Which option is NOT characteristic of a backdraft?

A backdraft is a dangerous fire phenomenon that occurs when a fire that has consumed most of its oxygen goes unventilated, leading to smoke accumulation and high heat concentration. The defining characteristics of a backdraft include smoke buildup, sudden ignition, and high heat concentration.

In a backdraft scenario, as the fire consumes the available oxygen, it creates an explosive potential. When the conditions are right—typically when fresh air is introduced—the accumulated gaseous smoke ignites rapidly, resulting in a sudden and violent explosion.

The absence of a free-burning fire is significant in understanding backdrafts. A free-burning fire typically denotes a well-ventilated situation where flames are actively consuming fuel and oxygen. In contrast, a backdraft occurs in a confined space where the fire has smoldered, making it a distinct condition from a free-burning fire. Therefore, the answer indicating that a free-burning fire is not characteristic of a backdraft accurately reflects the nature of this hazardous fire condition.