Federal Motor Vehicle Safety Standards; Fuel System Integrity of Compressed Natural Gas Vehicles; Compressed Natural Gas Fuel Container Integrity |
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Topics: National Highway Traffic Safety Administration
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Barry Felrice
Federal Register
December 19, 1994
[Federal Register: December 19, 1994]
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DEPARTMENT OF TRANSPORTATION
49 CFR Part 571
[Docket No. 93-02; Notice 06]
RIN 2127-AF14
Federal Motor Vehicle Safety Standards; Fuel System Integrity of
Compressed Natural Gas Vehicles; Compressed Natural Gas Fuel Container
Integrity
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).
ACTION: Supplemental notice of proposed rulemaking (SNPRM).
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SUMMARY: This notice proposes to amend Standard No. 303, Fuel System
Integrity of Compressed Natural Gas Vehicles, and Standard No. 304,
Compressed Natural Gas Fuel Containers. With respect to Standard No.
303, the notice proposes additional labeling requirements for
compressed natural gas (CNG) vehicles. With respect to Standard No.
304, the notice proposes to specify additional performance requirements
that would ensure a CNG fuel container's integrity. The proposes tests
include environmental cycling tests, an impact test, a gunfire test, a
flaw tolerance test, a pendulum impact test, and a drop test. Along
with the vehicle labeling requirements, the notice proposes additional
labeling requirements for CNG containers. These tests and performance
requirements, which are based on the Natural Gas Vehicle Coalition's
voluntary standard, NGV2, are intended to ensure the structural
integrity of CNG containers.
DATES: Comments on this notice must be received by the agency no later
than February 17, 1995.
ADDRESSES: Comments on this notice should refer to the above docket and
notice number and be submitted to: Docket Section, National Highway
Traffic Safety Administration, Room 5109, 400 Seventh Street SW.,
Washington, D.C. 20590. Telephone: (202) 366-5267. Docket hours are
9:30 a.m. to 4:00 p.m., Monday through Friday.
FOR FURTHER INFORMATION CONTACT:
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).
SUPPLEMENTARY INFORMATION:
Outline
I. Background
A. General Information
B. Previous Agency Rulemakings
II. Agency Supplemental Proposal
A. General
B. Environmental Cycling Test
C. Road Salt Environmental Test
D. Charpy Impact Test
E. Gunfire Test
F. Damage Tolerance Tests
1. General Considerations
2. Flaw Tolerance Test
3. Pendulum Impact Test
4. Drop Test
G. Bonfire Test Fuel
H. Labeling Requirements
1. CNG Containers
a. Labeling Information
b. Label Location
2. Vehicle Labeling
I. Other Safety Issues
J. Leadtime
K. Benefits
L. Costs
III. Rulemaking Analyses and Notices
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 14.7 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
has more than doubled from 10,300 in 1990 to 23,800 at the end of 1992.
The number of CNG vehicles is projected to again double to an estimated
50,800 vehicles in 1994. As discussed in detail in a final rule
published on April 22, 1994, establishing Standard No. 303, Fuel System
Integrity of Compressed Natural Gas Vehicles, recent Federal
legislation, as well as the need to meet environmental and energy
security goals, will lead to increased 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
liquefied petroleum gas (LPG) as a motor fuel. (55 FR 41561). The ANPRM
sought comment about the crash integrity of vehicle fuel systems, the
integrity of fuel storage containers, and pressure relief for such
containers.
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 focused on the integrity of the
entire fuel system, and (2) equipment requirements that focused on the
fuel containers alone. In that notice, the agency proposed specific
requirements applicable to the initial strength, durability, and
pressure relief characteristics of CNG containers. In addition, the
agency sought comments about the effects of corrosion and cold
temperature extremes on CNG containers, and their rupture without
fragmentation.
NHTSA received a large number of comments to the docket addressing
the January 1993 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 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 believe that Federal
requirements about the CNG fuel container integrity are needed and
should be implemented as quickly as possible.
In addition to comments addressing the proposed requirements for
durability, strength, and pressure relief, some commenters favored the
promulgation of requirements about corrosion resistance, high and low
temperature extremes, damage tolerance, and rupture characteristics of
CNG containers.
As noted above, NHTSA recently established Standard No. 303. It
specifies vehicle performance requirements for the fuel system of
vehicles fueled by CNG. The Standard enhances the fuel system integrity
of CNG vehicles by subjecting the vehicles to crash testing and placing
a limit on the post-crash pressure drop in the fuel system. The
Standard specifies frontal, rear, and lateral barrier crash tests for
light vehicles and a moving contoured barrier crash test for school
buses with a GVWR over 10,000 pounds.
NHTSA has also issued a final rule that establishes a new Federal
motor vehicle safety standard, Standard No. 304, Compressed Natural Gas
Fuel Containers, that specifies tests and performance requirements
applicable to a CNG fuel container's durability, strength, and pressure
relief. 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 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. These requirements are based on
specifications in NGV2, a voluntary industry standard addressing CNG
fuel containers which was adopted by the American National Standards
Institute (ANSI)\2\.
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\2\NGV2 was developed by an industry working group that included
container manufacturers, CNG users, and utilities.
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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 wall. 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.
II. Agency Supplemental Proposal
A. General
Based on comments to the January 1993 NPRM and other available
information, NHTSA has decided to issue this supplemental notice of
proposed rulemaking (SNPRM), to propose additional performance
requirements and tests to ensure a CNG container's structural
integrity. Among the proposed tests are environmental cycling tests, a
low temperature impact test, a gunfire test, a flaw tolerance test, a
pendulum impact test, and a drop test. One environmental cycling test
would evaluate a container's resistance to internal corrosion and high
humidity as well as the effects of high and low temperatures on a
container. A second environmental test would evaluate a container's
resistance to road salt and other acidic chemicals. The impact test,
known as the Charpy test, would evaluate a metal container's brittle
fracture characteristics under low temperatures. The gunfire test would
evaluate container fragmentation. Three tests, the flaw tolerance test,
the pendulum impact test, and the drop test, would evaluate a
container's resistance to external damage. Specifically, the flaw
tolerance test would evaluate a container's exterior resistance to
abrasion; the pendulum impact test would evaluate a container's ability
to withstand a sharp external blow; and the drop test would evaluate a
container's ability to withstand a blunt external blow. This notice
also proposes labeling requirements applicable to CNG vehicles and
labeling requirements for CNG containers in addition to those required
by the CNG container final rule.
Each of the proposed performance requirements and test procedures
are modeled after provisions in NGV2 or are similar to those
requirements. The agency tentatively concludes that modeling the
Federal standard after NGV2 would be the best way to regulate how a CNG
container reacts to such conditions as corrosive substances,
temperature extremes, external damage, and rupture. In some instances,
the agency departed from NGV2's performance requirements and test
criteria to be consistent with 49 U.S.C. 30111 (formerly section 103 of
the National Traffic and Motor Vehicle Safety Act, 15 U.S.C.
Sec. 1392). That statute commands the agency to issue ``motor vehicle
safety standards'' that are practicable, meet the need for motor
vehicle safety, and are stated in objective terms. One example of such
a departure can be found in the environmental cycling performance
requirement for internal corrosion. Instead of stating that there shall
be no ``evidence of distortion, deterioration, or failure,'' the
proposal states that the container ``shall not leak or be distorted.''
Another example can be found in the gunfire test conditions. Instead of
stating that ``(t)he distance from firing location to test container is
not to exceed 46 meters,'' the proposal states that ``(t)he distance
from firing location to test container is 46 meters.'' The most
significant differences between the proposal and NGV2 are discussed
below.
B. Environmental Cycling Test
Section 1-18(d)(2) of NGV2 includes an environmental cycling test
to prevent the unreasonable corrosion of a CNG container's internal
surface. In addition, this test evaluates the effect that high humidity
as well as high and low temperatures have on the CNG containers.\3\
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\3\The Charpy impact test also evaluates low temperature
performance for metal containers and liners because some metals are
susceptible to brittle fracture at low temperatures.
