Ok, I'm going to wade in again, at the begining of this thread caving clubs were mentioned, sounds obvious but caving and abandoned mine exploration are two different animals, some cavers will be familiar with abandoned mines, some maybe not, so far as I am aware most caves are natural formations, most mines are not, mines were bloody dangerous enough when men worked down them, they are potentially lethal when abandoned.
Anyone who is not familiar with mining methods pertaining to the type of mine to be explored should swot up on the subject, most of us know these methods, this can forewarn us of the dangers to look out for, anyone who doesn't and gets into these old mines with others of a similar ilk might as well put one slug in the barrel give it a spin and pull the trigger or wear a blindfold.
Pillars removed, hanging wall pressure, pulled out stopes, false floors that look like rock, blind covers that could be holding up more dirt than you can shake a stick at, a winze/raise under a shallow flooded level that you have been walking along with no problem, old timbers, gas from decaying timbers/metalwork, vegitation etc, no ventlation whatsoever, ventilation flows that can change without you knowing or between site visits, flash flooding, getting lost, just to highlight some.
Remember that sometimes it's just a series of unknown or seemingly unrelated events that are out to get you.
Maybe someone can refresh my memory, only a few years ago there was someone that was working/renovating an old abandoned shaft or something similar, could have been in East Cornwall or Devon, somehow a mistake was made and I think he plunged down, I believe he lost his life? It made the local TV news I seem to recall.
Have a nice day.
Lozz.