What indicates that a fire is approaching backdraft conditions?

Smoke rolling out of openings is a key indicator that a fire may be approaching backdraft conditions. Backdraft is a dangerous phenomenon that occurs when a fire has consumed most of the oxygen in a confined space, causing it to smolder. As the fire begins to run out of oxygen, it produces a significant amount of dense, dark smoke. If oxygen is suddenly introduced into the environment, for example, by opening a door or window, this can lead to a rapid ignition of the available gases, causing an explosive situation.

The presence of smoke rolling out of openings suggests that there is a buildup of heat and gases inside the structure. The rolling smoke often indicates that the superheated gases and smoke are not just stagnant but have a dynamic behavior that could result in a backdraft if proper ventilation is not conducted carefully. Observing this behavior alerts firefighters that they need to employ caution and possibly consider safe ventilation measures to prevent the dangerous conditions associated with a backdraft scenario.

The other options, while indicative of fire conditions, do not specifically signal the impending danger of backdraft. Smoke settling close to the ground suggests that there is still sufficient heat, but doesn't specifically indicate a buildup of heat and gases leading to backdraft. Dense black smoke shows that combustion is occurring