A FIRE ENGINEERING APPROACH IN REDUCING THE DESIGN CAPACITY OF SPRINKLER TANK IN HONG KONG

by

Ronald Wong Abstract Sprinkler system is one of the most effective fire service installations in preventing fire spread in a confined space. All new buildings with commercial, industrial or institutional occupancies are required to install automatic sprinkler system in accordance with Loss Prevention Council (LPC) Rules for Automatic Sprinkler Installations with local modifications. The design capacity of the sprinkler tank can be determined by the Precalculated Method or the Fully Hydraulically Calculated Method. Most of the Authorized Persons (AP) would prefer to choose the Precalculated Method as it is much simple and easy to follow. The minimum duration of water available is 30, 60 & 90 minutes for Light Hazard, Ordinary Hazard and High Hazard respectively. Under the current practice, the storage of water can be reduced by one-third if a direct link from the sprinkler system is connected to the Fire Service Communication Centre. A fire engineering analysis into the activation of sprinkler heads is conducted and the result indicates that the operation time of a sprinkler system may last from a few minutes to a few hours depending on the number of sprinkler heads to be activated. LPC and Singapore Civil Defense Force (SCDF) have proposed that the size of the sprinkler tank can be reduced without affecting the performance of the system by the speedy response from the fire department. Practically, the size of the sprinkler tank can be reduced by almost a half provided that there is no water supply restriction to the town mains of the affected area and the firefighters can respond to the fire scene as indicated in the performance pledge and provide a sufficient flow to the sprinkler inlets.

2

Table of Contents

Page

Abstract 2 Table of Contents 3 Introduction 4 History of Automatic Sprinkler System 6 Requirements for Automatic Sprinkler System in Hong Kong 8 Classification of Occupancies in LPC Rules 12 Water Supplies for Automatic Sprinkler System 14 Design Capacity for Sprinkler Tank 17 Fire Fighting Policy in Hong Kong 21 Theoretical Operation Time for Automatic Sprinkler System 24 Revised Design Capacities in LPC Technical Bulletin 30

Reducing the Size of Sprinkler Tank in Singapore 32 Conclusion 34 Recommendation 36 Appendix I 38 Reference 49

3

Introduction Sprinkler system has universally been recognized as one of the most effective fire extinguishing system in controlling the spread of a fire in a confined space. All new buildings in Hong Kong with commercial, institutional or industrial occupancies must install automatic sprinkler system. Loss Prevention Council (LPC) Rules for Automatic Sprinkler Installations with local modifications are used as guideline for installation, acceptance and maintenance of sprinkler system. In line with the guideline, the system must provide a tank for water storage. The design capacity of this tank depends on several factors and assumptions. According to the LPC Rules, the design capacity of the sprinkler tank can either be obtained from Precalculated Method or Fully Hydraulically Calculated Method. In most of the building projects, the Precalculated Method has preferably been selected by the Authorized Persons (AP) as it is much simpler and straight forward. The classification of hazard groups, the height difference of the highest sprinkler and the lowest sprinkler, water supplies from single ended feed or both ended feed town mains and the provision of direct link to the Fire Service Communication Centre (FSCC) are crucial factors in the determination of suitable design capacity. In recent years, Water Supplies Department (WSD) has provided an excellent service for maintaining the supply of fresh water unrestricted at all times in Hong Kong. Moreover, a good network of street hydrants has been installed in those newly developed regions. As a result, firefighters and fire service installations have a reliable source of water supplies for enhancing their performance in case of fires. Under the current firefighting policy in Hong Kong, the fire cover standards are based on a Risk Categorization System which assigns districts to different risk categories A, B, C, D or E with A being the highest risk and E being the lowest. A performance pledge which provided an indication in the response of the Hong Kong Fire Services Department (HKFSD) to fire incidents had been set up a few years ago. All building fires in built-up areas should be responded in six minutes and between nine to twenty-three minutes to those in areas of dispersed risks and isolated developments. Therefore, plenty of fire stations were built all over the city to ensure that the performance pledge is achievable. It has been stated clearly in the LPC Rules that the flow from town mains to the sprinkler system may be reduced by fire brigade operations. Provided that those high standards of services from the WSD and HKFSD can be maintained in the future and there will not be any major change in the fire cover standards, the design capacity of the sprinkler system may be reduced accordingly.

4

History of Automatic Sprinkler System Water has widely been used as the most common fire extinguishing agent for firefighting and fixed firefighting systems like automatic sprinkler system all over the world as it is readily available and low cost. Due to its strong intermolecular forces (such as hydrogen bonding), water has a high value of specific heat capacity (4186 J / kg K) and latent heat of vaporization which amongst to its excellent extinguishing power. Although the activation of sprinklers in the sprinkler system may not always be able to extinguish the fire, its cooling ability can protect the life safety and structural elements of a sprinkler protected building by containing the fire until it can be extinguished by other means. Automatic sprinkler system has been invented for more than a hundred years. In 1723, the first prototype of automatic fire extinguishing system on was recorded in English history (Puchovsky 1999). It consisted of a cask of water, a chamber of gunpowder, and a system of fuses. In 1852, the perforated pipe system represented the first form of a sprinkler system used in the United States. In 1885, John Wormald of Mutual Fire Insurance Corporation of Manchester, England developed the first set of rules for the installation of automatic sprinkler systems and it was published in London by the Fire Officers Committee (FOC) in September 1888. In 1887, similar rules were prepared in the United States by the Factory Improvement Committee of the New England Insurance Exchange. Since then, the effectiveness of sprinkler systems has been improved with an accelerated rate of technology. As a result, fire insurance companies in many countries offered an annual premium reduction to building owners who installed automatic sprinkler systems to their properties. It has also become a mandatory requirement to install sprinkler system in buildings with high fire load in many countries. United Kingdom and United States have been the leading countries in research and development of automatic sprinkler system. British Standards Institution (BSI) and National Fire Protection Association (NFPA) have developed BS EN 5306: Part 2: 1990 and NFPA 13 as standards for design, installation and maintenance of automatic sprinkler installations for Europe and America respectively. Other countries like Japan, Germany and China have also developed their own standards for automatic sprinkler system.

