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The demand valve develops a free-flow while filling the DSMB. This can deplete the contents of the scuba cylinder rapidly, and since the DSMB is commonly deployed at the end of the dive, when the breathing gas has reached a critically low level , this can put the diver in a situation of inadequate gas supply for a safe ascent.
The threads of cylinder and valve must be of matching thread specification, clean and full form, undamaged and free of cracks, burrs and other imperfections. Tap marks [note 3] are acceptable and should not be confused with cracks. Other neck surfaces will also be examined to be sure they are free from cracks.
A major difference between rebreather diving and open-circuit scuba diving is in fine control of neutral buoyancy. When an open-circuit scuba diver inhales, a quantity of highly compressed gas from their cylinder is reduced in pressure by a regulator, and enters the lungs at a much higher volume than it occupied in the cylinder.
Underwater diving can be described as all of the following: A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. . Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a ...
Rebreather diving, closed-circuit or semi-closed-circuit scuba; Freediving or breathhold diving, where the diver completes the dive on a single breath of air taken at the surface before the dive. Snorkelling allows breathing at the surface with the face submerged, and is used as an adjunct to free diving and scuba.
Scuba gas planning is the aspect of dive planning which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive profile, and can be critical to the safety of the dive. The scuba diver by definition is independent of surface supply and, in general, must carry all gas needed for the dive, though ...
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Open water – Unrestricted water with free vertical access to the surface Blue-water diving – Diving in mid-water where the bottom is out of sight; Black-water diving – Open ocean mid-water diving at night; Penetration diving, also known as overhead environments – Diving under a physical barrier to a direct vertical ascent to the surface