In issue 2: Depth Deeper than a submarine

In the 1960's, the medical community believed that 50 meters was the maximum depth a human being could reach before being crushed. Enzo Maiorca was the first to reach that depth. Since then, competitive freedivers have quadrupled that record in spite crushing effects of water pressure. How is this possible? Let's see.

Deepest SCUBA and Breath-Hold Dives

Diving to 130 feet (40 meters)

Recreational Scuba

Recreational scuba: 60-100 feet

Dives to this depth minimize risk of decompression sickness after surfacing, which is caused by accumulated nitrogen in the bloodstream.

Scuba divers take special care to ascend at less than 1 foot per sec and make a decompression safety stop at 20 feet for 5 min.

Beyond 100 feet, divers may start to experience nitrogen narcosis, which causes divers to lose their faculties. Staying just a few minutes too long can require lengthy decompression.

Recreational Breath Hold

Recreational freedive: 30-100 feet

Divers are limited by their level of comfort and training. Officially, 78 feet is an intermediate dive, while 130 feet is a requirement for an AIDA freediving instructor.

Freedivers can descend and surface quickly. There is no risk of nitrogen narcosis or decompression sickness from the air content in the lungs.

Dolphins typically do not descend deeper than 150 feet.

Diving to 331 feet (101 meters)

Technical Scuba

This is the recommended limit for technical SCUBA. This depth is more dangerous. It requires special training and lots of equipment. Even a short dive can require over an hour of decompression under water.

There is a high risk of nitrogen narcosis. Oxygen is toxic past 200 feet (60 meters) and can cause a fatal seizure. To mitigate these risk, divers substitute helium for nitrogen in their gas tanks.

Some divers use a "rebreather" instead of SCUBA, which involves additional risks like passing out from excess CO2.

On One Breath Without Fins

This is the world record a breath-hold dive without fins. Divers do a type of breast stroke to reach the target depth and return. This is the purest form of competitive freediving.

After reaching negative buoyancy, divers "free fall" to their target depth, conserving oxygen and energy for the more difficult way back.

Diving to 419 feet (128 meters)

Extreme Scuba

Few people dive on compressed air or even trimix this deep. Safety SCUBA divers at freediving competitions cannot descend this deep.

Some extreme divers have dived deeper on air. The record for a dive on regular compressed air is 509 feet (155 meters) by a diver who nearly perished due to narcosis.

On One Breath With Fins

This is the world record for an unassisted dive with fins on a single breath. Divers typically wear a monofin and do the dolphin kick.

In the "free immersion" discipline, where competitors do not wear fins but pull themselves along a rope, the record is 396 feet (121 meters).

Diving to 702 feet (214 meters)

WWII U-Boat Crush Depth

This is within the crush depth for a WWII U-boat. Only 3 people have dived deeper on SCUBA. The Guinness World record is 1090 feet (332 meters). This is extremely dangerous. The descent would take about 15 minutes and require over 12 hours of decompression under water.

Past 600 feet there is pitch darkness.

No-Limits Freediving Record

It's also the deepest a human being has gone on a single breath. Freedivers in the "No-Limits" discipline ride on a sled to push the body to extreme depths and return by way of a balloon.

While this is dangerous, there have only been a couple of deaths at competition events in the whole history of the sport. There have been some serious injuries. Nitrogen narcosis and decompression sickness can occur at these depths.

This is the depth limit for humpback whales.

Go back
130' (40m)
330' (101m)
419' (128m)
702' (214m)
Sources: Deep Diving and AIDA Records

Lung Compression at Depth

Since the lungs are filled with gases, they are compressed under pressure. At 100 meters, the lungs are compressed to the size of oranges.

At the surface

Visual Water Pressure Calculator
Pressure doubles at 10 m

0 m
0 m

The greatest pressure change is near the surface. At 30 meters, the pressure is 4X that at the surface, including 15 psi of pressure from the atmosphere.

At ____ (____) at sea, there're ____ pressing on each square inch of your body. It's like a ____ person standing on your chest.

The lungs would be ____% of normal size if it were not for the blood shift to the core.

Source: NASA (converted to PSI): Pressure (psi) = Depth (m) x 1.5 + 15 = Depth (ft) x 0.46 + 4.6

Blood Protects The Lungs

When divers started regularly diving past 50 meters, it became clear that something was preventing fatal collapse of the lungs as predicted by the formula.

As the lungs are compressed, blood moves to the chest. Since blood is not compressible, it keeps the chest cavity from crushing completely. The spleen also contracts, releasing more blood.

In contrast, SCUBA fills a diver's lungs with compressed air, which acts against the ambient pressure. The downside of this (besides the heavy equipement) is that compressed air contains more nitrogen and oxygen, which creates the three big risks of deep SCUBA diving: Nitrogen Narcosis, Decompression Sickeness, and Oxygen Toxicity.

How to Simulate Pressure

Method 1: If you're able, you can try exhaling all the air in your lungs. Then while holding your breath, do a few more forced exhalations. It will feel like someone is standing on your chest.

Method 2 (only with supervision!): Freedivers also practice "negatives" in the pool to further increase the effects of pressure. A diver exhales completely and sinks to the bottom. In a shallow, pool you can lie right on the bottom. Since the lungs are empty, the pressure at even 1 meter creates an intense sense of pressure. The vacuum in the chest pulls the air from the throat cavity.

Lung Damage From "Squeeze"

Many competitive deep divers suffer an injury called "squeeze", usually minor. When lungs are extremely compressed, lung damage may occur. Most of the time, divers come up, spit out a bit of blood, and are fine. It can manifest as a slight cough. Diving without adequate training or ignoring warning signs can lead to squeeze. If you suspect you've experienced sqeeze, abort diving and rest. Fatalities from squeeze are rare even in extreme freedivers and are preventable.

Keeping Inner Ear From Collapse

The sinuses are another air-filled space that compresses and expands with pressure (think of your ears popping on an air plane). To prevent the ear drums from rupturing, divers use the tongue to draw air from the lungs and push the air into the inner ear.

At great depths equalization becomes increasingly difficult. Not only is there less air volume in the lungs to draw out, the vacuum in the lungs and throat makes it hard to even move the tongue. Ear injuries are not uncommon. One controversial technique is to flood the inner ear with water instead of air, eliminating the air space.

Breath-Hold at 4,000 Feet

Whales face even greater pressures when they dive. There is evidence they can dive much deeper than 4,000 feet at pressures over 1,800 lb per square inch!

Photo credit: Gabriel Barathieu