Would digging out the collapses increase the amount of oxygen in there? We went the other day and got down the tram tunnel so far and we seemed to be fine and didn't notice any difficulty breathing was just the water level and mud was quite high so I didn't go to the end as I didn't want wet feet-dont know if it was that deep when you went, - there was a lot of rain at weekend when we went or if I just need to man up and deal with the wet mud in my wellies lol. I would go back and if digging the collapses and clearing them out would get more oxygen in there I wouldn't mind giving it ago. enjoyed your report and Acids too. Thanks
I got over the collapse no bother but on the other side more or less straight away noticed a difference in my breathing so I took a few photos then went back, on the way down the collapse I began moving some off the rock and it moved very easily-in fact it was sliding down in to the water as I was coming down back to the main tunnel. This makes me think It wouldn't be very hard to move at all. However like you said its the lack of oxygen no matter how easy the rocks move I'd still be using what little oxygen there is up. Shame really but better to be safe than sorry I suppose 
Thanks
