Mendip Co2 Levels Going Up ?

The Old Ruminator

Well-known member
Last week we had close to %3 Co2 but this week the levels had increased to over %5. Only the surface shot today as nobody fancied digging in that.

 

The Old Ruminator

Well-known member
Well yesterday's Co2 / Radon lecture came up with a few observations if I have got the hang of it.

Co2 and radon follow similiar spikes this time of the year suggesting higher levels are mostly down to changes in ventilation and higher rainfall in Autumn. Ventilation slows down when the air temperature and cave temperature are at similiar levels . Changes in air pressure seem to have minimal effect. The Co2/radon spike can be very short covering just a day or two. Levels can then flatten with another spike repeating a week or so later. Caves can be affected in different ways with little Co2 or concentrations at the top of the cave or at the bottom. Some monitors do not go above %5 so beware true readings may be higher. Also as spikes and troughs can vary over a week it is not certain that one " safe " day will lead to the next. HSE workplace safe levels are remarkably low percentage wise and nowhere near the exposures seen in caves. Normal Co2 in air is around %0.04 or 400 ppm. Co2 can also be released from carbonate rocks by dissolution though cave Co2 is largely the result of microbial action in the soil being carried down by water percolation.
If I have summarized the incorrectly please advise.
 

Lockchopper

New member
Go and spray some potassium hydroxide around down there. 5% is exceedingly nasty. I've been in 13% O2 and 3% CO2 and it was horrible.
 

The Old Ruminator

Well-known member
Three industrial fans were fitted to the top of the entrance pipe at Vurley and run for two hours making little difference. That was a couple of weeks ago when the spike had dropped to around %2. This week its back up to %6 but we are hoping the colder weather will improve ventilation. We will take another reading on Monday. Unfortunately with the 7m deep entrance pipe showing such high levels we cannot go down the cave to check Co2 levels further down. Some sort of autonomous monitoring system would be good particularly if a record and graph could be logged and compared to external influences.
 

ZombieCake

Well-known member
Some cheerful reading: https://inspectapedia.com/hazmat/Carbon_Dioxide_Hazards.php
Been CO2'd a couple of times and, as others have said, wouldn't recommend it.
 

pwhole

Well-known member
Is the O2 being measured as well? It's an interestingly (though no doubt frustrating for you) high level of CO2 for only 7m down.
 

mrodoc

Well-known member
Carbon dioxide levels higher nearer the surface usually as that's where it is coming from. Oxygen depletion unlikely unless there is a process to drive levels down. This is unlikely in a natural draughting cave.
 

mikem

Well-known member
Could this have something to do with it:
http://www.nature.com/news/2010/100324/full/news.2010.147.html

Mike
 

mrodoc

Well-known member
Well spotted Mike, and I am sure you are right. Increased respiration in warmer conditions is bound to raise carbon dioxide levels. It is a world wide phenomenon after all.  An impressive piece of research and fills in a gap in the jigsaw. Donald Trump wont believe it!
 

caving_fox

Active member
Anyone know what the recovery time is after CO2 (hopefully not CO) exposure is?

I've always assumed that once you're back out in fresh air/passage you start to feel better almost right away. But I've had a couple of instances where I'm wondering if there's a more delayed effect too, in that fitness/stamina seems to not recover for a day or so longer than would usually be the case with 'just' going caving. - I know it's very variable and subjective to measure how you feel after a trip, and hard to pinpoint actual causes, with plenty of confounding factors (beer, age, coughs, et al).
 

braveduck

Active member
On the news yesterday. CO2 levels shot up last year and are now the highest
on the planet for over 800,000 years .That is Eight Hundred Thousand Years.
So you Mendip types should not be complaining about having your fair shair
of it . ;)
 

ZombieCake

Well-known member
Anyone know what the recovery time is after CO2 (hopefully not CO) exposure is?
Bad headaches, in one case coughed up goo on reaching fresh air, couple of days or so to get over it. Bit like a really bad hangover (so I'm told  :ang: ) but without the pleasure of the night before, allegedly.
Most recent in Tynings a year or two ago.  Odd thing was it wasn't that far past the entrance pitches where you'd expect there to be some air circulation.  Think everyone felt a bit crap on that trip.  I am a bit asthmatic so don't know if that has any bearing on things. Anyway CO2 best avoided if at all possible.
 

The Old Ruminator

Well-known member
The trouble is in not knowing the levels before you go in. Perhaps all Mendip clubs should invest in a decent meter. We are currently borrowing one but looking to get one permanently. Certainly this year is far worse in Vurley than last year . The high C02 episode last year was ended when the cave flooded though there is no sign of that this year for the moment. Also knowing where the Co2 is " ponding " in the system helps. We are in a large karst closed basin with deep soil cover ( 7m of loess ). There is verdant grass in the basin though now it has been cut. None of these factors help. Also we have a deep wide concrete tube entrance. Maybe the Co2 is worse here but we cannot get beyond this to check. Hopefully the cold weather will reduce microbial soil activity. We will check again this week.
 
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