I am specifically curious about workings with one effective ventilation point.

Following a discussion about how air pressure influences the "breathing" and flow through multi-access workings, I'm interested specifically in workings with one access point. There is an interesting mine in the area which was trialled in the 40s. It is deep, extensive and hugely interesting.

I first dropped the shaft with a gas meter hung off my waist and rather alarmingly almost abseiled into a definate layer of poor air. I got out pronto. Since that incident, we have been back and dangled our meter down and noted a few things. (throughout the summer)

*Sometimes there is a gradual gradient of O2.
*Sometimes (still weather) this gradient is very marked
*The height of the interface varies (like a mercury barometer)

I have a hypothesis which states that cold air should sink into a shaft and into the workings below (with a 12-15 degree air temp and 100% humidity) it air should fall into the shaft and then "pour" into the workings, thus ventilating them. Prolonged cold should insure that this setup is quite pervasive.

The snag could be that a static thermal gradient is formed by turbulence in the shaft.

I went back with my gas lamp set on a very very low flame, as to extinguish about 16% (according to my sketchy calculations) and pulled it out still burning. Sure, the solution is to go back with the electronic meter and measure it accurately, but that will be next week.

So, does bloody cold weather ventilate workings with one shaft for access?

I'm interested in your experiences/observations before I go back and have another attempt at getting in.

I have no experience at all of this however it appears entirely logical that if the outside air is cold, then the warmer air from the mine will rise up the shaft thus ventilating the workings.

Although only one entrance as you say, there must have originally been others that are now filled in or collapsed, also possible natural faults and fissures. Normally there would be no air flow, but under these conditions an air flow could partially be 'forced'.

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We were in an ironstone mine yesterday and although we’ve never previously encountered terrible air like in other mines in the area we would normally expect the air to be a bit stale in the farthest reaches.
The air yesterday was perfect, with oxygen levels very surprisingly never dropping below 20.9%. Now this was a drift mine so I don’t know how it would tie in with your findings.

A drift would allow cold air to "wedge in" beneath the hot stuff with greatest velocities at the top/bottom extremes (I assume) without much mixing.

I'm unsure what would happen in a 4x5ft shaft (about 160ft deep) also, I have a feeling there is a partial collapse down there, which would screw things up a bit.

Since we've had very cold weather for a long time, it should have allowed some good percolation in my opinion. Having said, I could equally be very wrong indeed.

Interesting, if you are detecting low O2 in a shaft on a downward test the oxygen has obviously been replaced by something heavier, if that happens to be CO2 it is about 1.5 heavier than air but easily intermixed by any slight disturbance ( surface breeze etc).
If the heavier gas is H2S it may have a bearing on the reaction of the safety lamp flame but as it replaces O2 the lamp should still extinguish?
The shaft atmoshpere is going to be around 50F degrees and probably at high humidity so I assume in the current weather a lot of water vapour movement around the interface boundary?
As you state there is also the intermixing caused by barometric variations which will be (proportional?) to the enclosed volume of the shaft and connected spaces.

This seems to fall in line with your test experiences so far.

There is nothing down there apart from nitrogen and oxygen. The low oxygen is due to the oxidation of pyrite.

We shall see. I have a feeling that it would be almost impossible for the air not to pour down the shaft into the workings. The meter will tell the truth though.

I was expecting diffusion would be a bigger player, but the boundary seems to be in the order of 6-60ft with the top and bottom of the shaft having the same levels.

An interesting link.

http://www.jstor.org/pss/3858815 

If, in certain cases, CO2 in produced by pyrite oxidation the CO2 would be below the nitrogen level anyway if any such lower (connected) spaces exist in the shaft in question?

Edit: Tales of GPO linesmen bucketing CO2 out of manholes suggests very low mixability of air/CO2.

I assume they are talking about a variety of ferro-oxidation bacteria which breathe out CO2. Not sure it's quite as straightforward as saying "aerobic"

I assume that the cause of the oxygen depletion is the same as in all the surrounding mines and dealt with at length on the "bio-oxidation" thread.

I suppose there is only one way to find out.

I assume they are talking about a variety of ferro-oxidation bacteria which breathe out CO2. Not sure it's quite as straightforward as saying "aerobic"

I assume that the cause of the oxygen depletion is the same as in all the surrounding mines and dealt with at length on the "bio-oxidation" thread.

I suppose there is only one way to find out.

Not my strong point Chemistry but I'm sure your further investigations will shed some light on a complex (to me) issue. 🙂

Stuey, does your gas tester have the spigot for a tube for remote testing?

My old one did, but it sounded like a trials bike, which was irritating. My other one was as big as a 1 year old cat and of a similar degree of inconvenience when dangled from ones waist.

My chum and I went halves on a singing, dancing 4 gas meter which is a lot smaller.

Despite mucking about under waste tips and rubbish shafts, I've only seen a few ppm of H2S, no CO ever and about 4%lel, which is ****** all. I'd go for an oxygen only meter each time, on the proviso that you could either disarm the alarm or reset it to any setting. Otherwise you find that all hell breaks loose below 19.5% which is pretty much an HSE arbitary level.

I find my oil lamp pretty good, but would want to know that air in a shaft was above 16%, which a lamp can't really tell you.

Just a thought that your measurments may be easier to record from the surface via a marked 6 mm tube, can be picked up cheap sometimes.

Edit: Is there any old pipework down the shaft?

The meter records minimums and we just muck around lowering and raising it. You can also view it's readings via time if you care, but that's more complex.

The shaft also has a very very slight underlay, which could help separate the cold and warmer air slightly.

I can't say I've heard anything about temperature mentioned regarding ventilation, apart from historically, there was an incidence of major freezing in a particular winter hundreds of fathoms from surface. That was a downcast shaft though.

Not that relevant to this topic although in some ways related but temperature can play a role.
There is an interesting but complicated paper on fog formation and removal in sub-artic mines. http://lib.tkk.fi/Diss/2007/isbn9789512287789/ 

Getting back to your original message (remembering I know nothing about mine ventilation apart from reading on here) given a closed shaft I can see no reason why dense cold air at the surface would not sink down it. The strength of the surface wind may well play a part. Sorry that's not particularly helpful.

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