The underwater diving environment, or just diving environment is the natural or artificial surroundings in which a dive is done. It is usually underwater, but professional diving is sometimes done in other liquids. Underwater diving is the human practice of voluntarily descending below the surface of the water to interact with the surroundings, for various recreational or occupational reasons, but the concept of diving also legally extends to immersion in other liquids, and exposure to other hyperbaric pressurised environments.
The diving environment is limited by accessibility and risk, but includes water and occasionally other liquids. Most underwater diving is done in the shallower coastal parts of the oceans, and inland bodies of fresh water, including lakes, dams, quarries, rivers, springs, flooded caves, reservoirs, tanks, swimming pools, and canals, but may also be done in large bore ducting and sewers, power station cooling systems, cargo and ballast tanks of ships, and liquid-filled industrial equipment. The environment may affect equipment configuration: for instance, freshwater is less dense than saltwater, so less added weight is needed to achieve diver neutral buoyancy in freshwater dives. Water temperature, visibility and movement also affect the diver and the dive plan. Diving in liquids other than water may present special problems due to density, viscosity and chemical compatibility of diving equipment, as well as possible environmental hazards to the diving team.
Benign conditions, sometimes also referred to as , are environments of low risk, where it is extremely unlikely or impossible for the diver to get lost or entrapped, or be exposed to hazards other than the basic underwater environment. These conditions are suitable for initial training in the critical survival skills, and include swimming pools, training tanks, aquarium tanks and some shallow and protected shoreline areas. Open water is unrestricted water such as a sea, lake or flooded quarry, where the diver has unobstructed direct vertical access to the surface of the water in contact with the atmosphere. Open-water diving implies that if a problem arises, the diver can directly ascend vertically to the atmosphere to breathe the ambient air. Wall diving is done along a near vertical face. Blue-water diving is done in good visibility in where the bottom is out of sight of the diver and there may be no fixed visual reference. Black-water diving is mid-water diving at night, particularly on a moonless night.
An overhead or penetration diving environment is where the diver enters a region from which there is no direct, purely vertical ascent to the safety of breathable atmosphere at the surface. Cave diving, wreck diving, ice diving and diving inside or under other natural or artificial underwater structures or enclosures are examples. The restriction on direct ascent increases the risk of diving under an overhead, and this is usually addressed by adaptations of procedures and use of equipment such as redundant breathing gas sources and guide lines to indicate the route to the exit. Night diving can allow the diver to experience a different underwater environment, because many marine animals are nocturnal. Altitude diving, for example in mountain lakes, requires modifications to the decompression schedule because of the reduced atmospheric pressure.
Underwater
An underwater environment is an environment of, and immersed in, liquid water in a natural or artificial feature (called a body of water), such as an ocean, sea, lake, pond, reservoir, river, canal, or aquifer. Some characteristics of the underwater environment are universal, but many depend on the local situation.
A number of human activities are conducted in the more accessible parts of the underwater environment. These include research, underwater diving for work or recreation, and underwater warfare with submarines. This environment is hostile to humans in many ways and often inaccessible, and therefore relatively little explored.
An immediate obstacle to human activity under water is that human lungs cannot naturally function in this environment. Any penetration into the underwater environment for more than a few minutes requires artificial aids to maintain life. The raised ambient pressure is a problem for any gas-filled spaces like the mouth, ears, paranasal sinuses and lungs. and can cause barotrauma. The raised pressure also affects the solution of breathing gases in the tissues over time, and can lead to a range of adverse effects, such as inert gas narcosis, and oxygen toxicity. Decompression must be controlled to avoid bubble formation in the tissues and the consequent symptoms of decompression sickness. With a few exceptions, the underwater environment tends to cool the unprotected human body. This heat loss will generally lead to hypothermia eventually. Entrainment of a diver by moving water can cause injury by impacting the diver against hard objects or moving them to inappropriate depths.
Depth range
One of the more obvious environmental constraints on diving is the ambient pressure, which is a function of depth and density.
The recreational diving depth limit set by the EN 14153-2 / ISO 24801-2 level 2 "Autonomous Diver " standard is . The recommended depth limit for more extensively trained recreational divers ranges from for PADI divers, (this is the depth at which nitrogen narcosis symptoms generally begin to be noticeable in adults), to specified by Recreational Scuba Training Council, for divers of the British Sub-Aqua Club and Sub-Aqua Association breathing air, and for teams of 2 to 3 French Level 3 recreational divers, breathing air.
