Wet Pipe Sprinkler System: A sprinkler system employing automatic sprinklers attached to a piping system containing water and connected to a water supply so that water discharges immediately from sprinklers opened by heat from a fire.

Dry Pipe Sprinkler System: A sprinkler system employing automatic sprinklers that are attached to a piping system containing air or nitrogen under pressure, the release of which (as from the opening of a sprinkler by heat from a fire) permits the water pressure to open a valve known as a dry pipe valve, and the water then flows into the piping system and out the opened sprinkler(s).

Preaction Sprinkler System: A sprinkler system employing automatic sprinklers that are attached to a piping system that contains air, with a supplemental detection system (smoke or heat detectors) installed in the same areas as the sprinklers. There are three distinct types of Preaction Systems.

 

Single Interlock Preaction: A single interlock system admits water to sprinkler piping upon operation of detection devices.

Non-Interlock Preaction: A non-interlock system admits water to sprinkler piping upon operation of detection devices or automatic sprinklers.

Double Interlock Preaction: A double interlock system admits water to sprinkler piping upon operation of both detection devices and automatic sprinklers.

 

Deluge Sprinkler System: A sprinkler system employing open sprinklers (or open nozzles) that are attached to a piping system that is connected to a water supply through a valve that is opened by the operation of a detection system (smoke or heat detectors) installed in the same areas as the sprinklers. When this valve opens, water flows into the piping system and discharges from all sprinklers (or open nozzles) attached thereto.

Foam Sprinkler System: Any of the previously described systems connected to a special foam concentrate reservoir at the system riser that automatically delivers a combination of foam and water when the system is activated.

Antifreeze Sprinkler System: A wet pipe sprinkler system employing automatic sprinklers that are attached to a piping system that contains an antifreeze solution and that are connected to a water supply. The antifreeze solution is discharged, followed by water, immediately upon operation of sprinklers opened by heat from a fire.