Pike River mine survivor Daniel Rockhouse escaped an explosion but was almost overcome by carbon monoxide poisoning. Isaac Davison looks at how the gas affects humans.
What is carbon monoxide?
A colourless, odourless, tasteless, non-irritant gas, which can be produced by incomplete burning of fuels.
Carbon monoxide can come from camping cookers used where there is not enough oxygen for complete combustion, and from car exhausts. At Pike River, it was caused by the blast, which was probably caused by a methane buildup. Carbon monoxide is also produced naturally in the human body.
How does it affect humans?
In the blood, oxygen is carried around the body by attaching to a protein called haemoglobin.
But when carbon monoxide is inhaled into the lungs, it attaches to the protein, preventing oxygen from doing so. This deprives organs, most importantly the brain, then the heart, from receiving the oxygen they need to function and survive.
A low level of carbon monoxide poisoning can produce a headache, but larger amounts can lead to unconsciousness, the heart ceasing to beat, and death.
Auckland Medical School head Des Gorman said: "If you're a good young buck, a non-smoker, you might be able to breath high levels because you've got good heart function. If you're older with a crook heart, then a much lower level will knock you out."
Chronic smokers already have between 5 to 10 per cent of their haemoglobin bound to carbon monoxide.
How is carbon monoxide poisoning treated?
Someone who has suffered carbon monoxide poisoning will be treated in a similar way to a diver who has the bends.
If a person is knocked unconscious by the gas, it is likely they will require treatment. The treatment involves oxygen therapy: either high-flow oxygen through a mask at normal atmospheric pressure, or being put into a hyperbaric chamber at increased pressure.
The two miners to emerge from the Pike River mine tunnel regained their strength after carbon monoxide poisoning by breathing from a compressed air line in the mine's tunnel.
How can methane contribute to an explosion?
Methane is released when coal is mined. At a concentration of 5 to 15 per cent and combined with oxygen, methane can cause an explosion. It needs to be ignited - e.g. from electricity, or friction ignition (rock on rock, pick on rock, spontaneous combustion).
What is the temperature and atmosphere in the mine likely to be like in the wake of an explosion?
Mining safety expert Professor David Cliff, from the University of Queensland, said the peak temperature of the explosion would reach about 1220C.
The residual temperature would have depended on the size of the explosion compared to the volume of the mine.By Isaac Davison