Author Topic: C02 question  (Read 935 times)

Online Tomferry

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C02 question
« on: October 20, 2021, 08:43:19 am »
Hello everyone  :bounce:

I have been out in a few irons mines recently with Chrisjc now covid has gave us all a much deserved break .So the mines are pillar and stall a traditional style of working very large in size. 


The question is what causes the high percentage of co2? If you hit for EXAMPLE 13.8 %o2 and had 7.5%co2 present what is causing this ?

The iron in the mine itself is a 10ft seam so a 6ft has been worked out 2ft above your head and 2ft on floor for the trams remain so their is a monster amount of iron in their the pillars remain and the ribs of the tunnel also . This iron is “drinking”’the o2 which I understand so how does co2 then  appear ?

Offline Duncan Price

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Re: C02 question
« Reply #1 on: October 20, 2021, 09:28:34 am »
The question is what causes the high percentage of co2? If you hit for EXAMPLE 13.8 %o2 and had 7.5%co2 present what is causing this ?

I can't answer this question directly.  How are you determining %O2 and %CO2?

I'm asking this because some gas meters measure %O2 (using an electrochemical cell - basically a battery that produces a current proportional to the partial pressure of oxygen in the atmosphere) and calculate %CO2 by assuming that %N2 is 79 and therefore %CO2 = 79 - %O2

...another thing, I looked up the compositions of ("ironstone"- it can be a variety of minerals - the stuff in the Cleveland Ironstone Formation contains siderite which is iron (II) carbonate - acidification of this will give you CO2 and FeO which can oxidise and deplete %O2.
« Last Edit: October 20, 2021, 09:41:18 am by Duncan Price »

Online Tomferry

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Re: C02 question
« Reply #2 on: October 20, 2021, 10:07:52 am »
This is the iron stone bed we are in .


https://en.m.wikipedia.org/wiki/Inferior_Oolite

I shall have to check the gas monitor question

Offline Brains

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Re: C02 question
« Reply #3 on: October 20, 2021, 11:35:38 am »
Quite often it is the absence of O2 rather than a build up of CO2 or other gasses. The iron ore absorbs oxygen causing the bad air. In pillar and stall the ventilation will short circuit leaving areas of bad air. Ideal candle lantern or oil lamp territory, if it goes out so do you! Flammable or toxic gasses will be very rare so a flame safety lamp or gas meter aren't vital per se

Online Tomferry

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Re: C02 question
« Reply #4 on: October 20, 2021, 12:31:47 pm »
Quite often it is the absence of O2 rather than a build up of CO2 or other gasses. The iron ore absorbs oxygen causing the bad air. In pillar and stall the ventilation will short circuit leaving areas of bad air. Ideal candle lantern or oil lamp territory, if it goes out so do you! Flammable or toxic gasses will be very rare so a flame safety lamp or gas meter aren't vital per se


But if the iron is absorbing it causing the bad air then surly their is a build up of co2 ? Co2 is classed as a toxic gas and we encounter it regularly over this way the 5x picks it up a lot , I am unsure why we are finding this . What causes it ? :shrug:

I personally think a 5x is a must in iron mines as you can be at a acceptable level of o2 to breath and find dangerous levels of co2 .

Offline Fishes

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Re: C02 question
« Reply #5 on: October 20, 2021, 12:40:04 pm »
Absorption of oxygen by iron ores won't generate CO2. It will just reduce the 02 level.

That doesn't rule out other sources of CO2 or other gasses though.

Offline pwhole

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Re: C02 question
« Reply #6 on: October 20, 2021, 02:15:50 pm »
On a trip into Hillcarr Sough, the O2 levels at the terminal choke got very low indeed, but I don't remember the CO2 levels being particularly bad. I presume this was due to the shale cap and bad ventilation rather than direct substitution. We would have died if the CO2 was in direct proportion to the lack of O2, which was reading 10.6 I think when I decided to turn back, as I didn't have a rebreather on me.

I guess one of the few benefits of smoking is that you can tolerate lower levels :)

Offline AR

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Re: C02 question
« Reply #7 on: October 20, 2021, 02:26:10 pm »
This is one that Les Riley is probably the best person to ask, him having managed Dragonby for many years! If there's old timber around in the workings, then the decay of that will be releasing some CO2, but also if there's no air movement then the raised levels may be more down to the heavier CO2 collecting at the lowest points. I've heard of cases where people described being "chased out" by blackdamp; what had happened was that the CO2 had settled in the lower part of the level they were walking through and their movement stirred it up.
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Offline ttxela2

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Re: C02 question
« Reply #8 on: October 20, 2021, 03:30:25 pm »
Absorption of oxygen by iron ores won't generate CO2. It will just reduce the 02 level.

