Abstract
The determination of particle size is essential to the evaluation of airborne dust hazards. A set of 18 slides was prepared and circulated among 30 persons of varying experience in particle size determination. They made 206 particle size determinations. Statistical evaluation of the results are presented. Industrial hygienists with very little or very much experience in the total field of industrial hygiene demonstrated the greatest variance of measurement. Those in the experienced group are primarily in the supervisory category, and their errors appear to be due to a lack of constant use of the microscope. Practice, rather than experience, seems to be the main criterion of accuracy in particle size measurement.