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

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 93-02; Notice 07]

RIN 2127-AF42

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; response to petitions for reconsideration.

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SUMMARY: On April 25, 1994, NHTSA published a new Federal motor vehicle

safety standard, Standard No. 303, Fuel System Integrity of Compressed

Natural Gas Vehicles. The standard limits the amount of allowable CNG

leakage after a crash test by limiting the post-crash pressure drop of

the fuel system. Ford Motor Company, Chrysler Corporation, and the

American Automobile Manufacturers Association, submitted petitions for

reconsideration of the final rule. The issues raised in the petitions

include the allowable pressure drop limit, submitted by Ford and

Chrysler, and other pre-crash test conditions and procedures, submitted

by AAMA. NHTSA is denying the petitions of Ford and Chrysler concerning

pressure drop limit, and denying in part and granting in part the

requests by AAMA.

DATES: Effective Date: The amendments made in this rule are effective

September 1, 1995.

Petitions for Reconsideration: Any petition for reconsideration of

this rule must be received by NHTSA no later than February 9, 1995.

ADDRESSES: Petitions for reconsideration should refer to the docket and

notice number of this notice and be submitted to: Administrator,

National Highway Traffic Safety Administration, 400 Seventh Street, SW,

Washington, DC 20590.

[[Page 2540]] 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: On April 25, 1994, NHTSA published a new

Federal motor vehicle safety standard (FMVSS) for the fuel system

integrity of compressed natural gas (CNG) vehicles (59 FR 19648). The

new standard, FMVSS No. 303, Fuel System Integrity of Compressed

Natural Gas Vehicles, limits the amount of allowable CNG leakage after

a crash test. This is done by placing a limit on the post-crash

pressure drop of the fuel system. Vehicles with a gross vehicle weight

rating (GVWR) of 10,000 pounds or less are subject to front, rear, and

side impact crash tests. Schoolbuses with a GVWR greater than 10,000

pounds are subject to moving contoured barrier crash at any point and

angle on the vehicle. The purpose of the new standard, which becomes

effective September 1, 1995, is to reduce deaths and injuries caused by

fires resulting from fuel leakage during and after crashes involving

CNG vehicles.

Ford Motor Company (Ford), Chrysler Corporation (Chrysler), and the

American Automobile Manufacturers Association (AAMA) submitted

petitions for reconsideration of the final rule. The issues raised in

the petitions include the post-crash pressure drop limit of the fuel

system, and procedures and test conditions prior to crash testing. A

discussion of each issue and the agency's response follows.

Pressure Drop Limit

The final rule, as specified in S5.2(a), sets the allowable

pressure drop in the CNG fuel system one hour after any crash test as

follows:

(1) 1062 kPa (154 psi), or

(2) 895 (T/VFS), whichever is higher.

T is the average temperature of the test gas in degrees Kelvin,

stabilized to ambient temperature before testing. Average temperature T

is determined by measuring ambient temperature at the start of the

test, and then every 15 minutes until the test time of 60 minutes is

completed. The sum of the five ambient temperatures is then divided by

five to yield average temperature T. S7.1.7 of the final rule specifies

that ambient temperature is not to vary more than 5.6 deg.C (10

deg.F) during the course of the test. VFS is the internal volume

of the high pressure portion of the vehicle fuel system.

The other allowable pressure drop, 1062 kPa (154 psi), represents

the smallest pressure drop measurable using existing pressure drop

measurement technology is test gas temperature varies no more than 5.6

deg.C (10 deg.F). The agency established this level based on comments

from AAMA and others in response to the agency's January 21, 1993

notice of proposed rulemaking (NPRM) (58 FR 5323). In its comments on

that notice, AAMA stated that using a state-of-the-art capacitance type

pressure transducer could still result in pressure drop measurement

error of 106.1 kPa (15.4 psi) if test gas

temperature varied no more than 5.6 deg.C (10

deg.F). This is due to the cumulative errors attributable to pressure

transducer accuracy, thermal zero shift, thermal coefficient

sensitivity, and analogue-digital conversion. These factors, coupled

with the accepted engineering practice that measurement error should

not exceed ten percent of the value being measured, led to the

conclusion that pressure drops less than 1062 kPa (154 psi) should not

be measured.

The above pressure drop established in the final rule represents

the maximum allowable CNG leakage, 895 (T/VFS), within the limits

of current pressure drop measurement technology, 1062 kPa (154 psi).

