What Are Halons And How Do They Work ?
They are low-toxicity, chemically stable compounds that have been used for fire and explosion protection throughout this century. Today, Halon 1211 (a liquid streaming agent) is used mainly in hand-held fire extinguishers and Halon 1301 (a gaseous 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.
Three things must come together at the same time to start a fire. 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 to 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.
Who Uses Halons?
Historically, the largest single user of halon 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 The U.S. Government uses halon for military applications (in ships, aircraft and tanks), for protecting fragile historical documents such as the Bill of Rights, and even protection of the President's limousine.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. 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.
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 the more potential for destroying the ozone layer.
Halon use worldwide is significantly less than that of 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 halons account for less than 20% of ozone depletion.