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In the ANPRM and NPRM, NHTSA noted that the level of impurities in
CNG (i.e., gas quality) could influence the fuel container's integrity.
Specifically, certain compounds in CNG could lead to stress corrosion
cracking, corrosion, fatigue or other internal harm to the container's
integrity. Such harm could cause the CNG containers to fail. The agency
initially decided not to propose a performance test to address a CNG
container's ability to withstand corrosion, since the agency was not
aware of any readily available performance test that would address the
failure modes at issue. Nevertheless, in the NPRM, NHTSA requested
comments about the need for a requirement addressing corrosion and, if
so, what tests and performance levels are most appropriate. In
particular, the agency requested comment about the practicability of
using the NGV2's environmental cycling test. In the NPRM, the agency
specifically asked whether, instead of adopting the first sentence of
the test verbatim, the agency should say ``One representative container
free of any protective coating shall be cycle tested as follows, and
shall not leak * * *''
Commenters on the NPRM stated that there are two principal ways to
regulate containers to prevent unreasonable internal corrosion: (1)
Regulating the gas quality or (2) regulating container performance.
NGVC, Pressed Steel Tank Co., EDO, the National Fire Protection
Association, the American Automobile Manufacturers Association (AAMA),
Tecogen, and Ontario recommended that the agency adopt gas quality
requirements for CNG such as those set forth in a Society of Automotive
Engineers (SAE's) Recommended Practice SAE J1616, ``Fuel Composition
for Natural Gas Vehicles,'' February 1994. That recommended practice
addresses internal corrosion by limiting the amount of water and other
impurities in CNG.
After reviewing the comments and other available information. NHTSA
has decided to propose a corrosion resistance requirement for CNG
containers. The agency notes that under 49 U.S.C. 30101 et seq.
(formerly the Safety Act, 15 U.S.C. 1381 et seq.), NHTSA is authorized
to regulate the manufacture of motor vehicles and motor vehicle
equipment. However, it has no authority to regulate fuel quality since
fuel is not considered to be motor vehicle equipment. Therefore, NHTSA
cannot issue standards regulating the quality of CNG. Nevertheless, the
agency encourages the industry to improve gas quality for CNG vehicles
through voluntary standards such as SA J1616.
NHTSA has decided to propose a performance requirement to ensure
that a CNG container resists corrosion. Such a requirement would
prevent catastrophic failures of CNG containers due to internal
corrosion. This is particularly important since the agency only has
statutory authority to issue safety standards that regulate the
condition and performance of vehicles prior to their first consumer
purchase. The agency does not have any authority to require periodic
inspection of containers for corrosion. NHTSA is proposing to adopt an
environmental cycling performance requirement and test procedure
patterned after the ones in NGV2. The proposed performance requirement
is set forth in S7.5, and the proposed test conditions and procedures,
in S8.5.
NGV2 states that a ``container free of any protective coating shall
be cycle tested, without showing evidence of distortion, deterioration
or failure * * *'' The agency believes that while the term ``without
distortion'' appears to be objective, the terms ``without deterioration
or failure'' are too ambiguous and broad to permit their incorporation
in a Federal Motor Vehicle Safety Standard. Therefore, the agency has
decided not to include the terms ``deterioration'' and ``failure'' in
its proposal. Instead, the agency is proposing that its pass/fail
criteria for the environmental cycling test depart from NGV2 and state
that, when cycle tested, the CNG container ``shall not leak or
permanently change in external configuration or dimensions.'' NHTSA has
added the prohibition against leakage, since the absence of leakage can
be objectively determined. Further, the prohibition is consistent with
the environmental cycling test's safety goal and with the pressure
cycling test and hydrostatic burst test that the agency adopted when it
issued Standard No. 304.
Under today's proposal, the phrase ``shall not . . . permanently
change in external configuration or dimensions'' throughout the test is
intended to serve the same purpose as the NGV2 ``no distortion''
criterion. Thus, if there were a slight bulge in one location or if
there were a change in the container's volume by even one tenth of one
percent, the container would be considered to be distorted. A pass/fail
gauge could be adjusted to fit the container before the test, and then
used again after the test to verify that a container's dimensions had
not changed. NHTSA requests comments about this ``zero distortion''
requirement, and whether some amount of distortion should be allowed.
If so, how should the permissible amount of distortion be quantified
and measured? The agency also invites comments on how the no distortion
criterion might otherwise be objectively expressed. In addition, the
agency requests comments on whether there are other terms, such as
fiber delamination, which should be incorporated and how they could be
objectively defined.
As an alternative, NHTSA is considering a no leakage criterion as
the sole pass/failure performance requirement. However, under this
alternative, the agency would increase the two sets of 5,000 cycles to
9,000 cycles each. Thus, the standard would specify a total of 18,000
cycles instead of the 10,000 cycles currently specified in NGV2. The
agency tentatively concludes that the additional cycles would be
necessary since this alternative proposal would otherwise be less
stringent than NGV2 which contains additional criteria to disqualify
substandard containers, i.e., distortion, deterioration, and failure.
The agency further notes that 18,000 cycles is consistent with the
ambient pressure cycling in NGV2 and in FMVSS No. 304. That cycling
represents severe service, i.e., four refuelings per day, 300 days per
year for 15 years. The agency requests comments on this alternative,
and on other approaches that might be more appropriate. In addition,
the agency requests that commenters suggesting other approaches include
measurable pass/fail performance criteria and a proposed test
procedure.
Section S8.5 sets forth the procedures and conditions for the
environmental cycling test. As with the proposed performance
requirements, these provisions are modeled after NGV2. The agency has
tentatively adopted modified versions of certain provisions in order to
be consistent with the criteria that are within the agency's authority.
NGV2 further specifies that during the environmental cycling test
the container is pressurized ``using natural gas or methane.'' This is
part of the test's preconditioning phase in which a corrosive material
is introduced inside the container to determine its corrosion
resistance. The agency is proposing that only automotive grade natural
gas be used in the environmental cycling test. The agency believes that
specifying only one test gas would make the test more repeatable for
enforcement purposes. Further, although the major constituent of
natural gas is methane, natural gas does contain other minor
constituents which could make the test performed with natural gas more
severe than if only pure methane were used. Therefore, the use of
natural gas would represent a more severe scenario that is closer to
real world use. NHTSA requests comment on the appropriateness of using
only natural gas in the environmental cycling test, rather than
specifying both fuels.
NHTSA has decided to propose language addressing the use of
protective coatings that it believes is consistent with NGV2.
Specifically, S8.5.2 states that ``A CNG fuel container free of any
protective coating'' is cycle tested in a specified manner. The agency
believes that the phrase ``free of any protective coating'' refers to
temporary coatings such as oil and grease, so as not to inhibit action
from the corrosive materials during subsequent testing. The agency
further believes that it would be inappropriate for the agency to
preclude permanent coatings such as paint or other materials, since
this would discourage manufacturers from applying permanent coatings
that increase corrosion resistance. The agency requests comments on how
best to describe this concept. An alternative to the proposal to
specify ``free of any protective coating,'' would be to specify ``The
container shall be in the as manufactured condition.''
NHTSA is also proposing relative humidity conditions during the
environmental cycling test. Specifically, under the proposal, S8.5.2.2
would specify ``Condition the container for 48 hours at zero pressure,
60 deg. C (140 deg. F) and 95 percent relative humidity. To obtain the
specified temperature and relative humidity, spray with a fine spray or
mist of water at 60 deg. C (140 deg. F) in a chamber held at 60 deg. C
(140 deg. F).'' NHTSA requests comments on how the phrase ``fine spray
or mist of water'' could be made more objective, since different rates
of spray might influence the humidity level. As an alternative, the
agency is considering a rate of spray consistent with ANSI standard
Z26.1-1977, which is referenced in FMVSS NO. 205, Glazing Materials.
That provision specifies that ``The fine spray of water shall be under
a pressure of 172 to 207 kPa (25 to 30 psi) at the nozzle and in
sufficient volume to wet the container immediately upon impact.''
