Collection of fungal spores on air filters and spore reentrainment from filters into air

The collection of fungal spores on ventilation filters and their potential for subsequent reentrainment were compared with the collection and reentrainment of standard test particles. Potassium chloride (KCl) particles were selected as the standard test particles, as recommended by the ASHRAE standard 52.2. Penicillium brevicompactum and Penicillium melinii were selected to represent common fungal spores in indoor air. Two commonly used filters were tested: medium-efficiency filter medium A from a prefilter and higher efficiency medium B from a fine filter. The collection efficiencies of filters were determined at a face velocity to the pleated filter assembly of 2.54 m s(-1), which is typical for both filters. The collection efficiency was found to be slightly lower for fungal spores than for KCl particles of the same aerodynamic size. When the reentrainment velocity was the same as the loading velocity through the filter medium (0.56 m s(-1) for A, 0.09 m s(-1) for B), the reentrainment rate was less than 0.4%. When the reentrainment velocity was increased to 3.00 m s(-1), the reentrainment of fungal spores was higher than that of KCl particles: 2-6% far P. brevicompactum, 5-12% for P. melinii, and 0.2-0.6% for KCl particles. The differences in behaviour between fungal spores and KCl particles were attributed to aggregation and deaggregation of fungal spores-The higher reentrainment rate of P. melinii compared to that of P. brevicompactum can be explained by the different surface structure of these spores. The results suggest that during the startup of a ventilation system or during other operations, when the air velocity may suddenly increase, reentrainment of fungal spores can be significant. Furthermore, if fungal spores grow on the ventilation filters, the reentrainment rate may become even higher than measured in this study. (C) 2000 Elsevier Science Ltd. All rights reserved.