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Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2005

Spray Booth vs. Spray Room

Q. In NFPA 33 the definitions for spray room and spray booth differ. However our design group is in diagreement as to the intent for the distinction. The appendix clearly states that a room is not a booth and a booth is not a room but it is unclear what operational differences or restrictions really exist. Are there functions that can take place in one and not the other or does one have a more stringent requirement for ventilation or other means of protection?

A. You have asked a wonderful question and forced me to look at NFPA-33 and OSHA 29 CFR 1910.94(c)(1)(iii) again. OSHA itself appears to recognize the confusion and I refer you to their letter of clarification which you can find at:

After reading the letter and searching for "spray room" in NFPA-33 I conclude that there is no essential difference between the two. Apparently, the difference between "spray booth" and "spray room" is physical size even though dimensions are not given. I have also learned from the letter that the key issue in reading these documents is the determination of "dangerous quantities of" a substance.

The Ontario Fire Marshal (Canada) defines "Booth" and "Room" slightly differently:

Spray Booth means a power-ventilated structure that encloses or accommodates a spraying operation so that spray vapour and residue can be controlled and exhausted.

Spray room means a spraying area on a floor area or part thereof in which an open spraying operation is confined and that is separated from the remainder of the building in which it is located by a noncombustible vapour-tight separation.

In the absence of the OSHA letter I tend to think of a "spray room" as a totally enclosed room in which open spraying might or might not be conducted, but in which other spray booths might also be located. For instance, there are many coating shops in which an enclosed room houses several open-backed dry filter or water spray booths. Even though each booth is equipped with its own exhaust system, the room must be monitored for dangerous quantities of volatiles and perhaps it too will need an exhaust system.

I urge you to refer to the OSHA letter and see if you can determine anything different from what I've learned. Please get back to me with your comments.

Best wishes,

Ron Joseph

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