5

Requirements for Automatic Sprinkler System in Hong Kong HKFSDs requirements for automatic sprinkler system were printed on the Code of Practice for Minimum Fire Service Installations and Equipment (COP). Before 1974, the provisions of sprinkler system followed the FOC Rules (9th Edition). At that time, elevated tank, town main and F. S. inlet were sources of water supplies for sprinkler system. Any two of them were acceptable and found in many old buildings. In 1974, the revised COP adopted the FOC Rules (29th Edition) as the specified standard for general compliance by the building industry in Hong Kong. It stated that the town main alone was not acceptable as a source of water supplies because of the water supply restriction. Thus, a supply tank which could last for at least 30 minutes of water supplies for the sprinkler system should be provided in addition to the town main. Moreover, sprinkler systems were required for nearly all commercial and industrial buildings. In 1985, the responsibilities of FOC for automatic sprinkler installation passed to the Loss Prevention Council (LPC) on its formation. In 1990, the BSI embodied in full the requirements of the FOC Rules and produced a new British Standard, BS 5306: Part 2: 1990. Fire extinguishing installations and equipment in buildings. Specification for sprinkler systems. The combination of the new standard and the LPC Technical Bulletins formed the new LPC Rules for Automatic Sprinkler Installations and replaced the 29th Edition of the FOC Rules. In 1995, HKFSD adopt the new LPC Rules for local application with modifications specified in Lists One to Four annexed to the FSD Circular Letter No. 4/94. According to the current COP (June 1998), a Sprinkler System is defined 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.

Moreover, COP states the acceptance testing of the sprinkler system as follows:

The system should be tested in accordance with the Loss Prevention Council Rules on Automatic Sprinkler Installations (with suitable modifications pertinent to Hong Kong), or other standards and requirements as may be prescribed by the Director of Fire Services on account of the specific features of the system.

As specified in the current COP, all premises and areas of special risks are divided into 44 different categories of which 11 of these premises and areas of special risks mandatory require the provision of sprinkler system. These premises are as follows: (i) Basements which exceed 230 m2 of usable floor area; (ii) Bowling alleys; (iii) Commercial buildings low rise; (iv) Commercial buildings high rise; (v) Garages; (vi) Hotel low rise; (vii) Hotel high rise; (viii) Industrial/godown buildings low rise;

6

(ix) Industrial/godown buildings high rise; (x) Institutional buildings low rise; and (xi) Institutional buildings high rise. Although a sprinkler system is designed to deal with solid-fuel fires, it can hold a flammable-liquid fire in check and to extinguish an oil fire by deluge sprinklers or by water spray. Thus, it also stated in the COP that other premises and areas may require automatic fixed installations using water which may include Sprinklers, Drenchers, Deluge or Water Spray System by the risk of the premises and areas and these premises include: (i) Aircraft maintenance and repair facilities; (ii) Audio/visual production facilities; (iii) Boiler rooms; (iv) Bulk fuel storage; (v) Chemical manufacturing/processing plants; (vi) Cold storage areas (Group I) major (of and over 140m3 capacity); (vii) Cold storage areas (Group II); (viii) Container terminal yards and freight stations; (ix) Dangerous goods stores; (x) Petro-chemical complexes; (xi) Railway marshalling yards; (xii) Substation/Switchgear buildings; (xiii) Telephone distribution equipment, computer installations and similar installations. Nevertheless, many buildings are multi-occupancies in Hong Kong. These buildings are classified as composite buildings and the fire services installations and equipment required for each of the various usages of a composite building must confirm to the relevant categories of the current COP. Thus, for a composite building where ground floor used as commercial and upper floor as domestic, a sprinkler system is required for the protection of the commercial portion of the building.

7

Classification of Occupancies in LPC Rules In LPC Rules for Automatic Sprinkler Installation (2000), occupancies or parts of thereof are classified into three major hazard groups as follows: (i) Light Hazard (LH)

z In non-industrial occupancies where the quantity and combustibility of the contents are low, rooms and corridors not more than 126m2 in area and bounded by elements of construction with a fire resistance of not less than 30 min.

z Minimum duration of water available: 30 minutes. z No room may have more than six sprinklers. z Rooms larger than 126m2 or with walls of lower fire resistance are classified as

ordinary hazard, group I. z Examples of LH occupancies: Most areas of hospitals, hotels, institutions, libraries,

museums, nursing homes, office buildings, prisons, schools etc. (ii) Ordinary Hazard (OH)

z Ordinary Hazard (OH) is subdivided into: Ordinary Hazard, group I (OH I); Ordinary Hazard, group II (OH II); Ordinary Hazard, group III (OH III); and Ordinary Hazard, group III Special (OH IIIS).

z Minimum duration of water available: 60 minutes.In non-industrial occupancies, rooms which exceed the limits for LH are classified as OH I.

z Commercial and industrial occupancies involving the handling, processing and storage of mainly ordinary combustibles materials, which are unlikely to develop intensely burning fires in the initial stages are classified as either: OH I; OH II; OH III; or OH IIIS.

z OH I occupancies include: Restaurants and cafes, offices (not high rise) not meeting the requirements for LH.

z OH II occupancies include: Chemical works, bakeries and biscuits factories etc. z OH III occupancies include: Departmental stores and retail shops etc. z OH IIIS occupancies include: Theatres, film and television studios etc.

(iii) High Hazard (HH)

z Commercial and industrial occupancies having abnormal fire loads are classified as high hazard.

z Minimum duration of water available: 90 minutes. z HH is subdivided into:

process high hazards; high-piled storage hazards; potable spirit storage hazards; and oil and flammable liquid hazards.

