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When a fire occurs in a poorly ventilated space, it is possible that the fire will burn until the atmosphere becomes oxygen-depleted. Remember that, for combustion to take place, an oxidizer, in this case oxygen in the air in the room, must be present in sufficient quantity for the chemical reaction of combustion to be sustained. When the available oxygen has been consumed by the fire, the hot gases and aerosolized fuels will be present in high concentrations due to incomplete combustion because there is no longer enough oxygen for them to burn and not enough ventilation for them to escape. Although there may not be any visible fire anymore, this condition is very dangerous because all the reaction needs is more oxygen and it will start again. If oxygen is suddenly introduced into this environment, such as may happen when a closed door or window is opened, the accumulated hot gases and incompletely burned fuel in the air can suddenly ignite. The reaction is typically rapid enough to cause low order damage. This phenomenon is commonly known as a backdraft.