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To determine the appropriate occupational exposure limit (OEL) for a chemical when the standard 8-hour OEL is given and the work shift is extended to 12 hours, it is important to understand how to adjust the exposure levels.

The 8-hour OEL in this case is set at 10 parts per million (ppm). When the duration of exposure increases beyond the standard 8 hours, regulatory agencies often recommend recalculating the exposure limit to account for the additional time, typically using a method to ensure that the overall dose does not exceed safe limits over the extended period.

In adjusting the OEL for a 12-hour shift, a common approach is to apply the formula that reduces the permissible exposure limit proportionately based on the additional hours of exposure. This means calculating the permissible level for 12 hours based on the 10 ppm for 8 hours by using the equation:

OEL adjusted = (8-hour OEL) × (8/12)

Plugging in the values:

OEL adjusted = 10 ppm × (8/12) = 10 ppm × 0.6667 = 6.67 ppm

However, if we adhere to a simplified approach regarding common safety practice recommendations, rounding this down to a