(3) Water Vapor. The respiratory system can tolerate a wide
variation in the amount of water vapor contained in the air. Experience has
shown that the relative humidity in breathing gas should be at least 30
percent to prevent lung irritation. A relative humidity of over 90 percent
can be tolerated but condensation becomes a problem with equipment operation.
In general, the relative humidity of breathing gas should be between 50 and
70 percent.
(4) Hydrocarbons represent some of the most significant classes of
contaminants which may be present in a sealed environment.
(a) Sources. Sources of troublesome hydrocarbon contaminants
include (1) organic solvents in the form of paints, paint thinners, alcohols,
degreasing and dry cleaning agents, adhesives, metal cleaners, etc.; (2)
lubricating and fuel oils; (3) certain normally nonvolatile plastics (vinyls
and Teflon for instance) which, if subjected to high temperatures, will exude
toxic fumes; and (4) chamber inhabitants. Strict attention shall be paid to
not only what is used in the chamber but also what is locked in during
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