CO2 Monitor

[whitelackington]

Aubrey,                                                              "Cuckoo Cleeves"
if the concrete pipes were extendend upwards,
several feet above the surrounding field level,
then the ground of the hollow made up to resemble a mini Glastonbury Tor,
CO2 may not then settle in the entrance.
Mick

 

[Elaine]

It is all very interesting indeed. I wish I had more time to look into it as well. I wonder why the problem gets worse. My 16 years of caving is too little to see that it has got worse over the years, but other people seem to think it has. Is this a nationwide problem, or more common in the south? I can understand that airless digs and passages could suffer bad air, but on Mendip, stream caves also suffer. Does this happen elsewhere?
At Templeton we have had bad air recently but it has gone now the colder air arrived. Also having a lot of diggers at the bottom helps as we get hot and improve air circulation.
Respiration is stimulated by co2, as our bodies need to get rid of the co2 which encourages us to breathe.

 

[robjones]

A bit old but still sound: J.M.James, A.J.Pavey & A.F.Rogers 'Foul air and the resulting hazards to cavers', BCRA Transactions, vol.2, no.2, 1975, pp.79-88. The authors mention empirical tests for CO2 content of cave air:

Match is extinguished at 1% CO2

Candle is extinguished at around 3% to 4% CO" (some testers reported varting levels however, ranging at the most extreme from 2.3% to 10%; this may reflect different amounts of O2 in the air - see below concerning the non-linear replaement of O2 by CO2)

Carbide lamps extinguished at 5% to 6% (small helmet-mounted old-fashioned 'stinkies') and 8.9% to 10% (large hand-held miner's carbide lamps - I've used them in mines but suspect that they were rarely used by cavers; whether they equate to waist-mounted generator type carbide lamps typically used on expeditions I don't know; I suspect that cavers' generator types might be intermediate between stinkies and moner's hand lamps, at least based on volume of C2H2 evolved per unit of time).

The advice of this paper was "If a candle will not burn it is advisable to leave the cave at once" and "if a carbide lamp is extinguished (early warnings are a smokey flame and less light) then the caver is in severe danger".

The authors noted "a match is extinguished before a candle [1% CO2 versus 3% to 4% CO2] therefore the candle can only be lit while in good air".

Mid C19 inspectors of mines noted the practice of miners 'inclining the candle' - tilting it at an angle or even horizontal, to keep it alight in poor air to enable them to continue to work - the tallow (paraffin wax later, including today) would be consumed faster, but would stay alight in lower levels of O2 / higher levels of CO2. At its most extreme, the candle might even be held completely upside down to keep it alight to enable work to continue.

The authors note 'a candle can be recommended as the standard CO2 test for digs [with CO2 levels in the range 1% to 4% - they recommend using testing equipment above 4%]. If the CO2 rises above 4% (i.e. the candle goes out) - get out slowly'.

They recommend extreme caution if there are any vertical descents into potentially elevated levels of CO2 - the gas is 1.5 time as heavy as air and pools at shaft bottoms, noting ' climbing out of fopul air is much more difficult than might at first be expected because of the limited capacity for physical work of the caver in foul air'.

In CO2 levels above 6% they recommend breathing apparatus and the use of a cave diving approach - back up equipment, rule of thirds, etc.

Two inter-related factors: increased CO2 and O2 depletion. But note that the two are not always in perfect step - a 1% increase in CO2 does not automatically equate to a 1% decrease in O2. See Descent 79, Dec 1987/Jan 1980, p.5 article "Gas causes near-fatality in Welsh lead mine" for an incident when the O2 was stripped out of the atmosphere in workings beyond a sump, with the resulting CO2 apparently dissolved in the water, resulting in O2 depletion accompanied by N2 excess rather than CO2 excess. None of the party tasted anything odd in the atmosphere nor experienced panting, just listlessness - followed by unconciousness and convulsions in the case of the lead explorer who was dragged back out by his companions, with at least one other being so 'out of it' that he was basically lead out by the hand. Recovery was rapid in fresh air; the two leaders had no recollection of the event nor of their removal.

