KNOW YOUR FIRE EXTINGUISHERS

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Then — once you know that extinguisher manufacturers design some equipment to handle certain fire classes specifically (and to be installed where only one type of fire is a potential problem), and other units that have the ability to control two or three categories safely and effectively — you can begin the process of selecting the protective devices that best fit your situation.

Making the right choice might be a matter of life and death, too: In the case of an electrical fire, for instance, a conductive extinguishing medium (such as water) could transmit a lethal shock to the firefighter (you) in a split second. Furthermore, as a look at the accompanying chart will show, many Class B and C extinguishers are not effective against the most common (Class A) household fires.

There are still other considerations to keep in mind, even after you've determined the proper class of fire extinguisher for the task at hand. For example, the Purple K extinguishers ( see the chart ), which are actually more effective than sodium bicarbonate "quenchers", use a medium that's highly corrosive in a moist environment . . . and that factor might weigh against their use in certain applications.

By the same token, electronic components can be very sensitive to thermal shock as well as to corrosion . . . so a "gentle" Halon extinguisher — even though it'll be considerably more expensive to purchase and refill than would equipment using other mediums — would be the obvious choice where thousands of dollars of electronics are at stake.

HOW DO THEY RATE?

Besides being designed to deal with specific kinds of fires, an extinguisher is also manufactured to meet or exceed certain efficiency ratings established by Underwriters Laboratories. In fact, test fires are set under controlled laboratory conditions — with specific kinds and measured amounts of fuels — and extinguishers of specific capacities and containing various mediums are then used to put out those fires. Each piece of equipment's ability to handle the blazes determines its rating, and the operator's capabilities are considered, as well (professional firefighters are used for the tests in an effort to standardize the extinguishing process . . . which could vary in effectiveness with first-time users).

Fire extinguishers' ratings are recorded on a numerical scale, and arranged according to the class (A, B, and/or C) of fire in question. For example, a unit that's rated 1A-10BC is capable of knocking out an 8' X 8' (64-square-foot) pad of burning furring strips or 25 square feet of ignited petroleum. A larger "gun", rated at 4A-60BC, can handle 196 square feet of strips or 150 square feet of burning liquid. Both, of course, are also rated as suitable for fighting electrical fires. The test fuel samples do, however, change with increased rating levels (starting with the 10A category, for instance, 2 X 2's replace the furring strips), so there's not always a simple method of comparing the effectiveness of two units.

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