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Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Definition of "Thin Coating" in EPA Regulations

Q. I work for the Navy and attended your "Keeping a Paints and Coatings Facility in Compliance with Air Pollution Regulations" class a few years ago. I have a question I am hoping you can help me with. In the marine coatings NESHAP, a part of the "coating" definition is that it "can be applied as a thin layer". Here at our shipyard, the issue of what is "thin" is being debated. I cannot find any guidance in the EPA or other regulatory web sites. We need to develop an internal definition so we can consistently classify products. Some folks here say this is 2 mils or less, others 10 mils, and some even more. But it's all based on a "gut feel" for what is thin. We have some "coating materials" which are typically applied at 100 mils or greater. Do you have any suggestions on what would be an acceptable policy on "thin" that would be defensible to a regulator?

A. Thanks for your email. The word "thin" is not defined in 40 CFR Part 63.782.

In the Aerospace NESHAP the definition is: Coating means a material that is applied to the surface of an aerospace vehicle or component to form a decorative, protective, or functional solid film, or the solid film itself.

Based on my experience with the EPA and state regulations the term "thin" is relative and has no specific meaning. Any liquid coating that is applied to a surface to form a uniform film, qualifies under this definition. If the coating emits organic solvents it qualifies, regardless of its thickness. The EPA and states have several NESHAPs and numerous RACT surface coating regulations in which actual film thickness is not relevant. Therefore, I would ignore the word "thin" in the definition and assume that if your coatings contain VOC and, when applied, form a uniform film, then they qualify under the NESHAP.

Best wishes,

Ron Joseph

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