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. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as SCUBA equipment, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft, medical life support and first aid equipment, high-altitude mountaineering and anaesthetic machines.

Most breathing gases are a mixture of oxygen and one or more inert gases. Other breathing gases have been developed to improve on the performance of air by reducing the risk of decompression sickness, reducing the duration of decompression stops, reducing nitrogen narcosis or allowing safer deep diving.

A safe breathing gas for hyperbaric use has three essential features:

• it must contain sufficient oxygen to support life, consciousness and work rate of the breather.
• it must not contain harmful gases. Carbon monoxide and carbon dioxide are common poisons in breathing gases. There are many other possibilities.
• it must not become toxic when being breathed at high pressure such as when underwater. Oxygen and nitrogen are examples of gases that become toxic under pressure.

The techniques used to fill diving cylinders with gases other than air are called gas blending.