Firefighting
Reconnaissance and "reading" the fire

The first step in a firefighting operation is reconnaissance to search for the origin of the fire (which may not be obvious for an indoor fire, especially if there are no witnesses), to identify any specific risks, and to detect possible casualties. An outdoor fire may not require reconnaissance, but a fire in a cellar or an underground car park with only a few centimeters of visibility may require long reconnaissance to identify the source of the fire.

The "reading" of a fire is the analysis by firefighters of indications of thermal events such as flashover, backdraft or smoke explosion. It is performed during reconnaissance and fire suppression maneuvers.

The main signs are:

Spraying water on the ceiling in short pulses of a diffused spray (e.g., a cone with an opening angle of 60°) can be undertaken to test the heat of smoke: If the temperature is moderate, the water falls down in drops with a sound like rain; if the temperature is high, the water vaporizes with a hiss—the sign of a potentially extremely dangerous impending flashover.

Ideally, part of reconnaissance is consulting a plan for the building that provides information about structures, firefighter hazards, and in some cases the most appropriate strategies and tactics for fighting a fire in that context.
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