FAA Federal Aviation Regulations (FARS, 14 CFR)

Components, lines, and fittings, except those subject to the provisions of §23.1351(e), located behind the engine-compartment firewall must be constructed of such materials and located at such distances from the firewall that they will not suffer damage sufficient to endanger the airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not less than 2000 °F for 15 minutes.

[Amdt. 23-14, 38 FR 31816, Nov. 19, 1973]