Wool (2011)

They live beneath the earth in a prison of their own making. There is a view of the outside world, a spoiled and rotten world, their forefathers left behind. But this view fades over time, ruined by the toxic airs that kill any who brave them. So they leave it to the criminals, those who break the rules, and who are sent to cleaning. Why do they do it, these people condemned to death? Sheriff Holston has always wondered. Now he is about to find out.