Halons
Halons are used primarily as a fire extinguishing agents, both in built-in systems and in
portable fire extinguishers. There have been some reported uses as tracers for studies of
circulation both in the atmosphere and in buildings. All halons contain bromine which is
40-100 times more effective at destroying ozone than chlorine. Synergistic interactions
between bromine, derived mainly from the halons and methyl bromide, and and chlorine in
the stratosphere are responsible for 30-40% of the
Antarctic ozone hole.
The Montreal
Protocol on Substances That Deplete the Ozone Layer and its subsequent
amendments
called for the elimination of production on January 1, 1994. The most commonly used halons
are halon-1211 (CBrClF2), halon-1301 (CBrF3), and halon-2402 (C2Br2F4).
The numbering system for the halons is different but more simple than for that of the
CFCs. The first
digit from the left is for the total number of carbon atoms, second is for the number of
flourine atoms, third is for the number of chlorine atoms, and last is the number of
bromine atoms. Halon-1211 is used primarily in portable fire extinguishing systems in the
Western Hemisphere and Western Europe. Halon-1301 is used in flooding systems for fire and
explosive containment. Halon-2402 is used as a fire extinguishing agent in Japan, Russia,
China, and the former states of the Soviet Union. At the present, there are no known
drop-in replacements for the halons, although many groups are working on potential
replacements. Our division,
HATS, measures the halons in the
atmosphere by electron
capture-gas chromatography (EC-GC) and gas chromatography-mass
spectroscopy (GC-MS). Sub-samples of 100-250 cc are taken from the flasks of air
collected routinely at 10 remote sites around the world
and analyzed in Boulder, CO. Recently, a new technique was developed for EC-GC as part of
our ACATS project to
measure atmospheric halon-1211 without cryo-trapping. This technique has been added to our
new Stealth GCs which
will be installed under our in
situ program.
For more information on HATS's atmospheric
measurement program for the halons, please E-mail your questions or comments to Dr. James H. Butler.
Related Web Links:
- U.S. Navy Clearinghouse for the CFCs and Halons
- U.S. Navy Efforts to Reduce Emissions of the CFCs and Halons
- U.S. Environmental Protection Agency--Halon Q&A Home Page