Water Tanks for Fire Protection

7/28/2019 Water Tanks for Fire Protection

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Water Tanks for Fire Protection:

Proper Planning Helps Avert Disaster

TN_WT_04-2012

In emergency re-ghting situations, the de-mand for water can exceed the supply avail-able from the domestic water delivery system.This is especially true for suburban or rural ar-eas served by a well with limited delivery ca-pability. Buildings like schools, hospitals, pris-ons, ofce buildings, data centers, and otherinstitutional and commercial facilities need areliable and redundant water supply.

A properly designed and sized water storagesystem is an important component of any dis-tribution system. Water tanks are, withoutexception, the critical element in providingsafe, secure water especially during periods

of drought, infrastructure failure, and loss ofpumping capacity and ow during extensivere ghting. As a result, architects and engi-neers consistently turn to protected steel reprotection tanks to provide a reliable sourceof water at desired rates and durations for awide range of design conditions.

Fire departments around the country have

specic requirements for the submittal and ap-proval of the design, construction, installation,and maintenance of protected steel tanks thatsupply water for private re systems installedin accordance with NFPA 22-2008 Standardfor Water Tanks for Private Fire Protection.

Building and re codes may require a secondary, on-site water supply for high-rise buildings. Compli-ance may result in a secondary water supply equal to the hydraulically calculated sprinkler and hosestream design demand with a required duration time up to 30 minutes.


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The design of these water tanks must include:

Water supply to rell

Duration of use

Tank fabrication standards:UL-58, UL-142, UL-1746,AWWA D-100-05, AWWA D-102-06

Tanks capacity and/or actualusable gallons.

Overow/ll protection

Level monitoring

The requirements for onsite re protectionwater storage are set forth by the local recode in a Required Water Supply table andmust be dedicated to re protection use only

(see below). Usually if re sprinklers are notinstalled, the supply is per the calculated reow (ow rate x duration) as specied in thelocal re code.

Volume ofBuilding Fire Protection

Size Water SupplyUp to 10,000 sq. ft. 10,000 gallons

10,001 to 15,000 sq. ft. 30,000 gallonsOver 15,000 sq. ft. 45,000 gallons

Types of Water Supply

There are many different layouts for waterstorage tanks for re protection. Some willrequire a traditional drafting design (cisterntank) while others may provide a gravity owor pumped discharge (reservoir tank). In someinstances, the utilization of an ASME pressurevessel is required. Always contact your localre and building ofcials before moving aheadwith a storage tank project involving re-ghting systems.

Cisterns

Many communities have invested in under-ground or aboveground cisterns for re pro-tection. These cisterns can be large, some ofwhich can hold ten times as much as a retanker. NFPA has published guidelines regard-ing the location and volume of an appropri-ate re cistern based on the structure(s) it isdesigned to protect. Cisterns are atmosphericwater tanks with properly sized air vents toallow free ow of air during their lling and

draining cycles. The vent is critical in main-taining atmospheric pressure, especially inaboveground applications.

Most atmospheric tanks for re protection aresingle-walled. They are designed, constructed,and tested in accordance with UnderwritersLaboratories Inc. standards UL-58, UL-1746,or UL-142.

Additionally, the water tanks design and con-struction is governed by standards such asAmerican Water Works Association AWWAD100-05 Standard for Welded Steel Tanks forWater Storage, and the National Fire Protec-tion Associations NFPA 22-2008 Standard forWater Tanks for Private Fire Protection.

A water tanks single-walled construction usesone sheet of steel meeting ASTM standards.The material thicknesses will range from 12gauge to 1 , whether the tank is construct-ed of mild carbon steel or stainless steel. Flatanged or dished heads, continuous exteriorand interior welds on all joints, and a veri-able 5-psi factory air test ensures a safe andsecure storage tank. Additional ttings on atypical water tank for re protection will in-clude a single or Siamese dry hydrant withanti-vortex plate, a ll port,and a level indicator.

The volume of re protection water supply is usu-ally dedicated to re protection use only.


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Reservoir Tank

Fire protection reservoirs are protected steelwater storage tanks designed to provide suf-cient water supply for re suppression sys-

tems beyond that which the domestic waterfeed line serving the building can supply. Inother words, the re suppression deliverysystem needs an auxiliary and/or secondarymeans of water to satisfy the re ow.

