Enclosed cabs that protect operators are common on mining equipment, such as drills, wheel loaders, and haul trucks. As equipment ages, many of the original components on the cab enclosure deteriorate through normal operation in harsh mine environments. As a result, the effectiveness of the air filtration system and cab seals is lessened and the protection initially afforded to an operator is compromised, possibly exposing him or her to elevated levels of respirable silica dust. In an effort to improve protection of equipment operators, the National Institute for Occupational Safety and Health (NIOSH) entered into a number of cooperative research efforts with the mining industry and companies that manufacture and install cab enclosure units. Several studies regarding the effectiveness of these systems have been published for surface coal and noncoal operations. In these studies, units were installed on front-end loaders and overburden drills to reduce respirable coal and silica dust in the operator's cab. The units feature air-conditioning, heating, filtration, and pressurization systems that recirculate and filter a majority of the inside cab air combined with a smaller portion of outside makeup air. Outside air is cleaned with high-efficiency filters before it enters the cab, and the cab enclosure is maintained under a positive pressure. In this current study, NIOSH and Sigma Air Conditioning, Inc., entered into a cooperative cost-sharing agreement to evaluate the impact of retrofitting a haul truck at an underground limestone mine with a new filtration/pressurization system to reduce the operator's exposure to silica dust. After the new unit was installed and seals on the cab were upgraded, levels of respirable quartz dust in the cab decreased 63%.
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236