DS 2-8 Earthquake Protection for Water-Based Fire ... - FM Global

Earthquake Protection 2-8
FM Global Property Loss Prevention Data Sheets Page 65
P,R,S,U
- longitudinal
2
(50)
2½
(65)
3
(80)
4
(100)
C.3 Ground-Supported, Flat-Bottom Steel Tanks
1x10x5.1x0.5 =
(1 x 3.1 x 75 x 0.5) =
1x10x7.9x0.5 =
(1 x 3.1 x 116 x 0.5) =
2x10x10.8x0.5 =
(2 x 3.1 x 159 x 0.5) =
4x10x16.4x0.5 =
(4 x 3.1 x 241 x 0.5) =
=
=
26 lb
(116 N)
40
(180)
108
(493)
328
(1494)
502 lb
(2283 N)
The most common type of tank used in areas where seismic protection is required is the ground-supported,
flat-bottom steel tank. The tank can either provide a suction supply for an adjacent fire pump, or act as a
gravity tank to provide sufficient water pressure for the fire protection system. Only tanks that are FM Approved
for the appropriate earthquake zone (see Data Sheet 1-2) should be installed. Note that FM Approval typically
covers the tank and not the foundation. Foundation design is usually done separately from the tank design.
For ground-level tanks, there are four main seismic considerations. These include:
1. Flexibility of pipe connections to the tank,
2. Anchorage of the tank and foundation to prevent horizontal and vertical displacement,
3. Clearance around pipe penetrations through pump house or other structural walls, and
4. Proper steel thickness near the base of the tank to avoid “elephant-footing” (using an FM Approved
tank for the appropriate seismic zone will accomplish this).
In strong ground shaking areas, unanchored tanks may have significant vertical and horizontal displacements.
Depending on the diameter of the tank and the height-to-diameter ratio, these expected displacements may
vary. However, the main point is that unanchored tanks can create displacements that may not only damage
the tank, but also rupture the attached piping.
C.4 Other Codes and Standards
NFPA 13, Standard for the Installation of Sprinkler Systems, includes guidelines for protecting sprinkler
systems from damage in areas subject to earthquake. The guidelines contained in this data sheet for the
sprinkler system itself are similar in most respects to the NFPA standard. However, NFPA 13 does not address
earthquake protection of some items such as water supplies, pump systems and equipment that can impact
sprinkler systems.
Section 2.3.1 provides guidance on limitations, exceptions, changes, and additions necessary to bring
systems designed in accordance with NFPA 13 substantially into compliance with this data sheet.
Other NFPA standards that address the fire protection systems discussed in this data sheet are:
• NFPA 14, Installation of Standpipe and Hose Systems
• NFPA 15, Water Spray Fixed Systems for Fire Protection
• NFPA 16, Installation of Foam-Water Sprinkler and Foam-Water Spray Systems
• NFPA 20, Installation of Stationary Pumps for Fire Protection
• NFPA 22, Water Tanks for Private Fire Protection
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