As a bore hole is drilled down to the shaft at the Pike River mine, where 29 miners are still trapped, focus is on the gases that caused the initial explosion and which still make rescue incredibly dangerous for both miners and rescue crew.
This graphic from today’s Dominion Post outlines how methane forms and how it is extracted from mines.
PETER GRIFFIN 
A mixture of between 5% and 15% of it is mixed with air. Such a mixture will explode if ignited by a source of heat.
There is a range of mixtures which will explode and these can be predicted from gas samples which are projected on a graph of oxygen/methane mixtures where the axes run from 100% methane, 0% oxygen to 100% oxygen,0% methane. This graph can show the explosive triangle of all possible explosive mixtures which can be created
Deborah Blum has made this evident the focus of her latest blog post, as she tweeted:
My latest post, a chemical history of mine explosions & good wishes to New Zealand: The Methane Calculation http://bit.ly/d7mbVH
Rats, ‘event’ for ‘evident’ – spotted it just after submitting the comment. Sigh