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Fire Spread. If a fire is attacked early and efficiently, it can easily be confined to the area in which it started

If a fire is attacked early and efficiently, it can easily be confined to the area in which it started. If it is allowed to burn unchecked, it can generate great amounts of heat that will travel away from the fire area, igniting additional fires wherever fuel and oxygen are available. As the original fuel source is consumed, the heat, and thus the fire, will extend to new fuel sources.

Heat from a fire is transferred by one or more of three met­hods: conduction, radiation and convection.

Conduction is the transfer of heat through a solid body. For example, on a hot stove, heat is conducted through the pot to its contents. Wood is ordinarily a poor conductor of heat, but metals are good conductors.

In many cases the skilful application of water, particularly in the form of a spray, will retard or halt the transmission of heat by conduction. A water spray pattern absorbs heat more efficiently than a solid stream, because the smaller water droplets present more surface to the heat source. At the same time, less water is used.

Heat radiation is the transfer of heat from a source across an intervening space: no material substance is involved. The heat travels outward from fire in the same manner as light, that is, in straight lines. When it contacts a body, it is absorbed, reflected or transmitted. Absorbed heat increases the temperature of the absorbing body. For example, radiant heat that is absorbed by a sealing will increase the temperature of that sealing, perhaps enough to ignite its paint.

Heat radiates in all directions unless it is blocked. Radiant heat extends fire by heating combustible substances in its path, causing them to produce vapour, and then igniting the vapour.

Convection is the transfer of heat through the motion of heated matter, i.e. through the motion of smoke, hot air, heated gases produced by the fire.

When it is confined, convicted heat moves in predictable patterns. The fire produces lighter-than-air gases. Heated air, which is lighter than cool air, also rises, as does the smoke produced by combustion. As these heated combustion products rise, cool air takes their place; the cool air is heated in turn and then also rises to the highest point it can reach. As the hot air and gases rise from the fire, they begin to cool; as they do, they drop down to be reheated and rise again. This is the convection cycle.

To prevent fire spread, the heat, smoke and gases should be released into the atmosphere. It is imperative, that the fire be confined to the smallest possible area. If a fire is discovered, attempts should be made to close off all openings to the fire area until firefighting personnel and equipment can be brought into position to fight the fire.

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National Fire Protection Association
N F P A

«To promote the science and improve the methods of fire protection and prevention; to obtain and circulate information on these subjects and to secure the cooperation of its members and the public in establishing proper safeguards against loss of life and property by fire».

The National Fire Protection Association has two functions: one, to provide standards under the guidance of which fire waste may be checked; the other, to educate the public, so that loss of life and injury from fire will be reduced.

The Association's technical committee members are expert fire prevention engineers who serve without pay. Since 1924 the Association has maintained a staff of engineers to organize, stimulate and encourage fire prevention committees. These men have frequently recommended definite programs for the improvement of municipal fire hazard conditions. One of the Association's engineers is employed solely to promote wide recognition of the National Electrical Code, which governs the safe installations of electric wiring and equipment.

All the members take part in the great work of public education. Realizing that loss of life and injury by fire is a major cause of human suffering the Association's members are devoted to showing people how this destructive force can be controlled and fire waste eliminated. To make the public understand the tragic human suffering and economic burden of fire loss is the prime task of the Association and its members. The public must, therefore, be reached by the press, by the schools, from the lecture platforms, by means of radio, television, motion pictures and by general educational programs sponsored by fire departments, with message of fire protection and prevention.

Fire waste is also a serious economic waste. Property destroyed by fire is a total economic loss. The burden of fire loss is borne by every citizen. Much of the Association's literature is prepared with the object of educating the people in fire prevention.

The Association has sections composed of state, provincial and city fire experts. The Electrical Section of the Association, open to all members interested in electrical matters, is responsible for the development of new editions of the National Electrical Code, and provides a forum for general discussions of electrical hazards.

The Railroad Section of the Association, including representatives of large railroad systems, provides a medium for the consideration of activities in railroad fire protection.

The «Quaterly» magazine is unique in its special articles. The important fires occurring in the United States and Canada, with special reference to their origin, their extent and the manner of their extinguishment are described in the «Quaterly». The articles show how the majority of fires start and how, in the cases given, they were extinguished.

UNIT 3

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