8

Water Supplies for Automatic Sprinkler Installation in Hong Kong According to the Water Supplies Department (2004), more than 70 percent of flesh water in Hong Kong is supplied from Dongjiang (the East River). The long-term water supply agreement with Guangdong authorities signed in 1989 has secured sufficient water supplies to meet Hong Kong's needs well into the 21st century. It can provide with a maximum designed capacity of 1,100 million cubic metres per year. In 2002, the annual supply has been raised to 760 million cubic metres. Apart from this, water collected in a vast network of catchments and impounding reservoirs locally from rainfall makes up the rest of the water supply to Hong Kong. Therefore, water supply restriction as back in 1970s is no longer required provided that the current arrangements can be maintained in the future. In Hong Kong, a dual connection from the Government unrestricted supply ring main is provided for sprinkler system situated in the recognized waterworks unrestricted industrial supply zone. Twin connections (one from an unrestricted supply main and one from a distribution main) are provided for any sprinkler system situated outside the recognized unrestricted industrial supply zone, where practicable. In case if it is not practical to connect the sprinkler system to an unrestricted supply main, the provision of fire service tank to serve as secondary source for the fire service installation is required by the FSD. Either a single or dual ended connection can be given to serve the fire service tank of secondary source. Where direct connections to sprinkler system are to be from the Government mains, an additional butterfly valve is installed at a point on the supply pipe before the fire service inlet and as close as possible to the control valves of the connections (Water Supplies Department, 2005). Also, it is important to note that no part of any sprinkler system supplied from the Government mains is used for supplying any other services including other fire service installations. As stated in the LPC Rules, it is essential to ensure the continuity and reliability of water supplies. Nevertheless, the flow from town mains to the sprinkler system may be reduced by fire brigade operations. Currently, twelve types of water supplies methods are considered acceptable. However, not all of them are acceptable in Hong Kong. Single supply is considered by the FSD as unreliable water source. Only a superior water supply or duplicate water supplies with a sprinkler water storage tank can meet the requirement. Hence, the most common types of water supplies in Hong Kong are superior supply using gravity tank and superior supply using suction pumps. Superior supply using gravity tank can easily be found in government housing estate blocks where the ground floor and the lower floor are used as commercial and/or institutional purposes and the upper floors as domestic. The sprinkler tank is located on the roof of the building. Superior supply using suction pumps can be found in most of the buildings where wholly or partially being used as commercial, industrial, or institutional purposes. The sprinkler tank can be located at any level of the building.

9

Figure 1 Superior supply using gravity tank

Sprinkler Inlet

Elevated Tank

Figure 2 Superior supply using suction pumps

Sprinkler Inlet

Suction Tank

10

Design Capacity for Sprinkler System In LPC rules, two methods namely (i) Precalculated Method and (ii) Fully Hydraulically Calculated Method are used for pipework sizing of the sprinkler system and determining the design capacity of the sprinkler tank. Since most of the APs prefer to choose the Precalculated Method in Hong Kong because it is much simpler to derive than the Fully Hydraulically Calculated Method, the latter is not going to be discussed in this chapter. For the Precalculated Method, several factors must be determined in order to determine the design capacity of the sprinkler tank and they are as follows: (i) Hazard Group(LH, OH or HH); (ii) Difference between the height of the highest sprinkler and the lowest sprinkler (within 15,

30 or 45 m); (iii) Single ended feed or both ended feed; (iv) For single ended feed which is not dependent on inflow, whether direct link to Fire

Service Communication Centre is provided. As suggested in the FSD Circular Letter No.4/96 Part II paragraph 2.2.2,

a single ended feed from town main supplying suction tank will be accepted provided the tank has a capacity not less than two-thirds of the full holding capacity required for the particular hazard class and the sprinkler alarm is directly connected to the Fire Services Communication Centre.

This local reduction in sprinkler tank size implies that the time for the minimum duration of water availability would be decreased by 1/3 of the original minimum duration of water availability.

Hazard Group Original Minimum duration of water availability (minutes)

Minimum duration of water availability (minutes) (For single ended feed and not dependent on inflow with direct link connected to FSCC)

LH 30 20 OH 60 40 HH 90 60

Table 1 Minimum Duration of Water Availability for LH, OH & HH

11

For the Precalculated Method, Table 21, Table 22 and Table 25 of the LPC Rules are used to determine the design density of a sprinkler system. Hereunder is a combination of the three tables together with the local size reduction arrangement.

Capacity of Water Tank for Sprinkler System (LPC Rules)

Single end supply (not dependant on

inflow)

Both end supply

(dependent on inflow)

Hazard Group

Height of highest

sprinkler above lowest

sprinkler not

exceeding (m)

Design

capacity (m3)

LPC Table

21 & 22

Direct link

provided (m3)

2/3*Design Capacity FSD CL

4/96 Part II 2.2.2

Design capacity (m3)

LPC Table 25

15 9 6 30 10 6.7

Light Hazard

45 11 7.3

2.5 or, as given in table 21 or 24

less 0.03f, whichever is the greater 15 55 37 30 70 47

I

45 80 54

25 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 105 70 30 125 84

II

45 140 94

50 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 135 90 30 160 107

III

45 185 124

75 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 160 107

OH

IIIS 30 185 124

100 or, as given in table 22 or 24

less 0.06f, whichever is the greater High Hazard

Not Accepted FSD CL 4/96 Part II Para 2.2.1(b)

See LPC Table 23, 24 & 25

Table 2 Capacity of Water Tank for Sprinkler System Provided that the inflow of the both ended feed town main is sufficient, the design capacity of the sprinkler tank may be reduced as illustrated in the example below.

12

Example: For OH III where height of highest and the lowest sprinkler does not exceed 15 m, Required design capacity with single end supply = 135 m3 Allowed minimum design capacity with both ended supply = 75 m3 Difference = 135 75 m3 = 60 m3 Required inflow rate to compensate for a smaller tank = 60 / 0.06 = 1000 l / min for 60 minutes operation Thus, the AP must confirm with the WSD at the initial stage that an inflow rate of 1000 l /min could be obtained. If the inflow rate is not up to 1000 l / min, a larger sprinkler tank will required.

