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Federal Motor Vehicle Safety Standards; Compressed Natural Gas Fuel Container Integrity

American Government Special Collections Reference Desk

American Government

Federal Motor Vehicle Safety Standards; Compressed Natural Gas Fuel Container Integrity

Ricardo Martinez
National Highway Traffic Safety Administration
September 26, 1994

[Federal Register: September 26, 1994]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 93-02; Notice 05]
RIN [2127-AF14]

 
Federal Motor Vehicle Safety Standards; Compressed Natural Gas 
Fuel Container Integrity

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. 304, Compressed Natural Gas Fuel Containers, 
that specifies performance requirements applicable to compressed 
natural gas (CNG) fuel containers: a pressure cycling test evaluates a 
container's durability; a burst test evaluates a container's initial 
strength; and a bonfire test evaluates a container's pressure relief 
characteristics. In addition, the final rule specifies labeling 
requirements for CNG containers. The purpose of this new standard is to 
reduce deaths and injuries occurring from fires that result from fuel 
leakage from CNG containers.

DATES: Effective Date: The Standard becomes effective March 27, 1995.
    Incorporation by reference: The incorporation by reference of 
certain publications listed in the regulations is approved by the 
Director of the Federal Register as of March 27, 1995.
    Petitions for Reconsideration: Any petition for reconsideration of 
this rule must be received by NHTSA no later than October 26, 1994.

ADDRESSES: Petitions for reconsideration of this rule should refer to 
Docket 93-02; Notice 5 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, National Highway Traffic Safety Administration, 
400 Seventh Street, SW., Washington, DC 20590 (202-366-4931).

SUPPLEMENTARY INFORMATION:

Outline

I. Background
    A. General Information
    B. Previous Agency Rulemakings
II. Comments on the Proposal
III. Agency's Decision
    A. Overview
    B. Adopting Industry Standards
    C. Pressure Cycling Test
    D. Burst Test
    1. Safety Factor
    2. Hold Time Interval
    3. Sequential Testing
    4. Failure Criteria
    E. Bonfire Test
    1. Performance Requirements
    2. Types of Pressure Relief Devices
    3. Shielding
    4. Test Gas and Pressure
    5. Wind Velocity and Direction
    6. Bonfire Fuel
    7. Bonfire Test Fuel Pan Depth
    F. Labeling Requirements
    G. Leadtime
    H. Benefits
    I. Costs
VI. Rulemaking Analyses
    A. Executive Order 12866 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

    Natural gas is a vapor that is lighter than air at standard 
temperature and pressure.\1\ When used as a motor 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 in turn serves to increase the 
vehicle's driving range. Since natural gas is a flammable fuel and is 
stored under high pressure, natural gas containers pose a potential 
risk to motor vehicle safety.
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    \1\Standard temperature is 0 deg. Celsius or 32 deg. Fahrenheit 
and standard pressure is 101.4 kiloPascals (kPa) or 147.7 pounds per 
square inch (psi).
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    Vehicles powered by CNG have not been numerous to date, although 
they are increasing. The number of CNG vehicles in the United States 
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. As discussed in detail in a final rule 
regarding CNG vehicles published on April 25, 1994, recent Federal 
legislation, as well as the need to meet environmental and energy 
security goals, will lead to greater increases in the production and 
use of these vehicles. (59 FR 19648).

B. Previous Agency Rulemakings

    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) applicable to CNG fuel 
containers and the fuel systems of motor vehicles using CNG or 
liquified 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.
    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 focus on the integrity of the 
entire fuel system, and (2) equipment requirements that focus on the 
fuel containers alone.
    NHTSA decided to model the proposed requirements applicable to 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.Fahrenheit (i.e., fuels 
that are liquid under standard temperature and pressure). Vehicles 
manufactured to use only CNG are not subject to Standard No. 301 since 
CNG has a boiling point below 32  deg.F. 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 basing the CNG rulemaking on 
Standard No. 301, the agency believed that passengers of CNG vehicles 
would be afforded a level of safety comparable to that provided 
passengers of vehicles fueled by gasoline or diesel fuel.
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    \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.
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    With respect to the ``vehicle'' requirements for CNG vehicles, 
NHTSA proposed that the fuel system integrity requirements 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 
determined by measuring the fuel system's pressure drop after the crash 
test rather than fuel spillage, since CNG is a vapor and not a liquid. 
The allowable pressure drop for CNG fueled vehicles would be 
equivalent, as measured by the energy content of the lost fuel, to the 
allowable spillage of gasoline during Standard No. 301 compliance 
testing.
    With respect to the ``equipment'' requirements for CNG containers, 
NHTSA proposed a definition for ``CNG fuel tank'' and performance 
requirements that would apply to all such fuel containers manufactured 
for use as part of a fuel system on any motor vehicle, including 
aftermarket containers.\3\ Thus, while vehicles with a GVWR over 10,000 
pounds (other than school buses) would not be subject to Standard No. 
303, the CNG containers in those vehicles would be subject to the 
equipment requirements. The agency proposed that each CNG container 
would be subject to a pressure cycling test to evaluate container 
durability and a pressure burst test to evaluate the container's 
initial strength as well as its resistance to degradation over time. In 
addition, the NPRM proposed requirements to regulate how the container 
``vents'' its contents under specified conditions of elevated 
temperature and pressure.
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    \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.
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II. Comments on the Proposal

    NHTSA received a large number of comments to the docket 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 is 
necessary and appropriate. In fact, some commenters, including the CGA, 
the NGVC, and CNG container manufacturers stated that NHTSA should 
issue a Federal standard as soon as possible to facilitate the safe and 
expeditious introduction of CNG fueled vehicles. With respect to the 
equipment requirements, the commenters generally believed that Federal 
requirements about CNG fuel container integrity are needed and should 
be implemented as quickly as possible. The CNG vehicle industry, led by 
CGA and NGVC, expressed concern that lack of Federal regulations has 
created a problem for the industry, given the issuance of potentially 
conflicting industry and State regulations. Therefore, these commenters 
stated that CNG container manufacturers may not know the appropriate 
standards to which they should manufacture their containers. In 
contrast, the American Automobile Manufacturers Association (AAMA) 
stated that the vehicle system requirements are sufficient to regulate 
the overall integrity of CNG fueled vehicles and that separate 
requirements for CNG fuel containers are not needed. Nevertheless, AAMA 
provided detailed comments about the container proposal in case the 
agency decided to issue separate container requirements.
    The commenters addressed a variety of issues discussed in the NPRM. 
These issues include the appropriateness of adopting the American 
National Standards Institute (ANSI) voluntary industry standard known 
as NGV2;\4\ the pressure cycling requirements and test procedures; the 
burst requirements and test procedures, including the proposed safety 
factor, hold time interval, and need for sequential testing; the 
pressure relief requirements and test procedures, including types of 
pressure relief devices, shielding, test gas, test pressure, test fuel, 
and fuel pan depth; labeling requirements; leadtime; costs; and 
benefits.
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    \4\NGV2 is a recently issued voluntary industry standard that 
was adopted by the ANSI and addresses CNG fuel containers. It was 
developed by an industry working group that included container 
manufacturers, CNG users, and utilities.
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    NHTSA issued an SNPRM proposing to pattern the burst requirements 
more closely on NGV2, based on its consultation with other Federal 
agencies, its review of comments to the January 1993 proposal, and 
other available information. (58 FR 68846, December 29, 1993). NHTSA 
proposed a burst test that would link the use of particular designs and 
materials to compliance with safety factors tailored to those designs 
and materials. NHTSA requested comment on the appropriateness of 
requiring CNG containers to meet design and material requirements, such 
as those specified in NGV2, and to meet safety factors tailored to 
those requirements. As an alternative approach, the agency asked 
whether it should specify a catch-all high end safety factor for any 
container whose design and materials are not specified in NGV2.
    Most commenters supported the proposal to incorporate NGV2 into the 
Federal standard. However, AAMA and Ford opposed the design and 
material specific approach of NGV2.

III. Agency's Decision

A. Overview

    In today's final rule, NHTSA is issuing a new Federal motor vehicle 
safety standard, Standard No. 304, Compressed Natural Gas Fuel 
Containers, that specifies performance requirements applicable to a CNG 
fuel container's durability, strength, and venting. A pressure cycling 
test evaluates a container's durability by requiring a container to 
withstand, without any leakage, 18,000 cycles of pressurization and 
depressurization. This requirement helps to ensure that a CNG container 
is capable of sustaining the cycling loads imposed on the container 
during refuelings over its entire service life. A burst test evaluates 
a container's initial strength and resistance to degradation over time. 
This requirement helps to ensure that a container's design and material 
are appropriately strong over the container's life. A bonfire test 
evaluates a container's pressure relief characteristics when pressure 
builds in a container, primarily due to temperature rise. In addition, 
the final rule specifies labeling requirements for CNG fuel containers.
    As previously mentioned, the agency has issued a final rule 
establishing a new Federal motor vehicle safety standard, Standard No. 
303, Fuel System Integrity of Compressed Natural Gas Vehicles, that 
specifies vehicle performance requirements applicable to the fuel 
system of a CNG fueled vehicle. As explained in that final rule, the 
fuel system integrity requirements are comparable to those requirements 
in Standard No. 301. Like that Standard, the new requirements limit the 
amount of fuel leakage in specified 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.
    NHTSA believes that CNG containers must be evaluated in all 
possible failure modes and environments to which they may be subjected. 
Since the requirements contained in today's final rule do not address 
all these situations, the agency is currently investigating other 
possible requirements for CNG fuel containers and anticipates issuing a 
SNPRM that would propose performance requirements applicable to such 
characteristics as a CNG fuel container's internal and external 
resistance to corrosion, brittle fracture, fragmentation, and external 
damage caused by incidental contact with road debris or mechanical 
damage during the vehicle's operation. The agency tentatively believes 
that these additional performance requirements are critical for 
determining a CNG container's safety. In addition, the agency 
anticipates proposing additional labeling requirements that should 
provide critical safety information about inspecting a CNG container 
and its service life.
    NHTSA notes that it has no statutory authority to regulate certain 
aspects involving CNG containers, including inspection requirements 
during the manufacturing process, in-use inspection requirements, and 
retest requirements during use.

