The first three parts of this series covered an overview of chemical sensitivities, the critical importance of source removal and detailed cleaning, and products and processes that can be used for neutralization of chemical or biological residues that remain following cleaning. This section deals with the concept of off-gassing. It provides a basic summary of the off-gassing process as well as some specific suggestions for addressing residual chemicals. All of the same caveats about the approach to writing this series of articles that were laid out in part one still apply. In particular, the mention of particular products and processes are not related to any monetary gain on the part of the author but only as practical information and suggestions for consideration for the readers.
When discussing the concept of off-gassing, the term Volatile Organic Compounds (VOCs) quickly comes into play. VOCs are a large group of chemicals that have a high vapor pressure. This means that the chemicals have a tendency to evaporate from liquids or sublimate from solids (i.e., move directly from a solid phase to the vapor phase without becoming a liquid first) at room temperature. This volatility allows the chemicals to mix with the surrounding air. The organic portion of the definition means that the chemicals have a carbon component to them; and more specifically at least one carbon-hydrogen bond.