A wet pipe system is the most common type of fire sprinkler system, in which the sprinkler pipes are constantly charged with water under pressure.

For this reason, it is only suitable for use where there is no danger of frost, i.e. in climates where freezing never occurs or in buildings which are constantly heated during cold periods. Wet-pipe systems should not be considered when ambient temperatures can fall below 4°C (40°F).

The layout of the controlling valves of a typical wet system is shown and it includes the alarm valve, the combined drain and test valve, test valve, pressure gauges and alarm motor isolating valve, strainer, alarm motor and gong.

This type of system is the easiest to design and relatively straightforward to maintain. Wet-pipe systems always contain water under pressure and utilise a series of closed sprinkler heads.

When a fire occurs and produces enough heat to activate one or more sprinklers, the water is discharged immediately onto the fire. A Wet-pipe system should be the first choice of specifiers and designers alike, as they are inherently more reliable and less costly to maintain.

A dry pipe system is one in which pipes are filled with pressurised air or nitrogen, rather than water. The air pressure holds the Dry-pipe valve in a closed position.

Located in a heated space, the dry-pipe valve prevents water from entering the pipe until a fire causes one or more sprinklers to operate. Once this happens, the air escapes and the dry pipe valve opens. Water then enters the pipe network flowing through the open sprinklers onto the fire.

Dry pipe sprinkler systems provide automatic protection in locations where freezing is possible and are typically used in unheated warehouses, exposed loading docks and within commercial freezers.

The sprinkler pipe work of a dry system is installed with a gradual fall to permit drainage of the system. Drain valves at all low parts of the installation are opened periodically to allow drainage of any condensation.

Many people view dry pipe sprinklers as advantageous for protection in areas sensitive to water. This perceived benefit is due to a fear that a damaged wet pipe system will leak while dry pipe systems will not. In these situations, dry pipe systems will generally not offer any advantage over wet pipe systems. Should impact damage happen, there will only be a short discharge delay, i.e. 60 seconds, while air in the piping is released before water flows.

Deluge (spray) systems, as the name implies, deliver large quantities of water over specific areas in a relatively short period of time. These systems are used to protect against rapidly growing and spreading fires, typically involving flammable liquids and solvents etc.

Deluge systems are like automatic sprinkler systems with the exception that all nozzles (sprinkler heads) are open and will discharge water simultaneously when a control valve opens. These systems are designed to protect areas where fire is likely to spread rapidly and/or where cooling of surrounding equipment is necessary.

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A pre-action sprinkler system consists of a sprinkler system and an electrical detection system with pressurised air in the sprinkler pipework and water held back by the pre-action control valve. In the event of the operation of the electrical detection system the pre-action valve operates and allows water into the sprinkler pipework.

Pre-action systems differ from the normal wet systems in that the operation is initiated by an automatic detection system linked to the sprinkler system, and not by the sprinkler itself. Discharge of water can only occur, when, in addition to the detection system a sprinkler head operates. The operation of the detection system allows water to flow from the control valve into the sprinkler distribution network. A typical pre-action system is shown in the demonstration. When the detection device senses a fire, it opens the main valve, allowing water to flow through the pipes before the sprinklers are set off. When the heat activates the sprinklers, water is discharged immediately, as in a wet-pipe system.

In some instances, the pre-action system may be set up with a double interlock whereby pressurised air or nitrogen is added to system piping. The purpose of this feature is two-fold: first to monitor piping for leaks and second to hold water from the system piping in the event of inadvertent detector operation. The most common application for this system type is in freezer warehouses.

Pre-action systems are usually employed in areas that are at risk for serious water damage due to damaged sprinklers and/or piping.

They operate faster than dry systems but tend to be more expensive.

In Early Suppression Fast Response (ESFR) roof/ceiling mounted sprinklers can be used in warehouses in place of in-rack fire sprinkler systems. ESFR provides protection that exceeds that of in-rack systems.

With ESFR sprinkler heads further away from the fire than the sprinkler heads in an in-rack system, how is that possible? The answer lies in the three ways ESFR systems differ from conventional systems: speed, volume and droplet size.

Speed
ESFR sprinkler heads sense a fire and begin spraying water in half the time of conventional heads. The sooner the system starts to fight the fire, the smaller the fire will be – so it is more likely that the ESFR system will be capable of controlling the fire promptly.

Volume
Conventional heads discharge water at a rate of about 90 to 100 Litres per minute (lpm). ESFR heads can discharge water at a rate of 680lpm per minute.

Droplet size
ESFR heads emit larger droplets of water with greater momentum than conventional heads. When extra water is forced through conventional heads, it tends to come out as a mist and a greater percentage evaporates than when conventional heads flow at a normal rate. ESFR heads not only output larger amounts of water, but a greater share of the water reaches the fire, supporting the extinguishing process. Conventional systems are generally not designed to extinguish a fire, but rather to keep it from spreading by ‘wetting’ the area around the fire. These three factors build upon each other to increase ESFR’s efficiency. By detecting the fire sooner, discharging more water and increasing the likelihood of the water reaching the fire due to the larger the droplet size, ESFR systems can compensate for the sprinkler heads located within the storage racking.

Who can use ESFR?
For many (but not all) categories of product, ESFR technology can be used in warehouses with storage that does not exceed 10.7m (35 feet) in overall height and with a ceiling height that averages 12.2m (40 feet) or less. You will need to confirm with your insurance company and local authorities (i.e. fire and building inspectors) that ESFR is appropriate for the product being stored in your facility.

Foam-water sprinkler systems are installed to protect structures, equipment and facilities where a potential hazard for two-dimensional flammable liquid fire exists. These systems can provide prevention, extinguishment, control and/or exposure protection, depending on the application. Typically, foam-water sprinkler systems are installed in aircraft hangars, petrochemical plants, tank farms, fuel-loading facilities and power plants.

Upon activation of the fire detection system, the installation control valve set opens. Foam concentrate, stored in a bladder tank, and water are mixed using a proportioning device located above the Installation control valve. The Foam-Water mixture then enters the installation pipework and is discharged through the spray nozzles over the protected area.

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Wet / Dry riser systems are intended for the use of fire services to provide a readily available means of delivering considerable quantities of water to extinguish or to prevent the spread of fire.

If your fire risk assessment concludes that you may need the intervention of the Fire and Rescue Service to fight a fire, you must ensure that your riser systems or hydrants are working properly. Before installation of dry or wet rising mains, the local authority and the Fire Officer must be consulted to ascertain their exact requirements. Dry risers will be found in buildings more than 18 metres above ground level and in lower buildings which have excessive distances from entrances (>60m). Wet risers can be found in buildings more than 60 metres above ground level.

A Dry riser system consists of valves and pipework enabling the fire service personnel to pump water from Ground Level to the upper floors of a building whereas a wet riser system consists of valves and pipework which are kept permanently charged with water, supplied by dedicated wet riser fire pumps and a water storage tank.

A high-water mist system is a fire protection system which uses very fine water sprays. The small water droplets leave no residue and reduce water damage while being extremely effective in suppressing or extinguishing fires by: cooling both the flame and surrounding gases by evaporation.

Water mist systems are non-toxic and provide a much higher cooling capability.

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Low-pressure water mist systems combine the low water consumption, space-saving installations and other benefits of water mist systems with the price  advantage of sprinkler systems. This uses 50% less water, making it more cost-efficient while reducing water damage. This is a non-toxic solution with an increased cooling capability.