Water for Fire Fighting in High-rise Buildings

HORATIO BOND, SFPE, Chief Engineer National Fire Protection Association

N F P A S tanda rds provide guidance on water supplies for s t and- pipe or sprinkler systems in high-rise buildings, but fire flow, pressure ranges, and the use of tanks and pumps are matters of engineering.

T HE Standard for the Installation of Standpipe and Hose Systems, NFPA No. 14, and the Standard for the Installation of Sprinkler Sys-

tems, NFPA No. 13, provide guidance on water supplies for these services. The guidelines of both these standards require engineering judgment to determine what should be best for the situation in an individual building or structure. Here are some personal ideas on this engineering for which I have been asked recently. They cover some of the problems I see and some possible solutions.

S T A N D P I P E S

The NFPA Committee on Standpipes and Outside Protection has ap- pointed a subcommittee to review the Standard for Standpipes and Hose Systems, NFPA No. 14, and it is quite likely that future requirements will deal more comprehensively with high-rise buildings.

H A N D H O S E

In very tall buildings, it is necessary to divide the water supply for normal building services into zones in much the same way tha t public water systems are zoned in cities with numerous areas on hills. Hand hose for use by building occupants requires a different pressure range than tha t required for fire department lines. The regular water supply for sanitary and other uses within the various zones of a tall building also has different

NOTE: This paper was presented at the National Fire Protection Association Fall Conference, November 16, 1965, at Los Angeles, California.

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pressure requirements. These affect details of how the water supply piping systems are arranged.

F I R E F L O W

Fire department water supplies should be estimated for each floor of a high-rise building in much the same way tha t one estimates the fire de- par tment flow requirements in various districts of a city. For tunate ly , most very tall buildings will house light-hazard occupancies, and the com- par tmentat ion of fire-resistive construction can also be taken into account in making fire flow estimates. However, these estimates should be real- istically made. I recommend tha t the fire department of each ci ty be re- quired to approve the water supply for fire protection when a building permit is issued for a new building.

I t can be said that, because of light-hazard occupancy, few floors would require more than 500 gpm (gallons per minute); however, required flows would be increased for large floor areas and for the occupancy when it exceeds the light-hazard class. For example, restaurants and mercantiles (as a part of a high-rise building) would, in some cases, require flows above 500 gpm. I would expect it to be an exceptional building in which the fire department would estimate tha t it would ever need flows in excess of 1,000 gpm to protect the building contents. The exceptional cases would be those housing unusual fire loads or those subjected to an exposure hazard.

N U M B E R O F S T A N D P I P E S

As to the number of fire department standpipes to be provided in a building, the general rule should be a minimum of two, and more as in- crease in floor areas may demand. This requirement is not tied to the flow possible in a standpipe, but is rather to make possible a min imum of a two- position at tack on a fire. A single standpipe could be accepted in very small area situations, such as a small area tower section of a tall building. The criterion for determining tha t one standpipe is sufficient migh t be an estimate tha t a fire flow no greater than 250 gpm would be needed on any floor of the area.

P R E S S U R E Z O N E S

The pressures developed by the weight of the water in a system of piping for fire protection can be taken care of in the same way tha t they are handled in the domestic water system. In other words~ a tall building would be divided into zones. For each zone, a water supply for fire protec- tion would be designed to have pressures within the normal operating ranges. I am thinking about zones of ten to twelve stories. A check valve in each zone prevents the transmission of its pressures to the zone below.

In each zone of the fire protection piping, there should be a gravity or pressure tank supply. This would be supplemented with fire pumps to provide the required flow in the zone. (Fire pumps would not be used to

High-rise Buildings 161

fill gravity or pressure tanks; these would be filled from domestic water lines.)

In one pump arrangement, the pumps in the lowest zone take suction from a street connection; pumps in each other zone take suction from the gravity tanks in the zone below. The pump controls can be located with the pump in the lowest zone or in each zone, depending on what is most practical for the particular building concerned. A fire depar tment connec- tion would be provided in the lowest zone only.

You will note that my comments suggest that, so far as possible, de- tails of piping for fire protection be worked out to stay within normal pressure ranges. This, I think, is one practical answer to the problem of tall buildings.

Some arrangement, such as described above, is necessary to avoid excessive pressures in piping. To the extent that normal pressures are exceeded, special problems are introduced. Many of these can be met and may have to be met in some instances; however, unusual pressure ranges increase costs by imposing special design requirements and demanding special equipment. Also, fire fighters and building maintenance employees must be given the additional training they need to effectively use such specially designed systems.

