BackPage Primer from Environmental Building News
Volatile Organic Compounds:
Definitions Matter
The term "volatile organic compound" (VOC) means different things to different people. In high school or college chemistry class we learned that VOCs are a class of carbon-based compounds that readily become volatile (gaseous) under ordinary (atmospheric) conditions. Thus, we learned that VOCs are any of those carbon-based compounds that smell strong and readily evaporate—stuff like acetone, rubbing alcohol, and propane.
As used by ambient air quality regulators, the term VOC has a quite different definition. According to the U.S. Environmental Protection Agency (EPA) and other regulatory bodies, VOCs are organic compounds that readily volatilize under atmospheric conditions and that react in sunlight to generate smog. Thus, from a regulator’s standpoint, compounds are VOCs only if they contribute to certain type of outdoor air pollution.
These differences in definition have led to a lot of confusion. Especially in the green building community, we think of VOCs as contributors to indoor air quality (IAQ) problems—and the amount of VOCs is often our only IAQ metric for a product. But there are lots of compounds that meet a chemist’s definition of VOC but are not photoreactive so are not defined as VOCs by regulators. Some of these chemicals—including formaldehyde, methyl chloride, and many other chlorinated organic compounds—have serious health and ecological impacts. This was driven home by an exhibitor of sealant at the recent American Institute of Architects convention who said that his low-VOC product was the most toxic product he offers—because the carrier is perchloroethane, a hazardous solvent that is not considered a VOC by EPA.
Further complicating matters, some VOCs have potentially serious health effects, while others are relatively benign. And the amount or type of VOCs that are in a product may or may not be a good indication of what is released into the air—some react with ozone or with other compounds and morph into something new as they volatilize.
The label describing VOC levels in grams per liter on a can of paint indicates that paint’s contribution to smog formation. For indoor air quality purposes, we should look to results from chamber-testing protocols that analyze key VOCs individually. Most of these protocols reference California’s list of chemicals for which acceptable exposure levels have been established. These include California’s Section 01350 specification, Greenguard for Children and Schools, Indoor Advantage Gold, and Green Label Plus. Even these aren’t comprehensive, however—they don’t (yet) address many “semivolatile organic compounds,” among other chemicals. We have a ways to go before we can know when the air is really clear.
For more information:
“Get a Whiff of This: The Lowdown on Product Emissions Testing” EBN
Vol. 15, No. 9.
July 1, 2007
DISCUSSIONS
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Thank you for clarifying the important point that measuring VOCs according to EPA definition is not enough to assure us of good IAQ. The emissions testing that you mention is a great step forward, because it addresses a larger range of compounds than the simple "grams per liter" designation, and it does so in a more specific manner. Another important type of emissions testing is described in ASTM E981, which involves observations of health effects of emissions on laboratory mice which have been exposed to air samples containing emissions from products. It avoids the necessity of defining and identifying "VOCs" while directly measuring the neurological, respiratory and other effects of the air on the mice, and thus provides an evaluation of emissions from products that is complementary to the testing mentioned in your article.