Using the following formula, solve the problem below, and show your work.

TWA = CaTa + CbTb + ... + CnTn 8

TWA = Time-Weighted Average
Ca = Concentration of contaminant during the sampling period "a"
Ta = Time of sampling period "a"
Cb = Concentration of contaminant during the sampling period "b"
Tb = Time of sampling period "b"
Cn = Concentration of contaminant during the sampling period "n", where "n" is the last of a series of contaminants
Tn = Time of sampling period "n"

Note: All concentrations are in parts contaminant per million parts of air or milligrams of contaminant per cubic meter of air.

Air Sampling Problem: You are an industrial hygienist that is conducting personal sampling on a worker who is overseeing a production process involving use of toluene (Note: The Occupational Safety and Health Administration has established a Permissible Exposure Limit of 200 parts per million (ppm)). You are able to measure the following exposures:

500 ppm for 1 hour

100 ppm for 4 hours

225 ppm for 3 hours

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