Smoke detector spacing

[skeshesh]

Good day everyone and happy Friday!

NFPA 72, cir. 2007, 5.7.3.2.4.2 (5) allows for placement of one smoke detection device in an area with a footprint of 900 sq. ft. or less. Does this permitt overriding the 5.7.3.2.3.4 requirement of placing a smoke detection device withing a distance equal to 0.7 times the device spacing?

All comments are appreciated.

 

[steve66]

I can't find the paragraph you are talking about - do you have the reference number right?

Anyhow, I think I know what paragraph you are referring too, and I believe that does override the 0.7 spacing, FOR A SINGLE ROOM ENCLOSED WITH WALLS.

Steve

 

[skeshesh]

I can't find the paragraph you are talking about - do you have the reference number right?

Anyhow, I think I know what paragraph you are referring too, and I believe that does override the 0.7 spacing, FOR A SINGLE ROOM ENCLOSED WITH WALLS.

Steve

You're right its 5.7.3.2.3.5 for the 0.7 of the spacing rule, my mistake.

 

[steve66]

You're right its 5.7.3.2.3.5 for the 0.7 of the spacing rule, my mistake.

I was refering to the first one: 5.7.3.2.4.2(5), but after looking again, its right there. You've got to love the way they number 72 I'm so glad the NEC doesn't follow the same numbering style.

The 2007 handbook has an explination that says: With regard to 5.7.x.x.x.x(5), where smoke detectors are being used to fulfill a life safety objetive, a room of only 900 ft2 constrains the ceiling jet such that even when ceiling beams are present, the fire can be detected sufficiently early to achieve the objective. Where other objectives demand more rapid response, performance based desing methods should be employed.

So it wouldn't necessarly apply to an open area of 900 sf, unless the area is somehow enclosed or bounded in a way that the smoke is constrained.

Steve

 

[skeshesh]

Thanks for the response Steve.

I don't have the handbook so I dont have the additional explanation, but from what I can tell the explanation you referred to doesn't really justify overriding the 0.7 spacing rule, since that rule applies to smooth ceilings which by definition assumes no obstructions by beams or other obstructions. The fire code is pretty horribly organized and written. Fortunately the members of the construction team on this particular job (ower representative, inspectors and enviornmental crew) all happen to be great people. I'm still burried in a mountain of RFIs of course, but at least they don't go out of their way to argue every insignificant detail of my responses.

 

[steve66]

Thanks for the response Steve.

I don't have the handbook so I dont have the additional explanation, but from what I can tell the explanation you referred to doesn't really justify overriding the 0.7 spacing rule, since that rule applies to smooth ceilings which by definition assumes no obstructions by beams or other obstructions.

Yes, but the rule we are talking about falls under 5.7.3.2.4.2 which starts with: "For level ceilings the following shall apply:" So 5.7.3.2.4.2(5) should apply to all rooms with level ceilings.

Also, the handbook explination does say "even with ceiling beams present". So I still believe one detector is OK in a 900 sf room with or without beams. But I also don't mind agreeing to disagree After all, we are probably only talking about one detector.

Steve

 

[skeshesh]

Yea, I mean it's not that I disgaree with pretty much anything you've stated. I'm just saying the rule we're talking about has to do with how far the detector can be from the further corner of a room. This has nothing to do with beams or obstruction. The room I'm talking about is 900sq. ft. but its long and narrow, so that one detector is more than 0.7 from the corners of the room even if placed dead center. I might just put an extra detector so it's covered anyway, it's just a room here and there with this situation, it won't really effect the scope of the project or impact the cost in any meaningful way.