23.     Sprinkler System

23.0     General

COP-FSI defines "sprinkler systems" as "A system designed to discharge water under pressure from sprinkler heads (detecting devices) at / or near the point of origin of the fire and to sound an alarm."

23.1     General Concepts on Sprinkler Systems

23.1.1     Brief History of Sprinkler Development

Major A Stewart Harrison of the First Engineer Volunteers of London invented the first sprinkler in 1864.  However it was until 1874 when Henry S Parmelee of Connecticut of USA produced the first widely used automatic sprinkler with heat sensitive device, that sprinklers became widely used for fire protection.  Throughout this 125 years, many rules, codes, regulations and standards have been produced for automatic sprinkler installations, firstly started by the fire insurance associations and later by national authorities.  New sprinklers such as Early Suppression Fast Response Sprinklers have also emerged. The fire insurance company offers an annual premium reduction to the building owner for a properly installed with an automatic sprinkler system.  This premium reduction could be as high as 45%, provided that other fire safety features such as compartmentation, portable fire extinguishing equipment etc. as required by the insurance company, are also installed.  This annual premium reduction, together with the much less anticipated loss in case of fire, help encourage the building owner to spend an initial amount of money to install sprinkler systems.  A sprinkler system is usually about 1% to 1.5% of the total building cost, or 3% to 5% of the total electrical and mechanical services installation cost.

The UK and US have always been the leading countries in sprinkler research and development.  In recent years West Germany and Japan also contribute substantially in the sprinkler industry. The sprinkler rules used in Hong Kong are primarily Loss Prevention Council (LPC, UK) Rules for Automatic Sprinkler Installations, which comprise BS5306 Part 2 and LPC Technical Bulletins.

Occasionally the following sprinkler rules are also used: - National Fire Code 13-Standard for the Installation of Sprinkler Systems published by the National Fire Protection Association, U S A - Loss Prevention Data 2-8N-Installation of Sprinkler Systems, published by Factory Mutual Engineering Corporation of USA

23.1.2     The components of a Sprinkler System

The sprinkler systems are designed to deal mainly with solid-fuel fires, but can serve also to hold a flammable-liquid fire in check and to extinguish some oil fires (e.g. transformer oil fires) by deluge sprinklers, by purely using water.  With suitable foam concentrate added to the water, its fire fighting capability on oil fires can be greatly enhanced. Each system is designed for its particular function, and its features may vary widely according to the purpose.  In general, a system will consist of the following items: (Fig 25.1.2a)

A water storage capacity or adequate running supply, to feed the system. An adequate method of pumping water from the supply to the system. Distribution pipework capable of conveying all the water required to feed the

sprinkler heads, without unnecessary pressure losses. A sprinkler installation valve connected to a hydraulic motor alarm gong to give an

audible mechanical water motor alarm when the valve opens to allow water to flow to the sprinklers discharging water.

A series of distributor heads (i.e. sprinklers - close / open type; open jet nozzles) capable of passing the design flow rates of water and distributing the water as a spray, over the area to be protected.

A detector, or detector system, capable of actuating the fire fighting / protection system.  The detector can be the sprinkler itself or other detection device / system.

Other features include flow detectors, pressure switches for starting pumps, and control / signal monitoring alarm panels etc.  The sprinkler schematic diagram for a high rise building (Fig 25.1.2b) also helps explain these features.  Note the difference in location of sprinkler installation valves and the pressure switches for controlling pumps for high rise sprinkler installation (The highest sprinkler is more than 45m from the lowest sprinkler in the building) and low rise (within 45m.....) sprinkler installations.

See this link for some installations.

23.1.3     The Fire Hazards

Sprinkler systems are designed for three main classes of hazards, which are described in the LPC Rules as:-

Light Hazard (LH) Ordinary Hazard (OH) High Hazard (HH)

These hazards are further subdivided as follows:

LH - No subdivision OH Group I, II, III, III Special (IIIS) HH-Process HH, high-piled storage hazards, potable spirit storage hazards, oil and

flammable liquid hazards

The types of occupancy covered by each class are listed in Sections 5.2, 5.3 and 5.4 of the LPC Rules, highlighted as follows:

Light Hazard (LH) In non-industrial occupancies where the quantity and combustibility of the contents are low, rooms and corridors not more than 126 sq. m. in area and bounded by elements of construction with a fire resistance of not less than 30 min shall be classified as light hazard.

