Sprinklers under ducts

[KlemenJEM]

Hello,

I have a question regarding sprinkler protection under ducts. I understand that if the duct is wider than 1 meter (4 ft) there needs to be a sprinkler under it but if the duct is just below the ceiling does there also need to be a sprinkler above the duct?

If a have a group of ducts with a combined width of 5 meters (16,5 ft) with the highest point of a duct 25 cm (10 inches) under the ceiling do I need to place a sprinker head above and below the ducts?

 

[cdafd]

Without seeing it

I vote above and below

 

[UFT12]

1m in not 4 ft. You probably mean 1.2 m. Assuming we abide to NFPA 13, the sprinkler deflector above the duct will most likely be even less than 25 cm which means that you need to apply the three-times rule for obstructions lying in the first 18 in (46 cm) vertically from deflector. This is practically impossible. So you need the extra sprinkler below the duct regardless of its width. At least that is my interpretation of the standard for cases where the ceiling area is heavily compacted with various elements. Now, should you need the sprinkler above? The space is tight, not sure what good it will do since its pattern of discharge is questionable. However, eliminating sprinklers here and there will most likely put you in a situation spending time arguing with inspectors, AHJ or the likes that may not worth it. Also NFPA 13 is silent about such situations (or I think it is) and therefore common sense says sprinklers would be required above and below. So for me the rule is, is it practically feasible to install sprinklers? If yes, do it. If not, you have an argument to discuss.