Astronauts in the NASA space program need to adjust to life in space, where gravity woks very differently. Similarly, divers need to adjust for the very different way that their weight works underwater. BCDs help divers with this task. Scuba Buoyancy Compensation Devices (BCDs) are vital because they allow divers to regulate the correct neutral and positive buoyancy required on a dive. When a diver transfers air to the BCD air bladders from the dive tank, the diver can ascend. When a diver removes air from the BCD air bladders, he or she descends.

While you can rent BCDs, it is far safer to buy your own BCD. When you own your own BCD, you can become familiar with the device. That way, you know exactly where the dump valve and other emergency features are. As well, since every BCD has a slightly different configuration and buoyancy, owning your own BCD will allow you to adjust your device exactly. When buying your own BCD, there are several things you will want to keep in mind:

1) Your gender. Originally, BCDs were designed for male divers, because manufacturers assumed that men tended to dive most. Now, however, manufacturers create different BCDs for men and for women. BCDs designed for female divers have narrower shoulder straps and a shape more designed for the female body. As well, these BCDs tend to eliminate the chest strap or have relocated it to enhance comfort.

2) Style and fit. In a BCD, style and fit are about safety, not fashion. The right fit and style make it easier for you to move correctly and to use your BCD correctly underwater, making you safer. Currently, most divers prefer a jacket or vest style of BCD. This covers your back and has buckles or straps in the front. In addition, there are front-mounted BCDs, which look a little like life vests, and back-mounted BCD, which look like knapsacks. Jacket and vest designs have the advantage of providing both rear and front buoyancy. When selecting a fit, look for a BCD that does not slip or restrict your movement in any way. It should fit like a coat, with no bulging or sagging. It should be snug, but not tight. A correctly fitted BCD will allow you to reach all your valves and hoses easily. It will also not extend too far down. A too-long BCD can hamper the movement of your legs and make it harder to reach your weights.

3) Air bladders. There are two types of air bladder placement: wrapping or back. Both back air bladders and wrapping air bladders have their advantages and drawbacks, so this is a matter of personal choice. Some divers find one type of placement more comfortable than the other, so choose the type of air bladder that is most comfortable for you. Beyond placement, also consider lift capability. Your air bladders must be able to bring you safely to the surface when you are wearing all your gear. How much lift you will need will depend largely on your body type. Muscular men with little body fat will need the most lift. When considering the lift you need, also consider the weight of your gear and where you will dive. Cold water divers tend to require more lift, for example.

4) Integrated weight systems. In the past, a diver’s weight system consisted of a weight belt around the waist. An integrated weight system, however, distributes weight via 1-5 pound lead shot pockets across the BCD. An integrated weight system is considered safer because divers can dump some or all their weights in an emergency. This allows the diver to control their ascent and therefore suffer fewer of the health risks associated with a too-rapid ascent. An integrated weight system also reduces the weight and pressure on the waist and lower back.

5) Attachment options. BCDs are often used to attach diver gear, such as whistles, diving knives, and other safety equipment. When buying a BCD, look for enough sturdy D-rings and pockets on your BCD to carry all the diving gear you will need.