Hazardous Materials: Harmonization With International Standards

Federal RegisterFeb 10, 2026

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DEPARTMENT OF TRANSPORTATION

Pipeline and Hazardous Materials Safety Administration

49 CFR Parts 171, 172, 173, 175, 176, 178, and 180

[Docket No. PHMSA-2023-0111 (HM-215R)]

RIN 2137-AF64

Hazardous Materials: Harmonization With International Standards

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

PHMSA proposes to amend the Hazardous Materials Regulations to adopt certain international regulations and standards related to proper shipping names, hazard classes, packing groups, special provisions, packaging authorizations, air transport quantity limitations, and vessel stowage requirements. These amendments are intended to maintain consistency with the latest international standards and regulations, and to reduce costs to entities or individuals within the United States or to otherwise lower the cost of regulations on the United States economy.

DATES:

Comments must be received by April 13, 2026. To the extent possible, PHMSA will consider late-filed comments while a final rule is developed.

ADDRESSES:

You may submit comments by any of the following methods:

•

Federal Rulemaking Portal: http://www.regulations.gov.

Follow the online instructions for submitting comments.

•

Fax:

1-202-493-2251.

•

Mail:

Docket Management System; U.S. Department of Transportation, Docket Operations, M-30, Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590-0001.

•

Hand Delivery:

U.S. Department of Transportation, Docket Operations, M-30, Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590-0001 between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Instructions:

Include the agency name and docket number PHMSA-2023-0111 (HM-215R) or RIN 2137-AF64 for this rulemaking at the beginning of your comment. All comments received will be posted without change to

http://www.regulations.gov,

including any personal information provided. If sent by mail, comments must be submitted in duplicate. Persons wishing to receive confirmation of receipt of their comments must include a self-addressed stamped postcard.

Docket:

For access to the dockets to read background documents including the Preliminary Regulatory Impact Analysis (PRIA) or comments received, go to

http://www.regulations.gov

or DOT's Docket Operations Office (

see

ADDRESSES

Confidential Business Information:

Confidential Business Information (CBI) is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments in response to this NPRM 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 NPRM, it is important that you clearly designate the submitted comments as CBI. Pursuant to 49 CFR 105.30, you may ask PHMSA to provide confidential treatment to the information you give to the agency by taking the following steps: (1) mark each page of the original document submission containing CBI as “Confidential;” (2) send PHMSA a copy of the original document with the CBI deleted along with the original, unaltered document; and (3) explain why the information you are submitting is CBI. Submissions containing CBI should be sent to Steven Andrews, 1200 New Jersey Avenue SE, DOT: PHMSA-PHH-10, Washington, DC 20590-0001. Any comment PHMSA receives that is not explicitly designated as CBI will be placed in the public docket.

FOR FURTHER INFORMATION CONTACT:

Candace Casey, Standards and Rulemaking, at 202-366-8553, Pipeline and Hazardous Materials Safety Administration, U.S. Department of Transportation, 1200 New Jersey Avenue SE, East Building, 2nd Floor, Washington, DC 20590-0001.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary

II. Background

III. Incorporation by Reference Discussion Under 1 CFR Part 51

IV. Amendments Not Being Proposed for Adoption

V. Section-by-Section Review of NPRM Proposals

VI. Regulatory Analyses and Notices

A. Legal Authority

B. Executive Order 12866; Regulatory Planning and Review

C. Executive Orders 14192 and 14219

D. Energy-Related Executive Orders 13211, 14154, and 14156

E. Executive Order 13132: Federalism

F. Regulatory Flexibility Act

G. Unfunded Mandates Reform Act of 1995

H. National Environmental Policy Act

I. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

J. Privacy Act

K. Paperwork Reduction Act

L. Executive Order 13609 and International Trade Analysis

M. National Technology Transfer and Advancement Act

N. Cybersecurity and Executive Order 14028

O. Severability

I. Executive Summary

The Secretary of Transportation is directed by 49 U.S.C. 5120 to ensure that domestic regulations for the transportation of hazardous materials are generally consistent with the latest international standards and requirements, unless such standards or requirements are unnecessary or unsafe, or a more stringent safety standard is in the public interest. Consistent with this statutory requirement, the Pipeline and Hazardous Materials Safety Administration proposes to amend the Hazardous Materials Regulations (HMR) to adopt certain international regulations and standards, including changes to material incorporated by reference, hazardous materials descriptions and proper shipping names (PSN), hazard classes, packing groups (PG), special provisions, packaging authorizations, air transport quantity limitations, and vessel stowage requirements.

PHMSA anticipates that the adoption of the amendments proposed in this NPRM will maintain the current levels of safety achieved under the HMR. Harmonizing the HMR with international consensus standards is expected to also reduce delays and interruptions in the transportation of hazardous materials and promote the efficient and free flow of commerce by eliminating unnecessary, outdated, and conflicting regulatory requirements. Overall, the proposed amendments are intended to reduce costs to entities or individuals within the United States or otherwise lower the cost of regulations on the United States economy.

The following list summarizes noteworthy proposals set forth in this NPRM:

•

Incorporation by Reference:

PHMSA proposes to incorporate by reference updated versions of the following international hazardous materials regulations and standards: the 2025-2026 edition of the International

Civil Aviation Organization Technical Instructions for the Safe Transport of Dangerous Goods by Air (ICAO Technical Instructions); Amendment 42-24 to the International Maritime Dangerous Goods Code (IMDG Code); the 2023 edition of Transport Canada's Transportation of Dangerous Goods (TDG) Regulations; and the 23rd revised edition of the United Nations Recommendations on the Transport of Dangerous Goods—Model Regulations (UN Model Regulations).

•

Amendments to the Hazardous Materials Table:

PHMSA proposes amendments to the Hazardous Materials Table (HMT; § 172.101) to add, to revise, or to remove certain PSNs, hazard classes, PGs, SPs, packaging authorizations, bulk packaging requirements, and passenger and cargo aircraft maximum quantity limits.

•

Increase in authorized amounts of certain gases transported as limited quantities:

For modes other than air transportation, PHMSA proposes to extend the relief provided by the limited quantity provisions to four Division 2.2 (non-flammable and non-poisonous) compressed gases. This amendment would authorize these materials for transport as a limited quantity material in quantities up to 1000 ml (34 fluid ounces) per package, when transported in DOT specification cylinders or UN pressure receptacles. These materials are: “UN1006, Argon,” “UN1013, Carbon dioxide,” “UN1046, Helium,” and “UN1066, Nitrogen.”

•

Amendments to the Organic Peroxides Table:

PHMSA proposes amendments to the organic peroxides table in § 173.225, which lists individual organic peroxide formulations that are authorized for transportation without prior approval. The proposed amendments include the addition of three new formulations: (Dibenzoyl peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy) hexane, and methyl ethyl ketone peroxide (with a concentration limit of available oxygen ≤10 percent), that will no longer require prior approval when transported under the conditions outlined in the table, as well as the addition of a new authorized packaging for Di-(3,5,5-trimethylhexanoyl) peroxide, not more than 52 percent, stable dispersion, in water.

•

Amendments to provisions for the transport of tetramethylammonium hydroxide:

PHMSA proposes to adopt several changes pertaining to entries for Tetramethylammonium hydroxide (TMAH) to maintain consistency with changes adopted in several international standards in response to new incident and test data showing a toxicity hazard in addition to the previously identified corrosivity hazard. The proposed amendments include the addition of a new HMT entry for aqueous solutions, and revisions to the hazard classification, proper shipping name, or both, for existing entries of PG II and PG III TMAH solutions (UN1835), reclassification of TMAH solids (UN3423), the addition of two new special provisions, and revised packaging authorizations.

•

New provisions for sodium ion batteries:

PHMSA proposes to add new HMT entries and transport provisions for sodium ion batteries to maintain consistency with changes adopted in the 2025-2026 edition of the ICAO Technical Instructions and the 23rd revised edition of the UN Model Regulations. The new provisions in the international regulations regulate sodium ion batteries in the same way as lithium ion batteries and are intended to address anticipated increases in the use of sodium ion batteries as an alternative to lithium ion batteries.

•

New state-of-charge provisions for certain lithium and sodium ion batteries transported by air:

PHMSA proposes expanding current state-of-charge requirements to certain lithium and sodium ion batteries transported by air. The new provision would limit the amount of stored energy to 30 percent or less of the battery's capacity at the time of transport.

•

Improved Emergency Response Information for Lithium Batteries Transported as “UN3536, Lithium batteries installed in cargo transport unit lithium ion batteries or lithium metal batteries: ”

PHMSA proposes to amend Special Provision 389 to require that the emergency response information for UN3536 specifically identify the predominant type of energy storage battery installed in the unit (

e.g.,

lithium ion batteries or lithium metal batteries) and provide information on immediate methods for handling fires. When determining the predominant type of energy storage battery, PHMSA encourages shippers to consider which battery type provides electrical power to external devices or the power grid when units transported under UN3536 are in operation.

•

Exceptions for ammonium nitrate hot concentrated solution:

PHMSA proposes to add specific conditions under which solutions of ammonium nitrate

(hot concentrated solution)

can be transported under the HMT entry “UN2426, Ammonium nitrate” or can qualify for exception from regulation under the HMR. The proposed requirements for solutions of ammonium nitrate to be transported under UN2426 are based on concentration, water content, combustible material content, chlorine content, pH level, and temperature. These requirements were adopted in the 23rd revised edition of the UN Model Regulations to harmonize transport conditions and requirements multimodally.

•

Exceptions for nitrocellulose membrane filters used in rapid test devices:

PHMSA proposes to add a new special provision with specific packaging requirements for “UN3270, Nitrocellulose membrane filters,

with not more than 12.6% nitrogen, by dry mass”

to be excepted from regulation. These materials are most notably used in rapid test devices for infectious diseases and as substrates for bioanalytical tests as well as pregnancy tests. PHMSA's proposal would maintain consistency with changes adopted in the 23rd revised edition of the UN Model Regulations to facilitate further the transport of these items.

PHMSA anticipates that the proposals in the NPRM will produce safety benefits from harmonizing domestic and international regulations. PHMSA solicits comment on the need, benefits, and costs of the proposed HMR revisions; impact on safety and the environment; and any other relevant information. PHMSA also solicits comment regarding approaches to reducing the costs of the proposed HMR revisions while maintaining or increasing safety benefits and on any other specific changes (

e.g.,

greater flexibility regarding a particular proposal) that might improve the rulemaking. As further explained in the PRIA, PHMSA expects that the aggregate benefits of the amendments proposed in this NPRM for United States entities or individuals justify their aggregate costs.

II. Background

The Federal Hazardous Materials Transportation Law (49 U.S.C. 5101,

et seq.

) directs PHMSA to participate in international standard-setting forums for the transportation of hazardous materials in commerce and encourages alignment of the HMR with those standards (49 U.S.C. 5120). Harmonization of the HMR with international standards and regulations can reduce the costs and other burdens of complying with multiple or inconsistent safety requirements between nations.

PHMSA actively participates in the development of international standards for the transportation of hazardous materials and promotes the adoption of standards consistent with the HMR. Maintaining consistency between

current international standards and the HMR enhances safety by, among other things: (1) ensuring the HMR are informed by the latest international best practices and lessons learned; (2) improving understanding of, and compliance with, pertinent international requirements; (3) facilitating the flow of hazardous materials in commerce and avoiding risks to the public and the environment from handling and potential releases of hazardous materials due to delays or interruptions in transportation; and (4) enabling consistent emergency response procedures in the event of a hazardous materials incident.

When considering alignment of the HMR with new or amended international standards, PHMSA reviews each standard on its own merit, assesses its overall impact on transportation safety, and analyzes the economic implications associated with its adoption. PHMSA's goal is to harmonize with international standards without diminishing the level of safety currently provided by the HMR or imposing undue burdens on the regulated community.

In 1990, PHMSA's predecessor, the Research and Special Programs Administration (RSPA), comprehensively revised the HMR for greater consistency with the UN Model Regulations.

The UN Model Regulations constitute a set of recommendations issued by the United Nations Sub-Committee of Experts (UNSCOE) on the Transport of Dangerous Goods and on the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). The UN Model Regulations are amended and updated biennially by the UNSCOE and serve as the basis for national, regional, and international modal regulations, including the ICAO Technical Instructions and IMDG Code. PHMSA routinely updates the HMR to incorporate these biennial amendments.

55 FR 52401 (

c. 21, 1990).

PHMSA has evaluated the latest biennial updates to the international regulations and consensus standards and proposes to revise the HMR to adopt changes consistent with revisions to the 2025-2026 edition of the ICAO Technical Instructions, the Amendment 42-24 to the IMDG Code, and the 23rd revised edition of the UN Model Regulations, all of which were published by or in effect on January 1, 2025.

PHMSA also proposes to incorporate by reference these revised international regulations, as well as several new or updated International Organization for Standards (ISO) standards. The regulations incorporated by reference are authorized for use for domestic and international transportation, under specific conditions, in part 171, subpart C of the HMR.

Amendment 42-24 of the IMDG Code became mandatory on January 1, 2025. Voluntary compliance began on January 1, 2024.

On December 9, 2024, PHMSA issued a notice of enforcement discretion, stating that PHMSA and other Federal agencies that enforce the HMR (

i.e.,

the Federal Railroad Administration (FRA), the Federal Aviation Administration (FAA), the Federal Motor Carrier Safety Administration (FMCSA), and the United States Coast Guard (USCG)) will not take enforcement action against any offeror or carrier who follows the 2025-2026 Edition of the ICAO Technical Instructions and Amendment 42-24 of the IMDG Code when all or part of the transportation is by air with respect to the ICAO Technical Instructions, or all or part of the transportation is by vessel with respect to the IMDG Code, during the pendency of this rulemaking proceeding.

For transport by rail and highway to, from, or within the United States, PHMSA also stated that these agencies will not take enforcement action against any offeror or carrier who offers or accepts hazardous materials identified and described on a shipping paper, or packages either marked or labeled in accordance with these standards—provided that appropriate emergency response information consistent with 49 CFR part 172, subpart G accompanies the shipment. The December 9, 2024, notice of enforcement discretion remains in effect until withdrawn or otherwise modified.

PHMSA,

Notice of Enforcement Policy Regarding International Standards

(Dec. 9, 2024), available at:

https://www.phmsa.dot.gov/regulatory-compliance/phmsa-guidance/notice-enforcement-policy-regarding-international-standards.

PHMSA notes that items described and packaged for transportation under the respective international standards as UN0514 and UN3559, “Fire Suppressant Dispersing Devices,” must first be approved by the Associate Administrator in accordance with 49 CFR 173.56.

III. Incorporation by Reference Discussion Under 1 CFR Part 51

The National Technology Transfer and Advancement Act of 1995 (NTTAA; Pub. L. 104-113) directs Federal agencies to use standards developed by voluntary consensus standards bodies in lieu of government-written standards whenever possible. Voluntary consensus standards bodies develop, establish, or coordinate technical standards using agreed-upon procedures. PHMSA currently incorporates by reference into the HMR all or parts of numerous standards and specifications published by these bodies, which are otherwise known as standard development organizations (SDOs). In general, SDOs update and revise their published standards every two to five years to reflect modern technology and best technical practices.

The Office of Management and Budget (OMB) issued Circular A-119,

Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities,

to implement Section 12(d) of the NTTAA. This circular provides guidance for Federal agencies participating in voluntary consensus standards bodies and describes procedures for satisfying the reporting requirements in the NTTAA. PHMSA is responsible for determining which standards currently referenced in the HMR should be updated, revised, or removed, and which standards should be added to the HMR, under the NTTAA and Circular A-119.

Revisions to materials incorporated by reference in the HMR are handled via the notice-and-comment rulemaking process. PHMSA must also obtain approval from the Office of the Federal Register to incorporate by reference any new materials during that process. The Office of the Federal Register issued a rulemaking that revised 1 CFR 51.5 to require that an agency detail in the preamble of an NPRM the ways the materials it proposes to incorporate by reference are reasonably available to interested parties, or how the agency worked to make those materials reasonably available to interested parties.

Proposed changes to the material incorporated by reference in the HMR are discussed in detail in the Section 171.7 discussion in “Section V. Section-by-Section Review of NPRM Proposals.”

79 FR 66278 (Nov. 7, 2014).

The standards incorporated by reference in this NPRM are reasonably available to interested parties in several ways. The UN Model Regulations and the United Nations Manual of Tests and Criteria (UN Manual of Tests and Criteria) are free and easily accessible to the public on the internet (links are provided in footnotes as part of the section 171.7 discussion in “Section V. Section-by-Section Review of NPRM Proposals”).

