Hazardous Materials: Request for Feedback on Determining the Effectiveness of Pressure Relief Devices (PRDs) on Composite Overwrapped Pressure Vessels (COPVs), 12934-12936 [2025-04605]

Agencies

• Pipeline and Hazardous Materials Safety Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 90, Number 52 (Wednesday, March 19, 2025)]
[Notices]
[Pages 12934-12936]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-04605]


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DEPARTMENT OF TRANSPORTATION

Pipeline and Hazardous Materials Safety Administration

[Docket No. PHMSA-2024-0180, (Notice No. 2024-15)]


Hazardous Materials: Request for Feedback on Determining the 
Effectiveness of Pressure Relief Devices (PRDs) on Composite 
Overwrapped Pressure Vessels (COPVs)

AGENCY: Pipeline and Hazardous Materials Safety Administration (PHMSA), 
Department of Transportation (DOT).

ACTION: Notice; request for information.

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SUMMARY: PHMSA is publishing this notice to solicit information to 
evaluate the test design for proposed bonfire tests on fully charged 
composite overwrapped pressure vessels (COPVs) with different pressure 
relief devices; seek input on how test results could inform design 
guidelines for COPVs; and solicit feedback on the impacts of possible 
updates for design guidelines.

DATES: Interested parties are invited to submit comments on or before 
June 17, 2025. Comments received after that date will be considered to 
the extent possible.

ADDRESSES: You may submit comments identified by the Docket Number 
PHMSA-2024-0180 by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov. 
Follow the instructions for submitting comments.
     Fax: 1-202-493-2251.
     Mail: Docket Management System; U.S. Department of 
Transportation, West Building, Ground Floor, Room W12-140, Routing 
Symbol M-30, 1200 New Jersey Avenue SE, Washington, DC 20590.
     Hand Delivery: Docket Management System; Room W12-140 on 
the ground floor of the West Building, 1200 New Jersey Avenue SE, 
Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.
    Instructions: All submissions must include the agency name and 
Docket Number [PHMSA-2024-0180] for this notice. To avoid duplication, 
please use only one of these four methods. All comments received will 
be posted without change to the Federal Docket Management System (FDMS) 
and will include any personal information you provide.
    Docket: For access to the dockets to read background documents or 
comments received, go to https://www.regulations.gov or DOT's Docket 
Operations Office (see ADDRESSES).
    Privacy Act: In accordance with 5 U.S.C. 553(c), DOT solicits 
comments from the public. DOT posts these comments, without edit, 
including any personal information the commenter provides, to https://www.regulations.gov, as described in the system of records notice (DOT/
ALL-14 FDMS), which can be reviewed at https://www.dot.gov/privacy.
    Confidential Business Information (CBI): CBI is commercial or 
financial information that is both customarily and actually treated as 
private by its owner. Under the Freedom of Information Act (FOIA) (5 
U.S.C. 552), CBI is exempt from public disclosure. If your

[[Page 12935]]

comments responsive to this notice contain commercial or financial 
information that is customarily treated as private, that you actually 
treat as private, and that is relevant or responsive to this notice, it 
is important that you clearly designate the submitted comments as 
``CBI.'' Please mark each page of your submission containing CBI as 
``PROPIN.'' Submissions containing CBI should be sent to Andrew Leyder, 
Pipeline and Hazardous Materials Safety Administration, U.S. Department 
of Transportation, 1200 New Jersey Avenue SE, Washington, DC 20590-
0001. Any commentary that PHMSA receives that is not specifically 
designated as CBI will be placed in the public docket for this notice.

FOR FURTHER INFORMATION CONTACT: Andrew Leyder, Office of Hazardous 
Materials Safety, Research, Development & Technology, by phone at 202-
360-0664, by email at [email protected], or by mail at Pipeline and 
Hazardous Materials Safety Administration, U.S. Department of 
Transportation, 1200 New Jersey Avenue SE, Washington, DC 20590-0001.

