Small Room Rule

[midwestFCO]

I found the article in this month's NFPA Journal about the NFPA 13 Small Room Rule interesting and it does help clarify a sometimes confusing rule, but I am still stuck on one question. The rule allows the head to be no more than 9' from a single wall within a room 800 sq ft or less, but how do you measure that? Is it a straight line to the walls or should you also measure diagonally to the corners of the room?

Case in questions: I have a tenant renovation in progress, light-hazard office 2900 sq ft total with offices approximately 9.5' x 14' (133 sq ft). They are using the small room rule in these rooms, and if measured in a straight line they are a max of 8' from a single wall BUT, when measuring from the head to the corners they are about 10' 6" from the center of the sprinkler head. Is this allowed?

Thanks.

 

[midwestFCO]

I should clarify one thing. I said measured to the corner, but I did bring it back slightly so it was only measuring to one wall in the corner and not the actual corner, so it would be a "single wall" not the joining of two walls.

 

[FM William Burns]

It has always been my understanding that the measurement is intended to be at the horizontal or perpendicular plane of the head. The rational was that the corner floor area is far less than the area along the flat wall being, if it opens the pattern will cover the floor's surface area of the corner within the density limits. I would be interested to see other comments also.

 

[cda]

agree straight line

8.5.3.2.2 and 8.5.3.3.2 nfpa 13 2002 edition

but also look at

8.6.3.2.3 I call it the slant rule look in the appendix for an example

 

[midwestFCO]

Good information. Thanks so much!