Here is a link to PA's Dept of Deep Mining Safety, which is very interesting reading about mining disasters like the Jacobs Creek explosion in the Darr mine in 1908. 239 miners were killed a few days before Christmas.

Also has information about the robber barons/mining wars too:

http://www.dep.state.pa.us/dep/deputate/minres/dms/website/papers/minedisasters.htm