Once the accumulated unburnt gases begin to ignite, it is common for the flames to roll across the ceiling, resulting in a rapid increase in radiant heat, as shown in Figure 27. This condition could lead to flashover or further smoke ignition. The application of water into the upper layer may stop or delay the progression of the rollover. Similarly, if it is not possible to place water on the burning surfaces to prevent the redevelopment of the heat and unburnt gases, the crew should retreat to a point of safety, cooling the smoke as they go.