For technical divers, the recommended maximum depths are greater on the understanding that they will use less narcotic gas mixtures. is the maximum depth authorised for divers who have completed Trimix Diver certification with IANTD or Advanced Trimix Diver certification with TDI. is the world record depth on scuba (2014). Commercial divers using saturation techniques and heliox breathing gases routinely exceed , but they are also limited by physiological constraints. Comex Hydra 8 experimental dives reached a record open water depth of in 1988. Atmospheric pressure diving suits are mainly constrained by the technology of the articulation seals, and a US Navy diver has dived to in one. Greater depths can be achieved with submersibles, some of which are capable of "full ocean depth", the greatest underwater depth known on Earth.
The liquid environment Most diving is done in fresh water, sea water, and brack water, but brines, low density silts, drilling mud, petrochemical liquids, crude and refined oils, alcohol mixtures and other liquids may be dived in for special reasons.
Liquids other than water Density and viscosity of the medium are of primary importance, as it must be possible for the diver to sink and move around in the medium. Chemical compatibility with the diving equipment is also essential to some extent, though provided the equipment protects the diver adequately for the duration of the dive, it may be acceptable to dispose of it after the dive. Health risks due to possible contamination of the diver are also a concern, and some of these environments may classify as hazardous materials and require formal decontamination after diving.
Type and profile of substrate The diving environment can be strongly influenced by the substrate, as most diving activities are conducted near the substrate. Recreational diving sites are commonly chosen by what can be seen there, and that often depends on the geographical location and the bottom structure. Tropical coral reef is the most popular environment among recreational diving tourists, with rocky reefs and shipwrecks also popular, as they tend to both provide scenic topography and support ecological diversity. Rocky substrates can support high-profile structure, like walls, overhangs, talus caves, pinnacles and steep sided gullies. Caves are also sought after for their mystery and sometimes spectacular topography, and may also be dived as a way to explore the underwater extent of flooded areas, or to penetrate beyond sumps. Unconsolidated material such as shingle, pebbles, gravel, sand and silt tend to be relatively flat, and topographically dull, and the ecology in finer grained substrates tends to be largely infauna, but there are also regions known for high biodiversity of colourful and exotic animals and muck diving
When the substrate is out of visual range for the diver, the mid-water with no fixed visual depth reference can be of interest for pelagic fauna. Diving in this environment in good visibility is known as blue-water diving during the day, and black-water diving during the night.
Water conditions Physical conditions of the water or other diving medium influence the safety and practicability of a dive and can affect the choice of equipment used. These include motion of the medium, visibility and illumination, temperature, and pressure. These conditions are affected by weather, season and climate.
Motion and flow of the medium Motion of the water affects the diver's ability to move around and hold a position while performing an activity. Types of water motion include Ocean currents, river currents, tides, waves, surge, upwellings, overfalls, turbulence, springs, and sinks. Motion of water is generally caused by surface wind, gravity and localised pressure differentials.
A high energy underwater environment is one in which the water can move large particles around. Small particles tend to remain in suspension. The turbidity is likely to be high and visibility likely to be relatively poor, but the actions of divers are unlikely to have much influence on these characteristics. A low energy environment encourages deposition of small and relatively light particles, which can produce clear water, with silt deposits on the substrate, easily disturbed by divers to cause a silt-out, and sudden deterioration of visibility.
Visibility and illumination
Visibility, the distance at which objects can be seen in a medium, and illumination, the level of ambient natural of artificial light, are environmental factors which influence the ability of a diver to perform the goal of a dive, and can also strongly affect the safety of the dive. They can be independent of many of the other factors, and dependent on others. Low visibility and zero visibility are usually associated with poor illumination, but visibility can be good even at low light levels, and artificial lighting is available to increase illumination.
Water temperatures
Hot water is usually found in industrial environments or natural hot springs. Hot water can cause overheating of divers, and this can be difficult to prevent. Professional divers diving with surface-supplied equipment may use a flow of cooling water analogous to a hot water suit. Tropical water is the natural temperature of bodies of water in tropical regions, due to heating by the sun and cooling by wind. Maximum sea surface temperature can reach about . Temperate water is water cooler than tropical, and warmer than "cold water". For diving purposes this can be considered the temperature range in which a full wetsuit is acceptable thermal protection for most divers for most diving activities. The range of could generally be considered temperate water for diving. is water at temperatures which are tolerable for a short to moderate time unprotected, and in which heat loss can be managed without difficulty by passive insulation alone. A long-distance swimmer might find the temperature acceptable for a long but active immersion. Cold water is generally considered as temperatures below where regulator freeze becomes a significant possibility.