14 CFR § 23.2325

The following materials must be self-extinguishing—

Insulation on electrical wire and electrical cable;

For levels 1, 2, and 3 airplanes, materials in the baggage and cargo compartments inaccessible in flight; and

For level 4 airplanes, materials in the cockpit, cabin, baggage, and cargo compartments.

The following materials must be flame resistant—

For levels 1, 2 and 3 airplanes, materials in each compartment accessible in flight; and

Any equipment associated with any electrical cable installation and that would overheat in the event of circuit overload or fault.

Thermal/acoustic materials in the fuselage, if installed, must not be a flame propagation hazard.

Sources of heat within each baggage and cargo compartment that are capable of igniting adjacent objects must be shielded and insulated to prevent such ignition.

For level 4 airplanes, each baggage and cargo compartment must—

Be located where a fire would be visible to the pilots, or equipped with a fire detection system and warning system; and

Be accessible for the manual extinguishing of a fire, have a built-in fire extinguishing system, or be constructed and sealed to contain any fire within the compartment.

There must be a means to extinguish any fire in the cabin such that—

The pilot, while seated, can easily access the fire extinguishing means; and

For levels 3 and 4 airplanes, passengers have a fire extinguishing means available within the passenger compartment.

Each area where flammable fluids or vapors might escape by leakage of a fluid system must—

Be defined; and

Have a means to minimize the probability of fluid and vapor ignition, and the resultant hazard, if ignition occurs.

Combustion heater installations must be protected from uncontained fire.