NFPA 22 (2003) Special Requirements

NFPA 22 - 2003 Edition Standard for Water Tanks for Private Fire Protection

SUMMARY OF PROVISIONS MORE RESTRICTIVE THAN AWWA D100

The following list summarizes of special design considerations for tanks designed to NFPA 22, 2003 Edition. Although NFPA 22 does not require require compliance with all aspects of AWWA D100, tanks designed for conformance to NFPA 22 are generally AWWA D100 tanks meeting the following additional requirements.

1-6.1

The location of tanks shall be such that the tank and structure are not subject to fire exposure from adjacent buildings. If lack of yard yard room makes this impracticable, impracticable, the exposed steel work shall be suitably fireproofed or shall b e protected by open sprinklers.

1-10.1

The manufacturer shall warranty the tank for at least 1 year from the date of completion and final customer acceptance.

1-12.2

Confined entry requirements shall be posted at each shell manway.

1-13

Lightning protection shall be supplied to NFPA 780.

2-3.2

Roofs shall be designed for a (minimum) uniform live load of 25 psf.

2-3.3

Under normal circumstances the wind pressures shall be 18 psf on projected areas of cylindrical surfaces and 15 psf on projected areas of conical and doubly- curved plate surfaces. These loads shall be adjusted by the square of the (wind velocity to 100 mph) for wind speeds greater than 100 mph.

2-3.4

Earthquake design criteria shall be considered. Specific design criteria are are contained in the appropriate chapter for the particular pa rticular tank, or in local codes, whichever is more stringent .

2-3.8

The maximum allowable uniform live load (in pounds per square foot) and the maximum allowable concentrated load (in pounds) shall be identified on the design drawings and tank nameplate.

2-5

All tanks shall have roofs. An OSHA approved handrail (guardrail) shall be placed around the entire circumference of the roof. Tanks with ellipsoidal roofs or pedestal tanks shall have guardrails around the roof manholes and other accessories that require access.

2-6.1

When the steel roof is essentially air tight a substantial vent shall be placed above the water level. The vent pipe shall have a cross section equal to a minimum of one-half the area of the discharge pipe(s) p ipe(s) or fill pipe, whichever is larger. A corrosion resistant bird screen is required. The gross screen area shall be at least 150% of the crosssectional flow area of the discharge or fill pipe, whichever is larger.

ies - NFPA 22 Special Requirements

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This form is intended to be a convenient summary of the special requirements of NFPA 22 that exceed the minimum requirements of AWWA D100, Standard for Welded Welded Steel Tanks for Water Storage. This summary is not all inclusive. Consult NFPA 22 for complete requirements.


3-2.1.1

Plates materials shall meet the following (except as allowed by AWWA Section 14 when using Section 14 as the design basis): A36, A283 A, B, C, or D (grade D up to ¾” only [D100 limits Gr. D to ¾" for shell plates, 2.2.3.1.3]), A131A or B, A285 A, B, or C, A516 grades 55 or 60. (Note that NFPA 22, other than for A283 D, material put no additional restrictions on thickness or grades for shell plate. (AWWA D100, 2.2.3. 1 allows A36, A573, Gr. 58, A131 Gr. A & B, A283 Gr. B & C to be used for shell plates under the basic design, however, materials from Section 14 are allowable substitutes 2.2.3.3)

3.2.1.3

Structural shapes shall be to A36.

3-4.1

Maximum Bending Stresses: Tension: on net section, rolled steel Anchor bolts Bending: Tension on extreme fibers (except column base PLs) Column Base PLs Compression on extreme fibers of rolled sections and plate girders and built-up members for values as follows: ld/bt not in excess of 600 ld/bt in excess of 600

15,000 psi 15,000 psi

15,000 psi 20,000 psi

15,000 psi 9,000,000/ (ld/bt)

3-5.1.2

For tanks less than 50 feet in diameter, the minimum thickness of the lowest shell course is ¼". 3/16" shell plates are allowed only for upper rings of tanks less than 50 feet in diameter.

3-5.2

A corrosion allowance of 1/16" shall be added to the calculated sections of ALL interior bracing required to support the water content.

3-5.2

All interior bracing required to support the water content shall be open to facilitate cleaning and painting except that tubular sections shall be hermetically sealed to prevent internal corrosion.

3-5.2

The plate of tanks that are to contain salt or alkaline water shall be 1/16" thicker than calculated.

