In the very first ANDYSEZ I suggested that this series would benefit from a little feedback - I don't know what problems or concepts or whatever you are interested in, so you have to put up with my current preoccupations in these notes. Lets have some ideas, folks! This topic arises out of the need to prepare a leaflet for Bungonia on "foul air". Two earlier ANDYSEZs (in Newsletters 5 and 6) discussed carbon dioxide in caves from the point of view of karst chemistry. Now we are going to take a look at carbon dioxide in caves in relation to the cave visitor's chemistry. There are good discussions in James et al. (1975), James (1977), James and Dyson (1981), Halbert (1982), Osborne (1981, 1990).
Foul air is often raised as a hazard in caves and it certainly can be. Caves at Bungonia, Molong and Wellington in NSW and the lava tubes at Undara, for example, can have hazardous - even lethal levels of carbon dioxide. First let's review what we are dealing with. As you all know from reading the earlier ANDYSEZs carbon dioxide is a natural component of above ground and cave atmospheres. It occurs at levels of around 0.03% in the atmosphere and is usually slightly higher in caves where it plays a critically important role in the dissolution of carbonate rocks and in the mechanisms of speleothem deposition. In some caves very high levels of the gas can occur to levels which certainly do not support human life. Over 12% has been recorded from Wellington!
As I have observed before - nothing is simple. Remember that the dry atmosphere consists of nitrogen (~78%), oxygen (~21%) and various other gasses. We need oxygen and carbon dioxide (we will see why later), and the others are more or less irrelevant. James et al. (1977) point out that there are three types of foul air. Water vapour levels dilutes the other gasses and a moments thought will reveal that high humidities will exacerbate some of the problems discussed below.
Type 1 is found in caves in which speleothems are being deposited and arises from carbon dioxide outgassing from the depositing solutions. Carbon dioxide increases in the cave atmosphere diluting oxygen and nitrogen.
Type 2 is more complex and is produced by the metabolism of living organisms. In this case there is increased carbon dioxide and nitrogen and a decrease (not dilution) of oxygen.
Type 3 has high carbon dioxide, low oxygen and higher than expected nitrogen and other gases. It is produced by a number of causes including bacterial action under anaerobic conditions, fermentation and the injection of pollutants. In this case the oxygen has been diluted.
We need carbon dioxide to breathe; this gas triggers the breathing reflex and you would die if you enter a nitrogen/oxygen atmosphere with no carbon dioxide. Increasing levels of carbon dioxide cause a variety of problems which are summarised in the following quotation and table from James and Dyson (1981, p55):
If any work is undertaken then further quantities of carbon dioxide are produced, and must be eliminated by blood stream and the lungs, a route whose efficiency is now much decreased. Hence any increase causes a proportionate decrease in physical work capacity ... in many cave atmospheres an increase ... also means a decrease in oxygen levels so the effects are compounded. [remember the water content!]
... observed two types of individual response ... the common response is hyperventilation with some degree of ... (an expanding of the blood vessels near the skin resulting in redness); these subjects are commonly referred to as "pink puffers". A small minority do not hyperventilate but show signs of cyanosis (reduced oxygen in blood) and are called "blue bloaters". The reaction of the "pink puffer" is normal. That of the "blue bloater" is considered abnormal, or is at any rate a greatly reduced response to a raised carbon dioxide in the inspired air. Cyanosis occurs because hyperventilation is absent, causing lowered oxygen levels in the lungs. A "blue bloater" will therefore be in extreme danger ... in which he [or she] will suffer hypoxia and may become unconscious without warning. A known "blue bloater" should never enter a region of carbon dioxide without the warning companionship of a "pink puffer".Physiological Effects of Increasing Carbon Dioxide Concentrations [body at rest]
| Inspired CO2 (% in dry air) | |
| 0.1 | Effect not noticeable |
| 1 | Slight increase in rate & depth of respiration |
| 3 | Ventilation is doubled, slight headache common |
| 4 | Ventilation almost trebled, throbbing headache, flushed face, nausea, sweating |
| 5 | Ventilation more than trebled, nausea, headache, vomiting on removal |
| 6 | Ventilation six-fold, can be tolerated for several hours |
| 10 | Intolerable to breathe for more than a few minutes |
| 12 -15 | Unconsciousness within minutes - death follows. |
I can vouch for the six-fold breathing in 6% - the uncontrollable, runaway breathing is both physically exhausting and mentally disturbing.
Other than the fact that we are either pink or blue, and puffing or not puffing, how do we tell how much carbon dioxide there is around. Firstly we can buy gadgets ranging in price from around $250 to many tens of thousands. Neville Michie has recently developed a super system for both long term monitoring and spot use at Jenolan - I am sure he would be more than happy to quote! Or perhaps more immediately with can light a match, candle or gas cigarette lighter. Osborne (1990) citing and expanding upon James et al. (1977) use the following:
These figures relate to Type 2 (normal) 'foul air'. Matches are extinguished, and will not light, in air containing more than about 1% 2. As a general rule cavers are advised that if a match wont light they should get out [calmly]. Once ignited, candles will burn in up to 4% CO2. At about 4% candles are extinguished. Higher concentrations, approximately 6% are required to extinguish gas flames such as carbide lamps and gas cigarette lighters. Gas flames separate from the jet and elongate before extinguishing.
James et al (1975) and to a lesser extent James and Dyson (1981) provide some information on caver safety, first aid and so on. Irwin (1988) describes a homemade breathing apparatus for use in caves with elevated carbon dioxide levels.
What we have not discussed here is the issue of elevated carbon dioxide levels in tourist caves. There are two issues here and we will go into neither of them in depth. The first is the impact on guides and visitors. Osborne (1981, 1990), following on mining industry regulations, suggests that 0.5% should be the highest level that can be safely accepted for day-to-day work and considering that we do not know anything about our client's level of health and fitness - we should be careful and not expose our visitors to high levels. Judging by the way they puff coming up out of Jersey Cave at Yarrangobilly their fitness can't be high. Speaking of which, I recently read about a proposed development in China that was expected to have 2,800 steps in three kilometres!
The second issue is that of the re-dissolving of speleothems. Go back and read the ANDYSEZs in Newsletters 5 & 6. Les Kermode (1980) suggests that speleothems will start to be corroded when carbon dioxide concentrations reach above about 0.24%. The ANDYSEZs will indicate that it is more complicated than that - but it is a problem to be thought about! However, space precludes a full discussion here. But, remember the hazards attendant on artificially ventilating your cave.
There must be something good about CO2. There are at least four things! First, it makes you breathe. Secondly, it helps excavate caves and grow stals. And thirdly, as Howarth and Stone (1990) point out a whole variety of obligate cave dwellers need this useful gas to survive. And champagne!