fire fighting

fire fighting,

Fire-Fighting Strategy

Fire fighting strategy involves the following basic procedures: arriving at the scene of the fire as rapidly as possible; assessing the nature of the fire by determining its intensity and extent, the type and abundance of fuel, the danger of entering the fire area, and the most effective techniques for extinguishing the fire; locating and rescuing endangered persons; containing the fire by protecting adjacent areas; ventilating the fire area to allow for the escape of heat and toxic gases; and, finally, extinguishing the fire.

Fire-Fighting Personnel

In most cities, firefighters are trained members of government-supported organizations, such as fire departments. Elsewhere, fire-fighting organizations are primarily composed of volunteers, or "vols." Fire-fighting organizations also help design and implement fire-prevention programs, which may include such measures as building codes requiring fire alarms, regularly located fire-extinguishing equipment, internal fire walls to help contain a fire, sprinkler systems, the use of fire-retardant construction materials, and safe electrical wiring. Educating the public about fire safety and fire-prevention practices is an important part of all fire-prevention programs.

Fire-Fighting Apparatus

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.

Extinguishing Fires

For a fire to occur, there must be available oxygen, a supply of fuel, and enough heat to kindle the fuel. Therefore, the three basic ways of extinguishing fire are to smother it, to cut off the fuel supply, or to cool it below the flammability temperature. Fires are classified into four types: those in solids, e.g., wood, paper, and cloth; those in flammable liquids, e.g., gasoline, alcohol, oils, lacquers, and paints; those in electrical apparatus; and those in flammable metals such as magnesium. These are called, respectively, class A, B, C, and D fires.

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

Buildings are protected against fire most effectively by protective sprinkler systems. In most sprinkler systems, water circulates through overhead pipes whose outlets are normally closed; at high temperatures the outlets open, spraying water on the fire. Most large buildings also provide water for fire fighting through a standpipe system with hose connections on each floor. Forest and brush fires are fought by making a firebreak and by covering the fire with extinguishing substances. A narrow strip is cut and cleared in front of the fire down to mineral soil. Embers flying into the strip are put out, while water and other fire-extinguishing substances are spread from land-based vehicles or are dropped on the fire from the air. Oil-field fires demand multiple approaches: water streams, fogs, foams, and explosives may all be used simultaneously to quench a fire and prevent its reignition.

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.

Bibliography

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).