Another alternative would be to specify a relative humidity level of 95
percent. This would allow manufacturers and test facilities the
flexibility to determine how that level is achieved. The agency
requests comments on how best to specify relative humidity in the
environmental cycling test.
In comments to the NPRM, Norris and NGV Systems supported an
alternative corrosion test issued by the National Association of
Corrosion Engineers (NACE), NACE Standard TM0177-90. The NACE voluntary
standard includes several test methods for determining the sulfide
stress cracking resistance of steels. Sulfide stress cracking corrosion
can result from the presence of too much hydrogen sulfide in natural
gas. NHTSA requests comments on the appropriateness of using the NACE
test either in conjunction with or in lieu of NGV2's environmental
cycling test.
The NACE test provides a laboratory method but does not specify
acceptable results. If the agency were to incorporate the NACE test in
an FMVSS, it would be necessary to specify performance requirements.
The agency believes that this could be done by making the performance
requirements consistent with the ones already contained in the draft
International Standards Organization (ISO) standard for CNG containers
(Section A13). If the agency decides to adopt the NACE test, the NACE
Standard Tensile Test method would be used and subsized tensile
specimens (gauge diameter 2.54 mm) would be machined from the wall of a
finished container, placed under constant tensile load, and immersed in
the NACE test solution. Tests would be conducted to demonstrate that
the threshold stress exceeds 20 percent of the specified minimum yield
strength of the steel, where threshold stress is the maximum stress at
or below which no specimen fails the test for a period of 720 hours.
NHTSA requests comments on the need for the NACE test and various
aspects of the test, including the appropriateness of setting threshold
stress at 20 percent above the yield strength and the number of tests
which should be conducted to demonstrate this.
C. Road Salt Environmental Test
NHTSA has decided to propose a road salt environmental test for CNG
fuel containers to address the potential for container degradation due
to road salt and other acidic chemicals. The proposed test is in
addition to the environmental cycling test already discussed.
NHTSA has decided to propose this requirement after learning of two
CNG fiberglass fuel container failures which occurred in early 1994.
NHTSA is concerned about the exposure of container exterior surfaces to
acidic fluids, which may lead to stress corrosion cracking and
container failure. Depending on the environmental conditions present,
road salt or salt spray while driving in wet conditions, can be acidic
in nature. Therefore, the agency proposes this road salt environmental
test to address these potential safety problems.
The number of test cycles and the pass/fail criterion are the same
as those proposed for the environmental cycling test discussed earlier.
However, prior to cycling, the fuel container would be exposed to salt
spray in accordance with American Society for Testing and Materials
(ASTM) B117-73, ``Method of Salt Spray (Fog) Testing.'' This method of
salt spray testing is used in FMVSS NO. 108, Lamps, Reflective Devices,
and Associated Equipment for testing the corrosion resistance of
headlamps.
Under the proposal, a CNG fuel container would be exposed to the
salt spray for 240 hours, consisting of ten successive 24 hours
periods. Within each period, the container would be exposed to the
spray for 23 hours. During the 24th hour, the salt spray would not be
activated. Following the 240 hours of salt spray exposure, the
container would then be cycled for 5,000 cycles, through hydrostatic
pressurization, from not more than 10 percent of service pressure to
service pressure. Then it would be hydrostatically pressure cycled for
another 5,000 cycles from not more than 10 percent of the service
pressure to 125 percent of the service pressure. When tested in this
way, the container would be prohibited from leaking or permanently
changing in external configuration or dimensions.
NHTSA requests comments on the appropriateness of using this test
to address exterior environmental degradation of CNG fuel containers
due to road salt and other acidic chemicals. The agency specifically
requests comments on whether the proposed test would adequately address
the potential for stress corrosion cracking of fiberglass overwrap in
CNG fuel containers, and whether it should be applied to all types of
CNG fuel containers, including all metal, hoop wrapped with metal
liner, full wrapped with metal liner, and all composite for both
fiberglass and carbon fiber. NHTSA also requests comments on whether
the 240 hours of salt spray exposure appropriately reflects the amount
of exposure which can reasonable be expected during the life of a CNG
fuel container.
In addition, NHTSA requests comments on the pH level of the salt
solution used in the proposed test method. Under ASTM B-117, the pH
level of the salt solution is in the range of 6.5 to 7.2 at 35 deg.C,
although the method provides for an upward or downward adjustment in
pH. A downward adjustment of pH level would make the solution more
acidic, thereby representing more severe road chemicals which CNG
containers may encounter. It appears possible that stress corrosion
cracking of fiberglass may be accelerated with decreasing pH.
Therefore, the agency requests comments on whether a lower pH range for
the salt solution should be specified in the test method, such as three
to four.
NHTSA also requests comments on whether to specify the pass/fail
criterion for the salt spray test to ``no leakage'' in lieu of ``shall
not leak or be permanently changed in external configuration or
dimensions.'' Concurrently, the agency would also increase the number
of cycles during testing from two sets of 5,000 cycles each to two sets
of 9,000 cycles each. The agency requests comments on whether these
modifications in the number of cycles would be appropriate for the road
salt test as well as the environmental cycling test discussed earlier.
The agency also requests comments on the estimated cost of the salt
spray test and the extent to which current CNG containers would comply
with the requirements.
D. Charpy Impact Test
Section 1-12(d) and 1-13(e) of NGV2 set forth an impact test, known
as the Charpy test, and performance criteria to address brittle
fracture of steel CNG containers and liners under low temperatures.
NGV2 states that this test is an indicator of the performance of heat
treated steels.\4\ The Charpy test evaluates marginal heat treating
performance which can lead to poor fracture performance, degraded
resistance to stress corrosion cracking, and lessened fatigue
resistance.
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\4\ The Charpy test only evaluates steel CNG containers and
liners. The environmental cycling test evaluates composite materials
under low temperature conditions.
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In the NPRM, NHTSA requested comments on whether there is a safety
problem sufficiently serious to warrant establishing a requirement for
low temperature testing of CNG container materials. The agency
requested these comments due to its concern that certain materials such
as high strength steels can lose their ductility at low temperatures, a
situation that could lead to a container's catastrophic failure. The
agency requested specific comments on the Charpy impact test set forth
in NGV2.
NGV Systems, ARC, Comdyne, Pressed Steel Tank, EDO, Fiber Dynamics,
AAMA, Minnesota Gas, Amoco, Navistar, CNG Pittsburgh, and Manchester
commented about the need for cold temperature testing. All but
Manchester believed that the standard should include some sort of cold
temperature testing for containers. Manchester stated that the
container's service environment should be examined to determine if such
cold temperature testing is needed. Most commenters stated that
temperature extremes should be accounted for in the standard but did
not elaborate about the specific test. PST recommended that the agency
include the Charpy impact test in the Federal standard. AAMA and EDO
recommended that the containers be cycled at -40 deg. C (-40 deg. F)
and -50 deg. C (-58 deg. F), respectively.
After reviewing the comments, NHTSA has decided to propose amending
Standard No. 304 to include a low temperature test patterned after the
Charpy impact test. This test is set forth in sections 1-12(d) and 1-
13(e) of NGV2, which references Methods for Notched Bar Impact Testing
of Metallic Materials, ASTM E 23. Section 1-13(e) states that the
average energy absorbed by the three test specimens shall not be less
than 100 J/cm\2\. The minimum value for any one specimen shall not be
less than 80 J/cm\2\. Under the test, a pendulum swings down and hits a
specimen. The test device then measures the amount of energy
transmitted into the specimen needed to break it. If the specimen
breaks at low levels of energy, then it would fail the test. To
illustrate, while a substance such as glass would break at very low
energy levels, a non-brittle metal would break only at relatively high
energy levels. Specifically, the purpose of this test is to determine
the brittle fracture behavior of steels. It also evaluates the
performance of steels which have been heat treated as part of the
manufacturing process. An improper heat treatment process can result in
the material being brittle and thus more susceptible to fatigue and
stress corrosion cracking. Non-steel containers and liners need not be
tested to comply with the Charpy test because they are not heat treated
this way. The agency requests comments about the agency's decision to
propose the Charpy impact test. Is it appropriate to only apply these
requirements to Type 1 containers and Type 2 and Type 3 containers with
steel liners? In addition, NHTSA requests comments on applicable
performance tests for fracture and fatigue assessment of liner
materials other than steel, if such materials perform a structural
function, e.g., aluminum liners or containers. Along with this
information, commenters should include a description of the specific
performance tests recommended, along with objective pass/fail criteria.