No room may have more than six sprinklers.

Rooms larger than 126 sq. m. or with walls of lower fire resistance are classified as ordinary hazard, group I.

LH occupancies include hospitals, hotels, museums, libraries, other institutional buildings, offices.

Ordinary Hazard (OH) In non-industrial occupancies, rooms which exceed the limits specified for light-hazard classification shall be classified as ordinary hazard, group I. Commercial and industrial occupancies involving the handling, processing and storage of mainly ordinary combustible materials, which are unlikely to develop intensely burning fires in the initial stages, shall be classified as OHI, II, III, IIIS.

OHI occupancies include: restaurants, cafes, manufacturing processes with largely non-combustible products, e.g. abrasive wheel manufacturers, breweries, dairies, etc. OHII occupancies include: retail shops (with up to fifty employees), biscuit manufacturers, some chemical works, engineering works, potteries, tobacco factories. OHIII occupancies include: manufacturing processes of a greater hazard than Group II, but still not especially hazardous, e.g. aircraft, boots and shoes, carpets, clothing, corn and provender, paper goods, plastics (but not foamed plastics), warehouses (where storage is not above specified heights). OHIIIS occupancies include: cotton mills (processes preparatory to spinning), distilleries, match factories.

HH - Process Hazards: 4 Types (see LPC Rules) Aircraft hangars, firework manufacturers, manufacturers of foamed plastics and foamed rubber goods, paint and varnish, etc.

HH - High Piled Storage Hazards  

Category I Certain ordinary combustibles stored in bulk, in pallets or on racking, to heights exceeding 4m.

Category II

Various combustible goods stored to heights, exceeding 3m, e.g. baled cork, chipboard, alcohols and lacquers in cans, non foamed plastics, etc., on racks or in pallets.

Category III

Foamed plastics and foamed rubber products generally, celluloid, asphalt paper (vertical) rubber goods, etc., stored to heights exceeding 2.1m.

Category Offcuts and random pieces of foamed plastics and foamed

IV rubber, etc., stored to heights exceeding 1.2m.

23.1.4     Design Water Densities

Sprinkler systems are designed to give a design density of water discharge according to the category of hazard, and to maintain this density over certain specified minimum area, for a certain minimum period.

The water supplies available, the pumping capacity and the distribution pipework must therefore be designed to achieve the above minimum performance requirements for the appropriate hazard classes, summarised as follows:-  

HazardDesign Water Density

* Minimum Area (sq.m) 

Minimum duration of water availability

LH  2.25 mm/min. 84 sq.m 30 min.

OHI, II, III, IIIS

5.0 mm/min. 72, 144, 216 sq.m 60 min.

HH (Process)7.5 to 12.5 mm / min.

260 sq.m 90 min.

HH (Storage)7.5 to 30.0 mm/min.

260 to 300 sq.m 90 min.

Note:      * This minimum area is defined in LPC Rules (BS5306: Part 2 - Section 14) as AMAO - Assumed Maximum Area of Operation, and minimum duration of water availability is expressed in Table 24 of BS5306: Part 2.

23.1.5     Water tank sizes The effective full holding capacity for sprinkler water storage tanks for initial design reference are as follows (Check the Rules for exact sizes), if the city water supply is of single-end-feed in Hong Kong, i.e. water supplied from one mid-level reservoir:-  

LIGHT Hazard Class  

Height of highest sprinkler above lowest sprinkler not exceeding   (m)

Minimum capacity   (m3)

15 30 45

9 10 11

ORDINARY Hazard Class

Group Class

Height of highest sprinkler above lowest sprinkler not exceeding  (m)

Minimum capacity  (m3)

I15 30 45

55 70 80

II15 30 45

105 125 140

III15 30 45

135 160 185

III (Special)

15 30

160 185

HIGH Hazard Class  

Design density   mm / min  Minimum capacity   (m3)

7.5 10.0 12.5

225 275 350

15.0 17.5 20.0

425 450 575

22.5 25.0 27.5 30.0

650 725 800 875

However if the city water supply to the sprinkler tank is of double-end-feed, i.e. water supplied from 2 mid-level reservoirs in HKSAR, then the effective sprinkler water storage capacity can be reduced as follows:  

HAZARD Class

Minimum capacity(with inflow)  cu.mMaximum period of inflow for suction tanks (mins)

Light 2.5 30

Ordinary Group  I  II III  III (S)

25 50 75 100

60 60 60 60

HighNot less than minimum capacity stated in the above table (i.e. the earlier table)

90

With this reduction in capacity, there shall be an inflow from the city main, for that maximum period of inflow; with the inflow = [required amount of water flow rate to the sprinkler system X minimum period of duration of water availability stated in para.23. 1.4 MINUS  the actual effective water capacity ] / the maximum period of inflow.

