Automatic sprinklers — water supplies

Automatic sprinklers — water supplies

1.General 

Automatic sprinkler systems must be provided with a suitable and acceptable water supply. It must have a pressure and flow characteristic not less than that specified in the BS/LPC Rules. It must be automatic, thoroughly reliable and not subject to either frost or drought conditions that could seriously affect the supply. The supply should be under the control of the occupier of the building containing the 

installation or, where this is not practicable, the right of use of the supply must be suitably guaranteed. 

Close consultation must take place with
Water UK and/or the local suppliers, specifically to identify 

what supplies are available which will impact on the system design. 

The water must be free from any matter in suspension, which would be liable to cause accumulation in 

the system pipework. The use of salt or brackish water is not normally allowed. In special circum 

stances, where there is no suitable fresh water source available, consideration may be given to the use 

of salt or brackish water provided that the installation is normally charged with fresh water 

2.2 Types of water supply 

Water supplies are graded into three categories: 

Single, superior and duplicate. 

2.2.1 Single supply a single supply must be: 

(I) A town main capable of supplying the necessary pressure and flow requirements. 

(II) An automatic booster pump drawing water from the town main capable of supplying the 

necessary pressure and flow requirements. 

(III) An automatic suction pump drawing water either from a suction tank complying with 

BS/LPC Rules or a virtually inexhaustible source, i.e. river, lake, canal. 

2.2.2 Superior supply 

These will vary according to whether the system is a low’ or ‘high’ rise and will depend on the 

occupancy hazard rating. 

For low rise systems — a superior supply shall be: 

(I) A town main; or 

(II) Two automatic suction pumps from a suction tank; or 

(III) Two automatic booster pumps; or 

(IV) An elevated private reservoir; or 

(V) A gravity tank; or 

(VI) A pressure tank (for low hazard or ordinary hazards Group I occupancies only). 

For high rise systems — a superior supply shall be: 

(I) A gravity tank; or 

(II) An automatic suction pump arrangement in which each installation is served by either a 

separate pump or separate stage of a multi stage pump. 

2.2.3 Duplicate supply 

A duplicate supply shall include at least one of the suitable combinations given in Table 2.1 with the 

supply pipes from each source joined into a common trunk main as close as possible to the protect ed 

premises. 

A common trunk main may serve more than one installation but shall not:

(I) Traverse ground not under the control of the user; or 

(II) Be under a public roadway.

3. Details of particular supplies 

3.1 Town mains 

The mains water supply must be fed from both ends by mains, each of which must be capable of sustaining the required pressure and flow. The main at each end must not directly be dependent on a common trunk main in the town main system, and this must be fed from more than one source. 

The main must be capable of furnishing, at all times of the day and night, the minimum pressure and flow requirements for the appropriate category of risk. 

Duplicated connections from the main must be carried separately to the premises, which contain the sprinkler installation, and there should be a stop valve on the main between the two branches. if it is not possible to provide duplicate connections, special consideration may be given to the waiving of the requirement if there is a stop valve (secured open) on the town main immediately on each side of a single branch connection. 

In the event of a fracture or partial breakdown of the main, operation of the stop valves ensures that the supply is maintained by that part of the main, which is still functioning. 

3.2 Suction and booster pumps 

If a water supply is available with no head or only under limited pressure, a pump may be used to feed water into the installation at the required pres sure. in such cases, it is stipulated that the pumps providing a superior supply shall draw water from either a suction tank with full holding capacity equal to that required for the particular hazard class, or a secondary suction tank of smaller capacity with 

automatic inflow, provided it meets with BS/LPC requirements

The most important provisions relating to automatic pumps are as follow: 

(I) With an automatic pump supply consisting of two automatic pumps, a compression ignition (diesel) engine may drive at least one with each pump capable of providing the necessary pressure and flow. Where both pumps are electrically driven, they must either be powered from a supply independent of the other or automatically change over to an alternative supply should the first supply fail. With three automatic pumps, which may be a combination of electric and diesel, any two pumps together must be capable of providing the necessary 

pressure and flow independently. In both arrangements they must be capable of operating in parallel, i.e. with similar pressure and flow characteristics.

