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

American Government Special Collections Reference Desk

American Government Topics:  National Highway Traffic Safety Administration, Federal Motor Vehicle Safety Standards

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

Ricardo Martinez
Federal Register
December 28, 1994

[Federal Register: December 28, 1994]



National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 93-02; Notice 08]
RIN [2127-AF47]

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; response to Petitions for reconsideration.


SUMMARY: This rule provides a partial response to petitions for 
reconsideration of the final rule that established performance 
requirements applicable to compressed natural gas (CNG) fuel 
containers. The final rule specified a safety factor of 3.33 for use in 
evaluating the strength of carbon fiber containers. This rule takes the 
intermediate step of specifying a 2.25 safety factor for carbon fiber 
containers and makes several minor changes to the final rule. After 
thoroughly analyzing the large number of petitions for reconsideration, 
the agency plans to issue another final rule establishing a permanent 
safety factor for carbon fiber containers and addressing the other 
issues raised in the petitions for reconsideration. If the safety 
factor is increased, a two year lead time will be given.

DATES: Effective Date: The amendments in today's final rule become 
effective March 27, 1995.

Mr. Gary R. Woodford, NRM-01.01, Special Projects Staff, National 
Highway Traffic Safety Administration, 400 Seventh Street, SW., 
Washington, D.C. 20590 (202-366-4931).


I. Final Rule Establishing FMVSS No. 304

    On September 26, 1994, NHTSA published a final rule addressing the 
safe performance of compressed natural gas (CNG) containers\1\ (59 FR 
49010). The final rule established a new Federal motor vehicle safety 
standard, FMVSS No. 304, Compressed Natural Gas Fuel Containers, that 
specifies pressure cycling, burst, and bonfire tests for the purpose of 
ensuring the durability, initial strength, and venting of CNG 
containers. The 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. The 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. The 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. 
FMVSS No. 304 becomes effective on March 27, 1995.

    \1\When used as a motor fuel, natural gas is stored on-board a 
vehicle in cylindrical containers at a pressure of approximately 
20,684 kPa (3,000 psi). Among the terms used to describe CNG fuel 
containers are tanks, containers, cylinders, and high pressure 
vessels. The agency will refer to them as ``containers'' throughout 
this document.

    The new FMVSS is patterned after the American National Standards 
Institute's (ANSI's) voluntary industry standard known as ANSI/NGV2 
(ANSI/NGV2). ANSI/NGV2 and FMVSS No. 304 specify detailed material and 
design requirements for four different types of containers. 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 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.
    For each type of container, ANSI/NGV2 and FMVSS No. 304 specify a 
unique safety factor for calculating the internal hydrostatic pressure 
that the container must withstand during the burst test. The safety 
factors range from 2.25 to 3.50, depending on the material and design 
involved. The higher the safety factor, the more material is needed to 
comply with the requirement. To satisfy this aspect of ANSI/NGV2 and 
FMVSS No. 304, a container must meet both the applicable material and 
design requirements as well as the burst test.
    While FMVSS No. 304 follows ANSI/NGV2 in most respects, NHTSA 
departed from ANSI/NGV2 in deciding to require that carbon fiber 
containers comply with a higher safety factor for the burst tests. 
Specifically, FMVSS No. 304 specifies a safety factor of 2.50 for Type 
2 containers and 3.33 for Type 3 and Type 4 containers. In contrast, 
ANSI/NGV2 specifies a safety factor of 2.25 for carbon fiber 

II. Petitions for Reconsideration

    NHTSA received 133 petitions for reconsideration of the final rule 
that established FMVSS No. 304. The petitions were submitted by CNG 
container manufacturers, vehicle manufacturers, natural gas utilities, 
research and testing laboratories, and Canada and several of its 
provincial governments. Most of the petitioners addressed the carbon 
fiber safety factor. Many of these petitioners stated that the levels 
specified by the agency in the final rule are unnecessarily high from a 
safety standpoint. They further stated that the higher safety factors 
will unduly increase the cost of carbon fiber containers, thereby 
making them noncompetitive with other technologies. Some petitioners 
stated that NHTSA's safety factors are not harmonized with the Canadian 
Standards Association standard or the draft International Standards 
Organization standard, both of which specify a 2.25 safety factor for 
carbon fiber. On the other hand, at least one commenter supported the 
3.33 safety factor.
    While the carbon fiber safety factor was the most controversial 
issue raised by petitioners, some petitioners commented about other 
issues in the final rule. For example, some petitioners commented that 
FMVSS No. 304 prohibits certain materials, such as new or different 
aluminum and steel. Some petitioners wanted FMVSS No. 304 to include 
additional safety requirements found in ANSI/NGV2. A number of 
petitioners requested the agency to delay or withdraw FMVSS No. 304 
until the revision, currently underway, of ANSI/NGV2 is completed. 
Petitioners also raised questions about the need for a variety of 
technical amendments to FMVSS No. 304.

