Fire water system for process industries

“Despite water is the most important medium for fire protection, the issue of fire water system was not a high priority for most industrial processing facilities. Adequate fire water supply is essential to the operation of water based fire protection system.” – R. R. Nair

Introduction
Water is the most important medium for Fire Fighting. In spite of all technical advances, water is the cheapest, most efficient and environmentally friendly fire extinguishing medium. No amount of firefighting appliances or equipment would be much use, if sufficient quantities of water, under required pressure were not available for firefighting. Industries that process large quantities of highly flammable liquids must be protected by well-designed and properly installed hydrant systems. The design of firewater system for plants that process and handle large quantities of flammable products, such as petrochemicals, chemicals, fertilizers, etc. should take into consideration several important factors like water requirement, storage capacity, hydraulics, hydrant layout, fire pumps, monitors and sprinklers. The designers should ensure availability of adequate firewater in all parts of the entire plant; process units, product storage tanks, loading racks, buildings, etc.

Despite water is the most important medium for fire protection, the issue of fire water system was not a high priority for most industrial processing facilities. However, this aspect of fire protection has recently become a point of focus for many regulatory authorities which have consequently elevated its importance to these facilities. Adequate fire water supply is essential to the operation of a water based fire protection system. Yet, many of the occupancies are not aware that their supply may be insufficient for an optimal performance. This article will highlight the importance of fire water system for process industry.

Fire Water Supply and Storage
A good source of sufficient quantity of water supply is a basic necessity of hydrant system. Many plants handling large quantity of hydrocarbons such as petroleum refineries (See Fig 1) are located along waterways such as sea, river or lake, so that firewater availability is guaranteed. Plants that are not located near waterways will have to depend upon municipal water system, well water or both and these plants must ensure adequate firewater storage. Plants that depend on Municipal or well water should carefully consider their water requirements and have storage capacity readily available all the time, since it would not be possible to draw large quantity in a short time. A plant located near a waterway also needs water storage. Water has to be pumped by pumps driven by electric drive to the plant, and then it would be advisable to provide required firewater, since jetty pumps could fail during power outage. For this purpose consideration may be given to provide additionally diesel engine driven pumps also.

Fig 1– BPCL’s Petrochemical Complex at Kochi
(Courtesy: http://www.livemint.com/Industry/ZTYwCJaqkhD1C4tauonPtJ/JV-with-LG-Chem-off-but-Kochi-petrochemicals-project-not-sh.html)

Water storage tanks could be below ground or at grade level. Generally mild steel storage tanks, open top, are provided at grade level. The tank would have to be lined for corrosion protection, especially for seawater. A float to indicate level is necessary and levels should be checked in each shift. It would be also worthwhile to ascertain actual level once a day, so that one does not end up with low water level due to defective float gauge. The size of the storage tank should be sufficient to provide 4 to 6 hours supply at the estimated maximum firewater rates. This quantity of water would be adequate to extinguish or control almost all fires, except perhaps a catastrophic fire like the IOCL Terminal Fire, Jaipur (See Fig 2).

Fig 2 – IOCL Terminal Fire at Jaipur on 29-10-2009
(Courtesy: S.K. Roy, GM (HSE), CO, IOCL)

Water storage should be ensured at all times. What would be the best method to ensure this? When stored water is also used for other utilities from the storage tank, it is possible that at a time of fire emergency, required water capacity may not be available. Hence, it is absolutely necessary to provide separate water tanks for firefighting requirement. Firewater should never be used for other purposes such as process or utilities purposes.

Fire Water Requirements
If we realise the wide variety and varying intensity of fires that are possible in process industries in particular hydrocarbon processing facilities, then we can readily understand that calculating water requirements is extremely difficult and cannot be an exact science. Experience is a large factor in setting overall water requirements. The petroleum industries have evolved their own standards and systems over the years of experience and also from the excellent guidance from National Fire Protection Association (NEPA), U.S.A. It is also advisable to compare firewater requirements from similar industries, to serve as an order-of-magnitude check on calculated requirements.

