They are low-toxicity, chemically stable compounds that have
been used for fire and explosion suppression throughout this
century. Today, Halon 1211 (a liquid streaming agent ) is used
mainly in total flooding systems. These halons have proven to be
extremely effective fire suppressants, which are clean (leave no
residue) and remarkably safe for human exposure.
There things must come together at the same time to start a
fine. The first ingredient is fuel (anything that can burn), the
second is oxygen (normal breathing air is ample) and the last is
an ignition source (high heat can cause a fire even without a
spark or open flame ).
Traditionally, to stop a
fire you need top remove one side of the triangle - the
ignition, the fuel or the oxygen. Halon adds a fourth
dimension to fire fighting - breaking the chain reaction. It
stops the fuel, the ignition and the oxygen from dancing
together by chemically reacting with them. Many people
believe that halon displaces the air out of the area it is
dispensed in. Wrong! Even for the toughest hazards, less
than an 8% concentration by volume is required. There is
still plenty of air to use in the evacuation process.
How Damaging Is
Halon?
A compound's ability to
destroy ozone depends on many factors, including the
amount of chlorine and /or bromine that it contains.
To aid them in comparing compounds, scientists have
developed a relative scale called the ozone
depletion potential (ODP). Common refrigerants, like
those found in your refrigerator and in your car air
conditioner, have been assigned the value 1 as a
reference. Halon 1301 has the value between 10 and
16, meaning it has 10-16 times more potential for
destroying the ozone layer. Halon use worldwide is
significantly less than that of the CFCs, so even
though it is more damaging to the ozone layer, there
is not as much of it released into the atmosphere.
In fact, it is estimated that overall hallons
account for less that 20% of ozone depletion.
Historical, the largest single user of halons has
been the electronics industry. The protection of
vital electronics facilities, such as computer rooms
and communications rooms, is estimated to account
for 65% of Halon 1301 use. The U.S. Government used
halon for military application (in ships, aircraft
and tanks), for protecting fragile historical
documents such as the Bill of Rights, and even
protection of the President's limousine.
Halons are also used extensively in oil production,
electric power generation, and are required on all
commercial passenger aircraft Halon are also used
extensively in oil production, electric power
generation, and are required on all commercial
passenger aircraft.
Manufacturers who make everything from dolls to cars
use halon to protect their personnel and products.
How long Has
Halon Been Used For Fire Protection ?
Carbon
tetrachloride (Halon 104) was used prior to 1900,
even though its combustion by-products were lethal.
Due to a number of deaths, a search for something
safer began.
Several other halons were tried, but it was not
until 1947 that research by the Purdue Research
Foundation and the U.S. Army resulted in the
discovery of two effective low toxicity halons: 1211
and 1301. When used properly, these halons have an
excellent fire fighting record with little, if any,
risk.
What Alternatives Are
there?
There are a number of traditional fire extinguishing
agents, such as water, carbon dioxide, dry
chemicals, and foa that are good alternative to
halons for many applications. In addition, recent
research has led to the commercialization of new
agents and technologies. These fall into four basic
categories: halocarbon compounds, inert gas
mixtures; water-mist or fogging systems; and
powdered aerosol. The growing list of alternatives
to halon, in conjunctiopn with advanced detection
and fire resistant materials, provides protection
from a broad spectrum of potential hazards. For more
information on halon replacement agents, see the
March 1996 report (revision 12) of the EPA Questions
and Answer on Halons and their Substitutes, or
contact GIELLE. gli Halons in atmosfera.