Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2003

Capture Efficiency of Waterwash Spray Booth

Q. Does it seem reasonable to you that the PM/PM10 removal efficiency of a water curtain could be as high as 90 percent (or higher)?

I have been on the Internet for the better part of the morning and there is hardly anything on the subject. I'm writing a Part 70 operating permit for an organic coating operation that has water curtains controlling several spray booths claiming 95%. It's not that I don't believe it is possible, I just have to document those sorts of things in my permit supporting material so that U.S. EPA will sign off on it and not require testing (although I can't see how you would stack test something like this). Also, I found this on Australia's EPA web page, so I am confused:

"A water curtain is useful only to maintain booth cleanliness; it is not acceptable as a collection device. A separate wet collector should be incorporated in the unit along with the curtain."

Anyway, you seemed like a person who would know.

A. The efficiency of a waterwash spray booth depends on many factors, including the design, pressure differential across the venturi (the gap between the water level and the vertical sheet above the water), the chemicals in the water, the amount of sludge deposited in the exhaust section, etc. By the way, not all waterwash booths have a water curtain.

A properly running and well maintained waterwash spray booth can exceed 95% particulate capture efficiency, but I have visited umpteen facilities where the booth was not properly maintained and the efficiency was well under 90%. I've been to some very poorly maintained booths where I doubt that the efficiency was 50%.

For regulatory purposes the owner/operator can get a letter from the spray booth manufacturer in which he provides you with the particulate capture efficiency. If the owner/operator doesn't know the name of the vendor, or if the booth is old and he can't find the name plate, then you or he might want to find a comparable booth and get the vendor's literature to support the permit application.

There is no easy or inexpensive method for determining the capture efficiency experimentally. It can be done by performing stack tests, but these are expensive and do not necessarily represent the efficiency for all coatings, or all of the application scenarios.

As a permit writer, you might want to give the owner/operator the benefit of the doubt by assuming a high efficiency, but write some permit conditions that mandate that the booth be maintained according to the vendor's instructions. If I were the permit engineer, (and because I know about spray booths) I would be specific about the maintenance that is required. The conditions would be written to be enforceable.

If you don't really care about these issues, then perhaps simply issue the permit according to the vendor's literature. After you've done calculations for PM10 emissions you might find that they are not sufficiently high to spend so much time on this. On the other hand, if the particulates contain inorganic HAPs then my comments don't apply.

You might speak to Richard Thelen of JBI Booths ( There are other vendors of waterwash spray booths and you should be able to find them on the Internet.


What's New | About PCRC | Compliance Assistance | Regulations | Technical Info | News | Homeowners | Search | Disclaimer | Home

©2012 Paints and Coatings Resource Center