The ICAO Technical

Instructions, the IMDG Code, and all ISO standard references are available for interested parties to purchase, either in print or electronic versions through the organizations' websites. In addition, all standards that PHMSA proposes to incorporate by reference in the NPRM will be available for review, free of charge, at the PHMSA Headquarters, 1200 New Jersey Avenue, SE, Washington, DC 20590 during the comment period. Interested persons may email

candace.casey@dot.gov

to arrange for this in-person review.

United Nations,

UN Model Regulations 23rd revised edition,

(October 8, 2023), available at:

https://unece.org/transport/dangerous-goods/un-model-regulations-rev-24;

United Nations,

Manual of Tests and Criteria, Eighth revised edition

(November 27, 2023), available at:

https://unece.org/transport/standards/transport/

dangerous-goods/un-manual-tests-and-criteria-rev8-2023.

IV. Amendments Not Being Proposed for Adoption

PHMSA has determined that certain elements of updated international regulations and standards should not be adopted into the HMR (49 U.S.C. 5120). PHMSA has also determined that certain transport requirements should be authorized on a case-by-case basis through special permits rather than adopting them for general applicability in the HMR. Additional information about these topics is provided below:

•

Additional regulation for carbon and charcoal

—The International Maritime Organization (IMO), through its Sub-Committee on Carriage of Cargoes and Containers (CCC), adopted more stringent requirements than currently exist in the HMR for the transport of carbon (

e.g.,

activated carbon or carbon derived from animal or vegetable origin) in Amendment 42-24 to the IMDG Code. Most notably, the IMO removed the ability to exclude such carbon materials from classification as a Division 4.2 (spontaneously combustible material),

i.e.,

a self-heating material, by way of testing, and consequently the ability to be transported as unregulated.

Section 173.124 of the HMR currently requires carbon materials such as charcoal that are potentially spontaneously combustible because of self-heating properties to be tested by performing UN Test N.4, “Test method for self-heating substances,” in accordance with the UN Manual of Tests and Criteria (see Section 33.4.3.3) and either classified as a Division 4.2 material or excluded from regulation. This classification or exclusion applies to both bulk and non-bulk (

e.g.,

charcoal packaged for retail sale) quantities of carbon. Materials meeting classification criteria are described as “UN1361, Carbon,

animal or vegetable origin

” or “UN1362, Carbon, activated”, Division 4.2, and are subject to packaging requirements for bulk and non-bulk quantities, respectively. See §§ 173.212 and 173.242 for PG II and §§ 173.214 and 173.241 for PG III. In addition, hazardous materials transported under UN1361 and UN1362 are assigned stowage category “A”, meaning that these materials may be stowed “on deck” or “under deck” on a cargo or passenger vessel, and that they must be kept as cool as reasonably practicable and protected from sources of heat. These stowage requirements in the HMR are in alignment with the current requirements under Amendment 42-24 of the IMDG Code. In the absence of safety incidents related to the shipment of these materials, as well as the unlikelihood of unpackaged bulk shipments of carbon materials such as charcoal, PHMSA finds that the current requirements in the HMR provide the appropriate level of safety without imposing unnecessary burdens on transportation.

More specifically, Amendment 42-24 removed Special Provision 925 from the IMDG Code, which previously provided a blanket exception for non-activated carbon blacks of mineral origin, consignments of carbon that passed tests for self-heating substances UN Test N.4, and carbons produced by a steam activation process. Amendment 42-24 also removed packing provision PP12, which previously authorized the use of bags as packaging for materials transported in closed cargo transport units, for “UN1361, Carbon.” In addition, Amendment 42-24 removed Special Provision 223—which was previously applicable to carbon materials assigned to PG III—and permitted substances (except for marine pollutants) covered by the description “UN1361, Carbon, PG III” or “UN1362, Activated carbon, PG III” to be excepted from the IMDG Code when testing showed that the substances did not meet the established defining criteria for any hazard class or division. Amendment 42-24 replaced Special Provisions 925 and 223 with a new Special Provision 978, which specifically prohibits the use of the UN N.4 test to except carbon from the IMDG Code by limiting its application only to carbon produced by pyrolysis of an organic material such as bone, bamboo, coconut shell, jute, or wood. Special Provision 978 also requires additional precautions, such as a 14-day weathering period and periodic monitoring, while the material is stowed during transport. These changes also impacted the stowage requirements for materials transported in bulk containers with the aim of facilitating the dissipation and removal of accumulated heat generated by large amounts of densely stowed charcoal.

The IMO adopted the changes in Amendment 42-24 of the IMDG Code following incidents caused by spontaneous combustion of unpackaged bulk shipments of charcoal on board several vessels. The IMO concluded that removing Special Provisions 223 and 925 was needed because these special provisions could not be applied properly across all shipments given that charcoal is often manufactured at different remote production sites (charcoal piles) and consignments are often comprised of charcoal from different origins with different properties rather than being manufactured under standardized conditions.

PHMSA is not proposing to incorporate the changes adopted in Amendment 42-24 of the IMDG Code. While largely aimed at addressing fires associated with the movement of unpackaged bulk shipments of charcoal, the current IMDG Code requirements also apply to smaller packages of charcoal, such as those available for commercial retail use (

i.e.,

charcoal used for grilling). PHMSA believes that adopting these IMO requirements would unnecessarily burden manufacturers with new testing, handling, and packaging requirements for consumer products, particularly given the lack of domestic incidents and unlikelihood that unpackaged bulk shipments of carbon materials are being transported to and from the U.S.

PHMSA also disagrees with the IMDG Code prohibition on the use of UN Test N.4 to classify or exclude self-heating materials. PHMSA is not aware of any safety concerns or domestic safety incidents that justify the prohibition of the use of this test and believes that harmonizing the HMR with these particular sections of the IMDG Code would impose undue burdens for packaging and handling of carbon material without producing a corresponding safety benefit. Because shipments packaged in accordance with the IMDG Code are authorized for transport in the United States under § 171.22, PHMSA does not anticipate any commercial or economic hardships will result from failing to adopt these requirements.

•

Marking and labeling for battery powered vehicles

—The 23rd revised edition of the UN Model Regulations and Amendment 42-24 of the IMDG Code adopted a new special provision, Special Provision 405, for battery powered vehicles (“UN3556, Vehicle, lithium ion battery powered,” “UN3557, Vehicle, lithium metal battery

powered,” and “UN3558, Vehicle, sodium ion battery powered”). Special Provision 405 provides an exception for battery powered vehicles from marking and labeling requirements when not fully enclosed by packagings, crates, or other means that prevent ready identification, thereby requiring marking and labeling when fully enclosed by packaging, crates, or other means that prevent ready identification. Special Provision 405 is similar to an existing Special Provision A87 in the ICAO Technical Instructions. Special Provision A87 applies to articles but was assigned to battery powered vehicles in the 2024-2025 edition.

PHMSA is not proposing to adopt Special Provision 405 due to concerns raised in various international working groups regarding the necessity of the additional marking and labeling requirements. PHMSA believes that these requirements, which would require new marks and labels on a wide variety of popular consumer goods—

e.g.,

lawn mowers, scooters, motorcycles, wheelchairs—should be subject to further evaluation. PHMSA seeks comments regarding the potential benefits of additional hazard communication requirements for battery powered vehicles transported in fully enclosed packagings.

•

Non-removable specification markings

—The 23rd revised edition of the UN Model Regulations and the 2025-2026 ICAO Technical Instructions states that UN specification markings must be placed on a non-removable component of the packaging. A transitional exception allows packagings to continue to be marked as required prior to the adoption of the new requirement until December 31, 2026, and for any packagings marked in such manner prior to January 1, 2027, to be permitted for continued use. PHMSA anticipates determining that the transitional exception is unnecessary as the HMR already includes such a requirement in § 178.3(a), which states that packagings manufactured to a DOT specification or a UN standard must be marked with the proper specification marking on a non-removable component of the packaging. However, PHMSA seeks comments regarding the potential need for a similar transitional exception. Note that section 178.503(a) also applies the same requirement in § 178.3(a) to the marking of performance-oriented packagings.

This requirement was added in rulemaking HM-218. 65 FR 50450 (Aug. 18, 2000).

V. Section-by-Section Review of NPRM Proposals

The following is a section-by-section review of proposed amendments to harmonize the HMR with international regulations and standards.

Part 171

Section 171.6

Section 171.6 of the HMR provides information on the OMB control numbers assigned to information collections under the Paperwork Reduction Act of 1995. The paragraph (b)(2) table lists the HMR sections associated with each OMB control number. As this NPRM proposes to add new information collection requirements to HMR, PHMSA proposes to revise this table to include the section references where this new information collection request is specified. See paragraph (K), under the “Regulatory Analyses Notices” section for additional details regarding new information collection requests.

Section 171.7

Section 171.7 provides a listing of all consensus standards and regulations incorporated by reference into the HMR. PHMSA is proposing to add or revise the following references in § 171.7 in this NPRM:

All other standards that are set out as part of the regulatory text of § 171.7(w) were previously approved for incorporation by reference and no changes are proposed.

• The 2023 edition of the American National Standards Institute (ANSI) N14.1-2023, Nuclear Materials—Uranium Hexafluoride—Packagings for Transport in paragraph (d)(8), which is currently referenced in § 173.420. This standard provides criteria for packagings used for transport of uranium hexafluoride (UF6). It includes specific information on design and fabrication requirements for the procurement of new packagings intended for the transportation of UF6 in quantities of 0.2205 lb. (0.1 kg) or more. It also defines the requirements for in-service inspections, cleanliness, and maintenance for packagings in service. Packagings currently in service and not specifically defined in this standard will continue to be authorized for use, provided they are used within their original design limitations, and are inspected, tested, and maintained to comply with the intent of this standard. This standard also includes requirements for cylinder loading, shipping, and valves, plugs, and valve protectors. PHMSA evaluated this updated standard and believes that the revisions provide an enhanced level of safety without imposing significant compliance burdens. This standard has a well-established and documented safety history, and the adoption of the 2023 edition is expected to maintain the safety standard currently achieved under the HMR. The 2023 edition of ANSI N14.1 is available for purchase on the ANSI website at:

https://webstore.ansi.org/standards/pcc/ansin142023?source=blog.

• The 2025-2026 edition of the ICAO Technical Instructions in paragraph (t)(1) to replace the 2023-2024 edition, which is currently referenced in §§ 171.8; 171.22-24; 172.101; 172.202; 172.401; 172.407; 172.512; 172.519; 172.602; 173.56; 173.320; 175.10, 175.33; and 178.3. The ICAO Technical Instructions specify detailed instructions and requirements for the international safe transport of dangerous goods (

i.e.,

hazardous materials) by air. The 2025-2026 edition has been amended to align with the 23rd revised edition of the UN Model Regulations. Notable changes include new packing and stowage provisions, new and revised entries on its Dangerous Goods List, and editorial corrections. The 2025-2026 edition of the ICAO Technical Instructions is available for purchase on the ICAO website at

https://store.icao.int/en/shop-by-areas/safety/dangerous-goods.

• The 2024 edition of the IMDG Code (Amendment 42-24) in paragraph (v)(2) to replace Incorporating Amendment 41-22, which is currently referenced in §§ 171.22; 171.23; 171.25; 172.101; 172.202; 172.203; 172.401; 172.407; 172.502; 172.519; 172.602; 173.21; 173.56; 176.2; 176.5; 176.11; 176.27; 176.30; 176.83; 176.84; 176.140; 176.720; 176.906; 178.3; and 178.274. The IMDG Code is a unified international code that outlines standards and requirements for the transport of dangerous goods (

i.e.,

hazardous materials) by sea (

i.e.,

by vessel). Notable changes in Amendment 42-24 of the IMDG Code include new packing and stowage provisions, new and revised entries on its Dangerous Goods List, and editorial corrections. Distributors of the IMDG Code can be found on the IMO website at:

www.imo.org/en/publications/Pages/Distributors-default.aspx.

• The following ISO documents to add new and updated standards for the specification, design, construction, testing, and use of gas cylinders in paragraph (w):

—

ISO 535:2014,

Paper and board—Determination of water absorptiveness—Cobb method

in paragraph (w)(1). PHMSA proposes to

remove the 1991 version of this document, ISO 535:1991, which is currently referenced in §§ 178.707, 178.708, and 178.516, and to incorporate by reference the 2014 edition, ISO 535:2014 in its place. ISO 535:2014 specifies a method of determining the water absorptiveness of sized paper and board, including corrugated fiberboard, under standard conditions. This revised version contains changes to the introduction, annexes, and bibliography. The 23rd revised edition of the UN Model Regulations replaced the second edition with the third edition, and PHMSA proposes to mirror these changes for consistency. Replacing the 1991 version will allow references to updated annexed information and bibliographies, as well as for harmonization with other international standards, such as the 23rd revised edition of the UN Model Regulations, in which references to ISO 535:1991 have also been removed.

—

ISO 9809-4:2021,

Gas cylinders—Design, construction and testing of refillable seamless steel gas cylinders and tubes—Part 4: Stainless steel cylinders with an R m value of less than 1 100 MPa

in paragraph (w)(40). PHMSA proposes to incorporate by reference the second edition of this document, 9809-4:2021, and phase out the usage of the first edition, 9809-4:2014, by adding a sunset date of December 31, 2028.

These documents are to be referenced in §§ 178.71 and 178.75. ISO 9809-4:2021 specifies the minimum requirements for the materials, design, construction and workmanship, manufacturing processes, examinations and testing at time of manufacture for refillable, seamless, stainless steel gas cylinders with water capacities up to and including 150 L (

i.e.,

~40 gal.). As part of its regular periodic review process, ISO updated 9809-4:2014 and published the second edition, 9809-4:2021. The second edition includes changes to the requirements for inspection and testing, clarifications of drawings of the cylindrical parts of shells in Figure 3, and the addition of a new provision pertaining to shear stress calculations.

The sunset dates proposed for adoption in this NPRM are consistent with the phaseout date adopted in the 23rd revised edition of UN Model Regulations.

—

ISO 11114-1:2020, Gas cylinders—Compatibility of cylinder and valve materials with gas contents Part 1: Metallic materials

in paragraph (w)(51). PHMSA proposes to remove the second edition of this document, ISO 11114-1:2012, and the 2017 supplemental amendment, ISO 11114-1:2012/Amd 1:2017, currently residing in paragraphs (w)(50) and (w)(51), respectively, and referenced in §§ 172.102, 173.301b, and 178.71, and to replace these references with the updated third edition, ISO 11114-1:2020. This document provides requirements for the selection of safe combinations of metallic cylinder and valve materials and cylinder gas contents. This revised third edition includes all changes that were added in ISO 11114-1:2012/Amd.1:2017, clarification of the definition of the term “dry,” clarification in the table of compatibility, and various editorial improvements including updated references to incorporate Amendment 1.

—

ISO 11114-2:2021, Gas cylinders—Compatibility of cylinder and valve materials with gas contents—Part 2: Non-metallic materials

in paragraph (w)(52). PHMSA proposes to remove the second edition of this document, ISO 11114-2:2013, which is currently referenced in §§ 173.301b and 178.71, and replace that reference with the third edition, published in 2021. This document provides instruction on the selection and evaluation of compatibility between non-metallic materials for gas cylinders and valves and gas contents. It also applies to tubes, pressure drums, and bundles of cylinders. The third edition has been technically revised to include an update to Table 1 to include new non-metallic materials, and a new Table 2, which addresses non-metallic lining materials for gas cylinders.

—

ISO 11119-1:2020, Gas cylinders—Design, construction and testing of refillable composite gas cylinders and tubes—Part 1: Hoop wrapped fibre reinforced composite gas cylinders and tubes up to 450 l

in paragraph (w)(62). PHMSA proposes to incorporate by reference the third edition of this document in §§ 178.75 and 178.71. The second edition, ISO 11119-1:2012, is currently referenced in these sections. PHMSA proposes to add a sunset date of December 31, 2028, on the use of the second edition. This document is Part 1 in a three-part series. Part 1 specifies minimum requirements for the material, design, construction and workmanship, manufacturing processes, examination and testing at time of manufacture for certain Type 2 composite hoop wrapped gas cylinders or tubes intended for the storage and conveyance of compressed or liquefied gases, as well as cylinders and tubes with composite reinforcement of carbon fiber, aramid fiber or glass fiber (or a mixture thereof) within a matrix of steel wire with a minimum design life of 15 years. The most significant changes in the revised edition of Part 1 include: updates and corrections to references throughout the document; the addition of minimum fiber stress ratios; changes to the fire resistance test procedure; and newly added criteria for tubes above 150 L.

