14 CFR § 121.253
Powerplant fire protection
July 13, 2020
(a) Designated fire zones must be protected from fire by compliance with §§121.255 through 121.261.
(b) Designated fire zones are—
(1) Engine accessory sections;
(2) Installations where no isolation is provided between the engine and accessory compartment; and
(3) Areas that contain auxiliary power units, fuel-burning heaters, and other combustion equipment.