14 CFR § 125.151 - Powerplant fire protection.
(a) Designated fire zones must be protected from fire by compliance with §§ 125.153 through 125.159.
(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.