Which of the following is NOT a sign of backdraft?

The presence of visible flames is typically not a sign of backdraft. Backdraft occurs in a fire situation where there is a buildup of heat and smoke in an enclosed space that is oxygen-deficient. When enough oxygen is suddenly introduced, such as when a door or window is opened, an explosive ignition can occur, resulting in a rapid combustion of the smoke and gases.

Dense smoke, oozing smoke, and whistling sounds are all indicators of a backdraft situation. Dense smoke signifies a heavy concentration of unburned fuel and insufficient oxygen, while oozing smoke can indicate that conditions are right for a potential backdraft; smoke that appears to be seeping from a structure might suggest that superheated gases are present. Additionally, whistling sounds can signify changes in pressure within a confined space, further pointing to unstable combustion conditions.

In contrast, the presence of visible flames implies that combustion is already occurring and that there are adequate oxygen levels present, which is contrary to the scenarios leading to backdraft conditions.