Fire Extinguisher(redirected from extinguish)
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Fire-fighting vehicles have evolved into highly specialized equipment. Ladder trucks provide access to buildings as much as 100 ft (30 m) high; snorkel trucks enable firefighters to douse fires from above. In addition, modern fire apparatus includes rescue trucks, mobile laboratories, searchlight cars, double-ended tunnel engines, smoke ejectors, high-pressure spray trucks, foam trucks, and even coffee wagons. For fires of long duration there are tank trucks to bring extra fuel to the pumpers. The modern diesel pump delivers about 2,000 gal per min (8,000 liters per min) through lightweight hose 1 in. (2.5 cm) to 2.5 in. (6.3 cm) in diameter, reinforced with artificial fibers. A fireboat, not limited to hydrant supply, can deliver as much as 10,000 gal per min (40,000 liters per min). Airports have specially equipped crash trucks, and refineries have chemical applicators.
The commonly seen metal cylinder with a short hose attached is the soda-and-acid extinguisher; inside it, above a solution of soda and water, is a container of acid. When the extinguisher is inverted, the acid mixes with the solution and reacts with the soda to generate carbon dioxide; gas pressure then forces the solution out of the hose. A foam extinguisher is a cylinder containing water, sodium bicarbonate, an agent (often licorice powder) for strengthening the foam, and an inner container of aluminum sulfate powder. Mixed together, these ingredients form a foam of carbon dioxide bubbles. A carbon dioxide extinguisher consists of a tank of liquid carbon dioxide under pressure. When released, the carbon dioxide forms flakes that vaporize and blanket the fire.
Characteristics of Extinguishing Substances
Certain dry materials that melt and coat the burning material, thus excluding air, are useful against all classes of fire. In certain cases inert gases such as argon or nitrogen are used to fight fires in materials that would react dangerously with water or with other extinguishing agents; sodium and water, for example, is a dangerous combination.
Water, although supplanted somewhat by other materials, is still the most common substance used for quenching class A fires, which are the most common types of fire; water both cools and helps smother the fuel. Buckets of water are the simplest equipment for fighting small fires in solids. More effective are fire extinguishers capable of directing a stream of water. Wetting agents called detergents make water more penetrating, especially for such objects as cotton bales and mattresses.
Class B fires cannot be fought with water unless it is sprayed in a fine mist, for flammable liquids will usually float on water and spread. Foam is most often used to suffocate class B fires, particularly oil fires.
Since both water and foam conduct electricity, neither can be used against class C fires unless a fog nozzle, which produces tiny droplets that burst into a smothering blanket of steam, is employed. Halogen compounds and carbon dioxide are effective agents in fighting class C fires and are also used against flammable liquids and small fires in solids. Halogen compounds such as carbon tetrachloride turn into a vapor that settles over a fire, smothering it. Unfortunately, most halogen vapors are both toxic and corrosive; but for enclosed spaces where water damage would be as disastrous as fire damage, it is the agent of choice. In any case, nearly all professional firefighters today are equipped with oxygen tanks. Dry-chemical extinguishing agents, such as fine sodium bicarbonate, can be used on class B and C fires but are especially effective against class B fires.
Special Equipment and Techniques
History of Fire Fighting
Ancient Rome is known to have had a fire department consisting by the 1st cent. of approximately 7,000 paid firefighters. These fire brigades not only responded to and fought fires, but also patrolled the streets with the authority to impose corporal punishment upon those who violated fire-prevention codes. The inventor Ctesibius of Alexandria devised the first known fire pump c.200 B.C. but the idea was lost until the fire pump was reinvented about A.D. 1500. The only equipment available to fight the London fire in 1666 were two-quart hand syringes and a similar, slightly larger syringe; it burned for four days. Elsewhere in Europe and in the American colonies fire fighting equipment was equally rudimentary. The London fire stimulated the development of a two-person operated piston pump on wheels.