Recognised factors are readily available for developing firewater requirements of a typical hydrocarbon process plant which contains – towers, drums, exchangers, pumps, compressors, storage tanks, LPG spheres / bullets cable ways, conveyors, loading / unloading sheds, transformers, etc. Where flammable liquids having flash point below 65OC are normally used, are protected by medium velocity water spray system. In most cases the density of water application for the exposed area is 10.2 LPM/m2. Steel structural members and pipe racks also require fire water protection, at a lesser rate. However, the design engineer, based on the layout of equipment and also the specific industry experience, can increase the water application rate.

Once water requirements have been estimated, then the question arises how water application should be done – whether by water spray system or fixed water monitors? Experience over the years has been the guiding factor. Fixed spray system is recommended for such high hazard situations as uninsulated vessels containing highly flammable liquids, pumps handling volatile material, vessels that are so high that monitor streams would not reach, and equipment handling flammable material which could not be reached, due to location of other equipment around. Water application rate for fixed monitors or spray system are the same. Many chemical fires in particular hydrocarbon unit fires have been efficiently controlled and extinguished by quickly cooling through fixed monitors with simultaneous action of shutting off fuel supply. Fixed water monitors (See Fig 3) have a nozzle that can be adjusted for any elevation and can be rotated through 360O. Monitors can be quickly brought into service by simply opening one valve.

Fig 3 – A Typical Fixed Fire Monitor
(Courtesy : www.hymarineproduct.com)

They can also be locked into position and left unattended, which makes manpower requirements far less than hose systems. Monitor nozzle size should be selected 2.9mm (1½”) or 3.2mm (1¼”) nozzles giving 1350 – 1800 Litres per minute approximately at 7kg / cm2 pressure. In addition to fixed monitors provision can also be made for portable trolley mounted monitors (See Fig 4 and 5) provided for one hose connection from hydrant. These can be moved by one man and can be operated from necessary location very quickly. Although slower to bring into service, water supplied through hydrants and directed on the fire by hoses is an important back up for the fixed spray and monitor systems. Hydrants should be located around the periphery of the process unit at 30 meters centres so that hose streams from at least two directions can reach any portion of the process unit.

Fig 4 – A Typical Trolley Mounted Fire Monitor
(Courtesy: trade.indiamart.com)

Fig 5 – An overturned Trolley Mounted Fire Monitor after the fire of IOCL Terminal Fire at Jaipur
(Courtesy: S.K. Roy, GM (HSE), CO, IOCL)

The system uses hydrants with one or two 63mm (2½”) fire connections, each capable of giving 36m3 per hour at 7kg / cm2. Monitor / Hydrant locations should be carefully selected, based on equipment placement. Imagine at one plant, a hydrant was placed one meter away from a vessel. Assuming that vessel is on fire, can that hydrant be used?
Some companies, based on their own experience over a number of years, calculate firewater requirement on plot area, when equipment are located inside the plot with sufficient space all around and in between equipment, following spacing standards. Experience indicates that fire occurs only in one unit at any time and hence it is reasonable to calculate firewater requirements based on one fire at a time, since simultaneous fires at more than one location is remote. Taking into consideration, the maximum risk into plant, four hours minimum firewater storage should be provided. However, at present plants that process large quantity of flammable liquids in their operating units and storage tanks, design their fire protection facilities to fight two major fires simultaneously anywhere in the installation.
Before the calculated firewater volume becomes the basis for final design, ensure that it meets the statutory requirement of concerned authorities. It is advisable to discuss your design with the authorities concerned: Factory Inspectorate, Directorate of Fire Services and local Fire Brigade & also to get their approval.

