What is a common indicator of an impending flashover?

A common indicator of an impending flashover is significant heat build-up. During a fire, as the flammable materials and gases in the environment heat up, they reach a critical temperature where the risk of flashover increases dramatically. Flashover occurs when the combustible materials in the room ignite simultaneously, creating a fireball effect.

Significant heat build-up indicates that the room is reaching a temperature near the ignition point of all combustible materials. This heat can often be felt through thermal layers or observed as an increasing temperature on thermal imaging cameras. Recognizing this indicator allows firefighters to take necessary precautions, such as evacuating the area or employing tactics to cool down the environment before a flashover occurs.

The other options may not be as reliable for assessing the immediate risk of flashover. For example, smoke trapping in corners can suggest a buildup of gases, but it does not always correlate directly to the conditions that can lead to flashover. Similarly, the presence of flame shadows indicates heat and potentially combustible materials but does not provide the same level of risk assessment as significant heat build-up. A sudden drop in temperature frequently indicates fire suppression activities or loss of fire intensity and therefore is not associated with the approach of flashover.