Assessment of fungal (Penicillium chrysogenum) growth on three HVAC duct materials

Many building investigators have documented fungal biocontamination in heating, ventilating, and air-conditioning (HVAC) ducts. It has been suggested that emissions of spores and volatile organic compounds from the growing fungi may contribute to poor indoor air quality and result in adverse health effects. Laboratory experiments were conducted to evaluate the susceptibility of three types of ventilation duct materials (fibrous glass ductboard, galvanized steel, and insulated flexible duct) to fungal (P. chrysogenum) growth. Each sample was inoculated with spores of P. chrysogenum and incubated in a static chamber controlled at 97% relative humidity (RH) and 21 degrees C for six weeks. Culturable spores on each sample were enumerated before and after incubation to determine the extent of fungal amplification, The results indicated that, of the newly purchased duct materials, only the flexible duct supported moderate growth of P. chrysogenum. No fungal growth was detected on the fibrous glass and galvanized steel. The number of culturable spores on galvanized steel even decreased during the test period. Wetting the clean duct samples with sterile water did not increase amplification of the P. chrysogenum over the level seen without the wetting. Soiling the samples with dust collected from residential heating and air-conditioning systems enhanced the susceptibility of all three duct materials to fungal growth; however, at different levels of soiling. At a moderate level (0.4-0.7 mg cm(-2)) of soiling, growth occurred on the fibrous glass ductboard and the flexible duct, but not the galvanized steel, At a markedly higher level (9-18 mg cm(-2)) of soiling, growth was seen on the galvanized steel as well. The results of these experiments suggest that dust accumulation and/or high humidity should be properly controlled in any HVAC duct to prevent the growth of P. chrysogenum.