You are an industrial hygienist conducting personal sampling on a worker who is

Question

You are an industrial hygienist conducting personal sampling on a worker who is overseeing a production process involving use of acetone (Note: The Occupational Safety and Health Administration has established a Permissible Exposure Limit of 1000 parts per million (ppm) of acetone). You are able to measure the following exposures:

700 ppm for 3 hours
1300 ppm for 2 hours
900 ppm for 3 hours

What is the calculated TWA? What would you tell plant management in terms of exposure to acetone and compliance with the PEL?

Explanation / Answer

TWA = (CaTa + CbTb + ... + CnTn) Tn

Here, Ca = 700 ppm and Ta 3 hours

Cb = 1300 ppm and Tb =2 hours

Cc = 900 ppm and Tc = 3 hours

Time-Weighted Average = 700 ppm x 3 hr + 1300 ppm x 2 hr + 900 ppm x 3 hr /8 hr

                                       = 925 ppm

Permissible Exposure Limit PEL = 1000 parts per million (ppm)

Since 925 ppm is less than 1000 ppm, the 8-hour TWA exposure is acceptable.

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