Bad Air

One of the most exciting things in the mine exploring business is a shaft or adit with a healthy flow of air moving in or out of it. A good flow of air is an encouraging sign, indicating a lot of underground volume (cavers know this). Bad air is always a concern in any mine (or any enclosed space for that matter). Electronic air quality monitors can be obtained and worn. They are expensive and require periodic maintenance and calibration. Consequently I have never had the advantage of using one.
I have several stories to tell about bad air. Take note that the two in which I participated were in quite large mines with a healthy air flow at the entrance.

Story One

The first story is a tale I have heard about a mine down near Yuma, Arizona. As the story goes, 3 marines from the base nearby drove to this mine and made camp at the top of an inclined shaft that they intended to explore the next day. They built a fire and undoubtedly enjoyed a beautiful night on the desert. (Old mine dumps make wonderful flat places to camp, but be sure you locate and avoid any shafts or holes). The next day they tossed a rope down the shaft and one of them went down, only to collapse and fail to respond. A second went down to attempt a rescue and also expired in the attempt. Apparently the "exhaust" from their fire had filled the mine shaft with carbon dioxide (which is heavier than air), displacing necessary oxygen and suffocating these poor men.

Story Two

The second story involved myself and a companion. We had descended a vertical shaft about 400 feet to a place where the ladder simply ended. We then tied a rope to a sturdy anchor, and rappeled about 50 feet to a level we could see below us. After exploring this level we decided to descend the shaft further (the ladder had now resumed and was in good shape), but as soon as my eyes reached the floor level, I could take only a partial breath as the air was such as to make you choke. I came up out of there in a hurry! Although there was no visible sign of this whatsoever, the shaft below this point was filled with carbon dioxide. It looked just fine (carbon dioxide is as clear as good air). The level we were on led to an adit, so that the shaft we entered along with the adit kept the upper part of the mine reasonably well ventilated, but below this was not accessible to mankind without some kind of life support gear (too bad!). The transition from good air to deadly took place in the space of inches. We felt very fortunate that we had not rappeled into this pool of bad air, because if we had, I very much doubt that you would be reading this account. On a ladder, it would be quite easy to quickly reverse direction, but on rappel, I don't think there is any way it could be done.

Story Three

The last story is from long ago in a silver mine in the California desert. We had been underground for many hours, and were deep in the mine, below the 800 or 900 foot level and far from the shaft we had descended. My partner and I stepped over a wooden barrier and ducked our head below another and then descended a gentle slope into a fair sized stope. We had been feeling "low energy" for some time (the air was marginal) and we were using carbide lamps. I looked up at my friend and was amazed to see an extremely long blue flame coming from his lamp. I said, "we need to get out of here" and immediately began moving, my mind having jumped to the conclusion that the air was seriously deficient in oxygen, insomuch that the acetylene gas could not burn normally. My partner reported that my lamp was behaving the same way, and we consider ourselves fortunate not to have collapsed in this remote part of this mine. I seriously doubt that our bodies would ever have been found. Since this time, I have always valued the flame of a carbide lamp as an informal test of air quality. However, I have now switched to using electric (LED) headlamps and no longer have the benefit of this built in "air monitor".

Story Four

This one came from a reader in July of 2008:
My brother and I visited Virginia City about 8 or 10 years ago. The New Savage Mine was a project to open up the famous Savage Mine again, with new timbering and equipment. They boarded it up when the price of gold dropped. There was a screen that had been pulled back at the entrance and a hand painted sign "bad air." The tunnel looked very secure and I wanted my brother to enter with me. But he insisted we not do that. Two week later two teachers from Virginia City High School went in at the same spot, it had easy access. They began to feel faint and by then it was too late. They collapsed and died about 100 feet from the entrance. Bad air. I will always remember that close call.

A final caution

I was recently told about a situation that I was unaware of (and have little experience in since I usually am poking around in fairly dry mines in desert places). What look like inviting mines up the the mountains with a nice flow of water running out of them can have air depleted of oxygen due to the water running out of them. The water gets depleted of oxygen while trickling through the rocks before arriving at the mine workings. The oxygen depleted water then pulls oxygen out of the air as it flow through the mine workings, and this can very definitely lead to such low levels of oxygen as to be fatal, even fairly close to the mine entrance. This could have been a factor in the Virginia City story just above.
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Uncle Tom's Old Mine Info / tom@mmto.org