—

ISO 11119-2:2020, Gas cylinders—Design, construction and testing of refillable composite gas cylinders and tubes—Part 2: Fully wrapped fibre reinforced composite gas cylinders and tubes up to 450 l with load-sharing metal liners”

in paragraph (w)(66). PHMSA proposes to incorporate by reference the third edition of this document in §§ 178.75 and 178.71. The second edition and a required supplemental amendment, 11119-2:2012/Amd.1:2014, are currently referenced in these sections. PHMSA proposes to add a sunset date of December 31, 2028, on the use of these two documents, and to incorporate by reference the third edition, ISO 11119-2:2020. This document is Part 2 in a three-part series. Part 2 specifies minimum requirements for the material, design, construction and workmanship, manufacturing processes, examination and testing at time of manufacture for Type 3 fully wrapped cylinders or tubes with a load-sharing metal liner and composite reinforcement on both the cylindrical portion and the dome ends. The most significant changes in the third edition of Part 2 include: updated references; the addition of minimum fiber stress ratios; the addition of a new alternative for the drop test for certain cylinders; the addition of an alternative impact test for tubes 150 L or more; changes to fire resistance test procedure to make the test more consistent; and changes to the torque test.

—

ISO 11119-3:2020, Gas cylinders—Design, construction and testing of refillable composite gas cylinders and tubes—Part 3: Fully wrapped fibre reinforced composite gas cylinders and tubes up to 450 l with non-load-sharing metallic or non-metallic liners or without liners

in paragraph (w)(69). PHMSA proposes to incorporate by reference the third edition of this document in §§ 178.71 and 178.75. The second edition, 11119-3:2013, is currently referenced in these sections. PHMSA also proposes to add a sunset date of December 31, 2028, on the use

of the second edition. ISO 11119-3:2020 specifies requirements for composite gas cylinders up to 150 L water capacity and composite tubes above 150 L water capacity and up to 450 L water capacity, for the storage and conveyance of compressed or liquefied gases. This document is Part 3 in a three-part series. Part 3 specifies minimum requirements for the material, design, construction and workmanship, manufacturing processes, examination and testing at time of manufacture for Type 4 composite fully wrapped cylinders or tubes with a non-load sharing liner and composite reinforcement on both the cylindrical portion and the dome ends, and Type 5 fully wrapped cylinders or tubes without liners and with a test pressure of less than 60 bar, with water capacities up to 450 L. This document is intended for cylinders used for the storage and conveyance of compressed or liquefied gases; cylinders and tubes with composite reinforcement of carbon fiber, aramid fiber or glass fiber (or a mixture thereof) within a matrix; and for cylinders or tubes with a minimum design life of 15 years. The most significant changes in the third edition of part 3 include: the addition of a new alternative for the drop test for cylinders up to and including 50 L water capacity with dedicated compressed gas service; the addition of alternative impact test for tubes 150 L or more; changes to the fire resistance test procedure to make the test more consistent and the addition of a criterion for tubes above 150 L; changes to the torque test; and a new procedure for the pneumatic cycle test. ISO revised the 2020 editions of ISO 11119 Parts 1, 2, and 3 following comments received from regulators, manufacturers, and users of the standards worldwide. These changes were made to improve and to clarify test procedures, particularly in relation to large composite cylinders and tubes.

—

ISO 15105-1:2007, Plastics—Film and sheeting—Determination of gas-transmission rate Part 1: Differential-pressure methods

in paragraph (w)(82). PHMSA proposes to reference this document in Special Provision 43 in § 172.102 as a part of a condition for exception from the HMR for nitrocellulose membrane filters. This document specifies two methods for determining the gas transmission rate of single-layer plastic film or sheet and multi-layer structures under a differential pressure.

—

ISO 16148:2016/Amd 1:2020, Gas cylinders—Refillable seamless steel gas cylinders and tubes—Acoustic emission examination (AT) and follow-up ultrasonic examination (UT) for periodic inspection and testing—Amendment 1

in paragraph (w)(86). PHMSA proposes to incorporate by reference Amendment 1 of ISO 16148 into § 180.207 to supplement ISO 16148:2016. Amendment 1 is a short two-page supplemental correction for ISO 16148:2016, which gives procedures for the use of acoustic emission examination and follow-up ultrasonic examination during the periodic inspection and testing of seamless steel cylinders and tubes used for compressed and liquefied gases with a water capacity of up to 3,000 L. The use of this supplemental amendment would be required as this document includes a significant correction of Note 2 to Figure A.1 concerning the calculation of the depth of the notches used for calibration. PHMSA expects that the additional requirement to use this supplemental amendment will improve safety by requiring the use of improved engineering standards.

—

ISO 23826:2021, Gas cylinders—Ball valves—Specification and testing

in paragraph (w)(97). PHMSA proposes to incorporate by reference the first edition of this document into §§ 178.301b and 178.71. ISO 23826:2021 is a new standard specifying the design, type testing, marking, manufacturing tests and examination requirements for ball valves used as closures of refillable transportable gas cylinders, pressure drums, and tubes; main valves for cylinder bundles and valves for cargo transport units and multiple element gas containers (MEGCs) that convey compressed gases, liquefied gases, and dissolved gases. The new document fills an important gap as ball valves are explicitly excluded in other closure standards such as ISO 10297,

Gas cylinders—Refillable gas cylinder valves—Specification and type testing.

PHMSA expects that the addition of this reference document will facilitate the manufacture, design, and testing of various packagings used for the transport of hazardous materials.

All ISO standards can be found at:

www.iso.org/standards.html.

• The 2023 Edition of Transport Canada's Transportation of Dangerous Goods (TDG) Regulations in paragraph (bb)(1), to replace the 2017 edition, which is currently referenced in §§ 107.801; 107.805; 171.12; 171.22; 171.23; 172.401; 172.407; 172.502; 172.519; 172.602; 173.31; 173.32; 173.33; 173.301; 180.205; 180.211; 180.212; and 180.413. Like the HMR, the TDG regulations provide requirements for transportation of hazardous materials goods and activities relating to road, rail, air, and marine transport into, from, and within Canada. This paragraph lists 22 Statutory Orders and Regulations (SORs), which have since been consolidated into one point of reference, SOR/2001-286. PHMSA also proposes to remove references to these 22 SORs and only reference SOR/2001-286 for all of Transport Canada's TDG regulations. Transport Canada's TDG regulations are available online at:

https://laws-lois.justice.gc.ca/eng/regulations/sor-2001-286/.

• The 23rd Revised Edition (2023) of the United Nations Recommendations on the Transport of Dangerous Goods—Model Regulations (UN Model Regulations), Volumes I and II, in paragraph (dd)(1), to replace the 22nd revised edition (2021), which are referenced in §§ 171.8; 171.12; 172.202; 172.401; 172.407; 172.502; 172.519; 173.22; 173.24; 173.24b; 173.40; 173.56; 173.192; 173.302b; 173.304b; 178.75; 178.274. The UN Model Regulations present a basic scheme of provisions that allow uniform development of national and international regulations governing the various modes of transport. Amendments adopted in the 23rd revised edition of the UN Model Regulations include new UN numbers and provisions regulating the transport of sodium ion batteries, fire suppressant dispersing devices, disilane, gallium contained in articles, and trifluoromethyl tetrazole-sodium salt in acetone; a new special provision to increase the authorized volume for transport in limited quantities of some compressed gases of Division 2.2 without subsidiary hazards; more specific concentration limits for ammonium nitrate hot concentrated solutions; exceptions for nitrocellulose membrane filters; and an update to the requirements for the use of recycled plastics in packagings. The 23rd revised edition of the UN Model Regulations is available online at:

https://unece.org/transport/dangerous-goods/un-model-regulations-rev-23.

• The 8th Revised Edition of the United Nations Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, in paragraph (dd)(2), to replace the 7th Revised Edition, which is currently referenced in §§ 171.24, 172.102; 173.21; 173.56; 173.57; 173.58; 173.60; 173.115; 173.124; 173.125; 173.127; 173.128; 173.137; 173.185; 173.220; 173.221; 173.224; 173.225; 173.232; 173, appendix H; 175.10; 176.905; and

178.274. PHMSA also proposes to add a new reference to this document in § 173.169 in reference to the performance of test series 6(c) for fire suppressant dispersing devices. The UN Manual of Tests and Criteria contains standards, test methods, and procedures to be used for the classification of hazardous materials according to the UN Model Regulations. Amendments adopted in this eighth revised edition include: the addition of organic peroxides and polymerizing substances to the list of substances that should not be tested in the self-heating test to avoid false positives; a recommendation to use close-cup tests over open-cup tests for determining flash points; new provisions for the testing of sodium ion batteries; amendments to the classification of desensitized explosives according to the Globally Harmonized System of Classification and Labelling of Chemicals. The eighth revised edition of the UN Manual of Tests and Criteria is available online at:

https://unece.org/transport/standards/transport/dangerous-goods/un-manual-tests-and-criteria-rev8-2023.

• The 10th Revised Edition of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), in paragraph (dd)(3), to replace the 9th Revised Edition, which currently is referenced in § 172.401. The GHS is an international system standardizing hazard classification and communication. The HMR authorizes its use for labeling of packages. This revised edition contains updates addressing, among other items, further rationalization of precautionary statements to improve user comprehensibility while considering usability for labelling practitioners. PHMSA notes that the classification procedures for desensitized explosives that were added in this edition of the GHS are not related to transport classification and do not represent a requirement or criteria for obtaining an approval under the HMR. The 10th revised edition of the GHS is available online at:

https://unece.org/transport/dangerous-goods/ghs-rev10-2023.

• The 2025 edition of the Agreement concerning the International Carriage of Dangerous Goods by Road (ADR 2025), in paragraph (dd)(4), to replace the 2021 edition of the ADR (ADR 2021), which is referenced in §§ 171.8 and 171.23. The ADR outlines regulations concerning the international carriage of dangerous goods by road within the European Union (EU) and other countries that are party to the agreement. The HMR authorizes its use regarding the definition of a liquid material and transport of pi marked cylinders. This revised edition contains the amendments adopted in 2024 by the Working Party on the Transport of Dangerous Goods. ADR 2025 is available online at:

https://unece.org/adr-2025-files.

Section 171.8

Section 171.8 defines terms used throughout the HMR. PHMSA proposes to add a new definition, as adopted in the 23rd revised edition of the UN Model regulations, to this section for “sodium ion cell or battery” similar to lithium ion cell or battery. PHMSA expects that adding this definition will provide clarity and enhance safety, primarily by specifying which sodium ion battery types will be subject to the newly proposed provisions in this NPRM applicable to sodium ion batteries.

Section 171.23

Section 171.23 provides conditions and requirements for shipments of certain packages or materials offered for transportation or transported in the United States under the ICAO Technical Instructions, the IMDG Code, the Transport Canada TDG Regulations, or the International Atomic Energy Agency (IAEA) Regulations—as applicable. PHMSA proposes to amend paragraph (b)(5), which specifies conditions and requirements for certain materials, by adding conditions and requirements for fire suppressant dispersing devices. This amendment would be consistent with proposed changes that add new HMT entries “UN0514, Fire suppressant dispersing devices, 1.4S” and “UN3559, Fire suppressant dispersing devices, 9,” which add a new classification and packaging section and revise the explosives packaging section. Detailed summaries of these proposed changes are found in the discussions of Sections 172.101, 173.62, and 173.169 of the Section-by-Section Review.

Specifically, for this section, PHMSA proposes that prior to being transported under authorized international standards and regulations, the Associate Administrator must approve fire suppressant dispersing devices in accordance with §§ 173.56 and (new) 173.169 of the HMR. PHMSA also proposes to reorganize paragraph (b) so that the subject of each provision appears in alphabetical order. This proposed change is necessary to maintain oversight through the explosives approval process, which will allow PHMSA to ensure safe transportation under the new HMT entries and in accordance with the classification, packaging, and conditional exceptions from movement of these devices domestically and globally. Devices approved in accordance with an international competent authority may rely on that documentation for processing an explosives approval application in the United States.

Part 172

Section 172.101 Hazardous Materials Table (HMT)

The HMT summarizes terms and conditions governing the transportation of listed hazardous materials under the HMR. For each entry, the HMT identifies basic information such as the PSN, UN identification number, and hazard class and hazard label. The HMT specifies additional information or reference requirements in the HMR, such as hazard communication, assigned special provisions, packaging reference citations, and modal requirements, like quantity limits aboard aircraft, and vessel stowage restriction of hazardous materials aboard vessels. PHMSA proposes several changes to the HMT as discussed below. For purposes of the Government Publishing Office's typesetting procedures, proposed changes to the HMT appear under three sections of the HMT: “remove,” “add,” and “revise.” Certain entries in the HMT, such as those with revisions to the PSNs, appear as a “remove” and “add.” Proposed amendments to the HMT include the following:

New HMT Entries and Revisions to the Appendix B to § 172.101—List of Marine Pollutants

Fire Suppressant Dispersing Devices (UN0514 and UN3559)

PHMSA proposes to add two new entries to the HMT for fire suppressant dispersing devices to identify better these articles for purposes of classification, packaging, and handling for transportation. See the Section-by-Section discussion of Section 173.169 for a detailed discussion of fire suppressant dispersing devices and proposed requirements for their classification, handling, and transportation. The proposed new entries are “UN0514, Fire suppressant dispersing devices, 1.4S” and “UN3559, Fire suppressant dispersing devices, 9.” Fire suppressant dispersing devices are articles containing a pyrotechnic substance that disperse a fire extinguishing agent (or generate an aerosol) when activated, and do not contain any other hazardous materials. To address the prevalence of these articles, the UNSCOE created two new UN ID numbers and added entries to the

Dangerous Goods List (DGL) in the 23rd revised edition of the UN Model Regulations. PHMSA agrees that the addition of these two new entries to the HMT will provide a description that is more appropriate than “UN3268, Safety devices,

electrically initiated,”

and expects that the accompanying classification, packaging, and handling provisions will provide more consistency and for a safe method of transporting these articles.

Tetramethylammonium Hydroxide (UN1835, UN3423, UN3560)

PHMSA proposes several changes pertaining to tetramethylammonium hydroxide (TMAH) to align with the 23rd revised edition UN Model Regulations. TMAH is a quaternary ammonium compound used in the chemical industry in its solid form and as an aqueous solution. TMAH solutions are currently transported under “UN1835, Tetramethylammonium hydroxide solution,” as PG II or PG III, with TMAH solids being transported under “UN3423, Tetramethylammonium hydroxide, solid,” as a PG II. These materials are all classified as Class 8 (corrosive) material and assigned either PG II or PG III using the criteria in § 173.137 of the HMR. However, literature studies of incidents involving accidental human exposure shows that TMAH presents a toxicity hazard in addition to the currently identified corrosivity hazard.

The studies indicate that TMAH can cause systemic neurotoxic effects leading to respiratory failure and cardiac arrest in addition to chemical burns in the event of bodily exposure. The studies showed that fatalities occurred from exposure to 25 percent TMAH solution. Furthermore, acute dermal toxicity studies indicated increasing toxic properties as concentration of TMAH solutions increased. Consequently, the UNSCOE determined that there was a need for a revised classification for TMAH materials to account for toxic properties.

United Nations Economic Commission for Europe (UNECE),

Additional data on proposal ST/SG/AC.10/C.3/2022/24—Revision of classification of tetramethylammonium hydroxide

(June 16, 2022), available at:

https://unece.org/sites/default/files/2022-06/UN-SCETDG-60-INF22.e_0.pdf.

The proposed amendments include the addition of a new entry describing a TMAH aqueous solution of at least 25 percent TMAH—“UN3560, Tetramethylammonium hydroxide aqueous solution

with not less than 25 percent tetramethylammonium hydroxide”

in the HMT. This new entry would have a primary hazard of Division 6.1 (toxic), a subsidiary hazard of Class 8 (corrosive), and be assigned to PG I. Consistent with this new table entry for 25 percent TMAH aqueous solutions, additional changes are proposed for existing TMAH HMT entries to further account for the toxicity hazard and clarify their use, including revisions to the proper shipping names and descriptions, the hazard classification of PG II TMAH solutions (UN1835) reclassification of TMAH solids (UN3423) and revised packaging authorizations, and the assignment of two new special provisions (

i.e.,

408 and 409).

