The ocean’s depths pose a fundamental challenge: immense water pressure. As humans venture deeper, this powerful force significantly impacts the body, requiring specialized technologies.
Understanding Underwater Pressure
Underwater pressure, or hydrostatic pressure, results from the weight of the water column. It increases consistently with depth; for every 33 feet (10 meters) of descent in seawater, pressure increases by one atmosphere (ATA). At sea level, air pressure is 14.7 pounds per square inch (psi), or 1 ATA.
This escalating pressure directly affects gases. According to a principle similar to Boyle’s Law, gas volume is inversely related to applied pressure. As pressure increases with depth, gas volumes decrease proportionally. For instance, at 33 feet (10 meters) underwater, pressure is 2 ATA, compressing a gas volume to half its surface size. This compression significantly affects the body’s air-filled spaces.
The Body’s Response to Extreme Pressure
The human body is mostly incompressible water, so its solid and liquid tissues are unaffected by pressure changes. However, air-filled spaces are highly vulnerable to compression. This can lead to pressure-related injuries known as barotrauma.
Barotrauma occurs when pressure differences cause tissue damage in air-filled spaces. Common examples include ear and sinus barotrauma, leading to pain or membrane rupture. Pulmonary barotrauma, or lung squeeze, is a serious concern for freedivers. As a diver descends, lung air compresses; if volume decreases beyond residual, negative pressure can cause blood and fluid to enter alveoli, leading to injury.
Beyond physical compression, dissolved gases under pressure can have intoxicating or toxic effects. Nitrogen narcosis, or “rapture of the deep,” occurs when nitrogen at high partial pressures affects brain function, similar to alcohol intoxication. Symptoms include impaired judgment, euphoria, confusion, or stupor, noticeable beyond 100 feet (30 meters). Oxygen also becomes toxic at elevated partial pressures. Central nervous system (CNS) oxygen toxicity can lead to severe symptoms like convulsions, visual disturbances, and nausea.
Upon ascent, rapid pressure reduction can cause dissolved gases, primarily nitrogen, to form bubbles in tissues and the bloodstream, leading to decompression sickness (DCS), or “the bends.” These bubbles can obstruct blood flow, causing pain or severe neurological and respiratory issues.
Limits of Human Deep Diving
Humans explore ocean depths through various methods, each with pressure-related limitations. Freediving, relying on a single breath, pushes physiological boundaries. Highly trained freedivers utilize the mammalian dive reflex to conserve oxygen and manage lung compression.
Constant weight freediving records are around 123-136 meters (403-446 feet) for men and women. “No-limits” records, using a weighted sled for descent and buoyancy for ascent, reach around 214 meters (702 feet).
SCUBA (Self-Contained Underwater Breathing Apparatus) diving provides compressed breathing gases for longer underwater durations. Recreational SCUBA diving has depth limits of around 130 feet (40 meters) due to nitrogen narcosis and oxygen toxicity risks with standard air. Technical and commercial divers use specialized gas mixtures, like trimix (helium, oxygen, and nitrogen), to mitigate these risks, reaching depths beyond 300 meters (984 feet). These deeper dives necessitate extensive decompression stops to prevent decompression sickness.
For extreme depths, humans rely on technology that isolates them from ambient pressure.
Atmospheric Diving Suits (ADS)
Atmospheric Diving Suits (ADS) are rigid, one-person submersibles that maintain surface pressure inside. This allows occupants to work at depths without physiological pressure effects. Modern ADS units operate up to 700 meters (2,300 feet).
Submersibles and Bathyscaphes
Even deeper exploration requires submersibles or bathyscaphes, small submarines designed to withstand crushing pressures. These vehicles provide a shirt-sleeve environment, enabling exploration of the deepest ocean parts, such as the Challenger Deep in the Mariana Trench, 11,000 meters (36,000 feet) deep.