Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2004

Air Flow Analysis

Q. I have a question regarding your article on air flow analysis that I have been unable to solve myself. When this is related to forced-air down draft booths, does the OSHA regulation of 75-100 ft/min still apply? I have been told that there may be another reg. concerning down draft booths but have been unable to locate it. My concern is that our new booth exhausts 60,000 cfm with 1000 sq.ft. of booth (60 fpm average). I also know that there are some dead spots in the booth because, as you describe in your article, the paint hangs in the air and slowly falls to the floor (as the filter area does not cover all of the booth floor). I have conducted several air flow studies that already show this. Would these booth be considered legal? Thank you

A. Thank you for your e-mail. I have not seen anything directly in the OSHA regulations that differentiates downdraft spray booths from any others. Strictly speaking you're supposed to meet the 75-100 feet per minute requirement of Table G-10, but I know that some of the large reputable spray booth companies design for lower air velocities where the spray booth is very large and the concentration of solvents in the booth is low. Several letters have been written to OSHA on this topic and you can find them the agency's responses at:

I've searched the OSHA site and cannot find the letter that addresses your specific question; however, when you read OSHAs responses you will find that the agency tends to follow the guidelines of NFPA-33 which calls for the solvent concentration to be less than 25% of the LEL.

This morning I spoke to a representative of a large spray booth manufacturing company who told me that OSHA does not strictly enforce the air velocity requirements of Table G-10, but that the agency treats so-called violations as "de minimis". I checked at for the definition and found the following; "The full expression is de minimis non curat lex. This is a Latin phrase which means "the law does not care about very small matters". It can be used to describe a component part of a wider transaction, where it is in itself insignificant or immaterial to the transaction as a whole, and will have no legal relevance or bearing on the end result."
I suggest that you more thoroughly examine the letters that appear on the OSHA site, print them out and file them in case an inspector should issue you with a citation.

Best wishes,

Ron Joseph


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