14 CFR § 25.863

In each area where flammable fluids or vapors might escape by leakage of a fluid system, there must be means to minimize the probability of ignition of the fluids and vapors, and the resultant hazards if ignition does occur.

Compliance with paragraph (a) of this section must be shown by analysis or tests, and the following factors must be considered:

Possible sources and paths of fluid leakage, and means of detecting leakage.

Flammability characteristics of fluids, including effects of any combustible or absorbing materials.

Possible ignition sources, including electrical faults, overheating of equipment, and malfunctioning of protective devices.

Means available for controlling or extinguishing a fire, such as stopping flow of fluids, shutting down equipment, fireproof containment, or use of extinguishing agents.

Ability of airplane components that are critical to safety of flight to withstand fire and heat.

If action by the flight crew is required to prevent or counteract a fluid fire (e.g., equipment shutdown or actuation of a fire extinguisher) quick acting means must be provided to alert the crew.

Each area where flammable fluids or vapors might escape by leakage of a fluid system must be identified and defined.