Authors: GE Mizan, JI Phillips and T Nthoke
Source: Occupational Health Southern Africa. Vol 24 No.5 Sept/October 2018
Background: Despite the banning of asbestos in 2008, South Africa has a legacy of asbestos-containing materials (ACMs) extant in the environment. The number of asbestos cement (AC) roofs in the residential and industrial sectors is unknown but, in the low-cost housing sector alone, it is estimated that there are over one million. Eventually, these roofs will need to be replaced, using non-asbestos materials. Removal of AC roofs is regulated in terms of the Asbestos Regulations, 2001. However, there is no documented evidence that adherence to these regulations is protective for the community when large numbers of roofs are removed.
Objective: The objective of this study was to measure asbestos fibres in the air before and after a large-scale removal of AC roofs, and to estimate levels to which members of the community might be exposed.
Methods: Asbestos fibres in the air were sampled before and immediately after the removal of AC roofs, using air-sampling pumps. A total of 16 mixed cellulose ester (MCE) air filters were analysed using phase-contrast microscopy (PCM) and another 18 polycarbonate, gold-coated filters were analysed with scanning electron microscopy- energy dispersive spectrometry (SEM-EDS). The results were compared to the South African occupational exposure limit (OEL) of 0.2 f/ml and the UK clearance indicator for site reoccupation of 0.01 f/ml. Four bulk samples were obtained from the AC roofing material prior to removal to confirm the presence of asbestos, and to identify the types of asbestos fibres in the AC matrix, using SEM-EDS. The contractor work practices were observed during the removal process.
Results: No asbestos fibres were detected in air samples taken before, and immediately after, the removal of asbestos roofs, using the SEM-EDS. Several regulated fibres were counted using the phase-contrast microscopy (PCM) methodology before and after the removal. The corresponding fibre concentrations were all below the clearance indicator of 0.01 f/ml after the removal of the AC roofs. However, fibre concentrations corresponding to two of the air samples taken before the removal of the AC roofs were equal to the clearance indicator; and one was higher, at 0.02 f/ml. All four bulk samples taken from the roof material contained asbestos. Three of the four samples were found to contain a mixture of all three fibre types, i.e. chrysotile, crocidolite and amosite. The fourth sample contained chrysotile and crocidolite.
Conclusion: The removal of AC roofs did not result in elevated fibre concentrations in the households sampled. This suggests that pre-wetting of the AC and careful removal reduces the risk of fibre exposure.