What does smoke puffing in and out of a structure indicate?

Smoke puffing in and out of a structure typically indicates backdraft conditions. Backdraft is a phenomenon that occurs in a fire when a sudden introduction of oxygen causes an explosive increase in fire intensity. This can happen in situations where there is a buildup of unburned gases that are heated and can cause a significant risk when exposed to fresh oxygen. The characteristic smoke movement, puffing in and out of a structure, signifies that there are pockets of combustible gases present, and the build-up of heat and pressure may lead to a rapid combustion event once oxygen enters the space.

In contrast, growth-stage fire, imminent flashover, and impending structural collapse represent different aspects of fire behavior and hazard. A growth-stage fire refers to the expansion of the fire as it consumes more fuel, but it does not involve the same immediate risk of explosive conditions as backdraft. Imminent flashover indicates that the fire is approaching a state where all combustible materials in the room might ignite simultaneously, which is associated with uniform heat and flame spread rather than the puffing smoke characteristic of a backdraft. Impending structural collapse involves factors related to the integrity of the building and is typically assessed through signs of structural failure rather than smoke behavior. Thus, the behavior of smoke puff