Source: Amdt. 173-224, 55 FR 52617, Dec. 21, 1990, unless otherwise noted.
[[Page 445]]Sec. 173.50 Class 1--Definitions.
(a) Explosive. For the purposes of this subchapter, an explosive means any substance or article, including a device, which is designed to function by explosion (i.e., an extremely rapid release of gas and heat) or which, by chemical reaction within itself, is able to function in a similar manner even if not designed to function by explosion, unless the substance or article is otherwise classed under the provisions of this subchapter.
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Given the term "extremely" this cannot apply to mere slow burning propellant especially those that burn under 10mm/s.
Jerry