Chapter 5 — 1
This chapter has been included to explain the operating principles and the limitations of some of the
equipment currently used in free and scuba diving.
FREE DIVING EQUIPMENT
The reason we go diving is to view the spectacular underwater world. Unfortunately, our eyes are
designed to see through air. In water the view is blurred and distorted – and somewhat magnified.
The latter is the reason why divers exaggerate the size of the fish they see. Fishermen, who examine
their catch on the surface, do not have such an excuse for their blatant lying.
The way we compensate for the water/air interface distortion, is to add an air space in front of our
eyes. This can be achieved by air-filled contact lenses, swimming goggles or face masks. The last of
these is used by divers.
The variety of face masks on the market suggests that the ideal mask has not yet been developed for
the multitude of different face shapes.
The mask should cover the eyes and nose but not the mouth. Having the nose included allows the
diver to exhale into the mask to compensate for the changes in water pressure, and so prevent face
mask squeeze (see Chapter 12). The ability to exhale into the mask is also essential to clear a face
mask flooded with water. The mask should be shaped so that the diver's fingers can reach and block
his nostrils, to make ear equalising easier.
Ideally, the mask should have a small air volume so as to reduce the effort needed to equalise water
pressure during breath-hold diving. The face plate should be close to the eyes, to maximise the field
of vision. With a basic face mask this is limited by the nose. This problem could possibly be
overcome by radical nasal surgery, but is best achieved by an indented rubber nose piece which
allows the glass to be brought closer to the eyes. Clear plastic or glass side panels may also possibly
help. Although this arrangement generally improves peripheral vision, th