49 CFR 173.56 specifies the process which must be followed to obtain a DOT approval for the classification of explosives. All explosives must be examined and assigned a shipping description (proper shipping name), classification, and compatibility group by the Engineering and Sciences Division (PHH-20).
The Engineering and Sciences Division, within PHMSA's Office of Hazardous Materials Safety, processes the applications, relying on evaluation of the supporting data by scientists in the Office of Sciences (PHH-21). When an application is approved, a formal Classification of Explosives letter is issued on behalf of the Associate Administrator advising of any limitations or special requirements that must be observed, and assigning an "EX Number" signifying that the new explosive is approved for transportation in commerce.
Exceptions include those explosives produced by the U.S. Department of Defense or the U. S. Department of Energy that are self-classified by those agencies in accordance with 173.56.