In automotive engineering, the firewall (American English) or bulkhead (British English) is the part of the automobile body ( unibody or

body-on-frame Body-on-frame is a traditional motor vehicle construction method whereby a separate coachwork, body or coach is mounted on a strong and relatively rigid vehicle frame or chassis that carries the powertrain (the engine and drivetrain) and to wh ...

) that separates the

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...

compartment from the passenger compartment (driver and passengers). It is most commonly a separate component of the body or, in

monocoque Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French term for "single shell". First used for boats, ...

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

car A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billio ...

s for compartmentalisation. For example, a typical conversion of a production car for

rallying Rallying is a wide-ranging form of motorsport with various competitive motoring elements such as speed tests (sometimes called "rally racing" in United States), navigation tests, or the ability to reach waypoints or a destination at a prescribed ...

will include a metal firewall which seals the

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

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 Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Thicknesses can vary significantly; extremely thin sheets are considered foil (metal), foil or Metal leaf, leaf, and pieces thicker than 6 mm (0.25 ...

to the bodywork using

fibreglass Fiberglass (American English) or fibreglass ( Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass c ...

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

. In

aerospace engineering Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is s ...

, an

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

firewall isolates an engine from the other parts of the airframe. In single-engine aircraft, it is the part of the

fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

that separates the engine compartment from the cockpit. In most multi-engine propeller aircraft, the firewall typically divides the

nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

from the wing of the aircraft, or divides the nacelle into two zones. The word "firewall" is also used as a slang term for taking an engine to maximum power or acceleration.

See also