How to calculate how much water should be on site for fire suppression?

[texas transplant]

This is a new one for me, guess I have been very lucky up till now.

We have a parcel of land in the city that is not served by a water main. A church owns it and wishes to build a new church building on it. They want to build about 25,000 square feet total, type 2 construction. They are willing to construct a tank and pump on site for fire sprinklers and fire fighting.

The building will be sitting by itself, no other building related exposures. Next closest structure over 0.5 miles away.

Nearest fire hydrant is 0.7 miles from the front property line and the building site is another 0.4 miles from the front property.

Question is, what standard, formula, etc. do you all use to determine the minimum required amount of water storage on site.

We are under 2006 IBC and IFC.

 

[Coug Dad]

Look in Appendix B of the IFC. There are reductions up to 75 percent, but not less than 1,500, if the building is sprinklered.

3250 gpm for 3 hours if not sprinklered

may be reduced to as low as 1500 gpm if sprinklered

 

[mtlogcabin]

Go to appendix B in the IFC Table 105.1 A Type II with 25,000 sq ft structure requires 3,250 gallons per minute for 3 hours or 585,000 gallons of water. Now there are reductions allowed so get with the FM. Might be cheaper to extend the water main.

 

[cda]

how about the water for the sprinkler system???

sounds like require a fire protection engineeer to fiqure it out and submit

but the answers will give you guidance to check the engineer's work against.

 

[Insurance Engineer]

NFPA 13, (pick your edition, does not matter) church is a light hazard occupancy requires .10/1500 = 150 gpm + hose demand of 100 gpm= 250 gpm for 30 minutes= 7,500 gallons of water in a tank, pond, bladder, etc etc. If this was a dry system for whatever reason then .10/1950 = 195 gpm, hose requirement and duration is the same as a wet system, so a total of 8850 gallons.

If you start playing with quick response sprinklers and ceiling heights the 1500 design area can go as low as 900 sq. ft, so even less water.

So why does the IBC require 1500 gpm for a sprinklered building when NFPA 13 will be happy with 250 gpm????

From an insurance point of view 250 gpm is all that is required to get a sprinklered rate for the building.

 

[hlfireinspector]

Explain to them the requirments and up keep cost of tank and private water mains. Cheaper and better to extend water mains. I have been told ISO will not rate Ponds.

 

[AegisFPE]

IFC App B includes a modification for "Areas Without Water Supply Systems" to use the IWUIC. The WUI code allows for an analysis based on a "nonconforming" water supply, which could be no supply at all. The church may be able to utilize ignition-resistant construction and defensible space practices through applying the WUI code in the absence of installing onsite fire flow. This may require more advance planning and negotiation than providing onsite fire flow.

If they were to install a tank, it may be appropriate to strategically locate it and provide for stubs to neighboring properties so they could potentially recoup some of the cost by allowing additional parcels to be served. Alternatively, there may be a way for the water utility to lien the parcels that would be served along the main extension for the church to be reimbursed if/when those other parcels connect in the future. Either would probably involve more upfront cost than if the jurisdiction accepted a WUI evaluation.

 

[Insurance Engineer]

Explain to them the requirments and up keep cost of tank and private water mains. Cheaper and better to extend water mains. I have been told ISO will not rate Ponds.

If the pond supplies the sprinkler system and the pond, fire pump and sprinkler system met NFPA codes then ISO would approve it. They would need to review the plans and witness the fire pump test. Also ISO does approve ponds if it has an approved ISO suction point installed. Not all insurance companies use ISO rates so that may not even come into play.

The cost to run a mile of water main in NJ is about $50-75 a foot, that is a lot of $$. A 10K gallon tank and 250 gpm pump is about $20-30K. I just got doing a project like this for a church. When they looked at the cost of running a water main it was much cheaper to put in a tank. They installed a pressure tank so no pump to test, just an air compressor to maintain and the tank. The tank is underground except for the end which is exposed so it has minimal impact on how it looks, matter of fact if you do not know where to look you would not know it. The cost of the pressure tank was about the same as the tank and pump, but you have a lot less to maintain and less that can go wrong. A public water main is always the best option, but sometimes it just not cost effective.

 

[FyrBldgGuy]

Yes there are many ways to calculate water supply based on IFC, Chapter 5 and then Appendix B. ISO has a formula and so does NFPA 1142. But, the fire department is the key to answer. If they do not have the ability to transport water at a rate of 250 gpm for two hours then ISO will rate the area as unprotected. A tank that supplies a rate of 250 gpm for two hours is 30,000 gallons. Ponds can be used and if considered there are issues regarding open water sources. I have unfortunately had to clean the pump of more than one fire truck where craw fish were sucked into the pump from a pond. Minnows also make a very robust fish soup in a pump.

I always recommend beginning with Appendix B. Second, although church members have to pay for construction through donations and that can mean significant money issues and the desire to cut corners, it is my philosophy that I should try to keep them from going to Heaven before their time.

If you use NFPA 1142 as allowed in Appendix B, then make sure that an FPE does the calculation.

 

[texas transplant]

Update to OP

The church wants to toss the water main extention out of the mix because the cost of installation is going to be well over $75.00 a foot (terrain issues where the pipe must run and a bore job under an interstate highway). The church has retained a Fire Protection Engineer and this morning he told me he wants to use NFPA 1142 to size the tank. Appendix B of the IFC 2006 talks about NFPA 1142 in section B103.3., which seems to apply in a way as it is for "Areas without water supply systems". And it appears that the water supply would be considerably smaller using NFPA 1142. Any and all comments welcome.

 

[Coug Dad]

See what the FPE recommends and see if it is reasonable.

 

[permitguy]

If it's alright with the fire code official, go crazy!

 

[mtlogcabin]

Update to OPThe church wants to toss the water main extention out of the mix because the cost of installation is going to be well over $75.00 a foot (terrain issues where the pipe must run and a bore job under an interstate highway

We have what is called a "Developers Extension Agreement" that is used to help a developer that extends services to potentially recover cost over a 10 year period when future utility users hook onto services.

 

[FyrBldgGuy]

Just a couple of things. If the FPE suggests something less than 30,000 gallons it should be discussed with the Fire Chief. The ISO rating for the area will be affected. Verify the difference between the useable amount and the total amount. Open water sources have less useable water due to a number of factors. Even a tank will have some amount of water that is just not available. The FPE should also be looking at fire pump design. The fire pump should not be designed for sprinklers only. The minimum flow amount at a hydrant should be critical.