Thom,
I checked IBC after posting. It says the tank is to be sized for 30
minutes of the "hydraulically calculated sprinkler demand, including
the hose stream allowance". There is no mention of standpipe demand.
I might be wrong, but I have never seen "hose stream allowance" used
in context of anything but sprinkler calculations. Is it? Please let
me know. Could it be that the code writers know that a hose stream
allowance is part of a sprinkler demand calculation and that it might
be confusing if they did not flat out say standpipe demand if that is
what they really meant? I think that is a fair assumption, of course
sometimes it seems like the code committees conspire together over
drinks and with rousing laughter to, "make'm scratch their heads for
hours over this one."
Allan Seidel
St. Louis, MO
On Dec 12, 2008, at 10:02 AM, Thom McMahon wrote:
Allen:
I have to disagree with your assumptions.
1) just as you calc the greater demand, the sprinkler or the
standpipe, when
sizing pipe for the combination supply. You would do the same for the
secondary supply and use the same demand.
2) If you want to be literal, the sprinkler demand + the standpipe
demand
represents the sprinkler + Hose
If you'll refer back to the archives Steve L. noted that the
secondary tank
if incorporated into the design of the parking structure can be
placed under
the lowest ramp. A normally un-useable space.
3) WHEN IN DOUBT! Check with your AHJ. (Better to know what he
wants now
than latter.)
Thom McMahon, SET
Firetech, Inc.
2560 Copper Ridge Dr
P.O. Box 882136
Steamboat Springs, CO 80488
Tel: 970-879-7952
Fax: 970-879-7926
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Thursday, December 11, 2008 9:08 PM
To: [email protected]
Subject: Re: Hi Rise Secondary Source ... again
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
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