Text in force at 23-63: from 23-14, effective 20 Dec 1973.
[Components, lines, and fittings, except those subject to the provisions of Sec. 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.]
38 FR 31816 · Source