DESIGN The unit has been designed for the pharmaceutical industry to control the problem of powder contamination and reduce operator's exposure to powder; namely, the units protect the powder from blowing about and cross-contaminating other areas and products, and protect the operator from inhalation of potentially hazardous pharmaceuticals. Primarily conceived for the pharmaceutical industry, it can be used whenever there is a risk of dust contamination. OPERATING PRINCIPLE Air from the HEPA filter passes down over the enclosed space, then through two pre-filters and back to the Hepa filter plenum chamber. A small absolute filter mounted downstream of the fans generates a loss in the air recycling system, causing an inflow of air between the vinyl curtain and floor. The vertical air stream carries away powder generated and spilt in the