CO2

[Ralph]

We now have a set of accurate CO2 readings for the Knotlow - Hillocks system thanks to Masson CG. Readings taken on Sat 4 August.
Surface O2 20.9 %
Knotlow
Base of Climbing Shaft O2 19.0%
Chain Passage O2 17.4%
6m down 210 O2 19.0%
18m down 210 O2 18.6%
Hillocks
Entrance Chamber O2 20.6%
Entrance to coffin level O2 19.0%
Top of hand picked shaft O2 18.6% and falling
Surface reading still O2 20.9%
H2S, Lel, CO not detected.
A reasonably accurate estimate of CO2 levels can be determined by subtraction. Any of the other likely gasses would be fatal at a fraction of these levels.
TAKE CARE. If in doubt head out. It is not physiologically possible to "acclimatise" to high levels of CO2. There have been fatalities, thankfully not in caves.

 

[AdM Michael]

Wouldn't it be better to take CO2 reading rather than work by substraction of O2 levels?

Substraction of O2 levels works fine if CO2 is produced by oxidation (like rotting timber) but it doesn't work if 'trapped' CO2 is released from water. You might have different/much higher levels than you get from substraction of O2 levels.

What instrument did you use for the readings? A cheap&cheerful way to get CO2 readings if you don't have a sensor on your instrument are Draeger tubes. It'll be spotreadings only, but they are certainly more than good enough for what you want and better than substraction of O2 levels.

 

[bsaden]

The meter used was"Industrial Scientific" MX4 Iquad, which I understand does not test specifically for CO2 even though it is a multi-gas meter. On the descent as far as Chain Passage, all felt fine, a fresh cold breeze blowing even, but.....on turning around, it became VERY hard work making our way out again. But yes, a direct C02 reading would be interesting just to see the correlation.
Had we been a small party, without meter, we would undoubtedly have gone on, but who knows..........

 

[Ralph]

A CO2 meter is extremely expensive compared to single and multigas detectors. Draeger tubes are fine for one-off readings but don't give "continuous" readings which are more useful for use on a regular basis. About 3 years ago I ran a comparison test using a basic oxygen meter against a CO2 meter and multigas meter - the results were comparable and adequate for club use.
The O2 meter currently in use was bought by one particular club and the multigas meter by a generous individual who also funds the necessary re calibrations.

DCA invested in a couple of O2 meters and a rather expensive meter that could be left in situ for data logging of CO2 levels. However experience appears to show that if the meters are loaned out they don't seem to survive long.
Now if someone wants to donate a couple of grand we can measure in ppm? (but do we need to be that accurate?)
Incidentally all UK rescue teams now have gas testing facilities.

 

[Bob Smith]

I have a Telaire 7001 CO2 meter that requires Calibration sitting on the shelf, this also has a datalogging output if anyone is interested.

 

[mrodoc]

Cannot remember if I have ever shared this medical tale regarding physiological tolerance to CO2 (which varies from individual to individual). some years ago the Aussie navy had an applicant who nearly died during a training run having passed the medical examination with flying colours. He wanted to be a navy diver and was an experienced scuba diver with a legendary low air consumption. He nearly died because he maintained the same respiratory rate  exercising as he did at rest.  This resulted in near a fatal rise in blood carbonic acid levels because he was not flushing out his expired CO2. So it is possible to train oneself to very high levels - but not recommended!

 

[Jenny P]

There have been an increasing number of reports of "bad air", i.e. CO2 build-up, in various sites around the region.  Reports have come in recently from Knotlow, Hillocks, Water Icicle, Nettle Pot and Rowter.  In each case cavers have found it "hard going" despite knowing they weren't unfit: puffing and panting, hard work to get up an SRT rope, etc.  In some cases people have checked with lighters or matches and found that these would not light.

The reason for the excessive amounts of CO2 is not known, though the level of CO2 is almost always a little higher in caves and mines than in the open air.  Checks using gas meters are ongoing to try to find a pattern in the changing levels. 

Cavers need to be aware of the problem and exit the cave if things get really bad.  It would also help if reports are sent to the DCA Conservation Officer at conservation-off [at] theDCA.org.uk so that we know which sites to check.

