly likely there 
would be a fuel leak which would not be able to comply with the barrier 
crash test's leakage requirement.

F. Other Considerations

1. Vehicles Manufactured In More Than One Stage
    In the NPRM, NHTSA tentatively concluded that it would be 
practicable for final stage manufacturers of multi-stage vehicles to 
comply with this proposed rule. The agency reasoned that because the 
vehicle requirements in the proposed rule only involve those vehicles 
currently covered under Standard No. 301, final stage manufacturers are 
already subject to similar dynamic crash test requirements. NHTSA 
requested comment on the agency's tentative conclusion that final stage 
manufacturers could comply with the proposed requirements and provide 
the requisite level of safety. NHTSA requested comments about the 
effect of this rule on final stage manufacturers.
    Twelve commenters addressed the issue of how this rule would affect 
vehicles manufactured in more than one stage. Blue Bird, Thomas, 
Navistar, Washington State, CNG Pittsburgh, CHP, and Chrysler stated it 
would be appropriate for the proposed requirements to apply to multi-
stage vehicles. In contrast, four commenters--the National Truck 
Equipment Association (NTEA), NGV Systems, Ontario, and Niagara Mohawk 
Power Company--believed that the new standard should not apply to 
vehicles manufactured in more than one stage. These commenters were 
most concerned about how a final stage manufacturer could certify 
compliance to the Standard without performing crash tests.
    NHTSA is aware of the concerns of final stage and intermediate 
stage manufacturers about crash testing their vehicles. The agency 
notes that its regulations already provide that certification of an 
incomplete vehicle can pass through to the final stage manufacturer, 
provided that the final stage manufacturers take the necessary 
precautions to ensure they do not invalidate the certification. More 
specifically, the final stage manufacturers must ensure that they 
complete the vehicle without exceeding the GAWRs, altering any fuel 
system component, moving the center of gravity of the completed vehicle 
with the body installed outside the envelope of specifications provided 
by the chassis manufacturer, or otherwise violating that envelope. If 
the final stage manufacturer takes care to comply with all of the 
chassis manufacturer's specifications, the final stage manufacturer 
will not have to recertify the vehicle.
    If the final stage manufacturer decides not to comply with the 
specifications to the extent that the vehicle, in its final form, 
differed significantly from what was anticipated by the chassis 
manufacturer in specifying the envelope, and the basis for the 
incomplete vehicle manufacturer's certification was thus no longer 
valid, then the final stage manufacturer will have to accept the 
responsibility for certification.
    Pass-through certification is also not available for vehicles built 
on chassis lacking sufficient components to be certified as an 
incomplete vehicle. Some of the manufacturers that build these vehicles 
may be small businesses that may be unable to conduct their own crash 
tests.
    NHTSA notes that while manufacturers must certify that their 
vehicles meet all applicable safety standards, this does not 
necessarily mean that a manufacturer must conduct the specific tests 
set forth in an applicable standard. Certifications may be based on, 
among other things, engineering analyses, actual testing, and computer 
simulations.
    Moreover, a manufacturer need not conduct these operations itself. 
Manufacturers can utilize the services of independent engineers and 
testing laboratories. They can also join together through trade 
associations to sponsor testing or analysis. Finally, they can rely on 
testing and analysis performed by other parties, including the CNG 
container manufacturers. The container manufacturers typically perform 
extensive analyses and tests of their products and, in order to sell 
those products, will have a strong incentive to provide their 
customers, the vehicle manufacturers, with information that can be used 
to certify the vehicle to the applicable standard. Based on the above 
discussion, NHTSA does not believe that the requirements pose any 
significant certification burdens for the final stage manufacturers or 
other small manufacturers.
2. Benefits
    In the NPRM, NHTSA estimated the benefits from a CNG vehicle 
