ESFR under sloped ceiling partly >30' high 1

[SprinklerDesigner2]

I have a typical 500'x250' bent metal purlins on rigid metal frames spaced 25'-0" building.

Eave height is 24', roof pitch is 1 in 12 putting the peak at 34'-5" from underside of metal roof panel to concrete finished floor.

We are protecting wooden pallets stacked to 25'-0" high while maintaining a 3'-0" clearance between the sprinkler and top of storage (wooden pallets).

Looking at ESFR 16.8 sprinklers discharging at 52 psi per Table 12.1.9.1.2(c) "ESFR Protection of Indoor Storage of Idle Wood Pallets"

Minimum spacing is 8', maximum is 10'.

Normally I hang from the top lip of the bent metal purlin running the usual 2 1/2" branch line up in the purlin space.

On this building the first purlin is 0'-7 1/2" measured off the peak to the purlin lip I would hang to and then 5'-0" OC.

If I hang off on of the top purlins the next purlin on the opposite side down is either 6'-3" (to close) or 11'-3" (to far.

The only thing I can do is hang off the purlins on one side until I get to the peak then use trapeze hangers (uni-strut with U hangers) to maintain the 10'-0" spacing down the other side with the actual pipe being 1'-3" from the purlin.

Sprinklers will be 8'-4" OC so I will have 83.33 sq ft head spacing.

Is there any reason, once I travel far enough down the slope to a point where the roof < 30' AFF, where I can have one line spaced at 11'-3 (94 sq. ft. spacing) to once again catch a purlin?

Better to have four or five lines on trapezes than twelve.

 

[MGXFP]

I'm away from the office now, but do check the spacing requirements in 13. You may fudge some spacings to avoid structural interference; I have found the need to do so before. The last time I did this was when NFPA 13 2002 edition was enforced so hopefully the rules have not changed.

 

[SprinklerDesigner2]

NewtonFP,

The rules are pretty straight forward.

100 sq. ft. per head.

Minimimum 8'-0" spacing.

Maximum 12'-0" spacing where ceilings are <= 30' and 10' when ceilings exceed 30'.

Imagine bay spacing >20' and less than 24' with ceilings >30'. Couldn't do it with ESFR.

I am confident I can go to 12'-0" spacing, as long as I do not exceed 100 sq. ft. coverage, once the ceiling is < 30' but throwing out the question is sounds like a good idea.

 

[firepe]

SprinklerDesigner2,

You said "I am confident I can go to 12'-0" spacing, as long as I do not exceed 100 sq. ft. coverage, once the ceiling is < 30'"

I would NOT be so confident if I were you.

The NFPA installation rules are CLEAR. The height to determine design criteria for ESFR is based on the HIGHEST elevation. Where does it say that you may take liberties with that rule? If you have an engineer willing to make that determination, more power to you, but as a NICET Technician, by NICET rules, you should not be attempting to make such an interpretation.

I would suggest stick to the rules, and hang accordingly.

 

[SprinklerDesigner2]

firepe,

You are right, it was a poor choice of wording on my part. If I was that confident I wouldn't have asked the question.

3.3.4 Ceiling Height. The distance between the floor and the underside of the ceiling above (or roof deck) within the area.

What's an "area"?

If I had a 40,000 sq. ft. building with flat ceilings half of which was a high bay at 32' and the other half low bay at 28' would the maximum 10' spacing apply to the low bay area as well?

 

[firepe]

Simply put, Yes, it's all the same system, and the highest ceiling height MUST be used to determine the required ESFR design criteria.

Unless there was a significant separation between areas, such as a deep draft curtain, which I am not necessarily endorsing either.

Either way, Not something NICET had in mind for a certificant to determine.