This is significant because once the tissues become saturated, the time required to ascend from depth, to decompress safely, will not increase with further exposure. In saturation diving, the divers live in a pressurized environment, which can be a saturation system - a hyperbaric environment on the surface - or an ambient pressure or pressurised underwater habitat. This may continue for up to several weeks, usually with the divers living at the same or very similar ambient pressure to the work site, and they are decompressed to surface pressure only once, at the end of their tour of duty or contract. By limiting the number of decompressions in this way, the risk of decompression sickness and the total time required for decompression of each diver is significantly reduced at the cost of exposing the diver to other hazards associated with living under high pressure for prolonged periods. Saturation diving is an example of substitution of a hazard expected to present a lower risk than surface oriented diving for the same set of operations. Atmospheric pressure diving Atmospheric pressure diving isolates the diver from the ambient pressure of the environment by using an atmospheric diving suit (ADS), which is a small one-person articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of approximately one atmosphere. The ADS can be used for very deep dives of up to for many hours, and eliminates the majority of physiological dangers associated with deep diving; the occupant need not decompress, there is no need for special gas mixtures, and there is no danger of decompression sickness or nitrogen narcosis, and a greatly reduced risk of oxygen toxicity. Hard suit divers do not even need to be skilled swimmers, as swimming is not yet possible in atmospheric suits. The current generation of atmospheric suits are more ergonomically flexible than earlier versions, but are still very limited in personal mobility and dexterity compared to an ambient pressure diver. Use of an atmospheric suit may be considered as substituting a relatively low risk of crushing for a higher risk of decompression sickness and barotrauma, by using the suit as an engineered barrier between the diver and the hazards, or as personal protective equipment. Remotely operated underwater vehicles A remotely operated underwater vehicle (ROV) is an unoccupied, highly maneuverable, tethered mobile underwater device operated by