standard by comparing them to the benefits from Standard No. 301. The 
proposal referred to a NHTSA technical report on Standard No. 301's 
effect on motor vehicle fires in traffic crashes. That report estimated 
that Standard No. 301 has reduced fires in all passenger car crashes by 
14 percent. (``Motor Vehicle Fires in Traffic Crashes and the Effects 
of Fuel System Integrity Standard,'' DOT HS 807 675, November 1990.) 
The NPRM also discussed information submitted by NFPA about 1984-1988 
annual average automobile fire rates to the docket (Docket No. 73-20-
N15-027). These data contain information on the number of fires in 
passenger cars by type of material first ignited (gasoline, LP-gas, or 
natural gas). However, the agency stated that there were limitations 
with using these data, and thus they could not be used to enable the 
agency to determine the fire rate of CNG and LPG vehicles in comparison 
to gasoline fueled vehicles.
    Notwithstanding these limitations, NHTSA estimated in the NPRM the 
number of fires in CNG vehicles, assuming they have the same fire rate 
as gasoline powered vehicles. Based on Standard No. 301 fire rates and 
on one Department of Energy scenario of projected on-road alternative 
fuel vehicles, by fuel type, the agency estimated that there could be 
1,690 fires in CNG vehicles in the year 2010.
    NHTSA received only two specific comments about the benefits of the 
proposed rulemaking to establish requirements for CNG vehicles. Both 
Atlantic Research Corporation and NGVC commented that the agency's 
assumption about estimating future CNG vehicle fires is flawed because 
it assumes that CNG vehicles will have the same fire rate as gasoline 
powered vehicles. Both commenters stated that the fuel systems and the 
fuel flammability characteristics are completely different and thus 
would result in much lower fire rates for CNG vehicles.
    NHTSA acknowledges the favorable flammability characteristics of 
CNG relative to gasoline. CNG is lighter than air, and therefore should 
quickly dissipate upward. At the same time, however, CNG is under high 
pressure onboard the vehicle in contrast to conventional fuels. This 
high pressure could make a crash situation more volatile. However, 
without real-world crash data on CNG vehicles, no conclusions can be 
drawn. In assuming that CNG vehicles had the same fire rate as gasoline 
vehicles, the agency wished to provide some estimate of benefits, given 
the lack of real world accidents because of the relatively few CNG 
vehicles on the road.
    NHTSA analyzed data submitted by the American Gas Association (AGA) 
on 8,000 natural gas fleet vehicles. Based on vehicle miles travelled 
(VMT) during a three-year period, the fire rate for CNG vehicles is 
2.52 per 100 million VMT, compared with a gasoline vehicle fire rate of 
1.87, or 35 percent higher. However, the agency notes that the small 
sample does not allow a reliable analysis of the crash fire potential 
in CNG vehicles. With seven fires, the standard errors or the fire 
rates for these CNG vehicles are too big to make meaningful comparisons 
between CNG-equipped vehicles and their gasoline counterparts. While 
the agency does not have the data to determine comparable fire rates 
between gasoline and CNG vehicles, the benefits of this final rule are 
obtained by ensuring at least equivalent safety with gasoline vehicles.
3. Costs
    In the NPRM, NHTSA estimated that testing associated with the 
proposed vehicle requirements would cost approximately $58,530-$63,080 
per CNG body style. The agency estimated that the cost to perform a 
frontal, lateral or rear impact test would be $5,000 (with a total cost 
of $15,000 for three tests). The cost of the vehicle, which is 
destroyed during the test, is approximately $13,160 ($39,480 for the 
three vehicles to be used in the three tests). Thus, the total vehicle 
testing costs would be approximately $54,480. The agency requested 
comments about the costs of complying with the proposed requirements.
    NHTSA received two comments that addressed the cost of implementing 
fuel system integrity requirements for CNG vehicles. Navistar and Blue 
Bird stated that the agency underestimated the costs associated with 
testing school buses to the new CNG standard. Each stated that the cost 
associated with purchasing and testing school buses was substantially 
higher than the NPRM's estimate. Navistar estimated that for a six fuel 
tank design school bus, the costs would be as follows: chassis--
