Prof. Simon Mitchell

Simon works as an anaesthesiologist at Auckland City Hospital, a diving physician at North Shore Hospital (Auckland), and is Professor of Anaesthesiology at the University of Auckland. He is widely published in the diving medicine field with over 180 books, book chapters and scientific journal articles. For the last 3 years he has been ranked by Expertscape.com as the world’s foremost expert in decompression sickness. Simon co-authored the hyperbaric and diving medicine chapter for the last four editions of Harrison’s Principles of Internal Medicine. Simon was in the first teams to dive and identify three historic deep shipwrecks in Australia and New Zealand, including one in 2002 which was the deepest wreck dive undertaken worldwide at the time. He was in the 2020 and 2023 Wet Mules teams pushing the Pearse Resurgence (NZ) to 245m and performing the first deep rebreather dive using hydrogen. In 2026 he co-led an expedition to take arterial blood samples from elite freedivers at 80m. He was conferred Fellowship of the Explorers’ Club of New York in 2006, was the Rolex Diver of the Year in 2015, and a NOGI fellow in 2026.

Title: The oxygen clock revisited

As technical diving has progressed to longer dives, divers have frequently found themselves exceeding the central nervous system ('CNS') limits derived from the NOAA 'oxygen clock'. This has resulted in the limits frequently being ignored out of necessity. However, ignoring a widely accepted guideline leaves divers potentially vulnerable to criticism if something goes wrong. It is notable that despite the limits being exceeded, CNS oxygen toxicity anecdotally seems very rare. In 2025 a working group of experts was convened to review the evidence underpinning the existing NOAA limits, and whether there were grounds for revising them. This process resulted in a substantial modification of the time limit for exposure to 1.3 atm oxygen. This presentation will describe the revision process, the relevant evidence, the new 1.3 limit, and where we go from here. 

Title: Technical diving in extreme diving research

Technical diving adventures are typically built around exploration of caves or discovery of new shipwrecks that require deep and/or long dives. However, there is a small group of scientists worldwide who apply technical diving methods as a crucial part of the skillset required to conduct ground-breaking research in various fields such as marine biology, archeology, and studying diving itself. A conspicuous example of the latter has been our program to study the complications of extreme freediving. In February 2026 our team took arterial blood samples from three elite freedivers on dives to 20, 40, 60 and 80m, both at the bottom and back at the surface before the divers breathed. This had never been done before. The aim was to map the changes in oxygen and carbon dioxide in these amazing athletes during long deep dives. This presentation will document the story of planning and execution of this complex operation with technical diving at its core, the adventures we had in doing it, and I will tell you what we discovered.