What is the primary function of a buoyancy control device (BCD)?

The primary function of a buoyancy control device (BCD) is to help maintain neutral buoyancy underwater. This is essential for divers as it allows them to control their position in the water column without expending unnecessary energy. By adjusting the amount of air in the BCD, divers can become positively buoyant, negatively buoyant, or achieve neutral buoyancy, which is crucial for various diving activities such as hovering, exploring, or ascending and descending safely.

Maintaining neutral buoyancy allows divers to conserve air and energy, avoid rapid ascents or descents, and minimize the impact on the marine environment. This balance is particularly important when diving with a tank, as the weight and buoyancy can change as air is consumed.

Other choices do not accurately reflect the primary purpose of a BCD. For instance, while a BCD can influence a diver's speed indirectly through buoyancy adjustments, increasing speed is not its main intention. Storing extra oxygen is not a function of a BCD, as gas storage occurs in the tank, not the buoyancy control device. Finally, although some BCDs may provide slight insulation, they are not primarily designed to keep divers warm; that function is typically fulfilled by wetsuits or drysuits.