Validation of adapted DCIEM Heliox diving tables using nitrox decompression

For deep diving operations, Netherlands Navy divers use a breathing medium
called Heliox, which can be breathed at a constant fraction of 16% oxygen and
84% helium. During decompression on Heliox there is a requirement to decompress
on both air and oxygen. This type of diving is only done with Surface Supplied
Diving systems where an umbilical (gas hose) delivers the breathing medium to
the diver. The first stops during the decompression phase are conducted with
air and once the diver reaches 9 metres of sea water (msw), 100% oxygen is
used. This process therefore requires switching from the initial Heliox gas to
air and then to oxygen to complete the decompression requirement. Using nitrox
(60% oxygen and 40% nitrogen) as a decompression breathing gas could result in
a saving of about 10% to 15% in overall decompression times compared with the
standard heliox tables nowadays used. Furthermore only one switch in breathing
gas is necessary. A feasibility study performed by DRDC seems to underline this
hypothesis.

The proposed research intends to gather data to validate the hypothesis that
using Nitrox to decompress during Heliox diving will significantly decrease the
time and equipment requirements for decompression while being as safe as the
standard heliox tables nowadays used.

Observational study

Burden: all divers have to make 3-6 dives. Before the dive they have to fill in
a pre-dive questionnaire. During the dive they have to frequently score thermal
comfort. After each dive they undergo Doppler measurements for at least 3 times.

Benefits: For military diving, it is of importance to use safe diving tables.
Furthermore, diving tables with shorter decompression time could are
operational beneficial. However these shorter decompression times should not
lead to a higher incidence of decompression sickness (DCS).

Risks assessment, group relatedness: The risk of DCS associated with this dive
simulation can be considered as very small (< 1.0%). When a diver encounters
symptoms of DCS he will be treated according to the guidelines used within the
Royal Netherlands Navy, which are equal to those internationally used. Beside
the risk of decompression sickness, there is the risk for central nervous
system oxygen toxicity, which is estimated as < 0.01%. Furthermore, as
described in the information package subjects participating in this trial run a
small risk on hypothermia, hypercapnia, and hypoxia. All in all, we think the
risk of these simulations can be considered low, and equal to a real, wet
operational heliox dive.