$35,000, six fuel containers at $1,200 each--$7,200; six fuel container 
cages at $150 each--$900; associated valves, tubes, fittings, etc. 
$1,000; crash testing at $12,000 per test ($36,000 for three tests). 
Navistar stated that a minimum of two school buses and six crash tests 
would be needed for a total of at least $160,000. Blue Bird estimated 
that vehicle costs are in the range of $75,000 to $85,000 and each test 
costs approximately $15,000. It further stated that test costs could be 
several hundred thousand dollars per vehicle configuration given that 
multiple impact tests are often necessary to document conformance to a 
standard that requires impacts at any point and angle. If Blue Bird 
performed six tests on two school buses, the total cost would range 
from $240,000 to $260,000.
    After reviewing the comments, NHTSA believes that the cost 
estimates provided by Navistar and Blue Bird are reasonable. Thus, the 
total cost of testing school buses would be $160,000 per chassis and 
$260,000 for a school bus. NHTSA continues to believe that its estimate 
of $54,480 for light vehicles is still appropriate.
4. Leadtime
    In the NPRM, NHTSA proposed to make the vehicle requirements 
effective on September 1, 1994. The agency believed that this would 
provide a reasonable time period for manufacturers to make any vehicle 
modifications required by the rulemaking. Nevertheless, the agency 
stated that the proposed dynamic vehicle crash test requirements could 
make it necessary for vehicle manufacturers to make significant design 
modifications in order to comply with the proposal, especially since 
most CNG vehicles are currently manufactured in accordance with NFPA 
Standard 52. That standard specifies design-oriented requirements and 
does not specify a barrier crash test. The agency requested comment on 
the feasibility of this effective date.
    NHTSA received nine comments about the proposed effective date. 
Blue Bird, Flxible, and Navistar agreed with the proposed effective 
date of September 1, 1994. Flxible's agreement with the agency's 
proposed effective date was contingent upon the agency adopting its 
recommendations in the final rule. Navistar believed that the effective 
date should be earlier if possible.
    AAMA, the United States Department of Energy, NGV Systems, Volvo 
GM, and CNG Pittsburgh did not agree with the effective date proposed 
by the agency. NGV Systems, Volvo GM, and CNG Pittsburgh stated that 
the proposed effective date would be difficult to meet but did not 
recommend a specific date. AAMA and the U.S. Department of Energy 
recommended an effective date of September 1, 1995. However, AAMA's 
recommendation was contingent upon its recommendations being 
incorporated in the final rule. AAMA further stated that an earlier 
effective date would not be reasonable or practicable.
    In contrast, the NGVC, the CGA, and CNG container manufacturers 
have informed the agency that they want a CNG fuel integrity standard 
to be effective as quickly as possible. In addition, they favor having 
an opportunity to ``voluntarily certify compliance'' to the standard 
once the final rule is published. The CNG industry groups believe that 
it is necessary for a Federal standard to be in place as soon as 
possible given the expected increased demand for CNG vehicles in light 
of Federal and State fleet programs for clean fuel vehicles. They also 
favor quick adoption of a Federal standard to preempt state regulations 
that otherwise may be promulgated and to ensure that substandard CNG 
vehicles are not marketed.
    After reviewing the comments, NHTSA has decided to set an effective 
date of September 1, 1995. NHTSA is fully aware that the NGVC and CGA, 
which represent the natural gas industry, favor what amounts to an 
immediate effective date. Nevertheless, the agency believes that a 
leadtime of at least one year is necessary given that vehicle 
manufacturers will be required to certify compliance to an entirely new 
set of dynamic crash requirements. In the meantime, prior to the 
standard's effective date, the industry is free to market vehicles as 
meeting the CNG vehicle standard that takes effect in 1995. 
Manufacturers have taken this approach with respect to the agency's 
side impact requirements and air bag requirements. Therefore, to the 
extent feasible, the agency encourages manufacturers to manufacture 
their CNG vehicles to meet these new requirements before the date the 
standard takes effect.

