Sizing of Foam Concentrate Tank

[DTR]

I am designing a Foam Enhanced Deluge System, I have to do a Hydraulic Calculation around the longest yard path of my Fire Main to ensure that I can satisfy the minimum nozzle pressure.

Is there a code requirement to do a Hydraulic Calculation on the most hydraulically favourable route (ie highest flow rate) to ensure that the Foam Tank is sufficiently sized to meet the discharge duration.

 

[jcubedtr6]

NFPA 11 and NFPA 16 have the requirements on foam system design. If it is for a foam water sprinkler or spray system, the typical foam discharge time is 10 minutes with a density of 0.16 gpm/sq ft. You will have to calculate the suppression system discharge rate, times the discharge time, times the foam concentrate percentage (typ. 1%, 3% or 6%). This will give you the minimum foam concentrate required for the foam system.

Jay Jablonski
HSB PLC
800-417-3447 x 3430

 

[DTR]

Thanks for the response Jay, however the question / clarification I requested was from a Hydraulic perspective.

The hydraulic calculation used to size the foam concentrate tank is normally based on the longest yard path around the fire main. If I Hydraulically Calculate the system I have designed using the shortest yard path, the pressure at the nozzles is obviously a lot higher than if I use the longest yard path, this means that the system has a higher flow rate and therefore uses more concentrate than if I calculate it around the longest yard path, so my question is are there any NFPA code requirements that the shortest yard path (highest flow rate) is to be used for the sizing of Foam Concentrate Tanks?

The reason for me asking is that if I size the tank for 10 minutes duration of discharge using the longest yard path and then calculate the system operating around the shortest yard path the tank is only big enough to give a duration of discahrge of 5 minutes! which is below the 7 minute minimum given in NFPA11.

As a footnote all systems designed in accordance with British Standards (BS5306) state that the most favourable hydraulic calulation should be used to size foam/water storage tanks.