1. A complete fire-protection sprinkler system with sprinkler heads in which there is no water unless the system is actuated (either automatically or manually) in case of fire; esp. used in areas subject to freezing temperatures, or to avoid the hazards of leaking or bursting pipes.
2. A fire sprinkler system containing a network of pipes filled with air or nitrogen under pressure and equipped with an automatic sprinklers; when the sprinklers open, the air or nitrogen is released, thereby opening a valve (called a dry-pipe valve ) which permits water to enter the pipes and to flow out the opened sprinklers.