Spray booths and their exhaust ducts

[Shredocaster]

As per NFPA 13 2013, 22.4.1.2 "exception" one can design to Ordinary Hazard 2 for powder coating but does not get into the ductwork portion of the design . I would imaging the 30gpm/15 psi would still apply but seems to defeat the purpose of the exception.
Also - I see that some treat the ductwork/stack 12'-0" max spacing run on the horizontal only. I interpret otherwise. Am I missing something?

 

[TravisMack]

Typical paint booth is EH2. So the max sprinkler spacing is 12'. That may be where you are seeing that.

Travis Mack
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[Shredocaster]

Actually 33 - 9.4.6 of 2016 Clarifies the spacing within ducts to 12' horizontal and at the top of an exhaust riser to a maximum 24'. No clarification on calcs within a duct on OH2 permissible systems though.

 

[skdesigner]

I read it the same way as you Shred... duct sprinkler sprinkler requirements are in a completely separate section from the booth requirements, and there doesn't seem to be any reduction given for powder coating operations.

OH-2 in the booth is still a significant reduction, in terms of piping and number of sprinklers though. 5.6's instead of 8's or 11.2's saves the contractor some $$, more still if you can use the 15' max spacing and eliminate an entire branch line.

 

[stookeyfpe]

FYI because I'm assuming your hazard has ductwork: Most powder coating booths do not have an exhaust vent stack which are required for flammable spray finishing booths. The newer powder coating booths have an internal filter system within the plenum that captures the resin powder and discharges it into a filter pan. If a system has a duct system, it's probably routed to a dust collection system. The atmosphere, if properly designed, is operating at < 50% of the Minimum Explosive Concentration (MEC) of the dust. This allows the duct to be classified as General Purpose exhaust under most mechanical codes and eliminates the need for sprinklers.