Sprinkler Installation Under Duct

[umutus]

Hi everyone,
I am working as a Mechanical Site Engineer.

and I have a 2 questions,

-1st question
Consider a mechanical room which has 6-7m elevation.
We have our High Level upright sprinklers.
and we also have ducts which have width of higher than 80cm
Suppose these 2 horizontal ducts are in the same vertical axis.
So, what should be the minimum vertical distance between these 2 ducts in order to protect them by installing sprinklers between them.

-2nd question,
What should be the minimum distance of ( min 80cm width ) duct from the ground in order to protect the duct by installating sprinklers under it?

I have searched NFPA but i could not find the answer of my questions.

Thank you.

 

[UFT12]

First of all, NFPA 13 does not require additional sprinkler protection under ducts unless they are over 1.2 m in width or unless your case is ducts against the wall (in general a vertical barrier) or where consecutive ducts side by side constitute an overall width that would warrant protection.

With that said, unfortunately NFPA 13 does not provide clear requirements for the cases you describe because each can vary considerably. One can however reach to an answer by considering the entire aspects of fire protection, not just sprinkler requirements. My personal assessment would be

Question Nr. 2 - There is a reason for approaching question Nr 2 first.
If you believe that the area below the duct is tall enough to allow occupancy (can the space be used from a practical point of view? can someone fit/walk? can you store combustibles even if the space is fairly tight?) then most likely sprinklers would be required regardless of the height as long as there is some practicality of using the space as such. In general, if the space is not too low and sprinklers can be installed and we are talking for few sprinklers that adding them does not impact the overall cost, then sprinklers are needed because one of the very first installation requirements of NFPA 13 is that "Sprinklers shall be installed throughout".
At the very end, what is your available height you have?

Question Nr. 1
based on the principle described in Nr 2, one should assess the situation in a similar way. If the space between the two ducts cannot be used for occupancy (say a catwalk in-between) or combustibles (say cable trays etc), then sprinklers should not be typically required.

Also note that requirements from insurance carriers or any pertinent AHJ may require whatever the want, regardless of the above. One factor that surely influences the decision is the level of hazard in the area of protection. If it's too high, sprinklers may be warranted in any case and any way.

 

[umutus]

Hey UFT12

Thank you so much for your detailed explanation.

I got some help and I obtained some rules which are;

NFPA
- A.9.5.5.3.1.1
Where multiple levels of ducts, pipes, or other similar horizontal obstructions that are over 4 ft (1.2 m) wide are stacked vertically, additional levels of sprinkler protection between the vertical levels are not required. A single level of sprinklers beneath the lowest level of the obstruction is adequate, provided that the obstructions are noncombustible and that combustible materials are not stored between the levels.
- 9.5.5.3.1.5
Sprinklers shall not be required under noncombustible obstructions over 4 ft (1.2 m) wide where the bottom of the obstruction is 24 in. (600 mm) or less above the floor or deck.

In my question I asked 80cm width of duct that is because in our project we protect ducts which have the width of higher than 80cm.

Best regards.