Haven't been in a coal mine, but have been in a salt mine in Austria and in caves here in the US, and like you, Oldfart, wouldn't really want to spend much time "down under."

If the lights go out, black is an understatement.

Always wonder why, in mines, they don't construct concrete block "safety shelters" every so. Equip them with oxygen, emergency rations, etc. (I would think that they could be done inexpensively enough). Or backup air shafts.