3. Keep Two Thirds of Your Starting
Gas in Reserve to Exit the Cave
Over the years, there have been a number of cave-diving fatalities in which the victims either knew the way out, or had a good chance of finding the way out. They simply did not have sufficient breathing gas to make it.
Recreational divers, in particular, tend not to think about surfacing until the pressure in their cylinders drops to between 500 to 1,000 psi. This may seem like a no-brainer, but if divers use 2,000 psi or more to penetrate a cave, it is going to be very difficult to exit that cave on 1,000 psi or less. Should you factor in the unforeseen (loss of visibility, the need to share gas with other divers, etc.), the odds of divers surviving under such circumstances are exceptionally slim.
Trained cave divers learn to keep at least two thirds of their starting gas volume in reserve to exit. To date, this “Rule of Thirds” has proven to provide a sufficient safety margin — even in instances where divers’ exits have been slowed by poor visibility or momentary loss of contact with the guideline, or when gas consumption has increased, due to apprehension or the need to “share air” with another diver.
Maintain a Continuous Guideline to the Cave Exit »