How is the permissible exposure limit (PEL) for silica calculated?

The calculation of the permissible exposure limit (PEL) for silica is derived from the need to account for the percentage of quartz present in a sample. The formula used is PEL = 10 / (%quartz + 2).

This approach acknowledges that as the percentage of quartz increases, the allowable exposure limit must decrease to maintain workplace safety. Specifically, the "+2" in the denominator provides a buffer to ensure that even at low concentrations of quartz, the PEL does not become excessively high. Consequently, this formula allows for a quantitative representation of the risk associated with exposure to varying concentrations of quartz in silica dust.

In this context, the other options do not accurately reflect the correct relationship between quartz concentration and permissible exposure limits. For instance, options that involve addition or multiplication rather than division would not correctly depict the decreasing limit associated with increased quartz percentages. Therefore, the key to understanding why B is the right answer lies in its proper representation of the inverse relationship between quartz percentage and permissible exposure levels.