Day & Zimmermann — Hazardous Materials Safety Interpretation

Page 1U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration 1200 New Jersey Avenue, SE Washington, DC 20590 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#

Page 2be 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#

Page 3Cajar, J. 25-0089 From: INFOCNTR (PHMSA) To: Baker, Yul (PHMSA) Cc: Hazmat Interps Subject: FW: Request for Letter of Interpretation - 49 CFR §172.320(b)(1) Date: Friday, June 27, 2025 10:50:09 Attachments: DOT Letter of Interpretation .pdf Hi Yul, Please see the below interpretation request. Let us know if you need anything. Sincerely, Janaye From: Behrens, Matthew <Matthew.Behrens@soc-usa.com> Sent: Thursday, June 26, 2025 3:46 PM To: PHMSA HM InfoCenter <PHMSAHMInfoCenter@dot.gov> Subject: Request for Letter of Interpretation - 49 CFR §172.320(b)(1) You don't often get email from matthew.behrens@soc-usa.com. Learn why this is important CAUTION: This email originated from outside of the Department of Transportation (DOT). Do not click on links or open attachments unless you recognize the sender and know the content is safe. (PDF Attached of email) Dear PHSMA representative, Day & Zimmermann, Inc. respectfully requests a formal letter of interpretation regarding compliance with 49 CFR §172.320(b)(1). Specifically, we seek clarification on marking packaging "in lieu of an EX number, a national stock number issued by the Department of Defense 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”. In reviewing §172.320(b)(1), our understanding is that under certain conditions, it may be permissible to mark packages in a manner other than using an EX number issued by PHMSA. We seek clarification from PHMSA on the following points: Under what specific circumstances or conditions does PHMSA authorize the use of alternate markings "in lieu of an EX number"? Can and approved ATF coding system through a “marking variance” or an NSN be used for scenarios described below?#

Page 4The subsidiaries of Day & Zimmermann, Inc. (DZI)—namely American Ordnance, Day & Zimmermann Lone Star, and Day & Zimmermann Kansas—specialize in the production of explosive materials for both the Department of Defense and the commercial sector. Every facility holds a Federal Explosives License, granting them the legal authority to partake in numerous activities related to explosives, including importing, manufacturing, and trading in explosive materials. They must also maintain consistent adherence to their EX number, which is a prerequisite for handling explosives categorized under Hazard Class 1. Regulation 49 CFR §172.320(b)(1) outlines the marking requirements for the transportation of explosive hazardous materials, placing particular emphasis on alternatives to the use of an EX (explosive approval) number. Regulation Text: "(b) Except for fireworks, in lieu of the EX number, packaging containing explosive substances and articles may be marked with: 1. A national stock number issued by the Department of Defense; 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." Interpretation: National Stock Number (NSN): A number assigned by the U.S. Department of Defense (DoD) for explosives designated for military or defense-related purposes. Identifying Information (Product Code): Information, such as a product code defined in 27 CFR part 555, which pertains to commercial explosives regulated by the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). DZI key condition: To use these alternatives, DZI subsidiaries must ensure that this alternative number or code can be clearly associated or traced back to the originally assigned EX number. This means the NSN or product code is not random—it must correspond explicitly and verifiably to a valid EX approval number that PHMSA previously issued. Would this scenario apply to 49 CFR §172.320(b)(1)?#

Page 5On certain occasions when manufacturing explosives for the DoD, there are explosives that some contracts may allow the contractor to retain excess or rejected explosive materials for their own use, for sale in commerce. The excess explosive materials were manufactured under a DoD contract and a Government- Specific EX number was issued. A company cannot use a U.S. Government (USG) EX number to ship commercial explosives for non-government purposes. USG EX numbers are specific to U.S. government-owned, government-developed, or government-contracted explosives. PHMSA rules prohibit government EX numbers for private commercial distribution The only scenario where a USG EX number might be used in commercial transport is if a company is acting as a contractor shipping explosives exclusively for the government under a government contract, and the shipment is part of that government program. Alternative Situations: Specifically, to excess explosives manufactured under the DoD, a company would apply 49 CFR §172.320(b)(1) and instead of an EX number to ship the explosives in commercial commerce, the company would use an NSN that clearly linked to an existing EX number would be used. This alternative would not apply to commercially manufactured explosives that were not under a USG contract and would require an EX number because there is no NSN clearly linked to a non-USG explosive. Or A commercial explosives manufacturer that adheres to ATF product codes (per 27 CFR Part 555) can mark containers with the product code instead of the EX number, provided the product code directly corresponds with an assigned EX number. All commercial explosives must be marked in accordance with 555.109(c)(5) Identification of explosive materials (USG is exempt): A coding system and omit printed markings on the container that show all the required information. The Director must approve the application before the proposed coding can be used. This coding system is allowed to Federal Explosive Licensees by means of a “marking variance”.#

Page 6All DZI subsidiaries have approved marking variance that allow a coding system using the MIL-STD-1168C - Lot Numbering. ATF approved Lot Number coding: AO25D018-013B A. Manufacturers identification symbol B. C. Two-digit numeric code for the year of production A single alpha code signifying the month of production D. Lot interfix number E. Lot sequence number F. Lot suffix number The lot number is a unique code number assigned to a quantity or batch of a single ammunition end item (complete round, major component, propellants, etc.) which are manufactured or assembled by one producer under uniform conditions, and which is expected to function in a uniform manner. Ensures that inspectors or authorities can trace the shipment back to the manufacturer and gives all information to what the explosive is. The lot number is a unique code number assigned to a quantity or batch of a single ammunition end item (complete round, major component, propellants, etc.) which are manufactured or assembled by one producer under uniform conditions, and which is expected to function in a uniform manner. Ensures that inspectors or authorities can trace the shipment back to the manufacturer and gives all information to what the explosive is. Our intent is to ensure full compliance with federal hazardous materials regulations, and we seek authoritative guidance to support our operations. Thank you very much for your attention and guidance on this matter. We look forward to your response and clarification Respectfully, Matthew Behrens Director, ATF and Export/Import Compliance Day & Zimmermann M 3864065087 3975 Virginia Mallory Drive, Suite 200 | Chantilly, VA 20151#

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