NFPA72 smoke detector spacing reduction dut to heigth

[DavidCR]

Hello to every body.

Reading NFPA72 2002 edition, I cannot find to reference for the spacing reduction for spot tipe smoke detectors due to ceiling height.

I´ve been told to use the same heigth reduction that is indicated for heat detectors on table 5.6.5.5.1 ("Heat detector spacing reduction based on ceiling heigth"), but I cannot find the mention in the code that clarify how to apply a reduction for smoke detectors.

Any help, thanks a lot in advance.

 

[cdafd]

there is one for corridor like set ups, not sure about ceiling should be a circle like chart showing the reduction, can give you better answer when I have the book in front of me.

if there it has to be in the smoke detector section on spacing

 

[cdafd]

look at a.5.7.3.2.3E 2002 edition

and fiqure a.5.6.5.1.2 not sure about ceiling height though

as always you have to install per manufacture so you might start there first.

 

[Canook]

Question: If spot type smoke detectors are allowed to be ceiling or wall mounted in a corridor and on smooth ceilings spacing of 30 feet shall be permitted as a guide. Do you use the same guide if you wall mount the smokes in the corridors? Down loaded the specs on the smoke detector it refers NFPA 72 and local codes.
Thanks,

 

[cdafd]

Canook

If you are talking about smoke alarms in a house the answer would be yes,

 

[Canook]

CDAFD,
Sorry, hotel corridor.

 

[DavidCR]

I´ve not seen a smoke detector specification from a manufacturer that includes a note on ceiling heigt spacing reduction, does anybody would refer one as an example?

 

[cdafd]

Canook yes to your spacing question

 

[cdafd]

DavidCR


did you look at the sections I sited??

 

[cdafd]

DavidCR


ok here you go

look at 5.7.3.2.3 (E) and A.5.7.3.2.3(E) 2002 edition

which once again refers you to fiquire A.5.6.5.1(a) to A.5.6.5.1(g) and A.5.6.5.1.2

Do the math

 

[DavidCR]

Yes I´ve checked the out. Sorry, but the parragraphs you mention refer to the rules of spacing due to ceiling shape, but I don´t find the relation with the reduction due to ceiling heigth.

Going back; the doubt is this: it is clear for heat detectors that the ceiling heigth reduction is applied thru table 5.6.5.5.1. but for smoke detectors do I have to apply a reduction due to height???

Recently and reading the code better I found that in A.5.7.3.2.4(B):

"A.5.7.3.2.4(B) The spacing guidelines in 5.7.3.2.4(B) are based on a detection design fire of 100 kW. For detection at a larger 1-MW fire and ceiling heights of 8.53 m (28 ft) or less, smooth ceiling spacings should be used and the detectors can be located on the ceiling or the bottom of the beams."

So it looks that the answer is hidden in this apendix parragraph: looks like there is no need to apply a ceiling heigth reduction due to the fact that the spacing for smoke detectors is the same for ceilings up to 28ft. For me it is not totally clear but is the only thing I have found.

My doubt comes from a NFPA 72 seminar, the instructor mentioned to reduce spacing due to height the same way for heat or smoke detector with table 5.6.5.5.1., but now I have the doubt since I have come across with a particular case.

Other way you can help me in this matter is about your experience: ¿what do you do with spot type smoke detector spacing when you have ceiling heights in the order of 5(17ft) to 8m (26 ft)? Do you use the same "S" as it was a 3m (10ft) ceiling?

Am I missing something obvius??? Please tell, for me it´s better to make a ridicule for being corrected in order to learn.

 

[cdafd]

My last try

look at fiqure A.5.6.5.1g This is what I am use to spacing from 30 feet to 41 feet depending on shape.

The only other thing is to contact maker of smoke detector to see if thier listing allows adjustments due to ceiling.

 

[wiretie]

response to spacing question- there is no reduction based on clg hieght. if anything you can expand on spacing using cals in annex b 72 book . for documentation call system sensor.

 

[wiretie]

question-how can you determine when complete or partial covereage is required. i find only definitions and no clear answer to this.

 

[DavidCR]

Even "wiretie"´s question is not directed to the original post question, it is a good question I hope somebody can comment on.

 

[rbulsara]

I have not checked the code/standards, but I also believe that there is no guidelines for reduced spacing for smoke detectors based on height of the ceiling.

However, what matters is the "stratification" of smoke in high ceiling spaces. I believe there is some discussion on this in NFPA. Heat keeps rising until a ceiling obstructs it or the air cools down to its surroundings temperature. But smoke can just "hang" in somewhere in the middle and not reach the ceiling, like smog (stratification), if the air not moving. One of the solutions is to have multiple levels (staggered height) of smoke detectors in such spaces.

 

[cdafd]

question-how can you determine when complete or partial covereage is required. i find only definitions and no clear answer to this.


to me it is a specification issue or ahj issue

nfpa tells you how to install it

the specs or ahj tell you what is required