III. Agency Decision

    As explained below, NHTSA has decided to respond to the petitions 
for reconsideration in two stages. In today's final rule, the agency 
provides an initial, partial response to the issue of the appropriate 
safety factor for carbon fiber containers, pending completion of the 
reconsideration process. Today's notice also responds to several other 
technical issues whose resolution did not necessitate extensive review 
or consideration. Subsequently, the agency will issue a second notice 
finally resolving the issue of the safety factor for carbon fiber 
containers and responding to the balance of the issues in the petitions 
for reconsideration.
    Today's decision regarding the safety factor for carbon fiber 
containers will provide NHTSA with an opportunity to review and analyze 
all the information presented in the petitions for reconsideration on 
this issue, while allowing the manufacture of carbon fiber containers, 
subject to a safety factor of 2.25. After NHSTA has completed its 
analysis, the agency will then make a final decision on the appropriate 
safety factor for carbon fiber containers. The agency anticipates 
issuing this notice in the Spring of 1995. Depending on the conclusions 
arising from its review, the agency may take one of three actions: 
reaffirm its decision in this notice that the safety factor for carbon 
fiber containers should be 2.25; adopt the safety factors specified in 
the original final rule; or adopt a safety factor somewhere in between 
those two alternatives. If the agency decides at the conclusion of the 
reconsideration process to set safety factors at values higher than 
2.25, it will set an effective date of two years from the date on which 
the decision is published in the Federal Register to provide the 
industry with adequate lead time to manufacture such containers.
    NHTSA's two step approach to responding to the petitions will 
provide it with the time it needs to review and analyze the voluminous 
information submitted by the petitioners. That information includes, 
among other things, Brunswick's data on how the higher carbon fiber 
safety factor increases costs; Brunswick's test data on the long term 
durability of carbon fiber containers (these tests include tests 
relating to high pressure cycling, severe damage abuse, and acidic 
environment); EDO's test data on the long term performance of carbon 
fiber fuel containers, including high impact damage, severe abuse, 
corrosion resistance, accelerated aging, and exposure to chemicals; 
information from EDO and Brunswick about the number of carbon fiber CNG 
containers currently in use; Dynetek's information on the resistance of 
carbon fiber containers to acidic environments; Thomas Built's 
information on the safety record of carbon fiber CNG containers 
currently in-use; and NGVC's and AGA's information on the cost increase 
of carbon fiber containers due to the higher safety factor.
    The necessity for providing an initial, expedited response on the 
issue of the 2.5 and 3.33 safety factors for carbon fiber containers 
arises from several factors. First, the effective date for FMVSS No. 
304, i.e., March 27, 1995, is very near. Second, manufacturers have 
typically been building CNG carbon fiber containers to comply with a 
much lower safety factor, the 2.25 safety factor specified in ANSI/
NGV2. Third, the container manufacturers would incur significant cost 
in switching from the production of carbon fiber containers complying 
with a 3.33 safety factor. Today's notice will avoid the necessity of 
carbon fiber container manufacturers having to incur costs and make 
design adjustments in order to comply with requirements that may 
ultimately be found to be more stringent than necessary.
    Given its decision to defer resolution of the issue of whether to 
impose safety factors of 2.5 and 3.33 for carbon fiber containers, 
NHTSA was faced with making the further decision whether to specify any 
safety factor so that the burst test can be implemented pending 
completion of the reconsideration process. The choice was between not 
specifying any safety factor or specifying a 2.25 safety factor, the 
factor with which carbon fiber container manufacturers currently 
comply. Not specifying any safety factor at all would have permitted 
the manufacture of weaker, less safe carbon fiber containers. The 
agency has concluded that, pending a final decision on this matter, a 
2.25 safety factor should be adopted. NHTSA believes that this decision 
is appropriate for several reasons. First, this decision will assure 
that there is a minimum level of strength for CNG carbon fiber 
containers. Second, 2.25 is the value specified in ANSI/NGV2 and in the 
Canadian Standards Association standard. Third, manufacturers have been 
building CNG carbon fiber containers to this safety factor. 
Accordingly, adopting a 2.25 safety factor will promote safety, be 
consistent with current practice and not impose any additional costs. 
However, after thoroughly analyzing the data provided by the 
petitioners, the agency may decide to increase the safety factor to 
3.33 or some intermediate level. If this occurs, a two year lead time 
will be given.
    In today's final rule, NHTSA has decided also to amend two other 
aspects of the September 1994 final rule. In response to Norris 
Cylinder Company (Norris), section S6.2 is amended to state ``Each CNG 
fuel container manufactured on or after March 27, 1994, shall meet the 
requirements of S7 through S7.4.'' (Emphasis added). This change is 
necessary to reflect the actual effective date. Norris correctly stated 
that the final rule had incorrectly referred to containers manufactured 
on or after March 27, 1994.
    In response to several petitioners, including Ford and NGV Systems, 
section S5.5.1 is amended to include the phrase ``or its equivalent.'' 
These commenters correctly stated that the National Aeronautics and 
Space Administration (NASA) computer program referenced in ANSI/NGV2 
and FMVSS No. 304 is outdated. Therefore, including the phrase ``or its 
equivalent'' as ANSI/NGV2 does will assist manufacturers in their 
efforts to establish compliance with FMVSS No. 304.
    NHTSA notes that several petitioners criticized the agency for not 
establishing additional performance requirements to ensure the safety 
of CNG containers. For instance, Brunswick stated that ``The final rule 
does not incorporate critical safety tests and requirements that are 
part of the current ANSI/AGA NGV2 Standard and are necessary to insure 
    As explained in the September 1994 final rule, NHTSA anticipated 
issuing additional performance requirements, consistent with ANSI/NGV2, 
after the final rule was issued. The agency's decision regarding this 
sequence of notices was made to accommodate requests by Brunswick and 
other CNG container manufacturers for NHTSA initially to issue 
requirements to ensure a CNG container's durability, strength, and 
pressure relief. In keeping with that decision, NHTSA followed the 
final rule with a supplemental notice of proposed rulemaking (SNPRM) 
that proposes additional performance requirements, consistent with 
those in ANSI/NGV2, to evaluate 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. (59 FR 65299, 
December 19, 1994). As the agency stated in the SNPRM, the agency 
tentatively concludes that these additional performance requirements 
are critical for determining a CNG container's safety. In addition, the 
agency proposed additional labeling requirements that should provide 
important safety information about a CNG container's service life. 
Accordingly, NHTSA believes that the agency has already responded to 
the petitioners' suggestion that the agency was not adequately 
addressing other aspects of CNG container safety.

