Air Contaminants and Silica (General Industry) questions for the CSP

Question 1

An industrial hygienist is evaluating a worker's exposure to a single contaminant with an 8-hour TWA limit of 100 ppm. The worker spent 2 hours at 150 ppm, 2 hours at 75 ppm, and 4 hours at 50 ppm. Which conclusion is correct?

1. AThe 8-hour TWA is 91.7 ppm, which is acceptable only if respirators were worn
2. BThe exposure is unacceptable because the 150 ppm period exceeded 100 ppm
3. CThe 8-hour TWA is 100 ppm, so the exposure is exactly at the limit and not acceptable
4. DThe 8-hour TWA is 81.25 ppm, which is below 100 ppm, so the exposure is acceptable

Question 2

A foundry uses the scheduled monitoring option for respirable crystalline silica. Initial personal sampling of a core-room operator showed an 8-hour TWA between the action level and the PEL. The employer repeated the sampling six months later, and the result was below the action level. Nothing about production, process, controls, personnel, or work practices has changed since. What must the employer do next for this operator's group?

1. ADiscontinue monitoring, because the most recent result is below the action level
2. BRepeat monitoring within three months, because the earlier result was near the PEL
3. CRepeat monitoring within six months of the most recent sample, and continue until two consecutive measurements taken 7 or more days apart are below the action level
4. DRepeat monitoring within twelve months, because the latest result shows exposures are well controlled