Fixed Firefighting Systems HALON AGENT ~ Marine Notes

Fixed Firefighting Systems HALON AGENT

Fixed Firefighting Systems
HALON AGENT

GENERAL INFORMATION
The word Halons is short for "halogenated hydrocarbons", in other words,
hydrocarbons containing one or more of the halogens--fluorine, chlorine, or
bromine.
Halons have certain advantages over carbon oxide. Less Halon than carbon
dioxide, for example, would be needed to extinguish a fire of the same size. This is
an important consideration on ships with their weight and space limitations. In
addition, there is some evidence that Halons can extinguish engine room fires more
quickly than carbon dioxide can. The Halons used in firefighting systems are
thought to be effective in breaking the chain reaction which is the mechanism that
keeps fires going. Since the Halon extinguishes the fire by putting an end to this
reaction rather than by filling the room and displacing the oxygen, as carbon
dioxide does, lower concentrations can be used. Whereas carbon dioxide would
require a concentration of 28.5% to be effective, Halon 1301, which is typically
used onboard ships, will extinguish a fire at a concentration level of 6%. This could
be vitally important in the case of accidental release. Since the halon-air mixture
would contain 94% air and only 6% Halon, personnel trapped in an enclosed space
with it, would not be asphyxiated.
Halon is not manufactured anymore. It is regulated by the EPA as a greenhouse
depleting gas. Existing stockpiles may be purchased but no manufacturing is to
take place. If the system is discharged it will most likely be fitted with a new type of
extinguishing agent. Halon 1301 ( the Halon most commonly used for fire
extinguishing purposes) decomposes to form two toxic gases, hydrogen fluoride
and hydrogen bromide, when it is exposed to heat. The American Conference of
Governmental Industrial Hygienists has set recommended maximum exposure
levels for these two gases. If personnel must be exposed to them, the concentration
to which they are exposed should not exceed 3 parts per million (ppm), averaged
over the eight hour workday.
No data were available on how much hydrogen fluoride and hydrogen bromide
were generated when Halon was released or how effective Halon 1301 was in
extinguishing machinery space fires, when the Coast Guard began drafting safety
regulations for Halon. To acquire the necessary data, the Coast Guard, with
support from the marine firefighting industry, ran a series of tests in 1970 in the
engine room of a full-scale ship at the U.S. Coast Guard Fire and Safety Test
Detachment in Mobile, Alabama. The concentration of hydrogen fluoride measured
following release of Halon 1301 varied from 0.1 to 230 ppm and the concentration
of hydrogen bromide from 0.6 to 68 ppm. and More.

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