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AUTOMATIC FIRE SPRINKLER & HYDRANT SYSTEMS

Introduction
This is the earliest form of automatic fire detection & extinguishing system in use. It consists basically of Water discharge devices (Sprinklers), one or more sources of water (under pressure), water flow controlling devices (valves), distribution piping to supply water to the discharge devices, and ancillary equipments, such as alarm and supervisory devices.

A piping system connected with the main water supply is routed through all building sections to be protected. Sprinklers are installed in the piping network at certain intervals. The sprinklers are shut as long as then a stand-by condition exists. If there is fire the sprinkler located nearest to its source opens and discharges a finely dispersed spray of water onto the fire. As the individual sprinklers open automatically and independently of others, fire extinguishing is performed only where it is necessary.
Outdoor hydrants, indoor hose standpipes and hand hose connections are also frequently a part of the protection system.

In a sprinkler system, detection of fire is automatic and it’s by means of a fusible link. A valve in the sprinkler head releases the water when high temperature (68ºC - 100ºC) melts the fusible link. Basically, sprinkler protection involves the principle of the automatic discharge of water, in sufficient density, to control or extinguish a fire in its early stages. In planning for a system that fulfils this objective, several factors must be considered. These are grouped into 4 categories:

  1. The sprinkler system
  2. The features of building construction
  3. The hazards of occupancy
  4. The water supplies

NFPA 13 standard Classifies occupancies as light hazard, ordinary hazard and extra hazard, and provide schedule of pipes sizes, spacing of sprinklers, sprinklers discharge densities and water supply requirements for each class.

Typical examples of light hazards occupancies are offices, buildings, schools, churches, hotels, and apartment houses. Ordinary hazards occupancies include warehouses, and many manufacturing plants. Explosive plants, paints and varnish plants and oil refineries are example of extra hazard occupancies.

Types of Sprinkler System

  1. Wet Pipes System for Frost protected rooms
    In frost protected rooms the piping is filled with water to the last sprinkler
  2. Dry Pipes System for Frost Hazard rooms

    In frost hazard rooms the piping is filled with compressed air. The water supply extends to the dry pipe valve which is installed in a frost protected area. If a sprinkler opens, the pressure drop in the piping actuates the alarm valve and water is delivered into the sprinkler system.

Water Supply
Both, extent and method of water supply depend on risk classification and conditions at site. However, the water reservoir is principally calculated in such a way that under unfavourable conditions the expected fire extension will be under control.

Benefits
While sprinkler system has been an effective fire protection system for years, it has its drawbacks. Indeed, historically, sprinkler systems were designed solely to protect the integrity of buildings against fire rather than saving the contents of the building. To guarantee dependable water supply, we would require construction of bore holes or massive storage devices – a rather inexpensive proposition which is out of proportion to the limited effectiveness of water as an extinguishing agent.

Operating conditions
restored after a fire

After extinguishing of the fire, the system is rendered operative again by replacing the sprinklers which have been in operation.

 

 

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