CFR › Title 14 › Part 121 › §121.25314 CFR §121.253Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗Copy link(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.