Encapsulation of asbestos takes place when it is determined that the material can be effectively embedded and surrounded in an adhesive sealant that completely prevents the release of fibers. This form of asbestos control is sometimes considered an alternative form of abatement in its own right. The sealant either works by binding the asbestos fibers together or by coating the material to halt the release of fibers. The EPA explains that pipe, boiler and furnace insulation is sometimes repaired through encapsulation. Another, similar method of asbestos control involves covering, or enclosing, the materials. With enclosure, a protective wrap or jacket is placed over or around the asbestos-containing material to prevent the release of fibers.
Both methods are dependent on the condition of the asbestos containing materials, later use of the area, whether the material can support the encapsulant and whether the material remains wet from a leak. The EPA recommends individuals not attempt to encapsulate asbestos-containing materials alone, as they might actually exacerbate the exposure risks and cannot effectively determine if encapsulation or enclosure is the best method of containing the material. Instead, only trained asbestos handling professionals should perform these management techniques. Both forms of control allow the asbestos to remain in place, which is usually much cheaper than removal. However, the EPA explains that the encapsulation or enclosure of materials may make future asbestos removal far more difficult and costly.
Proper encapsulation requires the project monitor to verify that the encapsulating material has been applied according to the manufacturer’s specifications. Then core samples are taken to measure the depth of the penetrating encapsulant’s penetration, or to determine the surface film’s thickness for bridging encapsulants. To qualify as a penetrating encapsulant, it must penetrate the material to a depth of at least 1 cm. If it does not penetrate to this minimum depth, the material is considered a bridging encapsulant.
To test a material’s ability to support an encapsulant, the “pull test” is utilized, which tests for possible cohesion failure by affixing a surface with the bonding material and attaching weights until separation occurs or the test limit is reached. This testing is generally limited to downward-facing horizontal surfaces, unless some horizontal pull system has been rigged to exert a measurable force on a vertical surface.
- Oberta, Andrew F. (2005). Asbestos Control: Surveys, Removal, and Management (2nd ed.). West Conshohocken, PA: ASTM International.