Method-induced misclassification for a respirable dust sampled using ISO/ACGIH/CEN criteria

The single cut measurement of exposure to respirable dust is the accepted method of exposure classification in occupational hygiene. We previously showed that actual pulmonary tissue dose may be substantially different from the dose expected, or the indicated dose, based on measurements using current single cut methodologies. We now examine exposure misclassification of workers based on any single cut respirable dust measurement using the internationally accepted ISO/ACGIH/CEN single cut respirable dust measurement criteria. Hypothetical aerosols with 12 generalized size distributions typical of the method of aerosol generation (condensation, aged condensation, mechanical low energy, mechanical high energy and mixtures thereof) were assumed. Using previously reported models for sampler penetration and pulmonary deposition, Monte Carlo simulations of actual mass dose to pulmonary tissues in comparison to the dose estimate from an ideal respirable aerosol sampler were carried out. Measurement-based indicated doses were used to classify exposures into five exposure categories and these classifications were compared with the 'true' classifications from the dose-based exposure estimates. Misclassification rates were generally severe and were greatest for aerosols with mass median aerodynamic diameter (MMAD) <1 microm (approximately 100%) and MMAD 5-15 microm (65-95%). Misclassification rates were moderate (<20%) only for extremely coarse aerosols of MMAD>15 microm. Misclassification rates for oral and nasal breathing at 750 and 1500 ml tidal volume and 15 breaths/min were similar for each aerosol examined.