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Scuba diving equipment

Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Sadly, humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices. This is where SCUBA equipment comes in.

 

SCUBA (Self Contained Underwater Breathing Apparatus)

The famous Aqualung that was first created by Jacques Cousteau and Emile Gaganan consist of three major parts: Air cylinder, harness, and regulator. The cylinder is made out of steel or aluminium, and carries the oxygen supply. The regulator is the device that controls the pressure to be the same amount as the pressure in the water. The harness is the way in which the device is carried on the diver’s back. Today BCDs often incorporate the backpack/harness into one integrated unit.

 

Buoyancy & the BCD

A diver’s buoyancy is a very important part of scuba diving. To dive safely, divers need to be able to control their rate of descent and ascent in the water. A diver cannot rise to the surface too quickly without risking safety concerns, but at the same time, needs to be able to surface if there is a dramatic emergency such as equipment failure.

The buoyancy control device (BCD) can be used to adjust the overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth.

BCDs allow easy adjustments in the diver’s overall buoyancy. For open circuit divers, buoyancy can also be fine-tuned by increasing or decreasing the amount of air in the lungs.

 

Dive Suits

Diving suits such as wet, dry and semi-dry suits are used depending on the water temperature. In addition to keeping the diver warm, they also help prevent skin being damaged by rough or sharp underwater objects, marine animals, or coral.

A wet-suit is designed to trap water inside the suit, allowing your body temperature to heat it.

A dry-suit does exactly that – keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. This means the air inside must be equalized by inflation and deflation, similar to a BCD. Dry-suits fall into two main categories—neoprene and membrane; both systems have their good and bad points but generally the difference is:

Membrane: High level of diver manoeuvrability due to the thinness of the material, however that also means that a heavier weight belt may be required if diving in cooler water.

Neoprene: Low level of diver manoeuvrability due to the material being considerably thicker than membrane material (even when dealing with compressed neoprene) however the neoprene provides a higher level of insulation for the diver.

Dry-suit undergarments are often worn under a dry-suit as well, and help to keep layers of air inside the suit for better thermal insulation. Some divers carry an extra gas bottle dedicated to filling the dry suit. Usually this bottle contains argon gas, because it is a better insulator than air.

 

Diving Mask

A mask is needed when diving to ensure clear and constant vision underwater. The required features for the mask include a surface that cannot shatter or scratch, and a waterproof seal that molds around the diver’s face. Tempered glass is usually used to guarantee no scratching or shattering, and silicone rubber is used for the waterproof seal.

 

Fins

The next piece of equipment that is needed are fins. Fins are worn on the feet and are used to help accelerate the diver more quickly through the water. They are made up of two major parts: The blade, which needs to be firm to promote more power when the diver kicks, and the shoe, which needs to made of softer rubber for comfort.

 

Snorkel

A snorkel is also needed for scuba diving because it allows the diver to swim on the surface and have the ability to breath while face down in the water. It is made out of a mouthpiece consisting of rubber or silicone type materials and a tube pointed upward that allows the diver to breath.

 

Weight belts

These come in a variety of styles and types. The weight belts are designed to compensate for the positive buoyancy created by wearing a diving suit, thus allowing the diver to sink. The most important feature of any weight belt is the quick release buckle. This special type of release buckle allows the diver to quickly release and drop their weight belt in the event of an emergency.

 

Re-breather

Still rare, but becoming increasingly common, are closed and semi-closed re-breathers. While open-circuit sets vent off all exhaled gases, re-breathers reprocess each exhaled breath for re-use by removing the carbon dioxide buildup and replacing the oxygen used by the diver. Re-breathers release few or no gas bubbles into the water, and use much less oxygen per hour because exhaled oxygen is recovered; this has advantages for research, frogman, photography, and other applications. Modern re-breathers are more complex and more expensive than open-circuit scuba, and need special training and maintenance to safely use.

 

Gas mixtures

For some diving, gas mixtures other than normal atmospheric air (21 percent oxygen, 78 percent nitrogen, 1 percent other) can be used, so long as the diver is properly trained in their use. The most commonly used mixture is Enriched Air Nitrox, which is air with extra oxygen, often with 32 or 36 percent oxygen, and thus less nitrogen, reducing the effect of decompression sickness and nitrogen narcosis.

Several other common gas mixtures are in use, and all need specialized training. For example, oxygen with helium and a reduced percentage of nitrogen is known as trimix.

In cases of technical dives more than one cylinder may be carried, containing a different gas mixture for a distinct phase of the dive, typically designated as “travel,” “bottom,” and “decompression.” These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.

