Abstract
This study reports on the comparison of four outdoor asbestos abatement methods which have been used at a large petroleum refinery. These methods are: negative pressure enclosure; negative pressure glove bag; and two types of partial enclosures, open top (five-sided enclosure) and windscreen/extended barricade (less than five-sided enclosure). The air monitoring results for each method are compared in terms of downwind area, personal time-weighted average, and personal excursion limits for workers abating asbestos thermal system insulation. The results show that for a large sample set (>11,000) accumulated over a 3-year period, all downwind area asbestos concentrations at prescribed distances from the abatement activity are essentially equivalent for all four abatement methods, with geometric means of 0.004 to 0.005 fibers/cc (f/cc). The data indicate that negative pressure enclosures provide no added protection for bystanders, as compared with the other abatement methods normally used in outdoor petroleum refinery environments. The data support the use of partial enclosure methods in certain situations since they yield downwind area exposure potentials that are statistically equivalent to those of the negative pressure enclosure method. The negative pressure glove bag method was shown to yield the lowest personal time-weighted average exposure potential. The geometric mean for this abatement method was 0.008 f/cc, with a geometric standard deviation of 3.1, in comparison with both negative pressure and partial enclosures, which had geometric means in the range of 0.020 to 0.023 f/cc, with a maximum geometric standard deviation of 5.6. A similar observation was made for excursion limit samples, with the negative pressure glove bag method yielding a lower average concentration than the other methods. The excursion limit geometric mean for the negative pressure glove bag method was 0.017 f/cc, with a geometric standard deviation of 2.6. This can be compared with a geometric mean of 0.031 f/cc, with a geometric standard deviation of up to 4.6 for the other three abatement methods. The results show that trained workers using adequate wetting techniques and partial enclosures can achieve downwind area concentrations equivalent to negative pressure enclosures. All techniques yielded downwind perimeter concentrations well below the proposed Occupational Safety and Health Administration permissible exposure limit of 0.1 f/cc. When it can be used in an outdoor petroleum refinery environment by experienced crews, the negative pressure glove bag method yields the lowest personal asbestos exposure concentration in comparison with negative pressure and partial enclosures.