That doesn't rule out other sources of CO2 or other gasses though.

I have no idea how it works but given that amounts of oxygen are usually expresses as percentages surely it follows that if the percentage of oxygen goes down the percentage of the other gases must go up? Granted it's mostly nitrogen but I assume the most logical thing is that the other gases increase in proportion to the original make-up? However there might be something going on that favours CO2 taking the 'space' left by the missing oxygen over the nitrogen?


Offline paul

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Re: C02 question
« Reply #9 on: October 20, 2021, 04:21:07 pm »
Oxygen combines with other elements in a process called oxidation. One form of oxidation is to combine with Carbon, usually from an organic source such as burning or respiration. This results in the production of Carbon Dioxide when oxidation is "complete" or a mixture of Carbon Dioxide and Carbon Monoxide when not "complete".
If the oxidation is a result of Oxygen combining with an element other than Carbon, the no Carbon Dioxide or Monoxide is produced but instead the Oxide of the element with which the Oxygen had combined with, e.g. oxidation of Iron results in an Oxide of Iron we know as "rust".
So if the reduction of Oxygen is due to an oxidation of a Carbon compound, there is a reduction of Oxygen and corresponding increase in Carbon Dioxide. Oxidation of non-Carbon compounds will also reduce the amount of Oxygen but no change in Carbon Dioxide.
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Offline andrewmc

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Re: C02 question
« Reply #10 on: October 20, 2021, 06:28:08 pm »
Also you will notice CO2 buildup i.e. 'bad air'. If you hold your breath, the feeling of need to breathe you get is actually an increase in CO2 and thus the acidity of your blood.

You don't notice low levels of O2 until you keel over (supposedly it can cause euphoria when you are hypoxic, and it will of course eventually kill you).

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Re: C02 question
« Reply #11 on: October 20, 2021, 06:31:04 pm »
Iron mines seem to generate more CO2 than most mines. Coal and shale mines generate their fair share and limestone based mines are less bad.
Anything that can decay will help produce CO2. I don't know the chemistry of the decay in iron mines, just that they are prone to it.
If there is little or no ventilation, as often happens in large pillar and stall workings, the CO2 just lays there from the floor upwards depending on gradients of the seam.
It is very easy to walk down into a 'lake' of CO2 and be overcome. That is one reason why you should move gently with your detector in your hand hanging down. No point having your detector clipped to the collar of your overalls in this scenario. I have been in steeply dipping drifts, waist deep in CO2, where you could lower your meter and get a massive reading of CO2 and little oxygen then lift it up and get very little CO2 and plenty of oxygen. The only real cure is ventilation. Given that large iron mines would take a long time to explore and navigation is often difficult without good plans, it is better to give up at that point. Using breathing apparatus is a skilled job and only for short duration, not meant for primary exploration.

Calculations for blackdamp are not straightforward add and subtract. Air has a fixed percentage of oxygen to nitrogen. So it follows that if you reduce the oxygen content there is still the required ratio of nitrogen to that lower oxygen plus some 'spare' nitrogen, since only the oxygen has depleted not the air. So you add CO2 into that and that reduces the volume of air too.
Blackdamp is actually a mixture of CO2 and the excess nitrogen. This is why basic add and subtract of percentages don't follow through.
Obviously from the practical point of view, nitrogen will kill you just as well as CO2.
The next issue is whether you are measuring a CO2 lake or CO2 in the general body of the air (ie all mixed up). Mostly in fairly level workings where your party has been moving about you will be reading the general body. Therefore you will have CO2 and excess nitrogen affecting the oxygen reading. If you have the CO2 lake situation, the lake will be high or pure CO2 and the air above the lake will be general body with the oxygen replaced by excess nitrogen. Stir up the lake and you have big trouble.

At Dragonby we found that the CO2 levels would increase by around 1.5% in the general body during our three monthly absences. Ventilating during daytime for 6 days resulted in lowering the main areas back to good limits of around 0.5% general body. However, the further reaches off the main vent circuit would remain around 2% most of the time.
With no ventilation the whole mine would have filled with CO2 over some years. Only the entrance roads remaining clear by expansion/contraction of the air mass.
In fact when we re-opened one section of the mine that was cut off from the rest, it was full to within 100metres of the surface as you descended the inclined drift. Mind you, it had been fully closed off for around 25 years.