Both Ford and Chrysler petitioned the agency for reconsideration of

the above pressure drop limits in S5.2(a). Ford stated that it believes

the agency erred by disregarding certain information provided by AAMA

in its response to the January 1993 NPRM (58 FR 5323). Specifically,

AAMA stated that ``* * * a 10 deg.F change in the temperature of the

test gas would result in a 60 psi change in the pressure of the test

gas.'' Noting that the final rule allows the ambient temperature to

vary as much as 5.6 deg.C (10 deg.F) during the test, Ford stated

that a 10 deg.F drop in temperature could result in a 60 psi pressure

drop even with zero leakage. Thus, according to Ford, the pressure drop

limits in the final rule are, in effect, reduced by 60 psi when the

ambient temperature drops 10 deg.F and increased by 60 psi when the

ambient temperature increases 10 deg.F during the test. Ford asserted

that the pressure drop limits are, therefore, not reasonable,

practicable, or stated in objective terms as required by statute,

because they present arbitrary limits that vary depending on whether

ambient temperature decreases or increases. Ford further stated that an

appropriate corrective action would be to amend S5.2(a) so that it

states, ``For all vehicles, the pressure drop in the high pressure

portion of the fuel system, excluding pressure changes due to changes

in the temperature of the test gas, expressed in * * *.'' Ford's

recommended language is underlined. Thus, Ford's alternative would

eliminate that component of any pressure drop which is due to test gas

temperature change.

Chrysler, in its petition, provided an almost identical rationale

to that of Ford, stating that the pressure drop limits specified in the

final rule do not accurately measure fuel leakage when the internal

temperature of the gas causes change to the pressure within the fuel

system. However, Chrysler's suggested corrective action differs from

that of Ford. Chrysler requested that the agency amend the pressure

drop limits in the final rule to incorporate the 60 psi adjustment

needed to compensate for the possible change in gas temperature. Under

Chrysler's request, the amended pressure drop limits in S5.2(a) would

be:

(1) 1476 kPa (214 psi), or

(2) 895 (T/VFS) + 414 kPa (60 psi), whichever is higher.

Chrysler stated that ``[t]his would provide the needed compensation

without the added difficulty of measuring gas temperature within the

high pressure fuel system, which is difficult, impracticable, and risks

compromising the fuel system integrity.''

After reviewing Ford's and Chrysler's petitions for reconsideration

about permissible pressure drop, NHTSA has determined that the

requested modifications to S5.2(a) would be inappropriate. NHTSA

continues to believe that the pressure drop limits and test procedure

established in the final rule are the most appropriate and feasible,

and that they provide a relatively simple and accurate method to

determine CNG fuel leakage. The agency believes that under real world

test conditions, any variation in test gas temperature will not

significantly affect test results.

NHTSA notes that because CNG is a gas, and not a liquid, measuring

a safe level of allowable leakage after a crash test is much more

complex than measuring similar levels for liquid fuels. This is because

of the relationship between the temperature and pressure of a gas. The

two are directly proportional. A change in either, pressure or

temperature, directly affects the other.

In arriving at the allowable pressure drop limit and test procedure

established in the final rule, NHTSA addressed the issue of temperature

and pressure, along with other related issues [[Page 2541]] raised by

commenters on the January 1993 NPRM. These included whether to measure

test gas temperature during the 60-minute period following barrier

impact, whether to specify an ambient test temperature, the accuracy of

available pressure drop measurement technology, and the time period

over which pressure drop is measured. These, along with commenters'

concerns, presented complex, and, in some cases, competing issues to

resolve. There were a variety of possible solutions, some more feasible

than others, to the problem of measuring CNG fuel system leakage.

Contrary to the assertion made by Ford in its petition, the agency

considered the information provided by AAMA about the effect of

temperature on pressure. That information is specifically referenced in

the preamble to the final rule (59 FR 19652). In addition, the agency

noted in the preamble that several commenters, including AAMA, stated

that temperature variations should be compensated for when conducting

the crash test. However, neither AAMA nor other commenters suggested

any method to correct for this. After reviewing the components, NHTSA

decided not to specify an ambient test temperature, but to limit the

amount of ambient temperature variation during the 60-minute test

period to 5.6 deg.C (10 deg.F). A temperature variation exceeding

this amount will invalidate the test results. The agency noted that,

``Without such control, a large change in temperature could

artificially affect the test results.'' NHTSA continues to believe that

this test condition will sufficiently minimize changes in test gas

temperature, as well as pressure drop measurement accuracy.

