I was always lead to believe the 60 to 90 minute duration was driven by
response time of a reliable fire service as it relates to a given
property location.As to the volume,estimating the tank size by
density/area/duration is fine as far as pricing goes,but when it comes
down to job completion,you'd better have enough water in the tank to
satisfy actual installed conditions.No skimping allowed!
Lamar Vaughn,SET
On Fri, Aug 12, 2011 at 9:50 AM, [email protected] wrote:
So based on your assessment, if the fire isn't out in 45 minutes it
will burn forever?
Sorry but I find that logic flawed. Every fire at some point is
extinguished. I'm fully confident that the values of water duration
in 13 are based on more than a number pulled from the sky.
But in our conversations on how to determine water demand some want to
cut it to the exact .15 over 1500 sf when we all know that the flow
will not be exactly .15 gpm/sf from every head within the usually more
than 1500 sq. ft. So if there is reason to be skeptical that the
duration of 60 minutes isn't sufficient then why calc it to the gnat's
eyelash for flow?
How do you rationalize a statement like "...it doesn't matter what
size tank you use used, if this thing has a fire you'll be WRONG no
matter what, and there will be plenty of lawyers to say so." If you
followed the prescriptive Codes and Standards and designed the system
accordingly how could a lawyer say you did it wrong?
Sometimes I find the lawyer paranoia a bit overwhelming on this board.
Craig L. Prahl, CET Fire Protection CH2MHILL
Lockwood Greene
1500 International Drive
Spartanburg, SC 29304-0491
Direct - 864.599.4102
Fax - 864.599.8439
CH2MHILL Extension 74102
[email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Thom
Sent: Thursday, August 11, 2011 5:48 PM
To: [email protected]
Subject: RE: Water storage/NFPA 13 Proposal
If your fire was not under control, and being extinguished by the FDP
at 45 minutes, it won't be at 60 minutes either. The same can be said
for 75 minutes vs. 90 minutes. Those last few min. of tank supply are
the least important minutes. If your fire dept. doesn't have this
thing out by 45 min.
it's time to fall back, pull out the marsh mellows and dogs.
Sprinklers work, when they control the fire early, and the FDP
response times are prompt.
It doesn't matter what tank sizing you used, if this thing has a fire
you'll be WRONG no matter what, and there will be plenty of lawyers to
say so.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Mark
Sornsin
Sent: Thursday, August 11, 2011 2:39 PM
To: [email protected]
Subject: RE: Water storage/NFPA 13 Proposal
Bill:
I agree #1 is the easiest; but it can also result in tank sizes
considerably smaller than #3, which represents the actual design flow.
Local conditions can really alter the amount of overage a system
design might include - overage could range from 5% to well over 50%.
Given that I am unaware of problems where the tanks were undersized, I
am reluctant to believe we need the added volume required by #4.
As for having to do a design ahead of time, I don't see that as a real
problem. That's part of engineering (whether you're a NICET designer
or a PE). The fact that tanks normally come in standard sizes usually
affords some 'fluff' so that you don't necessarily have to have the
exact final design of the system prior to sizing the tank.
Mark A. Sornsin, PE| Fire Protection Engineer Ulteig Engineers, Inc.|
Fargo, ND [email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Bill
Brooks
Sent: Thursday, August 11, 2011 7:34 AM
To: [email protected]
Subject: RE: Water storage/NFPA 13 Proposal
I see four possible calculation approaches for the sprinkler demand
part of tank sizing:
1. Minimum Density x Tabular Design Area x Time 2. Minimum Density x
Actual Design Area (developed using the 1.2 rule) x Time 3.
Hydraulically Calculated Demand (Demand Calc) x Time 4. Hydraulically
Calculated Demand (Supply Calc) x Time
I intend to submit a Comment to clarify this.
#1 is the easiest for everyone, the others require the sprinkler
system to be fully designed before the tank size can be confirmed.
It's also evident that all of the methods other than #4 will mean
draining the tank in less than the required time duration.
Then of course is how to decide whether to use 60 minutes or 90
minutes or something in between for OH.
Bill Brooks
William N. Brooks, P.E.
Brooks Fire Protection Engineering Inc.
372 Wilett Drive
Severna Park, MD 21146-1904
410-544-3620
410-544-3032 FAX
412-400-6528 Cell
in the subject field)
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