Figure 1.

Full squares represent the net theoretical expansion of the gases’ hydrophobic site of action, using benzene as a model solvent, at the time paroxysmal narcotic episodes occurred using air, and hydrogen (H₂)-oxygen (O₂), helium (He)-H₂-nitrogen (N₂)-O₂, or H₂-N₂-O₂ breathing mixtures.

Note: Data show that whatever the gas mixture used the fractional expansion was remarkably similar (mean value: 0.0453 ± 0.0032%) at the time the dives have had to be stopped because of the occurrence of paroxysmal narcotic episodes including psychotic-like symptoms. Taking into account this expansion value, the onset depth for the occurrence of paroxysmal narcotic episodes in helium-oxygen mixture may be thus estimated between 930 m and 1,080 m (94–109 ATA). 1 ATA = 0.1 MPa. ATA: Atmosphere absolute.