Fixed firefighting equipment These can be split into two categories:

• manually operated such as hose reels and rising mains for use by the fire brigade

• automatically operated such as sprinklers and drenchers.

2.8.2.1 Manually operated systems (a) Hose reels

Hose reels usually comprise about 30m of hose wound onto a metal drum and connected permanently to the mains water supply. Their location should ensure that no part of the building is more than 6 m from the nozzle when the hose is fully run out. Water pressure should be sufficient to produce a 6 m jet of water from the highest hose reel. Hose reels have the advantage over extinguishers in that they can deliver an unlimited supply of water yet still be easy to operate and the nozzles can be adjusted to change from a jet to a spray or shut down completely at will. They should be checked monthly to ensure there are no leaks and that the outlet nozzle is not blocked. Once a year all the hose on the drum should be completely run out and the hose inspected and given an operational test.

(b) Rising main

There are two types of rising main, wet and dry. They are of the same construction with a pipe passing up through the building and having a Fire precautions 4.51

landing valve at each floor level. The landing valve allows the fire brigade to attach their hoses directly to it, saving time in getting water to the seat of the fire. As its name implies, the wet rising main is kept permanently charged with water either from a tank or by a booster pump. A dry rising main is empty with an inlet at its lowest point to which the fire brigade can connect their pump and so charge the main.

2.8.2.2 Automatically operated systems 2.8.2.2.1 Automatic sprinkler systems

Sprinkler systems are designed to provide an automatic means for detecting and extinguishing or controlling a fire in its early stages.

Although their role in the past has been primarily for the protection of buildings they are now having an increasing role in life safety. A

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sprinkler system comprises a range of pipework with regularly spaced sprinkler heads. The sprinkler heads are activated by heat when they discharge water onto the fire, and at the same time the drop in water pressure in the main trips the alarm.

A sprinkler head is an automatic water valve fitted with a deflector plate to give a specific spray pattern. The valve is sealed by a heat sensitive element which is designed to burst at a predetermined temperature. The heat sensitive element is either a specially designed solder seal or a heat sensitive bulb (Figure 2.17). The temperature at which the water is released is indicated by a colour code on the yoke arm for the solder type and by the colour of the liquid in the bulb of the bulb type (Table 2.4). One advantage of a sprinkler system is that only the heads in the vicinity of the fire operate, thereby reducing the extent of the water damage.

Four types of sprinkler system are available: wet pipe, dry pipe, alternate and pre-action. A wet pipe system is the most common where the pipework is filled with water under pressure. When a sprinkler head operates, water immediately discharges through it and continues until the system is turned off. This system is only suitable for buildings where it will not be subject to frost.

A dry pipe system can be used in unheated areas where water in the piping could be susceptible to freezing. Instead of water, the pipework contains air at a pressure which is sufficient to hold a head of water behind a valve which is located in an area not subject to frosts. When a sprinkler head operates, the drop in the air pressure allows that valve to lift releasing water into the pipework and hence to the particular head that has operated. A dry pipe is less efficient than a wet pipe system since there is a time delay before the water is discharged onto the fire.

This time delay can be reduced by the use of accelerator valves that release the contained air.

Table 2.4. Sprinkler head colour codes

Soldered type °C Colour of yoke arm

An alternate system, which is sometimes used in areas that are subject to freezing only during cold weather, allows either wet or dry operation to be selected.

A pre-action system is similar to a dry pipe system but is considered to be more efficient. It is used where an alarm is required in advance of the operation of the sprinkler heads. This is particularly useful in preventing accidental operation of the system. In a pre-action system heat or smoke detectors are installed throughout the protected area. When a detector is actuated an automatic water control valve admits water into the sprinkler pipework where it remains at pressure until a sprinkler head operates.

2.8.2.2.2 Drencher systems

Ensuring adequate firefighting provisions where large quantities of liquid or gaseous flammable materials are handled, e.g. chemical plants, tank farms, loading and off-loading installations, requires very large quantities of water. When a fire occurs in these situations it is often far more important to provide adequate cooling of the installation than it is to extinguish the fire. The vast amounts of water required call for excellent supply arrangements and when used can cause extensive flooding on the site if adequate arrangements have not been made to contain or direct the disposal of the fire water. It should be remembered that fire water is often contaminated by chemicals and its release into natural water courses should be prevented since it can cause severe environmental damage.

A drencher system operates in a similar manner to the pre-action sprinkler system except that the sprinkler heads are open (they have no heat sensitive element) so that on actuation of a separate detector, water is pumped into the pipework and is discharged through all the sprinkler heads.

2.8.2.2.3 Fixed foam installations

Foam installations are provided where there is a risk of flammable liquid fires, for confined spaces where access is difficult and for the total flooding of high-risk spaces. The systems can be automatically operated and may be connected to detector and alarm systems.

2.8.2.2.4 Carbon dioxide systems

Carbon dioxide provides good protection for hazardous plants such as electrical transformers and switchgear and also for computer rooms and control rooms. Carbon dioxide is usually stored as a liquid in large cylinders and connected by a system of pipework to discharge nozzles located in the protected area. Systems can be automatic but usually have a facility to be switched to manual operation in occupied areas. Since carbon dioxide is an asphyxiant, if the system is automatically operated a time delay and alarm must be built in to allow any occupants of the room to escape before carbon dioxide is discharged.

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2.8.2.2.5 Ho/on systems

Halon systems are very similar to those for carbon dioxide except that for a similar risk the storage cylinders would be smaller due the differences in extinguishing action. However, following the Montreal Protocol, halon production in the UK ceased at the end of 1993 although existing installations can continue to be used while the supply of recycled halon lasts. Alternate inert gas products are being developed and will become available.