<p>This study was conducted to evaluate the potential role of the environmental enclosure with an air cleaning system as a technology for controlling operators’ exposures to aerosols and criteria gases emitted by diesel-powered mobile equipment in underground environments. This laboratory evaluation was conducted using a testing facility custom designed to allow for evaluation of the environmental enclosures and associated Heating, ventilation, and air conditioning systems while being immersed in the diluted diesel exhaust. Four different configurations of the Heating, ventilation, and air conditioning system for the commercially available environmental enclosure of the underground mining load-haul-dump vehicle were evaluated at the custom-built test facility. The configurations were evaluated while immersed in the diluted diesel exhaust with a concentration of aerosols and criteria gases comparable to those in underground mines. The configurations fitted with high efficiency filter elements were found to provide more than 95 percent reductions in the number concentrations of diesel aerosols. The configurations with elements containing adsorbent reduced the NO₂ concentrations present outside of the enclosure in excess of the current personal exposure standards by more than 85 percent and increased NO concentrations by as much as 37 percent. None of the evaluated configurations had a substantial effect on the CO₂ concentrations present outside of the environmental enclosure system at concentrations equivalent to the current personal exposure standards for underground miners. The results suggest that air quality control systems could be optimized to allow for better control of the flow rates, pressurization of the enclosure, and influx of contaminants at the low-pressure zone of the systems. The control of CO₂ and NO exposures would continue to rest on supplying an adequate quantity and quality of fresh air to dilute those gases below targeted exposure standards.</p>