Masonry Magazine December 1986 Page. 36
Fire Extinguishers: Selection and Placement
Extinguishers are classified according to the type of fire they are designed to extinguish. Class A extinguishers are for fires involving ordinary combustible materials such as wood, paper, and cloth. Class B extinguishers are for fires involving flammable liquids, gases, and greases. Class C extinguishers are for fires involving energized electrical equipment. Class D extinguishers are for fires involving combustible metals such as magnesium, titanium, and sodium.
The Underwriters' Laboratories (UL) rating system for Class A extinguishers is based on the amount of water and the duration of discharge. The rating is indicated by a number followed by the letter "A." For example, a 2-A extinguisher contains 2.5 gallons of water and has a discharge time of 55 seconds. The minimum size extinguisher for light hazard occupancy is a 2-A. The maximum travel distance to an extinguisher is 75 feet.
For Class B hazards, the UL rating system is based on the square footage of flammable liquid that the extinguisher can extinguish. The rating is indicated by a number followed by the letter "B." For example, a 10-B extinguisher can extinguish a 10-square-foot flammable liquid fire. The minimum rating and maximum travel distance for Class B hazards are similarly determined, with two exceptions. For flammable liquid fires in depths greater than 1/4 inch, in an area larger than 10 square feet, protection should be provided by twice the tabled amount of Class B extinguishing potential. Pressurized flammable liquids and gases present a special problem. In this case, recommendations by manufacturers of these materials should be the basis for selection.
Because Class C fires require an extinguishing agent that will not conduct electricity, it is important that extinguishers installed near electrical hazards be rated for these dangers. Placement and capacity of Class C extinguishers for each major hazard are individually judged according to the size of the electrical equipment, its configuration and the effective range of the extinguisher stream.
Class D extinguishers must be within 75 feet of the hazard. Because use of the wrong extinguisher in Class D metal fires can cause an explosion, extinguishers for these hazards must be chosen carefully. They must be selected according to the specific metal involved, the area to be covered and recommendations made by the extinguisher manufacturer based on data from control tests it conducts.
Extinguishers in the home are useful for putting out small fires. Class A, B and C fires are all possible in a home, so a multi-purpose extinguisher should be provided. A garden hose that is kept connected and accessible is also a recommended firefighting tool for the home, providing it is not used on electrical fires.
Size and weight of a home fire extinguisher are important because women must be able to handle them. However, home extinguishers must still have enough capacity to cope with expected fires and should be chosen with care. These extinguishers should be installed in plain view where they are safe from damage. They should be near room exits which provide escape routes, and located so the top is no more than five feet above the floor.
Whether on the home front, the office or the factory, strategic placement must aid firefighting. We can't afford to lose even one battle in this war.
Reprinted with permission from the Journal of American Insurance.
Exploding Extinguishers
Because of possible explosion hazards, all inverting-type fire extinguishers should be replaced, according to the National Association of Fire Equipment Distributors (NAFED). (An inverting extinguisher is activated by turning it upside down). Hazardous inverting extinguishers include water cartridge and loaded-stream cartridge types. Production of these extinguishers was discontinued in 1971, but many are still in service.
Because inverting extinguishers are not under constant pressure, they are not classified as pressure vessels, and are not designed to meet pressure vessel safety codes. When operated, however, they can generate internal pressures great enough to stress the containers so that they may explode. Inverting-type extinguishers have shown a 22 percent failure rate in hydrostatic tests conducted with the extinguisher under much higher pressures than normally would exist. Under actual conditions of usage, some have exploded in use, causing a number of fatalities. The accompanying chart lists suggested replacements.
Suggested Replacements
Discontinued Type/UL Rating
Equivalent Replacement/UL Rating
Soda-Acid, 2½ gal. 2-A
Air Pressure Water, 2½ gal. 2-A
Water Cartridge, 2½ gal. 2-A
Water Pump Tank, 2½ gal. 2-A
Multi-purpose Dry Chemical 5 lb. 2-A:10-BC
Foam, 2½ gal. 2-A:6B
Light Water AFFF., 2½ gal. 2-A:20-B
Multi-purpose Dry Chemical, 5 lb. 2-A:10-BC
Loaded Stream Cartridge, 2½ gal. 2-A:1B
Loaded Stream Pressurized, 2½ gal. 2-A:1-B
Light Water AFFF., 2½ gal. 2-A:20-B
Multi-purpose Dry Chemical, 5 lb. 2-A:10-BC