The amount of pressure a human can withstand underwater depends on various factors, including the depth of the water, the duration of exposure, and individual differences in physiology and acclimatization to diving. Generally, humans can withstand the increased pressure associated with diving to a certain depth before experiencing adverse effects.
At sea level, the atmospheric pressure is around 1 atmosphere (ATM), which is equivalent to about 14.7 pounds per square inch (psi) or approximately 101.3 kilopascals (kPa). As a person descends underwater, the pressure increases by an additional 1 ATM for every 33 feet (10 meters) of seawater depth. So, for example, at 33 feet (10 meters) underwater, the pressure is 2 ATM, and at 66 feet (20 meters), the pressure is 3 ATM, and so on.
The human body can adapt to increased pressure to some extent through diving training and acclimatization. Scuba divers, for instance, undergo specialized training to handle increased pressure safely. For recreational scuba diving, most certified divers are limited to depths between 130 to 165 feet (40 to 50 meters) to minimize the risk of decompression sickness and other potential hazards.
At extreme depths, such as those encountered in technical or commercial diving, the pressure can become too great for the human body to withstand without specialized equipment like atmospheric diving suits or deep-sea submersibles. These technologies are designed to maintain a controlled internal pressure to protect the occupant from the crushing forces of the deep ocean.
In summary, while the human body can adapt to increased pressure to some extent, there are limits to what it can endure underwater. For recreational diving, depths beyond approximately 130 to 165 feet (40 to 50 meters) are generally considered unsafe without specialized equipment and training.