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Chapter 2 — 13
O
2
supports combustion vigorously and can cause normally non-flammable substances (such
as the occupants of a recompression chamber) to burn brilliantly if it is present at a
sufficiently high partial pressure.
Divers should be aware of the potentially explosive and combustible properties of oxygen, as
they may require to use it in first-aid, or be inadvisably enticed into diving with high oxygen
mixtures.
Nitrogen – N
2
This gas, which is the major constituent of air, is also colourless, odourless and tasteless. N
2
dissolves well in body fluids and tissues, causing
narcosis
at depth and
decompression
sickness
when it bubbles out of solution, after ascent.
It is termed an
"inert gas"
because it does not take part in human biochemical processes. The
Creator appears to have included this gas in air to prevent us from developing O
2
toxicity, and
to reduce the fire hazard.
Divers vary this N
2
/O
2
ratio (in Nitrox, oxygen enriched air or mixed gas diving) in an
attempt to improve on nature, extend diving durations, and reduce narcosis.
Carbon Dioxide – CO
2
This gas is also colourless, odourless and is said to be tasteless.
However if a diver inhales a mouthful of CO
2
from a buoyancy
vest inflated from a CO
2
cartridge it will be found to taste very
nasty, due to its formation of carbonic acid in water.
CO
2
is a by-product of cellular metabolism and we exhale
approximately 5% of CO
2
in our breath.
If a diver rebreathes some of his exhaled gas by using faulty
breathing equipment or an excessively long snorkel the CO
2
will accumulate in the body leading to toxicity. These effects
are discussed further in Chapter 22.
Carbon Monoxide – CO
This gas is colourless, odourless and tasteless. It cannot be detected by a diver and even in
trace amounts can cause loss of consciousness or death.
It is usually produced as a product of incomplete combustion of carbon containing compounds
and is a constituent of internal combustion engine exhausts and cigarette smoke.