Distance Between Ducts in Order to not Obstruct?

5/23/2024

We have an overhead ESFR sprinkler system under NFPA 13-2013 with K22.4 sprinklers.

There are ducts 14-inches to 20-inches in diameter that will be installed at 30-ft.

What is the required separation distance for them to be considered separate obstructions where we can omit sprinklers below, as long as they are 24" away (horizontal) from the overhead sprinklers?

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4 Comments

Pete H

5/23/2024 06:49:10 am

This got added in 2016 and isn't in 2013... but it answers your questions.

From NFPA 13 (2016 edition):

8.12.5.3.3 For pipes, conduits, or groups of pipes and conduits to be considered individual, they must be separated from the closest adjacent pipe, conduit, cable tray, or similar obstructions by a minimum of three times the width of the adjacent pipe, conduit, cable tray, or similar obstruction.

--

A.8.12.5.3.3 For example, a 1 in. diameter conduit would need to be 3 in. from the nearest pipe or conduit to be considered an individual obstruction. Otherwise the pipes and/or conduits would be considered as a group when applying the obstruction criteria in 8.12.5.3.1

--

So my answer is: 60" apart. It is not spelled out in the edition of code that has jurisdiction and is a gray area there. But you can answer the gray area by using the current requirements.

So given you have 20" in diameter, ducts,

Glenn Berger

5/23/2024 08:19:10 am

There currently is no hard rule for separation of obstructions. For ductwork and lighting, the spacing that Pete mentions above can be considered a good rule of thumb.

Steve Cooper

5/23/2024 09:17:29 am

The three times rule would be what is applicable to this situation. 20" duct, you would need to be 60" away from the edge of the obstruction. Please always keep in mind the AHJ since there is sometimes wiggle room with much smaller obstructions if they don't impact safety of the system.

danefre

5/23/2024 10:22:00 am

Agreed with Pete.

We typically push for collapsible (fabric) duct in ESFR buildings to avoid this situation. HVAC shuts off upon water flow alarm.

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Distance Between Ducts in Order to not Obstruct?

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