When the sprinkler senses the the hot gases from fire, each sprinkler head will open and spray water on to a fire. Only the sprinklers over the fire open. The others remain closed. This limits any damage to areas where there is no fire and reduces the amount of water needed.

The flow is calculated so that there is always enough to control a fire taking into account the size and construction of the building .Sprinkler heads can be placed in enclosed roof spaces and into floor ducts to protect areas where a fire can start without being noticed.