(II) Pumps should be housed at ground level, either in a separate incombustible building or in a 

room in the same building protected by a 2-hour fire resisting-structure. The room should be directly accessible from the out side and should be as small as practicable, to discourage it being used for other purposes. The building or room containing the pumps should be 

maintained at a temperature not below 4°C. In the ease of diesel pump rooms, the room should be well ventilatcd, sprinklered and 

maintained at a minimum temperature of 10°C. 

(III) Automatic priming equipment must be provided where necessary to ensure that the pumps will be fully primed with water at all times. 

(IV) The performance characteristics of the pumps should be such that the pressure falls progressively with the rate of demand. They must be capable of providing the rate of flow and pressure required at the highest and most remote parts of the protected premises. The output must be so controlled that there is not an excessive rate of discharge at the lowest level in areas close to the installation valves. To meet these conditions pumps must have performance characteristics complying with the requirements laid down. 

(V) Where permitted by the water authority, a pump may draw directly from a town main, provided the latter is capable of supplying water at all times at the maximum rated out put of the pump. 

(VI) The pump should be hilly operational within 30 seconds after starting. 

(VII) The pump should have a direct drive and must start automatically. Means should be provided for manual starting and once start ed the pump must run continuously until stopped manually. 

(VIII) Where an automatic pump forms the sole supply, a fall in water pressure in the sprinkler system, which is intended to initiate the automatic starting of the pump, shall at the same time 

provide a visual and audible alarm at some suitable installation, e.g. in the gate- house or by the installation control valves. 

(IX) A test for automatic starting of the pump must be carried out weekly. 

(X) Pumps must be driven either by an electrical motor or an approved compression ignition type of engine. The electric supply must be obtained from a reliable source, preferably from a public supply. Where a compression engine is used, provision must be made for two separate methods of engine starting, i.e. automatic or manual control, although a single starter motor is acceptable. 

(XI) Any switches to the electric power feed to motors must be clearly labelled: ‘Sprinkler pump motor supply — not to be switched off in the event of fire’. 

3.3 Elevated private reservoir — minimum supply capacity 

This is defined as similar to a ground reservoir but situated at a higher level than the premises to be protected. Certain conditions regarding capacity must be complied with before this type of reservoir can be used as a source of supply to a sprinkler installation. The minimum capacity ranges from 9m³- 

875m³ depending on the class of system installed; this is on the understanding that the stored water is used entirely for the sprinkler system. 

Where such reservoirs serve other than sprinkler installations, e.g. water for trade and domestic purposes, there must be a constant capacity of at least: 

• 500m’ in light hazard categories 

• 1,000m in ordinary hazard categories 

• 1,000m plus additional storage capacity of between 223 in High Hazard categories, 

depending whether the sprinkler sys tern is wet or alternate. 

In certain cases smaller capacities may be accept ed but only with the express approval of the LPC. 

3.4 Gravity tank 

A gravity tank is defined as a purpose built container. It is erected on the site of the protected premises at such a height as to provide the requisite pressure and flow condition at the installation valves. The tank must be adequately protected against freezing and, where it is not enclosed with in a tower, the top must he covered so as to exclude daylight and solid matter. 

The main provisions are: 

(I) The tank must have a minimum capacity of 9m for the light hazard class rising to

1,095m for the High Hazard. Should the capacity of the tank exceed these requirements, it is permissible to draw upon the surplus for other purposes by means of a side-outlet pipe, which must be positioned above the level of the quantity to he reserved for the sprinkler installation. 

(II) The quantity of the water required for the sprinkler installation must be automatically maintained. If the tank forms part of the sole supply to the system, the supply to the tank must he capable of refilling it to the required capacity within six hours. 

