See also: Underwater diving environment. The 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 pressurised environments. Some of the more common diving environments are listed and defined here.
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 confined water, 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 air. Wall diving is done along a near vertical face. Blue-water diving is done 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 environment is where the diver enters a space 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.
See main article: Recreational dive sites. The common term for a place at which one may dive is a dive site. As a general rule, professional diving is done where the work needs to be done, and recreational diving is done where conditions are suitable. There are many recorded and publicised recreational dive sites which are known for their convenience, points of interest, and frequently favourable conditions.
Diver training facilities for both professional and recreational divers generally use a small range of dive sites which are familiar and convenient, and where conditions are predictable and the environmental risk is relatively low.
Physiologically and legally a compression in a diving chamber is considered a dive. Various options for hypebaric transport and treatment exist, each with its own characteristics, applications and operational procedures.
Confinement can influence diver safety and the ability of the diver to perform the required task. Some types of confinement improve safety by limiting the ability of the diver to move into higher risk areas, others limit the ability of the diver to maneuver or to escape to a place of safety in an emergency.
Visibility in the diving medium directly affects diver safety and the ability to complete useful tasks. In some cases this can be mitigated by technology to improve visibility, but often the task procedures must be modified to suit the capacity of the diver, and the diver must have training and equipment bto deal with emergencies under more difficult circumstances.
Besides the hazards associated with the underwater environment itself, there are a considerable variety of hazard types and risk levels to which a diver may be exposed due to the circumstances of the dive task. Many of these are normally only encountered by professional specialists, and the means of reducing risk to an acceptable level may be complex and expensive.
The temperature of the diving environment can influence the equipment used by the diver, and the time the diver can be exposed to the environment without excessive risk.
The geographical location of a dive site can have legal or environmental consequences.
See also: Deep diving.
The recreational diving depth limit set by the EN 14153-2 / ISO 24801-2 level 2 "Autonomous Diver " standard is 20m (70feet). This is the depth to which a diver is assumed competent to dive in terms of the standard. The recommended depth limit for more extensively trained recreational divers ranges from 30m (100feet) for PADI divers, (this is the depth at which nitrogen narcosis symptoms generally begin to be noticeable in adults), to 40m (130feet) specified by Recreational Scuba Training Council, 50m (160feet) for divers of the British Sub-Aqua Club and Sub-Aqua Association breathing air, and 60m (200feet) 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. 100m (300feet) is the maximum depth authorised for divers who have completed Trimix Diver certification with IANTD or Advanced Trimix Diver certification with TDI. 332m (1,089feet) is the world record depth on scuba (2014). Commercial divers using saturation techniques and heliox breathing gases routinely exceed 100m (300feet), but they are also limited by physiological constraints. Comex Hydra 8 experimental dives reached a record open water depth of 534m (1,752feet) in 1988. Atmospheric pressure diving suits are mainly constrained by the technology of the articulation seals, and a US Navy diver has dived to 610m (2,000feet) in one.
From an oceanographic viewpoint:
Recreational divers will usually dive in the intermediate marine environment. Technical and commercial divers may venture into the deep water environment. The surf zone is usually too turbulent for safe or effective diving.
See also: Professional diving.