Removal of Asbestos from Difficult-to-Access Large Diameter Pipes: A Comparison of Wet Removal Methods

Abstract

Asbestos-containing materials have been widely used in buildings to insulate heating pipes and boilers. Throughout the lifetime of the heating system, occasional maintenance or alteration is required, and sections of the insulation must be removed. Full enclosure and glovebag techniques are widely used but have limitations if the pipes are difficult to access or have diameters greater than about 0.5 m. To assess how well commercially available systems for wet removal can suppress airborne fiber levels, a series of trials was conducted at a site undergoing a predemolition asbestos removal. All the systems used proprietary additives to a water-based solution to help improve the suppression of airborne fibers, but a variety of delivery systems, sprays, injection guns, and probes were used to deliver the product and to give a uniform wetting and penetration of the insulation. To simulate a removal/maintenance activity, a few meters of pipe insulation were removed, with a time limit of one working day for each of the four suppliers taking part. As a control, the demolition contractor also performed a wet removal using water. The airborne levels of asbestos produced during the initial setting up, various stages of removal and clean-up were monitored by personal and static sampling. The concentration of “regulated” fibers (fibers >5 μm in length, >3 μm in diameter, and aspect ratio 3:1) were measured using phase contrast microscopy, and the results from the different systems were compared. It was found that the two liquid injection methods used at this site considerably reduced the airborne emissions during the removal with short-term personal samples producing concentrations below 0.25 f/ml, if the insulation was adequately wetted. However, bagging and clean-up after removal produced increases of up to 1.9 f/ml, showing that careful work practices are needed at all stages. In this particular instance the spray application of liquid did not achieve the same degree of fiber suppression, with personal samples producing concentrations between 0.75 to 4.05 f/ml. The use of water alone gave the highest individual sample of 9.14 f/ml. The results showed that respiratory protection and enclosure are required, but as systems are refined and contractors become more familiar with them, levels could potentially be reduced to below 0.1 f/ml.