Interpretation Response #25-0089

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date: 03/27/2026

Company Name: Day & Zimmermann

Individual Name: Matthew Behrens

Location State: VA Country: US

View the Interpretation Document

Response text:

March 27, 2026

Mr. Matthew Behrens
Director, ATF and Export/Import Compliance
Day & Zimmermann
3975 Virginia Mallory Drive, Suite 200
Chantilly, VA  20151

Reference No. 25-0089

Dear Mr. Behrens:

This is in response to your June 26, 2025 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to marking packages containing explosives. Specifically, you seek clarification on § 172.320(b)(1) which states that in lieu of an EX-number a package of a Class 1 materials may be marked with a national stock number (NSN) issued by the Department of Defense (DoD) or identifying information, such as a product code required by regulations for commercial explosives specified in 27 CFR part 555, if the national stock number or identifying information can be specifically associated with the EX-number assigned.

We have paraphrased and answered your questions as follows:

Q1. With respect to § 172.320(b)(1), under what specific circumstances or conditions does PHMSA authorize the use of alternate markings in lieu of an EX number?

A1. Section 172.320(b)(1) authorizes the use of alternative markings in lieu of an EX number when the package is marked with a NSN issued by the DoD or identifying information, such as a product code required by regulations for commercial explosives specified in 27 CFR part 555.

Q2. Can an Alcohol Tobacco and Firearms (ATF) approved coding system, such as a lot numbering system authorized through a marked variance or an NSN be used as the required identification information associated with the EX number?

A2. Yes. An approved ATF coding system through an NSN is permissible provided it is specifically associated with the EX number.

I hope this information is helpful. Please contact us if we can be of further assistance.  

Sincerely,

Alexander Wolcott
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

172.320(b)(1)

Regulation Sections