Bill,
The number of rings that operates is a function of the occupancy. In a
light hazard occupancy, a fire will not operate sprinklers byond the
second ring unless something goes wrong. In more challenging
occcupancies, you get into the third, or even fourth wring, even if
nothing goes wrong.
The curves for claa I-IV are a very special case. They were developed
from testing in the late 60's and early 70's, when most existing
sprinkler system were simple pipe schedule designs. It was deemed
necessary to provide curves to allow as many existing systems to be
evaluated as possible. A curve was developed from testing of class II
commodity at a variety of densities. As would be expected, the number of
sprinklers that operated went down as the density went up. No safety
factor was applied to the curve. Each test was plotted as an unadjusted
point. Two tests of class III commodities were performed, and a curve
parallel to the class II curve was plotted through those two points.
Two test were performed on a class IV commodity, and the curve was
plotted the same way. The class I curve was drawn without any tests.
It's not pretty, but there you have it!
You will note that no protection requirements based on actual testing
subsequent to the class I-V tests have involved curves.
The reason that designs based on the curves have worked so well is that
they were based on tests using K5.6 sprinklers and the design
requirements were specified as densities and areas. As we have
subsequently learned, discharge density is not a fundamentel measure of
sprinkler performance. A 0.30 density is significantly more effective
from a K8.0 sprinkler than from a K5.6, and far more effective from a
K11.2 sprinkler. Economics have made the larger K-factors the normal
choice. That's the safety factor we have now.
Joe
Brooks, Bill wrote:
I laid out a 11.4 x 11.4 pattern (130 sq ft) and drew three rings. 1st ring
included 4 sprinklers (520 sq ft). 2nd ring included 12 sprinklers (1520 sq
ft). 3rd ring included 24 sprinklers (3120 sq ft). The numbers are
comparable to NFPA ~1500 sq ft and the DoD ~ 3000 sq ft.
The ring theory makes sense in this context. NFPA is looking for a two ring
design and DoD is looking for a three ring design? Was this purposeful? If
so it provides the basis for the 1500 sq ft minimum design area.
Using this approach, the 900 sq ft design looks like it has a very small
margin of error.
If we have this two ring NFPA design, what led to the development of the
area/density curves where density is decreased as design area is increased?
Bill Brooks
Pittsburgh, PA
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Joe
Hankins
Sent: Friday, March 16, 2007 2:49 PM
To: [email protected]
Subject: Re: Burning Ring of Fire (and the Flames Shot Higher)
Bill,
You are correct. Sometimes politics prevails.
Joe
Brooks, Bill wrote:
Joe,
I thought I understood your train of thought until I started considering
the
area reduction for quick response sprinklers. How many rings are there
with
a 10 ft ceiling height QR design? 900 sq ft or 5 heads.
Can I conclude the ring theory falls apart when this design approach is
used? It looks like you don't have your 1 ring cushion in this case.
Bill Brooks
Pittsburgh, PA
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Joe
Hankins
Sent: Friday, March 16, 2007 11:56 AM
To: [email protected]
Subject: Re: Minimum Supply Pressure
The idea that there is a huge difference between a 5-sprinkler fire and
a 15- or 30-sprinkler fire seems logical on the surface, but if you know
how sprinklers operate, you know they operate in rings. The heat that
operates sprinklers spreads in a circle from the fire origin. For
symetrically-spaced sprinkler system where the fire starts centered
among 4 sprinklers, there are 4 sprinklers in the first ring around
ignition, so there is virtually no difference between a 1-sprinkler
fire and a 4-sprinkler fire. If those sprinklers don't control the fire,
then any (and all) of the 12 sprinklers in the next ring can operate,
meaning that there is very little difference betwen a 5-sprinkler fire
and a 16 sprinkler fire. If you get into the next ring, then the number
is 36 sprinklers. So, the 1-ring "safety factor" between 4 and 16
sprinklers is the same as the 1-ring safety factor between 16 and 36
sprinklers. A 1-ring "safety factor" is not overkill in my book!
_______________________________________________
Sprinklerforum mailing list
[email protected]
http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
_______________________________________________
Sprinklerforum mailing list
[email protected]
http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
_______________________________________________
Sprinklerforum mailing list
[email protected]
http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
_______________________________________________
Sprinklerforum mailing list
[email protected]
http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