PHMSA proposes revisions to the TMAH solution (UN1835) shipping description to aid shippers with selecting the most appropriate hazardous materials description and to delineate clearly the classification and PG assignment. For the PSN “Tetramethylammonium hydroxide solution,” the term “aqueous” is added to clarify that the PSN applies to aqueous solutions of TMAH. See the Section-by-Section Review discussion of Section 172.102, Special Provision 408, for further context. Furthermore, concentration ranges corresponding to the assigned PG are added in italics to be used in addition to the PSN. Specifically, the revised hazardous materials description for the PG II entry would read “Tetramethylammonium hydroxide aqueous solution

with more than 2.5 percent but less than 25 percent tetramethylammonium hydroxide,”

and the PG III entry would read “Tetramethylammonium hydroxide aqueous solution

with not more than 2.5 percent tetramethylammonium hydroxide.”

With respect to the revised classification for TMAH solution (UN1835), PHMSA proposes to add a Division 6.1 subsidiary hazard for the PG II entry—

i.e.,

TMAH aqueous solutions containing more than 2.5 percent but less than 25 percent TMAH. This amendment addresses the data from human exposure incidents and toxicity studies that demonstrated an increasing toxicity property for TMAH solutions as concentration increased.

Similarly, for TMAH, solid (UN3423), which is currently classified as Class 8, PG II, the UNSCOE reclassified as a primary hazard of Division 6.1, a subsidiary hazard of Class 8, and assigned PG I. PHMSA agrees with this reclassification based on human experience and acute toxicity studies. PHMSA concurs with this determination due to the reclassification of the material to a PG I material. Therefore, PHMSA proposes to change the primary hazard from Class 8 to Division 6.1 in column (3) of the HMT and transition the Class 8 corrosivity hazard to a subsidiary hazard as designated in column (6) of the HMT. In addition, with this hazard reclassification, the PG for UN3423 would be changed from PG II to PG I. PHMSA also notes that in the latest revisions to the DGL in the UN Model Regulations, the limited quantity exception authorization for this entry was removed.

Lastly, PHMSA proposes to assign two new special provisions—Special Provisions 408 and SP 409—to these entries. Special Provision 408 would provide additional hazard communication instructions for certain mixtures containing TMAH and would be assigned to all three TMAH solution entries, stating that the use of those proper shipping names is limited to aqueous solutions comprised of water, tetramethylammonium hydroxide, and no more than one (1) percent of other constituents. This new special provision would also provide instruction that other formulations containing more than one percent surfactants and certain concentration ranges of TMAH (≥8.75 percent or, >2.38 to <8.75 percent, respectively) must be described using “UN 2927, Toxic liquid, corrosive, organic, n.o.s.,” while other formulations not meeting the criteria in the SP 408 must be assigned to an alternative appropriate generic or n.o.s. HMT entry.

PHMSA expects that providing instruction on the appropriate use of TMAH aqueous solution descriptions and generic or n.o.s. HMT entries for formulations other than aqueous solutions that contain TMAH would make things clearer for shippers of TMAH mixtures with regard to appropriate hazard communication and associated packaging requirements. PHMSA also proposes to assign new Special Provision 409 to all three TMAH solution entries and the TMAH solid entry to allow shipment using the current hazard communication through December 31, 2026, to allow time for offerors to adjust their hazard communication (see the Section-by-Section Review in Section 172.102 for additional information). PHMSA expects these hazard classification and communication changes will enhance safety by providing more appropriate packaging and transport requirements and more accurate hazard information for handlers of TMAH packages and emergency responders.

For clarity, n.o.s. means not otherwise specified (in the HMT).

Sodium Ion Batteries With Organic Electrolyte and Sodium Ion Batteries Contained in Equipment With Organic Electrolyte/Sodium Ion Batteries Packed With Equipment, With Organic Electrolyte (UN3551 and UN3552)

PHMSA proposes to add three new entries for sodium ion batteries to the HMT: “UN3551, Sodium ion batteries

with organic electrolyte,”

“UN3552, Sodium ion batteries contained in equipment,

with organic electrolyte,”

and “UN3552, Sodium ion batteries packed with equipment,

with organic electrolyte.”

These all describe materials of Class 9. The UN Model Regulations have recently adopted provisions regulating sodium ion cells and batteries in much the same way as lithium ion cells and batteries. Sodium ion technology has the potential to be a low-cost alternative to lithium ion batteries in certain applications. Both sodium ion batteries and lithium ion batteries are rechargeable energy storage devices, with sodium ion batteries using sodium ions to carry a charge and lithium ion batteries using lithium ions to carry a charge. Both present similar hazards due to their energy density. A key operational difference between sodium ion and lithium ion technology is that sodium ion technology can be discharged to zero volts (

i.e.,

a zero state-of-charge) without affecting the performance of the battery. Batteries using sodium ion technology can therefore be stored and transported in a completely discharged state, with terminals shorted if required, greatly reducing their hazard. However, PHMSA and the UNSCOE agree that the same requirements that apply to lithium ion batteries are appropriate for sodium ion batteries given that the two demonstrate similar risks.

Like previous versions of the UN Model Regulations, the HMR does not currently have a hazardous material description for sodium ion batteries. The current entry in the HMT of “Batteries, containing sodium” (UN3292) is applicable to various cell chemistries, such as sodium sulfur and sodium metal chloride which contain metallic sodium, but does not specifically address batteries of sodium ion cell chemistry. When evaluating the proposed adoption of requirements for sodium ion batteries, the UNSCOE analyzed the quantity and nature of gases emitted during the thermal runaway of sodium ion batteries from tests conducted at the French National Institute for Industrial Environment and Risks.

Results showed similarities between the quantity and nature of the gases emitted during the thermal runaway of sodium ion batteries and during the thermal runaway of certain types of lithium ion battery chemistries.

UNECE,

Sodium ion batteries: Assignment of a dedicated UN number and related special provisions—Follow-up on document ST/SG/AC.10/C.3/2020/45/Rev.1

(Sept. 20, 2021), available at:

https://unece.org/sites/default/files/2021-09/ST-SG-AC.10-C.3-2021-55e.pdf.

With the results of these tests, along with information indicating that by 2023 companies were planning to mass produce sodium ion batteries to alleviate supply chain issues with lithium ion batteries, the UNSCOE adopted provisions to regulate sodium ion batteries in the same manner as lithium ion batteries. PHMSA now aims to harmonize with current international regulations by adopting those same provisions.

PHMSA expects that as sodium ion batteries become more widely used, harmonizing the HMR with international standards will provide a baseline of uniform transport standards. For sodium ion batteries being transported domestically or exported by U.S. companies abroad, this standardization will ultimately allow for reduced burdens, increased efficiency, and avoid unnecessary costs for domestic industries—leading to less expensive product options for domestic consumers. See the Section-By-Section Review in Section 173.185 for further detail of the proposed classification, packaging provisions, and exceptions for sodium ion batteries.

In addition, PHMSA proposes to assign a new special provision for sodium ion batteries, and to make many of the existing special provisions related to lithium ion batteries applicable to sodium ion batteries. See the Section-By-Section Review in Section 172.102 for further details of proposed special provisions applicable to sodium ion batteries.

Lastly, PHMSA proposes to make one of the vessel stowage codes that is currently assigned to lithium ion batteries applicable to sodium ion batteries, including sodium ion batteries packed with, or contained in, equipment. PHMSA expects this change will enhance safety by ensuring sodium ion batteries are properly stowed when transported by vessel. See the Section-By-Section Review in Section 172.101, column (10) discussion of for additional details on this amendment.

Disilane (UN3553)

PHMSA proposes to add a new entry, “UN3553, Disilane, 2.1,” to the HMT. Disilane is a pyrophoric liquified gas under pressure that is spontaneously flammable in air and does not require spark or flame to ignite. Disilane is used primarily in the manufacture of integrated circuits in various electronics, including computer processors. Despite its pyrophoric properties, disilane is commonly transported under the generic shipping description, “UN3161, Liquefied gas, flammable, n.o.s. (Disilane).” As a part of their review of proposed amendments to the UN Model Regulations, the UNSCOE discussed the need for a more specific proper shipping name that would better reflect the flammable and pyrophoric properties of disilane. The UNSCOE concluded that the use of the generic description for disilane only reflects its flammability properties but not the pyrophoric properties. Unlike “UN2203, Silane” and other similar pyrophoric materials that are forbidden for transport by cargo aircraft, disilane, as currently transported under “UN3161, Liquefied gas, flammable, n.o.s. (Disilane),” is not forbidden for transport by cargo aircraft.

The UNSCOE concluded that a separate shipping description for disilane should be created to clarify the pyrophoric properties of the material and ensure that there is no possibility of disilane being transported by air.

Both UN2203 and UN3161 are forbidden for transport aboard passenger aircraft.

Consistent with the ICAO Technical Instructions for disilane, PHMSA proposes to add the entry to the HMT, noting that “Forbidden” would be indicated in column (9) for both passenger and cargo aircraft. For shipments by vessel, PHMSA proposes to assign stowage code D, which requires that the material is stowed on deck when transported on a cargo vessel and further limits the stowage of the material by vessel when passengers are present. In addition, PHMSA proposes to assign segregation codes, 40, 57, and 104 in column (10B) to require that disilane be segregated from living quarters, from chlorine, and from bromine to prevent hazardous reactions. These stowage and segregation provisions are consistent with the requirements adopted in Amendment 42-24 to the IMDG Code. PHMSA expects that adding this new entry and the new packaging provisions will enhance safety by providing a clearer hazard identification of disilane and ensuring that there is no possibility of this product being transported by air.

Gallium Contained in Manufactured Articles (UN3554)

PHMSA proposes to add “UN3554, Gallium contained in manufactured articles,” as a new entry to the HMT. Gallium is a silver white metal with a low melting point and, though corrosive to certain metals like aluminum, is widely considered a safer, non-toxic alternative to mercury. Gallium and its alloys are used in a variety of products in place of mercury products—such as thermometers and UV lamps. This transition away from mercury has been driven largely in response to the 2013 Minamata Convention on Mercury (

i.e.,

Convention).

The Convention aimed to reduce mercury emissions and exposure, through the reduced production, import, and export of mercury-containing products. Since 2017, manufacturers have explored substitutes to mercury-containing products.

To facilitate the use of this alternative material, PHMSA proposes new packaging provisions for this new entry to mirror the provisions for “UN3506, Mercury contained in manufactured articles”—which have been authorized in the HMR since 2013 and have a well demonstrated safety record.

See the Section-by-Section Review in Section 173.162 for additional information on the new packaging provisions for this entry. PHMSA expects that this new entry will provide consistency with international regulations and allow for a less toxic material to be integrated into the market.

United Nations,

2013 Minamata Convention on Mercury

(Oct. 10, 2013), available at:

https://treaties.un.org/doc/Treaties/2013/10/20131010%2011-16%20AM/CTC-XXVII-17.pdf.

UNECE,

Proposal to amend SP 366, making it also adjust to Gallium contained in manufactured articles

(Apr. 16, 2021), available at:

https://unece.org/sites/default/files/2021-04/ST-SG-AC.10-C.3-2021-17e.pdf.

78 FR 988 (Jan. 7, 2013).

Trifluoromethyltetrazole-Sodium Salt (UN3555)

PHMSA proposes to add a new entry, “UN3555, Trifluoromethyltetrazole-sodium salt in acetone,

with not less than 68% acetone, by mass,

3, PG II,” to the HMT. PHMSA proposes to add a new entry, “UN3555, Trifluoromethyltetrazole-sodium salt in acetone,

with not less than 68% acetone, by mass,

3, PG II,” to the HMT. Trifluoromethyltetrazole, sodium salt (TFMT-Na) in acetone is a desensitized explosive compound used as a precursor material for a new insecticide that is entering the market. Due to the explosive properties of the dry substance, it is only handled and transported as a homogenous solution in acetone. As a result of its unique properties, the UNSCOE agreed to create a new entry on the DGL to facilitate its transport as its use is expected to increase across various countries.

PHMSA proposes to mirror the UN Model Regulations' corresponding packaging provisions for this hazardous material by creating a new special provision, Special Provision 234. This new special provision will specify the authorized packaging for this material. In addition, PHMSA is assigning Special Provision 74 which would require that:

1. The material be protected from direct sunlight; and

2. The material be stored or kept in a cool and well-ventilated place away from all sources of heat.

PHMSA is also assigning Special Provision 162 to permit the material be transported under the provisions of Class 3, provided it is packed so that the percentage of diluent will not fall below the stated amount at any time during transport. PHMSA notes that the entry includes “Forbidden” in column (9) for both passenger and cargo aircraft, which is consistent with the ICAO Technical Instructions. PHMSA expects that the addition of this new HMT entry and associated authorized packaging requirements will facilitate the safe transport of this emerging product domestically and internationally.

Lithium Ion Battery Powered Vehicle, Lithium Metal Battery Powered Vehicle, and Sodium Ion Battery Powered Vehicle (UN3556, UN3557, and UN3558, Respectively)

PHMSA proposes to add three new entries to the HMT for vehicles powered by lithium ion batteries, lithium metal batteries, and sodium ion batteries to address the massive market growth in personal mobility devices, such as e-bikes, e-scooters, e-skateboards, and other lightweight vehicles. The proposed new entries are: “UN3556, Vehicle, lithium ion battery powered,” “UN3557, Vehicle, lithium metal battery powered,” and “UN3558, Vehicle, sodium ion battery powered.” These entries will provide more precise descriptions for vehicles powered by various battery chemistries (

e.g.,

lithium or sodium ion cells or lithium metal cells), rather than relying on the broadly used entry “UN3171, Battery-powered vehicle.” Currently, there are two distinct entries that cover products containing lithium ion and lithium metal cells and batteries (UN3480 and UN3090); however, the same differentiation does not exist for vehicles powered by various battery types. The UNSCOE addressed this lack of distinction, clarity, and consistency by adding these three new UN numbers and proper shipping names to the DGL in the UN Model Regulations. PHMSA agrees with the UNSCOE's solution and expects that the addition of these specific hazardous materials descriptions will provide a differentiation between vehicles powered by lithium batteries, sodium ion batteries and other battery powered vehicles and help to identify better the batteries in these vehicles for emergency response purposes. PHMSA does not expect that this amendment will impose additional costs as the packaging provisions are the same for each vehicle type. For example, non-spillable battery powered vehicles should continue to use the entry “UN3171, Battery-powered vehicle.” PHMSA expects that the addition of these new entries will facilitate the efficient transport of these hazardous materials by providing better shipping descriptions and more precise hazard communication.

Additions to Appendix B to § 172.101—List of Marine Pollutants

Appendix B to § 172.101—List of Marine Pollutants lists potential marine pollutants as defined in § 171.8 of the HMR. To align with Amendment 42-24 to the IMDG Code, PHMSA proposes to add isopropenylbenzene, 2-phenylpropene, and cobalt dihydroxide powder,

containing more than 10 percent respirable particles

to this list. Isopropenylbenzene is currently listed by name in the HMT under UN2303 and has the same chemical structure as 2-phenylpropene, which makes the two names synonymous. Following additional testing—which was required for compliance with the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations in the EU—the IMO agreed to add these entries to the list of marine pollutants in Amendment 42-24 of the IMDG Code. The testing results showed that the substance meets the criteria to be classified as an “Environmentally hazardous substance (aquatic environment)” as stipulated in section 2.9.3 of the IMDG Code.

With respect to the addition of cobalt dihydroxide powder

containing more than 10 percent respirable particles

to the marine pollutants list, in a previous rulemaking—HM-215Q—PHMSA added this material to the HMT as “UN3550, Cobalt dihydroxide powder

containing more than 10 percent respirable particles.”

PHMSA made that addition to harmonize with changes made to the Amendment 41-22 to the

IMDG Code and 2023-2024 edition to the ICAO Technical Instructions, and the 22nd revised edition of the UN Model Regulations, after testing required under REACH regulations determined that this material poses an inhalation toxicity hazard. This material was also added to the list of the marine pollutants in Amendment 41-22 of the IMDG Code; however, PHMSA inadvertently omitted this material as an entry on the list of marine pollutants under the HM-215Q rulemaking. Like isopropenylbenzene/2-phenylpropene, PHMSA added cobalt dihydroxide powder,

containing more than 10 percent respirable particles

because that material also meets the criteria under the IMDG Code to be classified as “Environmentally hazardous substance (aquatic environment).” PHMSA proposes to correct this unintentional oversight and add “Cobalt dihydroxide powder

containing more than 10 percent respirable particles”

to the list of marine pollutants. PHMSA expects that these amendments will help improve safety to the aquatic environment for the transport of these materials and that the harmonization of the list of marine pollutants will facilitate appropriate transport of these materials.