SUPPLEMENTARY INFORMATION:

I. Purpose

    PHMSA is publishing this notice to (1) solicit information to 
evaluate the test design for proposed bonfire tests on fully charged 
composite overwrapped pressure vessels (COPVs) with different Pressure 
Relief Devices; (2) seek input on how test results could inform design 
guidelines for COPVs; and (3) solicit feedback on the impacts of 
possible updates for design guidelines.

II. Background

    Pressure relief devices (PRDs) are standard equipment on all 
compressed natural gas containers. The function of a PRD is to vent the 
compressed gases in the case of a fire, preventing rupture and the 
subsequent high-pressure gas release with a possible ignition and 
explosion. If the gas is released at high-pressure in certain 
environments, the result could be catastrophic. Therefore, PRD design 
and manufacture must offer a degree of protection and reliability that 
meets or exceeds that of the cylinder to provide the proper degree of 
safety. Pressure vessels can be constructed using metal (e.g., steel or 
aluminum) or composite material (i.e., cylinder/tube is wrapped with 
continuous filaments held with metallic/polymer liners). Pressure 
vessels used for transporting flammable gases are equipped with PRDs to 
prevent explosions or ruptures during a fire. Per the Compressed Gas 
Association (CGA) pamphlet S1.1, both metallic pressure vessels and 
COPVs are typically equipped with CG-4 or CG-5 devices. These PRDs are 
designed to activate under a combination of excess temperature and 
pressure during a fire. The CG-4 device is more sensitive to 
temperature as it uses a fusible metal plug that melts at a lower 
temperature than those used in a CG-5 device.
    Though there have been issues of premature activation, PRDs 
historically have been used without major problems. Stainless steel 
DOT-approved cylinders are proven to be fire-resistant for 20 minutes 
without significant loss of yield strength. Due to heat conduction 
through these steel cylinders, the PRDs may be activated before 
cylinder rupture when exposed to excessive heat.
    In contrast, COPVs are more heat-insulating; the internal pressure 
of the cylinder typically will not reach PRD activating pressures 
before the resin in the COPV shell begins to fail. Consequently, COPVs 
will often rupture at lower internal pressures than their metallic 
counterparts because of hull breakdown, and the CG-4 and CG-5 PRDs 
never reach burst pressures.
    On February 11, 2018, a fire incident occurred involving a COPV 
hydrogen tube trailer equipped with Type CG-5 PRDs. A subsequent 
National Transportation Safety Board (NTSB) investigation (NTSB 
incident report number NTSB/HZM-19/02 PB2019-101398) indicated that the 
Type CG-5 PRDs installed on these COPVs had a lower setting than is 
required under CGA PRD standard CGA S1.1. The lower set pressure of the 
Type CG-5 PRDs resulted in premature activation of the devices and 
caused a fire. The fire then spread to adjacent COPVs, which had CG-5 
PRDs that did not function correctly, resulting in an explosion of 
several additional COPVs. NTSB determined that while a correctly rated 
CG-5 PRD may have reduced the risk of fire initiation, the CG-5 PRD 
would not have prevented the COPVs from exploding due to exposure to 
high heat temperatures.
    The NTSB report for this incident is available online at 59258 
(ntsb.gov). NTSB directed PHMSA to work with CGA to develop design 
guidelines for tube trailer pressure relief device vent systems in 
Recommendation H-19-21. To address that recommendation, a systematic 
evaluation of alternative PRDs in COPVs is necessary. There are 
alternative PRDs (e.g., CG-9 and CG-10) that use thermal activation 
rather than the pressure/temperature combination for activation. These 
PRDs are commonly used on NGV-2 composite tubes, which have different 
design specifications and operating conditions than COPVs regulated 
under the Hazardous Materials Regulations (49 CFR parts 171 through 
180). To evaluate whether thermally activated PRDs are effective 
alternatives for COPVs, PHMSA is proposing a test design for various 
PRDs subjected to bonfire tests on COPVs.

