Why do firefighters cut holes in the roof of a building?

Ventilation of a building is one of the most important, yet least understood, firefighting tactics. Fire conditions inside a building usually involve high temperatures and poor to zero visibility. In addition to slowing the attack of the fire, this heat and smoke is damaging all of the contents of the building. Depending upon conditions, heat and smoke can create very dangerous conditions resulting in backdraft (smoke explosion) or flashover (extremely rapid ignition). Smoke is really nothing more than unburned fuel; almost all of the constituents of smoke are combustible. High temperature smoke is particularly dangerous. By opening a large hole in the roof heat and smoke can quickly be removed from the structure. This rapidly improves conditions inside the building, hastening fire suppression.