14 C.F.R. § 121.245 Fire walls.
Title 14 - Aeronautics and Space
Each engine, auxiliary power unit, fuel-burning heater, or other item of combustion equipment that is intended for operation in flight must be isolated from the rest of the airplane by means of firewalls or shrouds, or by other equivalent means.
Title 14: Aeronautics and Space
PART 121—OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL OPERATIONS
Subpart J—Special Airworthiness Requirements
§ 121.245 Fire walls.
