A worker is involved in the removal of nitrocellulose coating from metal parts using methyl ethyl ketone (MEK) during his work shift. To evaluate his exposure, several samples from the employee's personal breathing zone were taken during the morning and afternoon. The air sampling data and results are shown below. It is assumed that the employee was only exposed to MEK vapors when he was wearing the sampling equipment at his job station. The sampling equipment was removed during breaks since no exposure was expected when the employee was not at his work station. Sample No Sample time (minutes) Results (ppm) 1 55 55 2 60 67 3 45 48 4 50 61 5 50 73 6 60 55 7 45 47 8 60 49 Calculate the 8h TWA exposure concentration of MEK. Was the exposure concentration of this employee above the PEL? Show your work. MEK PEL-TWA 590 mg/m3; MW= 72.1 g/mol