Water has always been the most common substance used to extinguish a fire. Water is usually readily available, is non-toxic, can be stored at atmospheric pressure and normal temperatures, takes the heat out of a fire, and is inexpensive. It is better than any other recognized liquid for fighting the majority of fires. In designing a fire protection system, the engineer must determine which system to select based on each system’s pros, cons, and code requirements. Each system has its own unique applicable use, which depends on the type of structure to be protected, the contents of the building, the severity of the fire, the anticipated fire growth rate, water sensitivity, ambient freezing conditions, and desired time until activation.
A wet pipe system is one in which water is constantly contained within the sprinkler piping. The wet system employs fixed fire sprinkler heads and sprinkler piping filled with pressurized water supplied from a dependable source at all times. When a sprinkler head activates or its fusible link melts, water is discharged immediately onto the fire. Water is discharged continually through the sprinklers that have activated over or near the fire, thereby minimizing water damage. Only sprinklers in the area of the fire that has reached the temperature required to melt, usually between 165°F and 212°F, will discharge water. Upon operation, the sprinklers distribute the water over the area to control or extinguish the fire.