SCUBA is an acronym for Self Contained Underwater Breathing Apparatus. In short, scuba diving is an underwater activity practiced with the help of a system or an apparatus (usually a tank and air pressure regulator) able to provide a reserve of gas (usually air) in order to allow the diver to breathe air during the immersion.

Table of contents
1 History
2 Nitrogen Narcosis Information
3 Things to do underwater
4 Scuba Glossary
5 Training and Certification
6 External links
7 Popular locations for SCUBA diving
8 Equipment Manufacturers
9 Equipment used in scuba diving
10 Movies that feature Scuba Diving
11 Scuba Magazines


See also Timeline of underwater technology.

The first known use of air tanks is in Italy, 15th century: Leonardo da Vinci affirmed in his Atlantic Codex (Biblioteca Ambrosiana, Milan) that systems were used at that time to artificially breathe under water, but he did not explain them in detail due to what he described as "bad human nature", that would have taken advantage of this technique to sink ships and even commit murders. Some drawings, however, showed different kinds of snorkels and an air tank (to be carried on the breast) that presumably should have no external connections. Other drawings showed a complete immersion kit, with a plunger suit which included a sort of mask with a box for air. The project was so detailed that it included a urine collector, too.

After Leonardo's studies, and those of Halley (yes, the astronomer), in the 19th century Augustus Siebe invented a sort of apparatus but still not completely independent of external air. His studies were perfected by the Frenchman Joseph Cabirol and later, more incisively, by Benoit Rouquayrol and Auguste Denayrouze, who added the first modern air tank.

In 1906 the first decompression tables ("quote decompression method") were released.

In 1915 Sir Robert Davis invented the "Submarine escape apparatus", by which a compressed oxygen bottle could be opened in water in case of need, sending air to mouth. Used air could be then expelled to a filtering "false lung" from where it is finally lost.

In 1925 Yves Le Prieur invented another better developed apparatus in 1933, working with compressed air. It could permit a 20 minute stay at -7 meters and 15 minutes at -15 (these data appear however to be re-checked).

In 1941, during WWII, these experimental apparatuses were used for one of the best known and most spectacular war actions: Italian "Decima Mas" (elite navy corps at the orders of commander Junio Valerio Borghese) entered at nighttime the port of Alexandria, Egypt, in immersion. They used special underwater vehicles ("maiali" = pigs) and breathing apparatus, and were able to silently attach miness on the bottom of the ships, that later were effectively sunk.

In July of 1943 the Frenchman Georges Comheines was able to reach -53 meters (~174 feet), off the coast of Marseille, with a two-bottles apparatus he had developed from Le Prieur's one. Immersion lasted 2 minutes (apparently out of decompression tables).

In the following October, Frédéric Dumas reached -62 meters (~200 feet), with the apparatus co-invented by Jacques Cousteau and Emile Gagnan and named Aqua-lung.

In 1958 the TV series SEA HUNT, introduced SCUBA diving to the TV audience.

Movies have also popularized the sport. SCUBA diving is featured in many James Bond films.

Nitrogen Narcosis Information

The maximum safe depth for normal scuba gear with normal air in the tank is certainly within 50 meters (~150 feet), beyond which nitrogen narcosis becomes an almost certain danger. Onset of narcosis is dependent on the workload, the physical conditions, and training of the diver but also depends on variable gas concentration in blood and lungs, that might change very suddenly with minimum changes of vertical speed (descent). Risk factors are different for each individual, and cannot therefore be reliably foreseen: the appearance of narcosis can be very rapid and faster than the capability of the diver to recognize it. Narcosis will also disappear once you ascend to shallower depth.

It is vital to remember that an accident can occur even in the very first meter of immersion, depending on personal conditions and hazards; every statistical report about accidents demonstrate that claimed "safe ranges" are nothing more than a rough recording of some data (episodically and not organically collected) with no scientific confirmation.

Diving can be an experience capable of producing unique emotions, but only with complete respect of safety rules. Any accident in water, even the "lightest" one, can bring to death to the untrained diver. The rising numbers of deaths in the early years of scuba forced training organisations of come up with minimum standards of training.

Opinion is divided as to whether one can learn to tollerate narcosis (as with alcohol, for example), but the reader is cautioned that there is no research to substantiate such claims.

If Enriched Air Nitrox is used, additional serious risks come from oxygen toxicity. Diving on pure oxygen becomes toxic at a depth of merely 10 ft. Breathing mixes become dangerous when the partial pressure of oxygen reaches 1,4-1,6 bar. Some people consider 1,2 bar dangerous pressure (and some others suggest never passing 0,9), that is reached at a very early depth.

