I hear that the NZ PM is calling for an investigation. In the...

I hear that the NZ PM is calling for an investigation. In the meantime, I found this report on the net

http://www.bbc.co.uk/news/world-asia-pacific-11833033

It explains a bit about the Methane levels - the part I found very interesting was:

"Methane gas is explosive in atmospheric ratios between 5% and 15%. In coal mines in the UK, we aim for less than 1% methane. At 1.25%, the power automatically cuts off, and at 2%, all miners are evacuated"

I am just speculating here but if PRC operated under a similar system maybe this is why the power went off and the electrician went in to investigate?