 

Breathing underwater

Early diving experimenters quickly discovered it is not enough simply to supply air in order to breathe comfortably underwater. As one descends, in addition to the normal atmospheric pressure, water exerts increasing pressure on the chest and lungs—approximately 1 bar or 14.7 psi for every 33 feet or 10 meters of depth—so the pressure of the inhaled breath must exactly counter the surrounding or ambient pressure in order to inflate the lungs.

By always providing the breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and virtually effortlessly, regardless of depth.

Because the diver’s nose and eyes covered by a diving mask, the diver cannot breathe in through the nose, except when wearing a full face diving mask. However, inhaling from a regulator’s mouthpiece becomes second nature very quickly.

Divers must avoid injuries caused by changes in air pressure. The weight of the water column above the diver causes an increase in air pressure in any compressible material (wetsuit, lungs, sinus) in proportion to depth. Pressure injuries are called barotrauma and can be quite painful, in severe cases causing a ruptured eardrum or damage to the sinuses. To avoid them, the diver equalizes the pressure in all air spaces with the surrounding water pressure when changing depth. The middle ear and sinus are equalized using one of two techniques.

The first technique is known as the “Valsalva manoeuvre,” which involves pinching the nose and gently attempting to exhale through it. The second technique is known as the “Frenzel manoeuvre,” which involves using the throat muscles in a swallowing motion. This manoeuvre is more difficult to master than the Valsalva manoeuvre.

The mask is equalized by periodically exhaling through the nose.

 

Decompression sickness

The diver must avoid the formation of gas bubbles in the body, called decompression sickness or “the bends,” by releasing the water pressure on the body slowly at the end of the dive and allowing gases trapped in the bloodstream to gradually break solution and leave the body, called “off-gassing.” This is done by making safety stops or decompression stops and ascending slowly using dive computers or decompression tables for guidance. Decompression sickness must be treated promptly, typically in a recompression chamber. Administering enriched-oxygen breathing gas or pure oxygen to a decompression sickness stricken diver on the surface is a good form of first aid for decompression sickness, although fatality or permanent disability may still occur.

 

Nitrogen narcosis

Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in divers who breathe high pressure gas at depth. The mechanism is similar to that of nitrous oxide, or “laughing gas,” administered as anaesthesia. Being “narced” can impair judgment and make diving very dangerous. Narcosis starts to affect the diver at 66 feet (20 meters), or 3 atmospheres of pressure. At 66 feet, Narcosis manifests itself as slight giddiness. The effects increase drastically with the increase in depth. Jacques Cousteau famously described it as the “rapture of the deep.” Nitrogen narcosis occurs quickly and the symptoms typically disappear during the ascent, so that divers often fail to realize they were ever affected. It affects individual divers at varying depths and conditions, and can even vary from dive to dive under identical conditions. However, diving with trimix or heliox prevents narcosis from occurring.

 

Oxygen toxicity

Oxygen toxicity occurs when oxygen in the body exceeds a safe “partial pressure” (PPO2). In extreme cases it affects the central nervous system and causes a seizure, which can result in the diver spitting out his regulator and drowning. Oxygen toxicity is preventable provided one never exceeds the established maximum depth of a given breathing gas. For deep dives, (generally past 130 feet/39 meters) “hypoxic blends” containing a lower percentage of oxygen than atmospheric air are used.

 

Refraction and underwater vision

Water has a higher refractive index than air; it’s similar to that of the cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye’s crystalline lens to focus light. This leads to very severe hypermetropia. People with severe myopia, therefore, can see better underwater without a mask than normal-sighted people.

 

Diving longer and deeper safely

There are a number of techniques to increase the diver’s ability to dive deeper and longer:

  • Technical diving—diving deeper than 40 meters (130 feet) and/or using mixed gases.
  • Surface supplied diving—use of umbilical gas supply and diving helmets.
  • Saturation diving—long-term use of underwater habitats under pressure and a gradual release of pressure over several days in a decompression chamber at the end of a dive

 

Underwater mobility

The diver needs to be mobile underwater. Streamlining dive gear will reduce drag and improve mobility. Personal mobility is enhanced by swimfins and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.

 

References

Barrett, Norman S.; Scuba Diving. London: F. Watts, 1988. ISBN 9780863136825

BSAC. The Diving Manual. ISBN 0-9538919-2-5

BSAC. Dive Leading. ISBN 0-9538919-4-1

BSAC. The Club 1953-2003. ISBN 0-9538919-5-X

Campbell, George D., III. Diving With Deep-Six. Retrieved December 22, 2007.

Halls, Monty. Scuba Diving. New York: DK Pub., 2006. ISBN 9780756619497

 

Credits

New World Encyclopaedia writers and editors along with the NZU Web Master rewrote and completed this article in accordance with New World Encyclopaedia standards.

 

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