Looking at installing a cable tray that runs the length of the room in an Ordinary Hazard Occupancy.
The cable tray is about 2-feet wide and the sprinklers are standard uprights. The cable tray is less than 18-inches below the sprinkler. However, the cable tray may be centered directly below some sprinklers, but off to the side for other sprinklers. What obstruction criteria from NFPA 13 (2016 Edition) would apply? Three Times Rule (Section 8.6.5.2.1.3)? If Three Time Rule applies, is that measured vertically, horizontally, diagonally, or all? Thanks in advance. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
6 Comments
Alex
10/4/2021 06:49:33 am
Hi Anonymous,
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Franck
10/4/2021 08:31:40 am
Alex cover it all.
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JI
10/4/2021 08:47:06 am
When using the Three Times Rule for an Ordinary Hazard Occupancy you only have to consider structural members when using it as per 8.6.5.2.1.4 NFPA 13 2016. Since the cable tray is not a structural element you do not use the three times rule here. When doing further reading in the annex you may exempt the cable tray as an obstruction assuming the sprinkler is not too close to the obstruction. The annex states the beam rule applies when water cannot spray on both sides of an obstruction due to how close the sprinkler is.
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Michael Lantaigne
10/5/2021 09:12:10 am
I agree with JI - the 3x rule only has to be applied to structural elements in light and ordinary hazard occupancies and the beam rule only applies when the top of the obstruction is level with or above the plane of the deflector.
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Jesse
10/4/2021 11:02:25 am
Agree with Alex.
Reply
5/30/2022 10:20:59 am
This information is really worthy for me as cable tray manufacturer.
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