B. Adopting Industry Standards

    In the NPRM, NHTSA explained its decision to propose pressure 
cycling and burst tests and requirements. While the agency's proposal 
was based on NGV2, the agency decided not to propose certain provisions 
of the voluntary industry standard that the agency tentatively believed 
might unreasonably restrict future designs. Similarly, NHTSA decided 
not to propose regulations issued by the Research and Special Programs 
Administration (RSPA)\5\ for CNG storage containers used on motor 
vehicles, explaining that the RSPA regulations do not address the 
conditions unique to the motor vehicle environment (e.g., increased 
cycling due to refueling and pressure relief when the cylinder is less 
than full). NHTSA further explained that in contrast to RSPA, NHTSA 
does not typically regulate design and materials since NHTSA is 
statutorily directed to issue performance-based safety standards.
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    \5\RSPA is an administration within the United States Department 
of Transportation that among other things regulates the 
transportation of hazardous materials.
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    NGVC and several CNG container manufacturers stated that NHTSA 
should adopt the voluntary industry standard that has been developed by 
the CNG industry working group. In support of this request, the 
American Gas Association (AGA) cited a 1982 Office of Management and 
Budget Circular that states ``It is the policy of the Federal 
Government to (a) Rely on voluntary standards * * * whenever feasible 
and consistent with law and regulation pursuant to law * * *.'' AGA and 
NGVC believed that the voluntary standards provide a higher level of 
safety than the regulations proposed by NHTSA. They further stated that 
if NHTSA were unable to adopt NGV2 due to its prescriptive nature, then 
NHTSA should still allow automobile and equipment manufacturers the 
option of certifying to the industry standard by referencing NGV2 in 
the regulations.
    In promulgating a CNG container standard, NHTSA has sought to the 
extent possible to adopt the tests and requirements set forth in NGV2. 
NHTSA was limited in its ability to do this by the National Traffic and 
Motor Vehicle Safety Act (Safety Act, 49 U.S.C. 30111), which commands 
the agency to issue ``motor vehicle safety standards'' as minimum 
standards of motor vehicle performance that are practicable, meet the 
need for motor vehicle safety, and are stated in objective terms. NHTSA 
found it necessary to modify certain elements of NGV2 to be consistent 
with this statutory mandate. For instance, the agency has not 
incorporated those aspects of NGV2 that are stated in nonobjective 
terms (e.g., a container shall not show ``evidence'' of deterioration 
or failure) NHTSA has decided to incorporate NGV2's design and material 
requirements since the agency has been unable to find or develop a 
meaningful dynamic performance requirement that would adequately 
evaluate a container's initial strength and susceptibility to 
degradation over time. The agency believes that the requirements are no 
more specific than necessary to achieve these safety purposes.
    NHTSA notes that it would be impermissible under the Safety Act for 
the agency to adopt FMVSS provisions referencing NGV2 in its entirety 
and stating that automobile and equipment manufacturers had the option 
of certifying compliance to NGV2 by referencing this voluntary industry 
standard. The Safety Act provides for manufacturer self-certification 
with respect to FMVSSs only. To be part of a FMVSS, the provisions of a 
voluntary industry standard must fully meet all of the requirements of 
the Safety Act. Since all of NGV2 does not meet these requirements, 
NGV2 may not be incorporated in its entirety. Even if NGV2 met these 
requirements, NGV2 could not be incorporated in the FMVSS except to the 
extent that the FMVSS made compliance with NGV2 mandatory.

C. Pressure Cycling Test

    In the NPRM, NHTSA proposed pressure cycling requirements that 
would require that the fuel container withstand a cycling test at 
ambient temperature, without any leakage or deformation exceeding one 
percent of any circumference. In the test, the container would be 
hydrostatically pressurized to the service pressure, then to not more 
than 10 percent of the service pressure, for 13,000 cycles. The 
container would next be hydrostatically pressurized to 125 percent of 
the service pressure, then to not more than 10 percent of the service 
pressure, for 5,000 cycles. The cycling rate would not exceed ten 
cycles per minute.
1. Number of Cycles
    The proposed cycling requirements were intended to establish 
minimum levels of safety performance for the durability of CNG fuel 
containers used in motor vehicles. The agency stated its tentative 
belief that the requirements are consistent with provisions in NGV2 and 
with RSPA regulations for containers used to transport CNG. The agency 
believed that the pressure cycling requirement would help to assure 
that a CNG container is capable of sustaining the cycling loads imposed 
on the container during refuelings. The number of cycles specified in 
the proposal, 13,000 plus 5,000, is representative of four refuelings 
per day, 300 days per year, for 15 years.
    AAMA, Norris, and Thomas commented on the number of pressure 
cycles. These commenters stated that the proposed number of cycles was 
excessive and not representative of the actual operating conditions the 
CNG containers would typically experience. AAMA and Norris stated that 
cycling the container at 125 percent of service pressure for 5,000 
cycles would be adequate. Thomas made inconsistent statements about the 
appropriate number of cycles. On the one hand, it stated that 9,000 
cycles at service pressure would be more reasonable than the proposed 
number of cycles. On the other hand, it stated that the agency should 
adopt NGV2 which specifies 18,000 cycles.
    After reviewing the comments and other available information, NHTSA 
continues to believe that the proposed number of pressure cycles 
accurately represents the extreme conditions that CNG fuel containers 
could experience during their lifetime, with a margin of safety. This 
is based on the large number of cycles to which fleet vehicles are 
subjected. The agency believes that the 5,000 cycles suggested by AAMA 
and Norris would not ensure the safety of vehicles that experience 
multiple refuelings each day, such as taxis and other fleets. NHTSA 
further notes that the number of cycles being adopted is consistent 
with the cycles in NGV2 and therefore establishes a minimum level of 
safety that is consistent with NGV2, a standard supported by a large 
majority of the commenters. Accordingly, the agency has determined that 
a CNG fuel container will be subject to 18,000 pressure cycles.
2. Failure Criteria
    In the NPRM, NHTSA proposed that a CNG fuel container would have to 
meet two test criteria to pass the pressure cycling test: (1) No 
leakage, and (2) no permanent circumferential deformation greater than 
one percent. The agency proposed these two criteria to provide 
objective means of evaluating a container's durability during 
compliance testing. NHTSA adopted the no leakage portion of the 
proposal from NGV2's pressure cycling test. The one percent deformation 
level, which is not in NGV2's pressure cycling test, was based on the 
Society of Automotive Engineers (SAE) Recommended Practice J10, August 
1985, a requirement involving the performance of metal air brake 
reservoirs. The agency proposed a limit on circumferential deformation 
to aid in determining when a container's failure was impending.
    No commenters objected to the no leakage criterion. Accordingly, 
the agency has adopted the no leakage requirement in the final rule. 
The agency believes that specifying that containers ``shall not leak'' 
provides an objective measure that will ensure that a container 
maintains its integrity by retaining its contents under pressure.
    Sixteen commenters addressed the issue of the allowable 
circumferential deformation criterion. The commenters were NGVC, 
Brunswick, Pressed Steel Tank (PST), Structural Composites Industry 
(SCI), Tecogen, CGA, AAMA, Amoco, Alusuisse, Oklahoma Gas, ARC, 
Flxible, Fiber Dynamics, Norris, Comdyne, and EDO. All the commenters, 
except Brunswick, believed that the agency should not include a 
deformation requirement in the pressure cycling or burst tests. The 
commenters believed that the test requirement is not appropriate for 
all container materials and designs. They stated that due to the nature 
of the different materials used in these containers, and their 
different rates of deformation under load, some materials such as 
fiberglass, would deform more than others, such as steel. The 
commenters also stated that deformation was not an indicator of 
impending failure and that the SAE brake reservoir test was not 
appropriate for a CNG fuel container application.
    NHTSA has decided not to adopt the one percent circumferential 
deformation requirement. In proposing this criterion, NHTSA tentatively 
concluded that it would be an appropriate indicator of the fuel 
container's durability characteristics. However, as the comments note, 
it is not an appropriate criterion because of the differing 
construction and materials used for CNG fuel container applications. 
After reviewing the comments and other available information, the 
agency now believes that limiting the circumferential deformation is 
not a meaningful way to determine a container's strength or impending 
failure, since the larger deformation experienced by some materials 
does not necessarily represent these characteristics. Instead, the 
agency believes that the no-leakage requirement, by itself, is the 
appropriate criterion to define a container failure, after being 
subjected to the pressure cycling test.
    Brunswick further commented that some container designs, such as 
full-wrapped composite containers, would deform in the axial direction 
in addition to the circumferential direction. To account for axial 
deformation, Brunswick recommended allowing a maximum five percent 
volumetric expansion of the container.\6\ Brunswick stated that this 
test is used to assure that the container material exhibits elastic 
behavior at expected operating conditions.
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    \6\Both RSPA's standards and NGV2 incorporate the concept of 
volumetric expansion. In these standards, the volumetric expansion 
is measured when hydrostatic testing is performed on the container 
at 1.50 to 1.67 times the service pressure. This test is a non-
destructive one, i.e., the container may be put into service after 
it is tested.
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    NHTSA agrees with Brunswick's statement that some container designs 
deform in the axial direction. Nevertheless, the agency believes that 
measuring volumetric expansion would not provide an appropriate measure 
of a container's impending failure in a destructive test (i.e., where 
the container cannot be used again). In addition, the NPRM provided no 
notice to amend the standard to measure such expansion in the axial 
direction. Since the pressure cycling and burst tests being adopted in 
this rule are capable of evaluating a CNG container's durability, the 
agency believes that another non-destructive test would be redundant 
and therefore is not needed. The agency further notes that the five 
percent maximum level of expansion would not provide a meaningful 
measure of a container's impending failure, since this level is based 
on a container's performance under less stringent test conditions.

