Travel Gas

A gas breathed during descent and the shallow part of a dive when the bottom mix is hypoxic and unsafe to breathe near the surface.

Travel gas is the mix a technical diver breathes on the way down when the bottom gas cannot be breathed safely at shallow depth. Deep trimix blends are often hypoxic: a mix like 10/70 carries only 10 percent oxygen, which at the surface gives an oxygen partial pressure well below the roughly 0.16 bar needed to stay reliably conscious. The diver therefore descends on a breathable travel gas and switches to the bottom mix at a planned depth where its PO2 has risen into the safe range.

A travel gas needs both a floor and a ceiling: it must be breathable from the surface and must not exceed its own maximum operating depth before the planned switch. Nitrox blends such as EAN32, or a normoxic trimix, are common choices, and on many dives the same cylinder does double duty as a deco gas on the way back up.

Every switch point is written into the run time, and the travel cylinder is analyzed and MOD labeled like any other mix on the dive. Discipline around switches is the whole game: breathing the wrong gas at the wrong depth, whether a hypoxic bottom mix near the surface or a rich gas at depth, is a leading cause of serious technical diving accidents.