Collection of biological and non-biological particles by new and used filters made from glass and electrostatically charged synthetic fibers.

UNLABELLED: Synthetic filters made from fibers carrying electrostatic charges and fiberglass filters that do not carry electrostatic charges are both utilized commonly in heating, ventilating, and air-conditioning (HVAC) systems. The pressure drop and efficiency of a bank of fiberglass filters and a bank of electrostatically charged synthetic filters were measured repeatedly for 13 weeks in operating HVAC systems at a hospital. Additionally, the efficiency with which new and used fiberglass and synthetic filters collected culturable biological particles was measured in a test apparatus. Pressure drop measurements adjusted to equivalent flows indicated that the synthetic filters operated with a pressure drop less than half that of the fiberglass filters throughout the test. When measured using total ambient particles, synthetic filter efficiency decreased during the test period for all particle diameters. For particles 0.7-1.0 mum in diameter, efficiency decreased from 92% to 44%. It is hypothesized that this reduction in collection efficiency may be due to charge shielding. Efficiency did not change significantly for the fiberglass filters during the test period. However, when measured using culturable biological particles in the ambient air, efficiency was essentially the same for new filters and filters used for 13 weeks in the hospital for both the synthetic and fiberglass filters. It is hypothesized that the lack of efficiency reduction for culturable particles may be due to their having higher charge than non-biological particles, allowing them to overcome the effects of charge shielding. The type of particles requiring capture may be an important consideration when comparing the relative performance of electrostatically charged synthetic and fiberglass filters. PRACTICAL IMPLICATIONS: Electrostatically charged synthetic filters with high initial efficiency can frequently replace traditional fiberglass filters with lower efficiency in HVAC systems because properly designed synthetic filters offer less resistance to air flow. Although the efficiency of charged synthetic filters at collecting non-biological particles declined substantially with use, the efficiency of these filters at collecting biological particles remained steady. These findings suggest that the merits of electrostatically charged synthetic HVAC filters relative to fiberglass filters may be more pronounced if collection of biological particles is of primary concern.

Employers' expectations of knowledge and skills of master's-trained industrial hygienists.

Certified industrial hygienists with recent hiring experience were surveyed about their expectations of competencies when hiring entry-level master's-trained industrial hygienists. Results were used to affirm educational objectives and program outcomes required by new program accreditation criteria. We received 129 completed surveys from 179 eligible participants agreeing to participate. Most of the respondents were employed in very large companies (>500 employees) and were evenly distributed in manufacturing, services, and public administration. More than 70% of respondents identified essential knowledge and skills in 11 topic areas that fall entirely within the categories of recognition, evaluation, and control. Environmental and management topics were identified as essential by less than 25% of the respondents. Nineteen competencies identified as essential by 60% of the respondents were entirely in the categories of recognition, evaluation, control, and communication. Less than 50% of the respondents thought competencies in the management area were useful but not essential. Air sampling pumps, sound level meters, noise dosimeters, and direct-reading instruments were the mostfrequently listed equipment with which industrial hygienists should be familiar. These survey results represent the first systematic input from employers on their expectations for competencies of master's-trained industrial hygienists.

Modeling evaporative loss of oil mist collected by sampling filters.

Oil mists can cause respiratory distress and have been linked to skin and gastrointestinal cancers in workers. Standard concentration assessment methods call for sampling these mists with fibrous or membrane filters. Previous experimental studies using glass fiber (GF) filters and polyvinyl chloride and polytetrafluoroethylene membrane filters indicate that mist sampled onto filters may volatilize. A model has been developed to predict the evaporation of mist collected on a fibrous sampling filter. Evaporation of retained fluid from membrane filters can be modeled by treating the filter as though it is a fibrous filter. Predictions from the model exhibit good agreement with experimental results. At low mist concentrations, the model indicates that evaporation of retained mineral oil occurs readily. At high mist concentrations, significant evaporation from the filters is not expected because the vapor accompanying the airborne mist is already saturated with the compounds in the oil. The findings from this study indicate that sampling mineral oil mist with filters in accordance with standard methods can lead to estimates of worker exposure to oil mist that are too low.