I'd be more worried about the sparking of the trolley power wire once he got underground. Then, if they should get in a methane pocket...........KABOOM! Coal dust could do the same thing. Methane is a huge problem in underground coal mines which don't have sufficient ventilation, and even in some that do.

Methane explosions killed 13 miners at the Jim Walter No. 5 coal mine in Alabama in 2001, and a dozen more at the Sago mine in West Virginia in 2008. Nothing to sneeze at.

Depends upon where the permanent ground water elevation is at.

Think about Pennsylvania, Kentucky, Virginia, West Virginia.....all coal states. What type of mining do they engage in in, for example, West Virginia? If you answered "mountaintop shaft" or "mountaintop removal" you'd be right. They also have such things as pumps to pump areas of a subsurface mine totally dry. They put a water collection sump at the lowest point in the mine, and then pump all the watrer out. Continuously.

There's other hazards involved in underground mining, in fact, too numerous to list. It used to be the most dangerous profession until safety awareness took over. Now, it's much, much better. Life in the underground is very unforgiving of mistakes. You have to look at and for potential hazards that might affect you AND your buddies. Coal happens to be the worst of all because of the weak roof rocks present....like shales and soft sandstones. Room and pillar mining is the rule for most longwall operations. The problems start to arise when you pillage the pillars on the way out, or when you over work machines, or when you overwork the men.

Hope that answers some of the questions.