When choosing a fire extinguishing system, one of the biggest hurdles you’ll have to overcome is the type of agent you either specify for the system or the type of system you purchase (mandated by the system configuration). Be forewarned: Some extinguishing agents are far more effective than others. Another consideration is the fuss over Halon. Let’s start at the beginning:

Halons are low-toxicity, chemically stable compounds that have been used for fire and explosion protection from the turn of the last century. Carbon tetrachloride (Halon 104) was used prior to 1900, but there was a catch: The combustion by-products were deadly. Given the number of fatalities caused by the combustion by-products, other compounds (including other Halons) were tried. In 1947, investigation by the Purdue Research Foundation along with 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. Today, Halon 1211 (defined as a "liquid streaming agent") is used primarily in hand-held fire extinguishers. Meanwhile, Halon 1301 (defined as a "gaseous agent") is used primarily in total flooding systems. These Halons have proven to be extremely effective fire suppressants, which are clean (leave no residue), colorless, odorless, and electrically non-conductive and prove to be remarkably safe for human exposure.

A Halon blend (or 1301) is far superior to the 1211 Halon propelled by nitrogen because it generates its own pressure -- performance does not degrade significantly as the extinguisher is emptied. Extensive toxicity evaluations have been compiled on Halon 1301 and 1211. These evaluations have consistently shown that Halon 1301 is the safest extinguishing agent available (although not safer than pure water), and that Halon 1211 is the second safest. Halon concentrations of about 5% by volume in air are adequate to extinguish fires of most combustible materials.

How do they work? According to the experts, three things must take place simultaneously to start a fire. The first ingredient is fuel (anything that can burn), the second is oxygen (sufficient air for human breathing is ample) and the last is an ignition source (keep in mind that high heat can cause a fire even if there is no spark or open flame). In order to stop the fire you need to remove one ingredient in the mix – the ignition source, the fuel source or the oxygen source. Halon is so effective because it adds a fourth dimension to fighting the fire: It breaks the chain reaction. It works this way by stopping the fuel source, ignition source and oxygen source from working together by way of chemical reaction. The most common extinguishing agents like water, carbon dioxide, dry chemical and foams attack the fire physically, depriving the fire of one or more of the three critical elements needed for propagation. Halon differs from all other extinguishing agents in the way it puts out the fire. It offers some of water's cooling effect and some of carbon dioxide's smothering action, but the essential extinguishing methodology lies in its capacity to chemically react with the components of the fire.

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A common fallacy about Halon is that it displaces the air from the area it’s dispensed into. That’s absolutely incorrect. According to folks in the know, for even for the toughest fire, less than an 8% concentration by volume is necessary. This means there is still plenty of air to use in the evacuation process.

Over time, the largest single user of Halon has been the electronics industry. Approximately 65% of all Halon 1301 in use is employed for the protection of electronics facilities (good examples include computer banks, communications facilities and so on). The U.S. Government uses Halon for a number of military applications (in ships, aircraft and land based vehicles such as tanks). Commercial aircraft also use Halons extensively (for example, each engine nacelle in a Boeing jet is protected by Halon). Halons are used extensively in oil production, electric power generation, and are actually required on most commercial passenger aircraft (in cargo and passenger compartments as well as in engine nacelles).

The ability of a compound to destroy ozone depends upon a number of factors, including the amount of chlorine and/or bromine contained within along with their chemical stability. In order to compare various compounds, scientists have developed a relative scale called the "Ozone Depletion Potential" (ODP). For example, common refrigerants, like those found in an older refrigerator and in the air conditioner of an older car, have been assigned the value of "1". Halon 1301 has an assigned value between 10 and 16, which means it has 10-16 (times) greater potential for destroying the ozone layer. Halons can definitely carve up the ozone layer. That’s a given, but there is also a catch:

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Halon use worldwide is significantly less than that of CFCs. Even though it is much more damaging to the ozone layer, there is simply not as much of it released into the atmosphere. It is estimated that overall, Halons account for less than 1% of the ozone depletion.