For example:

For OHIII, if the water flow rate required is 3600 l/min., the maximum period of inflow for the suction tank is 60 minutes, and the effective water storage is 90 cu.m; then the required water inflow in case of fire = [3600 litre/min x 60 min - 90,000 litre] / 60 min = 3599 litre/min, with inflow to last for 60 minutes.

Note that the effective water capacity is the amount of water that can be used effectively inside a tank without having the least sign of occurance of a vortex that could draw air into the water being conveyed to the pump.  For this purpose, a certain portion of  internal volume of the tank cannot be included in the effective capacity calculation.  Refer to the Sprinkler Rules for the details for ascertaining the effective water capacity.

23.1.6     The various sprinkler systems (See http://www.reliablesprinkler.com/sprinkler.htm)

The following systems are described in detailed in the LPC Rules.  

System Use

a. Wet Pipe System - all pipework filled with water (most widely installed type) 

Office, department store etc. for non-frozen normal temperature conditions.(See system schematic diagram at http://arch.hku.hk/teaching/intgtech/113.htm)

b. Dry Pipe System (with water under pressure below the valves)

Used where the system pipework may be subjected to freezing temperatures at any time of the year, or where the temperature conditions are artificially maintained close to or below freezing point such as in cold stores, fur vaults etc. or where the temperature is maintained above 70oC as in drying ovens etc.

c. Alternative wet and dry pipe system (a standard sprinkler system embodying a Composite Alarm Valve or a combination set comprising a Wet Alarm Valve and Dry Pipe Valve).

During the "Winter" period the system piepwork is normally charged with air under pressure, and the system below the valve with water under pressure. During the "Summer" period the Dry Pipe Valve is "decommissioned" and the system pipework is charged with water under pressure, operating as a standard Wet Pipe System.

d. Wet pipe or alternate wet and dry pipe system incorporating tail end dry pipe system.

Tail end for cold (frost) conditions and hot areas such as ovens.  Rarely applicable in Hong Kong.

e. Wet pipe system incorporating tail end alternate systems.

Tail end protected areas do not frost in certain time of the year.

f. Deluge sprinkler system (a system of

For industrial processes where simultaneous discharge of water is necessary e.g. oil filled

open sprayers or nozzles, controlled by a quick opening Deluge Valve which is activated by a system of heat detectors or sealed sprinklers installed in the same area as the open sprayers or nozzles).

transformer, oil tank cooling.

23.1.7     Sprinklers

A sprinkler (close nozzle type) is a nozzle set off after the heat sensing element (fusible alloy or glass bulb) is released from its normally tensioned location by the heat of the environment.  It serves dual purposes as a heat sensing device and a fire fighting device by discharging water.  Nearly all fires in sprinklered buildings are either extinguished or controlled by sprinklers.  Human intervention on the fire scene is essential after sprinkler discharge for ensuring that the fire is completely extinguished and will not burn back, the fire / water damage is minimised - (salvage work).

LPC (Loss Prevention Council) approves sprinklers, and issues.  A List of Approved Automatic Sprinkler Equipment which contains the approved sprinklers. The discharge patterns and philosophy of conventional spray and sidewall sprinklers are different (Fig 23.1.7a).

Sprinkler type, discharge pattern, temperature rating, and speed of response to fire, are key elements in classifying sprinklers (See http://www.reliablesprinkler.com/sprinkler.htm).

LPC performs about 20 tests for sprinklers before approving them.  These tests include bore check, checking crush load of glass bulb, thermal testing, pressure testing etc.

23.1.8     Other Components Other components include:

Pipework - See Section 5 of LPC Rules (i.e. Section 5 of BS5306: Part 2) . Water flow detector and pressure switch installed at sprinkler installation valve and at

electrically monitored subsidiary stop valve (LPC Rule 20.1.4 and Fig. TB.13.F1) to give remote indication at the Fire Control Room / Point with sprinkler flow detector signal to be connected to HKFSD Control Centre for automatic reporting of fire.

