[HR3
Home Page]During the summer of 1996, members of HR3 located a new Tennessee pit that contained "bad air". After posting a note on TAGNET and the Cavers Digest, several cavers posted follow-up messages that gave information on detecting bad air in caves. After receiving permission from the authors of the articles, HR3 decided to make their articles (along with other information about bad air) available here.
The term "bad air" (aka "foul air"), when applied to caves, refers to cave air that has low levels of oxygen and/or high levels of other gases such as methane, ammonia or carbon dioxide. Relatively uncommmon, bad air is thought to be the result of decomposing vegetation, high quantities of bat guano, or nearby volcanic activity. In the case of methane, bad air can be inflammable.
As mentioned above, bad air can have several sources in caves.
With regards to the cause of elevated levels of carbon dioxide, one of the most common types of bad air, Garry Smith had the following comments:
"It is a proven fact that CO2 enters caves by several methods. Each method has a bearing on the gas ratio composition of the cave atmosphere and its variation to that of the above-ground atmosphere. The main methods in which CO2 gets into caves are :
- CO2 is absorbed by the ground water as it passes through surface soil containing high concentrations of the gas, due to the decay of vegetation. This water percolates through the rock strata and enters the cave system, usually taking part in the calcite deposition cycle. In this instance the addition of extra CO2 to the cave atmosphere displaces O2 and nitrogen (N2).
- Secondly, CO2 may be a by-product of organic and micro-organism metabolism or respiration by fauna such as bats or humans. Simply the oxygen concentration is reduced in proportion to the increase in CO2. The N2 concentration stays constant.
- The other factor which one has to consider is that in deep caves where air movement is minimal, CO2 will build up in the lower part of the cave. So, even though the CO2 may have entered the cave by one of the two above mentioned methods, a very still cave atmosphere may allow CO2 to sink to the deepest part of the cave and displace O2 and N2. Thus building up the concentration of CO2 to a higher concentration, at the lowest point in the cave (Smith)."
When considering the effects of bad air on humans, one must consider 1) the effects of increased levels of "bad air" components such as carbon dioxide, and 2) the effects of decreased oxygen levels due to displacement from the "bad air" component.
Considering the effects of decreased levels of oxygen, I cite William Halliday's book American Caves and Caving :
"In some areas, certain passages or entire caves are said to be so deficient in oxygen that matches, candles, and carbide lamps will not burn. At low altitudes, however, most humans lose consciousness before reaching so low a level of oxygen that a carbide lamp goes out. The oxygen content of normal cave air is about 20 percent. Candles go out at about 16 percent; 15 percent is the approximate beginning level of dangerous hypoxia (lack of adequate body oxygen) with increasing, unrecognized grogginess. At 12 percent the situation is critical, and in 7 to 8 percent oxygen death is rapid. Carbide lamps are said to burn in oxygen concentrations as low as 8 to 10 percent (Halliday,76)."
For a common bad air component such as carbon dioxide, Garry Smith notes the follow effects in his research:
"Carbon Dioxide (CO2) is the body's regulator of the breathing function. It is normally present in the air at a concentration of 0.03% by volume. Any increase above this level will cause accelerated breathing and heart rate. A concentration of 10% can cause respiratory paralysis and death within a few minutes. In industry the maximum safe working level recommended for an 8 hour working day is 0.5% .
"...To the novice caver the first encounter with foul air is often a frightening experience. Typically there is no smell or visual sign associated with foul air and the first signs are increased pulse and breathing rates. Higher concentrations of CO2 lead to clumsiness, severe headaches, dizziness and even death. Experienced foul air cavers can notice a dry acidic taste in their mouth, however the average caver may not notice this effect (Smith)."
