Halon

Halons are a group of compounds obtained by replacing the hydrogen atoms of a hydrocarbon with other halogen atoms, such as bromine or fluorine. Halon 1211 is bromochlorodifluoromethane (CF₂BrCl) and halon 1301 is bromotrifluoromethane (CF₃Br). Halons are very stable and are widely used in fire extinguishers[?] where water or dry chemicals would cause other serious damage. At high temperatures, halons decompose to release halogen atoms that combine readily with active hydrogen atoms, depriving the fire of fuel.

There is concern that they are being broken down in the atmosphere to bromine, which reacts with ozone, leading to depletion of the ozone layer, along with other chlorofluorocarbons such as freon.