I'm a little confused by your explanation, but let me try and
describe as I see it. In situations with long enough branch lines,
22.4.4.1.1.1 would apply, which is the 1.2X rule. If the branch lines
are not sufficiently long to meet the 1.2X rule, then section
22.4.4.1.1.3 would apply. In both cases, the 1500 sqft (or whatever
the design area is) would need to be met. Remember, the commentary is
not part of the standard.
At 06:32 PM 1/20/2009, you wrote:
Good afternoon everyone, or evening for East coasters. I would like to get
a second opinion about a matter dealing with the commentary and 22.4.4.1.1
of the '07 edition. 22.4.4.1.1.1 says that I have to have my 1.2 length of
my remote area parallel with the branch lines. My question is how do you
approach a situation where the branch line is of insufficient length to meet
the 1.2 length.
For example, (this is not based on real numbers, so hopefully my
guess-timation doesn't further complicate the issue, if I have a center-fed
tree system, and I am calculating 1500 sf. I would typically be required to
have the longer length of my remote area be at least 47 feet long. What do
I do if my branch line is only 40 feet long (and say containing 7 heads)?
I have always understood that I would include all seven heads on the branch
line, then continue adding heads until I get to 1500 sf. So, I would calc 3
branch lines and an additional 3 heads. This wouldn't satisfy the 1.2
requirement. BUT, figure A.22.4.4.1(a) example D shows this type of
configuration. The commentary also says "To required more water to flow
through a smaller number of individual branch lines is hydraulically more
demanding than to require the same demand to be supplied by more branch
lines with fewer operating sprinklers."
We are working with a free-lance designer that is arguing the 1.2 length
MUST be met. So, in the example I gave he would treat the situation
oppositely than I would. He is arguing it is necessary to meet the 1.2
length, and will pick up more branch lines, but with fewer heads. His
argument is that the commentary after 22.4.4.1.1.3 only applies to that
section and not 22.4.4.1.1.1. And, near the end of the commentary is says,
"the requirements . are illustrated by System D if Figure A.22.4.4.1(a).
Note that the design area's longer dimension is along the cross main." He
was also taught to do it this way from one of the few FPE's in the state.
So, I would really appreciate it if I could get some feedback on this
example. Thank you all for your time, I know you all don't have much of it
to spare.
Thanks,
Jimmy Waite
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Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, Connecticut
www.fpdc.com
860.535.2080
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