Around 1 in 10 people do not experience panting in hightened CO2 / depleted O2, and instead tend to go very quiet and start turning a bit blue. The medical shorthand for the two sprts are 'pink puffers' and 'blue bloaters'. A friend is a blue bloater - he has been known to just sit quietly and become increasingly 'out of things' when companionss are complaining of shortness of breath and are panting. (in the Descent report, above, most of the group were known pink puffers so it was not a case of all of them by chance being blue bloaters)

O2 % by volume information, from J.D.Jenkins 'Coal Mines Rescue and Fire Fighting', 1956, chapter 7 'Mine gases and dusts', based on the depletion being made up by a gas other than CO2:

20.93% normal air supply

17.50% "flame lamps [i.e. 'Davy' lamps, NOT Carbide lamps] extinguished; work can be done in this atmosphere for several hours without any ill effects" [this is a c.1950s book; opinion m,ay be different today!]

13.00% "acetelyne lamps [i.e. carbide lamps] extinguished; considerably increased rate of breathing if work is being done" [this contradicts another volume I recall reading which observed that carbide lamps can burn in O2 concentrations that can result unconcious and death, and cited examples of rescuers equipped with breathing apparatus recovering bodies beside which carbide lamps continued to burn]

10.00% "lips turn distinctly blue; nausea and headache develop gradually and become more severe in time"

8.00%  "face takes on a blueish-grey tinge and breathing becomes very rapid; disablement occurs in about a quarter of an hour"

7.00% "face turns a leaden colour and distinct panting occurs, accompanied by paliptations of the heart; unconciousness rapidly ensues"

6.00% "complete loss of conciousness, followed by death in a matter of minutes"

2.00% "unconciousness in about 40 to 45 seconds without previopus panting, even if person is absolutely still; rapidly fatal"


CO2 % by volume information, from same volume:

0.03% normal air content

0.50% "lung ventialation is slightly increased"

2.00% "amount of air breathed is increased by 50%"

3.00% "lung ventilation increased about 100% even at rest, and becomes very laboured on exertion and fatigue ensues"

5.00% "the amount of  air breathed is increased 300%, and even at rest breathingh becomes very laborious"

6.00% "violent panting takes place and fatigue ensues up to the point of  exhaustion"

10.00% "intolerant panting, and severe headaches occur after a few minutes at this percentage"

above 10.00% "narcotic effect upon the system"

over 20.00% "death may ensure after a period of hours during which a state of coma exists"


CO is 300 time more preferentially taken up by the human body compared to CO2 - basically the human body preferentially scavenges CO from the atmosphere. CO is very toxic and causes collapse.


CO % by volume information, from the same volume on mine air:

0.02% (200ppm) "slight headache with some people after about 7 hours during rest or 2 hours during extertion; tightness across forehead"

0.04% (400ppm) "severe headache after 5 hours during rest and less than an hour during exertion; severe headache ensues at the end of this time, with dizziness, nausea and possibility of collapse"

0.10% (1,000ppm) "poisioning may easily take place and respiration is increased; palpitation occurs"

0.20% (2,000ppm) "unconciousness occurs after 30mins at rest or 10mins exertion; the coma and intermittent convulsions which result are often acompanied by depressed heart action and possibly death"

0.30% (3,000ppm) "coma accompanied by very weak pulse and reepiration, followed by respiratory failure and death"

1.00% "after 3mins at rest or 1min exertion unconciousness ensueres and is rapidly followed by death"

 

[graham]

Is this a nationwide problem, or more common in the south?

A good question. The majority of recent reports seem to be from the south. I can recall reports from Derbyshire, but few, if any, from the north.

 

[Peter Burgess]

If it is a problem due to higher average summer temperatures inducing greater gas production in the soil, then should we not have already heard of this problem from countries with warmer summers, like continental Europe?

 

[Les W]

I can recall reports from Derbyshire, but few, if any, from the north.

Derbyshire is pretty much north.

