Shallow water blackouts and lung squeezes are real risks for freedivers.
Unfortunately, not all freedivers know the problems associated with pressure and depth when deep sea diving.
We love freediving, but only when it's performed safely.
So, to ensure you can enjoy this awesome pastime to its fullest, here's everything you need to know about pressure and depth and problems from pressure in deep sea diving.
When freediving, the water pressure on the human body increases significantly as you descend underwater.
At sea level, the air around us exerts a pressure of 1 bar (or 1 atmosphere), a result of the 10,000 metres of air above. However, water is much denser than air so even a small dive dramatically increases the pressure on your body.
When learning to freedive for the first time you'll feel this pressure as you descend. The deeper you go, the greater the amount of water above you and so too the pressure.
It's a strange sensation, and it manifests differently depending on where the pressure is being applied. Knowing what to expect is half the battle.
As you dive deeper underwater, whether you’re freediving or spearfishing, the increasing pressure affects the air cavities in your body.
At 10 metres depth the pressure doubles to 2 bars (or 2 atmospheres). At 20 metres it increases to 3 bars and so on.
According to Boyle's Law, "If the temperature remains constant, the volume of a gas is inversely proportional to the absolute pressure". In simple terms, as pressure increases, the volume of air decreases.
For example, if you dive with 6 litres of air in your lungs, this volume reduces to 3 litres at 10 metres, 2 litres at 20 metres and 1.5 litres at 30 metres.
It's important to note that the amount of air doesn’t change, only its volume. A lack of understanding of this can lead to problems from pressure in deep sea exploring and freediving.
During a freedive, the compression of air is a noticeable effect, often felt as pressure in the ears, much like the sensation during an airplane landing.
Freedivers (like spearfishers and even surfers when riding big waves) need to equalize four primary air spaces: the ears, sinuses, mask and lungs.
While the lungs naturally compress with descent—assuming adequate flexibility or shallower depths—divers must actively equalize the ears, sinuses and mask to avoid discomfort or injury.
Another critical effect of increased pressure at depth is how it impacts gas exchange in the lungs. As the air in the lungs compresses its density increases, raising the partial pressure of oxygen.
This heightened pressure allows oxygen to cross the lung membrane into the bloodstream more easily, enabling freedivers to absorb oxygen at depths they wouldn’t be able to at the surface.
However, it’s important to note that this same effect poses risks for scuba divers, such as nitrogen narcosis and oxygen toxicity beyond 66 metres.
Freediving is an exhilarating sport, but one that comes with inherent risks.
When combined with a lack of knowledge or improperly assessing the effects of pressure and depth on the body, these dangers are amplified.
For freedivers, we offer Level 1, Level 2 and Level 3 freedive training courses that teach you how to both avoid and mitigate the risks listed below.
Freediving and scuba diving share this common risk: the inability to equalize the pressure in your ears while descending.
This can lead to burst eardrums, loss of hearing and even permanent damage.
To avoid this, divers must actively equalize their ears using techniques like Valsalva or Frenzel.
As mentioned earlier, as you dive deeper, the volume of air in your lungs decreases due to increased pressure.
At a certain point, if you continue to descend without releasing air from your lungs or equalizing them properly, the increased pressure can cause an injury known as lung squeeze.
Lung squeezes occur when the lungs cannot tolerate the amount of pressure they are put under. When this occurs the lungs can perforate and even collapse, leading to bleeding in the lungs and then the coughing up of blood.
Damaged sinuses
Like a burst eardrum, improperly equalizing the pressure in your sinuses can lead to serious injury.
Your sinuses serve an important function in equalizing the pressure in your head, and failure to do so can result in sinus barotrauma, which can cause blockages or damage to the sinuses.
Perhaps the most dangerous consequence of not understanding pressure changes and depth is shallow water blackout.
Shallow water blackout occurs where during ascent the pressure in the lungs decreases, this causes oxygen from the bloodstream to move into the lungs dropping the oxygen levels around the brain. This can lead to loss of consciousness and even potentially drowning.
Even seemingly shallow dives can pose a risk if proper precautions and knowledge are not taken into account. To mitigate or completely avoid these risks, it is essential to have a thorough understanding of pressure and depth while freediving and always dive with a buddy.
By being knowledgeable about how the body responds to increasing pressure at depth, deep sea divers and freedivers can ensure their safety and enjoy the sport without fear or danger.
While it’s not usually a problem for freedivers since we don’t breath compressed air, decompression sickness (otherwise known as "the bends") is primarily a risk for scuba divers who don’t follow proper ascent protocols after diving at depth.
Freedivers on occasion can get “the bends” if they do not obey a surface interval or if they dive past 60 metres on a single breath.
Decompression sickness occurs when nitrogen bubbles form in the tissues of the body due to rapid decompression, causing symptoms such as joint pain, chest pain, blood vessel damage, organ failure and neurological issues.
To prevent decompression sickness, scuba divers must know that decreasing pressure too quickly is dangerous. You need to adhere to safe ascent rates and include a safety stop during all deepwater dives.
It's also important to note that complications from decompression sickness can arise up to 24 hours after diving, so monitoring for symptoms post-dive is crucial.
Understanding changes in ambient pressure at depth and how it impacts the body of freedivers is essential to ensure a safe and enjoyable diving experience.
The best place to learn about everything to do with depth and pressure is with a trained and experienced freedive instructor.
We’re confident that with the right training you will have the confidence to freedive, learn to surf in Bali, snorkel and spearfish anywhere around the world.
Become a breathhold master today
