The mine explosion video - what it may tell us

CCTV video footage taken from a camera at the entrance to the Pike River mine was released last night and shows the impact of the pressure wave that resulted from the explosion deep within the mine.

Pike River CCTV footage capturing the pressure wave impact he 52-second piece of footage can be viewed on many news websites including TV3 here.

The Science Media Centre asked University of Queensland mine explosion and gas analysis expert, David Cliff, to explain what the footage may reveal about the underground explosion on Friday night.

David Cliff, Associate Professor at the Minerals Industry Safety and Health Centre at the University of Queensland comments:

The little piece of fabric Mr Whittall refers to in the video points downward prior to the explosion – normally it will be inclined into the mine to indicate air is flowing into the mine.

This would indicate an absence of air flow into the tunnel, because the pressure wave had already entered the tunnel. A rough calculation would suggest the pressure wave would take 2 minutes to cover 2km, travelling at 60km per hour.

Lose intensity
As the pressure wave travels over a distance, it will lose intensity and broaden – exactly the same as a water wave at sea. Thus the 52 seconds width is not a measure of intensity rather a measure of the distance from the source of the explosion.

Moves like a water wave
People should understand that the pressure wave of the explosion is just that it moves like a water wave so if the actual explosion wave has stopped combusting, the air transmits the pressure so the guys in the tunnel would have felt the shock wave and all the entrained dust etc, but the air would still have been breathable, as the actual gases from the explosion may not propagate all the way out of the mine.

They would expand up to five times their volume and create the pressure wave. Some mixing of gases is caused by the wave movement.

Pressure increase
Further into the mine the pressure would increase significantly and also the potential for irrespirable and/or toxic gases post explosion. Without seeing the gas monitoring information and having a feel for the distribution of gases it is not possible to identify where exactly the explosion originated.

Glimmer of hope
An interesting fact is that a pressure wave is not very effective in blind headings – i.e. roadways that have no connections, as the pressure wave will tend to compress the air in front of it against the end wall – thus actually protecting those that are close to the end wall from major damage and maintain air in that cavity – so that may be some glimmer of hope.

Snooker ball effect
However the explosion pressure wave would have reflected like a billiard ball off the walls and end walls and could have passed multiple times in differing directions throughout the mine – much like making a break at snooker where the balls hit the cushions multiple times.