Busy Open Ceiling as Obstructed Construction?

5/2/2019

If you have an open ceiling (both corridor and adjacent rooms), with a lot of ductwork and plumbing hugging the deck that may cause issues for sprinkler discharge, can you consider it obstructed construction and move the upright sprinkler 22" down from the deck to help avoid the obstructions? (Per NFPA 8.6.4.1.2)

No ceiling tile, ordinary hazard, not large beams either.

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5 Comments

Wayne Ammons

5/2/2019 07:53:11 am

My first instinct from a code perspective is to say that the construction type must be determined by the definitions given in NFPA 13 (obstructed vs. unobstructed construction). Anything else at ceiling level should be treated as objects creating obstructions and handled in accordance with the obstruction criteria outlined in NFPA 13. This may require additional sprinklers around, above, or below the obstructions.

If "a lot of ductwork and plumbing" is essentially creating a new "ceiling", there may be enough there to get the EOR and/or AHJ involved to make a call.

Jon Nisja

5/2/2019 10:21:27 am

I am coming at this from an AHJ perspective with a focus on fire dynamics. The primary objective in NFPA 13 is having the sprinkler activate. This is more critical that dealing with obstructions. The closer the sprinkler is to the ceiling, the more likely it is for the sprinkler to operate. Get it up high so it can activate then deal with obstructions. If you can only do one or the other, positioning at / near ceiling level is more critical than dealing with obstructions but in a perfect world you would deal with both. If the sprinkler positioning in relation to the ceiling allows it to activate, other performance objectives will be met (maybe not ideally) such as wetting adjacent combustible, cooling the upper ceiling jet / layer, and preventing flashover.

Troy Gouveia

5/2/2019 10:26:57 am

I would be careful with using the obstructed construction definition in this instance. The majority of the obstructed construction definitions are based on specific sq ft pocket sizes. The reason for this is that enhances smoke accumulation & convective heat transfer allowing the sprinkler to active in an appropriate time to control the fire. That being said if the ductwork and plumbing creates a new ceiling beneath the structure you could make the argument that a sprinkler line below the duct would active quicker then the sprinklers above said mechanical equipment & would also allow for greater spray pattern development.

In conclusion I agree with Wayne above consulting with the EOR & AHJ is the safest option.

PETE

5/2/2019 11:36:23 am

Good responses above. You are required to treat it as unobstructed per the 13 definition, if that's what it is. If there is an obstruction that prevents the sprinkler discharge from reaching the hazard, you are required to sprinkler beneath that in also.

Todd M. Delisle

9/11/2019 12:42:06 pm

This is a great question to see particularly after I had just read "Spot the Dot" by Steven Scandaliato, GOOGLE it, you'll appreciated it.

I think that the question (and article) clearly highlights one of the priorities that we all may forget at one time or another in our designs/layouts; (deflector) location, location, location. Location NOT for obstruction avoidance but for activation.assurance.

Busy Open Ceiling as Obstructed Construction?

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