The sprinkler installation valve set and alarm gong (Fig 23.1.8a). Pumps and tanks to be provided in accordance with Section 4 of LPC Rules to suit the

occupancies defined in Section 1 of LPC Rules. Pumps starting devices (Fig 23.1.8b).

23.1.9     A summary of key features of sprinkler systems

a. Classes of systems

- Light hazard (LH) - Ordinary hazard: subdivided into four groups

Group I                (OH1) Group II               (OH2) Group III              (OH3) Group III Special  (OH3S)

- High hazard   (HH)

b. Water source - acceptable water sources includes:

- town mains - elevated private reservoir - gravity tank - town main, automatic pump with tanks - automatic pump drawing water from river, sea

c. Installation control valve / sprinkler valve / deluge valve for deluge system

- controlling water entering the installation - sound the alarm when sprinkler head opens - allow drainage of water for testing and maintenance

d. Pipework

- riser (vertical pipe) - main distribution pipe:- with an electrically monitored subsidiary stope valve (i.e. a gate valve) connecting this pipe to the riser - distribution pipe, connecting to the main distribution pipe - range pipe, connected to the distribution pipe

e. Sprinkler heads

- must be of an approved type and must NOT be altered, and NOT painted by interior decorators - two categories: fusible solder     : a glass bulb to be ruptured by the expansion of a contained liquid at high surrounding air temperatures - Rating Colour of Bulb Colour of Yoke

57oC orange68oC red uncoloured (68 to 74oC)79oC yellow93oC green  white(93 to 100oC)

141oC blue  blue182oC mauve  yellow227 / 288oC black  red (227oC)

f. Fire services inlet (i.e. Sprinkler Inlet for sprinkler system)g. Spacing arrangement for sprinkler head

Standard spacing of sprinkler heads (See fig 23.1.9) S = design spacing of sprinklers on range pipes

maximum 4.6 m for LH maximum 4.0m for OH maximum 3.7m for HH

D = distance between rows of sprinklers values same as S

S X D = 21m2 or less for LH     12m2 or less for OH     9m2 or less for HH

For staggered arrangement of sprinkler heads, where it is desirable to space sprinklers more than the stipulated values for OH system on the range pipes. S = design spacing of sprinklers on range pipes    = maximum 4.6m D = distance between adjacent rows of sprinklers     = maximum 4.0m

h. Positioning of Sprinklers

Sprinklers should preferably be located between 75mm and 150mm below ceilings and roofs.  Where this is not practicable sprinklers may be installed at lower levels provided the deflectors of the sprinklers are not more than a.     300mm below the underside of combustible ceilings and roofs; or b.     450mm below the underside of fire-resisting ceilings and roofs. There must be a clear space of 300mm below the level of a deflector within a radius of 600mm from each sprinkler.

i. The sprinkler system for an office is commonly a wet sprinkler system (Note: Therefore a wet sprinkler alarm valve is used) with the entire system filled with water.  A jockey pump normally pushes the water pressure higher than the actual operation pressure for fighting fires.  Bursting of a sprinkler, with water discharging via a 10mm diameter nozzle – LH, and 15mm diameter nozzle – OH, will lower the system pressure to a pressure state that the jockey pump cannot maintain, causing the duty main pump to operate. The standby main pump will operate when the duty main pump cannot work.

23.1.10     Reference

LPC Rules for Automatic Sprinkler Installations - published by the Loss Prevention, UK.  LPC Rules comprise BS5306: Part 2 (Fire extinguishing installations and equipment on premises.  Part 2.  Specification for sprinkler systems), and LPC Technical Bulletins (TB).  Both BS5306: Part 2 and TBs are updated / added from time to time.  (The address of LPC is: Melrose Avenue, Borehamwood, Hertfordshire WD6 2BJ, UK.)

LPC List of Approved Fire and Security Products and Services.  Annual publication. Nash P.  The essentials of sprinkler and other water spray fire protection systems.  Building Research Establishment Current Paper CP79/75.  Department of Environment UK, August 1975. Nash P.  Young R A.  Automatic sprinkler systems for fire protection.  2nd Edition.   Paramount Publishing Limited.  1991.  (HKU Main Lib. 628.9252 N2) A paper by  K P Cheung on sprinkler system design and operation for high rise buildings.