13

Fire Fighting Policy in Hong Kong In a fire engineers point of view, a fire can behave in a much different manner in the pre-flashover stage and the post-flashover stage. Therefore, it is crucial that a fire can be extinguished or under control within the first few minutes of flaming combustion prior to the occurrence of flashover. Under such circumstances, the speedy response from the HKFSD is always essential. A mechanism has been set up by the Government to monitor the response from the department and this is the performance pledge. Within most areas, a six minutes standard attendance time is applicable for the building fires in Hong Kong. The six minutes can be broken down as follows: z The first minute would be required for the alarm of fire to be received by FSCC and

transmitted the information to the appropriate fire station. z The following four-minute target attendance time based on the traveling time of an

appliance from a fire station to the entrance of the building in which a fire has been reported to be used as a criterion for the siting of fire stations in built-up Urban Areas and certain part of New Territories.

z The final minute would be required for the connection of fire hoses to street hydrant and other preliminary/imminent work after the fire appliances reached the street level of the building on fire.

In general, the fire cover standards are developed on the basis of a graded fire risk system. All the districts in Hong Kong are graded by fire risk into five categories (A, B, C, D & E), with the existing six minutes standard attendance time kept for the two highest risk categories, but with the standard response time for the three lower categories reduced to 9, 15 and 23 minutes respectively. If the risk category of a district is upgraded, it will be necessary for the HKFSD to reassess whether fire appliances to be dispatched from the nearest existing fire station can respond to all the area of the district within the appropriate graded response time. It may be the case that a new fire station is required in a newly developed area, e.g. Tai Chik Sha. The graded response time and traveling time element for each category are summarized as follows:

Risk Category Graded response time in mins.

Traveling time element in mins.

A Congested central built-up areas 6 4 B Less congested inner built-up areas 6 4 C Areas of dispersed risk in outer

suburban and rural areas 9 7

D Areas of highly dispersed but accessible by road

15 13

E Outlying and remote areas not accessible by road

23 21

Table 3 Classification of Risk Category and Graded Response Time in Hong Kong

14

When this policy is compared with the standards of fire cover in other cities, it is clear that HKFSD have maintained a reputable achievement within the performance pledge.

City Response Time for Fire Incident Hong Kong 6 minutes (94.2% in 2003)1 London 1st appliance : 5 minutes (92.6% in 2003)2

2nd appliance : 5 minutes 3rd appliance : 8 minutes

New York Average 4 minutes 21 seconds in 20043 Singapore 8 minutes (85% in 2003)4 Macau 6 minutes (95% in 2003)5

Table 4 Response Time for Fire Incident in Other Cities

1 Hong Kong Fire Services Review 2002-2003, Hong Kong Fire Services Department

2 Progress against Best Value Performance Plan (April 2003 March 2004), London Fire & Emergency Planning Authority

3 Citywide Performance Indicator (01/01/04 12/31/04), New York City Fire Department

4 Singapore Civil Defense Force Annual Report 2004, Singapore Civil Defense Force

5 Performance Pledge, Macau Fire Service (http://www.fsm.gov.mo/cb/promise_cb.htm)

15

Theoretical Operation Time for Sprinkler System Since most of the occupancies who required to install automatic sprinkler system in Hong Kong fall into the Ordinary Hazard only, Light Hazard and High Hazard will not be discussed in this chapter. In LPC Rules, the design density is defined as the minimum density of discharge, in mm/min of water, for which a sprinkler installation is designed. The assumed maximum area of operation (AMAO) is defined as the maximum area over which it is assumed, for design purposes, that sprinklers will operate in a fire. The discharge (fd) of a specified group of sprinklers, in L/min is determined by multiplying the minimum design density and the AMAO. Example: For OH I, Discharge, fd = Minimum design density X AMAO = 5 mm/min X 72 m2 = 6.0 X 10-3 m3/s

Hazard Group Minimum design density

(mm min-1)

AMAO (m2)

Discharge rate, fd (m3 s-1)

OH I OH II OH III OH IIIS

5 5 5 5

72 144 216 360

6.0 X 10-3 12 X 10-3 18 X 10-3 30 X 10-3

Table 5 Discharge Rate for Ordinary Hazard Group I, II, III & IIIS For the supply of water, it is assumed that there are only two sources, i.e. the sprinkler storage tank and the refill from the town main. The refilling rate has been specified in the COP paragraph 5.27 as:

If the tank is situated at upper level of building and a transfer pump is required to relay water to the tank, the pump capacity shall be able to refill the tank to its full capacity within 6 hours.

Example: For OH I, Refilling rate, fr = Design capacity / 6 hours = 55 m3 / 6 X 3600 s = 2.55 X 10-3 m3 s-1

16

Hazard Group Height of

highest sprinkler above lowest sprinkler not exceeding (m)

Design capacity, Vc (m3) (Single end supply, not dependant on inflow)

Refilling rate, fr (m3 s-1)

OH I

15 30 45

55 70 80

2.55 X 10-3 3.24 X 10-3 3.70 X 10-3

OH II 15 30 45

105 125 140

4.86 X 10-3 5.79 X 10-3 6.48 X 10-3

OH III 15 30 45

135 160 185

6.25 X 10-3 7.41 X 10-3 8.56 X 10-3

OH IIIS 15 30

160 185

7.41 X 10-3 8.56 X 10-3

Table 6 Refilling Rate for Ordinary Hazard Group I, II, III & IIIS The supply of water will be based on: (i) The design capacity, Vc, (ii) The refilling rate, fr; and (iii) The time available to refill the storage tank, Tr. The demand of water will be based on: (iv) The number of sprinkler to be activated, N (N = 1, 2, 3, ); (v) The discharging rate, fd; and (vi) The time required to discharge the storage tank, Td. Since the supply quantity of water equals the demand quantity of water, the equation can be written as: Vc + fr Tr = N fd Td - Equation 1 But Tr = Td = T, T = Vc / (N fd fr) - Equation 2 Example: For OH I (Highest sprinkler Lowest sprinkler not exceeding 15 m), If N = 1, then T = 55 / (1 X 6.0 X 10-3 - 2.55 X 10-3) = 15942 s = 265.7 min i.e. If only one sprinkler head activated in this specific system, the sprinkler system can run for 265.7 minutes.

