14 CFR §121.247

1. (a)Be so made that no hazardous quantity of air, fluids, or flame can pass from the engine compartment to other parts of the airplane;
2. (b)Have all openings in the fire wall or shroud sealed with close-fitting fire-proof grommets, bushings, or firewall fittings;
3. (c)Be made of fireproof material; and
4. (d)Be protected against corrosion.