3-5.3

Design of the tank shell shall comply with AWWA D100. AWWA D100, Appendix C (Sec. 14) may be used provided that all requirements of Appendix C (Sec. 14) of the standard are met.

3-5.3.4

Where compression stress exists, selected plate thickness shall prevent local buckling

3-5.9

The maximum spacing of rafter is 2 PI (ft)


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This form is intended to be a convenient summary of the special requirements of NFPA 22 that exceed the minimum requirements of AWWA D100, Standard for Welded Steel Tanks for Water Storage. This summary is not all inclusive. Consult NFPA 22 for complete requirements.


3-6.2

Shell plates shall be cold rolled according to Table 3-6.2

3.6.7.1

The underside bottom plates shall be protected by one of the following: Underside of bottom painted after welding Lime applied to a clean sand base An oil sand layer used when permitted. Oiled sand layer, if used, shall be at least 4" thick.

3-7.3

Two easily accessible roof hatches 24 minimum size are required 180 degrees apart. One of the roof hatches must be provided with an interior ladder.

3-7.5

All outside ladders shall be equipped with a cage, rigid notched rail, or other listed ladder safety device.

3-7.6.1

Ladders shall not be attached rigidly to the bottom plate.

3-7.6.2

Ladders (inside) shall be supported at a maximum spacing of 12’.

3-7.7

Ladder side bars shall be a minimum of 2” x ½”.

3-7.8

All parts that are inaccessible after fabrication, but that are subject to corrosion, shall be protected by paint before assembly except that this requirement shall not apply to the overlapping surfaces of single-welded lap joints above the high waterline.

3-7.9.1

Interior surfaces exposed to water immersion or vapor phase zone above the high water level shall be primed per Inside Paint System No 1 in AWWA D102. Alternates as approved.

3-7.9.2

Exterior and interior dry surfaces shall be primed with one coat of lead free alkyd in accordance with Outside Paint S ystem No 1 in AWWA D102. Alternates as approved.

3-7.12

The painting and priming systems described in 3-7.9 through 3-7.11 shall be lead free.

9-1

Minimum concrete compressive strength for tank foundation is 3000 psi

9-2.1

Except for tanks on concrete slabs with 1" sand layer or asphalt impregnated expansion joint material, the junction of the tank bottom and the top of concrete ring wall shall be tightly sealed to prevent water from entering the base.

9-2.2

The concrete footing shall be a minimum of 2.5 feet below grade.

9-4.3

Anchor bolts exposed to weather, water, or corrosive environments shall be protected by: galvanizing corrosion-resistant coatings


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field-applied coatings 9-4.3

The minimum size for anchor bolts is 1 ¼" if the anchor bolts are not galvanized or corrosion-resistant alloy

9-6.4

Foundations shall not be constructed over buried pipes (side openings only)

11-1.15.2 Pipe connections in contact with water shall be not less than 2" pipe size. 11-1.15.2 The minimum thickness for pipe connections not greater than 5" nominal diameter shall be XS, for pipe connections of 5" nominal diameter shall be Std Wt 11-2.2.1 The minimum discharge pipe size for tanks not over 25,000 gallons shall be 6" nominal pipe size, for tanks over 25,000 but not over 100,000 shall be 8" nominal pipe size, and for tanks over 100,000 shall be 10" nominal pipe size. 11-2.13

Where a tank is used as the suction source for a fire pump, the discharge outlet shall be equipped with an assembly that controls vortex flow. The assembly shall consist of a horizontal steel plate that is at least twice the diam eter of the outlet on an elbow fitting, where required, mounted at the outlet a distance above the bottom of the tank equal to one-half the diameter of the discharge pipe. The minimum distance above the bottom of the tank shall be 6 in.

11-4.6

Tanks with automatic filling shall discharge inlets into the opposite half of the tank from the pump suction

11-5.2

The overflow pipe shall be at least one pipe size larger than the inlet unless the fill capacity (inflow rate) is known and the overflow capacity at least equals the fill capacity.

11-5.2

The over weir shall be a cone or concentric reducer at least 2" larger than the overflow pipe.

11-7.2

For dual use tanks (i.e. fire protection and domestic), the secondary use outlet must be located above the fire service capacity.

13

For tanks subject to freezing, extensive requirements for heaters are contained in Section 13.

Figure B-15 (a) Special suction antivortex d etail is required.


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NFPA 22 (2003) Special Requirements

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