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A descent of 10 metres (33 feet) in water increases the ambient pressure by an amount approximately equal to the pressure of the atmosphere at sea level. So, a descent from the surface to 10 metres (33 feet) underwater results in a doubling of the pressure on the diver. This pressure change will reduce the volume of a gas filled space by half.
The ambient pressure in water with a free surface is a combination of the hydrostatic pressure due to the weight of the water column and the atmospheric pressure on the free surface. This increases approximately linearly with depth. Since water is much denser than air, much greater changes in ambient pressure can be experienced under water.
The absolute pressure on an ambient pressure diver is the sum of the local atmospheric pressure and hydrostatic pressure. [ 5 ] [ 6 ] Hydrostatic pressure is the component of ambient pressure due to the weight of the water column above the depth, and is commonly described in terms of metres or feet of sea water .
A study published in 2009 in the journal Aviation, Space and Environmental Medicine campared ascent rates of 30 feet per minute and 60 feet per minute in recreational divers. The group using the faster ascent rate had higher bubble grades after the dive measured ultrasonically, which supports the hypothesis that slower ascents reduce ...
Pressure conversion between msw and fsw is slightly different from length conversion between metres and feet; 10 msw = 32.6336 fsw and 10 m = 32.8083 ft. [1] The US Navy Diving Manual gives conversion factors for "fw" (feet water) based on a fresh water density of 62.4 lb/ft 3 and for fsw based on a sea water density of 64.0 lb/ft 3. [1]
As a diver descends, the ambient pressure increases. At 10 meters (33 feet) in seawater, it is twice the normal atmospheric pressure at the surface. At 40 meters (a common recommended limit for recreational diving) it is 5 times the pressure at sea level. Pressure decreases with altitude above sea level, but less dramatically.
A dive profile is a description of a diver's pressure exposure over time. It may be as simple as just a depth and time pair, as in: "sixty for twenty," (a bottom time of 20 minutes at a depth of 60 feet) or as complex as a second by second graphical representation of depth and time recorded by a personal dive computer. Several common types of ...
A scuba diver moves underwater primarily by using fins attached to the feet; [49] external propulsion can be provided by a diver propulsion vehicle, or a towboard pulled from the surface. Other equipment includes a diving mask to improve underwater vision , a protective diving suit , equipment to control buoyancy , and equipment related to the ...