Dispersal of fungal spores from three types of air handling system duct material

Exposure to airborne microorganisms in indoor environments may result in infectious disease or elicit an allergic or irritant response. Air handling system components contaminated by fungi have been implicated in the dispersal of spores into the indoor environment, thereby serving as a route of exposure to occupants. This study was conducted to provide quantitative data on the dispersal of spores from fungal colonies growing on three types of duct material. Galvanized metal, rigid fibrous glass ductboard, and fiberglass duct liner were soiled and contaminated with a known concentration of Penicillium chrysogenum spores. The duct materials were incubated in humidity chambers to provide a matrix of growing, sporulating fungal colonies at a contamination level of 109 colony forming units (CFU) per duct section, consistent for all materials. For each experiment a contaminated duct section was inserted into the air handling system of an experimental room, and the air handling system was operated for three 5-minute cycles with an air flow of 4.2 m3 min–1. The duct air velocity was approximately 2.8 m sec–1. The airborne concentration of culturable P. chrysogenum spores (CFU m–3), total P. chrysogenum spores (spores m–3), and total P. chrysogenum-sized particles (particles m–3) were measured in the room using Andersen single-stage impactor samplers, Burkard slide impactor samplers, and an aerodynamic particle sizer, respectively. The highest airborne concentrations (104 CFU m–3; 105 spores m–3; 104 particles m–3) were measured during the first operating cycle of the air handling system for all duct materials with decreasing airborne concentrations measured during the second and third cycles. There was no significant difference in spore dispersal from the three contaminated duct materials. These data demonstrate the potential exposure for building occupants to high concentrations of spores dispersed from fungal colonies on air handling system duct materials during normal operation of the system.