Fire Sprinklers Continued from page 38
higher than the maximum sprinkler demand. In reality, the fire department is “taking this amount of
water away” from the available supply and the sprinkler sys- tem is “left” with a degraded water supply curve. This con- cept has been developed and promoted by J. Michael (Mike) Thompson, P.E.; a founding partner of the Protection Engineering Group. Mike has developed software providing a number of hydraulic tools, one of which plots supply vs demand curves in this fashion.
Density Concerning sprinkler system design, fire protection pro-
fessionals speak in terms of density; the rate of water appli- cation per unit area at the floor level. For example, an office space would typically be protected by a sprinkler system designed to deliver 0.10 gpm/sq.ft. This doesn’t sound like much water, but that conclusion is usually a result of never witnessing an actual sprinkler system discharge. Fire protec- tion professionals should not only know what NFPA 13 requires for various hazards but they should also have a “feel” for the numbers if they are to truly understand how these systems can/will perform. Participating in an actual sprinkler discharge demonstra-
tion or experiment is best to truly understand these designs, but short of that consider the following scenario: An Ordinary Hazard, Group 2 sprinkler system in a room that measures 10 feet wide x 10 feet long x 8 feet high operates and delivers 0.20 gpm/sq.ft. over the entire room’s floor area. Assume the room is watertight. After 10 minutes of dis-
1 12/14/09 9:16 PM
charge, the room would contain 200 gallons of water. That would be 3.2 inches deep across the entire room and weigh 1,670 pounds. Such a feel for the density gives the fire protection pro-
fessional a better understanding of the sprinkler system’s power, which is important when solving unusual problems or justifying a performance-based design.
Conclusion The above examines five random topics concerning fire
sprinklers system hydraulics. These and other issues must be well understood by fire protection professionals as part of designing a system that will not only comply with the requirements of NFPA 13 but also will provide the protec- tion intended by the design professional. n
Thomas W. Gardner, P.E., FSFPE, LEED AP; Alex
Munguia, P.E.; and April M. Musser, P.E. are from The Protection Engineering Group Inc. For more information, visit
www.pegroup-inc.com.
Edition, J. Lake, page 833. 3 Fire Protection Hydraulics and Water Supply Analysis, Second Edition, P. Brock, page 240.
today there are diffusers and digital flow meters with inter- nally fixed pitot tubes, which are more accurate and much easier to use. 2 NFPA 13 Automatic Sprinkler Systems Handbook, 2010
1 Although use of hand held pitot tubes is still prevalent,
Circle 25 on Reader Reply Form on page 65 Page 40/Plumbing Engineer May 2011
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