The Mine Safety and Health Administration, Department of Labor, requires coal mine operators to measure compliance with federal respirable dust exposure standards periodically using approved gravimetric samplers. However, the gravimetric approach, with its inherent delays, cannot provide dust concentration data quickly enough to allow on-site correction of inadequate dust control strategies or removal of personnel from harmful environment. Furthermore, alleged tampering with dust samples collected to determine compliance with standards prompted the Secretary of Labor to appint a special Respirable Dust Task Group to study options to improve monitoring and control of respirable coal mine dust. The Mine Safety and Health Administration's Task Group recommended that the U.S. Bureau of Mines develop a fixed-site monitor that would provide continuous information to the mine worker and mine operator regarding dust levels and the status of compliance with the applicable respirable dust standard. In response to the Mines Safety and Health Administration's response, the U.S. Bureau of Mines is investigating several sensor technologies for continuously monitoring respirable coal mine dust. One of these technologies is the Rupprecht and Patashnick Company tapered element, oscillating microbalance. The bureau is in the process of investigating the suitability of using this sensor in the high humidity and vibration environment of underground coal mines. Laboratory tests have indicated that, with modification, the sensor can meet the humidity and vibration requirements for underground coal mine use. Currently, the bureau is developing prototypes of a continuous dust monitor based on this technology. When available, these will be evaluated in underground coal mines.