I'll agree the sprinkler knows nothing, but that is irrelevant. We are
working with a mathematical model that will, if all the rules are
followed, give us a reasonable degree of confidence that it will
perform to the design intended, which is, in this case, to keep a fire
contained within the most demanding design area (or any other similar,
but less demanding
area) for a specified duration. So for OH I can space my sprinklers
along the ceiling at a MAXIMUM of 15 ft apart, in any direction
perpendicular to the walls, which is a maximum square footage per
sprinkler of 225 square feet, and a MINIMUM of six feet between them
for a total square footage of 36. So given Mike's layout, he is
well within the parameters of this rule.
Now though we run into another rule which states we cannot EXCEED 130
square feet of floor area per sprinkler in OH so if we run our
sprinklers at 15' apart on the line we can have a MAXIMUM distance
between lines a fraction over 8.5 feet. Since the sawtooth creates a
"compartment," so to speak, because of the obstructive nature of
the "wall" the "compartment"
distances are 8x15 per sprinkler so he is well within the spacing
rules regarding "throw," and since his horizontal space coverage area
at the floor is less than 130 sqft per sprinkler he is within the area
limitation for OH. His density will be a minimum of 0.15
gallons/min/sqft and presuming he has enough pressure to push that
quantity of water through the system to the 13 (before adjustments to
the design area, if any) design sprinklers the system will p[erform as
desired. Back to the ignorant sprinkler. Will it adjust to the
1.0'x7.5'x7.0'x7.5' layout and deliver exactly 0.15 gpm to each square
foot per minute? Of course not. What will happen though is the system
will supply enough water to up to 13 sprinklers anywhere in the system
to meet the design parameter (containment of the fire to no more than
1500sqft). We can feel confident about this since sprinkler systems
have been doing so for over a hundred years both in pipe schedule and
hydraulically designed configurations. In every system, there is a
prize and that is containment or suppression of a fire. There are
several design methods to obtain the prize and 13 is merely a
prescriptive set of rules to get us there. As long as we follow the
rules we'll be alright. If we want to play mathematician or fluid
dynamicist then we'll cease to be layout technicians and we'll get
distracted and our eyes will stray from the prize.
On Thu, Nov 30, 2017 at 9:33 AM, Nick Maneen <[email protected]> wrote:
You are correct. The sprinkler does not know it needs to throw water
in mainly one direction. It will be 15x14
*Nick Maneen, SET *
*c* 704.791.7789 <(704)%20791-7789>
*From:* Sprinklerforum [mailto:[email protected].
org] *On Behalf Of *Michael Hill
*Sent:* Thursday, November 30, 2017 12:30 PM
*To:* [email protected]
*Subject:* RE: Saw-Tooth Ceilings
Yes, the actual floor area is about 120ft² per sprinkler. Each
sprinkler has to spray 7’-0” towards the next line. The next
sprinkler is within 1’-0” of the vertical portion of the ceiling
(which I am considering an
obstruction) and will not spray any further in that direction. The
water will hit the obstruction and fall straight down. I know the
sprinklers can cover that 7’-0” spray, but I need to make sure it
does so at the correct density. So for hydraulic purposes is the
spacing considered 120ft² or is it 210ft².
My take is that the sprinkler is 7’-0” form a wall or obstruction, as
the sprinkler has to spray 7’-0” to cover to the low portion of the
saw-toothed ceiling. L=14 and S=15. So hydraulically that sprinkler
has to cover 210ft². I would like to say it is covering 120ft² but I
need to see where in NFPA-13 that it says I can do so.
Mike Hill
*From:* Sprinklerforum [mailto:[email protected].
org <[email protected]>] *On Behalf Of
*Ron Greenman
*Sent:* Thursday, November 30, 2017 12:09 PM
*To:* [email protected]
*Subject:* Re: Saw-Tooth Ceilings
If I'm understanding your description and question properly you are
covering about 116-117 sqft of floor area if one considers the 1'8"
rise at the tip of the tooth an obstruction, which I would, and your
"throw distance" along the slope is at 0-360 degrees=7.5'/90
degrees=7.0'/180
degrees=7.5 degrees/270 degrees=1.0'. That puts you within coverage
rules for OH, and throw range rules for SS sprinklers.
On Thu, Nov 30, 2017 at 8:33 AM, Michael Hill <[email protected]> wrote:
I am working on a firing range that is going to have a saw-tooth type
ceiling installed. I have a question about determining maximum
protection area per sprinkler.
The vertical portion is 1’-8” tall with the distance from the high
point to the low point being 8’-0”, measured along the slope.
Sprinklers need to be spaced close to the vertical portion of the
ceiling, to protect them from stray projectiles. The sprinkler will
end up being about 7’-0” from the low point of the ceiling, measured
along the slope. The sprinklers are about 8’-0” apart, but with a
1’-8” vertical portion of the ceiling between them. Sprinklers are
spaced 15’-0” apart along the branchline. See attached sketch (if
it came through).
Would the spacing be 15’ x 8’ or would it be 15’ x 14’?
I feel it should be 15’ x 14’ as any individual sprinkler needs to
cover 7’-0” in one direction, measured along the slope. I feel the
vertical portion of the ceiling is an obstruction and can almost been
interpreted as a wall that extends to the floor. I also thought I
needed to increase my design area for sloped ceiling for this
situation, but have since been shown the commentary in the handbook
that explains why it is not required for saw-toothed ceilings.
Maybe I am wrong about the spacing as well.
Mike Hill
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Ron Greenman
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253.576.9700 <(253)%20576-9700>
The Universe is monstrously indifferent to the presence of man.
-Werner Herzog, screenwriter, film director, author, actor and opera
director (1942-)
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Ron Greenman
[email protected]
253.576.9700
The Universe is monstrously indifferent to the presence of man.
-Werner Herzog, screenwriter, film director, author, actor and opera
director (1942-)