NHTSA appreciates the concerns expressed by Ford and Chrysler in

their petitions. However, as noted above, under real world test

conditions, any variation in test gas temperature will not

significantly affect test results. The agency believes there are three

leakage scenarios that could potentially occur during the 60-minute

test period following barrier impact: No leak, a large leak, and a

small or marginal leak condition. In the case of no leak, Ford and

Chrysler stated in their petitions that a 5.6 deg.C (10 deg.F) drop

in ambient temperature could result in a 60 psi pressure drop even

though there is no leakage. However, since the allowable pressure drop

established in the final rule is at least 1062 kPa (154 psi), a 60 psi

pressure drop will not affect compliance test results since it is well

below the amount allowed in the final rule. Similarly, in the case of a

large leak, any change in test gas temperature should not influence

compliance test results, since all or most of the gas will leak out

during the 60-minute test period, thereby making a non-compliance

obvious. Based on supplemental information which the agency obtained by

telephone from Ford and Blue Bird Body Company on the NPRM, the agency

believes these two conditions, no leak or a large leak, will account

for most of the leakage scenarios after real world CNG vehicle crash

tests. However, in the event there is a slow leak, NHTSA believes that

here, too, test gas temperature will remain relatively constant during

testing, due to thermal contact between the test gas and fuel container

walls. Any change in test gas temperature will tend to be offset by the

temperature or thermal energy of the surrounding container walls, which

along with the test gas have been stabilized to ambient temperature

prior to testing.

NHTSA rejects Ford's recommendation that the final rule exclude

pressure changes due to test gas temperature changes, because it would

require that test gas temperature be measured. NHTSA believes that this

would unnecessarily result in a more costly and complex test procedure.

Further, it could make the fuel system more vulnerable to leakage in a

crash, since an additional fuel system measurement fitting may be

required. In its petition for reconsideration, Chrysler referred to

this as ``* * * the added difficulty of measuring gas temperature

within the high pressure fuel system, which is difficult,

impracticable, and risks compromising the fuel system integrity.'' In

addition, supplemental information which the agency obtained by

telephone from Ford indicates that measuring gas temperature in a CNG

fuel system is not always accurate.

NHTSA also rejects Chrysler's recommendation that an additional 60

psi be added to the allowable pressure drop in the final rule. In the

case of an allowable pressure drop of 1062 kPa (154 psi), adopting

Chrysler's request would have raised this level by approximately 40

percent. The agency believes that that addition could make the

allowable pressure drop levels unsafe, since it would allow more fuel

leakage. This would be clearly 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.

For the above reasons, NHTSA denies the requests of Ford and

Chrysler regarding pressure drop.

Fill Condition

As part of the test conditions prior to CNG vehicle crash testing,

S7.1.1 of Standard No. 304 specifies that, ``Each fuel storage

container is filled to 100 percent of service pressure with nitrogen,

N2.'' S4 states that, ``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).''

In its petition, AAMA stated that since the final rule places no

absolute limits on the ambient temperatures at which testing may be

performed, but merely requires that ambient temperature not change more

than 10 deg.F during the course of the test, fuel storage containers

will not always be filled at and stabilized to a temperature of 20 deg.

Celsius (68 deg. Fahrenheit). According to the petitioner, the fill

pressure to be used for ambient temperatures other than 20 deg. Celsius

(68 deg. Fahrenheit) is unclear and therefore not reasonable,

practicable, or stated in objective terms. AAMA further stated that an

appropriate corrective action would be to amend S7.1.1 of the Standard

to state that, ``Each fuel storage container is filled with nitrogen,

N2, to 100 percent of service pressure adjusted for ambient

temperature.'' AAMA's suggested language is italicized.

After reviewing AAMA's petition for reconsideration about fill

pressure, NHTSA has determined that that organization's requested

modification to S7.1.1 would be inappropriate.

The agency's purpose in specifying that CNG containers be filled to

100 percent of service pressure in S7.1.1 is to provide a reference

point for the fill condition from which crash tests are performed,

e.g., 20,684 kPa (3000 psi) at 20 deg.C (68 deg.F). NHTSA recognizes

that since the final rule does not specify an ambient temperature at

which crash testing is performed, fuel containers will not always be

filled and stabilized to 20 deg.C (68 deg.F). This will result in CNG

container pressures which are different than if testing were performed

at 20 deg.C (68 deg.F), because of the relationship between gas

temperature and pressure. Thus, manufacturers may fill and stabilize

the CNG containers prior to testing to a pressure that is adjusted for

ambient temperature. The final rule does not prohibit this. However,

that pressure, which is adjusted for ambient temperature, must be such

that if ambient temperature were 20 deg.C (68 deg.F), pressure in the

CNG containers would be equal to service pressure. Since the final rule

does not prohibit this adjustment for ambient temperature prior to

testing, NHTSA sees no need to [[Page 2542]] adopt the revised language

suggested by AAMA. Therefore, AAMA's petition concerning fill condition

is denied.

Pressurizing the High Pressure Side

S7.1.2 of the final rule states that, ``Any shutoff valve at the

fuel container is in the open position.'' AAMA states in its petition

that some CNG fuel systems include additional manual shutoff valves in

the high pressure side of the fuel system, and that these valves must

also be open so that pressure is distributed to the entire high

pressure side of the fuel system. If these valves are closed, the

vehicle test conditions would not simulate, to the extent practicable,

conditions present in a real world crash. These observations led that

organization to conclude that the final rule is not reasonable or

practicable. In addition, AAMA stated that this aspect of the final

rule does not meet the need for motor vehicle safety. This is because

manual valves located downstream from the pressure measurement point,

if closed, would seal off part of the high pressure side of the fuel

system. Thus, pressure measurement upstream of the closed valve would

not detect a leak in the sealed off, high pressure portion of the fuel

system.