17

Assumed maximum number of sprinkler to be activated in a sprinkler system in a fire, Nm = AMAO / Maximum area coverage per sprinkler Example: For OH I, Nm = 72 m2 / 12 m2 Nm = 6 Hazard Group AMAO Max. area

coverage per sprinkler (Table 70, LPC Rules)

Assumed maximum number of sprinkler heads to be activated, Nm

OH I 72 12 6 OH II 144 12 12 OH III 216 12 18 OH IIIS 360 12 30 Table 7 Assumed Maximum Number of Sprinkler Heads to be Activated in Ordinary Hazard

Group I, II, III & IIIS The theoretical operation time of sprinkler system for Ordinary Hazard Group I, II, III & IIIS is calculated and attached at Appendix I. The result illustrated that a sprinkler system of any OH group may use up the water stored in the sprinkler tank from a few minutes to a few hours when the sprinkler heads activated. When the value of N increases, it takes much less time to consume the water in the sprinkler tank. Thus, the number of sprinkler heads to be activated in a fire is critical to the size of the sprinkler tank. Under normal circumstances, most of the fire can be under control by the activation of a few sprinkler heads. In case if the rate of fire spread is quicker than the rate of cooling by the water from the initially activated sprinkler heads, more sprinkler heads will be activated. This process will continue until all the water in the sprinkler tank has been used up. In other words, if the firefighting can respond to the fire promptly and replenish the sprinkler tank with adequate flow, the sprinkler system will be able to continue its function to control/extinguish the fire. Chow (2000) calculates the thermal activation time, ta to a set of sprinklers to be activated by a fire of heat release rate, Q. The results of the calculations are as follows:

18

Activation Time ta/s RTI = 42 (ms)1/2 RTI = 350 (ms)1/2

Sprinkler head position away from the fire axis (m)

Minimum heat release rate Qmin/kW

Ultra-fast t2-fire

Fast t2-fire

Medium t2-fire

Slow t2-fire

Ultra-fast t2-fire

Fast t2-fire

Medium t2-fire

Slow t2-fire

0 64 38 66 119 224 73 116 187 310 3 354 88 160 304 590 150 241 404 704 4.24 501 102 186 353 686 177 282 469 816 6 708 120 219 417 812 221 334 553 963 Table 8 Activation Time (Extracted from W. K. CHOW On the Sprinkler Tank Size and Fast Response Sprinkler Head) Since LPC Rules have specified that Ordinary Hazard are occupancies involving the handling, processing and storage of mainly ordinary combustibles materials, which are unlikely to develop intensely burning fires in the initial stages, it is reasonable to predict it as a fast t2-fire. As illustrated in the above table that it may take almost two minutes for the second nearest sprinkler to activate (160 s) after the activation of the first sprinkler head (66 s) for a fast response type sprinkler. More sprinkler heads may be activated if the fire is still out of control but they will only be activated one after another. This research has proven that the actual time required for a sprinkler system to use up its sprinkler tank is even longer than the result calculated from Equation 2.

19

Revised Design Capacities in LPC Technical Bulletin In LPC Technical Bulletin TB24: 1997: 1, the requirements for water storage capacities for OH and HH sprinkler systems were revised and superseded the relevant requirements of BS Clause 16. As stated in this bulletin, the volume of the stored water supplies was reduced but without changing the effectiveness of the sprinkler system. The measures to reduce water storage capacities were conditional on there being adequate safeguards which would ensure the satisfactory performance of the system. Conditions which may be specified to reduce water capacity requirements for sprinkler installations are as follows: Condition abbreviation

Condition

A On operation of the sprinkler installation, an alarm shall be automatically transmitted to an LPCB approved central station for fire alarm signaling.

H5 The maximum height of the roof or ceiling sprinklers above the floor does not exceed 5 m.

M The sprinkler installation is regularly maintained in accordance with TB6 and is the subject of a maintenance contract with an LPCB certificated or registered company in accordance with LPS 1048.

R Quick response sprinklers are used in all rooms, interconnecting rooms or corridors with floor areas exceeding the AMAO for the installation. Where intermediate level sprinklers are used in storage racks, these shall be quick response with quick response sprinklers at the ceiling or roof.

Table 9 Conditions to Reduce Water Capacity Requirements for Sprinkler Installations (Extracted from LPC Technical Bulletin TB24: 1997: 1) The revised design capacities, where tank is not dependent on inflow, for Ordinary Hazard precalculated installations are as follows:

20

Column 1 Column 2 Column 3 Column 4 Column 5

Design Capacity (V) Group Height of highest sprinkler above lowest sprinkler not exceeding

Wet pipe installations satisfying conditions A, H5, M, and R

Other wet pipe and Type 2 pre-action installations

All other installations

I M 15 30 45

m3 30 35 40

m3 55 70 80

m3 55 70 80

II 15 30 45

55 60 70

105 125 140

105 125 140

III (restricted storage)

15 30 45

70 80 95

135 160 185

135 160 185

III (storage)

15 30 45

Use capacity given in column 4

135 160 185

Not recommended

III S 15 30

Use capacity given in column 4

160 185

160 185

Table 10 Revised Design Capacity of Sprinkler Tank for OH (Extracted from LPC Technical Bulletin TB24: 1997: 1) Once the conditions as stated in Table 9 have been fulfilled, the size of the sprinkler tank can be reduced drastically. This reduction in the size of sprinkler tank is even greater than the one suggested by the HKFSD when the sprinkler system is directly linked to FSCC.