NHTSA agrees with the recommendations by AAMA and EDO that
containers be pressure cycled at low temperatures (e.g., -40 deg. C
(-40 deg. F)). The agency notes that this low temperature is consistent
with test conditions in NGV2 and NHTSA standards, including Standard
No. 105, Hydraulic Brake Systems, Standard No. 106, Brake Hoses, and
Standard No. 108, Lamps, Reflective Devices, and Associated Equipment.
The agency requests comment about whether the proposed test temperature
is appropriate.
In response to Manchester's comment that the service environment
should be examined to determine if cold temperature testing is needed
for a particular container, NHTSA notes that it would be impracticable
to determine what type of environment each individual container would
encounter. In establishing a requirement, the agency believes that it
is appropriate to test CNG containers in a worst case scenario, such as
the low temperature levels being proposed.
E. Gunfire Test
Section 1-18(j) of NGV2 includes a gunfire test that evaluates
whether a fully pressurized container fragments upon suffering a high
impact puncture. A similar puncture could occur in a motor vehicle
crash, causing the propulsion of container fragments at high speeds.
The gunfire test assures that a container will instead essentially
remain in one piece.
In the NPRM, the agency discussed a specific test criterion in
which the container would be permitted to rupture only if there were no
fragmentation. The container industry refers to this situation as
``leak before burst.'' Containers that leak before bursting are
designed to release their contents through the sidewall without
explosive fragmentation when the container becomes overpressurized. The
industry tests for this characteristic by piercing the pressurized
container with a gunshot. The area around the container is then
examined for fragmentation. The container is supposed to be designed so
that no fragments will break off during this failure. In the NPRM, the
agency requested comments about how to define the term ``without
fragmenting'' for regulatory and compliance purposes.
Brunswick, NGV Systems, PST, EDO, CNG Pittsburg, and AAMA commented
about container fragmentation. These commenters stated that in the
event of a rupture, the CNG fuel containers should be designed to
release their contents through their sidewalls without fragmentation.
Brunswick, AAMA, NGV Systems, EDO, and PST commented about how to
define the phrase ``without fragmenting.'' EDO recommended that the
container be required to remain ``in one piece.'' NGV Systems stated it
should be defined as ``no separation of parts such that projectiles are
possible.'' AAMA stated that it should be defined as ``no separation of
pieces exceeding one gram in mass from the fuel tank.'' Brunswick
stated that it should be defined as loss of small pieces not exceeding
30 grams (one ounce) in weight. PST also indicated that 30 grams (one
ounce) is an acceptable size.
Based on the comments and other available information, NHTSA has
decided to propose amending Standard No. 304 to include a gunfire test
similar to the one set forth in NGV2, with some modifications. The
agency believes that if a CNG container is punctured in a crash, the
failure should result in a controllable situation, e.g., fuel leakage,
rather than a catastrophic explosion of the container. A catastrophic
failure would present a much more serious failure mode than fuel
leakage through the sidewall, since fragments could be propelled in all
directions at high speeds and with tremendous force. Such fragments
could pose a significant safety risk to vehicle occupants and others
near the vehicle.
With respect to the performance criteria for the gunfire test, NGV2
states that ``The tested container shall reveal no evidence of a
fragmentation failure'' and ``Loss of small pieces of composite
material which would not have sufficient momentum to penetrate sheet
metal typically found in automobile construction shall not constitute
failure of the test.'' Under the second phrase, NGV2 allows the
fragmentation of small pieces, even though the gunfire test is intended
to prevent fragmentation.
NHTSA has tentatively concluded that some of NGV2's performance
requirements and test conditions are insufficiently objective for use
in a FMVSS. In order to establish objective, safety criteria, NHTSA has
decided to propose incorporating the recommendations by Brunswick and
PST to prohibit fragments exceeding 30 grams (one ounce) in mass.
Although the intent of the gunfire test is to demonstrate no
fragmentation, the agency understands that small composite pieces or
fragments are considered normal. Therefore, the agency has tentatively
concluded that to prohibit all fragmentation, as recommended by EDO and
NGV Systems would not be practicable. Similarly, the agency believes
that AAMA's recommendation to prohibit the separation of pieces
exceeding one gram (0.035 ounce) would not be practicable and would
involve very small pieces that could be difficult to measure. NHTSA has
tentatively concluded that prohibiting pieces in excess of 30 grams
would provide for a practicable, objective, and safe performance
criterion for the gunfire test. However, the agency requests comments
on the proposed size, and whether the standard should prohibit all
fragmentation or whether some smaller level of fragmentation would be
measurable and safe. What is the lightest container fragment that would
be readily measurable and would not pose an unreasonable risk to the
safety of motorists? NHTSA also seeks comment on whether the container
should be pressurized with nitrogen or air, since only one gas should
be used to assure consistency of testing.
NHTSA has tentatively determined that it is necessary to depart
from certain aspects of the gunfire test in NGV2 to make the agency's
proposed requirement objective and ensure repeatable test results. As
proposed in this notice, these modifications include specifying the
precise muzzle velocity, the projectile's path, and the precise
distance.
F. Damage Tolerance Tests
1. General Considerations
NGV2 addresses damage tolerance with three separate tests: a flaw
tolerance test, a pendulum impact test, and a drop test. In general,
the damage tolerance tests serve to evaluate damage caused by
incidental contact with other objects. Such contact can occur in a
variety of ways. For instance, containers mounted underneath the
vehicle could be damaged by road debris. Similarly, containers mounted
in the bed of a pickup truck could be damaged by cargo or tools being
thrown on them. The flaw tolerance test evaluates abrasive damage to
composite overwraps such as scratches and small cuts on the container.
If the overwraps are cut or gouged, they may unravel or delaminate,
possibly causing container failure. The pendulum impact evaluates sharp
blows to the container. The drop test evaluates blunt impacts to the
container.
NHTSA did not address damage tolerance in the January 1993 NPRM.
Nevertheless, CGA, Tecogen, Comdyne, ARC, and Brunswick commented that
a container's resistance to mechanical damage from incidental contact
or road debris should be tested. Of these commenters, only Brunswick
suggested a specific test procedure to determine container damage
tolerance. Brunswick stated that NGV2 adequately addresses resistance
to mechanical damage with the flaw tolerance, pendulum impact, and drop
tests. In addition, it stated that the effects of more severe damage,
such as a puncture, are addressed with the gunfire test.
NHTSA has decided to propose the three damage tolerance tests in
NGV2 because the agency has tentatively concluded that, during normal
use, CNG containers may be exposed to each type of external damage
addressed by these tests. This may be especially true for containers
sold in the aftermarket, since vehicle manufacturers would presumably
be more likely than vehicle converters to design their vehicles to
protect containers from exposure to road debris and other damage. This
is so because vehicle manufacturers can design a CNG vehicle with
container placement in mind. Converters are not involved in the
original designing of the vehicles they convert and may have to place a
container in a relatively vulnerable location given space limitations.
NHTSA is proposing to subject Type 1 containers to the drop test,
but not to the other two tests, since noncomposite metal containers are
generally not affected by the proposed damage evaluated by those tests.
Type 2, 3, and 4 composite containers would be subject to all three
damage tolerance tests. The agency requests comments about the
appropriateness of applying the proposed damage tolerance tests to the
different types of CNG containers.