Water Systems
A well-laid-out water system, of which the block technique is the best, is compulsory for good fire protection. In a small plant, a large loop or rectangle of lines could surround total operations, with cross connections passing besides the units or structures to be protected. Valves on this loop should be spaced so any section could be shut off in case of breakage. This would also facilitate directing the flow via the shortest distance to the fire scene. In a large plant, the water system could consist of a number of loops, each surrounding a group of blocks, as desired. Where fire-fighting water is taken from a large main line at nearly any location, pumps on the connecting line between loops can be made to serve more than any one loop. In other words, pumping capacity of several loops can be concentrated on any one loop in case of emergency. A water system layout should have hydrants (See Fig 6) at least each 30 meters and certainly no more than 60 meters apart, except where a line leads from one danger point to another with long stretches of safe areas. At units, lines should easily accommodate deluge and spray nozzles that can be used by one or two men to keep operating equipment and structure cool. Sufficient pressure should be available so that operating personnel won’t have to wait for arrival of fire engines.

Fig 6 – A typical Yard Hydrant with Hydrant Lines
(Courtesy: http://iotaautomation.wordpress.com/ 2013/03/22/fm-approved-fire-pump-room/)

The design of firewater distribution system takes into consideration two important factors viz. (i) knowledge of the system capacity with layout of hydrants, monitors, spray nozzles and (ii) the minimum pressure desirable at the extremity of the system is 5.6 kg/cm2 with 7 kg/cm2 anywhere in the process area. Further, it may be noted that 7 kg / cm2 nozzle pressure is the maximum that can be tolerated on a hand-held hose line by an operator. This is a consideration in setting maximum system pressures. Generally all piping is laid underground at about one meter depth. However, some plants that use salt water for firefighting, have laid their lines above ground, except in the process unit areas. This has been done since pipes lined with concrete, for corrosion protection against salt water does fail in due course. Further, in underground piping, detection of leaks and repair take much longer and poses a hazard at that time. Good practice calls for 20cm (8″) or larger mains with 15cm (6″) branches to individual hydrants. Experience has shown that at least of 15cm (6″) pipes are needed.

Fire Pumps
Centrifugal fire pump has become the standard today. Its compactness, reliability, easy maintenance, hydraulic characteristics and variety of available drivers – electric, steam turbines and internal combustion engines – have made centrifugal fire pump, most ideal for this service. An outstanding feature of a horizontal centrifugal pump (used when water level is above pump – atmospheric plus static suction) or vertical centrifugal pump (used when water level is below the pump – atmospheric suction) is the relation of discharge to pressure at constant speed, whereby discharge is reduced when the pressure head, increases. Firewater is pumped by a centrifugal pump having a relatively flat characteristic head / capacity curve. Discharge pressure is set by the minimum (See Fig 7 and 8) residual pressure requirement at the extremity of the system plus the system piping friction loss. Normally the residual pressure at the most remote hydrant should be at least 5.6 kg / cm2. This would indicate a pump discharge pressure of about 8.8 kg / cm2 in an adequately sized piping system. Selection of drive for the pump is important. From the standpoint of low maintenance, ease of start-up and operation, electric drive pump is preferable. However, at the time of power failure, electric drive pump would not be available. Hence, alternative pumps should be provided by turbine driven or engine driven (diesel or gasoline) or both.

Fig 7 – A typical Fire Pump Room with Electrical, Diesel and Booster Pump
(Courtesy: http://iotaautomation.wordpress.com/2013/03/22/fm-approved-fire-pump-room/)

Fig 8 – Fire Water Pump House after the fire of IOCL Terminal Fire at Jaipur
(Courtesy: S.K. Roy, GM (HSE), CO, IOCL)

It is a standard practice to provide diesel driven stand by fire pump. Suppose the firewater requirement is 410m3/hr. then an electric pump of 410m3/hr. and a diesel driven fire pump of similar capacity is provided. In remote places where power supply is not reliable, then both pumps could be of diesel engine driven pump. The principle is that the system should be met with alternative arrangement. In case all the pumps are electrically driven, then it is strongly recommended to provide emergency power supply from captive power generation facilities such as D.G. sets, etc. The route of the fire pump cable is critical. It should be an unobstructed and underground route exclusively provided for fire pump only. In large industries, Fire Engines and Trailer pumps will be very useful to boost firewater pressure at desired locations. Low capacity pressure maintenance pumps or ‘Jockey pumps’ are used to maintain pressure on the firewater system when not in use. The capacity of this pump should be sufficient to maintain pressure against leakage.

