Not all dust is the same. Not all dust particles that are in the air around us cause problems for our lungs. Some particles are too large and stick to other areas of our body before they can get to our lungs. Others are so small that we can breathe them in and out and they will not deposit in our lungs. The researchers in the study described in the previous exercise also measured respirable dust. This is dust that deposits in our lungs when we breathe it.

For the drill and blast workers, the mean exposure to respirable dust was 6.3 mg.y/m3 with a standard deviation of 2.8 mg.y/m3.

The corresponding values for the outdoor concrete workers were 1.4 and 0.7 mg.y/m3. Analyze these data using the questions in the previous exercise as a guide.