When should hot gases be displaced towards the floor?

Displacing hot gases towards the floor is a critical aspect of fire management, particularly during positive pressure ventilation (PPV). In this technique, high-velocity fans are used to introduce fresh air into a structure while simultaneously pushing the hot, smoke-laden gases towards the lower levels of the room or building. This process enhances visibility and reduces the risk of flashover by cooling the upper layers of air. Furthermore, by directing hot gases downward, it's easier for firefighters to access and extinguish the fire effectively, as the more hazardous conditions are moved away from the crew’s working area.

In contrast, using water hoses typically aims to cool the fire directly or reduce the heat in the immediate area rather than manage hot gases. Generating steam, while a by-product of applying water, has different implications, as it interacts with the existing hot gases in a way that doesn't specifically focus on displacing them downwards. Roof ventilation primarily involves removing hot gases and smoke upward to create an escape route and reduce heat, which contradicts the idea of displacing those gases toward the floor. Thus, the technique of positive pressure ventilation is specifically designed to manage hot gases effectively by moving them downward.