This type of water storage tank can either bean atmospheric tank or an ASME pressure ves-sel. Atmospheric water storage tanks requirea re pump to deliver water to the building.Tanks can be installed either underground oraboveground. Underground installations may

In many applications, ASME pressure vesselsare manufactured for use with re suppres-sion sprinkler systems. During normal opera-tion, this hydropneumatic tank is lled with2/3 water and 1/3 air to provide the velocity

factor needed for the sprinkler piping system.

The tank construction complies with the ASMECode, Section VIII, Division I and is welded inaccordance with ASME Section IX. The ASMEpressure vessels material of construction con-sists of SA516 GR70 carbon steel and type304 and 316 stainless (includes L grades).Most ASME vessels utilize anged tank ttings(raised or at face, slip-on weld neck, lap

joint). Manways are limited to 24 diametercylindrical or elliptical.

Coatings and Linings

A high-tech, high-solids polyurethane coat-ing system is the rst line of defense againstexternal and internal corrosion for re waterstorage tanks. In addition to meeting strictVOC air pollution regulations, these environ-mentally-friendly coatings offer applicationand quality advantages over their traditionalsolvent-based counterparts. After a surfacepreparation of either SSPC-SP6 or SP10 gritblast, these superior coatings are profession-

ally applied. They provide for exceptional ad-hesion characteristics by forming a strong,long-lasting bond to the steel substrate of thewater storage tank.For underground installations, external corro-sion protection systems employ a high-grade,self-reinforcing coating with a 1:1 format thatcan be applied in one coat to an almost unlim-ited thickness. Most manufacturers provide alimited 10-year warranty for corrosion whenusing this type of protective coating system ata 75- mil thickness.

When coating the inside of a water storagetank, the approach to corrosion control issomewhat similar. The internal polyurethanecoating used is highly resistant to corrosion,abrasion, immersion, waterborne chemicals,and cathodic disbondment. After internal sealwelding and surface preparation, the two com-ponent, quick setting, 100% solids coating isapplied to a 15-mil thickness.

According to NFPA, where a pressure tank is usedfor the re water supply, those who meet therequirement of ASME Boiler and Pressure VesselCode are acceptable.

require a vertical turbine re pump installeddirectly through the manway along with a

jockey pump and ll/level controls. The pump

can be completely enclosed in the manway orhoused in a prefabricated pump house locatedat nished grade. Tanks installed undergroundcan also be designed with one end penetrat-ing a buildings foundation wall providing ac-cess to the tank controls. An integral waterstop and link seal protects the building interiorfrom water intrusion. This design saves valu-able building space and eliminates the needfor a pump house.


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Highland TankOne Highland Road Stoystown, PA 15563Phone: 814-893-5701 Contact: Steve MapesEmail: [email protected]

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It is an exceptional coating for a re protec-tion water tank, so good that it is even usedin potable water storage tanks. They cure toform a tough, durable, non-toxic solid, so hardthat it will not impart any taste to the water

contents of the tank.

Insulation

Water storage tanks are insulated for a widevariety of applications. The thermal insulationhelps to prevent freezing and reduces energycosts associated with heating or maintain-ing heated water. A variety of insulation sys-tems can be applied to most above and belowground tanks. External batt and metal jacket insulationsystems are used primarily on abovegroundhorizontal and vertical tanks. This system of-fers a 360-degree wrap of mineral wool, ber-glass, or ceramic material. The insulation isthen wrapped in aluminum, stainless steel orHDPE sheets, which provide moisture and UVprotection. External spray-on and poured foam are an-other 360-degree wrap that can be used onabove or belowground tanks. Abovegroundinsulation applications utilize a standard two-

component urethane that expands and hard-ens to the desired R value based on insu-lation application thickness. When cured, a25 mil semi-rigid white acrylic weatherproofcoating is applied for surface protection.

For underground applications, urethanefoam is poured between the two steel wallsof a modied double-walled tank. This createsthe desired thermal insulation while maintain-ing the storage tanks internal and externalcorrosion control system.

The availability of an adequate and reliablewater supply is paramount in order to protectcommunities from the ever-present threat ofre. Protected steel water storage tanks area vital element within the municipal and ruralwater delivery system. Proper tank selectionand design is required to assure that life-sav-ing water can ow around the clock to sustainlong duration re suppression operations.
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Water Tanks for Fire Protection