par bon gaz, j'entends le gaz qui évitera l'hypoxie.
le nitrox 40% est hypoxique en surface...
The lowest fresh gas fraction that will give a 20% oxygen fraction in the breathing circuit close to the surface is:
le 60% = aucun risque
un 50% représenterait-il le bon compromis ?
http://www.teknosofen.com/dc55_tech.htm
The variation in FO2 vs. depth for the DC55 with a volume exchange ratio of 10% and various fresh gas mixes. Note that the oxygen fraction will be lower than 21% at shallow depth for some gases.