Relatively "safe" deep dives over 70 meters (~210 feet) can be done by well experienced divers using Heliox or Trimix gas mixes. As with Enriched Air Nitrox, special training is obligatory. These depths are however in a range that could recommend a boat-assisted immersion for a different air provision system, such as pneumatic pumps on surface.

Scuba diving requires training, and nobody should consider attempting to dive without professional instruction. Even experienced divers should never dive alone, but instead have a companion (or more) in sight. Some divers insist that just being in sight of each other is not enough, so they usually have a rope between them so they do not swim out of sight by accident. Using a rope, sometimes called a Buddy line, is not mandatory and is in some situations, such as diving inside wrecks, even considered dangerous by some divers.

Major deadly risk factors include:

  • Vertical speed (descent and ascent)
  • Lung problems i.e. (holding one's breath upon ascent which will cause your lungs to explode just as an overfilled balloon)
  • Running out of air (often due to secondary factors such as getting trapped by nets, rocks inside caves, etc).

Major diving diseases include:
  • Subcutaneous emphysema (gas under the skin tissue)
  • Nitrogen narcosis ('Rapture of the Deep')
  • Tympanum damage (damage to the eardrum caused by failing to equalize pressure in the inner ear).
  • Decompression sickness

"Decompression sickness" ("the bends") is caused by ascending from deep depths too quickly. Nitrogen from the air breathed dissolves in the blood at depth, and as the diver ascends, the nitrogen is released from the blood and forms bubbles throughout the diver's bloodstream, with painful and often fatal results. The prevention is to surface slowly from all dives, so that nitrogen can "de-gass" from the diver's blood without forming bubbles. Divers also ensure adequate de-gassing by performing one or more "safety stops" after long or deep dives, in which the diver hovers at a prescribed depth for a prescribed amount of time before actually surfacing. Dive Tables (and dive computers which use the tables) are used to calculate maximum bottom time, and recommend additional safety stops.

