Author Topic: More Mendip CO2  (Read 777 times)

Online The Old Ruminator

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More Mendip CO2
« on: August 02, 2018, 05:42:00 pm »
Curtain Chamber in Manor Farm was %4 CO2 this week and one caver described it as her worst ever trip. Other Mendip caves are currently affected.

Offline CavingPig

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Re: More Mendip CO2
« Reply #1 on: August 02, 2018, 08:17:28 pm »
I noticed CO2 in parts of Swildons last Thursday and Sunday, particularly in parts of the Short Round (especially between Tratman's Temple and the ducks); also in Blue Pencil; maybe slightly in the streamway. No idea of concentrations I'm afraid! Priddy Green Sink was fine.

Incidentally, if anyone has any theories as to why some people are more affected by CO2 than others I'd love to hear! I'm always the first to feel symptoms and they seem more intense than for other people. I don't taste it though, which my partner claims to!

Offline PeteHall

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Re: More Mendip CO2
« Reply #2 on: August 02, 2018, 10:00:27 pm »
I was down Swildon's on Friday night and found it pretty fresh. Sump 6 bypass is normally very bad, but even there it seemed fine... The air seemed so good in fact that I was quizzing some of the older members on the what's and why's of bad air during the summer.

Likewise, Charterhouse has a reputation for thin air, but when I was down there a couple of weeks ago, I found the air to be much fresher than usual...

Whatever causes it, it's not simple to predict!
The distance between stupidity and genius is measured only by success.

Online mikem

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Re: More Mendip CO2
« Reply #3 on: August 02, 2018, 11:37:38 pm »
Water levels being low means there is better air flow in some places than normal...

Mike

Online Aubrey

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Re: More Mendip CO2
« Reply #4 on: August 03, 2018, 12:36:02 am »
CO2 is produced in the roots of growing vegetation. There is less growth and therefore less CO2  being produced in the current drought.

make more cave - we have the technology!

Online The Old Ruminator

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Re: More Mendip CO2
« Reply #5 on: August 03, 2018, 09:37:57 am »
Perhaps Manor Farm is an anomaly. I do know some other Mendip digs are currently affected. Our team has a CO2 meter which is the one used at Manor Farm this week . Why is there CO2 in a drought if growth is restricted and there is no rain. We had hoped to check Vurley this weekend but some buffoon  ( :halo:) dislodged a boulder and blocked the cave.

Offline Bob Mehew

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Re: More Mendip CO2
« Reply #6 on: August 03, 2018, 10:15:23 am »
The source and transport of CO2 is very complicated and traditional explanations are patently incorrect.  For example the 'calcium bicarbonate / calcium carbonate deposition + release of CO2' explanation requires a lot more stall than is observed.  It is not just plants but also the decay of organic material in the soil and sub soil which contribute to a source of additional CO2 (above that normally in free air at 400ppm) within the air in soil.  So more CO2 will dissolve into the water.  But I have yet to do some calculations on the amount of water transport in the absence of the calcium bicarbonate mode to see if that gives sensible answers.  But in drought conditions, with no significant water movements it seems to me other transport routes are required to explain that possible source.  Also some rudimentary calculations suggest that there is insufficient visible organic material in cave to create the high CO2 directly.  In summary - a mystery.   

Online 2xw

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Re: More Mendip CO2
« Reply #7 on: August 03, 2018, 12:20:43 pm »
Bob, to what extent is their an input of exhaled CO2?

Offline mrodoc

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Re: More Mendip CO2
« Reply #8 on: August 03, 2018, 12:49:27 pm »
There were some good presentations on carbon dioxide in caves at UIS congress in Sydney last year. You can find the proceedings on line I believe. It is a universal problem and primarily related to microbial action in the soil. Regarding sensitivity to carbon dioxide, I have decided that it is a complex problem. I have problems breath holding for any length of time but my tolerance to it when inhaled seems to be higher than some although I don't like the breathlessness and sense of panic it induces. My brother in law feels really ill for a day after a trip in cave with more than probably 3% in the inhaled air.  Interestingly some diving physiologists have theorised that so-called nitrogen narcosis may in part be caused by carbon dioxide toxicity and certainly at great depths they do combine to form a lethal cocktail as in the Dragon's Breath cave death(s).We are hoping to do some data logging in our dig at some stage to assess day to day fluctuations. Having a draught is no protection against having high CO2 levels by the way.

Offline Bob Mehew

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Re: More Mendip CO2
« Reply #9 on: August 03, 2018, 12:53:54 pm »
Bob, to what extent is their an input of exhaled CO2?
The places being mentioned are not inhabited so persons exhaling CO2 is not a source.  Obviously when you go into a passage you are exhaling some CO2 and then it depends upon the size of the passage, potential for drafts and breathing rate.  The at rest breathing rate is between 12 and 20 breaths per minute, the tidal volume is around 1/2 litre and the level of CO2 in exhaled air is around 5% (see wikipedia respiratory system).  So that means one breaths out 20 * 1/2 * 5/100 or half a litre per minute.  So at one extreme if you have a large chamber with some air drafts, you will make no impact on CO2 level.  But in an air bell of say 1m diameter hemisphere, that is 0.26m^3 or 260 litre, you can see it would only take around 20 minutes for the CO2 level to build up to 4%.  (You may recall the Langstroth Pot incident where 3 people died in an air bell see https://www.brcc.org.uk/downloads/arch/archive20a.png and also the ...20b.png image.)

We are hoping to do some data logging in our dig at some stage to assess day to day fluctuations.
Have you got a instrument to that?  If so could you PM me?

Offline Benfool

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Re: More Mendip CO2
« Reply #10 on: August 03, 2018, 01:17:03 pm »
Caving Pig, there is a brilliant lecture by Simon Mitchell a Technical diver and Anesthetist from New Zeeland, on youtube regarding Respiratory Failure in Technical diving. It goes into the CO2 negative feedback loop and some of the physiology of carbon dioxide retainers, which might answer some of your questions. If you react quickly to CO2 you shouldn't think of this as a disadvantage, but as an advantage - you are far less likely to die of CO2 poisoning, which would be a really horrid way to go!

Definitely worth a watch (and the rest of Simon's videos) even for non-divers!

B


Online mikem

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Re: More Mendip CO2
« Reply #11 on: August 03, 2018, 01:55:26 pm »
Is manor farm drought affected or is the boggy area upstream still damp?

Mike

Offline Leclused

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Re: More Mendip CO2
« Reply #12 on: August 03, 2018, 02:08:11 pm »
For your information, a flemish caver who currently lives in France (Ardèche) has developed a rugged CO2 meter for cavers.

http://lab.speleo.nu/co2vking.php

On his website you can also find information about other climate project in French caves.

BR

Dagobert
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Offline rhychydwr1

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Re: More Mendip CO2
« Reply #13 on: August 03, 2018, 02:14:01 pm »
For your information, a flemish caver who currently lives in France (Ardèche) has developed a rugged CO2 meter for cavers.

http://lab.speleo.nu/co2vking.php

On his website you can also find information about other climate project in French caves.

BR

Dagobert


The only problem is, he does not give a price!