The battlefield commander had his plan set. It was to be an aggressive offensive pitting his infantry troops in a frontal assault on the enemy. The battalions and companies were in place. The subordinate commanders had been briefed on the plan and their roles. As any competent commander would do...
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The battlefield commander had his plan set. It was to be an aggressive offensive pitting his infantry troops in a frontal assault on the enemy. The battalions and companies were in place. The subordinate commanders had been briefed on the plan and their roles. As any competent commander would do, the general didn't commit all of his resources to the battle; some were held in reserve. Everything was ready.
One of the commander's chief concerns during the plan had been the flanks of the attacking forces. He worried that the enemy would spread to the sides and try to outflank his forces. He included additional units in the plan dedicated to cover the flanks of the attacking forces. He was protecting the exposures.
Sound familiar? The battle on a fireground is no less a pitched battle that any army would fight. There are many of the same elements and one of the most important areas in firefighting strategy is covering the exposures.
The enemy in firefighting is heat the heat that the fire produces, where that heat can travel and the effect that the heat will have on other combustibles. Exposure problems are a result of excessive heat. The fire extends within the structure or to another structure as the result of heat transfer, which occurs in three ways: conduction, convection and radiation.
Conduction involves heat transfer by direct contact of the heated material to another material. The transfer of heat is dependent on the conductivity of the material. Many metals are good conductors of heat; brick is not. Masonry walls usually provide exposure protection because of the low conductivity of the masonry material.
Convection is the process of heat transfer through a circulating medium, usually air. When a fireplace heats a room, the movement of the heat throughout the room is convection. In a fire, the heated air rises and transfers heat to other areas as it spreads out.
Radiation involves the transfer of heat by rays or waves in all directions from the source of the burning. In a fire, heat will radiate in all directions until it strikes an object. The radiant heat will then be passed to the object by conduction. Radiant heat can pass readily through glass and air.
The severity of the heat threat will also be affected by time, distance and shielding. Time is the duration of heat exposure on a potential fuel source. The longer it is exposed and unprotected, the greater the heat buildup and potential for ignition.
Distance affects the heat transfer threat to an exposure because the closer a structure is to the fire source, the more threatened it will be.
Shielding of the exposure from heat provides protection by breaking up the radiant heat wave and reducing the ability of combustibles to reach ignition temperature.
Three basic types of exposures at an emergency scene must be addressed: life exposure, the internal exposure and the external exposure.
The life exposures are the problems and potential problems that the fire presents to people. These people include firefighters, occupants, other emergency responders such as police, and curious bystanders.
While occupants of the fire building would normally be removed to an area of safe haven, consideration also must be given to removing occupants from exposed properties. If the exposure requires that firefighting forces have to enter and examine the structure, then consideration must be given to relocating the occupants as an exposure risk.
Likewise, firefighters and other responders must be considered an exposure. The incident commander, assisted by the safety officer and sector commanders, must ask questions: Are firefighters wandering around in unsafe areas? Should firefighters who lack an assignment be re-directed to a manpower pool in a safe area? Is there a collapse potential that requires all personnel to be moved?