Multiple Fire Hydrants Flowing
Multiple Fire Hydrants Flowing
(OP)
I have a 117K SF store that is sprinklered and we are following 2003 IFC. I get a 50% reduction thus I need to provide 3500 gpm for fire hydrants. We have multiple fire hydrants through the site. What is the minimum I must run a Fire Hydrant to achieve 3500 gpm. I.E. do I run two at 1500gpm and one at 500gpm? Or is 1500gpm a minimum for each Fire Hydrant, thus making me have to flow 3 at 1500gpm, putting me over the required 3500gpm?





RE: Multiple Fire Hydrants Flowing
I can't imagine anyone requiring 3x1500 when the total requirement is 3500 gpm. In any event, I would ask the fire department.
Normal fire fighting would not actually stress a system that hard. The 3500 gpm fire flow requirement includes a safety factor that is owned by the fire department. Same with the 20 psi minimum at the hydrant head. A friend who works for the Ventura County Fire Department told me back in the 1980s that a typical residential fire might require 500-750 gpm for 30-45 minutes, but if the fire jumps to another structure more would be needed. This is why they might require 1250 gpm for two hours.
Also keep in mind that 1500 gpm in a 6" hydrant lateral is a whopping 17 fps. At 1500 gpm you will probably lose maybe 2 psi in the lateral (L=30', C=130, d=6", Q=1500 gpm >> 4.7'=2.0 psi) and another 6 to 8 psi in the hydrant head (I have laboratory tested three American AVK hydrants at 6.3, 6.5, and 6.6 psi loss at 1500 gpm). Under these conditions, you need around 30 psi in the main to provide 20 psi at the hydrant head, not counting for elevation differences.
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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill
RE: Multiple Fire Hydrants Flowing
RE: Multiple Fire Hydrants Flowing
I may have misunderstood your comment about thrust blocks, but their sizing depends on maximum system pressure plus a safety factor and not on high flow rate.
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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill