December 8, 2018
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.
For most of my career I have never had the advantage of using one.
Recently I have changed my ways, and encourage you to read the
The following is worthy of careful study:
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.
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.
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
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".
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.
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.
Drop me a line!
Uncle Tom's Old Mine Info / firstname.lastname@example.org