21

Reducing the Size of Sprinkler Tank in Singapore In 2004, the Singapore Civil Defense Force (SCDF) announced a new guideline for a reduction of the size of the sprinkler tank in order to facilitate the installation of sprinkler systems in existing buildings that are not already protected by sprinkler system and that are in the classification of OH I, II & III and new buildings with similar hazards. With the timely response by the SCDF, the proposed design capacity should be adequate for the sprinkler system to control the fire spread till the arrival and the intervention by firefighters. However, there are a few restrictions to the new guideline and they are as follows: z It should only be applicable to buildings of habitable height not exceeding 60 m. z It does not apply to any building housing storage risks and chemical processes. The inflow is considered reliable if the water inflow rate at the inlet to the sprinkler tank is not less than 1.0 m3 / min and the inlet point is located at reduced level 125 m or below. The inflow is considered unreliable if the water inflow rate at the inlet to the sprinkler tank is less than 1.0 m3 / min or the inlet point is located at reduced level greater than 125 m. PUB approved float valve that is designed to open fully when there is a drop in water level to immediately replenish the tank. Also, the minimum design capacity of the sprinkler tank should be capable of providing 30 minutes adequate water supply for the sprinkler pump operation. For sprinkler system with a constant reliable inflow from the PUB mains to replenish the sprinkler tank, the effective tank storage capacities for the various hazard categories shall be as follows :- Hazard Group AMAO (m2) System demand

( l / min) Proposed minimum effective capacity of storage tank

OH 1 72 540 12.5 OH 2 144 1000 25.0 OH 3 216 1350 37.5

Table 11 Effective Tank Capacity for Reliable Inflow For sprinkler system with an unreliable inflow from the PUB mains to replenish the sprinkler tank, the effective tank storage capacities for the various hazard categories shall be as follows :- Hazard Group AMAO (m2) System demand

( l / min) Proposed minimum effective capacity of storage tank

OH 1 72 540 16.2 OH 2 144 1000 30.0 OH 3 216 1350 40.5

Table 12 Effective Tank Capacity for Unreliable Inflow

22

Comparing with the revised design capacities in LPC Technical Bulletin, the Singapores new guideline proposes a further reduction in the size of storage tank for the sprinkler system.

23

Conclusion All new buildings which include commercial, institutional or industrial occupancies are required to install automatic sprinkler system. LPC Rules with local modifications are the standards to be followed for installation, acceptance and maintenance of such system. The design capacity of sprinkler system can be determined by the Precalculated Method or the Fully Hydraulically Calculated Method. LPC Rules state that there should be a minimum of 30, 60 & 90 minutes of water supplies for LH, OH & HH respectively. HKFSD reduced the requirement of water supplies by 1/3 provided that a direct link from the sprinkler system is connected to the FSCC. As the HKFSD has committed a performance pledge to the public by achieving the graded response times for fires in buildings in six minutes for the built-up areas and nine to twenty-three minutes for areas of dispersed risks and isolated development, firefighters are capable of attacking the fire and supplying an inflow to the sprinkler inlet within a few minutes after the arrival to the incident. From a risk analysis viewpoint, it is clear that if the fire cover standards remain unchanged and the high standard of performance pledge can be maintained by the HKFSD, the size of the sprinkler tank can have a further reduction. LPC Technical Bulletin TB24: 1997 has stated clearly that the design density of the sprinkler tank could be reduced by almost half of the original size. However, several conditions have to be fulfilled before the reduction. A more flexible approach has been adopted by the SCDF. The size of the sprinkler system could be reduced even further subject to an adequate inflow. In view of the current situation in Hong Kong, a more pragmatic approach should be adopted by allowing a reasonable reduction of the design capacity of the sprinkler tank. A list of recommendations from this research is prepared in the next chapter.

24

Recommendations A revised table of design capacity of the sprinkler tank is prepared as follows:

Design Capacity of Water Tank for Sprinkler System

Single end supply (not dependant on

inflow)

Both end supply

(dependent on inflow)

Hazard Group

Height of highest

sprinkler above lowest

sprinkler not

exceeding (m)

Design

capacity (m3)

LPC Table

21 & 22

Direct link

provided (m3)

Design capacity (m3)

LPC Table 25

15 9 6* 30 10 6.7*

Light Hazard

45 11 7.3*

2.5 or, as given in table 21 or 24

less 0.03f, whichever is the greater 15 55 30^ 30 70 35^

I

45 80 40^

25 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 105 55^ 30 125 60^

II

45 140 70^

50 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 135 70^ 30 160 80^

III

45 185 95^

75 or, as given in table 22 or 24 less

0.06f, whichever is the greater 15 160 107*

OH

IIIS 30 185 124*

100 or, as given in table 22 or 24

less 0.06f, whichever is the greater High Hazard

Not Accepted FSD CL 4/96 Part II Para 2.2.1(b)

See LPC Table 23, 24 & 25

* 2/3 X Design Capacity FSD CL 4/96 Part II 2.2.2 ^ Under special conditions : DL, H5, M, FR & RC. Table 13 Revised Design Capacity of Water Tank for Sprinkler System

25

Condition abbreviation

Condition

DL On operation of the sprinkler installation, a direct link should be connected to FSCC.

H5 The maximum height of the roof or ceiling sprinklers above the floor does not exceed 5 m.

M The sprinkler installation is maintained in efficient working order at all times and shall be inspected by a registered fire service installation contractor at least once every 12 months.

FR Fast response sprinklers are used in all rooms, interconnecting rooms or corridors with floor areas exceeding the AMAO for the installation. Where intermediate level sprinklers are used in storage racks, these shall be quick response with quick response sprinklers at the ceiling or roof.

RC The location where the sprinkler system to be installed should be under Risk Category A, B or C of the Graded Fire Risk System.

HKFSD should constantly review the fire cover standards and the achievement of the performance pledge so as to keep up with the proposed water tank reduction strategy in sprinkler system. Nevertheless, a review to the existing standards for automatic sprinkler system should be conducted in a regular basis.

26

Appendix I Theoretical Operation Time of Sprinkler System for OH Group I, II, III & IIIS For OH I,

Height Vc N fd fr T (s) T (min) 15 55 1 0.006 0.00255 15942.03 265.7005 15 55 2 0.006 0.00255 5820.106 97.00176 15 55 3 0.006 0.00255 3559.871 59.33118 15 55 4 0.006 0.00255 2564.103 42.73504 15 55 5 0.006 0.00255 2003.643 33.39405 15 55 6 0.006 0.00255 1644.245 27.40409 30 70 1 0.006 0.00324 25362.32 422.7053 30 70 2 0.006 0.00324 7990.868 133.1811 30 70 3 0.006 0.00324 4742.547 79.04246 30 70 4 0.006 0.00324 3371.869 56.19782 30 70 5 0.006 0.00324 2615.845 43.59741 30 70 6 0.006 0.00324 2136.752 35.61254 45 80 1 0.006 0.0037 34782.61 579.7101 45 80 2 0.006 0.0037 9638.554 160.6426 45 80 3 0.006 0.0037 5594.406 93.24009 45 80 4 0.006 0.0037 3940.887 65.68144 45 80 5 0.006 0.0037 3041.825 50.69708 45 80 6 0.006 0.0037 2476.78 41.27967