Usually, electric motor drive is provided with automatic start-up. The pump could be started manually from control room or from fire station and also from the local switch at the pump. There is arrangement also for automatic start of the pump, in case system pressure falls below set pressure. Generally, manual shutting off the pump is provided. Engine driven pumps could be designed for manual start-up. First, the electric pump will be started, then engine driven, depending on requirement. Once the fire pump is started in an emergency, then an operator should be deputed immediately to keep a watch on the pumps and operate as necessary. Fire pumps should be procured from standard manufacturers. Care should be exercised as stated above, when providing electrical connection to fire pump motor, that it is directly from sub-station and not connected with other operating units. There were incidents in which, electric connection to the fire pump was also supplying to a facility, which was on fire. When power was shut, fire pump also could not be run.

Foam Systems
Hydrocarbon tank fires are extremely difficult to extinguish. Foam Systems are the only practical method of extinguishing large storage tank fires. The foam type usually used for this purpose is air foam. The most effective method of applying foam to burning tanks is by fixed foam delivery systems. Two systems may be used, surface or subsurface injection. Surface system uses foam outlets attached to the top of the tank shell to spread foam directly on the liquid surface. Subsurface system employs foam discharge nozzles located on the tank shell below the normal minimum liquid level, but above any expected water level in the tank. Foam rises through the tank liquid and spreads uniformly on the surface with foam injection. Subsurface foam injection is suitable for large diameter cone roof tanks but not for floating roof tanks. Tank fires are rare but they are very difficult to put out, because of the volume of product in the tank and much more so if the roof sinks. Tank fires have also been successfully extinguished by application of foam through portable foam towers.

For air foam system the foam solution delivery rate shall be at least, 5 LPM/m2 of liquid surface of the tank to be protected. Oil industry recommends minimum of 12 LPM/m2 for seal area of floating roof tanks and for floating roof-sinking rate 8.1 LPM/m2 of liquid surface area. The quantity of foam as per above, should available for sustained application vary between 45 minutes to 1½ hours, depending upon the type of product and type of fixed foam discharge outlets. Reference should be made to the guidelines available for this, regarding type of foam to be used for different products, application rate, length of time, type of discharge outlet etc. Foam may be introduced from permanently installed facilities located in the tankages area or from portable foam trucks (See Fig 9).

Fig 9 – A Typical Foam System consisting of foam compounds such as Protein, Fluroprotein, AR- FFFP, AFFF.
(Courtesy: www.shipmans.com)

Quality of foam compound is very important for successful extinguishments of fires. Several type of foam compounds such as Protein, Fluroprotein, Alcohol-Resistant Film Forming Fluroprotein (AR-FFFP), and Aqueous Film Forming Foams (AFFF) are available for different types of application. Foam suitable to the characteristics of the product and the type of discharge outlet, should be carefully selected.

Maintenance of Firewater Systems
The proper maintenance of firewater system needs no emphasis, since the system should be in good operating condition at all times. Fire pump is an important part of the fire protection system. Daily, fire pumps must be tested by the operators – check discharge pressure and discharge water from some convenient outlet (monitors) for a long enough time to indicate proper operation. Log this information in the operator’s logbook. On a monthly basis, fire officer, maintenance engineer, should also witness the fire pumps operation.

Run the pumps for sufficient time, check discharge after opening outlets equal to pump capacity also hydrant pressure at some convenient locations. At this time all automatic controls should also be checked to ensure that they are operating. Fire protection engineers also recommend to test hydraulic performance of the pump annually and check three points on the standard curve (1) shut-off; (2) overload (150 per cent of rated capacity); and (3) a convenient rate of flow at or near capacity rating. All hydrant outlets and monitors should be operated periodically (say) once a fortnight, to ensure that they are clear of obstructions. Possibility of waste materials or spilled cement linings blocking them the hydrant lines are not uncommon. Check also that hoses fit on the hydrants. Nozzles / hoses, branch-pipes etc., should also be tested. It is better to have all these recorded on a logbook, to have positive way to ascertain check out.

