Scuba divers use two basic types of air tanks. Both types are strapped to the diver’s back and provide clean air for the diver. Open-circuit sets provide an oxygen/nitrogen mix for the diver to inhale, who then exhales it into the water. This type of set is less expensive and is generally used in more shallow dives of less than 100 feet. Open-circuit sets come with one, two, or even three tanks, though sets with one tanks are most common. This type of set also goes by the name aqualung. Divers wearing an open-circuit set can be under water for 30 to 60 minutes, depending on their experience.

Closed-circuit sets, commonly called rebreathers, are used for deeper and longer dives. Rebreathers can allow for up to seven hours of underwater exploration. Rebreathers are designed to capture exhaled air, pass it through a scrubber, and circulate it back to the diver as useable air. How long a diver can stay under water is determined by the life of the scrubber and the water temperature.

Semiclosed rebreather sets allow for two to three times the underwater duration. In these types of sets, gas (air) is recycled but infused with a constant supply of fresh gas. Because some of the gas is recycled, the tanks for these sets are smaller than open-circuit tanks.

About the Author:

Dr. Randy Allan is a primary care physician who makes house calls in the Winnipeg, Canada, area. Dr. Allan enjoys scuba diving with his family in Australia, Belize, Thailand, and Mexico.