Bottom gas

Bottom gas is a term used in scuba diving to refer to the breathing gas carried by the diver for the main part of the dive. It is typically stored in a diving cylinder and supplied to the diver through a demand valve on a diving regulator. The composition of the bottom gas is chosen to be safe to breathe at the maximum depth of the dive, and may be a simple air mix, or a more complex breathing gas such as Nitrox, Heliox or Trimix.

Composition of Bottom Gas

The composition of the bottom gas is chosen to be safe to breathe at the maximum depth of the dive. The most common types of bottom gas include:

• Air: This is the most commonly used bottom gas. It is composed of approximately 21% oxygen and 79% nitrogen.

• Nitrox: This is a mixture of oxygen and nitrogen, where the oxygen concentration is greater than that in air. Nitrox is often used to extend the no-decompression limits of a dive, or to reduce the risk of decompression sickness.

• Heliox: This is a mixture of helium and oxygen. Heliox is used for very deep dives, as helium is less narcotic than nitrogen at high pressures.

• Trimix: This is a mixture of oxygen, helium and nitrogen. Trimix combines the benefits of nitrox and heliox, and is used for very deep or long dives.

Safety Considerations

The safety of the diver is the primary consideration when choosing a bottom gas. The gas must be safe to breathe at the maximum depth of the dive, and the diver must be trained and competent in its use. The risks associated with the use of different bottom gases include oxygen toxicity, nitrogen narcosis, and the risk of decompression sickness.

See Also

• Diving cylinder
• Diving regulator
• Breathing gas
• Scuba diving

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