Dating scuba tanks
Safety training is necessary to work with pure oxygen.
Scuba cylinders are probably the most recognizable piece of scuba equipment.
Trimix is a mixture of 3 gases (nitrogen, oxygen and helium) used to increase depth limits and/or dive times.
Whatever its percentages, this scuba tank gas mixture is exclusive to technical (decompression) diving: recreational divers do not use Trimix.
Most divers use scuba tanks filled with simple compressed air (filtered and dehumidified).
This results in a larger physical size than steel cylinders of the same capacity.
To withstand this high pressure, cylinders are carefully engineered from two common materials: steel or aluminum. Steel is stronger than aluminum, which allows the walls of steel cylinders to be thinner than aluminum tanks.