To evaluate filter efficiency and performance of environmental enclosures for tractors, 3- to 4-year-old tractor enclosure combinations (cabs retrofitted to tractors after manufacturing) were studied at a custom pesticide applicators facility. Optical particle counters were used to measure the aerosol number concentration inside and outside the cab. The ratio of these concentrations multiplied by 100 is termed percentage penetration, the amount of the aerosol that penetrates into the enclosure. For particles in the 0.3 to 0.4 microm range, penetration into the cab was reduced from 11 to 0.4% in the following sequential steps. First, manufacturing mistakes were corrected by fixing a bowed flange and inappropriate sealing of the sheet metal used to separate incoming air from air that had passed through the filter. This reduced aerosol penetration from 11 to 4.8%. Replacing gasket material on the used filter reduced penetration from 4.8 to 0.65%. This suggests that the filter gaskets are deforming and allowing leakage. Also, the filter media were evaluated for aerosol penetration as a function of particle size and were tested per the criteria stipulated in 42 CFR 84 for negative pressure air-purifying particulate respirators. These results showed penetration through the filter media of less than 0.03%, indicating that filter media were not a major source of aerosol leakage into the cab. The results suggest that the manufacturer should implement a quality control program to ensure that minimal aerosol penetration criteria into the cabs are met and an acceptable maintenance program exists to ensure compliance. Furthermore, the degradation of filter gasket material over time needs to be minimized to ensure that the environmental cabs continue to provide acceptable performance.
This case study demonstrates how methylene chloride exposures during furniture stripping can be reduced to below the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 25 ppm (as an 8-hour time-weighted average). Five surveys were conducted at one facility; the first four resulted in employee exposure geometric means from 39 to 332 ppm. For the fifth survey local exhaust ventilation was used at the stripping tank and the rinsing area, which together exhausted 138 m3/min (4860 ft3/min). Additional controls included providing adequate make-up air, adding paraffin wax to the stripping solution, raising the level of the stripping solution in the tank, and discussing good work practices with the employee. The employees' methylene chloride exposures during the fifth survey resulted in a geometric mean of 5.6 ppm with a 95% upper confidence limit of 8.3 ppm, which was found to be significantly lower than the OSHA PEL and the OSHA action level of 12.5 ppm. The cost of the ventilation system was $8900.
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