Twin rebreathers seem like a great solution to the redundancy question but they are complicated and bring their own problems.
My approach and some tips for the unwary.
Craig Challen is an Australian cave and shipwreck explorer and member of the Wetmules diving group. After commencing cave diving in the 1990s he was an early adopter of closed-circuit mixed gas rebreathers.
Notable explorations include the extension of Cocklebiddy Cave on the Nullarbor Plain of Australia in 2008 and the Pearse Resurgence in New Zealand over the last 10 years. He has additionally explored caves throughout Australia and New Zealand and in China, Thailand, Vanuatu and the Cook Islands.
Craig also has an avid interest in wreck diving and has explored wrecks over the last 15 years in the South China Sea, Solomon Islands, Australia, New Zealand, Thailand, Malaysia and Indonesia.
A veterinary surgeon by profession, now retired, Craig is also an enthusiastic helicopter and aeroplane pilot.
In July 2018, Craig participated as a diver in the Tham Luang cave rescue in Thailand.
Craig won the 2019 Australian of the Year award with fellow cave diver and friend, Richard Harris, for helping in the Tham Luang cave rescue.