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Understanding and Preventing Shallow Water Blackout in Freediving

Shallow water blackout (SWB) is a condition that occurs when a freediver loses consciousness underwater due to a lack of oxygen (hypoxia).

This phenomenon is particularly prevalent among freedivers, spearfishermen, and individuals who engage in repetitive breath-holding activities.

Despite its dangers, the risks associated with SWB are frequently misunderstood or underestimated.

Here, we will explore the causes of shallow water blackout, how to avoid it, the importance of never diving alone, and why the negative stigma around freediving is misplaced.

What is Shallow Water Blackout?

Shallow water blackout occurs when a person blacks out underwater due to hypoxia, which is a state of low oxygen in the brain. T

Shallow water blackout occurs when a person blacks out underwater due to hypoxia, which is a state of low oxygen in the brain. This typically happens after prolonged breath-holding or hyperventilation prior to diving.

Hyperventilation lowers the carbon dioxide (CO2) levels in the blood, which delays the urge to breathe and can cause a person to lose consciousness before realising they need to surface for air​​ (Underwater Hypoxic Blackout Prevention)​​ (DoveMed)​. Hyperventilation not only makes you less aware of your breath-hold but also decreases the available oxygen in your body. This is because hyperventilation reduces carbon dioxide levels, which causes oxygen molecules to bind more tightly to hemoglobin. As a result, less oxygen is released to the tissues, reducing your overall breath-hold time.

Think of it as your body going into power-saving mode. Just like your phone dims the screen and limits functionality to conserve battery, your body reduces oxygen consumption by causing a blackout to protect the brain from severe hypoxia​ (Underwater Hypoxic Blackout Prevention)​​ (DiverTown)​.

Symptoms of Hypoxia and Shallow Water Blackout

The symptoms of shallow water blackout can often be subtle and easy to miss. They include:

  • Lightheadedness or dizziness

  • Tunnel vision or blurred vision

  • Blue lips

  • Pale skin

  • Euphoria or a sense of calmness

  • Loss of motor control or coordination

  • Sudden loss of consciousness

  • Increase or decrease in speed

  • Visible stress

  • Strong contractions

  • Exhalation/bubbles

Shallow Water Blackout Does Not Equal Drowning

A critical point to understand is that shallow water blackout does not equate to immediate drowning. When a blackout occurs, the diver typically has 2 to 4 minutes to be brought to the surface by a buddy before irreversible damage or drowning happens​ (Divers Alert Network)​. During this period, the body’s natural response is to close the throat, preventing water from entering the lungs.

This is why it is crucial to remove your snorkel when diving. If you blackout with a snorkel in your mouth, it can act as a direct conduit for water to enter your lungs, leading to immediate drowning. Without the snorkel, your throat will instinctively close, providing a brief window during which your buddy can rescue you before your body attempts to take a final breath and potentially ingests water​ (Divers Alert Network)​.

Prevention Strategies

  1. Proper Education and Training: One of the most effective ways to prevent shallow water blackout is through education and training. Freediving courses teach proper techniques, safety protocols, and the physiological changes that occur during breath-hold diving. Such training is crucial for understanding and mitigating the risks associated with SWB​ (DiverTown)​.

  2. Avoid Hyperventilation: Divers should avoid hyperventilating before a dive, as this reduces CO2 levels and delays the body's natural urge to breathe. Instead, divers should practice controlled, deep breathing techniques to ensure they maintain a safe balance of oxygen and CO2​ (​​ (DiverTown)​.

  3. Use the Buddy System: Never dive alone. Always dive with a buddy who is trained to recognize the signs of distress and capable of performing a rescue if necessary. A dive buddy can monitor for symptoms of hypoxia and provide immediate assistance, significantly increasing the chances of survival in case of an emergency​ (DiverTown)​​ (Divers Alert Network)​.

  4. Gradual Adaptation to Depth: Divers should gradually increase their depth limits rather than making sudden changes. This allows the body to adapt to the increased pressure and reduces the risk of adverse physiological responses that could lead to a blackout​ (DiverTown)​.

