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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #21-0082

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

Interpretation Response Details

Response Publish Date:

Company Name: Onepoint4 Ltd.

Individual Name: Peter Shelley

Location City: Morpeth, Northumberland Country: GB

View the Interpretation Document

Response text:

December 9, 2021

Mr. Peter Shelley
Managing Director
Onepoint4 Ltd.
75 Chevington Green,
Morpeth, Northumberland
NE65 9AX United Kingdom

Reference No. 21-0082

Dear Mr. Shelley:

This letter is in response to your July 29, 2021, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to Class 1 (explosive) and Division 4.1 (flammable solid) materials and articles using hazardous materials. Specifically, you ask for confirmation that highly energetic substances and associated articles—which are normally classified and approved as Class 1 (explosive) materials—cannot be classified as Division 4.1 (flammable solid) materials without proper testing and subsequent approval by PHMSA.

We have paraphrased and answered your questions as follows:

Q1. You ask—specific to thermites and thermates and referencing your previous letters of interpretation requests (Ref. Nos. 18-0141 and 20-0015)—whether a company can self-certify a material as Class 4 or otherwise as non-hazardous and subsequently alter the material or make it a component of an article without needing an approval.

A1. As provided in § 173.22, it is the shipper's responsibility to properly classify and describe a hazardous material. If a material is not specifically listed by name in the hazardous materials table in § 172.101, then selection of a proper shipping name must be made from the general description entries corresponding to the specific hazard class, packing group, and subsidiary hazards of the material. When a material meets the definition and criteria of a hazard class, the shipper must assign an appropriate proper shipping name and UN identification number. While many hazardous material classification determinations are left solely to the shippers based on classification criteria in the HMR, specific provisions for certain hazard classes—such as Class 1 (explosive) materials and certain Class 4 materials—require a government approval.

For example, where the assignment of Division 4.1 (flammable solid) material versus Class 1 (explosive) material is concerned, offerors cannot self-classify the material as a flammable solid if the material also meets the definition of an explosive—as provided in § 173.50—which instead would require approval in accordance with § 173.56. The issuance of an approval indicates that a material—based on data from approved test labs—has been verified as an explosive or not and meets the criteria for inclusion or exclusion from Class 1.

With regard to necessitating a new approval if the material is altered or made a component of an article—as discussed in answer A3 below—any change to an explosive in the formulation, design, or process so as to alter any of the properties of the explosive, and any change to a material that is not an explosive but by the manner in which it was changed may render it now an explosive, would require new examination and a new approval. However, any PHMSA-approved explosives test lab, as described in § 173.56(b) may determine and confirm in writing to our Office that there are no significant differences in hazard characteristics from the material previously approved.

Q2. You ask whether thermites or thermates must be tested for an approval, even if they are not designed to function by explosion.

A2. The answer is yes. Because of their energetic properties, thermites and thermates are provisionally considered explosives until PHMSA issues an approval letter specifically excluding the material from Class 1 based on testing conducted by a DOT-approved test laboratory, in accordance with § 173.56.

Q3. You refer to a report which indicates that energetic properties of certain materials may be manipulated by pressing and shaping of powdered energetic material to control the burning surface area and burn rate (e.g., pressing and shaping into pellets/donuts by pressure, temperature, compression, sintering, etc.). You ask whether these materials—after being tested in one physical form—should be resubmitted for testing and PHMSA approval if they are then intended to be transported in another form or intended to be transported as a component of an article.

A3. The answer is yes. Under § 173.56(a)(2), any change to an explosive in the formulation, design, or process, so as to alter any of the properties of the explosive would require examination and meet the definition of a "new" explosive unless a PHMSA-approved explosives test lab, as described in § 173.56(b), has determined—and confirmed in writing to our Office—that there are no significant differences in hazard characteristics from the explosive previously approved.

Q4. You ask—noting that binder(s) may add additional energetic properties to a hazardous material such as a thermite or thermate—whether an energetic material without binder(s) and where binder(s) are subsequently added to the material requires re-testing and re-approval for classification purposes.

A4. The answer is yes. See answer A3.

Q5. You ask whether PHMSA will consider the use of binders and additives—such as polymers (e.g., Teflon®) and their role in combustion and sensitivity—in future testing of such thermite- or thermate-based substances/products.

A5. As discussed in answer A3, every separate formulation containing thermite or thermate would need to be considered on its own merit. Any previously classed thermite or thermate material would be considered a new explosive if a change has been made in the formulation, particle size, design, or process, so as to alter any of the properties of the explosive, including the use of binders.

Q6. You ask whether thermite and thermate compositions—with and without additional binders and additives that contribute to the overall energetic properties of the thermite and thermate compositions—can be transported on civil and commercial aircraft as substances or also contained in articles, without an approval.

A6. The answer is no. As discussed in answer A2, thermites and thermates are provisionally considered explosives. The conditions for transport by aircraft would be outlined in the final classification approval issued by PHMSA.

Q7. You ask how distinctions in classifications are made between a Division 4.1 (flammable solid) material (e.g., "UN3178, Flammable solids, n.o.s.") and a Division 1.4G pyrotechnic material (e.g., "UN0431, Articles, pyrotechnic") when transported in packagings and when contained in articles.

A7. Thermites and thermates, including articles containing either thermites or thermates, are provisionally considered explosives (see answer A2). The classification for these hazardous materials is based on tests and the resulting classification recommendation provided by a DOT-approved explosives test laboratory, which will result in a designated classification by PHMSA under § 173.56.

Q8. Further, you ask about Division 4.1 (flammable solid) materials that have been transported prior to the implementation of PHMSA's current approval process involving approved explosives test labs. You ask—regarding future shipments—if such energetic materials will be transported as part of an article, whether they will require re-testing by an approved explosives test lab regardless of whether the hazardous material was previously deemed to be a Class 1 (explosive) material or a Division 4.1 (flammable solid) material.

A8. The answer is yes. See answers A2 and A7.

Q9. You ask whether a thermite or thermate material that has been classified as a Division 4.1 (flammable solid) material and then is packed into a steel tube and intended to be transported would be considered an article requiring testing by an approved explosives test lab because thermite and thermate both have a practical pyrotechnic effect.

A9. Thermite or thermate packed in this manner may be considered an article, depending on the function of the steel tube. If the tube lends itself to the function of the product, then it may be classified as an article. If the thermite or thermate was excluded from a Class 1 determination and is subsequently transported as an article it would require re-approval as an explosive. However, if the tube is part of the packaging for purposes of handling and transport of the material and not a component part of an article, it may be considered packaging and does not have to be re-examined.

Q10. You ask whether a thermite or thermate material packaged in an oilwell cartridge would now fall under Class 1 (explosive) material or be required to undergo testing by an approved explosives testing lab.

A10. Oil well cartridges are defined explosives in § 173.59. Any article meeting this definition requires examination as an explosive under § 173.56.

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


Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division

172.101, 173.22, 173.50, 173.56, 173.56(a)(2), 173.56(b), 173.59

Regulation Sections

Section Subject
172.101 Purpose and use of hazardous materials table
173.22 Shipper's responsibility
173.50 Class 1-Definitions
173.56 New explosives-definition and procedures for classification and approval
173.59 Description of terms for explosives