Firewall (engine)

In automotive engineering, the firewall (American English) or bulkhead (British English) is the part of the automobile body (unibody or body-on-frame) that separates the engine compartment from the passenger compartment (driver and passengers). It is most commonly a separate component of the body or, in monocoque construction, a separate steel pressing, but may be continuous with the floorpan, or its edges may form part of the door pillars. The inner and outer surfaces of the firewall are often coated with noise, vibration, and harshness (NVH) absorber to prevent most engine noise from reaching the passenger compartment. The name originates from steam-powered vehicles, where the firewall separated the driver from the fire heating the boiler.

In competition, firewalls are found in specially prepared cars for compartmentalisation. For example, a typical conversion of a production car for rallying will include a metal firewall which seals the fuel tank off from the interior of the vehicle. In the event of an accident, resulting in fuel spillage, the firewall can prevent burning fuel from entering the passenger compartment, where it could cause serious injury or death. In regular stock cars, the firewall separates the engine compartment from the cabin and can, at times, contain fibreglass insulation. Automotive firewalls have to be fitted so that they form a complete seal. Usually this is done by bonding the sheet metal to the bodywork using fibreglass resin.

In aerospace engineering, an aircraft firewall isolates an engine from the other parts of the airframe. In single-engine aircraft, it is the part of the fuselage that separates the engine compartment from the cockpit. In most multi-engine propeller aircraft, the firewall typically divides the nacelle from the wing of the aircraft, or divides the nacelle into two zones.