D. Burst Test

1. Safety Factor
    With respect to the burst test, NHTSA proposed that a CNG fuel 
container would have to withstand an internal hydrostatic pressure of 
3.50 times the service pressure for 60 seconds, without any leakage or 
circumferential deformation over one percent. The multiple of the 
internal hydrostatic pressure, 3.50, is known as the safety factor. The 
agency tentatively concluded that the burst test, together with a 
pressure cycling test, would be sufficient to assure adequate levels of 
safety performance for both the strength and durability of CNG fuel 
containers used in motor vehicles.
    The proposal of a burst test with a safety factor was based in part 
on NGV2. NGV2 specifies several sets of detailed material and design 
requirements. For each set of those requirements, NGV2 specifies a 
unique safety factor for calculating the internal hydrostatic pressure 
that the container must withstand. The safety factors range from 2.25 
to 3.50, depending on the material and design involved. To satisfy this 
aspect of NGV2, a container must meet both the material and design 
requirements as well as the burst test.
    NGV2 specifies four types of container designs. A Type 1 container 
is a metallic noncomposite container. A Type 2 container is a metallic 
liner over which an overwrap such as carbon fiber or fiberglass is 
applied in a hoop wrapped pattern over the liner's cylinder sidewall. A 
Type 3 container is a metallic liner over which an overwrap such as 
carbon fiber or fiberglass is applied in a full wrapped pattern over 
the entire liner, including the domes. A Type 4 container is a non-
metallic liner over which an overwrap such as carbon fiber or 
fiberglass is applied in a full wrapped pattern over the entire liner, 
including the domes.
    The agency did not propose adoption of the material and design 
requirements of NGV2. Instead, the agency proposed a single safety 
factor of 3.50 for all containers, regardless of their materials or 
design. It tentatively concluded that the factor would not impede 
technological development, yet would assure an acceptable level of 
safety for all containers.
    CNG container manufacturers, CNG trade associations (NGVC and AGA), 
utility companies, the American Automobile Manufacturers Association 
(AAMA) and other commenters addressed the issue of the safety factor. 
Most commenters disagreed with the agency's proposal to require that 
all containers meet the same safety factor.
    NGVC, AGA, and the CNG container manufacturers generally believed 
that the material and design of the fuel container need to be taken 
into account in establishing an appropriate safety factor, if safe, 
cost-effective, and light-weight containers are to be produced. 
Establishing an overly high factor for a given combination of material 
and design could result in unnecessarily over-designed, heavy 
containers, according to these commenters. They believed that some 
materials, such as fiberglass, need a higher safety factor because they 
degrade faster over time. In contrast, a material such as steel 
maintains its strength for a longer time, and therefore containers made 
of it could be made safely with a lower safety factor.
    Many of these commenters recommended that NHTSA adopt the safety 
factors specified in NGV2. They stated that compared to the regulations 
proposed by NHTSA, the NGVC voluntary industry standard provides a more 
appropriate level of safety, given the need to specify safety factors 
based on the design and materials used.
    However, several commenters disagreed with certain safety factors 
specified in NGV2. CGA, PST, SCI, and NGV Systems supported a higher 
safety factor for containers using unproven materials. In particular, 
they were concerned with containers reinforced with carbon fiber 
overwrap, for which NGV2 specifies a 2.25 safety factor for all carbon 
reinforced containers, Types 2, 3, and 4.
    NGV Systems stated that a safety factor of 2.25 constitutes an 
``unacceptable safety risk,'' given the industry's limited experience 
with carbon fiber and lack of a significant data base demonstrating 
this materials safety and reliability. Accordingly, NGV Systems 
supported a safety factor of 3.5 for what it termed unproven designs, 
which may then be lowered as more experience and data accumulate. CGA 
recommended safety factors of 2.5 for all Type 2 containers and 3.33 
for all Type 3 and 4 containers, stating that these are used on all 
fiber reinforced compressed gas containers now in commercial use. CGA 
indicated that unlike other fiber overwrap used in the past for 
transportation pressure vessels, there is no commercial experience with 
the safety of carbon fiber reinforced containers for motor vehicle 
applications to justify a 2.25 safety factor for such containers. CGA 
stated that NGV2 does not adequately address damage tolerance concerns 
for carbon reinforced fully wrapped containers with low safety factors. 
PST recommended 3.33 for carbon fiber Types 3 and 4 containers. That 
commenter recommended such conservative safety factors until 
substantial data are accumulated on the use of carbon fiber containers 
in actual service. SCI provided similar comments, and recommended 
safety factors of 3.33 for the fully wrapped containers, which are 
Types 3 and 4.
    Three commenters stated that a single safety factor was 
appropriate. CNG Pittsburgh, a consulting firm, stated that a safety 
factor of 3.50 is conservative but reasonable for CNG fuel containers. 
AAMA stated that adopting NGV2's approach with various safety factors 
depending on the material and design involved would limit a 
manufacturer's choice of container designs and materials. EDO 
recommended a safety factor of 2.5 for all containers.
    NHTSA decided to issue an SNPRM proposing to pattern the burst 
requirement more closely on NGV2, based on its consultation with other 
Federal agencies, its review of comments to the January 1993 proposal, 
and other available information. In explaining its reason for issuing 
the SNPRM, NHTSA stated that there did not appear to be any procedures 
that could adequately test a container's susceptibility to degradation 
over time. Therefore, it believed that specifying a single safety 
factor would not protect in all instances against these problems since 
the strength of some containers is dependent on the specific material 
and method of design. Therefore, NHTSA decided to propose a burst test 
that would link the use of particular designs and materials to 
compliance with safety factors tailored to those designs and materials. 
The agency tentatively concluded that such an approach might be 
necessary to ensure the safe performance of pressure vessels used for 
fuel containers. The agency further noted that international standards 
addressing CNG fuel containers, including regulations of Transport 
Canada and those being drafted by the International Standards 
Organization (ISO) link the use of particular designs and materials 
with strength requirements suitable for those designs and materials.
    In the SNPRM, NHTSA requested comment on the appropriateness of 
requiring CNG containers to meet design and material requirements, such 
as those specified in NGV2, and to meet safety factors tailored to 
those requirements. The agency also asked about the effect of adopting 
NGV2 on future container technology, since the only way a container 
manufacturer could comply with the Federal standard would be by 
producing a container that uses those materials and designs specified 
in NGV2 if the agency incorporated NGV2's material and design 
provisions in the FMVSS. As an alternative approach, the agency asked 
whether it should specify a catch-all high end safety factor for any 
container whose design and materials are not specified in NGV2.
    NHTSA received 18 comments to the December 1993 SNPRM about 
adopting the design and material specific approach of NGV2. Sixteen 
commenters, including NGVC/AGA, CGA, CNG container manufacturers, 
public utilities, and two bus manufacturers supported the proposal to 
incorporate NGV2 into the Federal standard. Eleven commenters supported 
the safety factors in NGV2. Five others were concerned about the level 
of some safety factors in NGV2 or the use of relatively new materials, 
such as carbon fiber. CGA and SCI referenced their earlier comments to 
the NPRM, again recommending safety factors of 2.5 for all Type 2 
containers and 3.33 for all Type 3 and Type 4 containers. AAMA and Ford 
opposed the design and material specific approach of NGV2. AAMA stated 
that some of NGV2's requirements limit opportunities for future 
development of advance container design or materials that may not fit 
in the specifications in NGV2. No commenter favored having a catch-all 
high end safety factor.
    Based on the available information, NHTSA has decided to require 
CNG containers to meet the safety factors applicable to the design and 
material requirements specified in NGV2, except for carbon fiber. 
Specifically, the agency is specifying separate safety factors for 
containers using various materials (e.g., fiberglass, carbon, steel, 
aluminum) and different designs (non-composite, hoop wrapped or full 
wrapped composite containers, and welded). The agency believes that 
this approach will result in the manufacture of safe containers for CNG 
powered vehicles.
    NHTSA has decided to adopt the specific safety factors and related 
requirements set forth in NGV2, except for those safety factors 
specified for carbon fiber. While NGV2 currently specifies a safety 
factor of 2.25 for Type 2, 3, and 4 carbon fiber containers, NHTSA has 
decided to specify a safety factor of 2.5 for Type 2 carbon fiber 
containers and 3.33 for the Type 3 and 4 carbon fiber containers. The 
agency is requiring a higher safety factor for Type 3 and 4 containers 
since the fibers on those containers carry a greater proportion of the 
load than on Type 2 containers.
    NHTSA made this decision after reviewing all of the comments and 
information obtained in response to both the NPRM and SNPRM; meetings 
with container manufacturers, CGA and NGVC/AGA; and discussions with 
other Federal agencies, including RSPA. Comments and information were 
presented to support safety factors for carbon fiber containers, 
ranging from 2.25 to 3.5. Brunswick, in particular, submitted 
substantial test data and other technical information in support of 
NGV2's 2.25 safety factor for carbon fiber, including testing it 
performed on such containers which showed favorable results. RSPA 
recommended a safety factor of not less than 3.0 for carbon fiber, 
which is consistent with its FRP-1 and FRP-2 standards.
    Notwithstanding comments supporting the 2.25 safety factor, NHTSA 
has determined that under its statutory mandate, it is necessary to 
specify higher safety factors for carbon fiber containers. In adopting 
these more stringent requirements, NHTSA sought the advice of RSPA, 
which has accumulated significant experience and expertise through its 
efforts to regulate the safety of pressure vessels used to transport 
hazardous materials. Specifically, NHTSA has adopted RSPA's 
recommendation not to specify the 2.25 safety factor for carbon 
composite containers.
    The more stringent safety factors being adopted are consistent with 
RSPA's longstanding approach to initially adopt conservative 
requirements and subsequently modify the requirements, if further real-
world safety data become available supporting less stringent 
regulations. NHTSA has determined that applying this approach to the 
safety factors for carbon fiber containers is necessary, since carbon 
fiber containers have not been used extensively in motor vehicle 
applications. The agency believes that the higher safety factors are 
justified until further data are developed and become available on the 
use of carbon fiber containers in motor vehicle applications.
    NHTSA acknowledges that using such a safety-oriented approach may 
result in costlier and heavier carbon fiber containers. However, the 
agency believes that the requirements being adopted will not preclude 
the introduction and effective use of this new technology. Overall, the 
agency believes that the safety factors being specified for carbon 
fiber containers, along with the remaining safety factors it has 
adopted from NGV2 for other materials, will result in safe CNG 
containers.
    As for AAMA's comment, NHTSA shares that association's concerns 
about restricting future developments. However, based on comments by 
the container manufacturers and other Federal agencies, the agency 
believes that few, if any, designs beyond those accounted for in NGV2 
are planned. If a new container technology is developed, the agency 
will evaluate its safety in the context of a petition for rulemaking to 
amend the Federal safety standard.
    NHTSA has decided not to adopt the catch-all high level safety 
factor, which could allow containers incorporating materials or designs 
that have not been incorporated in NGV2 and thus might be detrimental 
to safety. The agency further believes that it would be inappropriate, 
at this time, to add a catchall factor. While such a proviso would 
facilitate innovation and design change, the agency agrees with 
commenters that specifying such a catchall might be detrimental to 
safety, since untested designs and materials would be permitted.
2. Hold Time Interval
    In the NPRM, NHTSA proposed that during the burst test, elevated 
pressure would have to be sustained for 60 seconds. The agency noted 
that while RSPA regulations also specify a 60-second period, NGV2 
requires a 10-second hold time interval once the maximum pressure is 
obtained. The agency believed that because NGV2 includes additional 
tests to qualify container designs and the agency was not proposing 
these additional tests, a shorter hold time would not be suitable.
    NHTSA received six comments addressing the appropriate hold time 
interval. All commenters except EDO believed the 60 second hold time 
requirement was not necessary. EDO stated that the requirement was 
``tough but reasonable.'' NGVC, Brunswick, PST, and ARC stated that 
specifying the hold time at 60 seconds instead of 10 seconds would not 
compensate for the lack of other NGV2 required tests. NGVC stated that 
the ten second hold time interval is not intended as a test of 
container strength, but as the time for the pressure in the container 
to stabilize. PST stated that along with the 3.5 safety factor, the 60 
second hold time would make an already conservative test even more 
stringent.
    After reviewing the comments and other available information, NHTSA 
has decided to specify a hold time of 10 seconds instead of 60 seconds. 
The agency notes that the proposal was based on a misperception of the 
hold time requirement's purpose. As the commenters stated, the hold 
period is included only to stabilize the pressure. It is not used as a 
surrogate for initial burst strength. Therefore, the reduction in hold 
time will not affect the test's stringency. In addition, the agency 
anticipates issuing a SNPRM that would propose additional performance 
requirements to evaluate other aspects of a CNG fuel container's 
integrity.
3. Sequential Testing
    In the NPRM, NHTSA proposed that a container that passed the 
pressure cycling test would then be subjected to the burst test. In 
proposing that the same fuel container be used in both the pressure 
cycling and burst tests, the agency believed that it would be 
appropriate to establish that the fuel container maintained its initial 
strength after being subject to the durability test.
    Seven commenters addressed the issue of using the same container 
for both the pressure cycling and burst tests. NGVC, AAMA, Comdyne, 
Pressed Steel Tanks, and Amoco stated that requiring the same fuel 
container for both tests would be unrealistic and overly stringent, 
because in real world situations, a container would not be subject to 
pressure cycling and burst conditions sequentially. They stated that 
otherwise unnecessary material would have to be added to strengthen the 
container so it could meet the burst test requirement after the 
pressure cycling test. These commenters believed such additional 
material would significantly increase the container's cost and weight 
to the extent that the container would no longer be economically viable 
to produce. They further stated that most containers that are currently 
produced to meet NGV2 or RSPA requirements would not be able to meet 
this requirement. In contrast, EDO and Metropolitan Suburban Bus 
Authority (MSBA) favored the use of sequential testing.
    After reviewing the comments and other available information, NHTSA 
has decided not to require sequential testing. The agency believes that 
using different containers in the pressure cycling and burst tests will 
provide an adequate measure of both the container's initial strength 
and its durability over its life, without imposing new cost burdens on 
the industry. The agency notes that such testing is consistent with the 
way in which industry currently tests under both NGV2 and RSPA 
standards. The agency further notes that in testing for compliance with 
some FMVSSs, the agency allows a manufacturer to use a separate vehicle 
or component for different tests within a standard. For example, three 
vehicles are crashed in Standard No. 301, and different brake hoses are 
used for various tests in Standard No. 106, Brake Hoses.
4. Failure Criteria
    In the NPRM, NHTSA proposed that to pass the burst test, a 
container would have to meet the same two performance criteria as in 
the pressure cycling test: (1) No leakage, and (2) no permanent 
circumferential deformation of more than one percent. The purpose of 
these requirements was to provide objective means to evaluate a 
container's compliance strength. NGV2 includes the no leakage 
criterion, but not the one percent circumferential deformation 
criterion. As explained in the section on the pressure cycling test, 
the deformation requirement was based on SAE Recommended Practice J10, 
August 1985, which addresses the performance of metal air brake 
reservoirs. The agency proposed a circumferential deformation limit to 
aid in determining a container's impending failure.
    After reviewing the comments, NHTSA is adopting the no leakage 
criterion to evaluate failure of the burst test. The agency has decided 
not to adopt the one percent deformation criterion because the agency 
believes that circumferential deformation is not a meaningful measure 
of a fuel container's impending failure in the burst test. See the 
section above regarding the pressure cycling test for a more 
comprehensive discussion about the agency's decision not to adopt the 
pressure deformation criterion.

