Design, Testing, and Modeling of Environmental Enclosures for Controlling Worker Exposure to Airborne Contaminants

Environmental enclosures such as cabs, booths, rooms, etc. are one of the mainstay engineering control methods for reducing operators' exposure to airborne contaminants generated outside the enclosure. In order to achieve a cleaner air environment, air filtration is typically incorporated into the enclosure's heating, ventilation, and air conditioning (HVAC) system. The National Institute for Occupational Safety and Health (NIOSH) has jointly conducted collaborative research efforts with HVAC system manufacturers, cab filtration/pressurization component manufacturers, original equipment manufacturers (OEMs) of industrial vehicles, and companies using these cabs/environmental enclosures. This report summarizes NIOSH's laboratory and field research results, provides key design guidelines for environmental enclosures, shows measurement methods for enclosure performance, and demonstrates mathematical modeling of filtration system designs.
Two key elements of an effective environmental enclosure are a good filtration system and an enclosure with good integrity (sealed isolation from the outside environment). A good filtration system should include filtering out at least 95% or greater of airborne respirable aerosols (dust, diesel particulate matter, liquid droplets, etc.) from the intake airflow with an additional recirculation filtering component for the inside air. Good enclosure integrity is also needed to achieve positive pressure to prevent wind-driven aerosol penetration into the enclosure, as well as to minimize air leakage around the filtration system. Test methods and mathematical modeling of environmental enclosures are also beneficial for quantifying and optimizing filtration system designs, as well as maintaining optimum protection factor (PF) performance for enclosure occupants. Occupational exposure sampling, particle counting methods, airflow measurements, and enclosure pressurization measurements are used to assess the effectiveness of environmental enclosures. Node analysis of filtration system designs are beneficial for examining the effects of filter placement, filter efficiency, airflow quantities, air leakage, and wind penetration on the environmental enclosure's air cleaning performance.


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