Hello. I am researching ancient and medieval mines. Mines go back to the stone age (e.g. Grimes Graves) and there are some spectacular bronze-age mines in Cornwall. I posted this on a caving group, and one reply was the suggestion that I post it again here.
Where I am interested in what the people here might know about is underground ventilation. Modern mines are comparatively easy to ventilate, thanks to electric motors and air propellers.
I am trying to work out what in an ancient mine excavated by archaeologists might have been dug out not for ore, but for ventilation. One way to look at this problem is to have a look at underground spaces that were not created by Man, and where ventilation for mine workers was a not a design consideration - natural caves, and to see how they vary.
Here are some questions, and if anyone here can tackle them, then please do.
In cave systems with more than one entrance, how common is natural air movement from one entrance to another? How strong does it get? How well-ventilated are cul-de-sac offshoots from the path of the air movement?
Do you have a rule of thumb for how many people can breathe safely in a volume of cave? How much difference would it make if you were hard at work mining, with hammers and chisels, rather than just sitting there admiring the stalactites?
If there is a fresh supply of air in one section of a cave, how far sideways into an unventilated section could you venture without needing modern breathing equipment? What about vertically?
When there is not enough good air, what happens? Do people start getting sleepy? What is the biggest problem? Is it carbon dioxide build-up? Can you escape that just by climbing ? Is it lack of oxygen? Is it quickly obvious to a caver when there isn't enough air, or can the danger creep up on you? If the problem is CO2, then as I understand it, this makes people sleepy and contented, which makes it extra-deadly. On the other hand, I would have thought that a lack of oxygen would be quite different - more likely to cause panic.
If you had a burning candle and were exploring a badly-ventilated cave, what would happen first - the candle goes out or you are incapacitated?
Are there caves where artificial ventilation shafts have been added, and did these work?
Are there big seasonal variations with ventilation?
I am aware that some natural caves have other unusual and dangerous gasses in them, but let us assume that the problem is just an absence of ventilation from the surface.
In caves with just one entrance, is a lack of air a massive problem, hugely limiting human exploration down there? Do some caves with only one entrance seem like gas-tight pockets, while others seem to get air somehow through unseen fissures in the rock?
Have people solved cave ventilation problems with any low-tech methods? Lighting a fire to create an up-draught near a shaft? Wafting air into the entrance with a big cloth sheet on a stick? Building a chimney over an entrance?
That's rather a lot of questions - sorry about that. Anything that will help me understand what early miners would have had to contend with regarding ventilation is appreciated. I've been talking to modern mining engineers, but I thought that cavers might have a better idea of bad ventilation underground than engineers who work all the time with massive electric ventilation equipment and modern ducting.