In NGV2, the criterion for each damage tolerance test is that the
container, after having a cut made into the container or being
impacted, must sustain 1,500 pressure cycles without evidence of
failure such as distortion or leakage. The only exception to this is
the drop test. The drop test in NGV2 requires two alternative sets of
cycling tests. If the container sustains damage that would cause its
rejection at a three year inspection interval specified by NGV2, the
container is tested for 1,500 cycles. In contrast, if the container
sustains damage that would cause it not to be rejected at a three year
inspection, it is tested for 18,000 cycles. The 1,500 cycles in NGV2
apparently corresponds to the maximum number of fills expected during
the three year inspection interval. Because NGV2 requires reinspection
every three years, it is structured to permit a level of damage to the
container that would keep it in service until the maximum inspection
interval of three years is completed. In contrast, NHTSA has no
statutory authority to require container inspection after the first
consumer purchase of the container.\5\
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\5\The agency is proposing labeling requirements to encourage
the periodic inspection of containers every 12 months, as explained
below.
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In today's notice, NHTSA is proposing 1,500 cycles for the flaw
tolerance and pendulum impact tests, and the more severe alternative of
18,000 cycles for the drop test. This is consistent with the manner of
cycles specified in NGV2, after which the agency is patterning its
proposal. However, since NHTSA has no authority to require the periodic
inspection of CNG containers, the agency requests comments on whether
1,500 cycles is adequate to assure the safety of a CNG container
throughout its life. As a alternative, the agency is considering
requiring 18,000 cycles for the flaw tolerance and pendulum impact
tests. This is consistent with the pressure cycling test in FMVSS No.
304 and with the drop test where no inspection would be involved. It
would also represent the worst case scenario for a container which
sustains damage early in its service life, but may not be subsequently
inspected, since 18,000 cycles represents four refuelings per day, 300
days per year for 15 years. The agency requests comments on the
appropriate number of cycles for the flaw tolerance, pendulum impact,
and drop tests to assure the safety of the traveling public.
2. Flaw Tolerance Test
Section 1-18(f)(1) of NGV2 sets forth a flaw tolerance test, which
evaluates a container's ability to withstand external damage caused by
abrasive material scratching a container, NHTSA is proposing to adopt
the flaw tolerance test in NGV2 with some minor modifications. The
agency's adaptation of these performance requirements and test
conditions and procedures is set forth in sections S7.8 and S8.8 of
this notice's regulatory text.
NGV2's flaw tolerance test specifies that the container shall be
tested ``without evidence of distortion, deterioration or failure'' and
``show no evidence of flaw propagation\6\ or other physical damage
likely to weaken the container appreciably.'' as explained in the
earlier discussion on the environmental cycling test, these performance
requirements contain subjective criteria that the agency believes need
to be modified to be objective and enforceable. The agency believes
that the terms ``without deterioration or failure'' and ``other
physical damage likely to weaken the container appreciably'' are
unreasonably ambiguous and broad. Therefore, the agency has decided not
to include, in the proposed requirement, the terms ``deterioration''
and ``failure'' and the phrase ``other physical damage likely to weaken
the container appreciably'' since these terms are not sufficiently
objective to include in a Federal standard and would not provide
measurable criteria for enforcement. The agency welcomes comments about
ways to refine terms to make them objective. In addition, the agency
requests comments on whether there are other terms, such as fiber
delamination, which should be incorporated and how they could
objectively be defined.
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\6\Propagation is defined as ``enlargement or extension (as of a
crack) in a solid body. (Webster's Ninth New Collegiate Dictionary)
---------------------------------------------------------------------------
Instead, the agency is proposing a modified version of the NGV2
pass/fail criteria for the flaw tolerance test that states that when
cycle tested, the CNG container ``shall not leak or permanently change
in external configuration or dimension.'' In addition, NHTSA is
proposing an additional performance provision to prohibit the growth of
a longitudinal cut made in the container. NHTSA has added the
prohibitions against leakage and increase in the size of cut since
compliance with them can be objectively determined. It is also
consistent with the flaw tolerance test's safety goal and with the
performance requirements for the presence cycling test and the
hydrostatic burst test in Standard No. 304. The agency previously
discussed the no distortion criterion in the environmental cycling
section and request similar comments here. In addition, the other
requirement being proposed for the flaw tolerance test is that the
``cut made in accordance with S8.8 for the purpose of this test shall
not increase in length, width or depth as a result of this test.''
NHTSA has tentatively determined that it is also necessary to
depart from certain aspects of NGV2's flaw tolerance test procedures
and conditions to make agency's flaw tolerance test objective and
repeatable. As proposed in this notice, these modifications include
specifying the precise dimensions and location of the flaw.
NGV2 specifies that a cut be made in the other wall at
approximately midlength and that the cut be not less than 0.75 mm
(0.030 inches) in depth. The agency is proposing additional provisions
to make the proposed FMVSS more precise, thereby increasing the test
procedure's objectivity and repeatability. For instance, the agency is
proposing to amend the standard to specify that the cut be 0.75 mm
wide. The agency tentatively believes that these dimensions represent
abrasions that containers may experience as a result of contacting road
debris. However, the agency requests comments on the cut's dimensions,
including the appropriate width, and whether the length, width, and
number of such cuts should be increased.
3. Pendulum Impact Test
Section 1-18(f)(2) of NGV2 sets forth a pendulum impact test which
evaluates a container's ability to withstand a sharp external blow.
NHTSA is proposing to adopt the pendulum impact test in NGV2 with some
minor modifications. The agency's adoption of these performance
requirements and test conditions is set forth in sections S7.9 and S8.9
of this notice's regulatory text.
NGV2 specifies that ``The tests shall be made on the points of the
container which are regarded as vulnerable. The points regarded as
vulnerable are those which are most exposed or weakest having regard to
the shape of the container and/or the way in which it is installed on
the vehicle.''
NHTSA has decided to propose modifying this provision since it is
not objective. Instead, the agency is proposing to require that the
pendulum impact test be conducted at ``any point and any angle.'' NHTSA
anticipates that to be able to certify compliance with the requirement,
manufacturers would direct the test impacts to the container's most
vulnerable points. Such a test procedure would be consistent with the
regulatory language specified in Standard No. 301's moving contoured
barrier test. The agency requests comments about whether such a test
condition would be appropriate for pendulum impact testing of CNG
containers.
4. Drop Test
Section 1-18(g) of NGV2 sets forth a drop test, which evaluates a
container's ability to withstand a blunt external blow. NHTSA is
proposing to adopt the drop test in NGV2 with some minor modifications.
The agency's adoption of these performance requirements and test
procedures is set forth in sections S7.10 and S8.10 of this notice's
regulatory text.
As with NGV2, NHTSA is proposing to specify that a container be
dropped at ambient temperature without internal pressurization or
attached valves. In the test, the container is held in a horizontal
position with the container's bottom 3.05 meters (10 feet) above the
surface onto which it is dropped.
Today's proposal, consistent with NGV2, specifies that the surface
onto which the CNG container is dropped ``shall be a smooth, horizontal
concrete pad or flooring.'' NHTSA notes that this definition of the
surface is not fully objective. As an alternative, the agency is
considering specifying that the surface be made of concrete that is at
least four inches thick. NHTSA requests comments on this alternative,
and on how the surface could otherwise be more objectively defined.
G. Bonfire Test Fuel
In the NPRM, NHTSA proposed that the fire for the bonfire tests be
generated by No. 2 diesel fuel. This fuel type was proposed so that the
standard would be consistent with the bonfire test in NGV2, which
specifies this type of fuel.
NGVC, CGA, AAMA, and Norris commented that the agency should
specify a different fuel to generate a bonfire that is more
environmentally sound. CGA stated that the large amounts of smoke that
would be created by burning 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.
In the final rule, NHTSA decided to specify the use of No. 2 diesel
fuel. The agency explained that it was aware of the environmental
problems associated with this type of fuel and would further study
whether other fuels should be used to generate the bonfire test.
However, the agency stated that until it could determine that a
different fuel is an appropriate (e.g., generates a fire of comparable
heat and intensity) replacement for No. 2 diesel fuel, that fuel will
be specified for generating the bonfire.