E. Bonfire Test

1. Performance Requirements
    In the NPRM, NHTSA proposed performance requirements for CNG fuel 
containers to address the need to withstand high temperatures and 
pressures without catastrophic failure. Large pressure increases due to 
exposure to flames could cause the CNG to escape catastrophically and 
result in an explosive fire. The agency proposed that the ability to 
withstand high temperatures and pressures be provided by a pressure 
relief device. More specifically, it proposed that compliance would be 
determined by first pressurizing the fuel container to 100 percent of 
service pressure with nitrogen or air and placing it over a bonfire 
until the container's contents are completely vented through a pressure 
relief device. A pressure relief device can prevent a container from 
experiencing high pressure for long periods of time. The agency 
proposed a second test to be conducted in the same manner, except the 
container would be pressurized to 25 percent of the service pressure. 
The second test would evaluate container performance when containers 
are partially filled. The purpose of the test is to reduce the 
explosion potential of CNG containers when exposed to high temperatures 
and pressures.
    The proposed requirements were based on NGV2. However, there were 
two differences between the agency's proposal and NGV2. First, under 
the NPRM, the container would be pressurized with nitrogen or air; in 
NGV2, it is pressurized by CNG. Second, under the NPRM, all fuel 
containers would be required to use a pressure relief device to 
completely vent the container's contents; in NGV2, the test is run for 
20 minutes or until the container is completely vented, whichever comes 
first. Therefore, under NGV2, a manufacturer could establish compliance 
either by a container successfully withstanding the test conditions for 
20 minutes without bursting or by completely venting its contents by 
means of a pressure relief device at some point during that 20 minute 
period. In the NPRM, the agency sought comment about whether to allow 
an alternative way of demonstrating compliance with the bonfire test 
that did not depend upon a pressure relief device. Under the 
alternative, a container would be considered to have passed the test if 
it did not burst during the test period. Compliance with the 
alternative would be achieved by designing a container so that it has 
sufficient strength to enable it to sustain the heat and pressure 
buildup during the test.
    Eleven commenters addressed the issue of whether containers should 
be required to have a pressure relief device. NGVC, EDO, ARC, Flxible, 
Manchester, Thomas, and MSBA agreed with the proposal to require 
containers to be equipped with such a device. They stated that a 
pressure relief device is an integral part of a CNG container and that 
its importance warrants a requirement that each container have one. In 
contrast, Brunswick, Comdyne, Pressure Technology, and AAMA stated that 
containers should not be required to have a pressure relief device 
because such a requirement would be design restrictive. Brunswick and 
Pressure Technology stated that the container should be required to 
``safely vent'' its contents without rupturing, whether the venting is 
done through a pressure relief device or the container wall. AAMA 
stated that a container should pass the requirement if it possesses 
enough strength to retain its contents throughout the test. ARC 
believed that the container sidewalls should not be permitted to 
rupture during the bonfire test.
    After reviewing the comments, NHTSA has determined that each CNG 
container must be equipped with a pressure relief device. This is 
necessary because each CNG fuel container needs to possess a means of 
releasing its contents in case the internal pressure or temperature 
reaches a dangerous level. By requiring containers to be equipped with 
a pressure relief device, the agency will ensure the safety of 
individuals, such as vehicle occupants and rescue personnel, who would 
be near a CNG vehicle in a fire. The agency notes that the conditions 
experienced in the bonfire test may be less severe than certain real-
world crash situations. Therefore, the agency is adopting a more 
conservative approach and requiring a pressure relief device for all 
containers. In addition, such a requirement is consistent with the 
practice of most container manufacturers and NGV2 which requires such a 
device on all containers.
    Based on the comments, NHTSA has decided to adopt NGV2's test 
criteria that allows the test to be completed after 20 minutes or when 
the container has completely vented, whichever comes first. Adopting 
these criteria alters the test in that while still requiring a pressure 
relief device, a container could comply with the bonfire test if it 
either completely vents its contents by means of a pressure relief 
device at some point during that 20 minute period or by successfully 
retaining the container's entire contents without bursting for the 
duration of the bonfire test (i.e., 20 minutes). The agency believes 
that each criterion appropriately measures a container's ability to 
withstand high temperature and pressure because the bonfire test 
represents extreme conditions. The agency emphasizes that in either 
case the CNG container must be equipped with a pressure relief device.
    NHTSA disagrees with the approach advocated by AAMA, Brunswick and 
Pressure Technology to allow containers to ``safely vent'' their 
contents from an area other than the pressure relief device such as the 
sidewall. The agency acknowledges that, as an alternative to a pressure 
relief device, pressure relief can be accomplished by allowing the 
overpressurized container to vent its contents at a controlled rate, 
without fragmentation, through the container's sidewall. However, there 
would be significant problems with this approach. First, it would not 
afford as high a degree of safety as requiring a pressure relief 
device. The agency continues to believe that the safest way to release 
CNG from an overpressurized container is through a pressure relief 
device because some sidewall ruptures could result in fragments being 
propelled from the container. Second, it would raise potential 
enforceability problems since the concepts of ``release its contents at 
a controlled rate'' and ``rupture without fragmentation'' are difficult 
to define objectively. Based on the above considerations, NHTSA has 
decided to require each CNG fuel container to either completely vent 
its contents through a pressure relief device or not burst when tested 
in accordance with the test conditions.
2. Types of Pressure Relief Devices
    The proposal did not specify the use of a particular type of 
pressure relief device. The agency is aware of three types of devices 
currently being used: (1) The rupture disc, which is designed to 
release CNG in the container when it reaches a specific pressure, (2) 
the fusible plug, which is designed to release CNG in the container 
when it reaches a specific temperature, and (3) a device that combines 
these two devices.
    Four commenters recommended the use of specific types of pressure 
relief devices. EDO recommended that the agency require the fusible 
plug device and prohibit the rupture disc device. EDO stated that a 
combination of hot conditions and overfill at the refueling pump could 
cause a rupture disc to activate, releasing CNG and causing a 
potentially dangerous situation. It further believed that the safety 
factor in the burst test would be sufficient to prevent over 
pressurization and that the pressure relief device should only open in 
a fire situation. Flxible stated that the agency should require a 
fusible plug to ensure pressure relief of partially filled containers 
subject to heat or fire. NYCFD stated that the agency should prohibit 
the combination fusible plug and rupture disc devices, claiming that 
over-charged containers exposed to high ambient temperature are likely 
to fail whether or not they are exposed to fire. Thomas commented that 
the agency should require the combination fusible plug and rupture disc 
device because it is required by NFPA 52.\7\
---------------------------------------------------------------------------

    \7\NFPA 52, Standard for Compressed Natural Gas (CNG) Vehicular 
Fuel Systems, is a voluntary standard adopted by the National Fire 
Protection Association that specifies guidelines for the ``design 
and installation of CNG engine fuel systems on vehicles of all types 
including aftermarket and OEMs and to their associated fueling 
(dispensing) systems.'' (NFPA 52, Sec. 1-1)
---------------------------------------------------------------------------

