By Garry K. Smith 1997

(I have only listed the conclusion of this excellent article on Carbon Dioxide in caves. Garry Smith has graciously allowed us to place his article on our board. He describes the symptoms and causes of bad air in caves and how to do in field testing. The full text reference is listed below. Please refer there for the complete article. I have also included several tables by Garry Smith)

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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.

Laboratory tests have proven that combustion of a match, candle or butane cigarette lighter will cease at about 14.5% to 15% concentration of oxygen. Twenty one percent (21%) being the oxygen concentration in normal atmosphere. Bearing in mind that humans on average breath out air containing 15% oxygen and this is enough to revive a person using mouth to mouth resuscitation. In fact humans can survive in an atmosphere containing 10% oxygen, so when the flame test just fails it is still measuring an atmosphere containing enough oxygen to survive.

The real danger is the carbon dioxide concentration which is the main trigger for the human body to increase the breathing rate. Prolonged exposure to a concentration of just 5 or 6% may be enough to cause suffocation. In the majority of cases, if a person has any of the symptoms of elevated carbon dioxide levels, a simple naked flame test will fail to ignite. This is a sure sign of foul air and it is time to get out.

Carbon dioxide when treated with respect is no worse than the other dangers in caves. Despite the possible dangers, caving is still safer than driving a motor vehicle, which most of us take for granted.

Comments are most welcome. Direct to Garry K. Smith via Electronic mail at or by snail mail to "5 Fourth St Seahampton 2286, NSW Australia"

Flame Conditions in relation to Percentage O2 in Air

MatchCandleButane Cigarette Lighter
21%-18% easily burns all of match>19% normal flame
17.5% Burns head and flame transfers down paraffin to wooden splint on most occasions17%-16.5% burns with elongated flame.
17%-16.5% ignited head and on nearly every occasion, burns down onto paraffin coating then extinguishes. 16.5%-16% flame begins to shrink, but candle remains alight
16%-15.5% ignited head just ignites paraffin coating on splint (some matches only)16% burns slowly with small flame
15% - head burns briefly with whispery flame & goes out.<15.0%, a burning paraffin candle is extinguished>15% O2, A Butane Cigarette Lighter can easily be lit and will stay alight.
14.5% - weak blue flame with orange top, just stays a light
<14.25% - Flame will extinguish
14% match head burns very briefly & goes out. (burns due to the O2 in potassium chlorate contained in the head.)14%-13% Large flashes of flame but will not stay alight
<13% head flares & extinguishes immediately (less than 0.5 seconds)12.5% sparks with partial ignition, small fireballs
<10% - no ignition, only hot sparks from flint.

Effects of CO2 on Humans

0.03%Nothing happens as this is normal
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 ventilaton 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 incrased by 100 percent, panting after exertion. Symptoms may include: headahces, 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.
25-30%Extremely high concentrations will cause coma and convulsions within one minute of exposure. Certain Death.

Effects of O2 deficiency on Humans

If we consider an atmosphere consisting of just N2 and O2, where the O2 is at a lower concentration than the normal atmosphere, the human body would be affected in the following manner.

Table 3. Generally accepted physiological effects of reduced O2 concentrations.

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.