Although a number of
human activities are conducted underwater—such as research,
underwater diving for
work or
recreation, and
underwater warfare with
submarines, the underwater environment is hostile to humans in many ways and therefore little explored. An immediate obstacle to human activity under water is that human
lungs cannot naturally function in this environment. Unlike the
gills of
fish, human lungs are adapted to the exchange of
gases at atmospheric
pressure. Any penetration into the underwater environment for more than a few minutes requires
artificial aids to maintain life. For solid and liquid tissues like bone, muscle and blood, the high ambient pressure is not much of a problem; but it is a problem for any gas-filled spaces like the
mouth,
ears,
paranasal sinuses and lungs. This is because the gas in those spaces is much more compressible than the solids and liquids, and reduces in volume much more when under pressure and so does not provide those spaces with support against the higher outside pressure. Even at a depth of underwater, an inability to
equalize air pressure in the
middle ear with outside water pressure can cause pain, and the
tympanic membrane (eardrum) can rupture at depths under 10 ft (3 m). The danger of
pressure damage is greatest in shallow water because the ratio of pressure change is greatest near the surface of the water. 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.
Hazards There are several classes of hazards to humans inherent to the underwater environment. • Absence of breathable gas, which can cause
asphyxia, specifically by
drowning. • Ambient pressures which could cause
barotrauma, or toxic effects of breathing gas components at raised partial pressures. • Ambient temperatures which may lead to
hypothermia, or in unusual cases, to
hyperthermia, due to high rates of heat exchange. • Solution of inert breathing gas components may lead to
decompression sickness if
decompression is too rapid. • Entrainment of diver by moving water in
currents and
waves can cause injury by impacting the diver against hard objects or moving them to inappropriate depths. •
Dangerous aquatic organisms of various sorts.
Ambient pressure diving In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold, or use breathing apparatus for
scuba diving or
surface-supplied diving, and the
saturation diving technique reduces the risk of
decompression sickness (DCS) after long-duration deep dives. Immersion in water and exposure to cold water and high pressure have physiological effects on the diver which limit the depths and duration possible in ambient pressure diving. Breath-hold endurance is a severe limitation, and breathing at high ambient pressure adds further complications, both directly and indirectly. Technological solutions have been developed which can greatly extend depth and duration of human ambient pressure dives, and allow useful work to be done underwater. Divers do not even need to be skilled swimmers, but mobility and dexterity are significantly degraded.
Submersibles and submarines A submersible is a small
watercraft designed to operate underwater. The term
submersible is often used to differentiate from other underwater vessels known as
submarines, in that a submarine is a fully autonomous craft, capable of renewing its own power and breathing air, whereas a submersible is usually supported by a surface vessel, platform, shore team or sometimes a larger submarine. There are many types of submersibles, including both manned and unmanned craft, otherwise known as
remotely operated vehicles or ROVs.
Remotely operated or autonomous vehicles AUV for underwater mine identification and destruction. From Norwegian minehunter KNM Hinnøy Remotely operated underwater vehicles and autonomous underwater vehicles are part of a larger group of undersea systems known as
unmanned underwater vehicles. ROVs are unoccupied, usually highly maneuverable, and operated by a crew either aboard a vessel/floating platform or on proximate land. They are linked to a host ship by a neutrally buoyant
tether, or a load-carrying
umbilical cable is used along with a tether management system (TMS). The umbilical cable contains a group of
electrical conductors and fiber optics that carry electric power, video, and data signals between the operator and the TMS. Where used, the TMS then relays the signals and power for the ROV down the tether cable. Once at the ROV, the electric power is distributed between the components of the ROV. In high-power applications, most of the electric power drives a high-power electric motor which drives a
hydraulic pump for propulsion and to power equipment. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle's capabilities. Autonomous underwater vehicles (AUVs) are
robots that travel underwater without requiring input from an operator.
Underwater gliders are a subclass of AUVs. ==Sciences==