Label Specification Requirements
Pipeline and Hazardous Materials Safety Administration · May 8, 2018 · Reference No. 17-0141
Interprets: 49 CFR § 172.407, 49 CFR § 172.407(c)(1)
Reggie’s quick take
Someone asked PHMSA about the 2-mm minimum line width for the inner border on diamond (square-on-point) hazard labels, which came from the HM-215M rule. The letter says that rule requires each diamond label to be at least 100 mm on each side, with a solid inner border 5 mm in from the edge and at least 2 mm thick. The letter says that minimum thickness caused unintended problems. PHMSA says the UN agreed in July 2017 that a minimum line width is not needed for safety. ICAO and IMO have dropped the size rules, and PHMSA plans to propose the same change in a future rulemaking. The letter does not say when that change will take effect.
Written by AI (Claude) on Oct 22, 2026. Robots make mistakes and leave things out, so the letter below is what counts. Not legal advice.
This letter is in response to your December 21, 2017, letter requesting clarification of the Hazardous Materials
Regulations (HMR; 49 CFR Parts 171-180) applicable to label specifications. Specifically, you are concerned
about recent amendments that mandated a specific inner border line width of at least 2 mm as adopted in the
final rule titled “Hazardous Materials: Harmonization With International Standards (RRR)” and published in the
Federal Register on January 8, 2015, under Docket No. PHMSA-2013-0260 (HM-215M).
The HM-215M final rule revised § 172.407(c)(1) to require that: (1) each diamond (square-on-point) label
prescribed in the HMR must be at least 100 mm (3.9 inches) on each side with each side having a solid line
inner border 5 mm inside and parallel to the edge; (2) the 5 mm measurement is from the outside edge of the
label to the outside of the solid line forming the inner border; and (3) the width of the solid line forming the
inner border must be at least 2 mm.
The HM-215M final rule provided transition periods for the adopted amendments, prescribing in § 172.407(c)(1)
(iii) that for domestic transportation, a label in conformance with the requirements of § 172.407(c)(1), revised
as of October 1, 2014, is authorized for use until December 31, 2016. The effective date was subsequently
revised to December 31, 2018, in a final rule published in the Federal Register on March 30, 2017, under
Docket No. PHMSA-2015-0273 (HM-215N).
The amendments described above were part of a broader effort to improve consistency across label
specifications and reduce transportation impediments worldwide. However, upon implementation of the
amendments, rather than improving consistency, it became apparent that the specification of a 2-mm line width
posed unintended consequences, such as those you highlight in your correspondence. As such, PHMSA worked
collaboratively at the 51st Session of the United Nations Sub-Committee of Experts on the Transport of
Dangerous Goods in July 2017 to address this issue, where it was agreed upon that specifying a minimum
thickness for line width was not necessary for safety reasons and an amendment was adopted as proposed.
The Sub-Committee further stated that organizations responsible for modal regulations were invited to amend
their respective transportation standards accordingly. Consequently, the International Civil Aviation
Organization (ICAO) and the International Maritime Organization (IMO) have both rescinded the size
requirements adopted in the 2015 United Nations Model Regulations effective January 1, 2019 and January 1,
2020, respectively. These amendments will be considered for implementation by PHMSA as expediently as
possible in an upcoming rulemaking action.
I hope this information is helpful. Please contact us if we can be of further assistance.
A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.