Let’s talk about the elephant in the room: Freediving blackouts
Freediving offers a unique experience that differs significantly from other forms of diving, such as SCUBA. However, it comes with its own set of risks, notably the occurrence of blackouts. Understanding the science behind freediving blackouts and how to prevent them is crucial for every freediver, from beginners to professionals.
The Phenomenon of Blackouts
In freediving, blackouts typically happen due to hypoxia – a reduced supply of oxygen to the brain. Unlike the gradual discomfort experienced during breath-holding on land, blackouts in freediving can occur suddenly and without warning, even when a diver feels completely fine moments before.
Types of Freediving Blackouts
Shallow/Deepwater Blackout: This is the most common type of blackout in freediving. It occurs due to the sudden drop in partial pressure of oxygen in the lungs and blood when a diver ascends. During a deep dive, the pressure underwater compresses the lungs, and the body adapts by shifting blood from the extremities to the chest (blood shift). As the diver ascends and pressure decreases, the oxygen in the lungs rapidly expands, but its partial pressure can drop below what is necessary to sustain consciousness. This can happen even if the diver felt fine at depth.
Static-Apnea Blackout: Happens without a change in pressure, often due to hyperventilation, which alters the blood's pH level and restricts blood flow to the brain.
Surface blackout, also known as shallow water blackout, is a phenomenon that occurs predominantly in freediving and spearfishing but can also happen in any activity involving breath-hold diving. It usually occurs at or near the surface of the water as the diver is ascending or immediately after surfacing. Understanding surface blackout requires an exploration of the physiological changes during a dive and the specific factors that contribute to this dangerous event.
Physiological Background of the surface blackout:
Partial Pressure of Oxygen (PPO2): As a diver descends, the increased pressure causes the partial pressure of oxygen in the lungs to rise, ensuring adequate oxygenation of the blood. However, as the diver ascends, this pressure decreases.
Boyle’s Law and Lung Expansion: The volume of air in the lungs expands as pressure decreases during ascent (Boyle’s Law). This can cause a drop in the partial pressure of oxygen.
Oxygen Transport to the Brain: The oxygen transported to the brain is adequate at depth due to high PPO2. However, during ascent, especially in the last few meters, the rapid reduction in pressure can cause a critical drop in PPO2, leading to hypoxia in the brain.
Figure 1: Illustration depicting relative lung size and oxygen concentration in relation to depth over time of common freedive blackout types. Courtesy: 2006 Breath-hold Workshop Proceedings
Personal Account of a blackout:
Many freedivers, including world record holders like Mandy Ray Cruickshank, have reported experiencing euphoric sensations before a blackout, with no apparent signs of distress. These accounts underline the deceptive nature of blackouts in freediving.
Prevention and Safety Measures
To mitigate the risk of blackouts, freedivers are advised to:
Avoid hyperventilation before dives.
Allow sufficient recovery time between dives.
Dive with a vigilant buddy system.
Recognize and respect their physical limits.
Consider using devices like the Freediver’s Recovery Vest for additional safety.
The Role of Education
Education plays a pivotal role in safety. Taking a certified freediving course provides hands-on practice in handling emergencies, including blackouts. Online resources can offer foundational knowledge but are not substitutes for in-person training.
Blackouts in freediving, while a serious concern, can be effectively managed with proper education, adherence to safety protocols, and a supportive community. As the sport continues to grow, so does the collective understanding and implementation of measures to ensure the well-being of every diver exploring the depths on a single breath.
Remember, safety in freediving is not just about personal precaution; it's about creating a culture where every diver looks out for one another. Dive safe, dive smart, and embrace the wonders of freediving with respect and awareness.