Asbestos in Buildings: The Difficulties of a Reliable Exposure Assessment

Abstract

Based on careful investigations carried out in 12 different buildings with and without friable asbestos containing insulation materials, different ways of exposure assessment are compared. Methods used are visual inspection algorithm, phase-contrast microscopy (PCM), direct reading instruments (FAM, fibrous aerosol monitor), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This last method was considered as a reference, because the complete size distribution of every type of mineral fiber can be assessed. The advantages and limitations of each method are discussed in the light of the results obtained. Among many others a few relevant findings may be cited: 1) In buildings where no known source of asbestos fibers exists high levels of fibers from unsuspected sources can be found. 2) The resuspension of settled fibers is one of the main sources of exposure and is related to the presence or activities of people in the concerned area. 3) The common belief that a ventilation system in contact with friable asbestos containing material is a major source of indoor pollution was not confirmed here. 4) In some situations all the chrysotile fibers longer than 5 μm were too thin to be seen either by PCM or SEM. 5) The size distribution varies according to the fiber type and the situation. The risk assessment based on a limited number of epidemiologic studies is strongly related to the method by which asbestos exposure is measured and to the relationship between the “old” methods used in the occupational environment and those presently used in nonoccupational situations.