Remote Area Length for Long Narrow Space?

6/12/2020

We have a long, narrow basement space which will be used for storage. Because of the direction of the structure, we plan to cover the long but narrow space by two branch lines with 8 sprinklers on each line. When we're trying to determine the remote area, NFPA 13 says that the minimum length along the branch line must be 1.2 x √(remote area), which for us is 2,000 sqft. This comes out to a minimum of six sprinklers. However, if we have two branch lines with six sprinklers each, we only reach 1,560 sqft.

Is there a maximum number of sprinklers that is required to be calculated along a branch line, or for narrow spaces does the design area just take a very long and narrow coverage until it reaches the required size, regardless of how it lays against the branch lines?

Thanks in advance!

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5 Comments

Glenn Berger

6/12/2020 10:12:38 am

Additional information is required to answer this question.

Is the storage space bounded by rated construction?

James

6/12/2020 10:14:56 am

For this project it is bound by exterior walls.

However, the same question could be posed for long narrow tunnels or passageways that are a couple branch lines wide.

Colin Lusher FPE link

6/12/2020 11:07:27 am

1.2 x √(remote area) is the MINIMUM length. You need to extend the remote area until you're calculating the full 2000 sq.ft. area, or the entire space, whichever is larger.

The only situation that I'm aware where you could reduce the area would be a corridor, or similar, that it protected by a SINGLE line of sprinklers, in which case you'd need to calculation a maximum of 7-sprinklers along the length of the space. But because you have TWO branch-lines, it doesn't sound like this would apply to you, and you'll need to use standard area/density remote area rules.

Franck

6/12/2020 01:36:16 pm

As indicated by Colin, you will have to take the 16 sprinklers (8 on the 2 branch lines) which will be the entire area if smaller than 2000 sq ft.
The 1.2 rule is only to make a calculation on a « shape » of a developping fire in a large area, being more conservative than using a square.
I used to work for an insurance company which used a 1.4 factor instead of 1.2 to be even more conservative (the more heads you take on branch lines, the more friction losses, thus the higher hydraulic demand in flow and pressure)
But the demand area should be 2000 sq ft (or the entire area if smaller) and in your case you have to consider more than 12 heads.

Bruce Verhei

6/15/2020 03:54:44 pm

You didn’t note edition of 13 in use.

After you follow comment by Collin, see note about which density to use in smaller areas.

Best.

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