To calculate the TWA, the concentration of a chemical in the air is measured at different times throughout the workday. These concentrations are then multiplied by the corresponding exposure time, summed up, and divided by the total time period to get the average exposure level. The formula is: TWA = (C1T1 + C2T2 + ... + CnTn) / T Where C is the concentration and T is the time for each measurement interval.
