Evaluation of the time weighted average of air contaminants with special references to concentration fluctuation and biological half time.

Statistical parameters with carbon felt dosimetry are analyzed and new sampling criteria are presented based on the analysis. In cass where the mean of measured time-weighted averages is kept two times the unbiased standard deviation below the maximum permissible concentration-time weighted average (MPC-TWA) and the values above MPC-TWA are observed with a frequency of less than 5%, compliance is determined with a confidence limit of 95% provided the biological half time of the contaminant is longer than 4 hours.