Two more men escaped unaided from the drift mine - a mine cut into the side of a hill where the coalseam is accessed horizontally - before emergency services arrived.
It facilitates a cheaper way of capturing greenhouse gases, which can either be pumped back into the coalseam, or be re-used to inject oilfields to increase recovery rates (OK, even I see the irony here).
The concept of heating underground coal to a combustion point may lead one to recall Centralia, PA, an abandoned town in Pennsylvania sitting on a coalseam which has been burning for 50 years, but the UCG controlled process makes that outcome highly unlikely.
Mr Thomas said water in any mine would be a risk but when the mine operator applies for a licence to work a particular reserve of coal, there is a national database with records showing where that seam had been worked before.