Les

Online ChrisJC

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Re: C02 question
« Reply #12 on: October 20, 2021, 06:59:19 pm »
In this particular case, the detection was by a GasPro with O2, CO2, CO, H2S and LEL sensors. The O2 went down and the CO2 went up as Tom says. The other three remained unmoved on zero.

The surprising thing was how close to the outside world we where, about 6 feet. The level is blocked off, but there is a small vent hole by which the detector was placed.

I did think that the CO2 was an outside phenomenon, as it is in a depression, but it was windy, and the detector was fine further away from the portal. So the high CO2 was issuing from the mine. The barometer was falling too.

Mysterious!

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Online Tomferry

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Re: C02 question
« Reply #13 on: October 20, 2021, 07:10:55 pm »
Thanks for taking the time to reply everyone , it is a extremely large iron mine it all has a slight fall on it but we are by far at the highest point and having these issues , it is truly outstanding how it changes due to the atmospheric pressure also . It appears all of my answers have been answered including my next one which was about black damp I have read the sums on the colliery book and I agree their far from simple.

so all the rusty metal inside the mine any timber and machines left will all increase the co2 presence

Foreign bodies getting washed in leaves and items on footwear etc

And natural according co2 which is in extreme levels since no one has been inside for 60+ years it will be a massive lake of it .

So the walls of the mine the roof and floor as we are in a monster slab of iron will they oxidise and cause this also ? Because now a percentage of ore has been removed leaving a void which contains o2 to cause this reaction?

Online mikem

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Re: C02 question
« Reply #14 on: October 20, 2021, 07:27:57 pm »
"The ironstones are [ALREADY] composed largely of iron oxide ooids (goethite and limonite), with smaller amounts of Fe-silicates (chamosite, berthierite, and glauconite) and Fe-carbonates (siderite), typically as cements."
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/ironstone
So that's unlikely to be the source of oxygen depletion - although the carbonates may be replaced by oxides to give off CO2.

However, from different source, but same website:
"They are found almost exclusively above coal seams"
So that may well be the cause.

As outside pressure drops the mixture will be sucked out of the mine, until equalised, & as it increases again atmospheric air will be pushed in (but both will be relatively tiny amounts) - just because you are at top of mine doesn't mean the whole place is full of such concentrations, there may be some other factor(s) causing a collection pocket effect.

Water running into the mine also carries atmospheric (& soil) CO2, which will be given off as the water evaporates (seeming paradoxical, the less water running in will result in more CO2 being released, as saturation tries to maintain itself)
« Last Edit: October 20, 2021, 07:47:05 pm by mikem »

Offline mrodoc

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Re: C02 question
« Reply #15 on: October 20, 2021, 09:22:45 pm »
Respiration produces CO2. That includes any organism that uses oxygen.

Offline alastairgott

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Re: C02 question
« Reply #16 on: October 21, 2021, 07:25:42 am »
This is the best description of some of the pitfalls of Bad gas I have ever come across, Thank you Les.

Iron mines seem to generate more CO2 than most mines. Coal and shale mines generate their fair share and limestone based mines are less bad.
Anything that can decay will help produce CO2. I don't know the chemistry of the decay in iron mines, just that they are prone to it.
If there is little or no ventilation, as often happens in large pillar and stall workings, the CO2 just lays there from the floor upwards depending on gradients of the seam.
It is very easy to walk down into a 'lake' of CO2 and be overcome. That is one reason why you should move gently with your detector in your hand hanging down. No point having your detector clipped to the collar of your overalls in this scenario. I have been in steeply dipping drifts, waist deep in CO2, where you could lower your meter and get a massive reading of CO2 and little oxygen then lift it up and get very little CO2 and plenty of oxygen. The only real cure is ventilation. Given that large iron mines would take a long time to explore and navigation is often difficult without good plans, it is better to give up at that point. Using breathing apparatus is a skilled job and only for short duration, not meant for primary exploration.

Calculations for blackdamp are not straightforward add and subtract. Air has a fixed percentage of oxygen to nitrogen. So it follows that if you reduce the oxygen content there is still the required ratio of nitrogen to that lower oxygen plus some 'spare' nitrogen, since only the oxygen has depleted not the air. So you add CO2 into that and that reduces the volume of air too.
Blackdamp is actually a mixture of CO2 and the excess nitrogen. This is why basic add and subtract of percentages don't follow through.
Obviously from the practical point of view, nitrogen will kill you just as well as CO2.
The next issue is whether you are measuring a CO2 lake or CO2 in the general body of the air (ie all mixed up). Mostly in fairly level workings where your party has been moving about you will be reading the general body. Therefore you will have CO2 and excess nitrogen affecting the oxygen reading. If you have the CO2 lake situation, the lake will be high or pure CO2 and the air above the lake will be general body with the oxygen replaced by excess nitrogen. Stir up the lake and you have big trouble.