89 FR 25434 (Apr. 10, 2024).

Revisions to the HMT Columns of Information

Column (1) Symbols

Section 172.101(b) describes column (1), which may contain one of six symbols: “+”, “A”, “D”, “G”, “I” and “W”. The plus (+) sign fixes the proper shipping name, hazard class, and packing group for that entry without regard to whether the material meets the definition of that class, packing group, or any other hazard class definition. When the plus sign is assigned to a proper shipping name in column (1) of the HMT, it means that the material is known to pose a risk to humans.

PHMSA proposes to add a (+) in column (1) of the HMT for the following entries: “UN1835, Tetramethylammonium hydroxide aqueous solution

with more than 2.5 percent but less than 25% tetramethylammonium hydroxide”,

“UN3423, Tetramethylammonium hydroxide, solid,” and “UN3560, Tetramethylammonium hydroxide aqueous solution

with not less than 25% tetramethylammonium hydroxide.”

As discussed below, PHMSA proposes to amend the hazard classification for these entries based on additional data regarding their toxicity (see additional discussion of TMAH amendments throughout the Section-by-Section discussion 172.101). The additions in column (1) would reflect the basis for these classification changes.

In addition, this proposed amendment would align with the changes adopted in the 23rd revised edition of the UN Model Regulations, which assigned Special Provision 279 to these entries. Special Provision 279, like the (+) in column (1), fixes the assigned classification or packing group based on human experience rather than the strict application of classification criteria. PHMSA expects this change will enhance safety by ensuring that these materials are properly classified and packaged to address the newly identified toxicity hazard.

Column (2) Hazardous Materials Descriptions and Proper Shipping Names

Section 172.101(c) describes column (2) of the HMT and the requirements for hazardous materials descriptions and PSNs. PHMSA proposes to revise the hazardous material description for “UN1835, Tetramethylammonium hydroxide solution, 8, PG II and III.” For the PG II entry, PHMSA proposes to add the word “aqueous” as part of the PSN and include a concentration range in italics to read “aqueous solution

with more than 2.5 percent but less than 25 percent tetramethylammonium hydroxide.

” For the PG III entry, PHMSA proposes to add the word “aqueous” as part of the PSN and include a concentration range to read “aqueous solution

with not more than 2.5 percent tetramethylammonium hydroxide.

” These proposals align with the proposed changes to the classification of TMAH material as discussed above. PHMSA expects that they will provide an additional level of safety for transportation of aqueous solutions of TMAH by more accurately describing the material.

PHMSA also proposes to modify the proper shipping name of “UN1010, Butadienes and hydrocarbon mixture, stabilized

containing more than 40% butadienes,

” by revising the concentration range in italics from “containing more than 40% butadienes” to “containing more than 20% butadienes.” PHMSA modified this hazardous material description in a prior rulemaking, HM-215G, by adding the italicized text that stipulated the 40 percent concentration of butadienes to describe better certain mixtures.

This change was intended to facilitate the classification and transport of mixtures of liquefied petroleum gases, which were already being classified under UN1010 in other countries. However, after evaluating typical shipments of butadiene/hydrocarbon-mixtures, the European Chemical Industry Council (Cefic) determined that most fall within the 20 to 40 percent butadiene concentration range. As a result, the current butadiene concentration requirement of 40 percent or more associated with the use of UN1010 means that less accurate PSNs, such as “UN1965, Hydrocarbon gas mixture, liquefied, n.o.s.,” or “UN3161, Liquefied gas, flammable, n.o.s.,” are used for many shipments of this material (

i.e.,

shipments with concentrations of butadienes below 40 percent). The UNSCOE reasoned that it was preferable to lower the concentration threshold to facilitate the use of the proper shipping description for a wider group of shipments, given that this PSN clearly reflects the specific danger of butadiene (

e.g.,

carcinogenic), as opposed to using a generic “n.o.s.” entry, such as “UN3161, Liquefied gas, flammable, n.o.s.” This change would provide emergency responders with immediate information regarding the material being transported and removes the need to seek out the shipping paper to determine that butadiene is involved in an incident. PHMSA agrees with this determination and expects that adjusting the concentration range associated with this PSN will improve safety by providing first responders with better information for effectively responding to incidents involving butadiene mixtures, as well as providing important carcinogenicity risk information for handlers of these mixtures.

69 FR 76044 (Dec. 20, 2004).

For the entries “UN3292, Batteries, containing sodium” and “UN3292, Cells containing sodium,” PHMSA proposes to revise the PSNs to “Batteries, containing metallic sodium

sodium alloy,” and “Cells, containing metallic sodium

sodium alloy,” respectively. This change will harmonize the entries with the UN Model Regulations, which revised the UN3292 entry to provide a clear distinction between sodium metal batteries and the new HMT entries for sodium ion batteries. PHMSA expects this proposal will improve safety by providing additional clarity to ensure shipments of batteries, specifically sodium metal batteries and sodium ion batteries, are properly classified, packaged, and transported.

Column (3) Hazard Class or Division

Section 172.101(d) describes column (3) of the HMT, which designates the hazard class or division corresponding to the PSN of that entry. As part of the changes for TMAH discussed above, PHMSA proposes to change the primary hazard class of “UN3423, Tetramethylammonium hydroxide, solid” to align with the with changes adopted in the 23rd revised edition of the UN Model Regulations. Currently, UN3423 is a Class 8 corrosive material, but both human exposure and toxicity studies have demonstrated that solid TMAH has a significant toxicity hazard as well. UN3423 demonstrates a toxicity hazard and meets the criteria for Class 8 and Division 6.1 hazards. In accordance with § 173.2a, a Division 6.1 hazard should be the primary hazard class as it has precedence over a Class 8 hazard when classifying a material with multiple hazards. For that reason, PHMSA proposes to replace “8” in column (3) with “6.1” and add Class 8 as a subsidiary hazard to column (6). PHMSA expects this proposed action will improve safety by more accurately communicating the primary hazard of the material and providing uniform hazard communication for international shipments.

Column (5) Packing Group

Section 172.101(f) describes column (5) of the HMT, which specifies one or more packing groups (PG I, II, or III) assigned to certain materials. A PG indicates the required level of packaging according to the degree of danger presented by hazardous materials.

PHMSA proposes to remove the PG assigned to two HMT entries: “UN2028, Bombs, smoke, non-explosive, with corrosive liquid, without initiating device” and “UN3165, Aircraft hydraulic unit fuel tank

(containing a mixture of anhydrous hydrazine and monomethyl hydrazine) (M86 fuel).

” PHMSA proposes to adopt these changes for consistency with the HMR, which does not assign PGs to articles in classes other than Class 1 in the HMT, and to align with the conventions adopted in the UN Model Regulations in 2012, which also removed PGs assigned to all articles in the DGL. PHMSA expects that removing this inconsistency will maintain the current level of safety for transport of these materials.

In addition, as a part of various changes discussed above pertaining to the hazard classification of TMAH, PHMSA proposes to change the PG of “UN3423, Tetramethylammonium hydroxide, solid” from PG II to PG I. This change in assignment from PG II to PG I is based on human experience and toxicity data that indicates a PG I toxicity hazard for TMAH solids is appropriate. PHMSA expects that this change will enhance safety by requiring a higher standard for packaging for this material.

Column (6) Label Codes

Section 172.101(g) describes column (6) of the HMT, which contains label codes representing the hazard warning labels required for a package filled with a material conforming to the associated hazard class and proper shipping name, unless the package is otherwise excepted from labeling. The first code is indicative of the primary hazard of the material. Additional label codes are indicative of subsidiary hazards.

For “UN3423, Tetramethylammonium hydroxide, solid,” which is currently classified as a Class 8 corrosive material, PHMSA proposes to revise the label code to indicate a primary Division 6.1 and subsidiary Class 8 hazard. For “UN3560, Tetramethylammonium hydroxide aqueous solution

with not less than 25% tetramethylammonium hydroxide,

” PHMSA proposes to add a 6.1 and 8 label code to correspond to this entry's primary and subsidiary hazards. For “UN1835, TMAH aqueous solutions

with more than 2.5% but less than 25% TMAH,

PGII,” PHMSA proposes to add a subsidiary Division 6.1 hazard, which would also be reflected in column (6). Accidental human exposure and acute dermal toxicity studies demonstrates the toxic properties of TMAH, which is discussed in greater detail above in the summary of amendments associated with the new TMAH solution HMT entry (

i.e.,

UN3560). PHMSA expects these changes will increase safety by more appropriately communicating the hazards of these materials.

Column (7) Special Provisions

Section 172.101(h) describes column (7) of the HMT, which assigns special provisions for each HMT entry. Section 172.102 provides for the meaning and requirements of the special provisions assigned to entries in the HMT. The proposed revisions to column (7) of certain entries in the HMT are discussed below.

For “UN1006, Argon,” “UN1013, Carbon dioxide,” “UN1046, Helium,” and “UN1066, Nitrogen,” PHMSA proposes to assign a new Special Provision 406, which would allow these materials to be transported in DOT specification cylinders and UN pressure receptacles as a limited quantity material in quantities not more than 1000 ml (34 fluid ounces) per package. For additional details on this new provision, see the Section-by-Section Review in Section 172.102.

For “UN1010, Butadienes and hydrocarbon mixture, stabilized

containing more than 20% butadienes,

” PHMSA proposes to assign new Special Provision 402, which would specify required conditions for transport under this entry. For additional information on this new special provision, see the Section-by-Section Review in Section 172.102.

For “UN1391, Alkali metal dispersions

Alkaline earth metal dispersions,” and “UN3482, Alkali metal dispersions, flammable

Alkaline earth metal dispersions, flammable,” PHMSA proposes to assign six special provisions,

i.e.,

Special Provisions 64, 65, T13, TP2, TP7, and a newly proposed Special Provision, TP42. These special provisions would provide clear direction as to which alkali metals and alkaline earth metals are included under these PSNs and would provide packaging flexibility by authorizing the transport of these materials, which are slurries comprised of metal powders and a hydrocarbon solvent, in portable tanks rather than limiting these materials to other bulk and non-bulk packaging provisions in §§ 173.201 and 173.244. These additional portable tank packaging provisions were adopted in the 23rd revised edition of the UN Model Regulations to facilitate the transport of alkali metals that are incorporated in liquid dispersions for the manufacture of items such as lithium battery anodes. As the global demand for lithium increases, particularly given the potential use in energy storage applications, the need has arisen for the international transport of alkali metal and alkaline earth metal dispersions in portable tanks. Prior to changes adopted in the UN Model Regulations, the DGL did not indicate any portable tank instructions for these materials. Consequently, these hazardous materials were not permitted to be transported in UN portable tanks unless a competent authority approval was granted. The newly assigned T and TP code packaging provisions were adopted for consistency with the Guiding Principles for the Development of the UN Model Regulations, which indicates that liquid Division 4.3 substances of PG I are—in principle—considered suitable for transport in portable tanks conforming to portable tank instructions.

To facilitate the transport

of these materials, PHMSA proposes to amend the associated packaging provisions to authorize the transport of alkali metal dispersions and alkaline earth metal dispersions in portable tanks that conform to tank instructions in Special Provisions T13, which requires a higher minimum test pressure of 6 bar, a minimum shell thickness of 6 mm, and prohibits bottom outlets; TP2, which provides a specific formula for the maximum degree of filling; and TP7, which requires that the vapor space has to be purged of air by nitrogen or other means. In addition, PHMSA proposes to assign a new Special Provision TP42 to add supplemental provisions for the transport of alkali metal dispersions that are considered highly reactive. PHMSA expects that by expanding the packaging options, these amendments will facilitate access to affordable, reliable, sustainable, and modern energy sources and offer greater flexibility in the packaging that may be used to transport these materials. For additional details on these TP codes, see the Section-by-Section Review in Section 172.102.

This document outlines the underlying principles that have been applied in developing the

UN Model Regulations and outlines the approach taken during the development of its provisions.

For “UN1835, Tetramethylammonium hydroxide aqueous solution

with more than 2.5 percent but less than 25 percent tetramethylammonium hydroxide,

PGII,” “UN1835, Tetramethylammonium hydroxide aqueous solution

with not more than 2.5 percent tetramethylammonium hydroxide,

PGIII,” “UN3560, Tetramethylammonium hydroxide aqueous solution

with not less than 25 percent tetramethylammonium hydroxide,

” and “UN3423, Tetramethylammonium hydroxide, solid,” PHMSA proposes to assign two new special provisions—408 and 409. Special Provision 408 would be assigned to UN1835 (PG II and PG III) and UN3560, and Special Provision 409 would be assigned to UN1835 (PG II and PG III), UN3560, and UN3423. Special provision 408 will provide instruction on appropriate hazardous materials descriptions for aqueous solutions of TMAH with differing formulations and constituents, while Special Provision 409 will provide a delayed compliance date for use of the new HMT entries and revised hazard information to allow industry time to adjust their hazard communication and associated packaging and handling provisions. See the Section-by-Section Review in Section 172.102 for additional discussion of these new special provisions. PHMSA expects that these proposed changes will facilitate the safe transport of these materials by clearly outlining the hazardous communications requirements.

For “UN2795, Batteries, wet, filled with alkali,

electric storage,

” “UN3292, Batteries, containing metallic sodium

sodium alloy,” and “UN3292, Cells, containing metallic sodium

sodium alloy,” PHMSA proposes to assign new Special Provision 401 to help to distinguish between shipping descriptions that describe batteries and cells with sodium as their electrolyte. Special Provision 401 will also be assigned to the proposed new entries for sodium ion batteries, “UN3551, Sodium ion batteries

with organic electrolyte,

” “UN3552, Sodium ion batteries contained in equipment

with organic electrolyte,

” and “UN3552, Sodium ion batteries packed with equipment,

with organic electrolyte.

” For additional information, see the Section-by-Section Review in Section 172.102.

For “UN2803, Gallium,” PHMSA proposes to assign Special Provision 365, which is also proposed to be amended in this NPRM. See the Section-by-Section Review in Section 172.102 for further discussion of amendment to Special Provision 365. Currently, “UN2803, Gallium” is only assigned to Special Provisions T1 and TP33, which provide requirements for portable tanks. Special Provision 365 would provide instructions on the use of “UN2803, Gallium,” or the newly added entry, “UN3554, Gallium contained in manufactured articles.”

For “UN3270, Nitrocellulose membrane filters,

with not more than 12.6% nitrogen, by dry mass,

” PHMSA proposes to amend the special provision that is currently assigned, Special Provision 43. This special provision would provide an exception from regulation for these materials that meet the packaging requirements specified in Special Provision 43. For additional information, see the Section-by-Section Review in Section 172.102.

“UN3423, Tetramethylammonium hydroxide, solid,” is currently assigned several special provisions, including IB8, which provides the list of authorized intermediate bulk containers (IBCs) for this material. PHMSA proposes to replace IB8 with IB7. This change is consistent with the proposed revisions pertaining to the hazard classification of TMAH solids. Like IB8, IB7 authorizes IBCs made of metal, rigid plastics, composite materials, and wood. But unlike IB8, IB7 does not authorize fiberboard or flexible IBCs. PHMSA finds that removing the authorization for fiberboard and flexible IBCs is an appropriate change to ensure continued safety for the transport of this material given the proposed revised hazards presented during transportation. Consistent with the revised assignment of IB7, PHMSA also proposes to replace IP2 with IP1. IP2 only requires certain IBCs to be offered for transportation in a closed freight container or a closed transport vehicle, whereas IP1 requires the use of closed freight containers or a closed transport vehicle for all IBC types that contain UN3423. Assigning IP1 is consistent with assignment of IP1 to other Division 6.1, PG I materials listed in the HMT. PHMSA proposes to replace T3 with T6 as well. Replacing T3 with T6 will increase the safety and performance requirements of these packagings by increasing the minimum test pressure from 2.65 bar to 4 bar. This change reflects the same change made in the latest edition of the UN Model Regulations.

