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Chapter 2 — 14
Air contaminated by carbon monoxide, if supplied in scuba cylinders or by surface supply to
divers, may have lethal results (see Chapter 23).
Helium – He
This is a colourless, odourless, tasteless gas, which is very light and very expensive. It is
obtained from underground natural gas sources found in North America and elsewhere.
It is used to dilute O
2
in gas mixtures breathed at great depths because it has little tendency to
produce narcosis (e.g. Heliox may be 90% He + 10% O
2
, or any other proportion).
Due to its very low density it readily escapes through small leaks in pipes and valves making
it difficult to retain. It is also a very effective conductor of heat, causing serious problems with
hypothermia
.
The low density of He alters the normal process of speech production causing "
Donald Duck
"
like
speech when a diver breathes this gas.
Hydrogen – H
2
This is a very lightweight gas that can replace N
2
to reduce narcosis at depth. Unfortunately it
can combine explosively with O
2
and the resultant water (H
2
O) is not sufficient to 'put out the
diver'. It is sometimes used with very low O
2
percentages, at great depths, by skilled
professional divers. It shares many problems with He.
Inert Gases:
Neon – Ne, Argon – Ar,
Radon – Rn, and Xenon – Xe
These are more biologically inert gases which are present only in trace amounts in the
atmosphere. They are of no importance to recreational divers.
Oil Gases
Because of lubrication needs in the compressor, oil vapors and hydrocarbons can be produced
which may then contaminate the air supply. See Chapter 24.