Personally I think the passive exhale dive gets its main benefit from reduced narcosis & DCS risk, as well as reduced effort during the descent.
I think it is deceptive to say that it reduces the chance of shallow water blackout -- true, but only because it makes deep water blackout more likely.
During an inhale dive, blackout typically occurs in the last 15m -- where the safety freediver is waiting. During an exhale dive, there is no reason to believe the blackout will occur at the end -- it could occur at 30 or 40m if the diver overstepped his limits -- and for most divers, diving with one or two safety freedivers only, there isn't anyone down at 40m to drag them back up.
However, the risk of blacking out at the absolute bottom (60m+) is minimized, due to decreased O2 toxicity & decreased CO2 narcosis... although the extreme negative pressure might cause a blackout...
Eric Fattah
BC, Canada
I think it is deceptive to say that it reduces the chance of shallow water blackout -- true, but only because it makes deep water blackout more likely.
During an inhale dive, blackout typically occurs in the last 15m -- where the safety freediver is waiting. During an exhale dive, there is no reason to believe the blackout will occur at the end -- it could occur at 30 or 40m if the diver overstepped his limits -- and for most divers, diving with one or two safety freedivers only, there isn't anyone down at 40m to drag them back up.
However, the risk of blacking out at the absolute bottom (60m+) is minimized, due to decreased O2 toxicity & decreased CO2 narcosis... although the extreme negative pressure might cause a blackout...
Eric Fattah
BC, Canada