What is the formula for calculating the permissible level if work hours exceed 8?

The formula for calculating the permissible exposure limit (PEL) when work hours exceed 8 is based on a standard which dictates that the allowable limit of exposure can be adjusted according to the number of hours worked. When the hours worked exceed 8, the permissible exposure level is calculated using the formula PEL = 400 divided by the number of hours worked.

This approach is derived from the need to ensure worker safety and maintain exposure limits in relation to time. The rationale here is that as the number of hours worked increases, the amount of acceptable exposure to lead must decrease to mitigate health risks. Therefore, dividing 400 by the number of hours ensures that longer work hours result in a lower permissible exposure.

In contrast, the other formulas presented do not accurately represent the calculation required for work hours exceeding 8. They either incorrectly manipulate the constants or switch the necessary variables, which would not appropriately calculate the allowed exposure based on increased work hours. The correct choice maintains the necessary balance between exposure time and safety standards in occupational health.