VOC sequestration
The process of sequestration—essentially removing VOCs from interior air and ‘sinking’ them into a solid material—has been used as a method for eliminating aldehydes and other compounds for more than 20 years. It is influenced by two factors: the boiling point of the VOC and the temperature of the interior air.
Health Canada classifies VOCs as organic compounds that have boiling points roughly in the range of 50 to 250 C (122 to 482 F). The compounds with the lowest boiling points are described as the most volatile and are the most difficult to extract from the air. Aldehydes fall into this category and, therefore, take more work to extract than other VOCs.
The temperature of the interior air affects whether the VOCs will be sunk into a material through desorption or absorption. The former is an endothermic reaction, meaning that it requires heat; the latter, however, is exothermic and gives off heat—this makes it more effective in colder room temperatures.
Up until recently, one of the most common ways for commercial builders to improve IAQ in finished, newly furnished buildings before being occupied was to use thermal desorption, a VOC sequestration process more commonly known as a ‘bake-out period.’ In essence, the building’s heating system is set to a high temperature to agitate large amounts of VOCs in new carpeting, furniture, and cabinetry. This removes it from the source into the air; the VOCs are then ventilated to the outside, where they will eventually be neutralized by ultraviolet (UV) rays from the sun.
This is effective, but only initially. The building materials and furnishings will still continue to release VOCs over time. Consequently, building product companies are developing new products that use the absorption method to continuously capture VOCs, trap them inside an interior surface, and neutralize them.
Walls usually make up about 60 per cent of a building’s interior surface, and they are constantly in contact with VOCs and other interior air impurities. This has led some building product manufacturers to include new VOC sequestration technology into gypsum board products.
The VOC sequestration process begins when the gypsum board comes in contact with VOCs through typical airflow. The drywall captures the VOCs, which chemically react with specialty additives within the board. The chemical reaction converts the VOCs to safe, inert compounds, which are permanently locked inside.
Such gypsum boards can be finished with breathable wallpaper or water-based acrylic and epoxy paints, as they will not hinder VOC absorption. They can be recycled in the same manner as regular gypsum board at the end of their useful life, and sent to a landfill without polluting groundwater. A benefit to contractors is these products handle like standard drywall during installation and do not require special tools.
Before specifying a VOC-reducing gypsum board, it is important to ensure it has been tested and proven by International Organization for Standardization (ISO) 16000-23, Performance Test for Evaluating the Reduction of Formaldehyde Concentrations by Sorptive Building Material. A passing grade on this 28-day test is proof the product permanently eliminates formaldehyde.
Conclusion
As design/construction professionals become more informed on how to make buildings more sustainable, a greater understanding is fostered of the importance of keeping building occupants healthy as well with improved IAQ. Building and design professionals are using better moisture management and ventilation strategies to ensure a dry building envelope and ward off mould growth. At the same time, manufacturers are working to minimize VOC content in their products.
Nevertheless, VOCs remain a significant threat to IAQ, especially in the form of cleaning supplies and air fresheners. As long as building occupants continue to use these items inside the building, VOCs will be in the air. It is to be expected, with ongoing scientific research, that formaldehyde and other chemicals will eventually be replaced in the formulas of all of these items, essentially eliminating them from interior air. Until then, design/construction professionals should do what they can to evacuate them from interior air.
By selecting low-VOC building materials and installing VOC-reducing gypsum boards in the walls of building projects, designers can counteract the spread of volatile compounds through interior air, improving IAQ and making a more pleasant interior environment for occupants.
Lucas J. Hamilton is the manager of building science applications for CertainTeed Corp. He is a physicist with more than 20 years of experience in construction and construction products manufacturing. Hamilton can be reached at lucas.j.hamilton@saint-gobain.com.
