Theory behind the Fire Flow Analysis 1

[train707]

Hello everybody,
I've been using Haestad Method's WaterCAD for the Fire Flow Analysis of my water distribution system related to sub-division project.

I found that my distribution system having 10", 8" and 6" dia. pipes can provide fire flow of 700 gpm at each node without lowering down the system pressure below 20 psi.

My question is- Is that Fire Flow available through each fire hydrant runing all simultaneously or runing one hydrant at a time?

 

[sam74]

Around here typical calcs would show running (with the required demand, 500 gpm here) the one hydrant that shows the worst overall (lowest) system pressures as compared to all other hydrants solitary runs with a minimum 2 gpm demand for each residential unit at the same time with a minimum 20 psi pressure.

 

[train707]

Sam74, thanks for your response. But what my concern is how does the WaterCAD analyses the fire flow? You might be familiar with the logic.

 

[msquared48]

Une hydrant might be ok to analyze for a residence, but I would think that for a larger retail or industrial building, two or three hydrants running would need to be considered more realistic, all maintaining the 20 psi minimum. Here you might have to consider the two or three alarm situation.

Mike McCann
MMC Engineering

 

[cvg]

700 gpm is probably insufficient fire flow. check with the fire marshal and wouldn't be surprised if required fire flow is closer to 2,000 gpm or more

 

[coloeng]

It's been a while since I used Haested's, but if I recall correctly, the flow that is provided in the fire flow analysis is for each hydrant flowing one at a time.

 

[train707]

Thanks coloeng. My assumption was same as yours.
Do you have any idea how do I change the scenario to simulate fire flow through two or more fire hydrants at the same time (for the worst case scenario)?