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In addition, hot smoke radiates heat to furniture and other combustibles in the compartment. This increases pyrolysis which adds more flammable fuel to the gas layer. Cooling the hot gas layer mitigates these hazards by slowing the transfer of heat to other combustibles and reducing the chances of the overhead gases igniting.

You can cool the hot gas layer by applying short pulses of water fog into it. With the nozzle set on a 40- to 60- degree fog pattern, direct it upward toward the gas layer and quickly open and close it in one- to two-second pulses (Figure 15.11). Remember that your intent is to cool the gases, not to produce a large volume of steam. When water droplets begin to fall out of the overhead smoke layer, it means that the gases have been cooled and you can stop spraying water into the smoke.If the fire continues to burn unchecked, the gas layer will regain its heat and the gas-cooling technique may have to be repeated.
The gas-cooling technique should be repeated as necessary while the hose team advances under the gas layer toward the fire. In narrow hallways, the fog pattern may need to be restricted. In large-volume compartments, the duration of the pulses may need to be increased slightly. Smoke — Visible products
of combustion resulting from the incomplete combustion of carbonaceous materials and composed of small particles
of carbon, tarry particles, and condensed water vapor suspended in the atmosphere, which vary in color and density depending on the types of material burning and the amount of oxygen.
Figure 15.11 The hot gas layer can be cooled with short pulses of water fog
as the attack team enters the structure. Courtesy of Dick Giles.
Direct Attack
The most efficient use of water on free-burning fires is made by a direct attack on the fire — usually from a solid or straight stream. The water is applied in short bursts di- rectly onto the burning fuels (often called “penciling”) until the fire “darkens down” (Figure 15.12, p. 768). Another effective technique (often called “painting”) is to cool hot surfaces to slow or stop the pyrolysis process by gently applying water and allowing it to run over the hot material. Water should not be applied long enough to upset the thermal layering (sometimes called thermal balance); the steam produced will begin to condense, causing the smoke to drop rapidly to the floor and move slug- gishly thereafter.
Direct Attack (Structural) — Attack method that involves the discharge of water or a foam stream directly onto the burning fuel.
Indirect Attack
When firefighters are unable to enter a burning building or compartment because of the intense heat inside, an indirect attack can be made from outside the compartment through a window or other small opening (Figure 15.13). This method of attack is not ideal where building occupants may still be inside or where the spread of fire to uninvolved areas cannot be contained. However, this may be the only method of at- tack possible until temperatures are reduced.


To make an indirect attack on the fire, a fog stream is introduced through a small opening and directed at the ceiling where the heat is most intense. The heat converts the water spray to steam, which fills the compartment and absorbs the bulk of the heat. Once the fire has been darkened down and the space has been ventilated, hose- lines can be advanced and water applied directly onto whatever is burning.
Indirect Attack (Structural) — Directing fire streams toward
the ceiling of a room or building in order to generate a large amount of steam. Converting
the water to steam absorbs the heat of the fire and cools the area sufficiently for firefighters
to safely enter and make a direct attack on the fire.
Direct and Indirect Attack
The difference between a direct attack and an indirect attack is the location from which the attack is started. An indirect attack is started from outside the compartment, and a direct attack is started from inside it. Skill Sheet 15-I-1 describes how to attack a structure fire with an exterior attack.
Combination Attack
A combination attack uses the heat-absorbing technique of cooling the hot gas layer followed by a heat-reducing direct attack on the materials burning near the floor level. The attack starts with short bursts, known as penciling, from a penetrating fog stream directed into the hot gas layer at the ceiling level (gas cooling) (Figure 15.14).
Combination Attack — Battling a fire by using both a direct and an indirect attack. This method combines the steam-generating technique of a ceiling level attack with an attack on the burning materials near floor level.