HALON

chemical compound used in fire fighting. A halon may be any of a group of halogenated aliphatic hydrocarbons, most of which are derived from methane or ethane by replacing some or all of the hydrogen atoms by atoms of the halogen series (fluorine, bromine, chlorine, or iodine). The effectiveness of halons in extinguishing fires arises from their action in interrupting chain reactions that propagate the combustion process. Halons are nonconductors of electricity and can be used in fighting fires in flammable liquids and most solid combustible materials, including those in electrical equipment; they are ineffective on fuels containing their own oxidizing agent or highly reactive metals, such as sodium or potassium. Halon 1301 (bromotrifluoromethane) is especially favoured for extinguishing fires involving electronic equipment because it leaves no residue and does not cause electrical short circuits or damaging corrosion of the equipment. Because halon is a compound considered destructive of the Earth's ozone shield, environmentalists have urged restriction of its use.