: How do those floaty balloon things work that divers use to quickly ascend?
In: 1
Divers wear something called a BCD – a buoyancy control device. It’s like a vest or backpack that can be filled with air from the diver’s tank or from their mouth. Air can be added to the BCD or released from the BCD. Divers also wear weights. The act of balancing the your weight and buoyancy is called “trimming.”
As we walk around on land, we experience 1 atmosphere (1atm) of pressure. At 10 meters (or 33ft) underwater, we experience 2atm. That’s 1atm of constant earth pressure, plus an additional atmosphere of pressure from the weight of the water around you. At 20m (66ft) we experience 3atm, and so on.
Scuba diving is an activity that requires a lot of management of your buoyancy, or trimming. As you descend, the air in your body and in your tank begins to compress. At 10 meters, the air in your tank compresses to 1/2 of its volume. That means a full tank at the surface is only half full at 10m. If you descend to 20m, the air in your tank is halved again. A full tank at the surface is only 1/4 full at 20m.
As the air compresses, it also compresses in your BCD. This is why you start to descend faster the deeper you go. You have to add more air to your BCD to trim against the weight you’re carrying. When you start to ascend, you begin experiencing less pressure, so the air in your tank and your BCD starts to expand, which makes you more buoyant. This is when you’d have to release air from your BCD.
Divers don’t usually use their BCDs to ascend. They do use them at the surface though, inflated, as like a life vest. When you’re submerged, however, air is valuable. You save more air by swimming upward than you do by filling your BCD and allowing it to carry you upward. You also have more control over your ascent.
Latest Answers