V. Rulemaking Analyses

A. Executive Order 12866 and DOT Regulatory Policies and Procedures

    NHTSA has considered the impact of this rulemaking action under 
Equal Opportunity 12866 and the Department of Transportation's 
regulatory policies and procedures. This rulemaking document was 
reviewed under Equal Opportunity 12866, ``Regulatory Planning and 
Review.'' This action has been determined to be ``significant'' under 
the Department of Transportation's regulatory policies and procedures 
because of the significant public and Congressional interest in the 
rulemaking. NHTSA has estimated the costs of the amendments in a Final 
Regulatory Evaluation (FRE) which is included in the docket for this 
rulemaking. As discussed in that document, NHTSA estimates that testing 
associated with the vehicle requirements will cost approximately 
$54,480 for light vehicles. More generally, the agency believes that 
the cost of the final rule is mostly testing costs and the benefits are 
derived by ensuring an equivalent level of safety with gasoline 
vehicles.

B. Regulatory Flexibility Act

    NHTSA has also considered the effects of this rulemaking action 
under the Regulatory Flexibility Act. Based upon the agency's 
evaluation, I certify that this rule will not have a significant 
economic impact on a substantial number of small entities. Information 
available to the agency indicates that currently there are very few 
businesses manufacturing passenger cars or light trucks for CNG use. 
The agency further believes that as the market expands for CNG 
vehicles, original vehicle manufacturers will begin to produce CNG 
vehicles because they will be able to do so at less expense than final 
stage manufacturers and alterers. Few, if any, original vehicle 
manufacturers which manufacture CNG vehicles are small businesses.

C. Executive Order 12612 (Federalism)

    NHTSA has analyzed this rulemaking action in accordance with the 
principles and criteria contained in Executive Order 12612. NHTSA has 
determined that the rule will not have sufficient Federalism 
implications to warrant the preparation of a Federalism Assessment. 
Nevertheless, the agency wishes to elaborate about its preemptive 
authority with respect to Federal motor vehicle safety standards given 
comments on the NPRM about potentially inconsistent State law.
    The AAMA and the NGVC/AGA stated that a Federal standard was 
necessary to preempt possible State and local regulations addressing 
CNG vehicles. AAMA stated that--

    Because the U.S. Energy Policy Act will require that both 
Federal and state governments become mandated ``fleet customers'' of 
alternative fuel vehicles, AAMA is apprehensive about the potential 
promulgation of a plethora of state alternate fueled vehicle 
regulations, each slightly different from one another, with an 
imposed standard or an alleged higher standard than the finalized 
applicable federal safety standard. In such a circumstance, there 
would appear to be no federal preemption protection for the vehicle 
manufacturer. It is, therefore, conceivable that to market these 
mandated alternate fuel vehicles, numerous vehicle versions would 
have to be designed, manufactured, and certified.

    Similarly, NGV/AGA expressed concern that State authorities may 
initiate different or more stringent standards for CNG systems. It was 
particularly concerned that NHTSA cannot preempt separate regulation of 
vehicles procured by State governmental agencies.
    As both commenters are aware, section 103(d) of the National 
Traffic and Motor Safety Act sets forth NHTSA's preemptive authority as 
follows: Whenever a Federal motor vehicle safety standard established 
under this title is in effect, no State or political subdivision of a 
State shall have any authority either to establish, or to continue in 
effect, with respect to any motor vehicle or item of motor vehicle 
equipment any safety standard applicable to the same aspect of 
performance of such vehicle or item of equipment which is not identical 
to the Federal standard. Nothing in this section shall be construed as 
preventing any State from enforcing any safety standard which is 
identical to a Federal safety standard. Nothing in this section shall 
be construed to prevent the Federal Government or the government of any 
State or political subdivision thereof from establishing a safety 
requirement applicable to motor vehicles or motor vehicle equipment 
procured for its own use if such requirement imposes a higher standard 
of performance than that required to comply with the otherwise 
applicable Federal standard.
    Pursuant to this statutory provision, once Standard No. 303 takes 
effect, no State or local government can have a standard in effect 
addressing the fuel integrity of CNG vehicles unless that standard is 
identical to Standard No. 303. Nevertheless, the statute permits a 
State to issue higher performance standards for CNG vehicles procured 
for the State's own use, notwithstanding AAMA's desire for the Federal 
government to preempt States from doing so. In other words, NHTSA has 
no authority to prevent States from issuing more stringent standards 
for vehicles procured for their own use.