(III) The use of one tank to supply installations in two or more buildings under separate owner ship is not allowed. 

(IV) The tank must be fitted with a depth indicator, a permanent ladder or stairway to permit access and the water must be kept clean and free from sediment. 

3.5 Pressure tanks 

A pressure tank is a cylindrical steel vessel with convex ends containing water under pressure. The pressure tank is an acceptable superior water supply for not more than one sprinkler system of Low Hazard or Ordinary Hazard Group I categories only, provided that: 

(a) the water capacity is not less than: 

• Sole supply: 

   (a) 7m³ for Low Hazard 

   (b) 23m³ for Ordinary Hazard Group I 

• Duplicate supply: 

    (a) 7m³ for Low Hazard 

    (b) 15m³ for Ordinary Hazard Group I 

(2) there is an approved arrangement for maintaining automatically the required air pres sure and water level into the tank under non-fire conditions. 

The general requirements for a pressure tank arc: 

(I) It must be housed in a readily acceptable position in a sprinkler protected building of incombustible construction used for no other purpose. The tank must be adequately protected against mechanical damage. The temperature of the room should be maintained above 40°C. 

(II) When used as a single water supply, the tank must he provided with an approved arrangement for maintaining automatically the required air pressure and water level in the tank under non-fire conditions. The arrangement should include an approved warning system to indicate failure of the devices to restore the correct pressure and water level. This arrangement is also advocated in cases where the tank provides the duplicate supply. 

(III) The tank must be fitted with air pressure gauges and a gauge glass to show the level of the water. Stop valves and back pressure valves must be provided on both the water and air supply connections to the tank and they must be fitted as close to the tank as possible (Figure 2.1). 

(IV) Where a pressure tank forms the sole supply to the installation, connections are not allowed to be taken from the supply for any purpose other than sprinklers. If it forms one source of duplicate supply, a pipe not exceeding 50mm may be taken from the combined water supply main to supply hydraulic hose reels for firefighting purposes only, subject to the pressure being replenished automatically as in (II) above. 

The maximum standing air pressure for pressure tanks is 10 bar. The air capacity should not be less than one third of the capacity of the tank when full. 

4. Pressure and flow requirements 

The BS/LPC Rules lay down the minimum requirements for pressure and flow in any particular 

sprinkler system. These will vary with the risk category. 

4.1 Low hazard and ordinary hazard classes 

For low hazard and ordinary hazard classes, the required pressure at the installation control valve is made up of: 

(I) A nominal pressure figure for a given rate of flow (see Table 2.2 on next page); plus 

(II) A calculated pressure figure (based on the difference in height between the highest sprinkler and the valve).

4.2 High Hazard Category 

In the first case of High Hazard Category, specific tables of figures are laid down by the BS/LPC 

Rules. The point of these tables is to ensure that the water supply is capable of providing the required 

flow and pressure at the level of the highest sprinkler in the High Hazard Category portion of the 

premises. The supply must meet the necessary density of discharge and AAMO specified for that 

particular class of occupancy. 

2.5 Proving of water supplies 

In the case of town mains, elevated private reservoirs and gravity tanks, facilities must be provided to 

enable provided tests to be carried out at the valves on each installation to verify that the water supply 

satisfies the requirements of pressure and flow specified for each hazard class. Water supplies from 

automatic pumps and pressure tanks are designed to meet the pressure and flow conditions appropriate 

to the hazard class and accordingly it is not necessary to require practical flow tests in these instances. 

Figure 2.1 Pressure tank and town main with back pressure valves.

6 . Fire brigade inlets

Sprinkler installations fed solely from water supplies of limited capacity such as a pressure tank, gravity tank or pump suction tank should, if possible and with the water authority’s permission, be fitted with a fire brigade inlet connection. This is to enable the brigades to pump water into the
installation by using their own equipment. The fitting of such inlets to other installations is a strong recommendation to ensure protection under practically all circumstances.