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The world of fire safety is everchanging. The rapidly changing pace of technology over the last 50 years has created great advances in fire protection. Along with their advantages, these new technologies may create drawbacks-some which may go undetected for years.
Such is the case with halon. Research conducted in the 1970s discovered a drop in stratospheric ozone over the South Pole. Researchers determined it had been caused by freon and other chlorofluorocarbons (CFCs) released into the air from aerosol cans, refrigerators and air-conditioning systems. In addition, it was discovered that halon, used in a wide range of fire-suppression systems, was responsible for damaging ozone.
Environmental regulations that followed have led to a ban on the manufacture and further distribution of halon. Consequently, researchers have been searching for a replacement that is environmentally friendly and does not deplete ozone. So far, researchers have found that no one single agent is the best replacement for halon in all applications.
When considering these alternatives, fire safety professionals must thoroughly assess the materials and environments to be protected. They must also evaluate the agents and their potential effectiveness in each application.
HISTORY OF HALON
Halon came about as a result of a 1940s U.S. Army project to find a replacement for carbon tetrachloride CCl4 (CarbonTet). Considered a clean fire extinguishing agent, Carbon-Tet was an excellent fire extinguisher; however, the byproducts produced by thermal decomposition were found to be toxic.
Several agents were tested, and two products selected as the best new extinguishing agents. The term "halon" includes all fully halogenated hydrocarbons-that is, a carbon atom bonded with a combination of hydrogen and/or a member of the halogen group. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). Of these, the first three are important to fire science. Halon 1301 and Halon 1211 are trademark names licensed by DuPont. The "1211" and "1301" designations are derived from the presence or absence of each halogen. Halon 1211's chemical name is BrF2ClC; Halon 1301 is BrF3C. The bromine and chlorine make these compounds excellent fire extinguishing agents as well as powerful ozone destroyers.
Halon 1301 is a total flooding agent designed for enclosed areas, while Halon 1211 is a steaming agent intended for use in hand-held...