Robert W. Aldrich
U.S. Dept. of Labor, Office of the Solicitor, Mine Safety and Health Div., 4015 Wilson Blvd., Arlington, VA 22203
Several federal agencies have developed regulations to protect employees from health hazards in the workplace by establishing time-weighted average exposure limits. In order to ensure that exposures remain within acceptable limits, regulations have also included criteria for conducting accurate sampling. Accurate measurements of exposure can be obtained only when the instruments used are functioning properly and have been calibrated to the manufacturer's specifications. Inaccurate measurements can lead to not only incorrect or unrepresentative worker sampling, but also can result in ineffective action by the employer if it becomes necessary to take corrective actions to reduce exposures to allowable levels. As a result, from a legal point of view, measuring instruments must be properly calibrated and maintained before they are used to measure worker exposures. In addition, the issue of instrument accuracy is important because courts have determined that in order for measurements to be considered ``legally certain,'' they must be accurate to within a 95% confidence.