III. Request for Feedback

    The objective of this project is to assess the effectiveness of 
various PRDs when subjected to bonfire tests on fully charged COPVs. 
The test results will determine the optimal number, type, and location 
of PRDs to install in fully charged COPVs. The goal is to prevent 
potential cylinder ruptures similar to the one described in the NTSB 
investigation and recommendations reports. These test results can 
inform future pressure vessel design guidelines.
    The specified COPVs are:
    a. Type 3 COPVs with 16'' outside diameter, 120'' length, and 
5,400-psig test pressure.
    b. Type 4 COPVs with 16'' outside diameter, 120'' length, and 
5,400-psig test pressure.
    PRDs to be tested are CG-4, CG-5, CG-9, and CG-10 PRDs that meet 
the requirements set forth in pamphlet S1.1 of the CGA.
    Bonfire testing will be completed under four different pressure 
vessel configurations at three different locations for each PRD. Each 
bonfire will be applied for a minimum of 30 minutes.
     One type 3 COPV with a CG-4 PRD at each end will be used, 
with the center of the fire at three different locations (PRD exposed 
to fire 6'' and 10'' away from the fire).
     One type 4 COPV with a CG-5 PRD at each end will be used, 
with the center of the fire at three different locations (PRD exposed 
to fire 6'' and 10'' away from the fire).
     A steel pipe with a CG-9 PRD will be used, with the center 
of the fire at three different locations (PRD exposed to fire 6'' and 
10'' away from the fire).
     A steel pipe with a CG-10 PRD will be used, with the 
center of the fire at three different locations (PRD exposed to fire 
6'' and 10'' away from the fire).
     One type 4 COPV with a CG-9 PRD at each end will be used, 
with the center of the fire at three different locations (PRD exposed 
to fire 6'' and 10'' away from the fire).
     One type 4 COPV with a CG-10 PRD at each end will be used, 
with the center of the fire at three different locations (PRD exposed 
to fire 6'' and 10'' away from the fire).

[[Page 12936]]

    PHMSA requests comment on the following questions to assist in our 
evaluation of the proposed research and development with a scope as 
specified above.
    1. Would the results from the proposed testing adequately inform 
design specifications for vent systems?
    2. Is the number of COPV tubes in the above test matrix adequate 
for a representative test of the COPV, or should additional COPV tubes 
be tested to ensure replicability?
    3. Is a bonfire test of at least 30 minutes sufficient to test 
activation of the PRDs? If not, what would be a sufficient minimum 
duration to test PRD activation?
    4. Should a minimum bonfire temperature be specified to test PRD 
activation? If so, what should the minimum bonfire temperature be?
    5. Is the number of bonfire tests (one for each configuration) 
sufficient to test PRD effectiveness? If not, how many replicates of 
the test should be conducted?
    6. Would testing at 6'' and 10'' away from the center of the fire 
be sufficient to capture differences in fire location from the PRDs? If 
not, what fire distances/locations are recommended?
    7. Should different operating pressures be tested? If so, what 
other pressures should be tested?
    8. Do the proposed COPV/PRD combinations provide an accurate 
comparison of temperature/pressure-activated PRDs to temperature-
activated PRDs? If not, which COPV/PRD combinations should also be 
considered in addition to the above testing matrix?
    9. What other variables, if any, should be included in testing?
    10. Are there other existing safety concerns about COPVs and PRDs 
that PHMSA should be aware of?
    11. What, if any, are the cost impacts of using CG-9 or CG-10 PRDs 
on COPVs instead of CG-4 or CG-5?
    12. How common is the current use of CG-9 or CG-10 PRDs for COPVs 
used to transport flammable gases?
    13. Should the allowable PRDs for COPVs used to transport flammable 
gases be limited to CG-9 or CG-10?

    Issued in Washington, DC, on March 14, 2025.
Yolanda Y. Braxton,
Director, Operations System Division, Office of Hazardous Materials 
Safety, Pipeline and Hazardous Materials Safety Administration.
[FR Doc. 2025-04605 Filed 3-18-25; 8:45 am]
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