How to adapt decompression procedures to exceptional dives?

Authors:

Gouin E, Dugrenot E, Gardette B. Diving Hyperb Med (2025) 

Article summary:

Deep diving presents significant physiological challenges for humans. The recent rise of closed-circuit rebreathers (CCR) has enabled more divers to reach unprecedented depths. This study, conducted by Emmanuel Gouin, diver and expedition physician for Under The Pole, in collaboration with the medical and physiology team involved in the CAPSULE program, explored the physiological limits and challenges of extreme deep diving and the strategies developed to overcome them. 

This study is based on the experience of deep divers. Eight CCR divers (one woman, seven men) with experience beyond 200 meters were interviewed about the preparation, planning, and execution of such dives. The profiles of their deepest dives were analyzed. All were highly experienced divers with dives ranging from 209 to 302 meters deep. The results show that gas usage procedures (gas density, ppO2) and decompression procedures (ascent rate) do not comply with current recommendations in order to reduce decompression time (ascent time). In fact, decompression could take more than 10 or 15 hours for the deepest dives, exposing divers to other risks such as cold, dehydration, etc. However, failure to follow the recommendations led to decompression sickness in three out of eight divers after their deepest dives. 

The study highlights the uncertainty surrounding compliance with deep diving standards and points to the importance of rigorous dive preparation, the use of rebreathers suitable for very deep diving, surface safety support, and divers' technical skills in order to reduce the risks, which remain excessively high, of deep diving. The use of a dry underwater habitat could improve decompression conditions for divers (allowing them to eat, drink, stay dry, etc.) and encourage compliance with the inevitably long decompression times.