IV. Rulemaking Analyses

A. Executive Order 12866 and DOT Regulatory Policies and Procedures

    NHTSA has considered this rulemaking action in connection with 
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. In the final rule, 
the agency concluded that most of the performance requirements in the 
standard are already being met by CNG fuel container manufacturers, who 
produce and test containers in accordance with ANSI/NGV2. CNG container 
manufacturers would not incur a cost increase for meeting the 
requirements in the bonfire test and the pressure cycling test. 
However, the agency concluded that the decision to increase the safety 
factor for carbon fiber containers would have an impact on CNG 
container manufacturers. The agency estimated that increasing the burst 
test safety factor from 2.25 to 3.33 would result in a direct cost 
increase of 37.1 percent and weight increase of 35.1 percent for 
containers that meet the 2.25 safety factor. These estimated cost and 
weight increases were arrived at through analysis and interpolation of 
information provided by Brunswick. The agency refers interested parties 
to the ``Final Regulatory Evaluation'', FMVSS No. 304, Fuel System 
Integrity, Compressed Natural Gas Containers, September 1994, for 
details on the additional cost incurred for a 3.33 safety factor. The 
agency's decision to specify a 2.25 safety factor for carbon fiber 
containers would negate this cost increase to container manufacturers, 
as they currently manufacture containers to this value. Since the 
agency is taking this intermediate step to lower the factor to the 
value which is currently met by container manufacturers, the agency 
does not see a need to perform a new regulatory evaluation, at this 

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 


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

    Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 CFR 1.50. (inches).

Sec. 571.304  [Amended]

    2. Section 571.304 is amended by revising S5.5.1, S6.2, and S7.2.2, 
as follows:
* * * * *
    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), or its equivalent.
* * * * *
    S6.2  Each CNG fuel container manufactured on or after March 27, 
1995 shall meet the requirements of S7 through S7.4.
* * * * *
    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.......................................     2.25     2.25     2.25

* * * * *
    Issued on December 21, 1994.
Ricardo Martinez,
[FR Doc. 94-31847 Filed 12-22-94; 10:49 am]

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