Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2003

Spray Booth Design - Interlocking Doors

Q. Four questions: Are the doors of a down draft booth required to be interlocked with the ventilation and spray application? If they are, where in NFPA 33 does it say that?

A. I am not aware of any codes that require the doors to be interlocked. You might WANT the doors to be interlocked if you have a positive pressure booth because under these conditions the solvent vapors and overspray can escape into the workplace and affect the health and safety of the unprotected factory workers. When the doors are open in a negative pressure booth, dust and dirt from the outside contaminate the painted parts and might require you to rework or even reject them. This has nothing to do with whether the booths is downdraft or side draft. In fact, there are many three-sided, open-backed booths that do not violate any regulation.

Q. If the above is not required can you operated the down draft booth with the doors open?

A. Yes

Q. I realize that performance may be compromised, but is it a code requirement for those doors to be closed?

A. To the best of my knowledge, no there is no code requirement.

Q. The other part of that question is, are the powder coating products that dangerous, do you know of incidences caused by powder coating fires?

A. All or most powder of any kind, not only powder coatings can explode if the concentration is within a specific range. Grain elevatiors have exploded. High concentration aluminum dusts on ships have exploded. I have been into powder coating operations where I was not allowed to use a flash on my camera in case I triggered the fire suppression system. You can learn more about this by reading the Powder Coating Handbook sold by the Powder Coating Institute or by calling a vendor of powder coating booths, such as Nordson.