D. National Environmental Policy Act

    In accordance with the National Environmental Policy Act of 1969, 
NHTSA has considered the environmental impacts of this rule. The agency 
has determined that this rule will have no adverse impact on the 
quality of the human environment. On the contrary, because NHTSA 
anticipates that ensuring the safety of CNG vehicles will encourage 
their use, NHTSA believes that the rule will have positive 
environmental impacts since CNG vehicles are expected to have near-zero 
evaporative emissions and the potential to produce very low exhaust 
emissions as well.

E. Civil Justice Reform

    The rule will not have any retroactive effect. Under section 103(d) 
of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. 
1392(d)), whenever a Federal motor vehicle safety standard is in 
effect, a state may not adopt or maintain a safety standard applicable 
to the same aspect of performance which is not identical to the Federal 
standard. Section 105 of the Act (15 U.S.C. 1394) sets forth a 
procedure for judicial review of final rules establishing, amending or 
revoking Federal motor vehicle safety standards. That section does not 
require submission of a petition for reconsideration or other 
administrative proceedings before parties may file suit in court.

List of Subjects in 49 CFR Part 571

    Imports, Motor vehicle safety, Motor vehicles.

PART 571--[AMENDED]

    In consideration of the foregoing, 49 CFR part 571 is amended as 
follows:
    1. The authority citation for part 571 continues to read as 
follows:

    Authority: 15 U.S.C. 1392, 1401, 1403, 1407; delegation of 
authority at 49 CFR 1.50.

    2. Section 571.303, a new safety standard, Standard No. 303, Fuel 
System Integrity of Compressed Natural Gas Vehicles, is added to part 
571, to read as follows:


Sec. 571.303  Standard No. 303; Fuel system integrity of compressed 
natural gas vehicles.

    S1. Scope. This standard specifies requirements for the integrity 
of motor vehicle fuel systems using compressed natural gas (CNG), 
including the CNG fuel systems of bi-fuel, dedicated, and dual fuel CNG 
vehicles.
    S2. Purpose. The purpose of this standard is to reduce deaths and 
injuries occurring from fires that result from fuel leakage during and 
after motor vehicle crashes.
    S3. Application. This standard applies to passenger cars, 
multipurpose passenger vehicles, trucks and buses that have a gross 
vehicle weight rating (GVWR) of 10,000 pounds or less and use CNG as a 
motor fuel. This standard also applies to school buses regardless of 
weight that use CNG as a motor fuel.
    S4. Definitions.
    Bi-fuel CNG vehicle means a vehicle equipped with two independent 
fuel systems, one of which is designed to supply CNG and the second to 
supply a fuel other than CNG.
    CNG full container means a container designed to store CNG as motor 
fuel on-board a motor vehicle.
    CNG fuel system means all components used to store or supply CNG to 
a vehicle's engine.
    Dedicated CNG vehicle means a vehicle equipped with one fuel system 
and designed to operate on CNG.
    Dual-fuel CNG vehicle means a vehicle which is fueled by two fuels 
simultaneously, one of which is CNG and the second is a fuel other than 
CNG.
    High pressure portion of a fuel system means all the components 
from and including each CNG fuel container up to, but not including, 
the first pressure regulator.
    Service pressure means the internal pressure of a CNG fuel 
container when filled to design capacity with CNG at 20 deg. Celsius 
(68 deg. Fahrenheit).
    S5. General requirements.
    S5.1  Vehicle requirements.
    S5.1.1  Vehicles with GVWR of 10,000 pounds or less. Each passenger 
car, multipurpose passenger vehicle, truck, and bus with a GVWR of 
10,000 pounds or less that uses CNG as a motor fuel and that is 
manufactured on or after September 1, 1995 shall meet the requirements 
of S6, except S6.4.
    S5.1.2  Schoolbuses with a GVWR greater than 10,000 pounds. Each 
schoolbus with a GVWR greater than 10,000 pounds that uses CNG as a 
motor fuel and that is manufactured on or after September 1, 1995 shall 
meet the requirements of S6.4.
    S5.2  Fuel system pressure drop: barrier crash.
    (a) For all vehicles, the pressure drop in the high pressure 
portion of the fuel system, expressed in kiloPascals (kPa), in any 
fixed or moving barrier crash from vehicle impact through the 60 minute 
period following cessation of motion shall not exceed:
    (1) 1062 kPa (154 psi), or
    (2) 895 (T/VFS); whichever is higher

