The ocean covers more than 70% of the planet’s surface, yet the vast majority of its volume remains unexplored. This immense aquatic world presents a profound challenge due to the crushing pressure and complete darkness of the deep. While unmanned robotic probes have reached the seabed of the deepest trenches, determining how far a person can physically go requires distinguishing between direct human presence and the use of protective, specialized vehicles. This separates the physiological limits of the human body operating freely from the technological limits of engineered submersibles.
Human Limits in the Water Column
The maximum depth a person can reach without a protective shell is governed by the severe physiological consequences of water pressure. In free diving, where a diver relies on a single breath, the current absolute record, achieved with a weighted sled for descent, stands at 253 meters (830 feet). This extreme feat utilizes the mammalian dive reflex to conserve oxygen and tolerate the compression of the chest cavity.
Competitive free diving records, where the diver must ascend without assistance, are significantly shallower, hovering around 120 meters. Beyond the limits of a single breath, divers using compressed gas face obstacles related to gas toxicity and decompression sickness. The increasing partial pressure of nitrogen causes nitrogen narcosis, a reversible impairment that can produce effects similar to drunkenness at depths as shallow as 60 meters (200 feet).
To manage this, technical divers replace nitrogen with helium in breathing mixtures, creating gases like Trimix or Heliox. Even with these advancements, the human body under pressure is subject to oxygen toxicity and High-Pressure Nervous Syndrome (HPNS), which manifests as tremors and cognitive impairment below 150 meters. The deepest an individual has ever worked in open water using saturation diving—a technique where divers live in a pressurized environment—was 534 meters (1,750 feet), achieved in 1988. The deepest pressure exposure ever tolerated by a human was a simulated dive in a hyperbaric chamber, reaching a pressure equivalent of 701 meters (2,300 feet).
The Deepest Reaches by Submersible
To achieve the absolute deepest human descent, an explorer must rely on a vehicle designed to withstand the ocean’s most extreme environment: the Hadal Zone. This zone contains the deepest trenches, including the Mariana Trench in the western Pacific Ocean. The deepest point within this trench is known as the Challenger Deep.
The first successful crewed descent to this location was accomplished in 1960 by the U.S. Navy bathyscaphe Trieste, piloted by Jacques Piccard and Don Walsh. The vessel, which used gasoline for buoyancy and iron pellets for ballast, reached approximately 10,916 meters (35,814 feet). This record stood for over fifty years, demonstrating the extraordinary engineering required for survival.
The next crewed visit occurred in 2012 when filmmaker James Cameron made a solo dive in the submersible Deepsea Challenger, reaching 10,908 meters (35,787 feet). This dive proved that modern, compact vehicles could reach the deepest point on Earth. The current depth record, however, belongs to explorer Victor Vescovo, who, as part of the Five Deeps Expedition, made multiple dives in his submersible, the DSV Limiting Factor.
Vescovo’s deepest descent in 2019 was recorded at 10,934 meters (35,872 feet) to the bottom of the Challenger Deep. The DSV Limiting Factor is the first commercially certified vehicle capable of repeatedly reaching full ocean depth, marking a new era for deep-sea access. The ability to return multiple times has allowed for scientific study and exploration beyond the capacity of earlier, less repeatable missions.
Overcoming the Extremes of Deep Sea Travel
The primary challenge of deep-sea travel is the overwhelming hydrostatic pressure, which increases by one atmosphere (14.7 psi) for every 10 meters of descent. At the bottom of the Challenger Deep, the pressure exceeds 1,000 atmospheres, or roughly 15,750 psi. This is the equivalent of having the weight of fifty jumbo jets pressing on the submersible. The deep ocean is also marked by near-freezing temperatures, typically between 1 and 4 degrees Celsius, and a total absence of sunlight.
To counteract these forces, submersibles rely on specific engineering solutions, starting with the shape of the crew compartment. The spherical shape distributes external pressure evenly across its surface, making it the most structurally efficient design to resist compression. The DSV Limiting Factor’s pressure hull is constructed from thick, high-strength titanium, a material chosen for its favorable strength-to-weight ratio and resistance to corrosion.
Other components, such as cameras and scientific equipment, must be housed in their own pressure-resistant titanium or ceramic casings. The vehicle’s buoyancy is managed using syntactic foam, a composite packed with microscopic glass spheres that prevents crushing. This allows the submersible to descend and ascend under controlled conditions. These technological advances transform the vehicle into a self-contained, high-pressure refuge, allowing humans to explore the planet’s final frontier.