I don't have the exact IBC words in front of me. I think the tank is
sized for sprinkler demand and the sprinkler hose stream allowance.
It would say standpipe demand if they wanted it to be a standpipe
demand secondary supply. You would have a huge tank it were to supply
both. The tank is already relatively large from the architect's point
of view when it is sized for sprinkler demand and hose stream. For
example, the bottom high rise floor is often mercantile and you might
easily have a 1.8 overage in that sprinkler system. The actual
sprinkler demand might be 1500*0.15*1.8 or 405 gpm. Add 250 hose for
655 gpm. 30 minutes of that is 19650 of stored gallons so therefore
the tank has to be bigger than 19650 g. Suppose it meant to supply
both. That might easily be 405 + 750 for 1155 gpm. 30 minutes of that
is 34650 gallons of storage that needs to be somewhere near the
elevation of the fire pump. Try telling the developer or architect of
the 80 foot high rise with a building footprint taking up the entire
lot that there must be room for 35000 gallons of full time water
storage taking up xx number of precious parking stalls.
Allan Seidel
St. Louis, MO
On Dec 11, 2008, at 12:35 PM, Dave wrote:
Greetings all..
I know I brought up this general topic once before but bear with me
on it again. IBC-2006 Section 903.3.5.2 is the requirement for
secondary on-site water supply in high rise buildings. Presuming
we have an eligible building it comes down to sizing the storage
tank or vessel.
Code says 30 minutes of sprinkler demand - no problem on that
part. It gets muddy at 'including hose stream allowance' -- here's
my dilemma.
This is a high rise building and it also requires a standpipe to
NFPA 14. Many times this means a combination riser for sprinkler
and standpipe. Now NFPA 14 tells us that when designing such
combinations we do not apply the hose stream allowances of NFPA 13
since 14 is the hose stream standard when it comes to a standpipe
system - still with me ??
How do I use a hose stream allowance for tank sizing when Im told
not to apply hose stream allowances in the overall design and in
reality the FD will be hooking up 2 1/2" hoses to the hose valves
and pulling +200 GPM for hoselines. Do we calculate the 250 GPM as
the 'hose stream allowance'? If we use the 100 GPM hose stream in
NFPA 13 in spite of all this then we will be flowing +200 and
having only designed for 100 GPM we will no longer have the 30
minutes of sprinkler duration in a common riser system.
What say everyone else - I'm totally up in the air and need
something to go with.
Dave P.
AHJ in NJ
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