Jenny Potts
Hon. Secretary, Derbyshire Caving Association

 

[JAM]

So it is possible to train oneself to very high levels - but not recommended!

So exactly  what system is needed for higher tolerance? Is it the same system that is required for lactate buffering? I ask as I used to ingest sodium citrate in my bike racing days to help increase buffering of carbonic acid. It appeared to work as my recovery was far far faster with this addition than without.

 

[graham]

The reason for the excessive amounts of CO2 is not known ...

We have had similar situations on Mendip in the past few years, including caves where CO2 had never previously been a problem over a fifty year period. Clearly the issues are climate related, but I suspect that every case is different, being contingent on the local environment. Caution is required at all times, especially, it seems in summer.

 

[AdM Michael]

...  Draeger tubes are fine for one-off readings but don't give "continuous" readings which are more useful for use on a regular basis. ...

Fully agree that tubes are for spot readings only, but they are available at a reasonable price, can be stored for a long time without any need for calibration and what is more important are more accurate than electronic devices, but will require a lot more training reading than a display on a meter.

I'm taking spot readings with Draeger tubes in various show mines in Germany on a regular basis as part of the inspection scheme. All readings are in general between 0.03% and 0.50%. I did compare gasmeter and tubes in the past and there's a maximum difference of 0,02 % between tubes and a gasmeter with a CO2 sensor straight from calibration.

Tubes are ok if it's the same locations every time and a limited number of readings. There's no big advantage in speed since you need to wait a few seconds/minutes for a gasmeter to adapt if accurate readings are required due to temperature and pressure differences. Although meters take continuous readings, you're still down to sort of spot readings due to the waiting time in the end. Any other 'continuous' readings should be considered as a rough guess and possible early warning.

Rule of thumb:

temperature difference between 2 locations in degrees equals the time in minutes you've got to wait at the new location before taking a reading

Although originally developed for surveying instruments this also seems to apply to other instruments like gasmeters.


What are the limits (EH40, Mines & Quarries Act, ...) you want to work to and what are the maximum errors in the readings you'd allow for?
Only Hillocks Entrance Chamber would have fully qualified under EH40 using subtraction of O2 readings any other readings would have been above one limit or the other (long term exposure 0.5% / 5000 ppm and long term exposure 1.5% / 15000 ppm) and you shouldn't have been in anything below 19.4% O2 although O2 down to 19% (without taking the reason for the oxygen deficiency into account) would have been ok according to M&Q. What's your limit?

But there's one more thing to consider with gasmeters which is the fresh air calibration of the sensors (most cases on switching the instrument on). Fresh air calibration normally means whatever amount of O2 is available at the time of the calibration is considered to be 20.9% by the instrument. Some Instruments will allow you to disable this function or will give you an option. It's always good to know the settings on your instrument as quite a few people tend to switch their meter off while travelling to save the battery.
Next time you switch on again underground have you've still got 20.9% O2???
Was it really 20.9% O2 on surface/at fresh air calibration???

Some interesting questions to consider when using a gasmeter.

 

[AdM Michael]

... The reason for the excessive amounts of CO2 is not known, ...

Small amounts of rotting organic matter can cause big problems. Any chance of 'contamination' by explorers / cavers or any timbering in old mines? I've taken readings in a mine which was fine otherwise but less than 1 m? of timber in a dead end contaminated a few hundred metres of passage with up to 0.5% CO2 all the way to the next link with the intake air ways.
There might be other solutions as well.

 

[shotlighter]

Low O2 means irrespireable air. If in your final moments you're really that interested wether CO2 or some other gas has displaced the O2- or it's just O2 depletion, then go ahead, buy a CO2 or other meter.
Otherwise does it really matter. This isn't analytical chemistry, it's a guide to wether the airs breathable or not. O2 measurement is fine by me as long as there's not an otherwise toxic atmosphere.
If that's a worry, either you're going underground in  some very questionable spots or you are getting a bit paranoiac - you can't eliminate all risk. Where do you stop, carrying Geiger counter on every trip?