PHMSA proposes to assign Special Provision 162 (as proposed to be amended, see discussion in Section-by-Section Review in Section 172.102 for additional information) to ten additional entries on the HMT. Currently, Special Provision 162 is only assigned to desensitized explosives classed as Division 4.1 solids. PHMSA proposes to amend the text of Special Provision 162 to include desensitized explosives classified as Class 3 flammable liquids. PHMSA also proposes to assign Special Provision 162 to some additional Division 4.1 hazardous materials for which this standard applies but which were not previously specified. PHMSA proposes to assign Special Provision 162 to the following Class 3 and Division 4.1 hazardous materials as follows:

• “UN1204, Nitroglycerin solution in alcohol

with not more than 1 percent nitroglycerin,

3, PG II”.

• “UN2059, Nitrocellulose, solution, flammable

with not more than 12.6 percent nitrogen, by mass, and not more than 55 percent nitrocellulose,

3, PG I”.

• “UN2059, Nitrocellulose, solution, flammable

with not more than 12.6 percent nitrogen, by mass, and not more than 55 percent nitrocellulose,

3, PG II”.

• “UN2059, Nitrocellulose, solution, flammable

with not more than 12.6 percent nitrogen, by mass, and not more than 55 percent nitrocellulose,

3, PG III”.

• “UN2555, Nitrocellulose with water

with not less than 25 percent water, by mass,

4.1, PG II”.

• “UN2556, Nitrocellulose with alcohol

with not less than 25 percent alcohol by mass, and with not more than 12.6 percent nitrogen, by dry mass,

4.1, PG II”.

• “UN2907, Isosorbide dinitrate mixture

with not less than 60 percent

lactose, mannose, starch or calcium hydrogen phosphate,

4.1, PG II”.

• “UN3064, Nitroglycerin, solution in alcohol,

with more than 1 percent but not more than 5 percent nitroglycerin,

3, PG II”.

• “UN3319, Nitroglycerin mixture, desensitized, solid, n.o.s.

with more than 2 percent but not more than 10 percent nitroglycerin, by mass,

4.1, PG II”.

• “UN3343, Nitroglycerin mixture, desensitized, liquid, flammable, n.o.s.

with not more than 30 percent nitroglycerin, by mass,

3, PG II”.

• “UN3344, Pentaerythrite tetranitrate mixture, desensitized, solid, n.o.s.

Pentaerythritol tetranitrate mixture, desensitized, solid, n.o.s.

PETN mixture, desensitized, solid, n.o.s.,

with more than 10 percent but not more than 20 percent PETN, by mass,

4.1, PG II”.

• “UN3357, Nitroglycerin mixture, desensitized, liquid, n.o.s.

with not more than 30% nitroglycerin, by mass,

3, PG II”.

PHMSA expects that assigning this special provision will enhance safety by ensuring that both solid and liquid desensitized explosives are subject to uniform performance standards for the diluent during transportation.

PHMSA proposes to make corrections to multiple HMT entries that were inadvertently modified in previous rulemakings. Specifically, PHMSA proposes to remove IP8 from column (7) of the HMT for the following assigned UN numbers: “UN2246 Cyclopentene”, “UN1593, Dichloromethane,” “UN1164 Dimethyl sulfide,” “UN1891, Ethyl bromide,” “UN2622, Glycidaldehyde,” “UN2288, Isohexenes,” “UN2612, Methyl propyl ether,” “UN2460, 2-Methyl-2butene,” “UN1234 Methylal,” “UN1265, Pentanes, PGII,” and “UN1278, 1-Chloroproane.” IP8 states that ammonia solutions may be transported in rigid or composite plastic IBCs (31H1, 31H2 and 31HZ1) that have successfully passed, without leakage or permanent deformation, the hydrostatic test specified in § 178.814 of the HMR at a test pressure that is not less than 1.5 times the vapor pressure of the contents at 55 °C (131 °F). IP8 was meant to be assigned to ammonia solutions, but due to an editorial error, IP8 was assigned to these UN numbers, which are not ammonia solutions.

Finally, for “UN2555, Nitrocellulose with water

with not less than 25 percent water, by mass,

4.1, PG II” and “UN2556 Nitrocellulose with alcohol

with not less than 25 percent alcohol by mass, and with not more than 12.6 percent nitrogen, by dry mass,

4.1, PG II,” PHMSA proposes to assign Special Provision 197. This special provision was inadvertently removed from these entries in the HM-215Q final rule.

PHMSA expects that this correction will provide enhanced safety by removing conflicting packaging provisions from these entries.

89 FR 25434 (Apr. 10, 2024).

Column (8) Packaging

Section 172.101(i) explains the purpose of column (8) in the HMT. Columns (8A), (8B), and (8C) specify the applicable sections for exceptions, non-bulk packaging requirements, and bulk packaging requirements, respectively. Columns (8A), (8B), and (8C) are completed in a manner which indicates that “§ 173” precedes the designated numerical entry. Column (8A) contains exceptions from some of the requirements of the HMR. The referenced exceptions are in addition to those specified in subpart A of part 173 and elsewhere in the HMR. The word “None” in this column means no packaging exceptions are authorized, except as may be provided by special provisions in column (7).

For “UN3423, Tetramethylammonium hydroxide, solid,” and based on the proposed classification changes to a Division 6.1 (8), PG I material, PHMSA proposes to remove the “154” in column (8A), which currently directs the reader to exceptions for Class 8 (corrosive materials) and to replace it with “None.” In addition, in column (8B), “213” would be replaced by “211” to direct users to the requirements for authorized non-bulk packagings for solid hazardous materials in PG I in § 173.211. Lastly, in column (8C), “240” would be replaced with “242” to direct users to requirements for authorized bulk packagings for certain medium hazard liquids and solids, including solids with dual hazards. PHMSA expects that these changes will improve safety by providing more appropriate packaging requirements based on the newly identified hazards posed by this material.

Column (9) Quantity Limitations

Section 172.101(j) explains the purpose of column (9) in the HMT. Column (9) specifies quantity limitations for packages transported by air and rail. Column (9) is divided into two columns: column (9A) provides quantity limits for passenger aircraft/rail, and column (9B) provides quantity limits for cargo aircraft.

To align with changes adopted in the 2025-2026 edition of the ICAO Technical Instructions, PHMSA proposes to amend the quantity limitations for TMAH solids (UN3423), consistent with reclassification of this entry. With the proposed new Division 6.1, PG I primary hazard for UN3423, different quantity limitations are required. PHMSA proposes to replace “15 kg” with “1 kg” in column (9A) and to replace “50 kg” with “15 kg” in Column (9B), which is consistent with the quantity limits for other Division 6.1, PG I entries in the HMT. PHMSA expects this proposed change to improve safety by appropriately limiting the quantities of this material when transported by rail and air.

Column (10) Vessel Stowage

Section 172.101(k) explains the purpose of column (10) of the HMT and prescribes the vessel stowage and segregation requirements for specific entries. Column (10) is divided into two columns: column (10A) [Vessel stowage] specifies the authorized stowage locations on board cargo and passenger vessels; and column (10B) [Other provisions] specifies special stowage and segregation provisions. The meaning of each code in column (10B) is set forth in § 176.84.

For “UN1791, Hypochlorite solutions, PG III,” PHMSA proposes to make a correction to the HMT entry. In its HM-215Q rulemaking, PHMSA removed the stowage codes 53 and 58, which require stowage “separated from alkaline compounds” and “separated from cyanides,” respectively.

These stowage codes were intended to be applied to several HMT entries to ensure proper segregation between acids and both amines and cyanides, but should not have included “UN1791, Hypochlorite solutions.” When this removal of the stowage codes 53 and 58 was implemented in HM-215Q, PHMSA inadvertently omitted the removal of the aforementioned stowage codes for the PG III entry. Therefore, PHMSA proposes to remove the stowage codes 53 and 58 from column (10B) of “UN1791, Hypochlorite solutions, PG III.” PHMSA expects that this correction will remove the burden faced by shippers who have had to segregate hypochlorite solutions for compliance with the HMR, which is inconsistent with the requirements of the IMDG Code.

89 FR 25434 (Apr. 10, 2024).

For “UN2067, Ammonium nitrate-based fertilizer,” PHMSA proposes to assign stowage code 116 in column (10B) (as proposed to be amended, see discussion in Section-by-Section Review of § 176.84). This stowage code is currently assigned to “UN1942, Ammonium nitrate,

with not more than

0.2% combustible substances, including any organic substance calculated as carbon, to the exclusion of any other added substance,

” and PHMSA proposes to also assign it to “UN2067, Ammonium nitrate-based fertilizer.” This change in stowage requirements was adopted in Amendment 42-24 of the IMDG Code because these substances have similar chemical properties, pose similar hazards, may be transported in the same way (

e.g.,

conventional reefer ship, and stored in areas that contain multiple compartments or on vessels with tween deck storage). PHMSA expects this new assignment to provide clarity and consistent direction regarding how these ammonium-based hazardous materials are to be stowed to ensure vessel safety.

For “UN2303, Isopropenylbenzene,” PHMSA proposes to assign stowage code 25 in column (10B). This stowage code requires that the hazardous material be “protected from sources of heat.” This new stowage requirement for UN2303 was added in Amendment 42-24 to the IMDG Code because the material is liable to polymerize and is generally stabilized with a small quantity of 4-

tert

-butylcatechol, which should be stored at temperatures not exceeding 30 °C. PHMSA agrees with the addition of this extra stowage requirement and expects that protecting the material from sources of heat will enhance safety by ensuring that the stabilization methods applied to these packages will not become ineffective during transport by vessel.

For “UN3129, Water-reactive liquid, corrosive, n.o.s., PG II and III,” “UN3130, Water-reactive liquid, toxic, n.o.s., PG II and III,” and “UN3148, Water-reactive liquid, n.o.s., PG I, II, and III,” PHMSA proposes to revise vessel stowage requirements in column (10A). Currently, these entries are assigned stowage category “E.” Stowage category “E” indicates that a material may be stowed “on deck” or “under deck.” PHMSA proposes to change the code in column (10A) for these entries to stowage category “D.” This would indicate that these entries must be stowed on deck only and would not be permitted to be stowed under deck. As these materials will not be allowed to be stowed under deck, PHMSA also proposes to revise column (10B) by removing assignment of stowage code “85,” which states that a material stowed under deck must be in a mechanically ventilated space, from the entries UN3129 and UN3130. PHMSA also proposes to add new stowage code “160” to column (10B) to the entries UN3129, UN3130, and UN3148. This new code will indicate that these materials must be stowed away from potential sources of ignition. These changes in stowage requirements mirror those adopted in Amendment 42-24 to the IMDG Code to address a hazard communication conflict.

Currently, there is no general “n.o.s.” entry for liquids classified as a Division 4.3 (dangerous when wet) that also meet the flammable liquid definition (

i.e.,

water-reactive liquids, flammable, n.o.s.), because the Division 4.3 classification would take precedence in hazard classification in accordance with § 173.2. Therefore, shippers are required to classify and to describe these materials as “UN3148, Water-reactive liquid, n.o.s.,” which does not provide any indication that the liquid also meets a flammable liquid definition. This requires carriers to assess the flashpoint of a Division 4.3 liquid described as “UN3148 Water-reactive liquid, n.o.s.,” “UN3130, Water-reactive liquid, toxic,” or “UN3129, Water-reactive liquid, corrosive, n.o.s.,” by requesting a safety data sheet, which imposes avoidable administrative burdens for both carriers and shippers. To address this, the IMO revised the stowage categories for the entries discussed from “E” to “D,” which would prohibit these materials from being stored under deck regardless of their flash point. This amendment would alleviate the burden for carriers to determine material flashpoints to identify their prescribed stowage locations. PHMSA agrees with these revisions and proposes to amend the entries as discussed above.

The IMDG code also requires packages containing flammable gases and flammable liquids having a flashpoint of less than 23 °C to be stowed away from potential sources of ignition. However, there are currently no stowage codes that memorialize this requirement. To address this, the IMDG code added new stowage code “SW31,” which indicates that flammable liquids having a flashpoint of less than 23 °C must be stowed away from potential sources of ignition, and assigned it to UN3129, UN3130, and UN3148. PHMSA expects that harmonization with these vessel stowage amendments will alleviate carriers from having to determine a material's flash point and its correct stowage location.

For “UN3536, Lithium batteries installed in cargo transport unit

lithium ion batteries or lithium metal batteries,

” PHMSA proposes to change the code in column (10A) for this entry to stowage category “D.” This code would mean that this entry must be stowed “on deck only” on a cargo vessel or on a passenger vessel carrying a number of passengers limited to not more than the larger of 25 passengers, or one passenger per each 3 meters of overall vessel length, but the material is prohibited on a passenger vessel in which the limiting number of passengers is exceeded. For column (10B), PHMSA proposes to add Codes “25” and “40.” As stated in § 176.84(b), Code “25” means that the material must be protected from sources of heat, and Code “40” means that the material must be stowed “clear of living quarters.” The thirty-ninth session of the CCC finalized these same changes as adopted in Amendment 42-24 of the IMDG Code for UN3536 based on position papers showing significant safety concerns with the way “lithium battery energy storage cabinets” were being regulated for stowage aboard vessels. These papers demonstrated, through simulations of fires and explosions involving the “energy storage cabinets,” that a significant risk of rupture of the hull structure of ships exists when these containers are stowed in certain positions below deck. Further, it was shown that there was significant risk to the life and safety of the crew when fires involving these containers occur and they are stowed under deck. For these reasons, the CCC, as provided for in Amendment 42-24 of the IMDG Code, adopted provisions that require stowage on deck, and in some cases, a prohibition of transport on certain vessels. Amendment 42-24 of the IMDG Code also adopted provisions that would add safety precautions by protecting the containers from sources of heat and requiring stowage clear of living quarters. PHMSA expects that these new requirements will address the hazards identified by the simulations discussed in these papers and incidents of thermal runaway associated with the transportation of “lithium battery energy storage cabinets.”

For “UN3555, Trifluoromethyltetrazole-sodium salt in acetone,

with not less than 68% acetone, by mass,

3, PG II” (TFMT-Na), PHMSA proposes to add two new vessel stowage and handling codes. In Amendment 42-24 to the IMDG Code, under column 16a of the DGL, this new entry was assigned four stowage and handling codes which require for UN3555 that: it must be protected from sources of heat (SW1); cargo transport units be shaded from direct sunlight (SW11); it must be stored in cool ventilated space (H3); and that it must be kept as cool as reasonably practicable (H2). PHMSA is assigning codes “12” and “25,” which correspond to H2 and SW1, respectively. However, the HMR do not have corresponding vessel stowage and handling codes for “SW11”

and “H3,” therefore, PHMSA proposes harmonizing with the IMDG Code to add corresponding provisions by creating two new vessel stowage codes, Code 158 and Code 159. Code 158, like SW11, would instruct that “Cargo transport units shall be shaded from direct sunlight. Packages in cargo transport units shall be stowed to allow for adequate air circulation throughout the cargo.” Code 159, like H3, would instruct “During transport, it should be stowed (or kept) in a cool ventilated place.” PHMSA expects that these stowage and handling provisions will provide the appropriate level of safety for the transport of this material on vessels.

For “UN3560, Tetramethylammonium hydroxide aqueous solution

with not less than 25 percent tetramethylammonium hydroxide,

” PHMSA proposes to add a new stowage code “D” in column (10A). This code would mean that the material must be stowed “on deck only” on a cargo vessel, or on a passenger vessel carrying a maximum of 25 passengers, or one passenger for each three meters of overall vessel length, but if the limiting number of passengers is exceeded the material is prohibited onboard the vessel. This new stowage location aligns with provisions in Amendment 42-24 to the IMDG Code. In addition, in column (10B), PHMSA proposes to assign stowage code “52,” which states that materials must be stowed “separated from” acids. Section 176.83(c)(2)(iii) defines “separated from” for “on deck” stowage (category D) as separated by a distance of at least six meters (20 feet) horizontally. The assignment of these new stowage and handling requirements aligns with provisions in Amendment 42-24 to the IMDG Code. PHMSA expects this proposed change to improve safety by ensuring that this material is stowed in an appropriate location and under appropriate conditions, such as being separated from packages containing acids when transported by vessel.

