Hypoxia in the Community: Prologue

The topic of blackouts is a common discussion throughout freediving communities. Risk management, awareness and preparedness are vital components to competently and safely managing these scenarios when they occur. Management of these hypoxic events begins with being educated on the subject of hypoxia, understanding why these events occur and learning how best to manage them.

There is no ignoring that hypoxia and in turn hypoxic events occur in freediving. Turning a blind eye to the reality of this is one of the more reckless things that one can do in this beautiful sport. A hypoxic event is a response our body has due to the depletion of oxygen in the cells, tissues and/or body as a whole. This is known as hypoxia. Hypoxic events are more commonly described as ‘blackouts’ and ‘near blackouts’ which are also known as Loss of Motor Controls (LMCs) and Sambas. It’s very likely that if you stick with this sport long enough you will witness one of these events at some point first hand.  

Acknowledging the Disconnect: 

It is apparent that there can, at times, be a disconnect between recreational freedivers and the reality of blackouts and LMCs. It can be easy to remove ones’ self from the fact that events like this can occur until a hypoxic event has either been experienced or witnessed.  Free divers generally acknowledge the risks of hypoxia but at times there is a lack of respect when it comes to embracing the protocols and management systems that were created and designed to be implemented to help minimize the dangers and risks associated with these events. Unfortunately, it often takes this first hand experience before many freedivers acknowledge the reality of the risks associated with the sport. To help bridge that gap with this disconnect we have asked a few local freedivers to share their first hand experiences with hypoxic events for us.

Our hope, through this, is to allow the lessons learned from some of our community members’ experiences to shed light on the reality of this subject. Before diving into the dirty details of these stories with our local community members we need to bring it back to our two previous questions. Why do these hypoxic events occur and how do we manage the scenario at hand when they do occur? 

The basics of a blackouts hypoxia

Having a proper understanding of the physics and physiology of freediving is beneficial on many levels in this sport. One of the ways it will benefit you is by allowing you to better understand hypoxia and why these types of hypoxic events occur. Nerding out on the science and having a full understanding of Boyle’s Law and Dalton’s Law of Partial Pressure will help you better understand the relationships between pressure, volume and density. It is within the scientific relationships guided by these 2 laws that we become more susceptible to hypoxic events as we freedive.  

The purpose of this blog post isn’t to give you a full lesson on the science behind hypoxic events as there is a lot of great instructional material, programs and courses out there that fulfill that need. The general basics however can be broken down as follows to help you better understand hypoxic events. 

Hypoxia and the types of blackouts

There are two main types of blackouts in freediving that we will focus on. Performance Freediving International (PFI), which is the instructional system that I instruct at Bottom Dwellers Freediving, classifies these blackouts as ‘ascent’ and ‘recovery’ blackouts. The type of blackout is defined by the mechanisms that contribute to the blackout itself. In general, when blackouts are discussed in freediving they get tossed under the veil of ‘shallow water blackout’. Scientifically there are ways to distinguish between the mechanisms which create those blackouts and in this blog we’ll focus on the two mentioned above. 

Boyle’s Law

Water is dense… much more dense than the air of our atmosphere. Salt water is even more dense than fresh water but, for these general purposes, it’s not enough to make a notable difference and we’ll just focus on the salty brine that we all love and enjoy so much. As we freedive and move deeper through the water column, pressure increases fairly rapidly.

Pressure is measured in units known as Atmospheres of Pressure (ATA). For every additional ten meters of depth in this salt water environment, an additional 1 ATA will be felt. Thus, by ten meters of depth we will already be subjected to a second ATA of pressure doubling the amount of pressure that was exerted on our bodies while at the surface. This change in pressure is shown as 1 ATA at the surface and changes to 2 ATA at ten meters of depth. According to Boyle’s Law and assuming that temperature remains the same (which we will for these basic purposes) there is an inversely proportional relationship between volume and pressure. This indicates that at ten meters of depth (and now 2 ATA) our lung volume would already now be half (i.e. 1 over 2, ½ or 50%) of what we had at the surface. Now that’s a pretty drastic change in your lung volume and we’ve only descended ten meters! As we continue to dive deeper pressure continues to increase by 1 ATA for every ten meters of depth, while volume continues to show the inversely proportional relationship to pressure.

Have you ever been freediving and felt like you’re out of air at fifteen meters even though you only left the surface fifteen seconds prior? This is due to the relationship between volume and pressure, the reduced volume of air that is now occupying your lungs and how the autonomic functions of your body are responding to this volume decrease. At twenty meters of depth and 3 ATA your lung volume will now be one third (33%) of what it was at the surface. You might assume that this would indicate lower oxygen levels at this depth but that would be incorrect. This is where Dalton’s Law comes into place.  

Ascent Blackouts

Although increased pressure results in decreased volume, this reduction in volume actually increases gas density. This relationship allows your body to access more oxygen for cognitive behaviour under the added pressure than you would otherwise have access to at the surface. Pretty amazing right!? That same amazing relationship between physics and our physiology is actually the reason we are so susceptible to blackouts and LMCs while freediving. By pressurizing our body and utilizing the oxygen (which we would only realistically have access to while at depth under pressure) we subject ourselves to a scenario where we’re able to utilize more of the oxygen we would require for cognitive and conscious behaviour at the surface while operating at depth without even knowing we are doing it.

