Resuspension of bacterial spore particles from duct surfaces

Allergen-containing particles resuspended from building floors or outdoor-air-entrained particulates can deposit on the surfaces of supply air ducts. These particles can later be resuspended into the supply air because of duct vibration and turbulent flow. This study investigates the resuspension rates of bacillus thuringiensis bacterial spore particles (0.4-25 μm) from a vibrating duct surface with air flow swirl velocities ranging from 0 to 2.5 m/sec. Resuspension rates increased by ∼ 2 orders of magnitude for all particle sizes in the 0.3-2.5 m/sec range of swirl velocities. One minute averaged resuspension rate ranged from 10^-5 to 0.1/min. For particle sizes above about 10.0 microns, depending on swirl velocity magnitude, a relatively sharp drop-off in resuspension rate is observed. These results further indicate that the substantial spore residence time of nine months on the metal surfaces before conducting the resuspension disturbance experiments does not inhibit the resuspension propensity of the spores significantly.