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>Since we are concerned about exposures to elevated PO2's, >it seems to me that we should be considering the use of "airbreaks" >during the deep decom stops (ie, take an "air break" prior to starting >onto nitrox during decompression). >As to what to use for these "air breaks", it is essential that the >inspired PO2 be less than 0.5 ATA, and the closer to 0.21ATA, the better. >So, what should we be using for these "air breaks" when at deeper stops?? >Obviously, air is not going to give us a PO2 of less than 0.5ATA at depths of >greater than around 45.6fsw, so we have to consider another breathing mix >for this use. Two comments on this. A secondary reason for the use of high PIO2 during decompression after dives using He as a diluent is to avoid dilutional hypoxia. The greatest risk of inducing dilutional hypoxia will be immediately after the first pull towards the surface (at the deepest decompression stop) when He off-gassing rate is greatest. Normally this is no problem as the PIO2 is sufficiently high, but switching to an inspired PIO2 of 0.21 bar at this time is likely to result in hypoxia as the PAO2 will be much lower than the PIO2. This would need to be considered in choosing the "break gas". I would suggest that if the PIO2 never exceeds 1.6 bar, that "air breaks" are not critical (please do not try this at home), particularly during this early stage of the hyperbaric oxygen exposure. regards, David Doolette ddoolett@me*.ad*.ed*.au*
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