NHTSA has decided to propose to amend the bonfire test conditions
to allow alternative types of fuel, given the environmental
difficulties resulting from No. 2 diesel fuel. One alternative would be
to allow manufacturers to conduct the test with any fuel that generates
a flame temperature equivalent to that of No. 2 diesel fuel. Under this
alternative, any fuel that generates a flame temperature of 850 deg. to
900 deg. C (the flame temperature of No. 2 diesel fuel) for the
duration of the test, would be permitted. To verify the flame
temperature of 850 deg. to 900 deg. C for a period of 20 minutes, or
until the container is fully vented or fails, three thermocouples would
be located on the container's bottom, 102 mm above the fuel surface, as
measured before the fire is started. The thermocouples would be placed
so that one would be at the center of the container's bottom and one on
each side of the container where the dome and sidewall intersect. NHTSA
requests comments about the appropriateness of this alternative,
including the use of flame temperature to define ``equivalence'' among
fuel types. Would a different fuel characteristic such as Btu/lb be
more appropriate? If a commenter believes that an alternative approach
would be more appropriate, it should submit the test procedures
associated with such an alternative.
H. Labeling Requirements
1. CNG Containers
a. Labeling information. In the NPRM, NHTSA proposed to require
that container manufacturers certify that each of their containers
comply with the proposed equipment requirements by permanently labeling
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 manufactured after the
standard's effective date should be entitled to display the DOT symbol.
Thomas stated, without elaboration, that the labeling requirements of
NGV2 should be adopted. NHTSA's proposal did not include certain
information specified in NGV2, including the type of container,
inspector symbols, trademarks, manufacturers's part number, and serial
numbers.
In the CNG container final rule, NHTSA decided to adopt the
proposed labeling requirements with a slight modification from the
proposed format. In item (a), the agency 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].'' In the final
rule, the agency decided not to require the other additional items of
information in NGV2 since the agency had not proposed requiring such
information. Notwithstanding the agency's decision not to require this
additional information, the agency explained that a manufacturer may
list such information on the label, provided that the additional
information does not obscure or confuse the required information. In
particular, NHTSA urged manufacturers to include the container type,
e.g., Type 1, 2, 3 or 4, since the agency had adopted NGV2's design and
material specifications in the final rule. The agency believed that
specifying the type of container would facilitate oversight of
compliance tests since each type of container is required to undergo a
hydrostatic burst test with a safety factor unique to that type.
In the final rule, NHTSA also explained that it anticipated
proposing additional requirements about the CNG fuel container's label.
The agency is now proposing to amend S7.4 to specify that CNG
containers be labeled with the following additional information:
(1) The container designation (Type 1, 2, 3, or 4),
(2) The statement ``CNG ONLY,''
(3) The statement: ``This container should be visually inspected
after a motor vehicle accident or fire and at least every 36 months for
damage and deterioration in accordance with the Compressed Gas
Association (CGA) guidelines C-6 and C-6.1 for Type 1 containers and C-
6.2 for Types 2, 3, and 4 containers.''
(4) The statement: ``Do Not Use After ____________,'' inserting the
year that is the 15th year beginning after the year in which the
container is manufactured.
NHTSA believes that it would be in the interest of motor vehicle
safety to add this information to the CNG container label. Adding
information about container type, e.g., Type 1, 2, 3 or 4 would be
consistent with the agency's adoption of NGV2's design and material
specifications in the CNG final rule. The agency believes that
specifying the type of container would facilitate oversight of
compliance tests since each type of container is required to undergo a
hydrostatic burst test with a safety factor unique to that type. Adding
the phrase ``CNG ONLY'' would assure that CNG containers are used only
for CNG and are not used for other fuels for which the containers were
not designed, such as liquefied petroleum gas (LPG).
Since NHTSA has no statutory authority to require the periodic
inspection of CNG containers after the first consumer purchase, adding
information about periodic inspections would help assure their safe use
after this time. Such statements would alert owners to the desirability
for reinspection over time or in the event of an accident. The agency
notes that the proposed requirement is consistent with NGV2's
guidelines for visual inspection of CNG containers every 36 months.
Reference to the CGA guidelines would provide standardized criteria by
which to inspect containers built by different manufacturers. The
agency is proposing use of the visual inspection guidelines contained
in CGA C-6, C-6.1, and C-6.2, and not those for hydrostatic testing. In
addition to the proposal that the container be inspected after an
accident or at least every 36 months, NHTSA requests comments about the
need to specify both a time interval and a mileage interval (e.g., the
agency could require the following statement: ``This container should
be visually inspected after a motor vehicle accident or fire, and for
damage or deterioration at least every 36 months or 36,000 miles,
whichever comes first, in accordance with . . .''). What time and
mileage intervals would be most appropriate? Would an agency
requirement for inspection every 12 months be appropriate?
NHTSA is proposing to require information about the container's
service life in the belief that this information would help assure that
a CNG container is removed from service after its design service life
expires. As commenters on the NPRM stated, this is especially important
since there is a finite period during which CNG containers can be used
safely. The agency is proposing 15 years because CNG containers built
to follow NGV2 have a design service life of 15 years. Nevertheless,
since containers may be built for a service life other than 15 years,
the agency would allow a manufacturer to specify the service life
length appropriate to its containers.
The agency requests comments about the need for each of these
proposed items of information and alternative ways to specify this
information.
b. Label location. In response to the NPRM, EDO and NYCFD stated
that the label should include certain labeling information such as the
maximum fill pressure at a location close to the fill receptacle.
NHTSA has decided to propose requirements related to the label's
location. Accordingly, the agency has decided to propose that the
containers be installed in a manner that ensures the visibility of the
container labeling. Specifically, the agency is proposing to require
the label to be near the end of the container containing the outlet
valve, since such a location would help ensure that the label would be
more visible during refueling. The agency notes that NGV2 contains a
similar requirement.
2. Vehicle labeling
The CNG vehicle final rule did not specify requirements for the
labeling of CNG fueled vehicles. In this SNPRM, the agency is proposing
to amend Standard No. 303 to include two items of information.
S5.3.1 The statement: ``Maximum service pressure ________ kPa
(________ psig).''
S5.3.2 The statement ``See instructions on fuel container for
inspection and service life.''
The agency believes that the first item of information would help
assure that CNG containers are not overfilled during refueling. The
second item is intended to assure that vehicle owners and operators are
informed about the important safety information on container
inspection. In addition, the agency is proposing that for vehicles
manufactured or converted prior to the first sale to the consumer, the
manufacturer provide this information in writing to the consumer,
either in the owner's manual or on a one page statement. The agency
requests comments about the need for vehicle labeling and written
information bearing this and other information.
I. Other Safety Information
NHTSA requests comments on the following additional issues related
to the safe performance of CNG containers. What are the safety
implications of fast-filling CNG containers during refueling, which can
result in pressure levels of 125 percent of service pressure due to the
heat of pressurization? Do the initial permeation rates of CNG
containers constructed of nonmetallic liners remain constant over the
life of the container? What are the consequences of gas permeation from
vehicles fueled by multiple CNG containers? What are the degradation
characteristics of vinyl esters and thermoplastic resins for composite
material? Should containers and container liners have longitudinal or
circumferential welds?
J. Leadtime
NHTSA is proposing to make the requirements in this notice
effective one year after publication of the final rule in the Federal
Register. The agency believes this would be a reasonable time period
for container manufacturers to test their containers and certify
compliance to the additional tests being proposed in this notice. The
agency anticipates that container manufacturers would readily be able
to certify compliance to the proposed requirements. This is because
container manufacturers already certify compliance with NGV2, which is
essentially consistent with the proposed requirements. The one
exception is the proposed salt spray test. The agency requests comments
about the leadtime. Does one year provide sufficient time for
manufacturers to certify compliance to the proposed requirements? Would
the addition of the proposed salt spray test require a longer leadtime
than one year?
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 one year. Manufacturers have sought
to achieve early compliance with other agency requirements\7\ such as
those relating to dynamic side impact protection and air bags. 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.
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\7\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 statte, a certification is a
statement that a vehicle or item of equipment meets all applicable
Federal Motor Vehicle Standards that are then in effect. Therefore,
until a standard is effective, manufacturers may not certify
compliance with it.
