Which is a sign of a potential backdraft situation?

A potential backdraft situation is typically indicated by the buildup of smoke and the absence of visible flames. In this context, smoke buildup signifies that there is an accumulation of unburned gases within the structure, which can reach a flammable concentration. When there is little to no oxygen available for combustion, flames may not be visible, yet highly flammable conditions can still exist. This situation presents a serious risk because opening the structure's access points can introduce oxygen, potentially leading to a rapid ignition of the confined gases, resulting in a backdraft.

While visible flames and heat, rapidly increasing temperatures, and changes in flame color can indicate various fire conditions, they are not specifically indicative of backdraft risks. Visible flames suggest that combustion is occurring, and rapidly increasing temperatures may mean the fire is growing rather than indicating a backdraft. Changes in flame colors may simply reflect the materials burning or the temperature of the fire, rather than the critical buildup of smoke and gases that signals a potential backdraft scenario.