Underwater search and recovery is the process of locating and recovering underwater objects, often by divers, [1] but also by the use of submersibles, remotely operated vehicles and electronic equipment on surface vessels.
Most underwater search and recovery is done by professional divers as part of commercial marine salvage operations, military operations, emergency services, or law enforcement activities. [2] [3]
Minor aspects of search and recovery are also considered within the scope of recreational diving.
The scope of professional search and recovery includes the following applications:[ citation needed ]
Search and recovery diving is also frequently undertaken as part of recreational diving, and most diver training organisations have dedicated training courses on the subject. Search and recovery is generally considered a more hazardous speciality diving course. [nb 1] [ citation needed ]
Underwater search and recovery used to form a mandatory component of the Advanced Open Water Diver training course for many North American diver training agencies, [nb 2] which, in addition to learning basic search and recover skills, also assisted in teaching students to cope with task loading.[ citation needed ]
Although the scale, value and equipment used in commercial and recreational search and recovery are enormously different, the basic premise remains the same in each case.
Underwater searches, much like above water searches, are designed around specific search patterns. The most common forms of underwater search patterns are:
The patterns are usually performed by divers in pairs or teams below the water, but they can also be conducted by use of a tender who may be a snorkeller at the surface, a person on a towing boat, or a person located on the shore.[ citation needed ]
In simple search operations, the patterns will usually be conducted by the divers simply looking visually for the object. In more sophisticated search operations, underwater magnetometers or hand held sonar may be used.[ citation needed ]
Diver training traditionally divides searches into two categories, specific and non-specific.[ citation needed ]
A specific search is an attempt to locate a known object in a known area where it was believed to be lost even if the time period is undefined, and the search terminates upon the location of the object. The classic example of this would be an item lost overboard from a boat, which needs to be recovered.
A non-specific search is a search for either a type of object or anything valuable within the dive locale. The discovery of a relevant object does not usually terminate the search until the entire search area has been covered, or the search terminates early for other reasons (air supply, no decompression limits, etc.).
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Recovery techniques depend upon the type and size of the object, and the depth at which it is found. [4] : Ch. 2
Smaller objects, such as a coin or camera, can simply be carried up by the diver. Training agencies vary in what they specify to be the maximum apparent weight that can be safely carried up unassisted by a scuba diver, but normally the limit is set around 15 pounds (7 kg), though this will depend on the reserve capacity of the buoyancy compensator,the diver's skill in buoyancy control, and the consequences of a loss of buoyancy control. Anything heavier represents a material change to the diver's buoyancy control, and may put the diver at risk from an uncontrolled ascent if contact with the object is lost during ascent. Professional surface supplied divers working from a bell or stage can carry heavier objects to the stage, but they usually have an option to use a lifting line independent of the diver transport platform.[ citation needed ] Similarly, small objects can be recovered directly by lifting by an ROV or crewed submersible with manipulator capability. [4] : Ch. 2
Medium-sized objects are normally recovered using a lifting bag, and professional divers are trained in lifting bag techniques (it is usually considered specialty training in recreational diving). The most common hazard is entanglement with lines whilst filling the lifting bag from the diver's alternate air source. This risk, when coupled with the possibility of rapid ascent following the freeing of the object from suction caused by it being embedded in the bottom sediment, can seriously compromise the safety of the recovery team if done improperly. Lift bags can be rated up to several tons, but these are beyond the capacity of most recreational divers, and there is no recreational diver training for their use.[ citation needed ] A cubic metre of air per tonne at ambient hydrostatic pressure is needed. This is not practicable for cylinders carried by the diver (the most common scuba cylinder size has a total capacity of 80 cubic feet (2.3 m3) at surface pressure). Large lifting bags are normally filled from a low-pressure compressed air hose from the surface, which may be attached directly to the lifting bag.
Significantly larger objects usually require specialised industrial lifting equipment, such as a winch attached to a boat or platform, or specialised equipment to seal and dewater sunken vessels. [4]
Search hazards are determined by the environment of the search area and type of the search. Recovery hazards are related to the object to be recovered, the local environment through which it is to be moved and the method and equipment to be used. There is a large variety possible for all of these, and while some may not be known beforehand, it is usually possible to make a reasonable estimate based on experience with similar situations.
Search and recovery operations are part of the professional diver's working skill set, and will be included in entry-level training. [5] Public safety divers' occupation and job description is based on underwater search and recovery, and they may learn more techniques than other professional divers.
Search and recovery is a class of underwater work, and is out of scope for general recreational diving. Nevertheless, many recreational divers choose to learn the skills and have access to limited training and equipment through recreational diver training providers, and consequently there is also certification available. [6]
A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. Scuba is an anacronym for self-contained underwater breathing apparatus. Although strictly speaking the scuba set is only the diving equipment that is required for providing breathing gas to the diver, general usage includes the harness or rigging by which it is carried and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge. In the looser sense, scuba set has been used to refer to all the diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment or scuba gear. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface-supplied diving systems and is allowed by the relevant legislation and code of practice.
