An operator was exposed to copper dusts and mists on 3 occasions over an 8-hour workday. Copper dusts and mists have a TWA OEL-RL of 0.2 mg/m3. In this occasion, three samples were taken which yielded results of 0.21 mg/m3 between 8:00am and 10:00am, 0.27 mg/m3 between 10:00am and 1:30pm, and 0.15 mg/m3 between 1:30pm and 4:00pm. 

(a)Based on this information, calculate the operator’s 8-hour TWA. (6)

 (b)According to your answer is the operator safe or not and why? 

formulae: 8-hour time weighted average (TWA) exposure (mg/m3) = (C1T1+C2T2+⋯+CnTn)/8