What are the preferred agents for engine/APU/EPU fires?

• A. Dry chemical is always the first choice for engine fires.
• B. ARFF should always use water from a distance.
• C. Foam is not allowed on engine fires.
• D. Flight crew uses onboard bottles first; ARFF prefers clean agents, can use foam if unavailable, and dry chemical may damage engines.

Answer: (D)

Engine/APU/EPU fires call for rapid suppression with minimal risk to the engine’s delicate components, so extinguishing choices favor clean agents that absorb heat without leaving harmful residues. Flight crews are trained to deploy onboard extinguishing bottles first, which can quickly knock down a fire in the engine area before ARFF arrives or can intervene more effectively. This quick onboard action helps prevent the fire from spreading and reduces damage while search-and-rescue or evacuation steps are handled.

ARFF teams prioritize clean agents because they rapidly cool the fire without fouling moving parts, electrical systems, or fuel pathways inside the engine compartment. If a clean agent isn’t available, foam can be used to blanket and cool the area and help separate fuel from air, offering another effective option. Dry chemical, although strong for many fire types, can leave abrasive residues and may damage engine components or systems, so it is used only when other agents aren’t accessible or when there’s a direct need for rapid knockdown and no better alternative is available.