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K. Benefits
As explained earlier, NHTSA anticipates that the number of CNG fuel
vehicles will increase greatly in the near future, in light of
directives by the Clinton Administration and legislation by Congress to
develop vehicles powered by cleaner burning fuels. This notice will
enhance the safety of this growing population of vehicles, since CNG
containers will be required to comply with the tests in Standard No.
304. The necessity for certifying compliance with the Federal
requirements will provide added assurance that the containers are safe.
The benefits of the proposal to issue additional requirements
applicable to CNG containers are to provide assurances of the
structural integrity of the CNG containers. The agency is adding one
test not currently part of NGV2 (the salt spray test) to simulate
environmental roadway conditions. In addition, by helping to minimize
any safety concerns associated with CNG vehicles, this rule should
result in positive environmental impacts.
L. Costs
For six of the seven tests proposed, there would be no additional
costs of upgrading current containers to comply with the proposed
requirements, since CNG container manufacturers already comply with
NGV2. Similarly, there would be no additional compliance test costs for
these six tests, since the manufacturers already meet the NGV2 tests.
Testing and container costs for these six tests are estimated to range
from $13,800 to $30,650 per container size and type. The agency does
not know whether existing containers can meet the proposed salt spray
test, and what costs might be incurred if the containers do not meet
the proposed test. The agency estimates that the testing and container
cost for the salt spray test to range from $1,220 to $4,130. Total
testing and container cost for the proposal are $15,020 to $34,780. The
agency has made the criteria in some of the tests more objective than
NGV2 by changing unacceptably subjective and broad terms to more
measurable and therefore more objective criteria.
Rulemaking Analyses and Notices
A. Executive Order 12866 (Federal Regulation) 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 Preliminary Regulatory
Evaluation (PRE) which has been placed in the docket for this
rulemaking. As discussed in that document, NHTSA estimates that total
testing and container costs for this proposal are $15,020 to $34,780
per container size and type. The agency believes that a CNG container
which meets the current industry standard, NGV2, would also comply with
the requirements of this proposal, with the exception of the salt spray
test.
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 would not have a significant
economic impact on a substantial number of small entities. For six of
the seven tests, there will be no small business impacts since the
proposed standards are already being met. Comments are requested on
current compliance with the salt spray test and whether this would have
small business impacts. Information available to the agency indicates
that the 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 would 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 would have no adverse impact on the
quality of the human environment. On the contrary, because NHTSA
anticipates that ensuring the safety of CNG vehicles would encourage
their use, NHTSA believes that the rule would have positive
environmental impacts since CNG vehicles are expected to have near-zero
evaporative emissions and the potential to produce very low exhaust
emissions as well.
E. Civil Justice Reform
The proposal 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.
Public Comments
Interested persons are invited to submit comments on the proposal.
It is requested but not required that 10 copies be submitted.
All comments must not exceed 15 pages in length. (49 CFR 553.21).
Necessary attachments may be appended to thee submissions without
regard to the 15-page limit. This limitation is intended to encourage
commenters to detail their primary arguments in a concise fashion.
If a commenter wishes to submit certain information under a claim
of confidentiality, three copies of the complete submission, including
purportedly confidential business information, should be submitted to
the Chief Counsel, NHTSA, at the street address given above, and seven
copies from which the purportedly confidential information has been
deleted should be submitted to the Docket Section. A request for
confidentiality should be accompanied by a cover letter setting forth
the information specified in the agency's confidential business
information regulation. 49 CFR Part 512.
All comments received before the close of business on the comment
closing date indicated above for the proposal will be considered, and
will be available for examination in the docket at the above address
both before and after that date. To the extent possible, comments filed
after the closing date will also be considered. Comments received too
late for consideration in regard to the final rule will be considered
as suggestions for further rulemaking action. The NHTSA will continue
to file relevant information as it becomes available in the docket
after the closing date, and it is recommended that interested persons
continue to examine the docket for new material.
Those persons desiring to be notified upon receipt of their
comments in the rules docket should enclose a self-addressed, stamped
postcard in the envelope with their comments. Upon receiving the
comments, the docket supervisor will return the postcard by mail.
List of Subjects in 49 CFR Part 571
Imports, Incorporation by reference, Motor vehicle safety, Motor
vehicles, Rubber and rubber products, Tires.
In consideration of the foregoing, the agency proposes to amend
Standard No. 303; Fuel System Integrity of Compressed Natural Gas
Vehicles and Standard No. 304: Compressed Natural Gas Fuel Container
Integrity, in Title 49 of the Code of Federal Regulations at Part 571
as follows:
PART 571--[AMENDED]
1. The authority citation for Part 571 would continue to read as
follows:
Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166;
delegation of authority at 49 FR 1.50.
Sec. 571.303 [Amended]
2. In Sec. 571.303, S5 would be amended to add S5.3 through S5.3.2
and S5.4 which would read as follows:
* * * * *
S5.3 Each CNG vehicle shall be permanently labeled, near the
vehicle refueling connection, with the information specified in S5.3.1
and S5.3.2. The information shall be visible during refueling, in
English, and in letters and numbers that are not less than 4.76 mm (3/
16 inch) high.
S5.3.1 The statement: ``Maximum service pressure ________ kPa
(________ psig).''
S5.3.2 The statement ``See instructions on fuel container for
inspection and service life.''
S5.4 When a motor vehicle is delivered to the first purchaser for
purposes other than resale, the manufacturer shall provide the
purchaser with a written statement of the information in S5.3.1 and
S5.3.2 in the owner's manual, or, if there is no owner's manual, on a
one-page document. The information shall be in English and in not less
than 10 point type.
* * * * *
3. Section 571.304, Standard No. 304; Compressed Natural Gas Fuel
Container Integrity, would be amended by revising S7.4, adding S7.5
through S7.11, revising S8.3.2 through S8.3.4, S8.3.6, and S8.3.7, and
adding S8.5 through S8.11.3, to read as follows:
Sec. 571.304 Standard No. 304, Compressed natural gas fuel container
integrity.
* * * * *
S7.4. Labeling. Each CNG fuel container shall be permanently
labeled, within 30.5 cm (12 inches) of the end of the container
containing the outlet valve, with the information specified in
paragraphs (a) through (h) of this section. The information 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) The statement: ``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.
(e) The container designation (e.g., Type 1, 2, 3, 4).
(f) The statement: ``CNG Only.''
(g) The statement: ``This container should be visually inspected
after a motor vehicle accident or fire and at least every 36 months for
damage and deterioration in accordance with the Compressed Gas
Association (CGA) guidelines C-6 and C-6.1 for Type 1 containers and C-
6.2 for Types 2, 3, and 4 containers.''
(h) The statement: ``Do Not Use After ____________,'' inserting the
year that is the 15th year beginning after the year in which the
container is manufactured.
* * * * *
S7.5 Environmental cycling test. Each CNG fuel container shall not
leak or permanently change in external configuration or dimensions,
when tested in accordance with S8.5.
S7.6 Charpy impact test. Each steel container and each steel liner
shall comply with the requirements of this section. When three 5 x 10
mm specimens of a steel container or steel liner are tested in
accordance with S8.6--
S7.6.1 Each specimen shall absorb not less than 80 J/cm\2\ before
breaking.
S7.6.2 The average of the amounts of energy absorbed by the three
specimens before breaking shall be not less than 100 J/cm\2\.
S7.7 Gunfire test. Each CNG fuel container shall comply with this
section. When a container is tested in accordance with S8.7, no piece
exceeding 30 grams in mass shall separate from the container.
S7.8 Flaw tolerance test. When tested in accordance with S8.8,
each Type 2, Type 3, and Type 4 CNG fuel container shall not leak or
permanently change in external configuration or dimensions. In
addition, the cut made in accordance with S8.8 for the purpose of this
test shall not increase in length, width or depth as a result of this
test.
S7.9 Pendulum impact test. Each Type 2, Type 3, and Type 4 CNG
container shall not leak, when tested in accordance with S8.9.
S7.10 Drop test. Each CNG fuel container shall not leak, when
tested in accordance with S8.10.