    After reviewing the comments, NHTSA has concluded that the standard 
should not specify the type of pressure relief device with which a 
container may be equipped. The NPRM and SNPRM did not provide 
sufficient notice for the agency to adopt such a specification as part 
of this final rule. Further, the agency believes that the bonfire test, 
which is performed at both 100 percent of service pressure and 25 
percent of service pressure, will adequately evaluate a container's 
ability to vent its contents in a high temperature/pressure situation. 
In the first test, the combination of the 100 percent service pressure 
condition and the high heat from the bonfire will cause the container's 
pressure to increase rapidly. This test evaluates a container's ability 
to vent its contents at high temperatures and pressures. In the second 
test, the 25 percent service pressure condition and the heat will cause 
the container's temperature to increase before the pressure in the 
container reaches a critical point. This test evaluates a container's 
ability to vent its contents at high temperatures, where the container 
is at a less than full condition.
3. Shielding
    NHTSA notes that there are two types of shielding that can affect 
the performance of pressure relief devices in bonfire tests: (1) 
``Vehicle-based protective shielding'' that is placed around the 
container in the vehicle to protect the container from surrounding 
heat, and (2) ``test shielding'' that is placed over the pressure 
relief device to prevent flames from contacting the device. Test 
shielding is, as the name suggests, installed only for the purpose of 
conducting bonfire tests. Unlike vehicle-based protective shielding, it 
is not used to affect real world performance.
    In the NPRM, NHTSA recognized that some CNG vehicles may have 
vehicle-based shielding installed to protect the containers from 
exposure to heat. Nevertheless, the agency proposed that no vehicle-
based shielding be used during the bonfire test because Standard No. 
304 is an equipment standard, and applies to CNG containers, not to 
vehicles. Further, since the presence or amount of shielding could vary 
from vehicle to vehicle, the agency tentatively concluded that the 
containers should be tested in the worst case situation, i.e., without 
any vehicle-based shielding. Nevertheless, the agency stated that it 
did not want to discourage vehicle manufacturers from including 
shielding in CNG vehicles as an added safety feature.
    NHTSA received six comments addressing the use of vehicle-based 
shielding during the bonfire test. PST, EDO, ARC, Ontario, and NGVC 
agreed with the agency that vehicle-based shielding of the container 
should not be used during the bonfire test. They believed that such 
shielding could detract from or mask the results of the test. In 
contrast, AAMA stated that ``[i]f a manufacturer chooses to add the 
additional expense to protect the fuel tank from exposure to potential 
flame, the protection ought to be allowed in any test as representative 
of the tank's use in the vehicle.''
    After reviewing the comments, NHTSA has decided not to permit 
vehicle-based shielding of the container during the bonfire test. As 
explained in the NPRM, the bonfire test is intended to evaluate the 
container and not the vehicle. Since this is an equipment standard, the 
tests are designed to ensure that the containers are safe for 
installation in any vehicle, regardless of the amount of protective 
vehicle shielding, if any, with which it is equipped. The agency 
disagrees with AAMA's contention. Using vehicle shielding in compliance 
testing would not ensure that a container could perform safely under 
worst case conditions (i.e., no vehicle-based shielding of any type or 
extent) that the container could encounter during its service life 
(e.g., if the container is subsequently placed in a different vehicle).
    Test shielding consists of a metal plate over the pressure relief 
device and is permitted, but not required, under NGV2 for purposes of 
the horizontal bonfire test. In the horizontal test, the CNG container 
is positioned over the bonfire with its longitudinal axis in a 
horizontal position. In the NGV2 vertical bonfire test (container 
longitudinal axis in a vertical position), pressure relief device 
shielding is also permitted, but not required, except where the CNG 
container is fitted with a pressure relief device on both ends. In that 
case, the bottom pressure relief device must be shielded. The goal is 
to not allow flames to impinge directly on any relief device. This may 
be done through test shielding, or by orienting the container so as to 
avoid flame impingement on any pressure relief device. Without this 
metal plate, the flames could contact the pressure relief device, 
possibly causing it to vent the container prematurely. If this 
occurred, the bonfire test results would neither evaluate the CNG 
container as a whole nor accurately reflect the container's pressure 
relief characteristics.
    CGA and PST opposed allowing shielding of the pressure relief 
device during the bonfire test. They commented that shielding the 
pressure relief device during the bonfire test would not be 
representative of a real-world crash fire situation. CGA stated that 
allowing, but not requiring shielding to be placed around pressure 
relief devices could produce non- repeatable results. PST stated that 
excessive shielding around the pressure relief device could cause an 
otherwise acceptable design to fail the test, but did not elaborate as 
to how this could occur.
    NHTSA has decided to require test shielding of the pressure relief 
device during the horizontal bonfire test. The agency notes that the 
purpose of this test is to replicate the effect of fires on the 
pressure relief device and the fuel container as a system. Requiring 
shielding will assure that the bonfire test is evaluating the fuel 
container as a whole, rather than merely the pressure relief device, 
since a flame that impinges on the pressure relief device, could 
activate prematurely. Requiring shielding, rather than simply allowing 
it, will assure repeatable and consistent test results. The rule also 
requires shielding of the pressure relief device during the vertical 
bonfire test, except where the container is fitted with a pressure 
relief device on only one end. In that case, the container is 
positioned with the pressure relief device on top, so as to avoid 
direct contact with the flame.
4. Test Gas and Pressure
    In the NPRM, NHTSA proposed that the CNG container be pressurized 
with either nitrogen or air to 100 percent of service pressure for the 
bonfire test. The agency acknowledged that NGV2 specifies the use of 
CNG, but tentatively concluded that using nitrogen or air as the test 
gas would be safer than using CNG.
    AAMA and Tecogen recommended that CNG be used as the test gas. 
Tecogen further commented that the container manufacturers have 
historically conducted such tests using CNG and are therefore well 
aware of the necessary safety precautions. It further stated that using 
CNG as the test gas would reveal the pressure relief valve's 
effectiveness with respect to the discharge rate. AAMA commented that 
CNG should be used as the test gas because the thermal properties of 
CNG differ from those of nitrogen and air and NGV2 specifies the use of 
CNG as the test gas. AAMA also recommended that the CNG containers be 
pressurized at the start of the test to 95 to 100 percent of service 
pressure, but offered no rationale.
    After reviewing the comments, NHTSA has determined that using CNG 
as the test gas would better reflect the real-world conditions in a 
fire, since the test gas would be the same as the gas used in CNG 
containers. The agency notes that the bonfire test addresses the 
responsiveness of the pressure relief device and that air and nitrogen 
have different thermal properties than CNG. Therefore, the pressure 
relief device might perform differently if air or nitrogen were used 
instead of CNG. In the NPRM, the agency explained that using CNG as a 
test gas might not be safe. These initial concerns have been allayed by 
the comments indicating that manufacturers are aware of and accustomed 
to taking the necessary safety precautions when using CNG as a test gas 
to evaluate a container. NHTSA notes that it decided not to specify CNG 
as the test gas in the CNG vehicle standard. Nevertheless, the agency 
believes that differences in reaction to heat are important for the 
bonfire test, which involves high temperatures, but not for crash 
tests, which do not involve such temperatures.
    NHTSA continues to believe that it is necessary to pressurize the 
CNG container to 100 percent of service pressure at the outset of the 
test. The agency has determined that the containers need to be tested 
at full service pressure to represent the worst case scenario.
5. Wind Velocity and Direction
    In the NPRM and SNPRM, NHTSA did not address the allowable wind 
velocity and direction. The agency received comments from NGVC, CGA, 
and PST stating that a limit should be placed on wind velocity to 
increase the bonfire test's repeatability.
    After reviewing the comments, NHTSA has decided to specify that the 
average wind velocity at the container during the test may not exceed 
2.24 meters per second (5 mph). The agency believes that permitting 
higher crosswinds would vary or reduce the flame's heat. Therefore, 
placing limits on the crosswind assures the test's repeatability and 
the level of stringency that the agency anticipated in proposing this 
test.
6. Bonfire Fuel
    In the NPRM, NHTSA proposed that the fire for the bonfire tests be 
generated using No. 2 diesel fuel. This fuel type was proposed so that 
the standard would be consistent with the bonfire test in NGV2, which 
also specifies this type of fuel.
    NGVC, CGA, AAMA, and Norris commented that the agency should 
specify a different fuel to generate the bonfire that is more 
environmentally sound. CGA stated that the large amounts of smoke that 
would be created by burning the diesel fuel are contrary to the 
environmental objectives of developing CNG vehicles. NGVC and Norris 
suggested using a CNG or propane grill for the test.
    After reviewing the comments and other available information, NHTSA 
has decided to specify the use of No. 2 diesel fuel in the final rule. 
The agency is aware of the environmental problems associated with this 
type of fuel and will further study whether other fuels should be used 
to generate the bonfire test. However, until the agency can determine 
that a different fuel is an appropriate replacement for diesel fuel, 
the Standard will specify No. 2 diesel fuel for use in the bonfire 
test.
7. Bonfire Test Fuel Pan Depth
    In the NPRM, NHTSA proposed that the bonfire test pan containing 
No. 2 diesel fuel be at least 100 centimeters (cm) deep. The agency 
specified a depth to ensure that there would be an adequate amount of 
fuel to run the test.
    AAMA, Comdyne, CGA, Alusuisse, and PST commented that the fuel pan 
depth was excessive. Alusuisse stated that a pan of the proposed size 
would contain more than 1,000 liters of fuel. PST stated that a 100 
millimeter (mm) depth would be more reasonable. CGA, AAMA, and Comdyne 
stated that the depth of the fuel pan should not be specified so long 
as a sufficient quantity of fuel is provided for the test.
    The agency intended to propose a depth of 100 mm. However, due to a 
typographical error, it proposed a depth of 100 cm. NHTSA agrees that a 
fuel pan with a depth of at least 100 cm would be too deep. NHTSA also 
agrees that the fuel pan's depth does not need to be specified, 
provided that there is a sufficient amount of fuel to maintain the fire 
for the duration of the test. Accordingly, the agency has removed the 
requirement for fuel pan depth and has replaced it with the provision 
that there be ``sufficient fuel to burn for at least 20 minutes.'' The 
agency believes that this provision is consistent with the test's 
purpose of simulating a severe fire by raising the container's 
temperature and pressure by completely surrounding it with flames 
produced by a specific fuel type.

F. Labeling Requirements

    In the NPRM, NHTSA proposed to require that container manufacturers 
certify that each of their containers complies with the proposed 
equipment requirements and permanently label the container with the 
following information: the symbol ``DOT'' to constitute a certification 
by the manufacturer that the container conforms to all requirements of 
the standard; the date of manufacture of the container; the name and 
address of the container manufacturer; and the maximum service 
pressure. The agency stated that labeling the container would provide 
vehicle manufacturers and consumers with assurance that they are 
purchasing containers that comply with the Federal safety standards. In 
addition, the agency believed that the proposed requirement would 
facilitate the agency's enforcement efforts by providing a ready means 
of identifying the container and its manufacturer.
    EDO, NGVC, Thomas, NYCFD, and Volvo GM addressed the proposed 
labeling requirements. EDO and NYCFD stated that the label should 
include the maximum fill pressure at a location close to the fill 
receptacle. NGVC recommended that a blank area for the container 
installation date be included in the label to be filled in by the 
installer. Volvo GM stated that only containers that are manufactured 
after the standard's effective date, and therefore actually subject to 
the standard, should be entitled to display the DOT symbol as 
certification of compliance with the standard. Thomas stated, without 
elaboration, that the labeling requirements of NGV2 should be adopted. 
NHTSA's proposal did not include certain additional information 
included in NGV2, including the type of container, inspector symbols, 
trademarks, manufacturer's part number, and serial numbers.
    After reviewing the comments, NHTSA has decided to adopt the 
proposed labeling requirements with a slight modification from the 
proposed format. In item (a), the agency has modified the proposal 
which states ``The tank manufacturer's name and address'' to state the 
following: include the statement that ``If there is a question about 
the proper use, installation, or maintenance of this container, contact 
[manufacturer's name, address, and telephone number].''
    The agency has decided not to require the other additional items of 
information in NGV2 since the agency did not propose the inclusion of 
such information in the NPRM. Notwithstanding the agency's decision not 
to require this additional information, a manufacturer may list such 
information on the label, provided the additional information does not 
obscure or confuse the required information. In particular, NHTSA 
encourages manufacturers to include the container type, e.g., Type 1, 
2, 3 or 4, since the agency has decided to adopt NGV2's design and 
material specifications in this final rule. Specifying the type of 
container should facilitate oversight of compliance tests since each 
type of container is required to undergo hydrostatic burst tests, but 
with different safety factors.
    In the upcoming SNPRM, NHTSA anticipates proposing additional 
requirements about the CNG fuel container's label, including the 
container type. In addition, the agency anticipates proposing that the 
label include an additional statement addressing the container's 
inspection and maintenance. Specifically, the label would state that 
``This container should be visually inspected after an accident or fire 
or at least every 12 months for damage and deterioration in accordance 
with the applicable Compressed Gas Association guidelines.'' The agency 
believes that such a statement would alert owners to the desirability 
for reinspection over time or in the event of an accident. NHTSA will 
also propose requirements related to the label's location, in response 
to EDO's and NYCFD's comment that the maximum service pressure should 
be labeled in an area close to the fill receptacle.

