SamT said:
Has anyone ever died in a limestone (i.e. no culverts/coal/shale etc) cave due to CO2 poisoning.
Yes - as mentioned above.
However there is a lot of evidence that the concentration of CO2 is increasing in some caves. We have started measuring the levels using accurate meters so we can then get an understand what is happening and what dangers there may be.
The immediate danger is not from suffocating from carbondioxide but from the natural human reaction of near panic and "out of here" which affects even hard fit cavers when exposed to high concentrations of CO2. The chances of an accident are greatly increased under these circumstances because the person is not totally in control of their actions. I have witnessed this several times and it is almost unbelievable when you see it.
Rescue would be near impossible if someone did injure themself, because the high CO2 would also affect potential rescuers and they would be unable to exert the muscle power to move a casualty.
Even at slightly lower concentrations of CO2 cavers loose coordination and do unexpected things. Last week we were measuring the level in a local hot spot when one of the party completely missed the obvious way out and later walked straight into the cave wall. He became very anxious to get out after only 14 minutes underground. The maximum concentration of CO2 encountered was only 3.4%. (This person has been doing 6-7 hour working trips every weekend).
With the onset of colder weather we expect the CO2 problem to diminish but also expect it to be back next summer. The build up in digs and other confined spaces which is generated by cavers breathing is unlikely to be any different throughout the winter months. It is should be very localised and easily relieved by leaving the dig.
So far there are only a few caves which are badly affected for long periods but I can assure everyone that visiting them is best avoided.
