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  • FIRE CONTROL WATER SUPPLY

    NFPA 1142 says on page 11 that a typical dwelling needs a minimum water supply of 3,429 gallons for fire control. Does this mean putting the fire out? If there was a housing development with 1,500 dwellings, does this mean that 5.1 million gallons of water would be needed in a worst case scenario where all housing might be on fire? I don't understand how a water supply for a worst case scenario is calculated. I'm trying to figure out the amount of water needed for fire protection above and beyond the domestic water needs. I'm an ordinary citizen, not a fire fighter.

  • #2
    Thank you for your reply. The problem is that nothing has been built yet, no homes, no commercial establishments. The development is going into a rural wooded area where groundwater will be the source of the water supply. There are no large aquifers, and it is solid rock underneath the surface. I'm trying to size the fire protection needs with only two facts known: 1,500 homes and 76 acres of commercial development proposed. Developers will have to drill for water and it is unknown what they will find. What is needed is the number of gallons of well yield to cover domestic purposes (600,000 gallons per day) and the fire protection needs in a worse case scenario (x gallons stored in a water tower with the rest). I'm looking for x.

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    • #3
      Does this cover all 1,500 homes and the 76 acres of commercial development? This is the thing that confuses me. I can understand the calculation for a single structure, but how do you calculate the water supply if, for example, all 1,500 homes are on fire? Is there a limit to a worse case scenario?

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      • #4
        Let's assume that all 1,500 dwellings will be 100 feet apart. The setting of this development is in a rural area that is now pretty much covered with trees. The developer will probably leave many trees as the place is to be an upscale residential community. In a worse case scenario, there might be a wildland fire, drought conditions, and wind. If the fire initially spread to 100 of the homes, would that mean 500 gallons per minute for two hours for each home? That would amount to (100 homes)(500 gpm)(60 minutes)(2 hours) = 6,000,000 gallons of water. Is this the way you calculate the water supply needs for a large number of homes? Or, if you used the NFPA-1142 criteria of 3,429 gallons as the minimum water supply for fire control for a dwelling, for 100 homes you get 342,900 gallons. Why is there such a large discrepancy between the two calculation methods?

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        • #5
          If you have 100 homes involved, you don't need 500gpm for each.

          For this simple reason: You can't apply water to all of them, just those at the perimeter of the conflagaration.

          By the time the fires at the perimeter are extinguished by water, those on the inside have burned to ashes and self-extinguished from lack of fuel left to burn.

          Similiarly, you don't calculate water needs assuming every house is on fire, since you won't have to ability to apply water to all those houses simultaneously.
          IACOJ Canine Officer
          20/50

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          • #6
            Knowing the ISO ratings might help. The development will be undertaken in the northern part of Culpeper County, Virginia. I have a place in Rappahannock County, Virginia. Rappahannock County is only three miles away from the development. I believe Warren County, Virginia, which is north of Rappahannock County has an ISO-5 for the town of Front Royal and ISO-9 for the county. Page County, Virginia, to the west, has, I believe, an ISO-5 for the town of Luray and ISO-9 for the county. I don't know if Rappahannock County or its county seat of Washington, VA., have any ISO ratings. Nor do I know if Culpeper County has any ISO ratings. If you could find out these ISOs at least I'd know if they had been surveyed by ISO.

            As to water supply needs, NFPA 1142 defines an adequate and reliable water supply as that which is sufficient every day of the year to control and extinguish anticipated fires in the municipality, particular building, or building group served by the water supply. It seems to boil down to what one means by "anticipated fires." Maybe I've gone overboard on the worst case scenario aspect. Since this is a new development, all new mains, hydrants, storage tank(s) will be needed. Also, a beefed up fire department.

            The problem is interesting as the availability of groundwater is the key to the size of the development. Hence my interest in the fire protection water needs.

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            • #7
              I'd like to thank all, especially the7tuwer, for the good information. I have a much clearer picture now of fire protection water needs. I've also checked other topics with the search button and picked up more good information on ISO, water towers, etc. If anyone knows the ISO ratings of the places noted in one of the messages above, let me know. Thank you again.

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