Surface-supplied diving equipment

Surface-supplied diving equipment usually includes communication capability with the surface, which improves the safety and efficiency of the working diver.

Lightweight demand helmets are available in open circuit systems (used when breathing standard air) and closed circuit (reclaim) systems (which may be used in order to reduce costs when breathing mixed gas such as heliox and trimix: the exhaled gas is returned to the surface, scrubbed of carbon dioxide, re-oxygenated, recompressed into storade cylinders and may be returned to the diver or used for a later dive).

[4] The helmet may be of metal[5] or reinforced plastic composite (GRP), and is either connected to a neck dam or clamped directly to a dry suit.

Attachment to the neck dam is critical to diver safety and a reliable locking mechanism is needed to ensure that it is not inadvertently released during a dive.

As a result, gas cost is a significant factor in deep open circuit diving with helium-based mixtures for long periods.

The bonnet is attached and sealed to the corselet at the neck, either by bolts or an interrupted screw-thread, with some form of locking mechanism.

The front port can usually be opened for ventilation and communication when the diver is on deck, by being screwed out or swung to the side on a hinge.

Some helmets have an extra manual valve known as a spit-cock, which can be used to vent excess air when the diver is in a position where the main exhaust can not function correctly.

[16][12] The corselet, also known as a breastplate or gorget, is an oval or rectangular collar-piece resting on the shoulders, chest and back, to support the helmet and seal it to the suit, usually made from copper and brass, but occasionally steel.

In structure it is the front section of a lightweight helmet from above the faceplate to below the demand valve and exhaust ports, including the bailout block and communications connections on the sides.

Some models require a bailout block to provide alternative breathing gas supply from the umbilical and bailout cylinder, but are not suitable for accepting an alternative air supply from a rescue diver, while a few models accept a secondary demand valve which can be plugged into an accessory port (Draeger, Apeks and Ocean Reef).

[22][23] The unique Kirby Morgan 48 SuperMask has a removable DV pod which can be unclipped to allow the diver to breathe from a standard scuba demand valve with mouthpiece.

The breathing gas is delivered from a source at the surface to the diver underwater via a hose and one of several options for distribution, monitoring, and control.

It contains a hose to supply the breathing gas and usually several other components, which may be stipulated by legislation or code of practice.

The diver's end has underwater connectors for the electrical cables, and the air hoses are usually connected to the helmet, band mask, or bailout block by JIC fittings.

[26][27] Hookah, Sasuba and Snuba systems are categorised as "air-line" equipment, as they do not include the communication, lifeline and pneumofathometer hose characteristic of a full diver's umbilical.

[citation needed] The exception is the gasoline engine powered unit, which requires a much higher level of training and topside supervision for safe use.

Small 12 volt diaphragm compressors are used for recreational hookah, with a delivery of around 1.8 bars (26 psi), which severely limits the depth to which air can be supplied.

[30] Piston compressors for hookah deliver air at higher pressures, up to about 9 bars (130 psi), and are usually driven by a small 4-stroke petrol engine.

[11] Primary and reserve gas is supplied to the panel through shutoff valves from a low-pressure compressor or high-pressure storage cylinders ("bombs", "bundles", "quads", or "kellys").

The accumulator functions as an additional water trap, but the main purpose is to provide a reserve volume of pressurised air.

Reducing the partial pressure of the inert gas component of the breathing mixture will accelerate decompression as the concentration gradient will be greater for a given depth.

Any substitution may introduce counter-diffusion complications, owing to differing rates of diffusion of the inert gases, which can lead to a net gain in total dissolved gas tension in a tissue.

The usual configurations for surface-supplied bulk gas storage are large single cylinders of around 50 litres water capacity, often referred to as "J"s or "bombs", "quads", which are a group (sometimes, but not necessarily four in number) of similar cylinders mounted on a frame and connected together to a common supply fitting, and "kellys" which are a group of "gas storage tubes" (long large volume seamless transportable gas storage pressure vessels, with water capacity between 150 litres (5.3 cu ft) and 3,000 litres (110 cu ft)) usually mounted in a container frame or trailer, and usually connected together to a manifold with a common connection fitting.

For surface oriented dives, this may require gas for decompression, and bailout sets generally start at about 7 litres internal capacity and can be larger.

The harness is fitted with several heavy duty D-rings, fixed to the webbing in such a way that the full weight of the diver and all their equipment can be safely supported.

The only time the diver may want to be positively buoyant is when on the surface or during a limited range of emergencies where uncontrolled ascent is less life-threatening than remaining under water.

Unwanted positive buoyancy is dangerous to a diver who may need to spend significant time decompressing during the ascent, so the weights are usually attached securely to prevent accidental loss.

Heated water continuously flows into the suit and is distributed by perforated internal tubes down the front and back of the torso and along the limbs.

[46] Surface oriented mixed gas diving spreads may also be used, but are less common, and are likely to be associated with projects which are too deep for air but require only a short working time at depth.