  5. Set Realistic Breath-Holding Limits: Divers should set realistic time limits for breath-holding activities and avoid pushing their limits excessively. Taking sufficient breaks between dives allows the body to recover and replenish oxygen levels​ (DoveMed)​.

  6. Surface Interval Time Adhering to adequate surface intervals between dives is crucial for preventing shallow water blackout. A surface interval is the time spent at the surface between dives, allowing the body to off-gas accumulated CO2 and replenish oxygen stores. This recovery period helps maintain optimal physiological conditions, reducing the risk of hypoxia on subsequent dives. Molchanovs recommends using the following formula: SI = P × T Where: SI = Surface Interval, P = Pressure and T = Time For example, a 1-minute dive at a depth of 10 meters (2 bar pressure) would result in: P(2) × T(1) = 2 minutes of recovery. This practice helps ensure divers are well-oxygenated and prepared for their next dive​ (DoveMed)​​ (Divers Alert Network)​.

Steps to Take if Someone Experiences a Blackout While Diving

  1. Get them out of the water: Safely bring the person to the surface and out of the water to ensure they do not inhale water.

  2. Ensure airways are clear: Make sure their airways are unobstructed to facilitate breathing.

  3. Remove their mask: Take off the mask to improve airflow.

  4. Perform "blow, tap, talk":

  5. Blow gently on their face.

  6. Tap their shoulders (though Molchanovs suggests not tapping, so this step can be skipped if following their advice).

  7. Talk to them to stimulate a response.

  8. Begin rescue breaths: If they do not regain consciousness after a few rounds of "blow, tap, talk," start rescue breaths.

  9. Administer oxygen: If available, provide 100% oxygen.

  10. Seek medical assistance: Call for professional medical help depending on the severity of the situation.

  11. End the dive session: Cease all diving activities to focus on the individual's recovery and safety.

Importance of Never Diving Alone

Diving alone is highly dangerous because there is no one to assist in case of a shallow water blackout or other emergencies. The buddy system is a fundamental safety measure in freediving and spearfishing. A trained buddy can recognize the early signs of hypoxia, retrieve a distressed diver, and perform rescue breaths or CPR if necessary. This immediate response can be the difference between life and death​ (DiverTown)​​ (Divers Alert Network)​.

Addressing the Negative Stigma Around Freediving

Freediving often carries a negative stigma due to the perceived risks associated with the sport. However, with proper training, safety measures, and a strong emphasis on education, freediving can be a safe and rewarding activity. The risks of shallow water blackout and other hazards can be significantly mitigated through adherence to safety protocols and continuous learning. Freediving enthusiasts are passionate about the sport and often advocate for increased awareness and education to promote safe diving practices.

The Last Breath Documentary

For those interested in learning more about the dangers of underwater blackout and the importance of safety in freediving, the Netflix documentary "Last Breath" provides a gripping exploration of a deep-sea diver's harrowing experience. This documentary underscores the critical nature of safety protocols and the risks associated with underwater activities.

Do you want to become a safer diver?

At Deep Sensations Freediving, we are committed to promoting safe and enjoyable diving experiences.

We offer comprehensive freediving courses that cover essential safety techniques, breath-hold training, and emergency response procedures.

By enrolling in our Beginner and Advanced freediving courses, you can gain the knowledge and skills needed to dive safely and confidently.

Our Molchanonovs and SSI courses are internationally recognised and will make you and your buddy's safer in the water.

Sign up for a course today and take the first step towards mastering the art of safe freediving. Visit our website to learn more and join our community of passionate and responsible divers.


Shallow water blackout is a serious risk for divers, but with proper education, training, and adherence to safety measures, it can be prevented. Understanding the causes and symptoms of SWB, practicing safe diving techniques, and always diving with a buddy are critical steps to ensuring a safe and enjoyable freediving experience. Let’s work together to raise awareness, dispel misconceptions, and promote the positive aspects of freediving as a sport and a way of life.

For more information and to sign up for our courses, visit Deep Sensations Freediving today. Stay safe and dive responsibly!


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