Skin diving

Skin diving, underwater swimming and diving with or without self contained underwater breathing apparatus (SCUBA). The simplest apparatus is the snorkel, generally used with goggles, or mask, and flippers. An aqualung consists of compressed-air cylinders with an automatic demand regulator that supplies air at the correct pressure according to the diver's depth. “Closed-circuit” SCUBA contains a chemical that absorbs carbon dioxide from exhaled air.