NFPA 22 Water Tanks for Private Fire Protection – A short Note
In cases
in which the municipal water supply is not available, reliable, or it cannot
provide adequate flow for the fire pump, a fire pump and water storage tank
needs to be used. This is because a fire pump alone can only increase the water
pressure; it cannot increase the flow available. Water storage tanks and pumps
are usually seen in facilities with systems that have a significant water
supply demand, such as large warehouses. Water storage tanks can be made of
various materials such as wood, steel, concrete, fiberglass-reinforced plastic
(FRP), and rubberized fabric.
NFPA 22, Standard for Water Tanks for Private Fire Protection, provides the minimum requirements for the design, construction, installation, and maintenance of tanks and accessory equipment that supply water for private fire protection.
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Core Chapters |
Chapter 1 |
Introduction |
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Chapter 2 |
Referenced Publication |
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Chapter 3 |
Definitions |
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Chapter 4 |
General Information |
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Types of Tanks |
Chapter 5 |
Welded Carbon Steel and Composite Concrete and Carbon Steel Gravity
Tanks and Suction Tanks |
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Chapter 6 |
Factory Coated, Bolted Carbon Steel Tanks |
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Chapter 7 |
Pressure Tanks |
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Chapter 8 |
Wood Gravity Tanks and Suction Tanks |
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Chapter 9 |
Embankment Supported Coated Fabric Suction Tanks |
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Chapter 10 |
Concrete Gravity Tanks and Suction Tanks |
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Chapter 11 |
Fiberglass Reinforced Plastic Tanks |
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Constructional |
Chapter 12 |
Tank and Tower Foundations in the Ground |
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Chapter 13 |
Steel Tank Towers |
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Chapter 14 |
Pipe Connections and Fittings |
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Chapter 15 |
Valve Enclosures and Frost
Protection |
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Chapter 16 |
Tank Heating |
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Chapter 17 |
Acceptance Test Requirements |
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Chapter 18 |
ITM of Water tanks |
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Annex A |
Explanatory Material |
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Annex B |
Typical Installations |
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Annex C |
Informational References |
TYPES OF TANKS USED IN FIREFIGHTING
GRAVITY
TANK
A storage tank
that uses elevation as a source of pressure, which might be capable of providing
the necessary head pressure to operate a fire suppression system or used to provide
water to a fire pump.
SUCTION TANK
A tank that provides water to a fire pump for which a minimal
amount of head pressure is provided.
BREAK TANK
A tank providing suction to a fire pump whose capacity is
less than the fire protection demand (flow rate times flow duration).
PRESSURE TANK
A tank that uses air or some other gas under pressure to expel
its contents.
BLADDERTANK (not the one Bladder tanks used as foam
concentrate tanks installed in Inaccordance with NFPA16 or NFPA11)
A pressure
tank containing air and water separated by a flexible membrane (bladder).
FIREFIGHTING
WATER TANK MATERIAL
A
firefighting tank can be fabricated using one of the following materials:
SIZING
OF FIREFIGHTING WATER TANK
·
A tank shall be sized so that the stored supply plus
reliable automatic refill shall meet the system demand for the design duration.
·
•A break tank shall be sized for a minimum duration
of 15minutes with the fire pump operating at 150percent of rated capacity.
PURPOSE
OF BREAKTANK
SIZING
OF FIREFIGHTING WATER TANK
CALCULATION
OF THE NET CAPACITY OF FIREFIGHTING TANK
FOR
SUCTION TANKS:
the net capacity shall be the number of gallons between the inlet of the overflow and the level of the vortex plate.
FOR
ALL TANKS OTHER THAN SUCTION TANKS:
the net capacity shall be the number of gallons between the inlet of the overflow and the discharge outlet.
FILLING
OF FIREFIGHTING WATER TANK
The water supply shall be capable of filling the minimum
required fire protection volume within the tank in a maximum of 08 hours.
The tank shall be kept filled, and the water level shall never be more than 4in. (102mm) below the designated fire service level.
DISCHARGE
PIPE SIZING OF FIREFIGHTING WATER TANK
The minimum discharge pipe sizing shall be based on the hydraulic demand of the systems attached to the tank but shall not be less than 06inch.
FIREFIGHTING
WATER TANK OVERFLOW
The
over flow pipe shall have a capacity greater than the fill connection but shall
not be less than 03inch. throughout.
The
in let of the over flow pipe shall be located at the top capacity line or high water.
FIREFIGHTING
WATER TANK DRAIN.
A drain pipe of atleast 02inch. That is fitted with a
controlling valve and a 1∕2inch. Drip valve shall be connected to the tank
discharge pipe near its base and on the tank side of all valves.
PRESSURE
TANK SIZING EXAMPLE
A Pressure tank is to be used to provide a 30min water supply
to a system with a hydraulically calculated demand of 140gpm (530L/min) at a pressure
of 118psi (8.14bar). Due to near by component pressure ratings, it is important
that airpressure in the tank not exceed 175psi (12.0bar). To determine the minimum
size tank.
Solution
Solve for A,
A = 0.7
It means proportion of air in the tank is 70%.
We have been given sprinkler demand as 140 GPM for 30
minutes, yielding a water requirement of 4200 gallons (which is going to be in
30% of the tank)
Hence, the Total size of the pressure tank would be 14,000
gallons.
WOOD
GRAVITY TANKS AND SUCTION TANKS
EMBANKMENT-SUPPORTED
COATED FABRIC SUCTION TANKS
CONCRETE
GRAVITY TANKS AND SUCTION TANKS
FRP
TANKS
ANTIVORTEX
PLATE
WHEN
TO INSTALL "ANTI-VORTEX PLATE"?:
Where a tank is used as the suction source for a fire pump, the discharge outlet of the tank shall be equipped with an assembly that controls vortex flow.
PURPOSE
OF USING "ANTI-VORTEX PLATE"?
ANTI-VORTEX Plate is installed in the suction line of fire pumps to control the turbulence in flowing water, They are simple in design and very effective in controlling the velocity of the fluid thus preventing cavitation to fire pumps and damage to impellers.
DIMENSIONS
OF "ANTI-VORTEX PLATE"?
The
assembly shall consist of a horizontal steel plate that is at least twice the
diameter of the outlet on anel bow fitting.
Large,
standard size anti-vortex plates [48in.X48in.(1219mm×1219mm)] are most
common and are desirable, as they are adequate for all sizes of fire protection
pump suction pipes normally used
INSTALLATION
DIMENSIONS
Mounted at the outlet a distance above the bottom of the tank
equal to one-half the diameter of the discharge pipe or 152mm which
ever is greater.
ANTI-VORTEX
PLATE INSPECTION
Inspection
of anti-vortex plate shall be after completion of the tank construction,
and before filling the tank with water.
The
inspection shall verify that the horizontal steel plate and long radius elbow are
installed properly and meet the requirements of dimensions and installation height
mentioned above.
1. NFPA 22
2. 21st edition of the Fire Protection Handbook
3. https://firepiping.com/en/fire-tanks/
4. https://www.beltecno-global.com/blog/fire-fighting-tank
5. https://www.nfpa.org/news-blogs-and-articles/blogs/2024/10/30/nfpa-22-and-water-storage-tanks