Although virtually all home fires are rapid molecular chain reactions requiring oxygen, there are certain differences too, based on exactly what material is being burned. Still, research has shown that there are only three basic in-home fire classifications, and particular fire-fighting strategies work best against each of these three fire types.
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The three fire classifications are known as Type A, Type B, and Type C.
Type A fires involve the burning of common combustible materials such as wood, paper, fabric, many plastics, and rubber. They are typically extinguished by the heat-absorbing effect of water (or water-based liquids) or by smothering the fire with a dry chemical.
Type B fires are burning flammable fluids including gasoline, oil, kitchen grease, tar, oil-based paints, and also natural gas. These fires are usually extinguished with dry chemicals, carbon dioxide, foam, or a liquefied gas (also known as halon).
Type C fires involve burning electrical equipment such as wiring, electronic devices, and electric appliances. Type C fires must be extinguished with something that won’t conduct electricity (in order to avoid an electrocution hazard) such as a dry chemical, carbon dioxide, or halon. (There is also a Type D fire, that involves burning metals, but this is unlikely in a home.)
Often, fire-prevention specialists advise that your kitchen fire extinguisher be a BC type, while the others in your home be multipurpose ABC units.
Fire extinguishers capable of handling the A and B classifications are also rated for the size of fire they can adequately handle. In other words, a extinguisher designated 2A has double the fire-extinguishing capacity of a 1A model. When a fire extinguisher is labeled for Type C fires, it simply means the extinguishing agent won’t conduct electricity. There are no numerical prefixes used to rate Type C extinguishers. Often, fire-prevention specialists advise that your kitchen fire extinguisher be a BC type, while the others in your home be multipurpose ABC units. Of course, buying an extinguisher with a higher AB numerical prefix (such as 2A40BC) has more fire-fighting capacity than one with a lower numerical prefix (such as 1A10BC).
Fire Extinguisher Types
The first truly modern portable extinguishers were soda-acid extinguishers. These were designed with a sodium-bicarbonate-and-water solution in a container mounted under another container containing sulfuric acid. When the extinguisher was turned upside down, the contents of the two containers mix and formed carbon-dioxide gas. This pressurized gas then forced a liquid out through the hose to extinguish the fire.
Today, soda-acid extinguishers are still found in some older buildings. However, for the most part, they’ve been gradually replaced by other types of extinguishers. The following sections will discuss the kinds that are now commonly available for home use.
Water is still the most commonly used extinguishing agent—but only for Type A fires. It cools the burning material and smothers the fire by depriving it of oxygen. Simple ways to use water in the home are with a bucket or a garden hose.
Ammonium Phosphate (Dry Chemical)
Ammonium-phosphate dry-chemical fire extinguishers are generally called multipurpose extinguishers. They have ABC ratings, and therefore will work against all home fire classifications. (Numerical prefixes, if present, depend on the particular model.)
With these extinguishers, monammonium phosphate is the extinguishing agent. When it’s dispersed, it’s a fine powder. Therefore, you should keep the dispersal spray away from your face to avoid inhaling these dusty chemicals. Because this fine chemical powder can be broadly distributed, cleanup can sometimes be tedious after spraying it. A dry-chemical ammonium phosphate extinguisher will put out an electrical fire but it will most likely ruin any electronic equipment with which it comes in contact.
Sodium bicarbonate fire extinguishers simply use baking-soda powder as their extinguishing agent. These units are rated BC for grease, oil, and electrical fires. (Numerical prefixes, if present, depend on the model.) Sodium bicarbonate extinguishers create no odor, and clean up problems are minimal. As stated earlier, baking soda doesn’t work against Type A fires, that is wood, paper, fabric, or plastic fires.
Carbon dioxide fire extinguishers are also rated for Type B and Type C fires. When carbon-dioxide units are activated, they release extremely cold, snow-like carbon dioxide particles. These smother the fire and then immediately vaporize. Carbon dioxide extinguishers pose no odor or cleanup problems. However, because they are not recommended for Type A fires, their effectiveness is limited.
Halon fire extinguishers Are designed to extinguish Type B and Type C fires. They have been used in computer rooms and on airplanes because, unlike multipurpose dry-chemical extinguishers, halon does not damage electronics and it leaves no residue. Obviously, this is quite a plus. However, these extinguishers contain liquefied halocarbon gases (carbon compounds containing chlorine or fluorine, etc.), which have been shown to damage the Earth’s protective ozone layer. As a result, since 1994, halon fire extinguishers have no longer been allowed to be sold to the general public. However, those purchased before the ban, can be still be used. So, if you have one in your home that’s in working order, and its use will not conflict with your eco-philosophy, it can still be a usable, home fire-fighting tool.
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