In cave diving what does the rule of thirds mean?

+1 vote
asked Mar 22, 2017 in Scuba Diving by Cvet (3,369 points)

3 Answers

+2 votes
answered Mar 24, 2017 by H2OAddict (105 points)

The rule of thirds is a safety measure commonly used when diving overhead environments such as caves, caverns, and wrecks. 

The typical scuba tank has 3000psi or 210 bar. With the rule of thirds, you use 1/3 in, 1/3 out, and 1/3 as reserve. Therefore, when you reach 2000psi or 140 bar you turn the dive and begin heading back the way you came. In theory you will use the same amount of gas while traveling that distance and will maintain the final third in the event something doesn't go as planned. 

It is a much more conservative diving style due not having direct access to the surface. 

+1 vote
answered Mar 26, 2017 by Traderdon (15 points)
One third of air in one third out one third for emergency
+1 vote
answered Apr 5, 2017 by George1224 (5,147 points)
1/3 in, 1/3 out, 1/3 reserverd for a 3 to 5 min safety stop at 15 to 20 feet
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