A quick ? regarding NFPA 13's Small Room Provision

[bdk]

Hey guys,
I am new to this Forum and I have a question regarding the small room provision in NFPA 13 2002 edition.

I have a room that is a light hazard occupancy, the dim of this room is 19’-3” x 16’-5 ½”. Due to the grid layout, lighting and diffusers, there is minimal space in the center of the room for sprinklers. Because it is a center of tile job, the best spacing I can come up with for 2 sprinklers is 7’-6” from one wall and 9’-0” from the other. Would this room be acceptable with only 2 heads or would I need 4 heads since it does not match up with the small room provision figures?

Section 8.6.2.1.2 states that the SxL or As shall not be applied to sprinklers in small rooms, rather the area of the room shall be divided by the number of sprinklers in the room. (I understand this)

Section 8.6.3.2.4 states that a sprinkler can be located up to 9’ from a single wall but spacing limitations of 8.6.3 and area limitations of table 8.6.2.2 (a) shall not be exceeded. I read this as meaning that when the area of the room is divided between the number of sprinklers in the room, that area shall not exceed 225 sq. ft.

The part that is really causing me problems is the figures in the Annex (figure A.8.6.3.2.4 (a) – figure A.8.6.3.2.4 (d)). Are these figures just diagrams or do the dimensions refer to a maximum room space? In figure A.8.6.3.2.4 (b) If a head is spaced at 9’-0” from one wall (south wall) does this mean it can only be a maximum of 6’-0” from the other wall (north wall) or can if be up to 7’-6” away from that wall (north wall) if the area of the room divided by the number of sprinklers is less then 225 sq. ft.?

 

[SprinklerDesigner2]

The diagrams.

http://img375.imageshack.us/img375/7606/smallroomsra6.jpg

I interpret these to mean the actual physical area covered by a single sprinkler can not exceed 225 sq. ft..

 

[SprinklerDesigner2]

I hit the send button by mistake.

"The part that is really causing me problems is the figures in the Annex (figure A.8.6.3.2.4(a) – figure A.8.6.3.2.4(d)). Are these figures just diagrams or do the dimensions refer to a maximum room space?"

I think they are just diagrams. The total area of the room divided by the total number of sprinklers can not exceed 225 sq. ft.. Figure A.8.6.3.2.4(a) makes clear the area covered by the sprinkler on the right clearly covers a physical area of 247.5 sq. ft. but the area of the entire room is 450 sq. ft..

But, as always, I am interested on hearing what others say.

 

[cdafd]

do not have 13 in front of me,but have you read the definition of small room, and not sure if that will help you.

 

[cdafd]

Not sure of the question but as long as you have the complete room covered and only one head is not more than nine feet off the wall you should be ok, small room can be up to 800 sq ft.

 

[SprinklerDesigner2]

"Not sure of the question but as long as you have the complete room covered and only one head is not more than nine feet off the wall you should be ok, small room can be up to 800 sq ft."

Actually you can have two or more up to 9' off any one wall as shown in the example provided in NFPA #13 Figure A.8.6.3.2.4(d).

http://img375.imageshack.us/img375/7606/smallroomsra6.jpg

I think one of the questions had to do with physical coverage and could a head cover more then 225 sq. ft. The sprinkler on the right in Figure A.8.6.3.2.4(c) shows the sprinkler on the right clearly covering an area 15'-0" x 16'-6" for a total covered area of 247.5 sq. ft..

I think the answer is you are allowed to be up to 9'-0" off one wall but but all other spacing rules, distances off other walls and distance between heads, apply (7'-6" off wall 15'-0" between heads) and the total heads divided into the room area can not exceed 225 sq. ft..

Take the two examples I made fearlessly made up.

http://img259.imageshack.us/img259/9577/smallroomlayoutes2.jpg

The room on top would be acceptable while the one on the bottom would not be.

 

[cdafd]

SprinklerDesigner2

I guess if you look at the pictures it helps.
Maybe I have seen it and forgot about it.

Learn something new all the time. Thank you for today's lesson.

 

[bdk]

So the consciences is that the figures don’t really mean anything, as far as a max room size (besides being less than 800 sq. ft.).

As long as the sprinkler is only 9’-0” or less from one wall, 7’-6” from the other walls and the area of the room divided by the number of sprinklers is 225 sq. ft. or less.

 

[SprinklerDesigner2]

"As long as the sprinkler is only 9’-0” or less from one wall, 7’-6” from the other walls and the area of the room divided by the number of sprinklers is 225 sq. ft. or less."

This is the way I understand it.