S7.11 Road salt environmental test. Each CNG fuel container shall
not leak or permanently change in external configuration or dimensions,
when tested in accordance with S8.11.
* * * * *
S8.3.2 The CNG fuel container is positioned so that its
longitudinal axis is horizontal. Attach three thermocouples to measure
temperature on the container's bottom side along a line parallel to the
container longitudinal centerline. Attach one at the midpoint of the
container, and one at each end at the point where the dome end
intersects the container sidewall. 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. Attach three thermocouples to
measure temperature on the container's bottom side along a line which
intersects the container longitudinal centerline. Attach one at the
midpoint of the bottom of the container, and one each at the point
where the dome end intersects the container sidewall. Subject the
container 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 suspended at a distance
above the fire such that the container bottom surface temperatures
specified in S8.3.6 are achieved.
* * * * *
S8.3.6 The fire is generated by any fuel that generates a flame
temperature between 850 deg. and 900 deg.C for the duration of the
test, as verified by each of the three thermocouples in S8.3.2 or
S8.3.3.
S8.3.7 The fuel specified in S8.3.6 is such that there is
sufficient fuel to burn for at least 20 minutes. To ensure that the
sides of the fuel container are exposed to the flame, the surface area
of the fire on a horizontal plane is such that it exceeds the fuel
container projection on a horizontal plane by at least 20 cm (8 inches)
but not more than 50 cm (20 inches).
* * * * *
S8.5 Environmental cycling test procedures.
S8.5.1 Adjust a pass/fail gauge to fit the container before the
test.
S8.5.2 After the removal of any protective coating or temporary
coating such as oil or grease, a CNG fuel container is cycle tested as
follows:
S8.5.2.1 Precondition the container's interior as follows: Fill
container \1/2\ full with water, pressurize container to 1.0 psi with
hydrogen sulfide, increase pressure to 50 psi with carbon dioxide, then
increase pressure to 67 percent of the service pressure with automotive
grade natural gas. Maintain the pressure at room temperature for 15
days, then increase the room temperature to 60 deg.C (140 deg.F) and
hold for 15 days. Depressurize the container, drain and dry. Add an
amount of compressor oil sufficient to coat the interior surfaces of
the container. Pressurize to 67 percent of the service pressure using
automotive grade natural gas and hold for 15 days at 60 deg.C (140
deg.F) room temperature. Depressurize the container.
S8.5.2.2 Condition the container for 48 hours at zero pressure, 60
deg.C (140 deg.F) and 95 percent relative humidity. To obtain the
specified temperature and relative humidity, spray with a fine spray or
mist of water at 60 deg.C (140 deg.F) in a chamber held at 60 deg.C
(140 deg.F).
S.8.5.2.3 For 5,000 cycles at 60 deg.C (140 deg.F) and 95
percent relative humidity, hydrostratically pressurize the container
from (1) a level not more than 10 percent of the service pressure, to
(2) 125 percent of the service pressure.
S8.5.2.4 Stabilize at zero pressure and ambient conditions.
S8.5.2.5 For 5,000 cycles at -40 deg.C (-40 deg.F),
hydrostatically pressurize the container from (1) a level not more than
10 percent of the service pressure to (2) the service pressure.
S8.5.2.6 The cycling rate does not exceed 10 cycles per minute.
S8.5.3 Determine that the container has not leaked or permanently
changed in external configuration or dimension. With respect to changes
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one
in S8.5.1.
S8.6 Charpy impact test procedures.
S8.6.1 Cut one set of three longitudinal 5X10 mm Charpy Vee notch
specimens from one container or liner. Each specimen is then tested at
-40 deg. C (-40 deg. F) in accordance with the Methods for Notched Bar
Impact Testing of Metallic Materials, ASTM E 23.
S8.7 Gunfire test procedures. A container is pressurized with
nitrogen or air to service pressure. The container is then impacted by
a 0.30 caliber armor-piercing projectile having a muzzle velocity of
853 meter/second (2,800 feet/second). The container is positioned so
that the projectile impact point is in the container sidewall, with the
trajectory passing through the container longitudinal centerline at an
angle of 45 degrees and exiting through the opposite sidewall. The
distance from the muzzle to the test container is 46 m (50 yards).
S8.8 Flaw tolerance test procedures.
S8.8.1 Adjust a pass/fail gauge to fit the container before the
test.
S8.8.2 Make a 25.4 mm (1 inch) long longitudinal cut into the
outer wall of a CNG test container at its midlength. The cut's depth is
0.75 mm (0.030 inch) and width is 0.75 mm.
S8.8.3 For 1,5000 cycles at ambient temperature, hydrostatically
pressurize the container from (1) a level not more than 10 percent of
the service pressure, to (2) the service pressure.
S8.8.4 Determine that the container has not leaked or permanently
changed in external configuration or dimension. With respect to changes
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one
in S8.5.1 or S8.81.
S8.9 Pendulum impact test procedures.
S8.9.1 The container is empty and at 21 deg.C (70 deg.F).
S8.9.2 A pendulum impact testing fixture is used for the test. The
impact body is a steel pyramid with equilateral triangle faces and a
square base. The summit and the edges of the pyramid are rounded to a
radius of 3 mm (0.12 inch). The center of percussion of the pendulum
coincides with the center of gravity of the pyramid. The center's
distance from the axis of rotation of the pendulum is 1 meter (40
inches). The total mass of the pendulum referred to its center of
percussion is 15 kg (33 pounds). The energy of the pendulum at the
moment of impact is not less than 30 Nm (22.1 ft-lbf).
S8.9.3 During the test, the container is held in position by the
end bosses or by the mounting brackets.
S8.9.4 The impact body strikes the test container at any point and
any angle on the container.
S8.9.5 For 1,500 cycles at ambient temperature, hydrostatically
pressurize the container from (1) a level not more than 10 percent of
the service pressure to (2) the service pressure.
S8.9.6 Determine that the container has not leaked.
S8.10 Drop test procedures.
S8.10.1 The container is drop tested at ambient temperature
without internal pressurization or attached valves. The container is
held in a horizontal position with the bottom 3.05 meters (10 feet)
above the surface onto which it is dropped. The surface is a smooth,
horizontal concrete pad or flooring that is 4 inches thick.
S8.10.2 For 5,000 cycles at ambient temperature, hydrostatically
pressurize the container from (1) a level not more than 10 percent of
the service pressure to (2) 125 percent of the service pressure, and
then for 13,000 cycles from (1) a level not more than 10 percent of the
service pressure to (2) the service pressure.
S8.10.3 Determine that the container has not leaked.
S8.11 Road salt environmental test procedures.
S8.11.1 Adjust a pass/fail gauge to fit the container before the
test.
S8.11.2 A CNG fuel container, free of any protective coating, is
cycle tested as follows:
S8.11.2.1 Subject the container to a salt spray (fog) test in
accordance with ASTM B-117-73, ``Method of Salt Spray (Fog) Testing,''
for 240 hours consisting of ten successive 24 hour periods. During each
period, the container shall be mounted in the middle of the chamber and
exposed for 23 hours to the salt spray. The spray is not activated
during the 24th hour.
S8.11.2.2 For 5,000 cycles at ambient conditions, hydrostatically
pressurize the container from (1) a level not more than 10 percent of
the service pressure to (2) 125 percent of the service pressure.
S8.11.2.3 Stabilize at zero pressure and ambient conditions.
S8.11.2.4 For 5,000 cycles at -40 deg. C (-40 deg. F),
hydrostatically pressurize the container from (1) a level not more than
10 percent of the service pressure to (2) the service pressure.
S8.11.2.5 The cycling rate does not exceed 10 cycles per minute.
S8.11.3 Determine that the container has not leaked or permanently
changed in external configuration or dimension. With respect to changes
in the container's external configuration or dimension, adjust a pass/
fail gauge to fit the container. Compare the measurement with the one
in S8.11.1.
Issued on: December 9, 1994.
Barry Felrice,
Associate Administrator for Rulemaking.
[FR Doc. 94-31016 Filed 12-16-94; 8:45 am]
BILLING CODE 4910-59-P