NFPA 13 8.8.5.3.2 - sprinkler under obstructions over 4ft wide

[EricDesilets]

Hi !

I'm new to Eng-Tips and in the fire protection field as an engineer.

I recently had a discussion with a colleague about NFPA 13 8.8.5.3.2 which tells us that sprinklers shall be installed under fixed obstructions over 4 ft wide.

We were both arguing in order to determine if the 4 ft wide rule is applied in both directions (length and width).

In other words, do we have to protect under obstructions that are at least 4 ft wide and long or as soon as an obstruction gets to 4 ft in one direction we have to protect under it?

We believe that it needs to be in both direction but I wanted to have the opinion of more experienced professionals.

Thanks for your help!

 

[TravisMack]

I believe it is the 2019 edition that clarifies this. The width is defined as the smaller of the 2 dimensions (Length / width). So, if you have a duct that is 24" wide x 20" deep and 100' long, you don't need to put sprinklers under it. Just because it runs 100' (which is obviously >48") doesn't mandate sprinklers. The width is considered 24" which is <48".

There is no need to over complicate this.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[UFT12]

Abstract from A.10.2.7.3.2, edition 2019.

"The width of an object is the lesser of the two horizontal dimensions (with the length being the longer horizontal dimension). Sprinkler protection is not required under objects where the length is greater than 4 ft (1.2 m) and the width is 4 ft (1.2 m) or less."

So I guess that makes it clear.

 

[EricDesilets]

Thanks for the reference UFT12!

We don't have NFPA 13 2019 yet in the office but I'll definitely look to have it soon.

 

[MatthewJWillis]

I believe it was added in the 13 edition..

R/
Matt