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What are the different kinds of scuba diving?
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1.  Open circuit scuba diving is a type of recreational diving that involves using a compressed air tank and a regulator to breathe underwater.
2.  Semi-closed circuit scuba diving is similar to open circuit, but uses a second tank filled with an inert gas such as helium or nitrogen for breathing.
3.  Closed circuit scuba diving is a more technical form of recreational diving where the diver wears a full face mask connected to a high pressure hose which supplies oxygen from a surface supply.