Reduction in number of airborne bacteria by air cleaning devices in a closed space.

A need for reducing the concentration of microorganisms in the air of dental operatories has been assumed. The purpose of this study was to evaluate the effectiveness of two methods of air cleaning in reducing the number ( airborne bacteria in a closed space. Tests for clearance of Bacillus subtilis spores from static and dynamic aeroso1 " were conducted in a 70 experimental room. The air cleaning devices were a portable electronic air cleaner with a capacity of 175 cfm (tested in combinations of one, two, and three) and a high efficiency particulate air (HEPA) filter module with a capacity of 800 cfm (tested singly and as a pair). Both devices cleaned and circulated room air only. Tx'e time required for complete clearance of spores from a static aerosol decreased as air capacity increased, from an average of 19 minutes at 175 cfm to 8 minutes at 800 cfm. With forced ventilation at 800 cfm, an average of 5 minutes was required. When a dynamic aerosol was disseminated over a 10-minute period, spore concentrations plateaued after several minutes, the level depending on the rate of air flow through the cleaning devices, Cleaning efficiency was maximum when the theoretical turnover of room air occurred once every 1 1/2 to 2 minutes. No difference was observed between the efficiency of the electronic and HEPA devices. Forced ventilation at 800 cfin produced results comparable to those of HLPA filtration at the same rate.