I have an obstruction question regarding what I feel is a gray area of NFPA 13. I'm looking at obstructions greater than 18 inches below sprinklers.
NFPA 13 states that any obstruction over 4 ft wide requires sprinkler protection under the obstruction. What if you have multiple parallel obstructions that are less than 4 ft wide with gaps in between? For example, multiple 36-inch diameter parallel pipes with 6 inches of space between each pipe. I feel that even if these obstructions do not require sprinkler protection below per code, they would still significantly alter the listed spray pattern of the sprinkler. I have seen some info regarding a 50% rule, but I can only find that in code as it relates to ceiling fans. I am curious what other opinions are. Thanks! Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
8 Comments
Randy
1/27/2020 09:59:34 am
I would agree that the code does not require additional sprinklers beneath these particular pipes. You use the word "significant" - but 4' is inherently defined as the width threshold for being "significant"
Reply
Alex
1/27/2020 10:43:01 am
Great question. One thing to consider is the ability for the obstruction to form a layer of hot gas beneath it in a sufficient manner for a head to operate. A bank of large diameter piping can probably cause turbulence in the buoyant gases, but is not likely to "hold down" a layer of hot gas like a continuous 4 ft obstruction would.
Reply
Franck
1/27/2020 02:17:30 pm
As you said, this is the grey area. Each pipe individually is not an obstruction, but all together doesn’t make you feel comfortable
Reply
Franck
1/27/2020 02:22:35 pm
The 50% rule (sometimes it is 70% or even 80%) is often a reference for shelves in racks (when do we consider open shelves or solid shelves)
Reply
Wayne Ammons
1/27/2020 03:25:51 pm
If there are no clear guidelines outlined in chapter 8 of NFPA 13 (prior to the 2019 edition) on how to address the continuous and/or noncontinuous obstructions in a specific scenario, interpretation can tricky and may require discussion with the engineer of record and AHJ. You could try getting a formal interpretation from NFPA or utilizing NFSA's Expert of the Day service to help determine an appropriate protection scheme.
Reply
Matthew King
1/28/2020 11:39:00 am
An obstruction is anything that changes the discharge of a sprinkler head.
Reply
Ed
1/29/2020 01:11:50 pm
Just came across this very same issue on one of my jobs. The AHJ suggested I install heads above and below to remedy the situation.
Reply
Matthew King
2/3/2020 11:50:20 am
I agree. On the job I reference above, they are adding pipe runs. Our overhead sprinklers were obstructed, they are add heads below. We have had several comparable situations when making modifications to duct runs.
Reply
Leave a Reply. |
Free SignupSubscribe and learn something new each day:
CommunityThank You to Our Top
October '20 Contributors!
Your PostThe ToolkitSprinkler Designer or Engineer?
Get all of our tools, including the Sprinkler Database, Friction Loss Calculator, Fire Pump Analyzer and more: Filters
All
Archives
January 2021
Daily
Daily discussions are open-ended fire protection, fire alarm, and life safety questions submitted anonymously for the benefit of sharing expertise and learning from other perspectives. Anyone can submit a question here:
Exam Prep2020 PE Prep Guide
(Available Now!) PE Prep Series
(Available Now!) 2020 PE Prep Series
Current Leaderboard (Click to enlarge) PE Problems
Visit July-October for daily Fire Protection PE Exam sample questions.
Solutions are posted the day after posting. Comment with your solutions, questions or clarifications. Please note that questions posted are unofficial and in accordance with NCEES rules are intended to be similar to actual exam questions, not actual exam questions themselves. |