The new rule, industry sources say, will force painting contractors and other professional coatings applicators to use the much more flammable acetone in cleanup of application tools and equipment.

The new rule, which does not affect retail-consumer or DIY paint users, is the result of the SCAQMD's amendment of its existing rule 1171 on solvent cleaning operations. Rule 1171 previously had applied only to stationary sources of VOC emissions, and had excluded architectural and industrial maintenance coatings users. The amendment extended the rule's provisions to professional users of architectural coatings, effective July 1, 2005.

Robert Wendoll, Environmental Affairs director at Los Angeles-based Dunn-Edwards Corp., said the rule change prohibits the use of solvents with a VOC content of greater than 25 grams per liter (g/L). "That leaves soap and water or acetone," he said.

"Our concern is that acetone is highly flammable, and if it's used as a paint thinner you are significantly increasing the danger of fire," Wendoll said. "Just a static spark can set it off." The rule change also brings into play extensive regulatory provisions on the storage of flammable materials. Wendoll said acetone, while defined as a non-VOC under SCAQMD regulations, possesses a much lower flash point than conventional mineral spirits-based paint thinners.

Dunn-Edwards is asking the SCAQMD to consider evaporation data on acetone in a technology assessment that is required one year before the new solvent-cleanup rules go into effect in mid-2005. The company says the evaporation rate of acetone is approximately 41 times greater than conventional paint thinner, causing acetone to contribute more to the formation of atmospheric ozone pollution, or smog, than paint thinner. Industry representatives agree that acetone's reactivity rate is much lower than paint thinner's. But the higher evaporation rate of acetone more than offsets the reactivity difference, they say.

Wendoll said Dunn-Edwards plans to hire a technology expert to monitor VOC emissions during cleanup operations involving acetone. "We're offering to do this as a supplement to their own data," he said.