An overhead or penetration diving 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.
Recreational diver training is the process of developing knowledge and understanding of the basic principles, and the skills and procedures for the use of scuba equipment so that the diver is able to dive for recreational purposes with acceptable risk using the type of equipment and in similar conditions to those experienced during training.
Diving activities are the things people do while diving underwater. People may dive for various reasons, both personal and professional. While a newly qualified recreational diver may dive purely for the experience of diving, most divers have some additional reason for being underwater. Recreational diving is purely for enjoyment and has several specialisations and technical disciplines to provide more scope for varied activities for which specialist training can be offered, such as cave diving, wreck diving, ice diving and deep diving. Several underwater sports are available for exercise and competition.
Recreational diving or sport diving is diving for the purpose of leisure and enjoyment, usually when using scuba equipment. The term "recreational diving" may also be used in contradistinction to "technical diving", a more demanding aspect of recreational diving which requires more training and experience to develop the competence to reliably manage more complex equipment in the more hazardous conditions associated with the disciplines. Breath-hold diving for recreation also fits into the broader scope of the term, but this article covers the commonly used meaning of scuba diving for recreational purposes, where the diver is not constrained from making a direct near-vertical ascent to the surface at any point during the dive, and risk is considered low.
The buddy check is a procedure carried out by scuba divers using the buddy system where each diver checks that the other's diving equipment is configured and functioning correctly just before the start of the dive. A study of pre-dive equipment checks done by individual divers showed that divers often fail to recognize common equipment faults. By checking each other's equipment as well as their own, it is thought to be more likely that these faults will be identified prior to the start of the dive.
A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface.
Underwater divers may be employed in any branch of an armed force, including the navy, army, marines, air force and coast guard. Scope of operations includes: search and recovery, search and rescue, hydrographic survey, explosive ordnance disposal, demolition, underwater engineering, salvage, ships husbandry, reconnaissance, infiltration, sabotage, counterifiltration, underwater combat and security.
Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Scuba Schools International (SSI) is a for-profit organization that teaches the skills involved in scuba diving and freediving, and supports dive businesses and resorts. SSI has over 2,500 authorized dealers, 35 regional centers, and offices all over the world.
Diver rescue, usually following an accident, is the process of avoiding or limiting further exposure to diving hazards and bringing a diver to a place of safety. A safe place generally means a place where the diver cannot drown, such as a boat or dry land, where first aid can be administered and from which professional medical treatment can be sought. In the context of surface supplied diving, the place of safety for a diver with a decompression obligation is often the diving bell.
Marine salvage is the process of recovering a ship and its cargo after a shipwreck or other maritime casualty. Salvage may encompass towing, lifting a vessel, or effecting repairs to a ship. Salvors are normally paid for their efforts. However, protecting the coastal environment from oil spillages or other contaminants from a modern ship can also be a motivator, as oil, cargo, and other pollutants can easily leak from a wreck and in these instances, governments or authorities may organise the salvage.
Salvage diving is the diving work associated with the recovery of all or part of ships, their cargoes, aircraft, and other vehicles and structures which have sunk or fallen into water. In the case of ships it may also refer to repair work done to make an abandoned or distressed but still floating vessel more suitable for towing or propulsion under its own power. The recreational/technical activity known as wreck diving is generally not considered salvage work, though some recovery of artifacts may be done by recreational divers.
Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
Supervised diver specifies the training and certification for recreational scuba divers in international standard ISO 24801-1 and the equivalent European Standard EN 14153-1. Various diving organizations offer diving training that meets the requirements of the Supervised Diver. A diving certification which corresponds to the Supervised Diver allows for recreational diving under the direct supervision of a divemaster or recreational diving instructor in open water. Most diving organizations recommend not to exceed a diving depth of 10 to 12 metres. After the successful completion of a training equivalent to the Supervised diver, training can be extended to the Autonomous diver certification level.
Dive leader is the title of an internationally recognised recreational diving certification. The training standard describes the minimum requirements for dive leader training and certification for recreational scuba divers in international standard ISO 24801-3 and the equivalent European Standard EN 14153-3. Various organizations offer training that meets the requirements of the dive leader standard. Some agencies use the title "Dive Leader" for their equivalent certification, but several other titles are also used, "Divemaster" may be the most widespread, but "Dive Supervisor" is also used, and should not be confused with the very different status and responsibilities of a professional diving supervisor. CMAS affiliates certifications which meet the requirements of CMAS 3-star diver should meet the standard by default. The occupation of a dive leader is also known as "dive guide", and is a specialist application of a "tour guide".
The following outline is provided as an overview of and topical guide to underwater diving:
Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.
The following index is provided as an overview of and topical guide to underwater diving:
Scuba diving tourism is the industry based on servicing the requirements of recreational divers at destinations other than where they live. It includes aspects of training, equipment sales, rental and service, guided experiences and environmental tourism.