 

[bograt]

CO2 is not a problem, its not toxic, its not going to poison you. All it does is replace the oxygen in your little bit of air so its not there for you to breathe.
Hence, the trouble is oxygen depletion, insufficient oxygen leads to suffocation, major cause of fatality through CO2.

MODERATION: the above comment has been striked through so it doesn't get taken as gospel truth by a skim-reader, but retained in context for the benefit of the continuity of this important thread

 

[droid]

The problem IS CO2 concentration. It causes hyperventilation, and is lethal.

Low O2 concentrations simply lead to tiredness. A drop of 1% in absolute O2 would hardly be noticeable. A rise of 1% in absolute CO2 would be deadly.

 

[graham]

CO2 is not a problem, its not toxic, its not going to poison you. All it does is replace the oxygen in your little bit of air so its not there for you to breathe.
Hence, the trouble is oxygen depletion, insufficient oxygen leads to suffocation, major cause of fatality through CO2.

Sorry, no, that is a very dangerous post and must be challenged. Increased CO2 levels are dangerous to deadly I forget the exact figures (MRODoc?) but above 4% it can kill you. A 4% reduction in O2 will not kill you.

 

[mrodoc]

Severe oxygen depletion is more dangerous in that the stimulus to breathe is provided by rising levels of carbon dioxide not low levels of oxygen. One loses consciousness without warning in an oxygen depleted atmosphere whereas, unless one is 'immersed' in very high concentrations of carbon dioxide one recognizes a problem and can take steps to deal with it. This is because the body is provided with sensitive detectors of changes in co2 levels but much weaker ones for low oxygen levels.  Hence the practice of hyperventilation before free diving can be dangerous as hypoxia intervenes before co2 levels rise sufficiently in the blood to signal a return to the surface.

 

[Aubrey]

CO2 is not a problem, its not toxic, its not going to poison you. All it does is replace the oxygen in your little bit of air so its not there for you to breathe.
Hence, the trouble is oxygen depletion, insufficient oxygen leads to suffocation, major cause of fatality through CO2.

CO2 IS A PROBLEM underground!

Apart from the heavy breathing and lack of energy cavers can become disorientated and do some quite bizare things. One very experienced caver/digger walked straight into the wall in Cuckoo Cleaves a couple of years ago. We were only there to check the CO2 level and as it was 3.5% everyone was on their way out.

Another quite alarming effect is what I call 'get out itus' where the caver suddenly panics and scrambles towards the exit, ignoring everything and everyone in the way. This is quite common and is obviously very dangerous.

 

[Bob Mehew]

The BOC Material Safety Data Sheet (see http://apps.risd.edu/envirohealth_msds/CO2.pdf ) (and a quick Google search) indicates there is no quotable LD50 value, that is the level at which 50% of the subjects exposed to a given level of gas will die.  It does state the  Immediately Dangerous to Life and Health (IDLH) level is 50,000ppm which I reckon is 5%.  The IDLH is claimed to be "A concentration from which one can escape within 30-minutes without suffering permanent injury" (see http://www.uigi.com/MSDS_gaseous_CO2.html  ).  The UK Short Term Exposure Limit is 1.5% for 15 minute exposure whilst the 8 hour Occupational Exposure Standard is 0.5%.  As mdodoc indicated, the tolerance by different individuals varies widely so what one person can tolerate and walk away feeling fine, another person could well become less able and have a head ache for some while afterwards. 

 

[Cookie]

This is a very useful summary that is worth studying. http://www.cscc.org.uk/wiki/doku.php?id=information:co2

My understanding is that in the cave environment it is the increase in CO2 that is normally the problem rather than the decrease in O2. In an ideal world you would want to know both O2 and CO2 and others, CO for example.

 

[Retri]

have been down nettle and hillocks recently and I thought I was just getting unfit, but it seems that may not be the case.

I did find it much harder going in hillocks than nettle, although we were only breathless when moving, resting brought our breathing back to normal, but exiting the engine shaft was very tough going, I have climbed higher pitches with little trouble, but on this occasion I did have to rest a couple of times on the rope