Surface-supplied diving

[14] Inspired by a fire accident he witnessed in a stable in England,[15] he[clarification needed] designed and patented a "Smoke Helmet" to be used by firemen in smoke-filled areas in 1823.

In 1834 Charles used his diving helmet and suit in a successful attempt on the wreck of HMS Royal George at Spithead, during which he recovered 28 of the ship's cannon.

[20] Expanding on improvements already made by another engineer, George Edwards, Siebe produced his own design; a helmet fitted to a full-length watertight canvas diving suit.

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

the exhaled gas is returned to the surface through a reclaim valve, a type of back-pressure regulator in the helmet, via the umbilical, scrubbed of carbon dioxide, filtered of odour and micro-organisms, re-oxygenated, and recompressed to storage.

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.

[32][33][34] 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.

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).

[37][38] 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 diver's end has underwater connectors for the electrical cables, and the hoses are usually connected to the helmet, band mask, or bailout block by JIC fittings.

[40][41] 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.

[31] 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").

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.

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 his 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.

[53] 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.

This is important, as it is there to prevent backflow of air up the umbilical if the line is cut, and if it fails the diver may suffer a helmet squeeze, or a neck dam flood.

[26] Compared to scuba diving, dressing the diver in[a] is a relatively laborious process, as the equipment is bulky and fairly heavy, and several components are connected together by hoses.

[26] The traditional buoyancy condition of the working surface-supplied diver is "heavy", or negatively buoyant, with sufficient apparent weight to move around on the bottom by walking.

This was more important with the standard diving dress, where inadvertent positive buoyancy could have fatal consequences if poorly managed and degraded to an uncontrolled buoyant ascent.

This can be useful if he needs to climb a structure, shotline or topographical feature, and the umbilicals can not be safely used to lift the divers due to snags or sharp edges.

[41] Divers face specific physical and health risks when they go underwater with diving equipment, or use high pressure breathing gas.

Professional diving operations tend to be less tolerant of risk than recreational, particularly technical divers, who are less constrained by occupational health and safety legislation and codes of practice.

Nitrox, which contains more oxygen and less nitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness at depths to about 40 metres (130 ft).

Compressor diving was shown, and so called, used for pa-aling fishing, in episode 1 (Oceans: Into the Blue) of the BBC television series Human Planet.