'Air' - An Article.

[Tim Watts]

I've chosen to do a couple of lengthy trips recently in places containing 'bad' air.

Its prompted me to post this not to scare anyone but because its important that people have the knowledge to make their choices - and recognize potential symptoms!

See below:

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Bad Air, Gases, Caves (& Mines!)

by  Robert B

This article was written to provide some basic information on the various kinds of gases and bad air that may be encountered in caves. It is not intended to make anyone paranoid about going into caves.  An understanding of the potential hazards may help to reduce the risk of accident. The vast majority of caves have a good flow of air, so accumulations of the gases listed below will be in such small amounts they will not be harmful to those passing through. However, during your caving lifetime, you will probably encounter bad air and one or more of the gases listed below in accumulations that may be harmful to you.

Gases that can be encountered underground may be toxic, flammable, or asphyxiating. Most gases found in caves are naturally occurring, and are hard to detect without instruments. Naturally occurring gases found in caves are; carbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4), nitrogen (N2),  nitrogen oxides (NO) (NO2), and radon, Rn @ wt (C12) 222 or (O16) 222 @ no 86.

Also, some caves have what is commonly called "bad air". Bad air in caves is usually caused by either poor air flow, or oxidation of sulfides  that deplete air of oxygen content, leaving only nitrogen and/or carbon dioxide. Another name for bad air is:

Oxygen, (O2) deficiency, --- Normal oxygen content of air is 20.9%. When the oxygen content drops below 19.5% the air is considered oxygen deficient, even though many people can work when oxygen content is as low as 17%. Any place in a cave where there is poor air flow can be oxygen deficient, and if you are exerting yourself, your respiration will decrease the oxygen, and increase the carbon dioxide. In an oxygen deficient atmosphere the mind does not function properly, and you may not recognize any symptoms of danger and remain in the oxygen deficient atmosphere, or continue into a more dangerous area until you black out. People react differently to oxygen deficiency, and a given person may not always react in the same way. You should listen to what your body is telling you, and it will generally tell you when something is wrong. If your respiration rate changes dramatically for no apparent reason, leave immediately. * *  ..."flame of a lighter forms a gap between flame and nozzle at 18.5% (O2).   1 inch gap between flame and nozzle at 17.5% (O2), and lighter goes out but can be relit. At 17% lighter can't be relit, and this is where most cavers would bail out of a trip"...

Carbon dioxide, (CO2)-- is colorless, heavier then air and sinks to the low passages in caves. In high concentrations it may displace oxygen and be an asphyxiant. Carbon dioxide concentrations occur when oxygen is depleted by oxidation of sulfides and magnetites, and the sulfur combines with ground water creating a weak acid that reacts with carbonate rocks to generate carbon dioxide. Carbon dioxide also responds to barometric changes by flowing out of the rock when pressure is low, and in when pressure is high. Walking through these gases will stir them up, and they can displace enough oxygen to cause a person to black out. Low concentrations of carbon dioxide can be detected by an alert person at levels that are not harmful. An increase in respiration rate should be noticeable at 0.5% (CO2). Respiration rate is twice normal at 3% (CO2) and 10%
(CO2) can be fatal after a few minutes.

Nitrogen, (N2)-- is the major component of the air we breathe, (about 79%),but at elevated concentrations it replaces oxygen and is an asphyxiant. It is slightly lighter then air. Like carbon dioxide, nitrogen can be present in high concentrations if the oxygen is depleted by oxidation of sulfides. Nitrogen also is generally related to barometric pressure, flowing into rock during high pressure, and out during low pressure. The flow of gas will be greater if the rock is highly fractured, or from open water courses. Dangerous levels can build up because gas will flow into rock at much slower rates then out. If oxygen levels are normal, nitrogen should be no problem.

Methane, (CH4)--- is colorless, odorless, highly flammable, and lighter then air. Methane can be expected anywhere there is carbonaceous rock. It presents two hazards; it is easily ignited in concentrations of 5% to 15% in air, in effect causing an explosion, and in higher concentrations it is an asphyxiant because it dilutes the oxygen. Methane, being light, accumulates in high places.

Hydrogen sulfide, (H2S)-- -is colorless, heavier then air, toxic and smells like rotten eggs at low concentrations. At high concentrations the sense of smell is deadened, and serious problems will result. Hydrogen sulfide can form from ground water and sulfides. If the slightest smell of rotten eggs is detected, leave immediately.

Radon gas, Rn @wt (C12)222 or (O16)222 @no 86---a heavy gaseous chemical element, is a decay product of uranium and other radioactive minerals. Radon gas presents a serious internal alpha radiation hazard to the lungs because it can decay to it's daughters while in the lungs. The daughters are particles
that adhere to the lining of the lung and can deliver considerable alpha energy to the lung in a short time. Radon levels are usually controlled by natural ventilation of a cave. Poor natural ventilation can result in high concentrations of radon over a number of years. Low oxygen generally indicates high radon, but normal oxygen can accompany high or low radon. So, if a cave is well ventilated, you will have little to worry about, unless you are going to be in the cave for long periods of time.

Radiation---hazards are of two types. The obvious hazard is gamma rays given off by uranium minerals. Alpha and beta radiation levels are hazardous only in extremely unusual conditions. The other hazard is from radon daughter products resulting from the decay of radioactive minerals as explained under radon.

[Ian A]

This is a really good article, I saw it somewhere once before and it is a great way to remain informed

[Tim Watts]

This one is even better and much more useful in terms of real figures, effects etc.

I fear that all to many people don't appreciate to dangers, and those who do may not be familiar with the symptoms. And even those who have/use gas meters might not understand what all the numbers mean.

We get it drummed into us at work and have to wear a quad gas meter all the time when out and about. It might seem a bit over dramatic at times - but there have been plenty of times in my direct experience where they have saved lives.

I regularly have to wear full Breathing Apparatus to enter confined spaces to gas test prior to giving the green light for a work party to enter, and also have to spend quite a bit of time on training courses and refresher courses in full BA conducting confined space rescues, casualty handling and stretcher handling with rope work operations etc. Believe you me, I'd hate for anyone to get rendered unconscious underground because their chances would be diddly squat.

So, even though i know much of the text might be a bit of a boring read, you owe it to yourself to give it at least a brief read through. Look for some of the symptoms and effects at very least and be mindful of how you are feeling underground.

Took me a few days to feel 'right' after a recent all day digging trip not so far from home where CO2 is know to 'pool'.


http://wasg.iinet.net.au/CO2ASFpaper.html

(also attached here as easy to read/print PDF version)

[mike leahy]

cracking article tim. well found