ISO Fire Flows

[SprinklerDesigner2]

I am just curious about what might be the ISO fire flow for 65,000 sq ft non-combustible UPS type terminal building?

The building has full wet pipe system and it is in a big field with nothing around it but open space 500' in any direction.

Water at the street is 50 static, 20 residual flowing 750 gpm and even with the building sprinklered my gut tells me it doesn't meet the ISO fire flow requirement.

1,000 gpm? Nahhhh... I found some online spreadsheets and it is looking more like 2,000 gpm? A 1,500 gpm pump needed for an OH2 sprinkler system?

I am not using this information for anything other than I am simply curious... the only answer that would count in my book would be from the building professional of record because the decision sure as heck ain't mine to make!

 

[MGXFP]

I haven't done the math for this scenario but the calculation is a simple one. You are probably correct at 2,000 GPM @ 20 psi. The variables include type of construction, area, windows etc.

The important take away from this is, perhaps, that fire flows and sprinkler demands are two different animals.

I believe the ISO calculation is used to determine some insurance rates for building owners and insurance rates for cities.

 

[SprinklerDesigner2]

I am not an expert in this area but let's assume the required fire flow is 2,000 gpm then without any public water I would be looking at a 1,500 gpm fire pump.

If we have 750 gpm @ 20 psi available from the city main then a 1,000 gpm pump should do the trick delivering a total of 2,250 gpm @ 20 psi?

It appears the civil engineer came up with the 150,000 gpm tank and that has to be to meet the fire flow. Darn tank is coming to better than $200k once the foundation and pumphouse is added to it.

 

[chicopee]

If the data about the municipal water supply is correct, then a fire pump rated at 1500psi will damage the water main and probably the fire pump. You just don't have enough water and pressure in the municipal water line. You should look at either connecting another water line from another point in the town water piping loop or install a water tank.
Since the sprinkler system to the terminal was undoubtedly hydraulically calculated, check the data plates attached to the sprinlker alarm check valves for additional information about the water requirement and supply

 

[SprinklerDesigner2]

Fire pumps don't make water they just boost pressure. In Georgia we are required to have at least 20 psi residual pressure, at the pump suction, with the pump operating at 150%.

Given the fire flows made available to us a tank, probably 150,000 gallons, has always been in the equation. Given a 20 psi residual at 750 gpm if fireflows are required the largest pump I would dare put on that line would be 400 gpm.

 

[TravisMack]

I would be looking at a break tank. What is your water supply duration? Let's assume 2 hours. So, with 2000 gpm demand, you have 240k gallons of required demand. The city can supply 750 gpm @ 20 psi. Since your city supply will be filling the tank from the top, I would adjust that for elevation of water discharge at top of tank. So, just for fun, let's say the city can supply 650 gpm for your project.

650 gpm * 120 = 78k gallons. So, your tank, provided with an automatic fill line and float valve would need to store 240k-78k gallons, or 162k gallons.

For your fire pump, you are going to need a minimum of 1500 gpm pump as a 1250 gpm won't be listed to give 2000 gpm @ 150% of capacity. So, the 1500 gpm pump is your capacity. Since you are getting a pump no matter what, I would look at a rating that will be the highest you can get based on power to the building. I mean if you are already putting a pump in, you may as well get the biggest bang for the buck in pressure so you can reduce your fire sprinkler system piping.

Travis Mack
MFP Design, LLC

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