Like many free divers my age I was taught that hyperventilation just prior to going underwater could increase the duration of our breath hold, and thus the depth and duration of the dive. While studying the topic now over breakfast, I’m learning that this is wrong, and that hyperventilation before a dive only improves the chances of death by a phenomenon called Shallow Water Blackout. SWB is far scarier than sharks, waves or boats as it can happen suddenly and without notice, leaving the diver unconscious and in serious danger of drowning. I’d always thought SWB was a result of poor physical fitness (frankly, I had no idea about the cause), though now I’m learning that although science still doesn’t understand the phenomenon completely, there seems to be consensus that hyperventilation is a bad idea.
Free divers like me were misled by common knowledge that hyperventilation increases oxygen saturation in the bloodstream which allows for a longer dive. In fact, hyperventilation merely decreases CO2 levels which are a natural trigger to tell the body when it needs more air. By hyperventilating we are artificially removing this important trigger and giving ourselves the false sensation we can go longer underwater than we think. This may be the reason some breath hold divers suddenly pass out and die when they might not feel an overwhelming urge to breathe (at least that’s what those who have survived SWB sometimes report). This is a real eye-opener for me, and I will give up hyperventilation as a skin diving technique and will have a good talk with my daughter about the dangers of a trick I already taught her to do.