Oxygen Depletion in Caves

The Old Ruminator

Well-known member
Currently we have %2 CO2 and %17 O2 at the bottom of Vurley. To my mind its a worrying combination. I wonder how many CO2 affected caves in the UK have been tested for O2. What is happening here ? Just two people do a quick trip for sampling so I dont thing the oxygen depletion can be accounted for by that. Does the CO2 partly displace the oxygen ? Not entirely it seems as the percentages dont add up. I presume %14 oxygen would be hypoxic and a bigger party on the 20m pitch could deplete ambient levels even further. We have had no respite from CO2 since last year and worry now that we will never be able to work at the bottom of the cave. Vurley is unique on Mendip for various reasons but this instance is not a happy one.

From Wiki -

"  When oxygen level dips below 19.5% v/v, the air is considered oxygen-deficient, where oxygen concentrations below 16% volume are considered highly dangerous for humans.[31 "
 

maxf

New member
Perhaps you could build a scrubber to lower the co2 level (tube full of sofnilime with a fan on one end) and empty a cylinder of oxygen down there ?

No idea what size passage you have this may not work....
 

mikem

Well-known member
Has air quality got significantly worse or have cavers got more fussy since giving up carbide & cigarettes?

Lots of studies show animals living in burrows & humans on the Tube survive depleted oxygen levels!
 

Bob Mehew

Well-known member
The adage that CO2 and O2 add up to 21% is based on an assumption that the missing O2 has been converted one for one into CO2.  That is not always correct.  Two exceptions spring to mind, one is that the O2 is trapped elsewhere and the other is that CO2 is added from other sources as often occurs in caves. 

The first question I would ask is how confident are you of the accuracy of your measurements?  Have the meter(s) been calibrated over a range of concentrations?  As opposed to the routine start up check of fresh air being 21% O2 and 400ppm CO2. 

The second question is have you checked for other noxious gases?
 

mrodoc

Well-known member
Bob is quite right. From a diving physiology point of view one can be in trouble breathing oxygen at an adequate partial pressure if the carbon dioxide percentage in the inhaled mixture is high. The body can only handle so much CO2 before it becomes toxic. The problem with low oxygen levels is that we are tuned to high levels of CO2 not low levels of oxygen.  Respiration is primarily driven by carbon dioxide levels which is why entering a severely O2 depeleted atmosphere is so dangerous - you just fade into unconxciousness without any warning.  Similarly hyperventilating before prolonged breath holding can lead to black out before the rising levels of CO2 in the blood create an overwhelming stimulus to breathe.

What is interesting about Vurley is that from my experience, it is a section of cave that seems to particularly provoke a reaction to raised CO2. After descending the 20 metre pitch in a big rift I feel more comfortable as I do all the way down the next two 6 or 7m pitches, and last time leaving the cave it wasn't until I reached the top of the 20m pitch that I felt breathless. I find this really puzzling.
 

The Old Ruminator

Well-known member
" Mac " is doing our readings and is very careful with calibration. We now have data loggers on the surface as well as the cave. Might be useful to see how they relate. Vurley is in a large closed basin with verdant grass. The soil layer is 7m of loess so all in all its an unusual setting.
 

Graigwen

Active member
mrodoc said:
The problem with low oxygen levels is that we are tuned to high levels of CO2 not low levels of oxygen.  Respiration is primarily driven by carbon dioxide levels which is why entering a severely O2 depeleted atmosphere is so dangerous - you just fade into unconxciousness without any warning.  ing.

This is how Aber CC came close to two fatalities years ago. They entered an oxygen depleted but not Co2 enriched atmospere in an old mine. There was no stimulus to gasp for air, just very rapid tiredness and collapse. The oxygen deficiency was attributed to long term rotting of wood, the Co2 produced by decomposers' respiration presumably being removed by solution in water.

.
 

PeteHall

Moderator
mikem said:
Air was always bad at gibbets brow, so they pumped extra in from the surface.
I believe that pumping out bad air is preferable to pumping in fresh air, the latter risking leaving pockets of bad air in the cave.
That said, we used a bouncy castle blower to blow a high volume of fresh air into a dig with great success. Blowing in enabled the use of cheap collapsible ducting and the bouncy castle blower was by its design able to push a significant pressure head created by a long length of pipe. We figured that the sheer volume of air movement was sufficient to displace any bad air pockets through turbulence.
 

mikem

Well-known member
"Mental functions become impaired at 10 to 14%"
https://sciencing.com/minimum-oxygen-concentration-human-breathing-15546.html
 

mikem

Well-known member
PeteHall said:
I believe that pumping out bad air is preferable to pumping in fresh air, the latter risking leaving pockets of bad air in the cave.
It does depend where the replacement air is going to come from, if you're directly below the entrance then it is likely to be from the surface, but at somewhere like vurley it could be from a worse area than you are already in. Also depends what the problem is - pockets of denser CO2 are relatively easy to remove by vacuuming, compared to low oxygen levels.
 
Graigwen said:
mrodoc said:
The problem with low oxygen levels is that we are tuned to high levels of CO2 not low levels of oxygen.  Respiration is primarily driven by carbon dioxide levels which is why entering a severely O2 depeleted atmosphere is so dangerous - you just fade into unconxciousness without any warning.  ing.

This is how Aber CC came close to two fatalities years ago. They entered an oxygen depleted but not Co2 enriched atmospere in an old mine. There was no stimulus to gasp for air, just very rapid tiredness and collapse. The oxygen deficiency was attributed to long term rotting of wood, the Co2 produced by decomposers' respiration presumably being removed by solution in water.

.

Quite a close shave that one ! We had one semi conscious chap me and Rob Jones of this parish pulled out feet first from a crawl then scarpered PDQ.  We already sent out the other 3 or 4 of the partys. We were surprisingly calm at the time - objectively in great danger but without the fear that I quite irrationally get from (perfectly safe) SRT. in retrospect it gives me the willies since If any of us had made it through the boulder choke we'd not have got back, or if more bad air had made it's way into our bit...
 
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