where T is the average temperature of the test gas in degrees Kelvin, 
stabilized to ambient temperature before testing, where average 
temperature (T) is calculated by measuring ambient temperature at the 
start of the test time and then every 15 minutes until the test time of 
60 minutes is completed; the sum of the ambient temperatures is then 
divided by five to yield the average temperature (T); and where 
VFS is the internal volume in liters of the fuel container and the 
fuel lines up to the first pressure regulator.
    (b) For bi-fuel or dual fuel CNG vehicles, the test requirement in 
S5.2(a) shall apply to the CNG fuel system, and the test requirement of 
Standard No. 301 shall apply to the other fuel system, if that standard 
is applicable.
    S6.  Test requirements: fuel system integrity. Each vehicle with a 
GVWR of 10,000 pounds or less shall meet the requirements of any 
applicable barrier crash test. A particular vehicle need not meet 
further requirements after having been subjected to a single barrier 
crash test.
    S6.1  Frontal barrier crash. When the vehicle traveling 
longitudinally forward at any speed up to and including 30 mph impacts 
a fixed collision barrier that is perpendicular to the line of travel 
of the vehicle, or at any angle up to 30 degrees in either direction 
from the perpendicular to the line of travel of the vehicle, with 50th 
percentile test dummies as specified in part 572 of this chapter at 
each front outboard designated seating position and at any other 
position whose protection system is required to be tested by a dummy 
under the provisions of Standard No. 208, under the applicable 
conditions of S7, the fuel pressure drop shall not exceed the limits of 
S5.2.
    S6.2  Rear moving barrier crash. When the vehicle is impacted from 
the rear by a barrier moving at any speed up to and including 30 mph, 
with test dummies as specified in part 572 of this chapter at each 
front outboard designated seating position, under the applicable 
conditions of S7, the fuel pressure drop shall not exceed the limits of 
S5.2.
    S6.3  Lateral moving barrier crash. When the vehicle is impacted 
laterally on either side by a barrier moving at any speed up to and 
including 20 mph with 50th percentile test dummies as specified in part 
572 of this chapter at positions required for testing to Standard No. 
208, under the applicable conditions of S7, the fuel pressure drop 
shall not exceed the limits of S5.2.
    S6.4  Moving contoured barrier crash. When the moving contoured 
barrier assembly traveling longitudinally forward at any speed up to 
and including 30 mph impacts the test vehicle (schoolbus with a GVWR 
exceeding 10,000 pounds) at any point and angle, under the applicable 
conditions of S7, the fuel pressure drop shall not exceed the limits of 
S5.2.
    S7.  Test conditions. The requirements of S5 and S6 shall be met 
under the following conditions. Where a range of conditions is 
specified, the vehicle must be capable of meeting the requirements at 
all points within the range.
    S7.1  General test conditions. The following conditions apply to 
all tests.
    S7.1.1  Each fuel storage container is filled to 100 percent of 
service pressure with nitrogen, N2. The gas pressure shall 
stabilize to ambient temperature before testing may be conducted.
    S7.1.2  After each fuel storage container is filled as specified in 
S7.1.1, the fuel system other than each fuel storage container is 
filled with nitrogen, N2, to normal operating pressures. Any 
shutoff valve at the fuel container is in the open position.
