I was reading a thread on the topic of "Bad air" on another website and thought that it might be a good idea to post some details of "bad air" on here too.

The following is taken from the other website although it does not address either Radon gas or radiation (both of which were really outside the scope of the thread).

This is a tricky subject and a dangerous one to get wrong.

The most common cause of “bad air” is oxygen depletion caused by the oxygen being displaced by another gas (such as carbon dioxide, Nitrogen (elevated levels thereof), methane or hydrogen sulphide).

However, elements of these other gases can exist without significantly depleting the concentration of oxygen and can cause serious problems even though a “cigarette lighter” would remain lit (especially hydrogen sulphide (the gas that smells like rotten eggs and usually comes from sulphides in the rocks and stagnant water)).

Methane can ignite if the air has at least a 5% concentration (you can’t smell methane) and, being lighter than air, rises. So if you are holding your lighter up in the air (as I guess most of us might), you might find a nice little pocket to blow you up (although this is obviously very rare).

Hydrogen sulphide is, in itself, toxic and does not need to deplete the oxygen level to harm you. If you smell “bad eggs” you should really leave immediately.

Another important aspect of “bad air” is the level and concentration of oxygen which is, normally, 21%. If it drops below 19.5% it is considered “deficient” and you have to remember that if you are exerting yourself you are drawing in more oxygen and expelling more carbon dioxide. If the oxygen level drops below 19.5% (either because you have transposed it into carbon dioxide or other gases are present) you could find yourself suffering from asphyxiation (to one degree or another) and, of course, if the whole party suffered together, you would not likely be aware of it. This actually happened to a group of cavers and scientists deep in a cave (or a lava tube?) on Mount Tiede in Tenerife a couple of years ago where most of the party actually died.

A cigarette lighter will stay lit until the oxygen level reduces to 17% - by that time, it may be too late (although you can still function at that level provided you are still compos mentis).

Sorry to be such a “bore” on this subject but I do think it is worthwhile taking the issue of “bad air” seriously and it is certainly worth our while understanding as much about it as possible.

Ian

if you look om ME you will also find a bit about black air , just to confuse the topic a little more !!!!!!!!!!

all the information needed is here http://www.mine-explorer.co.uk/white_papers/6.pdf

I know this is an oldish thread.

That's why I use a 4 gas detector when I'm underground. To put it into context I was with a group in Ogof Dydd Byraf we'd stopped in a man sized passage waiting to go down a electron with a tight squeeze. In a relatively sort period, with people breathing in this small space the O2 topped to 19.2%. If you've ever done Ogof Dydd Byraf you'll know that the airflow is fairly good in there but there was a couple of occasions when the O2 dropped and I got some reading on the H2S and Methane.

Nice! The club Captain has recently obtained a gas detector for club use which we have yet to use but im sure will come in handy, As for the thread being old that dosent really matter for such an important subject which allways could do with a bump now and again.

M

An example of very bad air!!

It just became VERY important after tonights trip .... video coming up in the next few hours hopefully ...

Ian

you been somewhere naughty ?? do tell

We haven't been anywhere naughty, we have been in a "cave" (so you won't be interested ) but we did have an issue with air (or the lack of it) which you will see in the video when I can get it done. It is a genuine situation and was not staged - it does highlight the "bad air" problems extremely well.

The cave was the lower Afon Meirchion Cave in Cefn.



Ian

we do have a air monitor for such things . tut tut

.... and we had one with us .....

Quick question, where is the popcorn emoticon?

IMHO anything less than a 4 gas is next to useless.

'twas a BW Gas Alert Micro. As can be seen in video, O2 was down at about 19.2%. I posted a bit of info on the video clip at:

http://www.forum.ucet.org.uk/video-links-f12/caving-going-wrong-t658.htm