There are a few factors to consider when trying to determine a diver’s “crush limit”. The human body consists of up to 60% water, leaving 40% of body tissue. Air compartments surrounded by body tissue and the water percentile itself have different susceptibility to crushing. The easiest to crush are our air spaces such as our middle ear, sinuses and our lungs. So, how deep can you dive before being crushed?
In short, a diver can’t simply be crushed by the weight of water. Even at extreme depths.
How deep can you dive before being crushed?
Human bone crushes at about 11159 kg per square inch. This means we’d have to dive to about 35.5 km depth before bone crushes. This is three times as deep as the deepest point in our ocean.
The 40% of non-water non-gaseous minerals and tissues such as salts, proteins, fats and lipids are virtually impossible to compress similar to water.
Let’s look at the most basic physics that determine volume changes with pressure in an effort to work out how easily a diver’s air spaces could be crushed. Boyle’s law states the linear relationship between depth, pressure, volume and density in water. For the purpose of this article we are assuming 1 bar for 10 meters of water.
See the Boyle’s law table below.
Because water is virtually incompressible we are focusing on the crushing of air spaces within our body first.
Scuba divers and free divers rely on equalising to prevent damaging their bodies. They compensate for static water pressure by adding equal gas pressure into their air spaces as the atmospheric pressure of the depth they are diving in. This prevents their air spaces from collapsing under pressure.
In order to answer, how deep can you dive before being crushed?, we are going to ignore the other limitations we face when diving to great depths. These include differential pressure (saturation and off-gassing), gas toxicity and narcosis to mention a few.
Read more on these limitations in How Deep Can You Scuba Dive?
Getting Crushed With vs Without A Pressure Suit
Diving often requires some form of exposure protection to be worn in order not to get too cold. Depending on the suit worn a diver is subjected to variable degrees of crushing.
No Pressure Suit means that we dive with the water touching our body all around and we only need to equalise our own air spaces. A skin suit or wetsuit won’t change this. The only way this diver will be crushed is when the water in the diver’s body solidifies. Otherwise as long as the diver is able to equalise their air spaces with gas, they prevent being crushed.
A Pressure Suit traps a gas bubble around the diver underwater. To prevent crushing, divers need to ensure gas pressure inside the suit is equal to the water pressure outside the suit. Dry suit divers learn to add gas to their suits as they descend in order to prevent “suit squeeze”, a very painful side effect.
Learn more about How Does A Drysuit Work?
If suit pressure drops, the decrease in gas volume inside the suit would crush the diver. Commercial divers double check their non-return valve before their dives. Failure of this valve in the event of a gas supply failure would create a vacuum inside the suit crushing the diver. At great depths, high pressure would completely crush the diver. At lower pressure however, the diver’s lungs would collapse still resulting in a death by crushing.
An Atmospheric Suit is a hard suit able to withstand the pressure of the surrounding water on its own. The gas inside these suits is at 1 bar (same as our atmosphere). By being rigid, the water will not crush the diver inside these suits. John Lethbridge first conceptualised the atmospheric diving suit in 1715. The depth limits of these suits is currently around 700 meters. Venturing beyond these suits’ maximum operating depths has the potential to crush the diver in the event of a suit failure.
Can Pressure Turn Water Into A Solid?
We all know solid water as ice. A gas turns into a liquid if cooled enough. In turn, a liquid turns into a solid if cooled enough. This is how we turn water into ice. So, freezing a human would kill them, however, that is not technically crushing them and not what we are looking for.
Kinetic-molecular theory determines the effects of temperature and pressure on liquids.
As mentioned above it is theoretically possible to cool any liquid to arrest particle movement, making it a solid. Since we are not looking for when a human freezes, let’s look at pressure. It is theoretically possible to apply enough pressure to a liquid to restrict particle movement enough in order to turn the liquid into a solid. Water is rather incompressible. Solidifying water requires immense pressure. This amount of pressure does not occur in any diving conditions on our planet.
If the water pressure was high enough in order for water to solidify under its own weight, we would be unable to submerse ourselves or dive into such water. Similar in that we can’t go diving in ice.
The deepest point in our ocean is just on 11 kilometers. Since the water down at those depths is still liquid and not solid, there is not enough depth in our ocean to solidify water simply with pressure. Water remains a liquid at even 1101 bar or pressure. The human body would therefore not solidify under that pressure.
How much water pressure can the human body take?
As established above, the human body is 60% water. Earlier I mentioned how bone crushes at about 11159 kg per square inch which is not achievable by diving on earth. Our other body minerals and salts are virtually incompressible along with water. In theory as long as a diver equalises their own air spaces or that of the suit they wear, they avoid being crushed. There is no body of water deep enough to exert sufficient pressure in order to solidify water or compress salts, proteins, fats and lipids or even to crush bone in our atmosphere and gravitational field.
Diving depths have always intrigued people. Non-return valves failing and crushing divers in early pressure suit diving further highlighted this fear. How deep can you dive before being crushed therefore can’t be answered definitively. Achievable depths with SCUBA and even free diving are not enough to crush a diver.
Read more on Discover Scuba Diving Depth Limit