G. Leadtime

    In the NPRM, NHTSA proposed to make the equipment requirements 
effective on September 1, 1994. The agency believed that this would 
provide a reasonable time period for manufacturers to make minor 
modifications in container design. This proposal was based on the 
agency's belief that the proposed requirements were similar to RSPA 
standards currently in effect. The agency requested comment on the 
feasibility of this effective date.
    NHTSA received eleven comments about the proposed effective date 
applicable to the container requirements. The commenters were TMC, the 
U.S. Department of Energy, TBB, Oklahoma Gas, NGVC, EDO, Volvo/GM, 
AAMA, ARC, Navistar, and NGV Systems. EDO and Navistar requested that 
the final rule be issued as early as possible. DOE and Oklahoma Gas 
recommended an effective date of September 1, 1995. NGVC recommended an 
effective date of September 1, 1996, unless NGV2 were adopted which 
would permit an immediate supply of containers. NGV Systems stated that 
an earlier effective date would be difficult to meet since the rule, as 
proposed, would require new tooling, process development, and perhaps 
equipment modification. ARC stated that the rule, as proposed, would 
require major modifications, since its containers have been designed to 
comply with NGV2. AAMA and Volvo/GM stated that the effective dates for 
the vehicle requirements and the equipment requirements should not be 
concurrent.
    NHTSA notes that these comments were based on the requirements, as 
proposed in the NPRM. Since the final rule has been made essentially 
consistent with NGV2 (with the exception of carbon fiber containers), 
the agency anticipates that container manufacturers can for the most 
part already certify that containers, other than carbon fiber ones, 
comply with the new standard. This belief is based on comments on the 
NPRM and meetings with NGVC, the CGA, and CNG container manufacturers. 
With regard to manufacturers of carbon fiber containers, EDO indicated 
that it already complies with the standard and Brunswick indicated that 
it would need less than one month lead time for a safety factor greater 
than 2.25. Brunswick further stated that it would need an unspecified 
time period to modify the mounting brackets and other hardware. The CNG 
industry groups have informed the agency that they want a CNG fuel 
container 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 Federal standards to be in 
place as soon as possible, given the expected increased demand for CNG 
containers 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 containers are not marketed.
    After reviewing the comments, NHTSA has decided to establish an 
effective date six months after the final rule is issued. As explained 
above, most CNG containers can be certified to comply with the new 
Federal motor vehicle safety standard since they already comply with 
NGV2 or can be modified so that they comply within six months. 
Nevertheless, the agency believes that it is necessary to provide a 
leadtime of six months to allow manufacturers time to make whatever 
design changes are necessary and to conduct testing so that they can 
certify that their containers comply with the new standard. In the 
meantime, prior to the standard's effective date, the industry is free 
to advertise containers as meeting the CNG equipment standard that will 
take effect in six months.\8\ Manufacturers have taken the approach of 
seeking early compliance with respect to other agency requirements such 
as those relating to dynamic side impact protection and air bags. 
Therefore, the agency encourages manufacturers to seek, to the extent 
feasible, to manufacture their CNG containers to meet these new 
requirements before the date the standard takes effect.
---------------------------------------------------------------------------

    \8\However, the agency emphasizes that a manufacturer may not 
certify a container as meeting the equipment standard until the 
standard goes into effect. Under the Vehicle Safety Act, a 
certification is a statement that a vehicle or item of equipment 
meets all applicable Federal Motor Vehicle Safety Standards that are 
then in effect. Therefore, until a standard is effective, 
manufacturers may not certify compliance with it.
---------------------------------------------------------------------------

    With regard to the concern expressed by AAMA and Volvo GM that the 
effective date of the container regulation should precede that of the 
vehicle regulation, AAMA based its comments on the belief that it will 
need to know the performance of the containers it will use in the fuel 
systems of its vehicles. NHTSA notes that CNG containers now typically 
meet NGV2 and thus should comply with NHTSA's standards. Therefore, 
AAMA members already have access to and detailed knowledge about 
containers that should meet the new requirements.

H. Benefits

    In the NPRM, NHTSA addressed the proposal's benefits with respect 
to CNG vehicles. The notice did not directly address the benefits of 
regulating the CNG fuel containers.
    NHTSA received no comments directly addressing the benefits of 
regulating CNG containers. Brunswick criticized the proposal, believing 
that it would place carbon fiber containers at a competitive 
disadvantage. Brunswick stated that the proposed single burst factor 
would provide less benefits than if the agency adopted NGV2.\9\
---------------------------------------------------------------------------

    \9\Because NHTSA is adopting Brunswick's request for multiple 
safety factors, that commenter's concern about a single safety 
factor is moot.
---------------------------------------------------------------------------

    NHTSA anticipates that the number of CNG fuel vehicles will 
increase greatly in the near future, in light of directives by the 
Clinton Administration\10\ and legislation by Congress to develop 
vehicles powered by cleaner burning fuels. This final rule will 
increase the safety of this growing population of vehicles.
---------------------------------------------------------------------------

    \10\Executive Order 12844 increased by 50 percent the number of 
alternatively 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.
---------------------------------------------------------------------------

I. Costs

    In the NPRM, NHTSA stated that each container would cost $600. The 
agency further stated that the container testing costs would range from 
approximately $4,050 to $8,600 for each model of container.
    NGVC, NGV Systems, PST, Brunswick, ARC, Thomas Built, and Flxible 
addressed the costs of the proposal with respect to CNG containers. 
NGVC and the CNG container manufacturers stated that the proposal, 
especially given the single safety factor in the burst test 
requirements, significantly understated the costs of the rulemaking. 
Brunswick stated that container manufacturers would incur significant 
costs since they would have to redesign and requalify their currently 
designed tanks. As a result, it believed that the CNG containers would 
be more expensive and heavier. It estimated that the proposal would 
increase costs between 10 percent and 55 percent, depending on the 
material and method of construction. Brunswick further stated that this 
proposal would add many millions of dollars on an industry-wide basis.
    NGVC commented that the qualification tests could cost $20,000 for 
each model of container since many tests will be required on prototype 
containers. It stated that some manufacturers estimate that the design, 
manufacture, and qualification costs could approach $150,000 per 
container model, a figure that greatly exceeded NHTSA's estimate of 
$74,000.
    NHTSA believes that the basis for the comments about the costs of 
this rulemaking have been largely eliminated except in connection with 
carbon fiber tanks. The comments were based on the proposal for a 
single safety factor of 3.5 for all types of tanks. As noted above, the 
agency has decided to specify multiple safety factors that are 
consistent with NGV2 except in the case of the factors for carbon fiber 
containers. Since all the container manufacturers commenting on the 
proposal either already certify to or can comply with NGV2 without any 
design changes, the cost to manufacturers will be minimal for noncarbon 
fiber tanks.

V. 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 not reviewed 
under E.O. 12866, ``Regulatory Planning and Review.'' This action has 
been determined to be ``nonsignificant'' under the Department of 
Transportation's regulatory policies and procedures. 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 the cost for the pressure 
cycling, burst, and bonfire testing will range from $9,000 to $21,725 
per container size and type. In addition, the cost of the containers 
used in the test is estimated to range from $1,800 to $6,600. Since the 
safety factors in the burst test applicable to carbon fiber containers 
are more stringent than those in NGV2, the cost of those containers 
will increase. Based on comments by Brunswick and other information, 
the switch from carbon fiber containers meeting a 2.25 safety factor to 
carbon fiber containers meeting the factors adopted in this final rule 
will increase the container cost and the lifetime fuel costs about 8.75 
percent for vehicles equipped with Type 2 containers. Those costs would 
be range from $115 for passenger cars to $602 for heavy trucks. The 
switch would increase costs about 37.1 percent for vehicles equipped 
with Type 3 and Type 4 containers, resulting in a cost increase ranging 
from $496 for cars to $2,560 for heavy trucks.

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 businesses manufacturing CNG 
fuel containers are not 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. No 
state has adopted requirements regulating CNG containers.

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. 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 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, Incorporation by reference, Motor vehicle safety, Motor 
vehicles.

PART 571--[AMENDED]

    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; 
delegation of authority at 49 CFR 1.50.

    2. Section 571.5 is amended by redesignating (b)(7) as (b)(10) and 
adding new paragraphs (b)(7) through (b)(9), to read as follows:


Sec. 571.5  Matter incorporated by reference.

* * * * *
    (b) * * *
    (7) Standards of Suppliers of Advanced Composite Materials 
Association (SACMA). They are published by Suppliers of Advanced 
Composite Materials Association. Information and copies may be obtained 
by writing to: Suppliers of Advanced Composite Materials Association, 
1600 Wilson Blvd., Suite 1008, Arlington, VA 22209.
    (8) Standards of the American Society of Mechanical Engineers 
(ASME). They are published by The American Society of Mechanical 
Engineers. Information and copies may be obtained by writing to: The 
American Society of Mechanical Engineers, 345 East 47th Street, New 
York, NY 10017.
    (9) Computer Analysis by the National Aeronautics and Space 
Administration (NASA). This was conducted by the National Aeronautics 
and Space Administration. Information and copies may be obtained by 
writing to: National Aeronautics and Space Administration, 600 
Independence Avenue SW, Washington, DC 20546.
* * * * *
    3. A new Sec. 571.304, Standard No. 304; Compressed Natural Gas 
Fuel Container Integrity, is added to Part 571, to read as follows:


Sec. 571.304  Standard No. 304; Compressed Natural Gas Fuel Container 
Integrity.