AAMA stated that an appropriate corrective action would be to amend

S7.1.2 to state that ``* * * normal operating pressures. All manual

shutoff valves are to be left in the open position.'' AAMA's suggested

language is underlined.

After reviewing AAMA's recommendation about shutoff valves, NHTSA

has decided to amend S7.1.2 to state ``All manual shutoff valves are to

be in the open position.''

The agency believes that this change is consistent with the goal in

S7.1.2 which is to have the vehicle test conditions be representative

of real world crash test conditions and to meet the need for motor

vehicle safety. The agency was not aware that there may be manual

shutoff valves within the high pressure portion of the fuel system

other than those located at the fuel containers. In addition, the

phrase in S7.1.2 stating ``Any shutoff valve * * *'' was meant to refer

to manual shutoff valves. Based on the above consideration, NHTSA has

decided to adopt AAMA's request concerning pressurizing the high

pressure side.

Pressure Measurement Location

AAMA stated that the final rule does not specify how fuel system

pressure is to be accessed for measurement. In its response to the

January 1993 NPRM, AAMA stated that it

* * * is concerned about adding pressure transducers to points

in the fuel line solely for purposes of conducting the test. Doing

so creates a point of potential leakage where a fitting joint does

not exist in a non-test vehicle.

AAMA stated that if a NHTSA contractor were to test for compliance by

creating such a pressure measurement point, AAMA member companies

likely would object, pointing out that the fuel system on the vehicle

has been disrupted and therefore would not be representative of the

vehicle as manufactured. AAMA stated that it is not reasonable,

practicable, or appropriate to have a final rule that is silent on

where the pressure is to be measured, thereby leaving its selection to

the discretion of a NHTSA test contractor.

AAMA stated that an appropriate corrective action would be to add a

new S7.1.8, which states, ``The pressure drop measurement specified in

S7.2 (sic) is to be made using a location recommended by the vehicle

manufacturer.'' AAMA's proposed language is underlined. (Note: NHTSA

has verified with AAMA that it intended to reference S5.2 rather than

S7.2 in this statement.)

NHTSA agrees with AAMA's assessment. Based on additional comments

obtained from AAMA in response to the January 1993 NPRM, the agency

understands that vehicle manufacturers will be providing a tap point on

the vehicle's fuel system where pressure measurement is to be obtained.

It would be consistent with the intent of Standard 304 if that pressure

measurement of the fuel system were made at the location specified by

the vehicle manufacturer. Accordingly, AAMA's petition concerning

pressure measurement location is granted.

Miscellaneous Correction

NHTSA is also making a word correction to one of the definitions in

S4, which AAMA pointed out in its petition. The definition for CNG fuel

container currently reads CNG full container. Therefore, the word full

is changed to fuel.

Rulemaking Analyses

A. Executive Order 12866 and DOT Regulatory Policies and Procedures

NHTSA has considered the impact of this rulemaking action under

Executive Order 12866 and the Department of Transportation's regulatory

policies and procedures. This rulemaking document was reviewed under

E.O. 12866, ``Regulatory Planning and Review.'' This action has been

determined to be ``non-significant'' under the Department of

Transportation's regulatory policies and procedures.

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.

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

This final rule does not have any retroactive effect. Under 49

U.S.C. 30103, 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, except to the extent that the State requirement imposes a

higher level of performance and applies only to vehicles procured for

the State's use. 49 U.S.C. 30161 sets forth a procedure for judicial

review of final rules establishing, amending or revoking Federal motor

vehicle safety standards. That section does not require

[[Page 2543]] 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.

In consideration of the foregoing, 49 CFR part 571 is amended as

follows:

PART 571--[AMENDED]

1. The authority citation for part 571 continues to read as

follows:

Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166;

delegations of authority at 49 CFR 1.50.

2. Section 571.303 is amended by revising the definition of CNG

fuel container in S4, revising S7.1.2, and adding S7.1.8 to read as

follows:

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

natural gas vehicles.

* * * * *

S4. Definitions.

* * * * *

CNG fuel container means a container designed to store CNG as motor

fuel onboard a motor vehicle.

* * * * *

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. All

manual shutoff valves are to be in the open position.

* * * * *

S7.1.8 The pressure drop measurement specified in S5.2 is to be

made using a location on the high pressure side of the fuel system in

accordance with the vehicle manufacturer's recommendation.

* * * * *

Issued on: January 4, 1994.

Ricardo Martinez,

Administrator.

[FR Doc. 95-464 Filed 1-9-95; 8:45 am]

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