Air clearance sampling is conducted at the conclusion of an abatement project in order to ensure that the area is safe for re-occupation. When an abatement project is completed, the area should first be wet cleaned no fewer than three times and inspected visually to make sure that no visible asbestos dust or debris remains. After these tasks are completed, air clearance sampling should be conducted. In schools (K through 12th grade), all air clearance sampling must be performed using an aggressive technique. This means that the air inside the contained work area is agitated. This is usually done with a leaf blower. The blower is used to stir up any asbestos fibers that may have settled on horizontal surfaces. For these schools, twelve samples must be taken in total: five from different locations inside the work area, five from different locations outside of the work area, and two blank samples. Work area isolation and containment structures must not be removed until after air clearance sampling is completed. The analytical method for samples taken at schools must be performed using a method referred to as TEM. TEM stands for transmission electron microscopy. For most non-school projects, as few as three samples may be taken using non-aggressive techniques using an analytical method called PCM or Phase contrast microscopy. TEM is more costly than PCM and uses a more sophisticated high-powered method of magnification.
The safety regulations for asbestos abatement and removal projects are much less stringent in buildings that have been slated for demolition. Because such buildings will not be re-occupied, they do not need to be made safe for human occupation. For this reason, there are no federal regulations that require that air clearance sampling be conducted for abatement projects in buildings that will be demolished. However, many state and local regulations may require air clearance sampling in buildings slated for demolition, so it is important to make sure that you are familiar with all state and local applicable regulations before beginning any abatement project.