A summary of the effects from both oxygen reductions and carbon dioxide increases was provided by Smith in his research. They are given below (used with permission) :
| O2% by volume | Symptoms |
|---|---|
| Reduced from 21 to 14% | First perceptible signs with increased rate and volume of breathing, accelerated pulse rate and diminished ability to maintain attention. |
| Between 14 to 10% | Consciousness continues, but judgment becomes faulty. Rapid fatigue following exertion. Emotions effected, in particularly ill temper is easily aroused. |
| 10 to 6% | Can cause nausea and vomiting. Loss of ability to perform any vigorous movement or even move at all. Often the victim may not be aware that anything is wrong until collapsing and being unable to walk or crawl. Even if resuscitation is possible, there may be permanent brain damage. |
| Below 6% | Gasping breath. Convulsive movements may occur. Breathing stops, but heart may continue beating for a few minutes - ultimately death. |
| Concentration | Comments |
|---|---|
| 0.03% | Nothing happens as this is the normal carbon dioxide concentration in air. |
| 0.5% | Lung ventilation increases by 5 percent. This is the maximum safe working level recommended for an 8 hour working day in industry (Australian Standard). |
| 1.0% | Symptoms may begin to occur, such as feeling hot and clammy, lack of attention to details, fatigue, anxiety, clumsiness and loss of energy, which is commonly first noticed as a weakness in the knees (jelly legs). |
| 2.0% | Lung ventilation increases by 50 percent, headache after several hours exposure. Accumulation of carbon dioxide in the body after prolonged breathing of air containing around 2% or greater will disturb body function by causing the tissue fluids to become too acidic. This will result in loss of energy and feeling run-down even after leaving the cave. It may take the person up to several days in a good environment for the body metabolism to return to normal. |
| 3.0% | Lung ventilation increases by 100 percent, panting after exertion, Symptoms may include:- headaches, dizziness and possible vision disturbance such as speckled stars. |
| 5 - 10% | Violent panting and fatigue to the point of exhaustion merely from respiration & severe headache. Prolonged exposure at 5% could result in irreversible effects to health. Prolonged exposure at >6% could result in unconsciousness and death. |
| 10 - 15% | Intolerable panting, severe headaches and rapid exhaustion. Exposure for a few minutes will result in unconsciousness and suffocation without warning. |
| 25% to 30% | Extremely high concentrations will cause coma and convulsions within one minute of exposure. Certain Death. |
I cite Halliday's book American Caves and Caving :
"Except in some geothermal caves, abnormally high levels of carbon dioxide (CO2) cause or accompany all oxygen deficiences in North American caves. Natural processes cause CO2 levels of 1 to 2 percent in parts of many American caves, and higher levels in a few. The human body can survive surprisingly high concentrations of CO2. In caves it is distressing rather than lethal, and it serves as a valuable early warning signal of dangerously low levels of oxygen. Although 2 or 3 percent is about the maximum that will permit strenuous exertion, Australian "bad air cavers" have learned how to function in levels as high as 6 percent... CO2 is heavier than ordinary cave air, and cavers' breathing may further aggravate the oxygen-CO2 ratio - especially in deep, narrow holes. This becomes especially dangerous in rescues, particularly when the victim is wedged. In a 1977 rescue in Twiggs Cave, Maryland, oxygen readings were as low as 13 percent and CO2 possibly as high as 18 percent. Rescuers' mental processes were drastically slowed and confused. Work normally requiring a few minutes took four times as long. Despite use of air hoses and tanks, exhaustion and vomiting were common among the rescuers... Discretion rules. Anyone developing rapid, labored breathing in any section of any cave for any reason should get out immediately (Halliday,77)."
Yet again, I cite Halliday's book American Caves and Caving :
"Explosions of inflammable gases in caves are rare, yet probably more lethal that 'bad air'. One exception seems, at least so far, to be curious and amusing rather than harmful: exploding bubbles of inflammable gases trapped in stream-bottom mud in caves in the southeastern United States. Such gas -- probably methane or a mixture of similar gases -- results from the decomposition of plants swept into caves by storm waters. Momentary fireballs flare when cavers wade through such passages with carbide lights held at stream level. Large fireballs are dangerous. Cavers have been burned in West Virginia's Buckeye Creek Cave and elsewhere. Pockets of such gases might be expected where such streams end in siphons, but so far the ventilation of those caves seems to have been efficient. Potential hazards are so serious, however, that the National Cave Rescue Commission now recommends that no one use carbide lamps, candles, or any other open flame in such areas (Halliday, 78-9)."
