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sometimes not possible and the divers had to undertake their heavy tasks in
the slurry on feeling.
The greatest pressure under which the divers operated during the construc-
tion of the tunnel was about 7.5 bar. This was unheard of, and called for the
development of special techniques which applications would generally only
be found in the offshore-industry.
Dependent on the depth of the activity, various diving methods can be differ-
entiated. Up to a certain depth and also dependent on the duration of the oper-
ation, no special breathing apparatus was necessary and the divers inhaled
compressed air. At greater depths the divers made use of special gas mixtures
which they inhaled via a helmet. In periods in which lengthy operations had to
be undertaken under great pressure, the saturation diving technique was
applied.This meant that the divers did not come to the 'surface' pressure every
time, but between the activities they were also kept under pressure in a pres-
sure cabin. The divers then spent a longer amount of time in a cabin outside
the tunnel which was furnished as an accommodation.This made it possible to
avoid extremely long decompression periods.
Medical support
Before the boring activities commenced, all the aspects related to the diving
were extensively examined. In this, a number of doctors who are specialists
on diving were also involved. In the Netherlands it is a requirement that an
extensive working plan is drawn up together with an accompanying risks
analysis. This plan must be approved before the activities may commence.
Medical support during the entire duration of the project was desired and a
decision was made to have a medical specialist permanently present.
Furthermore, during the activities, a MAD-B diver (Medical Aid Diver) always
formed part of the diving team. All the divers involved (before, during and after
the activities) were subjected to extensive medical examinations such as a 'neu-
robehavioral evaluation system'. At the end of the project and after a couple of
years, the tests will be repeated to examine if it involves long term effects.
Fig. 11.28
The transportation of
the divers in the
pressure-shuttle
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