Automatic Sprinkler Systems

The automatic sprinkler systems is the most widely used fire protection system today and have been used to protect lives and property since the late1800’s. They are used in warehousing & distribution centres, schools, aviation & military facilities, power generation applications, commercial & leisure premises, manufacturing plants, residential buildings and many others.

Statistics show that where a fire occurs in a sprinkler protected property, 99% are controlled by the sprinklers alone of which 60% are controlled by 4 sprinkler heads or fewer. As a result, the damage caused from water damage extinguishing a fire is minimal when compared to the volumes of water used should a fire brigade need attend to extinguish the fire. Which would you prefer: 50 litres per minute two minutes after the fire starts and the fire under contained or 1000 litres per minute applied by the brigade after the fire has been burning for 20 minutes and the premises well a blaze?

The fear of “false alarm” where sprinklers activate through accidental discharge is a common concern but is very rare. Accidental discharge figures show that through all causes only 1 – 500,000 (per year of service) occur and as a result of manufacturing defect , 1 in 14,000,000(per year of service).

Through development and the wider usage of automatic sprinklers there are a number of standards which relate to sprinklers:

BS 9251: 2005 “Sprinkler systems for residential and domestic occupancies - Code of practice”.

For all other premises BS EN 12845:2005 (Fixed fire fighting systems - Automatic sprinkler systems - Design, installation and maintenance) and BS 5306:1990 (Fire extinguishing installations and equipment on premises Part 2: Specification for sprinkler systems) are used.
 

Compliance with these Rules is invariably specified by a client/owner if the sprinkler system is being installed at the behest of the insurer or if the insurer is offering a premium discount for the presence of sprinklers. Variations to these could include the use of FM Rules. Factory Mutual (now FM Global) is a US-based insurer which issues its own sprinkler standards for non-residential properties. There are other national and industry standards that may need to be adhered to. For further details please visit our technical library.

Understanding the rules and legislation is vital when designing a sprinkler system. Therefore, using an approved fire contractor such as Argus is important when undertaking a fire protection project. There are many other frequently asked questions about sprinkler systems. As the subject of automatic sprinkler systems is in depth only an overview can be detailed in this section of the Argus website. These are detailed further in our technical library. An overview of systems and components continues below.

Sprinkler systems overview.

Systems are designed to discharge a suitable amount of water for the risk involved as specified under various standards outlined above. Some lower hazard systems can be fed from the towns main where as High hazards usually require pumps and tank. The systems are designed to provide immediate fire defence when a fire occurs to protect lives and minimise material losses in the event of a fire. Fire brigades can take vital minutes to reach the scene, often arriving when the fire is out of control.

The essentials of a sprinkler system are:

• A reliable water supply
• Control valves
• Pumps (if insufficient water pressure present)
• Pipework
• Sprinkler heads

The system activates when the sprinkler head detects heat emitted from a fire. A sprinkler head is a heat-sensitive device which opens to release a spray of water when the heat-sensitive element reaches a specific temperature. Most sprinkler heads installed within the UK are the ‘glass bulb type’. This bulb is filled with a liquid and a small air bubble. As the bulb heats to its operating temperature, it fractures allowing the water to escape. Alternatively, there are “soldered strut” type sprinkler heads where the solder melts at the operating temperature to release the water. The sprinkler head operating temperature is selected to be 30°C above the highest anticipated ambient temperature. Under normal conditions in temperate climates a rating of 68°C or 74°C will be suitable.
 

When the sprinkler head activates, the pressure within system release through the open head and the control valves to opens to allow the flow of water from the town’s main into the system or, initiates the pumping system to maintain a flow of water to the head or heads that are activated. The system is designed to ensure the available water supplies will deliver the appropriate flow and pressure to the sprinkler heads to control or extinguish the fire

There are 5 main types of sprinkler system:

Wet-Pipe Sprinkler Systems are the most common type of system used. The pipe work is constantly charged with water and when the sprinkler head activates water discharges from the sprinkler heads immediately. These systems are appropriate for permanently heated buildings.

Dry-pipe sprinkler installations are appropriate for applications either where there is a danger of the water in the pipes freezing or in situations where there may be temperatures above about 70 degrees c. In a dry-pipe system the pipework downstream of the installation control valve is charged with air which is under sufficient pressure to prevent the entry of water into the delivery pipe work. Once the first sprinkler head operates the compressed air escapes through the head, the control valve opens to allow water to flow into the system pipework.

With Dry-pipe systems there is a time delay in releasing the air from the system before water discharges from the sprinkler heads. For this reason Dry-pipe systems are limited in size, generally to half the size of a wet-pipe system, and in some cases require more flow and pressure from the water supplies to cater for more sprinkler heads operating before water is discharged. For this reason consideration should be given to other means of frost protection, such as trace heating and lagging the sprinkler pipework.

Alternate Wet & Dry Pipe Systems are just that. They operate as either type and allow the premises occupier to protect the premises with a wet-pipe installation in the summer and a dry-pipe installation in winter. The same conditions on the size of the system and the water supplies apply here as for the Dry-system

Tail End Alternate or Tail End Dry-Pipe Systems are basically wet pipe installations in which apart of the system, the tail end (in conditions, for example, where it is liable to freeze), is dry or alternate wet & dry.

Pre-action Sprinkler Systems are primarily considered either where the accidental discharge of water due to mechanical damage to a sprinkler head or pipe is of prime concern or, where a dry-pipe system need to be primed to avoid the delays in operation, size of system and water supply considerations outlined above. The system operates in conjunction with an electrical fire detection system. Operation of the detection system will open the pre-action control valve and prime the system with water. A type 1 Pre-action control valve will not open if a sprinkler head alone operates or is damaged.

The choice of which system to use is determined by the project specific conditions. Therefore choosing an approved fire contractor such as Argus is important when undertaking any fire protection project to ensure compliance to the relevant and required standards.

There is extensive general guidance notes available in the technical library of this website, but we recommend that you contact us for advice regarding your specific project requirements.

The key to success of any project is the quality of the design.

Utilising the latest CAD technology and other software required for the hydraulic calculations our designers make sure that your fire protection system will work in practise as well as theory. Any project design changes can easily be accommodated and the fire system design changed, relatively easily and quickly.