For the answer to this question, caver Butch Fralia had this to offer on the Cavers Digest :
"I've followed the air quality measurement comments of the last few Digests with great interest. Over the last nine years I've participated in a volunteer cave research project at a Texas State Park. Of the 150+ caves on the park, the majority have some level of measurable CO2 accumulation ranging from detectable to deadly. Over the course of this project, the state has furnished air quality instruments for our use. One is an electronic oxygen meter (no longer available) and a Draeger device as mentioned by Mark Minton in Digest 5333. [Note: See below.] Using these instruments, we've taken literally thousands of air quality measurements.
"The Draeger instrument was by far the most reliable. The problem with the Draeger is the high cost of the tubes, of which one is expended with each measurement and not reusable. The Oxygen meter has a probe that must cleaned often and replaced about every three months. I don't know if later model instruments have this same problem. The oxygen meters are calibrated on the surface at 21% oxygen. It's easily knocked out of calibration while moving through tight passage areas.
"Unless a caver is involved in a research project such as the one on the state park, the cheapest and most reliable air quality instrument available is a BIC lighter. It can be obtained for about $0.97 at any convenience store and easily replaced when damaged or depleted. It's within the budgetary range of anyone who can afford to go caving in the first place. This may sound like a cop out to the folks who've offered all the fine advice on air quality instruments but......read on gentle caver!
"When caving in the Arbuckle Mountains, the BIC was the air quality instrument of choice though at the time, no one knew how reliable or accurate it was at the time.
"During the course of the state park project, we became curious at what oxygen levels the lighter would start reacting. Using the instruments we set up a number of controlled experiments and verified them with a number of repetitions over several years with different brands.
"The lighter will start reacting at 19.5% oxygen. The flame changes color and a small gap will begin to be noticeable between the flame and the jet. At 18% oxygen, the flame will burn about 1 inch above the jet. At 17% oxygen, the lighter goes out and can not be relit. As mentioned earlier, these measurements were very repeatable and could be verified by anyone with the instruments to do so.
"In our tests, 99% of the time the oxygen was displaced by an equal amount of CO2, such that 17% oxygen = 4% CO2. This was not always the case! In two caves, the measurements were typically out of balance where the CO2 was 2% higher than indicated by the oxygen level. This was repeated over years of data! At the very least, when the lighter no longer burns, STOP!
"I should mention at this point that the physiological effects of bad air result from the CO2 rather than oxygen deprivation! Most cavers, unless they are asthmatic, can tolerate 17% [O2] without much difficulty; they will breath heavier than normal for the amount of work being performed. At CO2 levels > 2%, the caver should cave slowly! Especially when climbing! High CO2 will result in a much higher rate of breathing, the skin will be flushed to pink, and you feel hotter than you'd expect in a 68 degree cave. Hallucination, panic and even passing out are typical reactions, especially when the CO2 level is greater than 4%. Coming back to the surface, headaches and even severe nausea may be experienced. This can be prevented by stopping in an area that has between 18% to 19% oxygen for at least 15 minutes before moving on to normal air. Those of us who smoke seem to be able to handle higher levels of CO2 than non-smokers since we're used to poor air quality anyway.
"If you can afford it and want to play, buy the Draeger for a reliable and accurate instrument, otherwise 'Flick you BIC!' (Fralia)"
Garry Smith comments further on the "Bic lighter test":
"Because an elevated CO2 concentration in caves corresponds to a depletion in O2, cavers have for many years used the naked flame test to determine whether the cave atmosphere contained an elevated level of CO2. The naked flame test involves lighting a match or cigarette lighter in the cave air, or carrying a burning candle into a suspected foul air area of the cave and the flame would extinguish when a particular concentration was reached. This test has in the past been widely accepted by the caving fraternity as a fairly accurate indications of percentage concentrations. During January 1997, I undertook extensive testing in controlled atmospheres which revealed that the Naked Flame Test is not a reliable test of CO2 concentrations, other than to indicate that the cave atmosphere is most likely dangerous to human life. In fact the naked flame is only measuring the O2 concentration and the CO2 has such a small influence over combustion that it can be ignored within the concentration range found in caves (Smith)."
So - even though the flame test is not a reliable one and can't be used to test carbon dioxide levels, it appears to be the only cheap testing alternative available to cavers to measure reduced oxygen levels. Smith gives the following advice:
"If sophisticated measuring equipment is not available, the best advice is to carry out a 'Naked Flame Test' when you or a member of your group experiences the first signs of labored breathing, headaches, clumsiness, loss of energy or any of the other signs associated with elevated concentrations of CO2. Ideally cavers should use a cigarette lighter flame. This will reduce the amount of unpleasant fumes emitted from matches burnt by people experimenting in the confines of a cave. The best advice is, 'If in doubt, get out', in an orderly manner (Smith)."
