Non-redundant Alternative Gas Sources
These include a secondary regulator on a manifolded twin set without isolation valve, a secondary regulator on a double cylinder valve on a single cylinder, an auxiliary second stage on a single regulator, and the pneumofathometer line for surface suppled divers.
The use of two independent regulators on independent cylinder valves supplied from the same cylinder is a system most applicable to cold-water diving, where a regulator can ice up and free flow, so the diver needs to be able to close the cylinder valve for that regulator, and fall back on a second regulator.
The pneumofathometer line on a surface supplied umbilical is a valuable backup supply in case of damage to the main supply hose, or if a diver needs to supply air to another diver on surface supply, as the usual configurations of helmet and full face mask do not allow buddy breathing of the conventional kind. The Pneumo line can be tucked into the neck dam or under the skirt of a full face mask, and provided the helmet or mask is not leaking heavily, will supply adequate air for an assisted ascent.
Read more about this topic: Alternative Air Source
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