The OFSA is the sensing element of Halon 1301 fire extinguishing systems used in military ground combat and tactical vehicles (such as the M992 Field Artillery Ammunition Support Vehicle (FAASV)). The OFSA responds to optical radiation from exploding atomized or vaporized hydrocarbons and energizes the fire extinguishing system within 3 to 4 ms, depending on the OFSA type (see 3.3.3.1.4), when an energy level equal to or greater than the large fire threshold is attained. The systems are intended for use in personnel areas and other compartments such as engine spaces. These systems are designed to protect against the potential danger of detonations, deflagration, and slow growth fires due to the presence of highly combustible fuels or other liquid hydrocarbons or flammable debris.