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Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2005

Airflow in Aircraft Paint Hanger (Spray Booth)

Q. In an paint hangar (152'L x 132'W x 46'H) with down-draft air flow wich are the minimum air flow velocities recommended:

a) in the vertical cross section (152'L x 132'W) of the hangar (without aircraft)
b) in the air exhaust entries in the floor.
c) in the suplies and exhaust ducts and stacks

A. Thank you for your question. I would like to be able to give you a definitive answer, but without actually seeing the facility and the aircraft that you paint, I can't guess. In any case, the hanger is large and I would not want to give you advice that turns out to be incorrect. Have you consulted with a spray booth designer?

I can tell you that in the USA OSHA calls for a velocity of 100 ft/min in smaller spray booths, and bulletin NFPA-33 suggests an air velocity that will guarantee that the concentration of solvents in the air never exceeds 25% of the LEL or LFL. In a large hangar such as yours, I doubt that you will ever approach 25% LEL; therefore, most spray booth companies do not design for an air velocity of 100 ft/min. On the other hand, I have conducted inspections of numerous aircraft hanargs where the velocity was so low that it was almost immeasurable. Consequently, overspray settled on the floor of the hangar rather than in the filters.

Again, I apologize for not being more helpful, but without seeing the facility I can't give you more help.

Best wishes,

Ron Joseph

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