Free diving on EAN Nitrox?

[Web Monkey]

I'm an experienced scuba diver and also a spearfisherman. I used to spearfish on scuba, but am beginning to prefer spearfishing while freediving instead. After reading about SWB (shallow water blackout) being the number one pressure related injury to free divers, I'm thinking about trying EAN 36 or EAN 40 to prevent SWB and maybe increase my bottom time.

As I understand it SWB is caused by a rapid drop in pO2 as the freediver ascends. Because pO2 is increased at depth, it may be possible to feel like you have enough oxygen at depth and starve yourself of it when you ascend causing unconsciousness.

If instead I dived with 36 or 40% O2, I should feel the urge to breathe far earlier than my oxygen reserves burn out even with decreasing pressure because the accumulation of breath-reflex inducing CO2 will still accumulate at the normal rate.

Pre-breathing O2 on the surface won't make a significant difference, since healthy people already have over 90% O2 saturation anyway. The most you could gain is a few percent.

In any case, freediving is dangerous enough when done normally. I wouldn't want to be screwing with my blood chemistry just before a breath-hold dive.

Terry