27

No. of sprinkler head activated vs Time for OH I

0

100

200

300

400

500

600

700

1 2 3 4 5 6No. of sprinkler head activated

Time

(min) OH I (15 m)

OH I (30 m)OH I (45 m)

28

For OH II,

Height Vc N fd fr T (s) T (min) 15 105 1 0.012 0.00486 14705.88 245.09815 105 2 0.012 0.00486 5485.893 91.4315615 105 3 0.012 0.00486 3371.869 56.1978215 105 4 0.012 0.00486 2433.936 40.565615 105 5 0.012 0.00486 1904.244 31.737415 105 6 0.012 0.00486 1563.896 26.0649415 105 7 0.012 0.00486 1326.763 22.1127115 105 8 0.012 0.00486 1152.074 19.2012315 105 9 0.012 0.00486 1018.034 16.9672315 105 10 0.012 0.00486 911.9333 15.1988915 105 11 0.012 0.00486 825.8613 13.7643515 105 12 0.012 0.00486 754.6356 12.5772630 125 1 0.012 0.00579 20128.82 335.480430 125 2 0.012 0.00579 6864.36 114.40630 125 3 0.012 0.00579 4137.703 68.9617130 125 4 0.012 0.00579 2961.384 49.3563930 125 5 0.012 0.00579 2305.848 38.4307930 125 6 0.012 0.00579 1887.932 31.4655430 125 7 0.012 0.00579 1598.261 26.6376830 125 8 0.012 0.00579 1385.656 23.0942630 125 9 0.012 0.00579 1222.972 20.3828730 125 10 0.012 0.00579 1094.475 18.2412530 125 11 0.012 0.00579 990.4128 16.5068830 125 12 0.012 0.00579 904.4208 15.0736845 140 1 0.012 0.00648 25362.32 422.705345 140 2 0.012 0.00648 7990.868 133.181145 140 3 0.012 0.00648 4742.547 79.0424645 140 4 0.012 0.00648 3371.869 56.1978245 140 5 0.012 0.00648 2615.845 43.5974145 140 6 0.012 0.00648 2136.752 35.6125445 140 7 0.012 0.00648 1805.986 30.0997645 140 8 0.012 0.00648 1563.896 26.0649445 140 9 0.012 0.00648 1379.039 22.9839845 140 10 0.012 0.00648 1233.263 20.5543845 140 11 0.012 0.00648 1115.36 18.5893445 140 12 0.012 0.00648 1018.034 16.96723

29

No. of sprinkler head activated vs Time for OH II

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12

No. of sprinkler head activated

Time

(min) OH II (15 m)

OH II (30 m)OH II (45 m)

30

For OH III,

Height Vc N fd fr T (s) T (min) 15 135 1 0.018 0.00625 11489.36 191.489415 135 2 0.018 0.00625 4537.815 75.6302515 135 3 0.018 0.00625 2827.225 47.1204215 135 4 0.018 0.00625 2053.232 34.2205315 135 5 0.018 0.00625 1611.94 26.8656715 135 6 0.018 0.00625 1326.781 22.1130215 135 7 0.018 0.00625 1127.349 18.7891415 135 8 0.018 0.00625 980.0363 16.3339415 135 9 0.018 0.00625 866.7737 14.4462315 135 10 0.018 0.00625 776.9784 12.9496415 135 11 0.018 0.00625 704.0417 11.7340315 135 12 0.018 0.00625 643.6234 10.7270615 135 13 0.018 0.00625 592.7552 9.87925415 135 14 0.018 0.00625 549.3388 9.15564615 135 15 0.018 0.00625 511.8483 8.53080615 135 16 0.018 0.00625 479.1482 7.98580315 135 17 0.018 0.00625 450.3753 7.50625515 135 18 0.018 0.00625 424.8623 7.08103930 160 1 0.018 0.00741 15108.59 251.809930 160 2 0.018 0.00741 5596.362 93.2727130 160 3 0.018 0.00741 3434.213 57.2368930 160 4 0.018 0.00741 2477.164 41.2860630 160 5 0.018 0.00741 1937.281 32.2880130 160 6 0.018 0.00741 1590.615 26.5102630 160 7 0.018 0.00741 1349.186 22.4864430 160 8 0.018 0.00741 1171.389 19.5231530 160 9 0.018 0.00741 1034.996 17.2499330 160 10 0.018 0.00741 927.0526 15.4508830 160 11 0.018 0.00741 839.4984 13.9916430 160 12 0.018 0.00741 767.055 12.7842530 160 13 0.018 0.00741 706.1212 11.7686930 160 14 0.018 0.00741 654.1559 10.902630 160 15 0.018 0.00741 609.3149 10.1552530 160 16 0.018 0.00741 570.227 9.50378430 160 17 0.018 0.00741 535.8518 8.93086430 160 18 0.018 0.00741 505.3855 8.423092

31

Height Vc N fd fr T (s) T (min) 45 185 1 0.018 0.00856 19597.46 326.624345 185 2 0.018 0.00856 6741.983 112.366445 185 3 0.018 0.00856 4071.303 67.8550545 185 4 0.018 0.00856 2916.141 48.6023545 185 5 0.018 0.00856 2271.611 37.8601845 185 6 0.018 0.00856 1860.418 31.0069745 185 7 0.018 0.00856 1575.272 26.2545445 185 8 0.018 0.00856 1365.918 22.7653145 185 9 0.018 0.00856 1205.683 20.0947245 185 10 0.018 0.00856 1079.095 17.9849145 185 11 0.018 0.00856 976.5625 16.2760445 185 12 0.018 0.00856 891.8241 14.8637445 185 13 0.018 0.00856 820.6175 13.6769645 185 14 0.018 0.00856 759.9408 12.6656845 185 15 0.018 0.00856 707.6193 11.7936645 185 16 0.018 0.00856 662.0384 11.0339745 185 17 0.018 0.00856 621.9742 10.3662445 185 18 0.018 0.00856 586.4824 9.774706

