They can also be broadly classified as having the buoyancy bladder as an integral part of the construction, or as a replaceable component supported inside the structural body.

Atmospheric pressure diving suits may use a trim tank similar to that on a submarine for small adjustments, but can be ballasted to be almost precisely neutral, and are virtually incompressible within their designed operating range.

A small amount of residual gas pressure on surfacing will be enough to eject the ballast water to establish positive buoyancy.

[7][6] This system is inherently more stable with hydrostatic pressure variation, and decreases buoyancy from the initial state, which is with a full cylinder of gas at the start of the dive.

To minimise the pressure rise caused by pumping ballast water into the cylinder when it is full, weighting is done for near neutral buoyancy at the start of the dive, with just enough positive buoyancy to safely swim at the surface with a full tank, and pump in a relatively small volume of water to descend, which is periodically increased during the dive to compensate for mass loss of breathing gas.

They are sometimes referred to as "horse collars" because of their resemblance, and are historically derived from the inflatable underwater demolition team (UDT) vest or Mae West life jacket issued to World War II flyers and divers.

The lower bladder was over the diver's stomach area, and was inflated by LP gas from the regulator, for buoyancy control underwater.

The effectiveness of a cummerbund depends on a waistline which is smaller than the circumference of the upper torso, and it may constrain free breathing if fitted too tightly.

Invented by Greg Flanagan in 1979 for North Florida cave divers, and further developed by William Hogarth Main,[12] the back plate and wing configuration is not a recent development, but has gained popularity because of suitability for technical diving where it is often used, as the technical diver often carries multiple cylinders on his back and/or clipped to D-rings on the harness webbing.

Depending on the construction details, the diver may need to carry up to four pounds of lead (two kilos) to counteract the positive buoyancy of an empty BC.

An average person has a surface area of about 2 m2,[18] so the uncompressed volume of a full one piece 6 mm thick wetsuit will be in the order of 1.75 × 0.006 = 0.0105 m3, or roughly 10 litres.

It must be possible to remain neutrally buoyant at the end of the dive, at the shallowest decompression stop, when almost all the diver's breathing gas has been used up.

[5] An unnecessarily large volume BC constitutes a greater risk of loss of control of ascent rate, particularly when combined with carrying more weight than is necessary to allow neutral buoyancy at the end of the dive with empty cylinders.

[19] There is a depth range in open circuit diving in which effectively stable neutral buoyancy can be maintained by adjusting the lung volume during the breathing cycle.

Similarly, the range is greater for a smaller total volume of non-respiratory ambient pressure gas space, as the variation in buoyancy is also proportional to this quantity, while the lung capacity of the diver is almost constant.

The scuba diver typically wishes to be trimmed nearly horizontally (prone) while under water, to be able to see and swim efficiently, but more nearly vertical and perhaps partly supine, to be able to breathe without a regulator when on the surface.

The effect of swimming with a head up angle, of about 15° as is quite common in poorly trimmed divers, can be an increase in drag in the order of 50%, which will adversely affect gas consumption.

[2] By inflating the BC at the surface, a conscious diver may be able to easily float face-up, depending on their equipment configuration choices.

This floating orientation is generally considered undesirable and can be minimised by relocation of some of the weights further to the rear, and using higher density cylinders (typically steel), which also move the centre of mass towards the back of the diver.

The usual inflation system is through a low-pressure hose from the primary breathing gas supply, but a dedicated direct feed pony bottle was common on early buoyancy compensators, and remains an option for some models.

This could theoretically reduce gas consumption, but is generally not considered worth the effort and the slight additional hazard of taking the DV out of the mouth underwater, and possibly having to purge it before breathing again.

The minimum consumption is by a diver who uses the correct amount to neutralise buoyancy and does not waste gas by overfilling, or by excessive weighting.

For deep technical diving it is considered prudent to supply the BC from a different regulator or cylinder to dry suit inflation gas, as this reduces the risk of simultaneous failure of both buoyancy control options by an order of magnitude.

The use of compatible quick connectors for both the dry suit and buoyancy compensator is also a way of reducing the risk of both items becoming unavailable during a dive, providing the diver has the dexterity and strength to disconnect and reconnect the fittings underwater.

Some had carbon dioxide inflation cartridges (a holdover, for surface use, of the Mae West flyer's lifejacket) to facilitate emergency ascent.

In 1968, dive shop owners Joe Schuch and Jack Schammel developed a more comfortable buoyancy compensator vest that featured a smaller buoyancy ring behind the diver's head, and a midriff section with sufficient volume to lift the diver's head out of the water in the event that one or both of its CO2 cartridges were activated for emergency ascent.

[5] In 1969, the original Control Buoyancy Jacket or "CBJ" was manufactured by Waverly Air Products of Chemung, NY and sold in dive shops throughout the east coast of the United States.

[31][32] Later products from competitors avoided patent infringement by eliminating some of the air path options, such as separating the bladder under the arms or over the shoulders.

This design was duplicated by other manufacturers and continues to be produced as of 2013[8] Rigid shell back inflation buoyancy compensators were marketed by U.S.

[citation needed] Other tech diving wing manufacturers include Ocean Management Systems, Halcyon, Apeks and Oxycheq.