During this year's Vertical Blue, we have witnessed a few freediving blackouts. Some were surface ones, others were underwater and Walid Boudhiaf's was a very deep, and fairly scary, one. Why do these elite freedivers blackout? What are the causes at competition level? And most importantly, how can one avoid it? In a recent interview, Sheena McNally, Canada's deepest woman in CWTB, taps into one mistake deep freedivers make at competitions before their dive.

Competitions Are The Safest Place  To Be Hypoxic

"In a competition, hypoxia is not a desirable result, and even though there are divers out there, diving at quite a high level, who seem completely comfortable to repeat that as a result, I’m not. When I had a blackout, I was really disappointed in myself. That said, if you're going to be hypoxic, the competition is going to be the absolute best place to be hypoxic. You're surrounded by safety divers, usually four, minimum three, doctors, nurses, and other divers, who are all certified and know how to deal with the situation. You're in very good hands".

Never Dive Alone

"The biggest problem, I would say, with hypoxia is if it happens when you're alone. If you go on YouTube or you start digging, you can find stories of freediver deaths and what these deaths are, I can't say 100% of them but let's just say 99%, are people who went out spearfishing and they went out without a buddy. I believe that every sport has risk and we mitigate risk in freediving by never freediving alone. We freedive with a buddy and, I would add, not anybody. It has to be a buddy who’s qualified and trained, somebody who knows how to deal with these responses, a certified buddy.

If you go out alone and you run into hypoxia, the problem is then there's no one there to help you. And the real risk is getting water in the airway. Say like, worst-case scenario, diver did something crazy and they suffered a blackout. Probably they will end up face down in the water and although they'll be okay for some sort of short window of time because their body will do everything it can to protect themselves from drowning, as their oxygen levels continue to drop, eventually they're going to take an involuntary breath and then it will become a drowning situation if they’re alone. There's no other outcome, they're not just going to lift their head and start breathing, no, they're not going to come back. Wherever they are, they're going to try to take an involuntary breath and that's where it becomes, I would say, super dangerous. But if there's a diver there, a trained body or safety who knows what they're looking at, they are trained in the response which is, I would argue, way more simple than anything I had to deal with in scuba diving in terms of safety. Then that person can be okay quite quickly and with no lasting effects".

Hyperventilation Can Be Dangerous

"At competition level, many blackouts occur because of how you breathe before you dive.
It is a lot about breathing and if you breathe in such a way that you kind of artificially lower your CO2 levels before you start, so you hyperventilate either knowingly or unknowingly, it can be really dangerous. We need something to give us signals of when is it time to go up, and it's not going to be oxygen, we don’t have a great sensor for that. But we have very sophisticated and strong signals that we get from CO2. Like, are my contractions normal, are they coming at the right time, are they early, are they late? This is all information that we're using to make the decision on when it's time to go up, but if we suppress our urge to breathe by hyperventilating before a dive, then, it's kind of like, we're turning off our alarm clock, we're turning off or we're delaying the signals that are telling us it’s time to go up. That means we could carry on a dive feeling great, but, really, we could be kind of approaching our loss of consciousness threshold at some point. So, I'd say, a big mistake before the dive has to do with breathing".

Watch Thibault Guignes Blackout
After A -100M Dive