At Dragonby we found that the CO2 levels would increase by around 1.5% in the general body during our three monthly absences. Ventilating during daytime for 6 days resulted in lowering the main areas back to good limits of around 0.5% general body. However, the further reaches off the main vent circuit would remain around 2% most of the time.
With no ventilation the whole mine would have filled with CO2 over some years. Only the entrance roads remaining clear by expansion/contraction of the air mass.
In fact when we re-opened one section of the mine that was cut off from the rest, it was full to within 100metres of the surface as you descended the inclined drift. Mind you, it had been fully closed off for around 25 years.

Les

Online mikem

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Re: C02 question
« Reply #17 on: October 21, 2021, 07:52:04 am »
Blackdamp is produced by coal (& presumably oil shales), so comes from beneath the ironstone. There is a good explanation of the hazards etc on:
https://en.m.wikipedia.org/wiki/Blackdamp

When the oxygen is removed the pressure in that area drops, so surrounding air (mostly nitrogen) moves in to fill the gap & more air will be sucked in from the surface, by whatever is the easiest route (but again you're only talking a tiny amount, so it won't noticeably affect oxygen levels as it will quickly disperse amongst the surrounding nitrogen).

Online ChrisJC

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Re: C02 question
« Reply #18 on: October 21, 2021, 08:40:21 am »
I am not aware of any oil shale or coal beneath this ironstone. I have just had a look on the BGS Borehole website, but none of the boreholes go very deep. They all seem to be just about proving the ironstone.

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

The area in question is near Finedon, Northants. I do notice however a bunch of boreholes (in black) near Stanwick which suggest deeper searching for something else! So maybe there is oil deeper down.

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Online mikem

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Re: C02 question
« Reply #19 on: October 21, 2021, 08:56:08 am »
From my first post - sciencedirect website about ironstones:
"They are found almost exclusively above coal seams"

Searching northants coal mines brings up:
https://www.northantslive.news/news/northamptonshire-news/gallery/inside-northants-abandoned-iron-ore-5953280

This does however suggest that there's no coal in area:
https://www.rootschat.com/forum/index.php?topic=494531.9
« Last Edit: October 21, 2021, 09:11:52 am by mikem »

Online Cantclimbtom

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Re: C02 question
« Reply #20 on: October 21, 2021, 09:01:53 am »
Looking at BGS around Finedon, especially looking a little West -  could it be the area there the ironstone is present in conjunction with Whitby Mudstone? Which they describe (https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=WHM) as "..Medium and dark grey fossiliferous mudstone and siltstone, laminated and bituminous in part.."   the word bituminous jumps out at me for black damp.

Dunno, do we have a tame geologist reading this?  (if not tame, at least vaguely house trained ;) )
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Online mikem

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Re: C02 question
« Reply #21 on: October 21, 2021, 09:10:40 am »
Of course, in some areas different beds are present / missing. The mudstone is apparently above the ironstone, so gases would be sinking down & could easily collect in pockets:
https://en.m.wikipedia.org/wiki/Whitby_Mudstone

Online LJR

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Re: C02 question
« Reply #22 on: October 21, 2021, 10:37:36 am »
Ironstones come in different strata groups. In the coal measures (around 300 million years) there are often ironstone bands in the coal and/or separate ironstone seams. Sometimes the iron was worked with the coal and other times separately. This stuff was generally a hard ore. I can't speak for all coal districts but this was the case in Derbyshire and North Staffs. Then there is the haematite mines of Cumbria, a different type of stone altogether.
Then the ironstones mined in Northampton and Lincolnshire which were Jurassic (200 million years) ores. These have no coal measures associated with them. The ore is really a soft limestone with added iron. Described by our mine geologist as a "ferruginous limestone" , not sure of the spelling there! The iron content was never high, 25% being good. The coal measures stuff was much better, as were the Cleveland ores. Cumbrian ore was the highest quality (I think).
The good thing about the Lincs and Northants stuff was that it had large reserves for opencast and underground mining and could be mechanised for maximum output. The result being the vast areas of pillar and stall workings that we are now discussing.

Online mikem

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Re: C02 question
« Reply #23 on: October 21, 2021, 12:00:40 pm »
Ferruginous is correct  :smartass:

 

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