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Chapter 5 — 15
A modern variant of this
system is used today in deep
diving. It utilises a smaller,
light-weight fibreglass or
aluminium helmet or mask in
conjunction with a dry or
warmed wet suit, enabling the
diver to swim and move more
freely. The tethering line may
go to the surface or a diving
bell. The diver usually
breathes gas mixtures which
include helium, to prevent the
development of nitrogen
narcosis.
Fig. 5.17
A modern professional diving mask in rear
with Standard Dress helmet in the foreground.