These relationships in Boyle’s and Dalton’s laws are why we become so susceptible to hypoxia and blackouts while freediving, in particular, on our ascents where the relationships are reversed. As pressure decreases, the volume of air in our body begins to increase. The density of oxygen in the blood, cells and tissues then in turn begins to decrease. As a result, our cells and tissues are spontaneously robbed of the oxygen we now require for cognitive behaviour, resulting in an ‘ascent’ blackout due to critical hypoxia.. The mechanisms to create an ascent blackout and the partial pressure of oxygen (PO2) flip, described above, is directly related to these laws and the relationships between pressure, volume and density as well as the rate of oxygen consumption by the freediver. 

Recovery Blackouts

Recovery blackouts have slightly different mechanisms in place but are as directly related to the affects pressure has on our body as ascent blackouts. During recovery blackouts critical hypoxia is reached upon surfacing and is correlated to blood pressure disruption which occurs due to the reduction in pressure on ascent. This is why recovery breathing is implemented in freediving. It combats the blood pressure disruption which, if left unchecked, can result in the recovery blackout which accounts for the majority of blackouts in freediving. 

Now that we have a solid understanding of the basic science behind hypoxia and the reason these two most common types of blackouts occur it is also important to consider what types of scenarios lead us to these situations. Regardless of how well trained an individual is in freediving, we are all susceptible to hypoxic events. This is why the number one rule in freediving is to never freedive alone.

Education and Training

The most valuable training accessible to anyone starting out in this sport is the training one gets from a basic level certification from a credible agency and certifying body. These certifications instruct you in the fundamentals of freediving with a focus on proper buddy system diving. There are many credible agencies out there to choose from, including but not limited to: PFI, AIDA, SSI, and Molchanov. The most important thing when starting out is to get some formal training right out of the gates. Having the proper training under your belt will set you up to be a safer, more proficient and more confident freediver.  In the event that a blackout or LMC should occur in front of you in a live diving environment you will have been prepared with hands-on experience in the motions of managing someone through some of these potential scenarios. Regardless of how well trained you are, if you’re diving alone you will be rolling the dice on your well being. It’s as simple as that. 

“I know my limits and dive within them… I’m fine…” is a sing-song we hear all too often in the world of freediving.

The variables with hypoxia

Now let’s brush the surface on what types of scenarios and variables contribute to hypoxia or increase the likely-hood of a blackout or LMC. General health, physical ability, physical environment, stress levels, peer pressures and the psychology behind freediving as well as general diet and habits all play into each and every dive we take. Freediving is an extremely mental sport and one of the most beautiful moving meditations one can experience. Finding the beauty in the ‘flow state’ which freediving provides is what draws many individuals deeper and deeper into the sport. It is used for cross training amongst many high level athletes to sharpen and strengthen the mind as well as train oxygen efficiency and carbon dioxide (CO2) tolerance. The mental aspects of this sport can, however, play against us and undermine us at the worst of times.

All of the variables mentioned above can play into our dives and our ability each and every day. “I know my limits and dive within them… I’m fine…” is a sing-song we hear all too often in the world of freediving. The fact of the matter is that there are just too many variables involved to always be in control and that’s why having a buddy there can mean the difference between diving another day or not. Some simple things you can do to enhance your abilities, performance and safety with freediving are the following: Dive in buddy systems with proper freediving supervision (i.e. one up, one down). Always complete your recovery breaths. Have a clear mind. Dive rested. Eat well/healthy, hydrate and follow surface-interval protocols. Being in-tune with yours and your dive buddies’ health and well-being will provide awareness that can benefit and add to the enjoyment and safety of your dives. 

Risk Management: Learn it to Execute it 

So what do you do if a hypoxic event affects your buddy during a dive? How do you properly manage this scenario? Unfortunately, this isn’t a topic that is easily and fully coverable in a blog but we have a valuable resource that we will provide you with to help get you a better understanding of the ins and outs of these processes. Ted Harty is owner of Immersion Freediving out of Florida and is a veteran PFI Freediving Instructor. In recent years he has created an online self paced instructional resource called www.freedivingsafety.com . This website was designed and created by Ted to help raise awareness on the subject of hypoxic events in freediving due to demand with regards to the ever growing number of cases in the sport.

www.FreedivingSafety.com provides a free online safety course. You will learn the truth about blackouts, how to minimize your risk, how to potentially save your buddies life should a blackout occur, as well as how to tell if you are wearing too much weight (you likely are…). While this online course is not a substitute for the hands on skills you learn in an in-person freediving class, it’s an excellent starting point from a trusted and reliable source.

We highly recommend that if you’re practicing breath holding in a liquid environment while freediving or snorkelling to any capacity, head over to the link provided and take the Freediving Safety program online. This program will virtually run you through basic freedive safetying protocols and techniques with a goal to make this basic knowledge more accessible to the general freediving community. This online course is not a replacement for the formal and hands on training you will get in a certifiable freediving course, however, it’s great knowledge to have access to if you’re getting out there before getting the chance to get a course under your belt. 

Making the Connection

Now let’s make the connection of the knowledge learnt here to real life events by showcasing real community members’ stories and scenarios. To do this we’ve reached out to 3 local Vancouver Island freedivers who have all experienced hypoxic events and blackouts in live diving environments in the last few years. These are real life examples and stories from our small and ever growing freediving community on the west coast of Canada. Brad Johnson, Galyn Franklin and Josh Marek have all shared their stories with one communal goal. The hope is that through bringing these stories from our local waters into perspective for the readers that we will shed a little more light on the reality of blackouts in freediving and the scenarios that surround them. Join us for Hypoxia in the Community: Episodes 1-3 for the first hand stories, emotions felt from the events at hand and the experiences learnt throughout these endeavours. 

Dive Safe,
The Spearfishing Canada team

Author: Chris Adair