At its most basic level, a sprinkler system consists of a network of pipes connected to a water supply via a main valve. The network extends throughout the whole of the area to be protected, with sprinkler heads (the detection devices) evenly spaced to cover the whole area. The sprinkler heads are always heat operated and are set to detect a small but established fire. When a fire is detected, the head which has detected the fire opens and allows water to flow. The head is designed in such a way that the flow of water is broken up into a spray and falls like heavy rain on the area under the head, the flow of water also causes an alarm to be sounded.
Contrary to popular belief, only heads directly affected by heat will allow water to flow. On almost all occasions only the one or two heads directly over the area of the fire will operate. These will usually be sufficient to control the fire and often extinguish it completely. The flow of water applied through each head is strictly controlled by design — the quantity being varied depending on the risk to be protected. Because heads only operate in the presence of a small fire, sprinkler systems very rarely cause unnecessary water damage.
Types of Sprinkler System
- Wet Pipe System: all the pipework is kept permanently full of water, right up to the sprinkler head. This type of system is standard in most buildings, and has the fastest response in terms of applying water to a fire. It should not be used in areas where there is a risk of freezing temperatures.
- Dry Pipe (Pre-action) System: intended for use in cold stores or similar premises where the temperatures are maintained below or close to the freezing point of water. The pipework is kept charged with compressed air to hold the water back below the control valve.
- Alternate System: used where temperatures vary seasonally. The system is kept “wet” during the summer period for the fastest response, and “dry”, ie charged with compressed air, during the winter to avoid freezing.
- Pre-action System: used in areas where the consequences of accidental discharge, due to mechanical damage, are considered unacceptable, eg rooms containing electronic data processing or electrical equipment.
Deluge Systems: used to protect certain special risks, where there is a possibility that an intense fire will develop very rapidly, eg oil-filled transformer equipment. Deluge systems (sometimes also called “fogging” or “drencher” systems) are usually used to protect relatively small, external risks.