I t will be recognized tha t fire department connections could be pro- vided t o serve each zone of fire protection piping. (They should be pro- vided if gravity storage is inadequate.) Such connections would require a check valve at the base of each zone and risers and a siamese connection for each zone. In very tall buildings, it might mean the use of extra strength piping for a part, at least, of the fire department connection riser.

The same observation can be made about the use of dry standpipes. They can be made to deal with heights up to about twenty stories without getting very far above pressure ranges with which the fire department normally works; but for taller buildings, you have the excess pressure to contend with.

S~milar considerations apply to supplying fire fighting piping in each zone from fire pumps located in the basement.

W A T E R S T O R A G E

Engineering judgment will determine how much of the fire flow should be provided in each pressure zone from a gravity tank in the zone and how much should be furnished by building fire pumps. Gravity water storage is feasible in tall buildings, as the gravity tank for any zone can be in- stalled about six floors above the zone served. The only exception is the top zone. If the gravity tank for this zone is not put on a tower, the top stories and roof can be protected with a pressure tank and fire pump.

If abnormal pressure ranges are to be avoided, one has to use a number of pumps in relay to get to the top of a very tall building. Gravity storage is preferable to that kind of pump supply. Generally, the principle of pro-

162 Fire Technology

riding practically all of the required fire flow from gravity storage should be followed. Figure 1 shows a piping system that could be used for fire protection in high-rise buildings.

The size of tanks is determined by the periods of time for which fire flow is to be provided. In municipal street distribution systems, two hours is specified for fire flows of the order of 500 gpm. Fire flows of two-hour

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GRAVITY l TANK

GRAVITY l TANK

FIRE

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DEPARTMENT CONNECTION

f

, . , 1 < : ,

FIRE PUMP

RISER

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FIRE PUMP

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FIRE PUMP

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STREET CONNECTION FIRE PUMP

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PRESSURE TA N KS

RISER

RISER

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Figure 1. A fire-fighting p ip ing system for tall buildings that avoids excessive pressure ranges, and is not limited by the total height of the building. Pressure zones are 10 to 12 stories. Water can be store'd in gravity tanks for any degree of effectiveness and reliability desired.

High-rise Buildings 163

duration will require gravity tanks considerably larger than those with which building designers are familiar.

I f hose streams are the protection contemplated, they must be ade- quately supplied to do the job.

S P R I N K L E R P R O T E C T I O N

This is a good place for me to observe that the only really effective and economical way to protect high-rise buildings against fire is to require tha t they be sprinklered throughout. In sprinklered buildings, some arrange- ment should be made so that, on each floor, there would be connections from the sprinkler system risers for fire department use. I t would be un- reasonable to ask a building owner to provide both a system of automatic sprinkler risers and a system of fire depar tment standpipes in a sprinldered building. For the normal light-hazard occupancy of high-rise buildings, hose connections permitted by the sprinkler rules should be adequate.

I am glad to note that many cities are taking a fresh look at their water requirements for fire fighting in tall buildings. Practice has not yet been affected significantly in the United States and Canada, but it soon could be. In some other countries, tall buildings are a new problem. In Sydney, Australia, sprinkler protection has been made mandatory for buildings taller than 150 ft, and may be required by the fire depar tment in buildings over 80 f t tall. In Japan, a recently enacted provision of the Fire Service Law requires buildings of 11 floors and over to be completely sprinklered. In other countries similar arrangements are being discussed for buildings above the reach of a fire depar tment aerial ladder, 100 f t to 150 ft.

The reach of an aerial ladder is probably the wrong basis for determin- ing which buildings should be sprinklered, but this does reflect the fire fighting access problem which becomes difficult as soon as one gets a few stories above the street. There are other fire fighting problems, such as the ventilation of heat and smoke and the disposal of water used in fire fighting. Sprinkler protection means smaller fires and reduced demands for ventilation and water. The access and ventilation problems have al- ready been recognized in our generally accepted practice of requiring sprin- kler protection for basements and sub-basements. In modern high-rise buildings the upper floors have the same access problems as basements.

The economics of sprinkler protection for high-rise buildings appear to lie in shortening the period for which fire flows are needed and in some- what smaller tanks for gravity water supplies for fire protection. How- ever, sprinkler protection is recommended because with it, fires in high- rise buildings could be manageable. Otherwise they probably are not.