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Industrial hygienists can compare "total" dust concentrations to higher inhalable concentrations using a value called the performance ratio. A commonly used performance ratio of 2.5 is used for dusts found in the workplace, after results from multiple studies were compiled. The objective of this study was to evaluate the "total" and inhalable dust performance ratio over a range of conditions to investigate whether the commonly used value of 2.5 varies between: (1) dust type (2) IOM and Button inhalable samplers and (3) distance from the dust source.
Dust concentrations were generated in a still air chamber using three dust types; sawdust, flour, and glass microbeads. The IOM, Button, and CFC samplers were used to measure concentrations at four locations increasing in distance from the source. Linear regressions in the form of [Inhalable mg m-3] = S x ["Total" mg m-3] were used to calculate the appropriate performance ratio, S. The intercept of this regression was forced through the origin. Linear regression was also used to examine whether the effect of distance on S was significant and a distance factor (β1) was calculated.
The calculated performance ratios, S, differed between sawdust, flour, and glass microbeads, and were 1.62, 2.82, and 2.97 respectively when comparing IOM concentration to CFC concentration. Performance ratios computed for the Button sampler for sawdust, flour, and glass microbreads were 0.82, 1.04, and 0.57 respectively. Performance ratios were significantly different (p=0.049) between the two inhalable sampler types. The IOM/CFC performance ratio for all three dusts averaged 2.47 (SD=0.74), whereas the Button/CFC performance ratio for the three dusts averaged 0.81 (SD=0.24). Only the IOM/CFC performance ratio had a statistically significant distance factor at α=0.05.
The authors caution against using a single performance ratio of 2.5 for all dusts due to the large variance involved with dust sampler and dust type. Distance from the source did not significantly affect the performance ratios computed under laboratory conditions. Industrial hygienists are advised to perform side by side sampling with inhalable and "total" dust samplers to create specific performance ratios appropriate for tasks found in the workplace.