What is the recommended minimum cylinder volume for an independent breathing gas source?

An independent breathing gas source is essential for deep diving and emergencies, providing an alternative air supply if main gas supplies are compromised. The recommended minimum cylinder volume of 120 cubic inches strikes a balance between ensuring adequate gas supply for an emergency while remaining manageable in terms of size and weight. This volume is typically enough to provide sufficient air for a diver to ascend safely or to reach a location where they can obtain additional air.

A smaller cylinder, such as those with 100 cubic inches, may not hold enough gas to cover the diver's requirements during critical situations, especially at greater depths where gas consumption increases. On the other hand, although a larger cylinder, like 150 or 200 cubic inches, could provide more air, it may be less practical regarding weight and buoyancy, making it more difficult for divers to maneuver effectively underwater. Thus, 120 cubic inches is widely accepted as a suitable minimum volume that ensures safety without compromising diver usability.