Section 172.102 (Special Provisions)

Section 172.102 lists special provisions applicable to the transportation of specific hazardous materials. Special provisions contain various provisions, including packaging requirements, prohibitions, and exceptions applicable to particular quantities or forms of hazardous materials. PHMSA proposes the following additions and revisions to the special provisions in this section:

Special Provision 43

PHMSA proposes to modify Special Provision 43, which is assigned to “UN3270, Nitrocellulose membrane filters,

with not more than 12.6% nitrogen, by dry mass

” in the HMT. These materials are most notably used in rapid test devices for infectious diseases like COVID-19, influenza, hepatitis, malaria, borreliosis, and other diseases, and as substrates for bioanalytical tests as well as pregnancy tests. Special Provision 43 states that to use this HMT entry nitrocellulose membrane filters—including paper separators and coating or backing materials—present in transport must not be able to propagate a detonation as tested by UN Manual of Tests and Criteria, Part I, Test Series 1(a). Special Provision 43 further states that nitrocellulose (NC) membrane filters in the form in which they are to be transported that do not meet the criteria for a Division 4.1 material, based on suitable burning rate tests and testing in accordance with the UN Manual of Tests and Criteria, Part III, are not subject to the HMR. Finally, NC membrane filters, each with a mass not exceeding 0.5 g, are not subject to the HMR when contained individually in an article or a sealed packet.

To further facilitate the transport of these items, which are often used in medical testing, the 23rd revised edition of the UN Model Regulations includes a new special provision assigned to UN3270 that adds conditions for exception from regulation without the need for testing. PHMSA proposes to adopt the provisions of this new special provision as part of Special Provision 43 in the HMR instead of a wholly separate special provision. Specifically, the special provision in the UN Model Regulations states that for a NC membrane filter with a nitrocellulose content that does not exceed 53 g/m

, and where the net mass does not exceed 300 g per inner packaging, the NC membrane filter is not subject to regulation under certain conditions. The conditions are that they are packed with paper separators with a minimum of 80 g/m

placed between each layer of NC membrane filters; and that they are packed to maintain alignment of the NC membrane filters and paper separators in accordance with three distinct configurations. This exception was adopted based on additional tests showing that NC membrane filters with a NC content less than 53 g/m

and an NC net weight not exceeding 300 g per inner packaging do not propagate a detonation and had burn rates justifying exclusion from classification as a Division 4.1 flammable solid in the configuration(s) defined by the provision. As stated previously, PHMSA proposes to adopt the conditions of the UN Model Regulation special provision as part of SP 43 and expects that doing so will facilitate the transport of these filters and reduce the burden of requesting a competent authority approval for transportation of each NC membrane filter type. In addition, this provision will improve the availability of the NC membrane filters for important medical devices, such as rapid test devices for determination of COVID-19 infections. PHMSA expects that the reduced regulatory burden for these products will translate to reduced costs for consumers of many commonly used products in the American pharmacological market.

Special Provision 134

Special Provision 134, which is assigned to “UN3171, Battery-powered vehicle or Battery-powered equipment,” currently indicates that the use of UN3171 only applies to vehicles or equipment powered by wet batteries, sodium batteries, lithium metal batteries, or lithium ion batteries that are transported with such batteries installed. However, with the introduction of three specific proper shipping names for battery-powered vehicles, the range of hazardous materials that can be transported under UN3171 is reduced to vehicles and equipment powered by wet batteries that are transported with such batteries installed. PHMSA proposes to amend Special Provision 134 to clarify that vehicles powered by lithium ion, lithium metal, or sodium ion batteries must be assigned to “UN3556, Vehicle, lithium ion battery powered,” “UN3557, Vehicle, lithium metal battery powered,” and “UN3558, Vehicle, sodium ion battery powered vehicle,” respectively, and to assign this special provision to these entries on the HMT. PHMSA also proposes to add language regarding vehicles transported in packagings to reiterate that, except for the battery, some parts of battery powered vehicles may be detached from the frame of the vehicle to fit in the outer packaging. This language reiterates language currently in § 173.220, which states that if a battery is removed from a battery powered vehicle (engines and machinery), and is packed in the same outer packaging, the package must be consigned as “UN3481, Lithium ion batteries packed with equipment,” “UN3091, Lithium metal batteries packed with equipment;” or “UN3552, Sodium ion batteries packed with equipment,

with organic

electrolyte.

” As this is only a clarifying editorial amendment, PHMSA expects the change will enhance safety by facilitating the proper description and classification of these vehicles and does not expect that this change will result in any additional costs for the regulated community.

Special Provision 160

Special Provision 160 is assigned to HMT entry “UN3268, Safety devices,

electrically initiated,

9,” and outlines conditions and criteria for use of the entry. Consistent with discussions of proposed changes to the HMR regarding fire suppressant dispersing devices in §§ 172.101, 173.62, and 173.169, PHMSA proposes to revise Special Provision 160 to include a statement to clarify that the HMT entry for “UN3268, Safety devices” does not apply to fire suppressant dispersing devices described in § 173.169, specifically, those articles that are properly classed and described as “UN3559, Fire suppressant dispersing devices.” PHMSA expects that these changes will enhance safety by facilitating the proper classification of these devices.

Special Provision 162

Special Provision 162, which is assigned to HMT entries that are explosive materials desensitized by liquid (typically water) and classified as a Division 4.1 flammable solid, specifies that these materials may be transported as a Division 4.1 only if packed so that at no time during transport will the percentage of diluent (

i.e.,

the liquid used to desensitize the explosive material) fall below the percentage that is stated in the shipping description. While developing provisions for UN3555, TFMT-Na, a flammable liquid desensitized explosive (as discussed in the Section-by-Section review), the UNSCOE determined that there are no comparable provisions for entries of flammable liquid desensitized explosives classified as Class 3 flammable liquids. Consequently, the UNSCOE determined that this provision (Special Provision 28 in the UN Model Regulations) should be amended to be applicable to flammable liquid desensitized explosives. PHMSA agrees with the UNSCOE and proposes to amend the text of Special Provision 162 to ensure desensitized explosives to be transported under the provisions of Class 3 or Division 4.1, as appropriate, are packed so that the percentage of diluent will not fall below that is stated, at any time during transportation. In addition, the amendment would require, in cases where the diluent is not stated, that the substance be packed so that the amount of explosive substance does not exceed the stated value. PHMSA expects that these changes will enhance safety by providing uniform requirements for the transport of desensitized explosives.

Special Provision 181

For shippers of lithium ion or lithium metal batteries that are “contained in” or “packed with equipment,” Special Provision 181 instructs that there are certain requirements when a package includes a combination of these lithium battery packaging configurations. This special provision requires that: the packages meet all applicable requirements in § 173.185; packages cannot exceed the quantity limits in columns (9A) and (9B) for passenger aircraft or cargo aircraft, as applicable; the package must be marked for lithium ion or lithium metal batteries packed with equipment; and the shipping paper must indicate the entry(ies) for lithium metal or lithium ion batteries (or a combination of the two) packed with equipment. With the addition of new entries for sodium ion batteries contained in and packed with equipment, and the application of provisions for lithium batteries to sodium ion batteries, PHMSA proposes to make this special provision applicable to lithium batteries contained in equipment and packed with equipment, as well as to sodium ion batteries contained in equipment and packed with equipment. PHMSA also proposes to assign Special Provision 181 to the following new HMT entries: “UN3552, Sodium ion batteries contained in equipment

with organic electrolyte

”, and “UN3552, Sodium ion batteries packed with equipment

with organic electrolyte.

”

This special provision ensures that the appropriate hazard communication for packages containing batteries both contained in and packed with equipment, indicating the slightly greater transport risk when batteries are packed with equipment versus when batteries are contained in equipment. PHMSA expects that extending this requirement will improve the level of safety achieved for lithium batteries to sodium ion batteries. Though the ICAO Dangerous Goods Panel (DGP) did not consider this change for the 2025-2026 ICAO TI, PHMSA expects that this requirement will be proposed and adopted in upcoming DGP meetings to provide consistency in the requirements for sodium ion batteries. PHMSA solicits comments on whether codifying this provision should be delayed until it is adopted in other international standards.

Special Provision 234

PHMSA proposes to add a new Special Provision 234 to provide packaging requirements for the new HMT entry, “UN3555, Trifluoromethyltetrazole, sodium salt (TFMT-Na).” This special provision mirrors the corresponding packaging and modal transport provisions in the UN Model Regulations. Specifically, PHMSA proposes that authorized packaging for TFMT-Na in acetone must be designed and constructed to prevent loss of the content of the phlegmatizer (

i.e.,

the acetone), must be transported in an upright position, and must be lead free. In addition, packaging must be limited to a maximum capacity of 250 liters (66 gallons).

Trifluoromethyltetrazole, sodium salt (TFMT-Na) in acetone is a desensitized explosive compound used as a precursor material for production of a new insecticide. Due to the explosive properties of the dry substance, it is handled and transported as a homogenous solution in acetone and currently is transported under a generic n.o.s. HMT entry. Because of its unique properties and expected increased use in insecticide manufacturing, the UNSCOE agreed to create a new entry on the DGL to facilitate its transport. As discussed earlier, Trifluoromethyltetrazole, sodium salt (TFMT-Na) is a product used in new products, such as insecticides. PHMSA expects that the addition of this new packaging provision will contribute to emerging industries by facilitating the transport of this material while providing a high level of safety.

Special Provision 252

PHMSA proposes to add a new Special Provision 252 assigned to “UN2426, Ammonium nitrate, liquid (

hot concentrated solution

).” This special provision would outline conditions under which solutions of ammonium nitrate can be transported under the HMT entry UN2426. According to this special provision, use of this entry would be based on concentration, water content, combustible material content, chlorine content, pH level, and temperature. Special Provision 252 would also outline criteria that ammonium nitrate solutions must meet to be excepted from regulation. The characteristics outlined in part (1) of Special Provision 252 reflect the existing requirements for transport of UN2426 in the Agreements Concerning the International Carriage of Dangerous Goods by Rail (RID) and by Road (ADR) and the IMDG Code. Given that these standards for transportation of

UN2426 are already recognized in the RID/ADR and IMDG Codes, incorporation of Special Provision 252 would provide clarity by bringing these standards directly into the HMR. Adopting these prescriptive requirements would add clarity to the classification of the material by communicating the thresholds above which the material is classified as hazardous. These requirements were also adopted in the 23rd revised edition of the UN Model Regulations to harmonize the transport conditions multimodally. PHMSA expects that adopting this special provision in the HMR will facilitate the movement of these solutions and improve safety by providing additional clarity on the classification of ammonium nitrate solutions.

Special Provision 328

Special Provision 328 instructs shippers on how to describe fuel cell systems containing lithium metal or lithium ion batteries. PHMSA proposes to make Special Provision 328 applicable to sodium ion batteries that are a component of a fuel cell system. Currently, the special provision only addresses lithium ion batteries and lithium metal batteries that are components of fuel cell systems. PHMSA expects this revision will help to ensure that fuel cell systems with sodium ion batteries are properly classified and that their hazards are properly communicated. Further, this revision harmonizes the HMR with the UN Model Regulations and ICAO Technical Instructions for the adoption of new provisions for sodium ion batteries.

Special Provision 360

Special Provision 360, which is assigned to “UN3091, Lithium metal batteries contained in equipment” and “UN3481, Lithium ion batteries contained in equipment,” currently indicates that vehicles powered solely by lithium batteries must be transported as “UN3171, Battery-powered vehicle.” This special provision serves to clarify that these batteries should be classified as “UN3171, Battery-powered vehicle,” rather than “UN3091, Lithium metal batteries contained in equipment,” or “UN3481, Lithium ion batteries contained in equipment,” if the battery provides motive power for a vehicle. As discussed in the amendments to the HMT (see the Section-by-Section Review in Section 172.101), in light of PHMSA's proposal to add new entries specifically for vehicles powered by lithium ion batteries, lithium metal batteries, and sodium ion batteries to the HMT, PHMSA proposes to amend Special Provision 360 to stipulate that vehicles powered by these batteries must be assigned to “UN3556, Vehicle, lithium ion battery powered,” “UN3557, Vehicle, lithium metal battery powered,” or “UN3558, Vehicle, sodium ion battery powered,” respectively. This proposal aligns with the proposed amendment to Special Provision 134 (discussed above). PHMSA expects that these changes will enhance safety by facilitating the proper classification of these vehicles. PHMSA does not anticipate there will be any costs associated with this clarification as shippers would be provided time to exhaust stocks of existing markings or labels with the currently used PSN.

Special Provision 365

PHMSA proposes to modify Special Provision 365 to include a reference to the proposed new HMT entry “UN3554, Gallium contained in manufactured articles,” and to assign this special provision to “UN2803, Gallium.” Currently, Special Provision 365 is assigned to “UN2809, Mercury,” which provides instructions to facilitate proper classification of mercury containing articles by directing users to “UN3506, Mercury contained in manufactured articles” and its associated provisions rather than UN2809, which is for elemental mercury. PHMSA proposes to amend the special provision to provide the same clarification for gallium by adding a reference to “UN3554, Gallium contained in manufactured articles,” and assigning it to the UN entry for elemental gallium, “UN2803.” PHMSA expects that this change will facilitate the transport of articles and manufactured items containing gallium and prevent avoidable costs to shippers. PHMSA expects that this will ensure these items are transported under the appropriate proper shipping name and that they will not be packaged and transported in accordance with the elemental gallium (UN2803) provisions for which there are fewer exceptions.

Special Provision 371

PHMSA proposes to revise Special Provision 371 by removing the requirement to follow the witness screen setup requirements provided in paragraph 16.6.1.3.5 of the UN Manual of Tests and Criteria, which conflicts with an exception from the requirement to have a witness screen as specified in 16.6.1.2(g). Special Provision 371 is assigned to “UN3164, Articles, pressurized pneumatic

hydraulic

containing non-flammable gas,

” and contains provisions to determine whether articles containing a small pressure receptacle with a release device can be transported under the entry “UN3164, Articles, pressurized pneumatic

hydraulic

containing non-flammable gas.

” Paragraph (a)(6) in Special Provision 371 requires an external fire (bonfire) test that follows the provisions of paragraph 16.6.1.2 (but specifically excepts paragraph (g)), as well as the provisions of 16.6.1.3.1 through 16.6.1.3.6, 16.6.1.3.7(b), and 16.6.1.3.8 of the UN Manual of Tests and Criteria. The requirement to follow 16.6.1.3.5, which outlines how to erect and place witness screens, conflicts with the exception from the requirement to have a witness screen, as provided in letter (g) of paragraph 16.6.1.2. To resolve that conflict, the UNSCOE removed the requirements to follow 16.6.1.3.5. PHMSA agrees with this correction and expects that it will facilitate the proper testing and classification of these materials.

Special Provision 379

Special Provision 379 provides conditions for exception from full regulation under the HMR for anhydrous ammonia adsorbed or absorbed on a solid contained in ammonia dispensing systems or receptacles intended to form part of such systems. Among these conditions, Special Provision 379 requires that receptacles containing adsorbed or absorbed ammonia must be made of a material compatible with ammonia as specified in ISO 11114-1:2012(E), “Gas cylinders—Compatibility of cylinder and valve materials with gas contents—Part 1: Metallic materials,” and an addendum published in 2017, ISO 11114-1:2012/Amd 1:2017(E). PHMSA proposes to revise Special Provision 379 to require receptacles to be made of compatible material as specified in updated ISO 11114-1:2020(E). This document was updated as part of ISO's regular periodic review and adopted for reference in the 23rd revised edition of the UN Model Regulations. PHMSA expects the use of these updated documents would allow safe transport of a wider variety of gases in newly developed types of metallic cylinders and valves without compromising safety.

Special Provision 389

Special Provision 389 provides packaging instructions and hazard communication requirements for “UN3536, Lithium batteries installed in cargo transport unit

lithium ion batteries or lithium metal batteries,

9.” PHMSA proposes to revise this special provision to provide clarity regarding the emergency response information that

accompanies shipments of UN3536. Specifically, PHMSA proposes that the emergency response information must specifically identify the predominant type of energy storage battery installed in the unit (

e.g.,

lithium ion batteries) and provide information on immediate methods for handling fires that may take place in these units.

On May 11, 2020, PHMSA published final rule HM-215O—a previous iteration of our recurring biennial rulemaking series to maintain harmonization with international regulations and standards.

One of the amendments finalized in HM-215O adopted a new entry in the HMT for the transportation of lithium battery energy storage systems that are transported in the form of a cargo transport unit. UN3536, Lithium batteries installed in cargo transport unit

lithium ion batteries or lithium metal batteries,

9” is intended to facilitate the transportation of large-scale battery energy storage systems. These devices are often used to provide electrical power in harsh, “off-grid” locations, or as part of an electrical utility facility that stores energy for subsequent use in the electrical grid.

PHMSA's understanding is that shipments assigned UN3536 are for systems that primarily contain rechargeable lithium ion batteries as the means of energy storage.

PHMSA seeks comment on our understanding of the types of lithium batteries transported using the UN3536 entry.

