Strip mining of coal is probably safest, although accidents can happen with large machinery. But, strip mining of coal is high on the list of environmental disasters around Pittsburgh as the Mon River was determined to be dead from open pit runoff. However, strip mining can be done safely WRT the environment and surface reclamation although it is more expensive. Coal is already twice the cost it was a few decades ago and these fatal accidents are sure to drive the cost higher. There is coal to last centuries and Peak Coal is still decades off, worst case.