The simple fact is, there are as many accidents in union mines as there are in non-union mines. We all have to wait to hear what happened here. From the sounds of it, with the permanent seals broken, it appears the explosion happened in the closed mine next door.
Coal mining is inherently a highly dangerous dangerous occupation.
I haven't seen any statistics, but I do know that fatal accidents are in a long-term trend downwards. Partly this is due to fewer men in the mines because of automation, but it is also due to improved safety standards.
But when an accident occurs, the search immediately starts to find out whose "fault" it was, without any serious consideration even being given to the possibility that it wasn't really anybody's fault.