Scuba diving is the act of swimming underwater while using a self-contained breathing apparatus. By carrying a source of compressed air, the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in Snorkeling and Free-diving, and is not hindered by air-lines to a remote air source. The scuba diver typically swims underwater by using fins attached to the feet. However, some divers also move around with the assistance of a DPV (Diver Propulsion Vehicle), commonly referred to as a "scooter," or by using surface-tethered devices called sleds, which are pulled by a boat.

Scuba diving emphasizes human interaction with the environment, in this case the majesty of the ocean or other bodies of water. It matches exercise with the spirit of exploration and the beauty of nature.

History of scuba diving

The history of scuba diving can be traced back to 1825, when William James developed a compressed air container that fit around a diver's waist. James developed the design, but no record was made of him using the device. The first recorded dive using a self-contained breathing apparatus was done by Charles Condert. Condert designed a horseshoe-shaped air container mounted to a helmet that allowed for constant flow of air to the head device. The diver used the helmet design many times, but died in 1832, because of a broken air tube.

In 1865, two Frenchman by the names of Rouquayrol and Denayrouse used a metal container that allowed the diver to breath air at the same pressure that was in the water. It helped greatly in the development of wreck and sponge diving.

Commandanat Yves Le Prievr of the French Navy developed a light weight, self-contained breathing apparatus and also started a diving club in Paris. Although Yves Le Priever's invention helped progress the idea of underwater diving, the machine was still not fully automatic.

The first fully automatic aqualung was made by Frenchman Georges Commeinhes and had a pressure of 150 bars. In 1942, in what could be considered one of the biggest moments in scuba diving history, Jacques Cousteau created an aqualung with the help of Emile Gagnan that was fully automatic as well. It had a inlet and exhaust tube that was fully automatic, and helped pave the way for modern scuba diving.


Besides the need for an underwater air chamber, there is other equipment needed to scuba dive successfully.

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. To ensure that no pressure damage occurs during the dive, the mask must cover the nose and ears as well.

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.

A snorkel is also needed for scuba diving because it allows the diver to swim near the surface and have a valve for breathing. It is made out of a mouthpiece consisting of rubber and a tube pointed upward that allows one to breath.

A diver's buoyancy is a very important part of scuba diving. In Scuba Diving, the 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. Increasing the buoyancy of the diver is centered on increasing the weight the diver carriers. The best way to do this is by the use of a wetsuit, or dry-suit, and by wearing a weight belt. In the case of a dry-suit, it does exactly that: Keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. 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.

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 maneuverability due to the thinness of the material, however that also means that heavy weight under-suit is required if diving in cooler water.
  • Neoprene: Low level of diver maneuverability 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.

A wetsuit or dry suit can also keep a diver warm in cold water. The weight belt must be placed in a way that allows for quick release in case of an emergency in which the diver needs to get to the surface.

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 aluminum, 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.

The most commonly used scuba set today is the "single-hose" open circuit 2-stage diving regulator, coupled to a single pressurized gas cylinder, with the first stage on the cylinder and the second stage at the mouthpiece. This arrangement differs from Emile Gagnan's and Jacques Cousteau's original 1942 "twin-hose" design, in which the cylinder's pressure was reduced to ambient pressure in one, two, or three stages which were all on the cylinder. The "single-hose" system has significant advantages over the original system.


Less common, but becoming increasingly available, are closed and semi-closed re-breathers. Open-circuit sets vent off all exhaled gases, but 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 sport 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.

Important safety issues

There are important physiological issues posed by diving.

Breathing underwater

Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices.

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.

The "Alfa" flag - Designates a vessel engaged in underwater operations with restricted maneuverability.1

Injuries due to changes in air pressure

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, in the same way that atmospheric air causes a pressure of 14.7 lbs per square inch at sea level. 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 maneuver," which involves pinching the nose and gently attempting to exhale through it. The second technique is known as the "Frenzel maneuver," which involves using the throat muscles in a swallowing motion. This maneuver is more difficult to master than the Valsalva maneuver.

The mask is equalized by periodically exhaling through the nose. If a dry-suit is worn, it too must be equalized by inflation and deflation, similar to a buoyancy compensator.

Effects of breathing high pressure gas

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 anesthesia. 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

A diver wearing an Ocean Reef full face mask

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 masks and diving helmets and fullface masks solve this problem by creating an air space in front of the diver's eyes. The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34 percent bigger and 25 percent closer in salt water than they actually are. Therefore, total field-of-view is significantly reduced and eye-hand coordination must be adjusted.

(This affects underwater photography: A camera seeing through a flat window in its casing is affected the same as its user's eye seeing through a flat mask window, and so its user must focus for the apparent distance to target, not for the real distance.)

Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic and custom corrective lenses are available for some two-window masks. Custom lenses can be bonded onto masks that have a single front window.

A "double-dome mask" has curved windows in an attempt to cure these faults, but this causes a refraction problem of its own.

On rare occasions, commando frogmen use special contact lenses instead, to see underwater without the large glass surface of a diving mask, which can reflect light and give away the frogman's position.

As a diver changes depth, he must periodically exhale through his nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles which only cover the eyes do not allow for equalization and thus are not suitable for diving.

Controlling buoyancy underwater

Diver under the Salt Pier in Bonaire.

To dive safely, divers need to be able to control their rate of descent and ascent in the water. Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as the diving weighting systems, diving suits (Wet, Dry & Semi-dry suits are used depending on the water temperature) and buoyancy compensators 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.

The downward force on the diver is the weight of the diver and his equipment minus the weight of the same volume of the liquid that he is immersed in; if the result is negative, that force is upwards. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, shrink as the diver descends, and expand as the diver ascends, creating unwanted buoyancy changes. The diver can inject air into some diving suits to counteract this effect and squeeze. Buoyancy compensator allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.

Spring Suit and Steamer.

Avoiding skin cuts and grazes

Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects, marine animals, or coral.

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.

Scuba dive training and certification agencies

Recreational scuba diving does not have a centralized certifying or regulatory agency, and is mostly self-regulated. There are, however, several large diving organizations that train and certify divers and dive instructors, and many diving related sales and rental outlets require proof of diver certification from one of these organizations prior to selling or renting certain diving products or services.

The largest international certification agencies that are currently recognized by most diving outlets for diver certification include:

  • American Canadian Underwater Certifications (ACUC) (formerly Association of Canadian Underwater Councils)-originated in Canada in 1969 and expanded internationally in 1984-certifications recognized worldwide.
  • British Sub Aqua Club (BSAC)-based in the United Kingdom, mostly for UK divers and clubs
  • European Committee of Professional Diving Instructors (CEDIP) based in Europe since 1992 but international certifications are recognized all over the world.
  • Confédération Mondiale des Activités Subaquatiques (CMAS), the World Underwater Federation
  • National Association of Underwater Instructors (NAUI)-based in the U.S.
  • Professional Diving Instructors Corporation (PDIC)-based in the U.S.
  • Professional Association of Diving Instructors (PADI)-based in the U.S., largest recreational dive training and certification organization in the world
  • International Training SDI, TDI & ERDi
  • Scuba Schools International (SSI)-based in the U.S.
  • YMCA scuba-based in the U.S., part of Young Men's Christian Association (YMCA), a Christian related organization (open to all faiths, ages and genders despite the historic name)
A scuba diver approaching the "1,000 Steps" dive site in Bonaire.
Scuba diving, grouped


  1. ↑, Vessel Not Under Command Retrieved December 22, 2007.


  • 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