Conclusion
Water is an ideal extinguishing medium for many applications. It is readily available, has great heat absorbing capabilities and can be used on a variety of fires. Water primarily extinguishes a fire by the removal of heat. It absorbs heat more effectively than any other commonly used extinguishing agent, due to its good thermal conductivity and its high latent heat of vaporisation. Water also has an important secondary effect, i.e. it provides a smothering action as well as cooling. Fire water systems are essential to the safety of many areas within the oil, gas and petrochemical industry. Only the salient features of firewater system have been discussed in brief, by no means this is exhaustive. It is recommended that reference should be made to relevant standards of Bureau of Indian Standards (BIS), Oil Industry Safety Directorate (OISD) Standards, National Fire Protection Association (NFPA) Standards, National Building Code (NBC) of India and also Tariff Advisory Committee (TAC) Guidelines.

References:

1. Bureau of Indian Standards – IS906, IS908, IS909, IS2097, IS3844, IS4928, IS4989, IS5714, IS8442, IS9668, IS13039, IS15394. New Delhi, BIS.
2. India – Factories Act, 1948 with Maharashtra Factories Rules, 1963. Mumbai, Labour Law Agency, 2011.
3. India – The Gas Cylinder Rules, 2004. Delhi, Universal Law Publishing Co. Pvt. Ltd.2005.
4. India – The Petroleum Act, 1934 with the Petroleum Rules, 1976. Allahabad, Law Publications (India) Pvt. Ltd, 1994.
5. Nair, R.R. – Equipment for Fire Protection, Industrial Safety Review, November 2012.
6. Nair, R.R. – Fire and Explosion Hazards, Industrial Safety Review, January 2013.
7. Nair, R.R. – Fire Prevention and Fire Protection, Industrial Safety Review, June 2012.
8. Nair, R.R. – Potential hazards of Chemicals, Industrial Safety Review, February 2012.
9. Nair, R.R. and Chakaravarti, S. – Safe Handling of Hazardous Chemicals, Bangalore, AICTE – CEP, 2001.
10. Nair, R.R. and Joshi, T.K. – Safety and Loss Prevention in Process Industries, Bangalore, AICTE – CEP, 2002.
11. Nair, R.R. and Veeraraghavan, R. – Fire Technology: Fire Prevention and Fire Protection, Bangalore, AICTE-CEP, 2002.
12. National Building Code of India 2005. New Delhi, Bureau of Indian Standards, 2007.
13. NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam, 2010.
14. NFPA 15: Standard for Water Spray Fixed Systems for Fire Protection, 2012.
15. NFPA 20: Standard for the Installation of Stationary Fire Pumps for Fire Protection, 2013.
16. NFPA 22: Standard for Water Tanks for Private Fire Protection, 2013.
17. NFPA Fire Protection Handbook, 19th Edition, National Fire Protection Association, USA.
18. OISD-STD 116: Fire Protection Facilities for Petroleum Refineries and Oil/Gas Processing Plants.
19. OISD-STD 117: Fire Protection Facilities for Petroleum Depots, Terminals, Pipeline Installations and Lube Oil Installations.
20. Roy S.K.: Presentation on Jaipur Terminal Fire, Indian Oil Corporation Ltd, October 2009.
21. Safety and Fire Protection Handbook edited by R. Veeraraghavan, Mumbai, Safe Technology, 2009.

About Author

Mr. R. R. Nair
Mr. R. R. Nair has more than 45 years’ experience in Occupational Safety, Health & Fire Protection. He is author of 15 books and about 65 articles in various topics on Safety, Health & Environment. He has carried out more than 50 safety / fire safety audits in various industries, occupancies including high rise buildings.

For more information contact:
M: 09224212544, Resi: 022 27665975
E-mail: [email protected]