32

No.of sprinkler head activated vs Time for OH III

0

50

100

150

200

250

300

350

1 3 5 7 9 11 13 15 17No. of sprinkler head activated

Time

(min) OH III (15 m)

OH III (30 m)OH III (45 m)

33

For OH IIIS,

Height Vc N fd fr T (s) T (min) 15 160 1 0.03 0.00741 7082.78 118.046315 160 2 0.03 0.00741 3042.403 50.7067215 160 3 0.03 0.00741 1937.281 32.2880115 160 4 0.03 0.00741 1421.085 23.6847615 160 5 0.03 0.00741 1122.098 18.7016415 160 6 0.03 0.00741 927.0526 15.4508815 160 7 0.03 0.00741 789.7724 13.1628715 160 8 0.03 0.00741 687.9058 11.465115 160 9 0.03 0.00741 609.3149 10.1552515 160 10 0.03 0.00741 546.8403 9.11400515 160 11 0.03 0.00741 495.9856 8.26642715 160 12 0.03 0.00741 453.7848 7.56308115 160 13 0.03 0.00741 418.2023 6.97003815 160 14 0.03 0.00741 387.7942 6.46323615 160 15 0.03 0.00741 361.5084 6.0251415 160 16 0.03 0.00741 338.5599 5.64266415 160 17 0.03 0.00741 318.3509 5.30584915 160 18 0.03 0.00741 300.4187 5.00697815 160 19 0.03 0.00741 284.3989 4.73998215 160 20 0.03 0.00741 270.0012 4.5000215 160 21 0.03 0.00741 256.991 4.28318315 160 22 0.03 0.00741 245.1769 4.08628215 160 23 0.03 0.00741 234.4013 3.90668915 160 24 0.03 0.00741 224.533 3.74221715 160 25 0.03 0.00741 215.4621 3.59103515 160 26 0.03 0.00741 207.0956 3.45159415 160 27 0.03 0.00741 199.3546 3.32257615 160 28 0.03 0.00741 192.1714 3.20285715 160 29 0.03 0.00741 185.4879 3.09146515 160 30 0.03 0.00741 179.2536 2.987561

34

Height Vc N fd fr T (s) T (min) 30 185 1 0.03 0.00856 8628.731 143.812230 185 2 0.03 0.00856 3596.423 59.9403830 185 3 0.03 0.00856 2271.611 37.8601830 185 4 0.03 0.00856 1660.086 27.668130 185 5 0.03 0.00856 1307.975 21.7995930 185 6 0.03 0.00856 1079.095 17.9849130 185 7 0.03 0.00856 918.3876 15.3064630 185 8 0.03 0.00856 799.3432 13.3223930 185 9 0.03 0.00856 707.6193 11.7936630 185 10 0.03 0.00856 634.779 10.5796530 185 11 0.03 0.00856 575.5351 9.59225230 185 12 0.03 0.00856 526.4056 8.77342730 185 13 0.03 0.00856 485.0042 8.08340330 185 14 0.03 0.00856 449.6403 7.49400530 185 15 0.03 0.00856 419.083 6.98471730 185 16 0.03 0.00856 392.4147 6.54024530 185 17 0.03 0.00856 368.9375 6.14895830 185 18 0.03 0.00856 348.1108 5.80184730 185 19 0.03 0.00856 329.5098 5.49183130 185 20 0.03 0.00856 312.7959 5.21326530 185 21 0.03 0.00856 297.6957 4.96159530 185 22 0.03 0.00856 283.9862 4.73310430 185 23 0.03 0.00856 271.4839 4.52473230 185 24 0.03 0.00856 260.036 4.33393330 185 25 0.03 0.00856 249.5145 4.15857430 185 26 0.03 0.00856 239.8113 3.99685430 185 27 0.03 0.00856 230.8345 3.84724230 185 28 0.03 0.00856 222.5055 3.70842630 185 29 0.03 0.00856 214.7567 3.57927830 185 30 0.03 0.00856 207.5294 3.458823

35

No. of sprinkler head activated vs Time for OH IIIS

0

20

40

60

80

100

120

140

160

1 4 7 10 13 16 19 22 25 28No. of sprinkler head activated

Time

(min)

OH IIIS (15 m)OH IIIS (30 m)

36

Reference Chow, W. K. On the Sprinkler Tank Size and Fast Response Sprinkler Heads, International Journal on Engineering Performance-Based Fire Codes, Vol. 2 No. 4 pp.124 126 (2000). Fire Protection Association. LPC Rules for Automatic Sprinkler Installations, London, UK, (2000). Hong Kong Fire Services Department. FSD Circular Letter No.4/94 (1994). Hong Kong Fire Services Department. FSD Circular Letter No.4/96 (1994). Hong Kong Fire Services Department. Code of Practice for Minimum Fire Service Installations and Equipment and Inspection, Testing and Maintenance of Installations and Equipment (1998). Hong Kong Fire Services Department. Hong Kong Fire Services Review 2002 2003 (2004). Planning Department. Final Report on Implementation of Data Alignment Measures for the Alignment of Planning, Lands and Public Works Data (2004). (Retrieved via Internet Explorer) http://www.hplb.gov.hk/eng/publication/dam.htm Puchovsky M. T. Automatic Sprinkler Systems Handbook, National Fire Protection Association, Inc (1999). Singapore Civil Defense Force. H1 Guidelines on Reduced Water Storage for Automatic Fire Sprinkler Systems in Buildings (2004). (Retrieved via Internet Explorer) http://www.scdf.gov.sg/html/info/pdf/Appendix%20H.pdf Water Supplies Department. Hong Kong Waterworks Standard Requirements for Plumbing Installation in Building (2004). (Retrieved via Internet Explorer) http://www.wsd.gov.hk/en/html/plumb/index.htm Water Supplies Department. Water Supplies Department Annual Report 2003 - 2004 (2005). (Retrieved via Internet Explorer) http://www.wsd.gov.hk/en/html/pdf/rpt0304/contents.html