For the answer to this question, caver John Lyles had these comments on the Cavers Digest :
"...I looked into inexpensive but usefully accurate instruments for the determination of bad air. To keep price low, single gas units were considered. CO2 is not usually available, instead CO. So I looked at oxygen deficiency meters alone (Lyles)."
Lyles listed these units:
| Unit | Cost, US dollars | Features | Contact |
|---|---|---|---|
| EPD model 450 OX | $299 | Oxygen sensor alarms at <19.5%; Settable over 0 - 25%; Has digital readout of level |
EPD 14 Hayes Street Elmsford, NY 10523 (800) 892-8926 |
| Davis model OX1 | $350 | Alarms at 19.5%; Similiar to EPD but no readout of actual value; Accuracy specified at +/- 1% from -5 to 113 deg F; Weight 3.8 oz |
Davis instruments 4701 Mount Hope Drive Baltimore, MD 21215 (800) 368-2516 |
Caver Mark Minton also mentioned use of a device called a Draeger, but no source of the device was mentioned.
Here are some experiences from caver Mark Minton, from the Cavers Digest :
"The recent comments about air quality measurement have centered around relatively expensive meters or grossly crude flame tests. A fairly accurate middle ground consists of "Draeger tubes" which are small glass tubes filled with an indicating compound that changes color upon exposure to a specific gas. They are simple to use. Just draw the specified volume of air you want to test into a pipette and pass it through the tube. The tube is graduated so that you can read off the concentration of the gas of interest contained in your air sample, in this case CO2. I do not know how expensive they are or where to get them, but I could probably dig that up if anyone is interested. They can't be too costly, as they are disposable (one use each). I have used them in a notorious bad air cave (Kaisers) here in Texas. We found near normal CO2 at the lip of the 10-m entrance pit, a few per cent half way down, and a whopping 9% at the bottom.
"By the way, you can't breathe 9% CO2 for long, as the first person down the pit discovered to her horror. Fortunately we came prepared with small scuba tanks and got her hooked up to one quickly. We hadn't expected the high CO2 to start that close to the entrance. I did the measurements later using a tank to breathe out of as I descended. Obviously some way to remotely sense the air would be preferable in vertical situations where one could suddenly end up in a dangerous environment. I have heard of someone descending a drop and passing out due to bad air! (I believe that was at the bottom of Sotano del Arroyo in Mexico in the '60's). In addition to CO2, methane can be a bad air component if there is organic debris decomposing underwater. In sufficient quantity, especially in the right mix with air, this could be very dangerous to carbide cavers. I purposely ignited large plumes of flame as I trudged through submerged methane laden silt in Sotano de Japones, in the same area of Mexico (El Abra). I certainly didn't want to wait until the gas reached head level to ignite on its own! Also in that area a caver free dove a sump and came up into a pocket of unbreathable air. He passed out and was rescued when his lifeliners saw his light drifting to the bottom of the water and hauled him out. There had been no sign of bad air on their side of the sump. That would be an especially difficult situation to test remotely.
"Oxygen levels are much less important, since normal breathing is inhibited by high CO2, even if the oxygen level would otherwise be breathable. Measuring oxygen would thus not be the best way to determine air quality. If you suspect seriously bad air, go slowly and take plenty of precautions (Minton)!"
Fralia, Butch. "Air Quality Measurements." Cavers Digest
(Internet Mailing List) July 2 1996.
Halliday, William. American Caves and Caving. (Revised Edition) New
York:Harper & Row, 1982.
Lyles, John. "Air Quality Indicator." Cavers Digest (Internet
Mailing List) June 25 1996.
Minton, Mark. "Air Quality Measurement." Cavers Digest (Internet
Mailing List) July 1 1996.
Smith, Garry. "Carbon Dioxide, Caves and You." Proceedings of the 21st
Biennial Australian Speleological Federation Conference 1997.
A condensed version of Smith's comprehensive paper is available for viewing here. (Used with permission)
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