What should a scuba tank for recreational diving be filled with?

A scuba tank for recreational diving should be filled with pure, filtered compressed air or Nitrox because these options are specifically designed for the conditions and depths typically encountered in recreational diving.

Compressed air, which consists of approximately 78% nitrogen and 21% oxygen, is the standard and most commonly used gas in recreational diving. It is safe for the depth limits typically encountered by open water divers and minimizes the risk of oxygen toxicity and other complications.

Nitrox, which is enriched with oxygen (usually containing between 32% and 36% oxygen), allows divers to spend longer times at specific depths and decreases the amount of nitrogen absorbed by the body, thus reducing the risk of decompression sickness. It is important that divers are trained in the use of Nitrox and understand the limits and guidelines associated with its use.

The other options, while they have specific applications, are not suitable for recreational diving. A mixture of helium and oxygen is typically used in deep diving or mixed-gas diving to manage issues related to narcosis and breathing gas composition at significant depths. A mixture of hydrogen and oxygen is not safe for scuba diving due to the volatility of hydrogen and the risk of explosion. Pure oxygen is generally only used at shallow depths in special conditions