How did I know Navi's reply was coming! Either from him, or someone else! There are many dangers to be had exploring an old mine like he said, cave-in's, dead air, etc, but with a little common sense and education it can be safer then crossing the street on a friday night knowing how many drunks there are out there! At least that's how I rationalize it!
Regardless, we will still explore the unknown as long as it's still there, so might as well take as many precautions as we can!
Westcoaster, that would be a great unit to have, would be nice to know how much!
I have explored a couple of mines with a friend who has worked underground for many years, and he told me what to look for.
The entrance is the biggest risk for cave-ins. Rotting timbers, loose rock on the floor are big give aways that it's probably not the safest place to go! After that, USUALLY the rock is fairly solid, at least from my experiences around here.
I always check if there is air movement, which means there is always a fresh air source coming into the mine. If I start down an adit, I will check for movement (usually see if I can see my breath being wisked away, or if it just hovers). If there is no breeze, I leave it alone. My buddy told me a story of a co-worker who was killed having his lunch break in a working mine, he crawled up into a small "room" just off the main adit. His co-workers found him there later dead with the sandwich still in his hand, and the bite he had taken still in his mouth. I believe CO poisoning was the killer. The main shaft was cold from the draft, so he climbed up into the warm room, but CO from whatever source had collected to a point where it didn't take long for him to succomb to it.
Just found a great link which describes the various gases and their effects in different quantities.
Mine Gases Explained
So, for those who haven't been concerned with air in a mine, now is the time to think about it next time you start exploring! If you feel a breeze, you know the air will be fresh, if it's stagnant, watch out! And of course you still have to be aware of shoring (timbers supporting the wall/ceiling), loose faults that can dump a lot of loose rock in the adit, and the biggest danger I've seen in mines around here are from raises which miners used to dump ore down from one level to another. I've seen a few raises which for whatever reason, had a "plug" of ore/mud in them release for unknown reasons, which almost completely blocks the adit. I've never seen one release, but have walked into one mine with a guy who used to work in it, and he was surprised to come across a plug! After that, I started watching raises when we came to them, and have noticed several that had ore behind the gate! Scary because you don't know how much material is there, or what it will take for it to release (rotten wooden/steel gate)! Best not to travel past that point unless you know for sure there is another exit past that point, or at the least have someone stay on the other side of the raise.
Raise
Rotten Shoring