Calculate the 8-hour TWA to carbon monoxide (CO) from the following information.

Question

Calculate the 8-hour TWA to carbon monoxide (CO) from the following information. You must show your work to receive credi The worker worked an 8-hour shift but had two 23-minute breaks during the shift where there was no exposure to CO. The samples were collected at the worker's work station where there was exposure to CO. You can assume that the exposures during the total sampling time are representative of the worker's exposure during the entire time he is at his work station. Result for sample 1 24 ppm, collected for 75 minutes Result for sample 2-62 ppm, collected for 118 minutes Result for sample 3-37 ppm, collected for 88 minutes Result for sample 4 46 ppm, collected for 99 minutes

Explanation / Answer

Here , There are some things to consider. The total time of break was 2*23 = 46 mins during which zero exposure was there. The sum of time during which the samples were taken is 75+118+88+99 = 380 mins. It means 54 mins were unsampled. (480 - 380 - 46 = 54 MINS) . As per the question , total sampling time is the total exposure time, it means for these 54 mins there was no exposure.

Now, to calculate TWA, Use the following formula

TWA = (c1*t1)+(c2*t2)......(c4*t4) / 480 mins

where c is concenteration is ppm and t is sampling time in minutes

TWA = 24*75 + 62*118 + 37*88 + 46*99 + 0*54 + 0*46 / 480

TWA = 35.26 PPM (almost close to preferred exposure limit PEL)

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