 

[Smithers]

I know this has been said before, but wherever you're digging underground you're likely to encounter elevated CO2 levels, for the simple fact that most digs take place in squalid little holes in obscure bits of cave system.  Sometimes you'll have good air circulation and sometimes you wont, but more often than not remote areas of cave are the last places to get new/fresh air.

What you've got to watch out for, is that if you're digging down and using caps and there isn't much on a draft the CO2 will sink to the bottom of the dig as its heavier than O2.  Also bear in mind that the fumes from capping may not clear easily either.

From my own personal experience, the longest I've spent at a digging head with one other person whilst changing over between capping and shifting rock was about 5-6 hours.  By the end of that we both had thumping headaches, but I imagine a lot of that was due to the fumes from caps and elevated CO2. 

Ultimately you want to watch out for are cramped digs where you end up digging downwards on your front or back.  These are real pigs, because by the time you've gotten a headache its often a lot more tiring to get out.

 

[Alex]

Hmm thankyou for all the info. From what I have read it appears I am in not much danger as for one I am not digging with caps or anything that goes *bang* I am simply removing sand with a trowel and then dragging out. I am about 5 minutes if that from the surface.

So from the information I have gleamed it seems as long as I am not cut off, not burning anything and don't spend longer then 6 hours in my sandy little tunnel then I will be fine, well with the exception of a headache at which point I would leave.

Unfortunately my dig is one of those going downwards but I guess athe fumes would only be elevated up to a certain point.

 

[Bob Mehew]

I am in not much danger as for one I am not digging with caps or anything that goes *bang*

So from the information I have gleamed it seems as long as I am not cut off, not burning anything and don't spend longer then 6 hours in my sandy little tunnel then I will be fine, well with the exception of a headache at which point I would leave.

Things which go bang introduce other gases which have much higher impact.  So yes just CO2 is less of a danger.  But I doubt if the 6 hour value will apply to your dig as it will depend upon many site specific factors.  Also Smithers said that 6 hours was the longest time he had spent digging presumably indicating he had to get out of other digs in less time.  Remember you can kill yourself fairly quickly by sticking your head in a plastic bag, your tunnel is only a bit larger.  It is your life you are playing with.

 

[potholer]

How well does CO2 separate out from exhaled breath over the timescales involved in transport from a dig face via convection?

In a dig, sloping down at ~30 degrees from the end of a draught-free large/high chamber, with the dig ~20m long and 1mx1m across, with a fully blocked end, there seems to be a pretty good convective flow, with fresh air flowing down at floor level, and exhaled air rolling out along the roof.

Would that work less well in a vertical dig - would a nice stable convection setup still happen, or would rising and falling air tend to mix more if the dig were straight down, rather than on a slope.
In the sloping dig, presumably wherever the digger and their second breathe out, their breath will rise to the roof and join the fairly constant flow out, partly breath, partly driven by their body heat.
For someone down a vertical pit, where their breath rises from second to second seems like it could depend where they're facing when they breathe out - would there be more turbulence in that situation, and more mixing of rising and falling air?

 

[owd git]

If you have  access to a fan from a p. c. a 6v. battery (hand lamp type with spring term's on top.) you could do so much better than convection.
O. G.

 

[potholer]

In the sloping dig, it's fine - air for the digger's loader does get less nice (at least at roof level) after 5-6 hours work, but that's more down to the diggers getting increasingly sweaty, and the fine dust from drag trays grinding over dry sandy mud.

 

[Alkapton]

If anyone has a CO2 detector, and does not mind lending it to me for a couple of days I would be eternally greatful.    I know a place that is known to have had very high CO2 - the thinking is that levels have decreased in the last few years (I've never had a problem but in the past others have had big problems)  It would be very good to get acurate readings at this time.

BTW.  The match / candle test is entirely inapropriate because there is present a floating layer of methane.  It would be nice to also get new readings for methane since it is a few years since tests were made - 13% in places.    I know water levels have changed recently (gone down - and not due to summer) so my guess is things are better than they were - But I've no way of telling.