Rule of thirds (diving)
Encyclopedia
In scuba diving
, the rule of thirds is a rule of thumb
that divers use to plan dives so they do not consume all the breathing gas
from the diving cylinder
before the end of the dive.
For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve. However, when diving with a buddy with a higher breathing rate and/or different volume of gas, it may be necessary to set one third of your buddy's gas supply as your remaining 'third'. This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.
Reserves are needed at the end of dives in case the diver has gone deeper or longer than planned and must do decompression stops before being able to ascend safely to the surface. In an overhead environment, the reserve allows a diver to donate gas to an out-of-gas partner, with enough gas available to bring both divers to the surface.
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
, the rule of thirds is a rule of thumb
Rule of thumb
A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...
that divers use to plan dives so they do not consume all the breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
from the diving cylinder
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....
before the end of the dive.
For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve. However, when diving with a buddy with a higher breathing rate and/or different volume of gas, it may be necessary to set one third of your buddy's gas supply as your remaining 'third'. This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.
Reserves are needed at the end of dives in case the diver has gone deeper or longer than planned and must do decompression stops before being able to ascend safely to the surface. In an overhead environment, the reserve allows a diver to donate gas to an out-of-gas partner, with enough gas available to bring both divers to the surface.