In 1648, Gov. Peter Stuyvesant of New Amsterdam (New York City) was the first in the New World to appoint fire inspectors with the authority to impose fines for fire code violations. Boston imported (1679) the first fire engine to reach America. For a long time the ten-person pump devised by the English inventor Richard Newsham in 1725 was the most widely used. The inventor Thomas Lote of New York built (1743) the first fire engine made in America. About 1672 leather hose and couplings for joining lengths together were produced; though leather hose had to be sewn like a fine boot, fabric and rubber-treated hose did not come into general use until 1870. A steam fire engine was built in London in 1829, but the volunteer fire companies of the day were very slow to accept it. When a group of insurance companies in New York had a self-propelled engine built in 1841, the firefighters so hindered its use that the insurance companies gave up the project. Finally, in Cincinnati, Ohio, the public forced a steam engine on the firefighters.
The aerial ladder wagon appeared in 1870; the hose elevator, about 1871. Gasoline engines were at first used either as pumping engines or as tractors to pull apparatus. In 1910 the two functions were combined, one engine both propelling the truck and driving the pump. Modern equipment is usually diesel powered, and multiple variations of the basic fire engine enable firefighters to respond to many types of emergency situations.
See P. R. Lyons, Fire in America (1976); C. V. Walsh and L. Marks, Firefighting Strategy and Leadership (2d ed. 1976); J. Robertson, Introduction to Fire Prevention (1989).
a device for stopping fires by means of fire-extinguishing substances. It is carried to the location where it is to be used and is operated manually.
A fire extinguisher consists of a cylindrical vessel with a volume of 1–100 cubic decimeters, a release valve, and a nozzle for forming a stream of the fire-extinguishing substance, which is usually forced out of the vessel by excess pressure within the vessel. The pressure can be maintained continuously (in fire extinguishers of the pressurized type), or it can be generated when the extinguisher is operated. Pressurized fire extinguishers are filled either with the fire-extinguishing substance alone or with a propellant (such as air or nitrogen) as well. In the second type the pressure may be generated by a propellant contained in a flask or as a result of chemical reaction of substances that are components of the fire-extinguishing material.
Among the substances used as fire-extinguishing materials are carbonic acid (carbon dioxide), chemical foams and mechanically produced aerated foams, halogenated hydrocarbons (ethyl bromide or Freon), powders, and water. The carbon dioxide in a fire extinguisher is in the liquid state; it leaves the extinguisher through a diffusing nozzle as a jet that consists of a gaseous phase and a solid phase (snow). Chemical foams are formed in a fire extinguisher as the result of a reaction between an alkaline solution (based on NaHCO3) and an acid solution (based on H2SO4) that takes place when the solutions are mixed before entering the nozzle. The foam ratio—that is, the ratio of the volume of foam to the volume of solution—is 4–6. Mechanically produced aerated foams are obtained by passing a 5–6-percent aqueous solution of a surface-active agent through the nozzle. The solution is broken down into small droplets in the atomizer of the nozzle. The stream of droplets is mixed with the air that is ejected into the nozzle, thus forming a foam with a foam ration of 6–8. In nozzles of the mesh type, foam is produced from bubbles that are generated on the mesh by blowing; the foam ratio in this case is 50–70. The jet of foam is 3–6 m long. Upon passing through the nozzle, the halogenated hydrocarbons form a stream of the aerosol type consisting of finely dispersed drops; powders produce a cloud-forming stream.
The uses of fire extinguishers depend on such properties as extinguishing capacity, the corrosive activity, toxicity, and electric conductivity of the fire-extinguishing substance, capacity, and ability to withstand vibrational loads.
The design of a fire extinguisher depends on the type of the fire-extinguishing substance and the means used to expel the substance. The steel gas cylinders of carbon dioxide fire extinguishers are built for operating pressures of 15 meganewtons per sq m (MN/m2), or 150 kilograms-force per sq cm (kgf/cm2). In all other fire extinguishers the pressure does not exceed 2 MN/m2. The vessels of small fire extinguishers that use powders can be made of plastic.
Fire extinguishers are checked throughout their period of use (beginning with the time of charging) for strength of the vessel and operability. Inspection intervals and procedures are determined in the specifications.
O. M. KURBATSKII