In 1997, members of the U.S. Deep Caving Team were preparing for a ground breaking project at Wakulla Springs. We had shiny new Cis-Lunar Mk5P rebreathers but little formal instruction. We were all test pilots in those days. tWe decided that we wanted to know what hypoxia felt like. Would we be able to detect it in time to bailout? Would we be incapacitated even after bailing out? Were our heads better than the audible and visual alarms that were supposed to protect us?

We set up a simple experiment in a classroom in Hudson, Florida. With an oxygen kit in hand, we intentionally cut off the oxygen supply to the rebreather and let the diver choose when to bail out. What we learned was that you should never try to repeat this experiment. In the face of hypoxia, you may not be able to revive the stricken diver.

We hope you learn that you should follow good protocols to prepare your rebreather including a proper pre-dive checklist. Prevention is the best action you can take. In the event that you experience an odd feeling on a rebreather, immediately bailout to open circuit gas or flush the counterlungs with breathable diluent. With fresh diluent* or open circuit gas you have bought time to figure out how to handle your emergency.

*Please note that CO2 emergencies can ONLY be solved with open circuit bailout. Diluent flushes do not solve CO2 emergencies.

Original footage supplied by Andrew Poole.

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