Trimix notation Tx O2/He (e.g. Tx 21/35). Helium reduces narcosis and O2 toxicity. Normoxic ≥21% O2, hypoxic <21%. Analyse each cylinder with O2 and He analysers before every dive. Calculate maximum PPO2 and END.
Using trimix for depths greater than 40 meters requires understanding gas mix planning, having He/O₂ analyzers, and knowing how to blend with a Nitrox stick. Divers debate the minimum knowledge required before taking a gas blending course, the availability of oxygen fills in different parts of Spain, and the real cost of technical gas. Oxygen toxicity is another point of concern.
Trimix is identified with the notation Tx O₂/He (for example, Tx 21/35 indicates 21% O₂, 35% He, and 44% N₂). Helium replaces part of the nitrogen to reduce narcosis and oxygen toxicity at depth, with its main disadvantage being high cost. Normoxic trimix maintains the oxygen fraction at ≥21%, suitable from the surface, while hypoxic trimix has less than 21% O₂ and requires a travel gas for the first meters. Before each dive it is mandatory to analyze each cylinder with O₂ and He analyzers.