Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2001

Which VOCs are Exempt Compounds and Which are Non Precursors of Ozone?

Q. I have been given information from Phillips 66 on the replacement solvent isohexanes, Cas# 8030-30-6 chemical name: hydrocarbons, C5 and up, C5-C6 Rich chemical family: Aliphatic hydrocarbon. They assure me this is a non-voc. Can you verify this? Thank you.

A. All volatile organic compounds are VOCs if they test positive per EPA Method 24 or 24a. I am in little or no doubt that the compounds mentioned in your email are, in fact VOCs, where the term refers to "smog formers".

The only non-VOCs, or "exempt compounds" are those listed in 40CFR51.100(s). For the full list please visit my website . Since the isohexanes are not on the list, then by DEFAULT they are VOCs.

It seems possible that Phillips 66 is not referring to "smog formers", but rather what was referred to as "non-precursors of ozone" in the old, and now essentially defunct Rule 66. In the years between 1966 and 1977 (and even beyond) state agencies made a differentiation between those compounds that formed smog quickly, and those that had very slow reaction rates. This is too complex a topic to be discussed here. Hence you might have been mislead by semantics and not intentional misinformation.

If my assumptions are correct then the compounds you have purchased ARE VOCs by current regulations and MUST be counted in your recordkeeping.

If you need to understand this and other topics more fully, I seriously encourage you to attend one of my environmental classes for painting operations. Please visit

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