The maximum depth a person can dive depends entirely on the technology used, as the immense pressure of the deep ocean presents a hostile and rapidly fatal environment to the unprotected human body. For every 10 meters a diver descends, the pressure increases by the equivalent of one full atmosphere. At just 100 meters, the body is under ten times the pressure experienced at sea level. This crushing force means the maximum depth is defined by whether the diver relies on a single breath, compressed air, or a protective mechanical shell. While human-powered diving limits are measured in hundreds of meters, the absolute deepest point reached by a person is measured in thousands.
The Extreme Depth of Breath-Hold Diving
The purest form of diving relies solely on the air a person can hold in their lungs, a discipline known as freediving. The absolute deepest recorded breath-hold dive, known as the “No Limit” category, was achieved by Herbert Nitsch, who reached a depth of 214 meters (702 feet) in 2007. The female record is held by Tanya Streeter, who descended to 160 meters (525 feet) in 2002. These depths are made possible by a biological adaptation known as the mammalian dive reflex, which is triggered by facial contact with cold water and pressure.
The dive reflex automatically slows the heart rate (bradycardia) and constricts blood vessels in the extremities to prioritize oxygen delivery to the brain and heart. As the diver descends, the increasing pressure compresses the air in the lungs dramatically, which would normally collapse the chest cavity. Highly trained freedivers counteract this with a blood shift, where fluid and blood from the limbs and torso flood the chest and organs. This helps equalize the pressure and prevents a potentially fatal lung squeeze. Even with these physiological safeguards, the deepest category of freediving is no longer officially sanctioned due to the extreme risks involved.
Physiological Barriers in Gas-Supplied Diving
When a diver uses a self-contained underwater breathing apparatus (SCUBA) or surface-supplied gas, the limiting factor shifts from a lack of oxygen to the toxic effects of gases under high pressure. Even breathing regular air, nitrogen narcosis begins to impair a diver’s judgment and coordination as the partial pressure of nitrogen increases. This effect, often compared to drinking alcohol, typically becomes noticeable around 30 meters (100 feet) and is a serious danger below 60 meters (200 feet).
To go deeper, divers must replace the nitrogen in their breathing mixture with helium, creating a blend known as Trimix. Below about 150 meters (500 feet), the high pressure on the nervous system causes High-Pressure Nervous Syndrome (HPNS), which results in tremors, dizziness, and cognitive dysfunction. Furthermore, the oxygen component of any gas mixture becomes toxic under pressure. If the partial pressure of oxygen exceeds safe limits (generally 1.4 to 1.6 atmospheres), it causes seizures that lead to drowning.
These combined issues mean that the maximum depth for gas-supplied diving is limited to the range of 300 to 500 meters, depending on the gas mixture and descent rate. The deepest simulated dive in a hyperbaric chamber reached over 700 meters, but the deepest open-water dive using saturation technique is generally considered to be in the range of 310 to 330 meters. A non-negotiable procedural limit for all deep gas diving is the extensive staged decompression required. This allows the inert gases dissolved in the body’s tissues to escape safely, preventing decompression sickness, or “the bends.”
The Absolute Deepest: Protected Atmospheric Diving
The only way for a person to reach the deepest parts of the ocean is to completely bypass the physiological constraints of pressure by maintaining a surface-level atmosphere around the body. This is achieved using Atmospheric Diving Suits (ADS) or deep-sea submersibles. These vessels are pressurized metal bubbles designed to withstand the crushing force of the water column, protecting the occupant from any pressure increase. The diver inside remains at one atmosphere of pressure, regardless of the external depth.
The deepest point ever reached by a person is the Challenger Deep, located at the southern end of the Mariana Trench. In 2019, explorer Victor Vescovo descended to a depth of 10,925 meters (35,843 feet) in his submersible, the DSV Limiting Factor. At this extreme depth, the pressure is more than 1,000 times that at sea level, but the pilot and passengers are completely isolated from it by a thick titanium hull. This mechanical protection allows humans to visit the deepest known point on Earth.