Lismore City Council
Learn about shallow water blackout prevention and stay safe in the water
People who hold their breath while swimming or practising breath-holding underwater in pools are at risk of “passing out” due to lack of oxygen. This phenomenon is commonly referred to as shallow water blackout and it is the result of a severe lack of oxygen to the brain.
What is it?
A person basically “blacks out” or faints in the water. For some, their lungs will take on water, leading to drowning, while others simply suffocate or die of other causes brought on by the breath-holding.
The following is what happens:
1. Hyperventilation
Overbreathing either consciously or as a result of over-exertion artificially lowers carbon dioxide levels.
2. O2 Drops
As the breath hold begins oxygen is metabolised and carbon dioxide levels increase. As the breath hold continues the body becomes started of oxygen.
3. Unconsciousness
Under normal circumstances increased carbon dioxide would trigger a breath, but because CO2 levels were so low on submersion (due to hyperventilation) there is not enough to initiate a breath and the swimmer loses consciousness.
4. Drowning
Once the swimmer loses consciousness, the body reacts and forces a breath. That causes the lungs to fill with water and without an immediate rescue a drowning death is all but certain.
Where can it happen?
Shallow water blackout can occur in any body of water (pool, lake, river, ocean or even bath tub) when breath-holding underwater, regardless of water depth.
Why does it happen?
Shallow water blackout usually occurs because of a lack of education, awareness and understanding of the dangers of breath-holding. It also occurs because of the lack of safety training for swimmers, free-divers, snorkelers and spearfishermen.
