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Bake-out - An Outgassing Solution?

By HHI Staff

Outgassing from a material can often be hastened by heating the material. As an example, a baked-enamel finish is often tolerable for sensitive people, whereas a conventional enamel paint might take many months to outgas by itself. A few years ago, the idea of heating materials to hasten outgassing was applied to entire buildings. This is called a bake-out. Initial results of bake-outs seemed to indicate that they could be useful in reducing VOC concentrations—but the procedure occasionally damaged parts of the building. For example, in one commercial building, the concrete floor slabs moved slightly causing carpet and vinyl flooring to buckle, a window cracked, and some wood doors warped. 

 

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A bake-out involves warming up the interior of a building with the furnace, for at least 48 hours, to an above-normal temperature (at least 95°F) and simultaneously ventilating the building at a higher-than-normal rate. This is easiest to do when indoor and outdoor temperatures are similar. In the middle of winter a furnace may be operating at capacity, and not be able to raise the temperature that much.

 

After some initial positive results, as researchers started investigating bake-outs more thoroughly, they encountered some unforeseen problems. For example, because it’s difficult to heat up an entire building uniformly (it takes longer to heat up a concrete floor slab than carpeting) there will be some surfaces where temperatures are lower than the air temperature. Moisture from the air, and some volatile gases, can condense on these cooler surfaces. In one 3-day, 90°F bake-out, alcohols, oxygenated compounds, and chlorinated chemicals were found in water that had condensed during the bake-out. Researchers also found that some chemicals were released into the air that aren’t released at normal room temperatures, and that the post-bake-out outgassing rates were hardly lower than the pre-bake emissions. Bake-outs seem to have little effect on formaldehyde levels in a building, probably because formaldehyde-containing materials, such as particle board, are thick enough to have a substantial reservoir of formaldehyde in them. It’s been suggested that part of the reduction in emissions that has been seen is due to the drying of concrete during a bake-out. This results in a lower relative humidity indoors, and lower outgassing rates.

 

The results of bake-outs are, at best, mixed. In fact, the concentrations of some compounds are higher after a bake-out, while others are lower. For thick materials, such as particle board, bake-outs have little long-term effect. Probably the best use of a bake-out is in a controlled setting by a manufacturer. In this way, a procedure can be tailored specifically to reducing emissions in one particular product. This is already being done successfully with baked-on paints.

 

 

 

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Bake-out - An Outgassing Solution?:  Created on August 17th, 2008.  Last Modified on February 28th, 2011

 

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