Using the following formula, solve the problem below, and show your work.
TWA = CaTa + CbTb + … + CnTn
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| 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?
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