    S1. Scope. This standard specifies requirements for the integrity 
of compressed natural gas (CNG), motor vehicle fuel containers.
    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 containers designed to 
store CNG as motor fuel on-board any motor vehicle.
    S4. Definitions.
    Brazing means a group of welding processes wherein coalescence is 
produced by heating to a suitable temperature above 800  deg.F and by 
using a nonferrous filler metal, having a melting point below that to 
the base metals. The filler metal is distributed between the closely 
fitted surfaces of the joint by capillary attraction.
    Burst pressure means the highest internal pressure reached in a CNG 
fuel container during a burst test at a temperature of 21  deg.C (70 
deg.F).
    CNG fuel container means a container designed to store CNG as motor 
fuel on-board a motor vehicle.
    Fill pressure means the internal pressure of a CNG fuel container 
attained at the time of filling. Fill pressure varies according to the 
gas temperature in the container which is dependent on the charging 
parameters and the ambient conditions.
    Full wrapped means applying the reinforcement of a filament or 
resin system over the entire liner, including the domes.
    Hoop wrapped means winding of filament in a substantially 
circumferential pattern over the cylindrical portion of the liner so 
that the filament does not transmit any significant stresses in a 
direction parallel to the cylinder longitudinal axis.
    Hydrostatic pressure means the internal pressure to which a CNG 
fuel container is taken during testing set forth in S5.4.1.
    Liner means the inner gas tight container or gas cylinder to which 
the overwrap is applied.
    Service pressure means the internal settled pressure of a CNG fuel 
container at a uniform gas temperature of 21  deg.C (70  deg.F) and 
full gas content. It is the pressure for which the container has been 
constructed under normal conditions.
    Stress ratio means the stress in the fiber at minimum burst 
pressure divided by the stress in the fiber at service pressure.
    S5  Container and material requirements.
    S5.1  Container designations. Container designations are as 
follows:
    S5.1.1  Type 1--Non-composite metallic container means a metal 
container.
    S5.1.2  Type 2--Composite metallic hoop wrapped container means a 
metal liner reinforced with resin impregnated continuous filament that 
is ``hoop wrapped.''
    S5.1.3  Type 3--Composite metallic full wrapped container means a 
metal liner reinforced with resin impregnated continuous filament that 
is ``full wrapped.''
    S5.1.4  Type 4--Composite non-metallic full wrapped container means 
resin impregnated continuous filament with a non-metallic liner ``full 
wrapped.''
    S5.2  Material designations.
    S5.2.1  Steel containers and liners.
    (a) Steel containers and liners shall be of uniform quality. Only 
the basic oxygen or electric furnace processes are authorized. The 
steel shall be aluminum killed and produced to predominantly fine grain 
practice. The steel heat analysis shall be in conformance with one of 
the following grades:

                                         Table One--Steel Heat Analysis                                         
----------------------------------------------------------------------------------------------------------------
                                               Chrome-Molybdenum                              Carbon-Manganese  
               Grade element                        percent          Carbon-Boron percent         percent       
----------------------------------------------------------------------------------------------------------------
Carbon.....................................  0.25 to 0.38.........  0.27 to 0.37.........  0.40 max.            
Manganese..................................  0.40 to 1.05.........  0.80 to 1.40.........  1.65 max.            
Phosphorus.................................  0.015 max............  0.015 max............  0.025 max.           
Sulfur.....................................  0.010 max............  0.010 max............  0.010 max.           
Silicon....................................  0.15 to 0.35.........  0.30 max.............  0.10/0.30            
Chromium...................................  0.80 to 1.15.........  N/A..................  N/A                  
Molybdenum.................................  0.15 to 0.25.........  N/A..................  N/A                  
Boron......................................  N/A..................  0.0005 to 0.003......  N/A                  
Aluminum...................................  0.02 to 0.07.........  0.02 to 0.07.........  0.02/0.07            
----------------------------------------------------------------------------------------------------------------
\1\``N/A'' means not applicable.                                                                                

    (b) Incidental elements shall be within the limits specified in the 
Standard Specification for Steel, Sheet and Strip, Alloy, Hot-Rolled 
and Cold-Rolled, General Requirements for ASTM A 505 (1987).
    S5.2.1.1  When carbon-boron steel is used, the test specimen is 
subject to a hardenability test in accordance with the Standard Method 
for End-Quench Test For Hardenability of Steel, ASTM A 255 (1989). The 
hardness evaluation is made 7.9 mm (\5/16\ inch) from the quenched end 
of the Jominy quench bar.
    S5.2.1.2  The test specimen's hardness shall be at least Rc 
(Rockwell Hardness) 33 and no more than Rc 53.
    S5.2.2  Aluminum containers and aluminum liners. (Type 1, Type 2 
and Type 3) shall be 6010 alloy, 6061 alloy, and T6 temper. The 
aluminum heat analysis shall be in conformance with one of the 
following grades:

                    Table Two--Aluminum Heat Analysis                   
------------------------------------------------------------------------
                                                           6061 alloy   
           Grade element            6010 alloy percent       percent    
------------------------------------------------------------------------
Magnesium.........................  0.60 to 1.00......  0.60 to 1.20    
Silicon...........................  0.80 to 1.20......  0.40 to 0.80    
Copper............................  0.15 to 0.60......  0.15 to 0.40    
Chromium..........................  0.05 to 0.10......  0.04 to 0.35    
Iron..............................  0.50 max..........  0.70 max.       
Titanium..........................  0.10 max..........  0.15 max.       
Manganese.........................  0.20 to 0.80......  0.15 max.       
Zinc..............................  0.25 max..........  0.25 max.       
Bismuth...........................  0.003 max.........  0.003 max.      
Lead..............................  0.003 max.........  0.003 max.      
Others, Each\1\...................  0.05 max..........  0.05 max.       
Others, Total\1\..................  0.15 max..........  0.15 max.       
Aluminum..........................  Remainder.........  Remainder.      
------------------------------------------------------------------------
\1\Analysis is made only for the elements for which specific limits are 
  shown, except for unalloyed aluminum. If, however, the presence of    
  other elements is indicated to be in excess of specified limits,      
  further analysis is made to determine that these other elements are   
  not in excess of the amount specified. (Aluminum Association Standards
  and Data--Sixth Edition 1979.)                                        

    S5.2.3  Structural reinforcing filament material shall be 
commercial grade E-glass, commercial grade S-glass, aramid fiber or 
carbon fiber. Filament strength shall be tested in accordance with the 
Standard Test Method for Tensile Properties of Glass Fiber Strands, 
Yarns, and Rovings Used in Reinforced Plastics, ASTM D 2343 (1967, 
Reapproved 1985), or SACMA Recommended Test Method for Tow Tensile 
Testing of Carbon Fibers, SRM 16-90, 1990. Fiber coupling agents 
(sizing) shall be compatible with the resin system. If carbon fiber 
reinforcement is used the design shall incorporate means to prevent 
galvanic corrosion of metallic components of the fuel container.
    S5.2.4  The resin system shall be epoxy, modified epoxy, polyester, 
vinyl ester or thermoplastic.
    S5.2.4.1  The resin system is tested on a sample coupon 
representative of the composite overwrap in accordance with the 
Standard Test Method for Apparent Interlaminar Shear Strength of 
Parallel Fiber Composites by Short-Beam Method, ASTM D 2344, (1984, 
Reapproved 1989) following a 24-hour water boil.
    S5.2.4.2  The test specimen shall have a shear strength of at least 
13.8 MPa (2,000 psi).
    S5.2.5  For nonmetallic liners, the permeation of CNG through the 
finished container's wall at service pressure is less than 0.25 normal 
cubic centimeters per hour per liter water capacity of the container.
    S5.3  Manufacturing processes for composite containers.
    S5.3.1  Composite containers with metallic liners. The CNG fuel 
container shall be manufactured from a metal liner overwrapped with 
resin impregnated continuous filament windings, applied under 
controlled tension to develop the design composite thickness. After 
winding is complete, composites using thermoset resins shall be cured 
by a controlled temperature process.
    S5.3.1.1  Type 2 containers. Type 2 containers shall have a hoop 
wrapped winding pattern.
    S5.3.1.2  Type 3 containers. Type 3 containers shall have a full 
wrapped ``helical or in plane'' and a ``hoop'' wrap winding pattern.
    S5.3.2  Type 4 containers. Composite containers with nonmetallic 
liners shall be fabricated from a nonmetallic liner overwrapped with 
resin impregnated continuous filament windings. The winding pattern 
shall be ``helical or in plane'' and ``hoop'' wrap applied pattern 
under controlled tension to develop the design composite thickness. 
After winding is complete, the composite shall be cured by a controlled 
temperature process.
    S5.3.3  Brazing. Brazing is prohibited.
    S5.3.4  Welding. Welding shall be done in accordance with the 
American Society of Mechanical Engineers (ASME) Boiler and Pressure 
Vessel Code, Section IX, Article II, QW-304 and QW-305 (1992). Weld 
efficiencies shall be in accordance with ASME Boiler and Pressure 
Vessel Code, Section VIII, UW-12 (1989). Any weld shall be subject to 
full radiographic requirements in accordance with ASME Boiler and 
Pressure Vessel Code, Section VIII, UW-51 thru UW-53 (1989). For Type 2 
and Type 3 liners, longitudinal welds and nonconsumable backing strips 
or rings shall be prohibited.
    S5.4  Wall thickness.
    S5.4.1  Type 1 containers.
    (a) The wall thickness of a Type 1 container shall be at least an 
amount such that the wall stress at the minimum prescribed hydrostatic 
test pressure does not exceed 67 percent of the minimum tensile 
strength of the metal as determined by the mechanical properties 
specified in S5.7 and S5.7.1.
    (b) For minimum wall thickness calculations, the following formula 
is used:

TR26SE94.000

Where:

S = Wall stress in MPa (psi).
P = Minimum hydrostatic test pressure in Bar (psig).
D = Outside diameter in mm (inches).
d = Inside diameter in mm (inches).

