Fire-Fighting System, Automatic

a system of equipment used to prevent, extinguish, localize, or block fires in enclosed spaces. Automatic fire-fighting systems are installed in buildings and rooms where the fire hazard is comparatively high. A distinction is made between systems that are actuated automatically and operate according to a predetermined program and those that are actuated by an operator; the former are called automatic fire protection systems, the latter fire protection units. An automatic fire-fighting system includes a sensor capable of detecting combustion, alarm signaling devices, fire-extinguishing equipment, starting and stopping devices, and feeders for the fire-extinguishing substance; in some cases, it includes control equipment for the production process being protected. Atomizers, foam generators, and pipe nozzles form and direct the stream of the fire-extinguishing substance, which may be a liquid, foam, powder, or gas. Fire-extinguishing substances are fed into the system from a centralized supply, such as a water supply, or from self-contained or combined feeders.

The most widely used systems employ water (sprinkler and drencher systems), carbon dioxide, aerosols, or powders. A sprinkler system consists of a grid of pipelines located on the ceiling of the room, with sprinkler heads attached to the pipes by threaded connections. The opening of a sprinkler is kept closed by a disk held in a closed position by a thermal lock. If the room temperature rises to a specified point, the lock is destroyed and the disk opens, admitting water to the room.

Drencher systems, which use nozzles without thermal locks, are actuated either by a sprinkler installed in a trigger air line or by a cable-type thermal lock. Automatic fire protection systems are classified according to the time elapsed between the start of the fire and the actuation of the system as ultrahigh-speed (to 0.1 sec), high-speed (to 3 sec), and standard (to 180 sec). The fire-extinguishing substance can be applied for periods ranging from 30 sec to 60 min.