The precise determination of the type and concentration of the constituents of
breathing gas is of vital importance in many diving operations. Adverse physiological
reactions can occur when exposure time and concentrations of various
components in the breathing atmosphere vary from prescribed limits. Analysis of
oxygen content of helium-oxygen mixtures shall be accurate to within + 0.5
percent.
The quality of the breathing gas is important in both air and mixed-gas diving. In
air diving, the basic gas composition is fixed, and the primary consideration is
directed toward determining if gaseous impurities are present in the air supply (i.e.
carbon monoxide, hydrocarbons) and the effects of inadequate ventilation (carbon
dioxide). Using analytical equipment in air diving is not routine practice. Analytical
equipment is generally employed only when it is suspected that the air supply
is not functioning properly or when evaluating new equipment.
Gas analysis is essential in mixed-gas diving. Because of the potential hazards
presented by anoxia and by CNS and pulmonary oxygen toxicity, it is mandatory
that the oxygen content of the gas supply be determined before a dive. Oxygen
analysis is the most common, but not the only type of analytical measurement that
is performed in mixed-gas diving. In deep diving systems, scrubbing equipment
performance must be monitored by carbon dioxide analysis of the atmosphere.
Long-term maintenance of personnel under hyperbaric conditions often necessitates
the use of a range of analytical procedures. Analyses are required to
determine the presence and concentration of minor quantities of potentially toxic
impurities resulting from the off-gassing of materials, metabolic processes, and
other sources.
The constituents of a gas may
be analyzed both qualitatively (type determination) and quantitatively (type and
amount) using many different techniques and instruments. Guidance regarding
instrument selection can be obtained from NAVSEA, NEDU, or from instrument
manufacturer technical representatives. Although each technique is not discussed,
the major types are listed below as a reference for those who desire to study them
in detail.
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Mass spectrometry
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Colorimetric detection
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Ultraviolet spectrophotometry
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Infrared spectrophotometry
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Gas chromatography
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Electrolysis
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Paramagnetism