85 FR 27810 (May 11, 2020).

U.S. Energy Information Administration,

Electricity explains—Energy storage for electricity generation

(Last accessed Nov. 19, 2025), available at:

https://www.eia.gov/energyexplained/electricity/energy-storage-for-electricity-generation.php.

U.S. Dept. of Energy,

U.S. DOE Energy Storage Handbook

(last accessed November 19, 2025), available at:

https://www.sandia.gov/ess/publications/doe-oe-resources/eshb.

Currently, the required portion of the proper shipping name for UN3536—Lithium batteries installed in cargo transport unit—does not distinguish between lithium ion and lithium metal batteries. Instead, this distinction is made through italicized text in the HMT, which is not required to appear on the shipping paper or emergency response information. PHMSA's Emergency Response Guidebook (ERG), a resource for use during the initial phase of a transport incident involving hazardous materials, provides differing guidance for fires involving lithium ion and lithium metal batteries. The ERG recommends applying water to a lithium ion battery fire to cool surrounding cells, while the ERG indicates that water and foam

should not

(emphasis added) be applied to a lithium metal battery fire. The entry in the ERG for UN3536 directs the reader to different guide pages depending on the type of battery used in the system—

i.e.,

Guide 147, if the cargo transport unit contains lithium ion batteries, or Guide 138, if the cargo transport unit contains lithium metal batteries.

Furthermore, a vehicle transporting UN3536 is required to carry emergency response information (ERI) with the shipping paper that can be used in the mitigation of an incident involving UN3536, including immediate methods to handle fires.

This information must provide the proper instructions for emergency response for the specific type of lithium battery technology contained in the cargo transport unit.

PHMSA,

Emergency Response Guidebook 2024,

available at:

https://www.phmsa.dot.gov/training/hazmat/erg/erg2024-pdf-accessible-english.

49 CFR part 172, subpart G.

A July 2024 incident in Baker, California, involving a motor vehicle transporting UN3536 and resulting in a fire, demonstrates the importance of providing accurate emergency response information. PHMSA observed that the information contained in the proper shipping name and the ERG guidance created confusion for emergency responders in an accident scenario involving the transportation of a battery energy storage system.

In particular, the UN identification (ID) number displayed on the cargo transport unit and the mandatory information from the shipping paper (

i.e.,

UN3536, Lithium batteries installed in cargo transport unit) did not indicate whether the cargo transport unit contained lithium ion batteries or lithium metal batteries. Emergency responders were unclear with respect to immediate measures to mitigate the incident due to uncertainty on whether or not they should apply water during the initial stages of the fire. PHMSA is concerned that similar situations may reoccur during the initial response to future incidents involving UN3536, leading to a reduction in emergency response effectiveness, and increased risks to persons, property, and the environment.

Caltrans,

Caltrans Statement on San Bernardino County I-15 Fire,

available at:

https://dot.ca.gov/news-releases/news-release-2024-027.

PHMSA proposes to clarify the requirements for the ERI that accompanies the shipment of UN3536 to improve emergency response. Specifically, PHMSA proposes to revise Special Provision 389 to state that the ERI that accompanies the shipment must identify the predominant type of batteries in the cargo transport unit (

i.e.,

lithium ion or metal batteries) and provide specific instructions that can be used in the mitigation of an incident, including a fire, involving the unit. PHMSA also proposes an editorial revision to create a paragraph structure for Special Provision 389 to clarify for the reader. PHMSA does not anticipate there will be any costs associated with this clarification, which aligns with existing emergency response information requirements (see § 172.602(a)). PHMSA expects this revision will result in benefits through increased compliance with the existing requirement, which will result in decreased risks to emergency responders' personal safety, and an improved ability to identify and to apply the correct emergency response actions during an incident. PHMSA seeks comment on these expectations.

Separately, PHMSA intends to work with the UNSCOE to pursue internationally harmonized changes to the HMT to create separate UN ID number and proper shipping name entries for cargo transport units containing lithium ion or lithium metal, as well as a new entry for cargo transport units containing sodium ion batteries to improve hazard communication for these energy storage systems. Following the completion of that work, PHMSA will consider—in a future separate rulemaking—revising the HMT to harmonize with those changes to improve emergency response without impeding international transportation of these devices. Until more specific proper shipping names and UN numbers are adopted to reflect predominant battery (

i.e.,

lithium metal or lithium ion) in cargo transport units specifically, PHMSA intends to consider the predominant battery to be the battery that provides electrical power when the container is in use and supplying power to the grid. PHMSA's understanding is that typically the main source of power for these units is a lithium ion battery because these battery types may be recharged which allows them to be used more than once.

Special Provision 400

PHMSA proposes to add a new Special Provision 400 and to assign it to the following new HMT entries: “UN3551, Sodium ion batteries

with organic electrolyte,

” “UN3552, Sodium ion batteries contained in equipment

with organic electrolyte,

” and “UN3552, Sodium ion batteries packed with equipment,

with organic electrolyte.

” This special provision will allow shippers to offer sodium ion batteries for transportation other than by air without being further subject to requirements of the HMR if certain

conditions are met. A similar special provision was adopted in the 23rd revised edition of the UN Model Regulations and Amendment 42-24 of the IMDG Code. As discussed in § 172.101 of the Section-by-Section Review, sodium ion batteries, unlike lithium ion batteries, can be discharged to zero volts without affecting the performance of the cell. This means batteries using sodium ion technology can be stored and transported in a completely discharged state, posing no risk from electrical energy. For that reason, PHMSA believes that adding this special provision to provide an exception from all other HMR requirements (except when transported by air), given that certain conditions are still in place, is appropriate and will maintain safety during transportation of these batteries.

At the 29th meeting of the ICAO DGP, the addition of this special provision to the 23rd revised edition of the UN Model Regulations was discussed but ultimately not adopted into the 2025-2026 ICAO Technical Instructions. The DGP stated that it could be confusing to require a battery mark on the packaging, which could lead to disruptions in the acceptance process. The DGP also stated that it would be difficult for anyone other than the manufacturer to know the other hazardous materials that are components of the battery, and to comply with the condition of the special provision that requires the components to be authorized as limited quantities. Therefore, PHMSA proposes to make this special provision authorized for all modes of transportation except for air.

For modes other than air transportation, Special Provision 400 will instruct those offering sodium ion cells and batteries, including those packed with, or contained in, equipment, that those cells and batteries will not be subject to the HMR if: (1) they are short-circuited to a point that they contain no electrical energy; (2) they meet some of the general design criteria for batteries in § 173.185(a); (3) the package is marked with the battery mark; (4) the package, except for cells or batteries contained in equipment, is capable of withstanding a drop test; (5) the cells and batteries contained in equipment are protected from damage; and (6) the components of the battery must be authorized as limited quantities.

Special Provision 401

PHMSA proposes to add a new Special Provision 401, which would provide instructions on the use of sodium ion battery related proper shipping names. PHMSA proposes to assign Special Provision 401 to the following HMT entries:

• “UN2795, Batteries, wet, filled with alkali, electric storage”

• “UN3292, Batteries, containing metallic sodium or sodium alloy”

• “UN3292, Cells, containing metallic sodium or sodium alloy”

• “UN3551, Sodium ion batteries with organic electrolyte”

• “UN3552, Sodium ion batteries contained in equipment with organic electrolyte”

• “UN3552, Sodium ion batteries packed with equipment, with organic electrolyte”

This same special provision was added to the 23rd edition of the UN Model Regulations and the 2025-2026 ICAO Technical Instructions following the addition of new entries for sodium ion batteries. Special Provision 401 is expected to assist in determining the appropriate proper shipping name given that there are now six possible shipping names for batteries that contain different electrolyte chemistries. The electrolyte chemistry used contributes to the battery and cell hazards, and therefore different packaging methods and hazard communication are required. PHMSA does not expect adding this special provision will impose additional costs, and that it will help shippers to determine the appropriate provisions applicable to the batteries they are intending to transport.

Special Provision 402

PHMSA proposes to introduce a new special provision, Special Provision 402, assigned to “UN1010, Butadienes and Hydrocarbon mixture, stabilized

containing more than 20 percent butadienes.

” This special provision would specify required conditions for transport under this entry, such as a specific vapor pressure which must not exceed 1.1 MPa (11 bar) and a density at 50 °C not lower than 0.525 kg/l at 70 °C. This new special provision adds requirements to increase safety and ensure stability during transportation of mixtures containing butadiene. The conditions outlined are in line with the test pressure and maximum permissible mass contents per liter of capacity for pressure receptacles and tanks, and are the basis for the markings of the receptacles and the tanks. PHMSA expects this change to improve safety and provide clarity and consistency for the description and classification of butadienes and hydrocarbon mixtures.

Special Provision 406

PHMSA proposes to add a new Special Provision 406 assigned to “UN1006, Argon,” “UN1013, Carbon dioxide,” “UN1046, Helium,” and “UN1066, Nitrogen.” This special provision would allow these materials to be transported, except by air, in the appropriate authorized DOT specification cylinders and UN pressure receptacles as a limited quantity material in quantities not more than 1.0 L (34 fluid ounces) per package. The packagings are further restricted by a maximum test pressure-capacity product not to exceed 152 bar liter (78 psig·ft

)—

i.e.,

the product of the size (capacity) of the packaging multiplied by the test pressure, cannot exceed 152 bar liters. The Division 2.2 gases assigned to this special provision would not be allowed to be packed together (in the same package) with other hazardous materials.

This proposed amendment would harmonize the HMR with the 23rd revised edition of the UN Model Regulations, which includes this special provision (

i.e.,

406) for limited quantity transport of these four Division 2.2 non-flammable, non-poisonous compressed gases. Prior to the addition of this special provision to the UN Model Regulations, to be transported as a limited quantity, these gases were limited to quantities not exceeding 120 ml (about four fluid ounces) per inner packaging. The HMR currently includes this limited quantity provision for compressed gases—that are not defined as aerosols—in § 173.306(a)(1). The change to the UN Model Regulations was based on and supported by past experience of safe shipments of these gases in accordance with regulations adopted by European countries (

i.e.,

ADR) in volumes exceeding 120 ml and the implementation of special permits with similar provisions issued by PHMSA.

The rationale behind limited quantity provisions, which provide exceptions for certain hazardous materials, is that when appropriately packed in lesser quantities, these materials pose a lower risk in transport than the same hazardous materials packed in larger quantities. As a result of that reduced risk, they are afforded some relief from general transportation requirements such as hazard labels. When transported as a limited quantity in accordance with proposed Special Provision 406, these hazardous

materials would be excepted from labeling, placarding, and shipping papers. The DGP determined that the special provision as adopted in the UN Model Regulations would not be of any substantial value for adoption for air transportation under the ICAO Technical Instructions because, though allowed to be transported in greater quantities as limited quantity material, they would still be subject to marking, labeling, and shipping papers. PHMSA agrees and proposes to exclude the use of this new special provision for air transport specifically. In addition, PHMSA intends to clarify that this provision does not provide shippers with an alternative classification for cylinders intended to be used as fire extinguishers that would otherwise be described and classified as “UN1044, Fire extinguishers.”

DOT-SP 20796 and DOT-SP 20936. UNECE,

Committee of Experts on the Transport of Dangerous Goods and on the Globally Harmonized System of Classification and Labelling of Chemicals—ST/SG/AC.10/C.3/2022/26 Increase of the limited quantity volume for Division 2.2 compress gases

(June 27-July 6, 2022), available at:

https://unece.org/sites/default/files/2022-04/ST-SG-AC.10-C.3-2022-26e.pdf.

This proposed amendment would also respond to a petition for rulemaking, P-1974, submitted by Hazmat Safety Consulting.

PHMSA expects that this proposed amendment will facilitate the transport of important commercial goods that include small cylinders of inert gases. In addition, PHMSA expects that this change will allow domestic sellers to capture economies of scale by offering consumers compressed gas products in larger size options without additional regulatory burden.

Regulations.gov,

PHMSA-2024-0204-P-1794,

https://www.regulations.gov/docket/PHMSA-2024-0204/document.

Special Provision 408

PHMSA proposes to add a new Special Provision 408 assigned to proposed revised “UN1835 Tetramethylammonium hydroxide aqueous solution,” PG II and III, and new “UN3560, Tetramethylammonium hydroxide aqueous solution.” The special provision would limit the use of these amended HMT entries to only aqueous solutions made of water, TMAH, and no more than one percent of other constituents. The special provision would also provide instruction that for other formulations containing TMAH, the material must be described using an alternative appropriate generic or n.o.s. HMT entry, except that formulations containing (1) a surfactant in concentration less than one percent and with not less than 8.75 percent TMAH must be described using “UN2927, Toxic liquids, corrosive, organic, n.o.s., 6.1, PG I;” or (2) containing a surfactant in concentration less than one percent and with more than 2.38 percent but less than 8.75 percent TMAH must be described using “UN2927, Toxic liquids, corrosive, organic, n.o.s., 6.1, PG II.” PHMSA expects that Special Provision 408 will increase safety by providing clearer instructions for appropriate selection of HMT for solutions containing TMAH, which will ensure the hazards of the material are properly communicated, and appropriate authorized packaging and modal transport requirements are maintained.

Special Provision 409

PHMSA proposes to add a new Special Provision 409 assigned to proposed revised “UN1835 Tetramethylammonium hydroxide aqueous solution,” PG II and III; revised “UN3423, Tetramethylammonium hydroxide, solid;” and new “UN3560, Tetramethylammonium hydroxide aqueous solution.” Special Provision 409 would allow shipments of TMAH materials to continue to be transported in accordance with the HMR requirements prior to the publication of a final rule until December 31, 2026. This special provision provides a delayed compliance date that would allow time for shippers and carriers to adjust to the revisions made to the TMAH HMT entries and associated requirements.

Special Provision A54

Special Provision A54 states that, notwithstanding the quantity limits in column (9B) of the HMT, lithium batteries (including those packed with, or contained in, equipment) may exceed a mass of 35 kg (77 lbs.) on cargo aircraft if they otherwise meet the requirements of § 173.185 and the Associate Administrator provides an approval prior to shipment.

At the 29th meeting of the ICAO DGP, the DGP adopted revisions to Special Provision A99 in the 2025-2026 ICAO Technical Instructions, which has the same requirements as Special Provision A54 in the HMR. These revisions applied the special provision to the new entries for sodium ion batteries. This is consistent with other provisions being adopted that regulate sodium ion batteries in much the same manner as lithium batteries based on their similar applications and similar hazards present during transportation. To make this special provision applicable to sodium ion batteries, PHMSA proposes to amend the special provision to reference both sodium ion batteries and lithium batteries. In addition, PHMSA proposes to assign Special Provision A54 to the following new entries: “UN3551, Sodium ion batteries with organic electrolyte,” “UN3552, Sodium ion batteries contained in equipment with organic electrolyte,” and “UN3552, Sodium ion batteries packed with equipment, with organic electrolyte.” This revision will harmonize the HMR with the UN Model Regulations and the adoption of provisions for sodium ion batteries.

Special Provision A100

Special Provision A100 is assigned to “UN3480, Lithium ion batteries” and prescribes state-of-charge requirements. Currently, this special provision states that lithium ion cells and batteries transported by air must be offered for transport at a state-of-charge not exceeding 30 percent of their rated capacity. In addition, lithium ion cells and batteries at a state-of-charge greater than 30 percent of their rated capacity may only be transported under conditions as approved by the Associate Administrator. PHMSA proposes to extend applicability of this state-of-charge requirement by assigning this special provision to additional lithium ion battery entries on the HMT and to revise this special provision to clarify its applicability. In addition, PHMSA proposes to apply this provision to new HMT entries for sodium ion batteries and vehicles powered by batteries. These changes are consistent with revisions in the 2025-2026 ICAO Technical Instructions.

Specifically, PHMSA proposes to assign Special Provision A100 to the following entries:

• “UN3481, Lithium ion batteries contained in equipment

including lithium ion polymer batteries

”

• “UN3481, Lithium ion batteries packed with equipment

including lithium ion polymer batteries

”

• “UN3551, Sodium ion batteries

with organic electrolyte

”

• “UN3552, Sodium ion batteries contained in equipment

with organic electrolyte

”

• “UN3552, Sodium ion batteries packed with equipment,

with organic electrolyte

”

• “UN3556, Vehicle, lithium ion battery powered”

• “UN3557, Vehicle, lithium metal battery powered”

• “UN3558, Vehicle, sodium ion battery powered”

At the 29th meeting of the ICAO DGP, an amendment was considered that would, under certain conditions, extend the existing provi

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