Outgassing refers to the release of gases during the aging and degradation of a material. These volatile organic compounds (VOCs) can negatively affect our health. New-car smell, and the film that forms on the inside of an automobile’s windshield, are a result of outgassing from the plastic interior. The synthetic fabric, vinyl, and cushioning are, in effect, evaporating various gases into the air we breathe. It has been reported that the VOC level inside a new car can be dozens of times higher than the level recommended in indoor air. Common VOCs found in cars include aldehydes, alcohols, plasticizers, aromatics, and alkanes—many of the same chemicals found in houses.
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Most of the modern materials created in the last fifty years outgas to some degree. Synthetic carpeting, paints, adhesives, kitchen cabinets, and wall paneling have all been implicated. This outgassing is a universal component of indoor air pollution and it can easily result in sinus and lung irritation. Some of the chemicals released are so powerful they can damage the immune system. Formaldehyde is probably the most studied chemical outgassed by modern building materials—but there are many others that have hardly been studied at all.
Outgassing can also sometimes damage antiques and art objects. When the Smithsonian Institution’s curators transport artifacts for traveling exhibitions, they carefully monitor the inside of the enclosed packing crates to make sure the outgassing isn’t damaging delicate objects.
A Canadian study that examined the VOC levels in new houses found that as soon as the occupants moved in, the total level of VOCs rose slightly. This was due to such things as occupant activities, furnishings, and cleaning products. The study also found that levels dropped to about half the pre-occupancy level after about six months, primarily due to the aging of outgassing sources such as carpeting, paints, and formaldehyde sources like kitchen and bath cabinetry. This study also found that ventilation had little effect on VOC levels—that removing the source of the VOCs would be more effective than ventilation in reducing overall levels.
There was an interesting study, undertaken to see how chemicals commonly found in the indoor air would affect telephone components and switching equipment, that has important implications for all aspects of the indoor environment. It was learned that there are definitely chemical reactions continually taking place in the indoor air between the various pollutants that are present. As a result of these reactions, there are VOCs and other compounds being created that weren’t there before. And these new compounds react with each other to create even more compounds. Thus, the indoor environment can be extremely complex, and it can be compared to a chemistry experiment in which dozens of random chemicals are combined without having any idea what will result. And this is the environment we are living in every day. As an example of what can happen, this report found that, if there are only 20 parts per billion of ozone in indoor air having an average level of ketones present, then irritating hydroxyl radicals will be formed. In fact, the concentration of hydroxyl radicals will be a whopping 10,000 times higher than if no ozone were present.
Many materials can absorb, then re-emit, various VOCs. This is called the sink effect, and because of it, you can remove a material that has been outgassing VOCs into the indoor air, and still have VOCs present because they were stored and released by other materials. Re-emissions from sink materials can result in longer exposures than would occur in the absence of sinks. Carpet, draperies, furnishings, wood, and gypsum wallboard all act as sinks. One study found that carpet and drywall acted as sinks for specific VOCs found in latex paint, and that the VOCs were released very slowly, at very low rates. This study predicted that it would take years for all the VOCs to be released, and that different VOCs are absorbed and released at different rates. Gypsum wallboard is a much stronger sink for formaldehyde than for other VOCs.
Testing for outgassing is often done in special chambers that allow scientists to accurately determine exactly what chemicals are given off by different substances.
(Note: This article is part of the original HHI Archives, and was believed to be accurate at the time of writing. The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)
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“The nations treasures take to the highway for a 12-city tour,” Smithsonian (May 1996): 48-59.
“Pollutant source strength in new houses,” Solplan Review (January 1998): 10-11.
“Indoor chemical reactions provide challenges to researchers,” IEQ Strategies (June 1997): 10-11.
“Predicting the behavior of indoor sinks,” Inside IAQ (Spring/Summer 1993): 8. #EPA/600/N-93-010.
“VOC emissions from latex paint: Sink effects,” Inside IAQ (Spring/Summer 1997): 1-4.
“Sorption and re-emission of formaldehyde by gypsum wallboard,” Inside IAQ (Spring/Summer 1993): 8. #EPA/600/N-93-010.
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