    S7.1.3  In meeting the requirements of S6.1 through S6.4, if the 
vehicle has an electrically driven fuel pump that normally runs when 
the vehicle's electrical system is activated, it is operating at the 
time of the barrier crash. If the vehicle has any high pressure 
electric shutoff valve that is normally open when the electrical system 
is activated, it is open at the time of the barrier crash. Furthermore, 
if any electric shutoff valve prevents sensing of system pressure by 
the pressure transducer when closed, it must be open for both the 
initial pressure measurement and the pressure measurement 60 minutes 
after the vehicle ceases motion from impact. Any valve shall be open 
for a period of one minute to equalize the system pressure.
    S7.1.4  The parking brake is disengaged and the transmission is in 
neutral, except that in meeting the requirements of S6.4, the parking 
brake is set.
    S7.1.5  Tires are inflated to manufacturer's specifications.
    S7.1.6  The vehicle, including test devices and instrumentation, is 
loaded as follows:
    (a) A passenger car, with its fuel system filled as specified in 
S7.1.1 and S7.1.2, is loaded to its unloaded vehicle weight plus its 
rated cargo and luggage capacity weight, secured in the luggage area, 
plus the necessary test dummies as specified in S6, restrained only by 
means that are installed in the vehicle for protection at its seating 
position.
    (b) A multipurpose passenger vehicle, truck, or bus with a GVWR of 
10,000 pounds or less, whose fuel system is filled as specified in 
S7.1.1 and S7.1.2, is loaded to its unloaded vehicle weight, plus the 
necessary test dummies as specified in S6, plus 136.1 kilograms (kg.) 
(300 pounds (lb.)), or its rated cargo and luggage capacity weight, 
whichever is less, secured to the vehicle and distributed so that the 
weight on each axle as measured at the tire-ground interface is in 
proportion to its GAWR. Each dummy shall be restrained only by means 
that are installed in the vehicle for protection at its seating 
position.
    (c) A schoolbus with a GVWR greater than 10,000 pounds, whose fuel 
system is filled as specified in S7.1.1 and S7.1.2, is loaded to its 
unloaded vehicle weight, plus 54.4 kg. (120 lb.) of unsecured weight at 
each designated seating position.
    S7.1.7  The ambient temperature is not to vary more than 5.6  deg.C 
(10  deg.F) during the course of the test.
    S7.2  Lateral moving barrier crash test conditions. The lateral 
moving barrier crash test conditions are those specified in S8.2 of 
Standard No. 208, 49 CFR 571.208.
    S7.3  Rear moving barrier test conditions. The rear moving barrier 
test conditions are those specified in S8.2 of Standard No. 208, 49 CFR 
571.208, except for the positioning of the barrier and the vehicle. The 
barrier and test vehicle are positioned so that at impact--
    (a) The vehicle is at rest in its normal attitude;
    (b) The barrier is traveling at any speed up to and including 30 
mph with its face perpendicular to the longitudinal centerline of the 
vehicle; and
    (c) A vertical plane through the geometric center of the barrier 
impact surface and perpendicular to that surface coincides with the 
longitudinal centerline of the vehicle.
    S7.4  Moving contoured barrier test conditions. The moving 
contoured barrier crash test conditions are those specified in S7.5 of 
Standard No. 301, 49 CFR 571.301.

    Issued on April 14, 1994.
Christopher A. Hart,
Deputy Administrator.
[FR Doc. 94-9824 Filed 4-22-94; 8:45 am]
BILLING CODE 4910-59-P

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