    S5.4.2  Type 2 containers.
    S5.4.2.1  The wall thickness of a liner to a Type 2 container shall 
be at least an amount such that the longitudinal tensile stress at the 
minimum design burst pressure does not exceed the ultimate tensile 
strength of the liner material as determined in S5.7 and S5.7.1.
    S5.4.2.2   The wall thickness of a liner to a Type 2 container 
shall be at least an amount such that the compressive stress in the 
sidewall of the finished container at zero pressure shall not exceed 95 
percent of the yield strength of the liner as determined in S5.7 and 
S5.7.1 or 95 percent of the minimum design yield strength shown in 
S5.7.3. The maximum tensile stress in the liner at service pressure 
shall not exceed 66 percent of the yield strength.
    S5.4.2.3  Stresses at the end designs at internal pressures between 
no more than 10 percent of service pressure and service pressure shall 
be less than the maximum stress limits in the sidewall as prescribed 
above.
    S5.4.3  Type 3 containers. The wall thickness of a liner to a Type 
3 container shall be such that the compressive stress in the sidewall 
of the finished container at zero pressure shall not exceed 95 percent 
of the minimum yield strength of the liner as determined in S5.7 and 
S5.7.1 or 95 percent of the minimum design yield strength shown in 
S5.7.3
    S5.4.4  Type 4 containers. The wall thickness of a liner to a Type 
4 container shall be such that the permeation rate requirements of this 
specification are met.
    S5.5  Composite reinforcement for Type 2, Type 3, and Type 4 
Containers.
    S5.5.1  Compute stresses in the liner and composite reinforcement 
using National Aeronautics and Space Administration (NASA) NAS 3-6292, 
Computer Program for the Analysis of Filament Reinforced Metal-Shell 
Pressure Vessels, (May 1966).
    S5.5.2  The composite overwrap shall meet or exceed the following 
composite reinforcement stress ratio values shown in Table 3.
    S5.6  Thermal treatment.
    S5.6.1   Steel containers or liners.
    S5.6.1.1  After all metal forming and welding operations, completed 
containers or liners shall be uniformly and properly heat treated under 
the same conditions of time, temperature and atmosphere prior to all 
tests.
    S5.6.1.2  All containers or liners of steel grades ``Chrome-
Molybdenum'' or ``Carbon Boron'' shall be quenched in a medium having a 
cooling rate not in excess of 80 percent that of water. ``Carbon-
Manganese'' steel grades shall be normalized and do not require 
tempering after normalizing.
    S5.6.1.3  All steel temperature on quenching shall not exceed 
926 deg.C (1700 deg.F).
    S5.6.1.4  All containers or liners or steel grades ``Chrome-
Molybdenum'' or ``Carbon Boron'' shall be tempered after quenching at a 
temperature below the transformation ranges, but not less than 
482 deg.C (900 deg.F) for ``Carbon-Boron'' steel or 565 deg.C 
(1050 deg.F) for ``Chrome-Molybdenum'' steel. ``Carbon Manganese'' 
steel grades do not require tempering after normalizing.
    S5.6.2  Aluminum containers or liners (seamless and welded). After 
all forming and welding operations, aluminum containers or liners shall 
be solution heat treated and aged to the T6 temper. The liner and 
composite overwrap shall meet the cycle life and strength requirements 
set forth in S7.1 and S7.2 of this standard.
    S5.7  Yield strength, tensile strength, material elongation (metal 
containers and metal liners only). To determine yield strength, tensile 
strength, and elongation of the material, cut two specimens from one 
container or liner. The specimen either has (a) a gauge length of 50 mm 
(2 inches) and a width not over 38 mm (1.5 inches), or (b) a gauge 
length of four times the specimen diameter, provided that a gauge 
length which is at least 24 times the thickness with a width not over 6 
times the thickness is permitted when the liner wall is not over 5 mm 
(3/16 inch) thick. The specimen shall not be flattened, except that 
grip ends may be flattened to within 25 mm (1 inch) of each end of the 
reduced section. Heating of specimens is prohibited.
    S5.7.1  Yield strength. The yield strength in tension shall be the 
stress corresponding to a permanent strain of 0.2 percent based on the 
gauge length.
    S5.7.1.1  The yield strength shall be determined by either the 
``offset'' method or the ``extension under load'' method as prescribed 
by Standard Test Methods for Tension Testing of Metallic Materials, 
ASTM E8 1993.
    S5.7.1.2  In using the ``extension under load'' method, the total 
strain or ``extension under load'' corresponding to the stress at which 
the 0.2 percent permanent strain occurs may be determined by 
calculating the elastic extension of the gauge length under appropriate 
load and adding thereto 0.2 percent of the gauge length. Elastic 
extension calculations shall be based on an elastic modulus of 69 GPa 
(10,000,000 psi) for aluminum, or 207 GPa (30,000,000 psi) for steel. 
If the elastic extension calculation does not provide a conclusive 
result, the entire stress strain diagram shall be plotted and the yield 
strength determined from the 0.2 percent offset.
    S5.7.1.3  For the purpose of strain measurement, the initial strain 
is set while the test specimen is under a stress of 41 MPa (6,000 psi) 
for aluminum, and 83 MPa (12,000 psi) for steel. The strain indicator 
reading is set at the calculated corresponding strain.
    S5.7.1.4  Cross-head speed of the testing machine is 3.2 mm (1/8 
inch) per minute or less during yield strength determination.
    S5.7.2  Elongation. Elongation of material, when tested in 
accordance with S5.7, shall be at least 14 percent for aluminum or at 
least 20 percent for steel; except that an elongation of 10 percent is 
acceptable for both aluminum and steel when the authorized specimen 
size is 24t gauge length x 6t wide, where ``t'' equals specimen 
thickness.
    S5.7.3  Tensile strength. Tensile strength shall not exceed 725 MPa 
(105,000 psi) for ``Carbon Manganese'' and 966 MPa (140,000 psi) for 
``Chrome-Molybdenum'' and ``Carbon-Boron.''
    S6  General requirements.
    S6.1  Each passenger car, multipurpose passenger vehicle, truck, 
and bus that uses CNG as a motor fuel shall be equipped with a CNG fuel 
container that meets the requirements of S7 through S7.4.
    S6.2  Each CNG fuel container manufactured on or after March 27, 
1994, shall meet the requirements of S7 through S7.4.
    S7  Test requirements. Each CNG fuel container shall meet the 
applicable requirements of S7 through S7.4.
    S7.1  Pressure cycling test at ambient temperature. Each CNG fuel 
container shall not leak when tested in accordance with S8.1.
    S7.2  Hydrostatic burst test.
    S7.2.1  Each Type 1 CNG fuel container shall not leak when 
subjected to burst pressure and tested in accordance with S8.2. Burst 
pressure shall be not less than 2.25 times the service pressure for 
non-welded containers when analyzed in accordance with the stress ratio 
requirements of S5.4.1, and shall not be less than 3.5 times the 
service pressure for welded containers.
    S7.2.2  Each Type 2, Type 3, or Type 4 CNG fuel container shall not 
leak when subjected to burst pressure and tested in accordance with 
S8.2. Burst pressure shall be no less than the value necessary to meet 
the stress ratio requirements of Table 3, when analyzed in accordance 
with the requirements of S5.5.1. Burst pressure is calculated by 
multiplying the service pressure by the applicable stress ratio set 
forth in Table Three. 

                       Table Three--Stress Ratios                       
------------------------------------------------------------------------
                  Material                     Type 2   Type 3   Type 4 
------------------------------------------------------------------------
E-Glass......................................     2.65      3.5      3.5
S-Glass......................................     2.65      3.5      3.5
Aramid.......................................     2.25      3.0      3.0
Carbon.......................................     2.50     3.33    3.33 
------------------------------------------------------------------------

    S7.3  Bonfire test. Each CNG fuel container shall be equipped with 
a pressure relief device. Each CNG fuel container shall completely vent 
its contents through a pressure relief device or shall not burst while 
retaining its entire contents when tested in accordance with S8.3.
    S7.4.  Labeling. Each CNG fuel container shall be permanently 
labeled with the information specified in paragraphs (a) through (d). 
The information specified in paragraphs (a) through (d) of this section 
shall be in English and in letters and numbers that are at least 12.7 
mm (\1/2\ inch) high.
    (a) The statement: ``If there is a question about the proper use, 
installation, or maintenance of this container, contact 
________________.'' inserting the CNG fuel container manufacturer's 
name, address, and telephone number.
    (b) The statement: ``Manufactured in ____________.'' inserting the 
month and year of manufacture of the CNG fuel container.
    (c) Maximum service pressure ________ kPa (________ psig).
    (d) The symbol DOT, constituting a certification by the CNG 
container manufacturer that the container complies with all 
requirements of this standard.
    S8  Test conditions: fuel container integrity.
    S8.1  Pressure cycling test. The requirements of S7.1 shall be met 
under the conditions of S8.1.1 through S8.1.4.
    S8.1.1  Hydrostatically pressurize the CNG container to the service 
pressure, then to not more than 10 percent of the service pressure, for 
13,000 cycles.
    S8.1.2  After being pressurized as specified in S8.1.1, 
hydrostatically pressurize the CNG container to 125 percent of the 
service pressure, then to not more than 10 percent of the service 
pressure, for 5,000 cycles.
    S8.1.3  The cycling rate for S8.1.1 and S8.1.2 shall not exceed 10 
cycles per minute.
    S8.1.4  The cycling is conducted at ambient temperature.
    S8.2  Hydrostatic burst test. The requirements of S7.2 shall be met 
under the conditions of S8.2.1 through S8.2.2.
    S8.2.1  Hydrostatically pressurize the CNG fuel container, as 
follows: The pressure is increased up to the minimum prescribed burst 
pressure determined in S7.2.1 or S7.2.2, and held constant at the 
minimum burst pressure for 10 seconds.
    S8.2.2  The pressurization rate throughout the test shall not 
exceed 1,379 kPa (200 psi) per second.
    S8.3  Bonfire test. The requirements of S7.3 shall be met under the 
conditions of S8.3.1 through S8.3.10.
    S8.3.1  The CNG fuel container is filled with compressed natural 
gas and tested at (1) 100 percent of service pressure and (2) 25 
percent of service pressure. Manufacturers may conduct these tests 
using the same container or with separate containers.
    S8.3.2  The CNG fuel container is positioned so that its 
longitudinal axis is horizontal. Subject the entire length to flame 
impingement, except that the flame shall not be allowed to impinge 
directly on any pressure relief device. Shield the pressure relief 
device with a metal plate.
    S8.3.3  If the test container is 165 cm (65 inches) in length or 
less, place it in the upright position and subject it to total fire 
engulfment in the vertical. The flame shall not be allowed to impinge 
directly on any pressure relief device. For containers equipped with a 
pressure relief device on one end, the container is positioned with the 
relief device on top. For containers equipped with pressure relief 
devices on both ends, the bottom pressure relief device shall be 
shielded with a metal plate.
    S8.3.4  The lowest part of the container is 102 mm (4 inches) above 
the liquid surface of the diesel fuel at the beginning of the test.
    S8.3.5  The CNG fuel container is tested with the valve and 
pressure relief device or devices in place.
    S8.3.6  The fire is generated by No. 2 diesel fuel.
    S8.3.7  The fuel specified in S8.3.6 is contained in a pan such 
that there is sufficient fuel to burn for at least 20 minutes. The 
pan's dimensions ensure that the sides of the fuel containers are 
exposed to the flame. The pan's length and width shall exceed the fuel 
container projection on a horizontal plane by at least 20 cm (8 inches) 
but not more than 50 cm (20 inches). The pan's sidewalls shall not 
project more than 2 cm (0.8 inches) above the level of fuel.
    S8.3.8  Time-pressure readings are recorded at 30 second intervals, 
beginning when the fire is lighted and continuing until the container 
is completely tested.
    S8.3.9  The CNG fuel container is exposed to the bonfire for 20 
minutes or until its contents are completely vented.
    S8.3.10  The average wind velocity at the container is not to 
exceed 2.24 meters/second (5 mph).

    Issued on September 16, 1994.
Ricardo Martinez,
Administrator.
[FR Doc. 94-23571 Filed 9-21-94; 1:13 pm]
BILLING CODE 4910-50-P

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