49 C.F.R. § 179.202-6

The DOT Specification 117 tank car must have a thermal protection system. The thermal protection system must:

(a) Conform to § 179.18 of this part;

(b) Be equipped with a thermal protection blanket with at least 1/2-inch-thick material that meets § 179.18(c) of this part; and

(c) Include a reclosing pressure relief device in accordance with § 173.31 of this subchapter.