Things to do underwater

  • Relax and watch the marine life
    • fish watching
    • coral reef watching
    • feeding the fish (this has become controversial in recent years)
    • look for sunken treasure
    • hunt for food (spearfishing) (spear gun) (is illegal in some countries. in some countries you must get a permit first)
  • Drift diving
    • Allowing the water current to move the diver down current, this is one of the most relaxing methods to dive.
    • Typically done in rivers or the ocean
    • Example - in Cozumel the boat takes the divers toward the south end on the island, the current runs from south to north, the divers exit the boat and drift north, the boat follows the trail of bubbles from the divers, when the divers surface the boat is waiting for them.
  • Wreck diving
  • Search & Recovery diving
    • Searching for an object using a pattern.
      • The size of the object and the visibility of the water help determine what pattern will be use.
    • After finding the object, returning it to the surface. Small objects can be carried up to the surface by the diver, larger objects may require the use of a lift bag.
      • Salvaging item from historical ship wrecks will land you in legal problems or jail
      • Mel Fisher is one of the best know treasure hunters
  • Underwater photography
  • Underwater videography
    • Using a film / video camera underwater
  • Marine life identification
    • Identifying & recording marine life seen in a given area
      • done as part of a survey or study
      • done for personal pleasure like bird watching
  • Ice diving
    • Requires special training to dive under the ice on a body of water
    • Instruction by a certified instructor - typically one day
    • Requires additional scuba equipment
      • A regulator modified for cold water use that will not freeze.
      • A harness
      • A safety rope attached to the harness
      • Typically a dry suit is worn to keep the diver warm
      • A hood to keep the divers head warm.
        • Optional full face mask to prevent cold water from contacting the divers face.
    • Requires additional personal
      • Line Tenders to manage the ropes
      • Safety diver
      • Divemaster
    • Requires additional equipment
      • A weatherproof area for the divers to suit up
    • Requires additional equipment to access the water below the ice
      • A chain saw to cut the ice
      • Snow shovel to clear the snow and ice from the area
  • Cave diving
    • Requires special training to enter and safely exit a cave - prevent your own death - do not enter a cave unless you and your buddy are trained cave divers.
  • Boat diving
    • Diving from a boat
    • Boats can range in size from a one man kayak to an ocean liner.
    • Many of the best diving sites are off shore and the boat provides access to these sites.
      • Six pack is a slang term for a small boat that can carry up to six divers.
        • Typically very fast boat with twin outboard engines
      • "Cattle boat" a slang term for a large boat that take a large group of divers
  • Night diving
    • Diving after sunset & before dawn reveals new animals that come out at night and corals that open at night to feed. Many divers enjoy this more than diving during the daylight.
    • Requires a primary and back-up light source. Typically water proof flashlights designed for scuba diving. Additionally scuba diver wear marker lights to help locate and identify them. Cylume Sticks were popular but environmental concerns as phasing them out in favor of battery powered glow sticks.
    • While night diving divers tend to move slower and more deliberately than during the day light. This leads to a more relaxing dive.
  • Altitude diving.
    • Diving in a body of water located above 1000 feet above sea level. Requires additional training and modified dive tables. Diver must limit the ascent rate to 30 feet pr minute or less.
    • Lake Tahoe would be an example of a location where altitude diving is done.
  • Dive propulsion vehicle - DPV
    • Driving an underwater propulsion vehicle
    • Care must be taken not to assend to fast while driving the vehicle
    • Vechiles range in size from small unit to mulit passanger units
  • Dry suit diving
    • A dry suit is a suit worn by scuba divers to keep water away from the diver's body. It is typically worn in water too cold for a wetsuit. Unlike a wetsuit, which traps a thin layer of water between the body and the suit, a dry suit has a neck and wrist seal to prevent water from entering, and the feet are usually enclosed. Divers add air to the suit to keep it from squeezing too tight on the body. In order to keep warm, dry suit wearers use either special underclothes or an electrical heating system.
    • Vulcanized rubber suit
    • Compressed neoprene suit
    • Shell suit
      • Trilaminate - Nylon/Butyl Rubber/Nylon
        • this type of suit offers no thermal protection, they divers wears undergarments for thermal protection.
        • offered in many colors
        • offered with self donning zipper than goes across the front of the suit, allows the wearer of the suit to close the zipper himself.
    • Zipper
      • the waterproof zipper is a product of the space age
      • some suits have a zipper across the back of the shoulders
    • Seals
      • Latex neck & wrist seals
        • can be trimmed to fit the owner of the suit, Latex seals are more delicate than neoprene and require more care.
      • Neoprene neck & wrist seals
        • can be trimmed if needed, neoprene seals will leak a little.
    • Inflator valve on chest to add air to the suit
    • Dump valve on left arm
      • automatically dumps air to prevent overinflation, this setting can be adjusted by the diver by rotating the top of the valve.
    • Manufacturers' web sites:
  • Underwater navigation
    • using a compass and other item to find your way around underwater
    • GPS will not work underwater, the wavelenght will not penetrate the water.
  • Communicating
    • Sign language: In most situations cummunications is facilitated with the use of simple hand signals. The most basic ones: Thumbs up = lets go up, thumbs down = lets go down, circle with thumb and index finger = I'm OK. Are you OK?, "cutting" throat with a flat hand = I'm out of air, wobbling a flat hand = something is wrong.
    • Using a torch/flashlight: The focused beam of a torch can be used for basic signalling as well. Drawing a circle on the ground in front of buddy = the OK signal, waving the torch = attention please!
    • Voice: When using special equipment, voice can be used for communication. Equipment usually consists of a full face mask with a submergible microphone and speaker and either a hard wired telepone-like setup or a through-water supersonic radio-like system.
  • NITROX diving
    • Diving with a mixture of air with the nitrogen/oxygen ratio different than ambient air during a dive.
    • Using nitrox is typically not the purpose of the dive but nitrox is used during the dive
  • Deep diving
    • diving below 100 feet / 30 meters.
    • 130 feet is the max depth for recreational scuba
  • Rebreather
    • a device which reuses part of each breath. See linked article for more information.

Scuba Glossary

; Skin: a
lycra suit worn by a diver in warm water or under a wet suit. ; Surface interval: the time between dives. divers need to track this time interval for planning the next dive. ; Time to fly: Divers must wait approx. 24 hours after the last dive before flying. ; Wall diving : Scuba diving along the face of a vertical wall ; Shore diving: Scuba diving that starts from the shore line ; Buddy System: Two divers that dive together as a team for safety ; Trash dive: a dive dedicated to removing trash from the underwater environment ; Divemaster: A professional level diver who is in charge of the dive. ; Beach master: A person on the beach who records when divers enter and exit the water. Typically used during scuba classes to keep track of the students, watch the gear, provide assistance when required. ; C-card: Certification card (proof of training or experience) ; Log Book: List of the dives a diver has recorded for proof of experience. ; Dive Tables: Give the maximum times that can be spent at depth, and pauses needed during ascent, before Decompression sickness becomes a danger. ; Navy Tables : A set of dive tables developed by the US Navy. Used by early divers as a method to determine maximum time and depth. ; Dive Shop : supplier of dive equipment or training, or organizer of dive expeditions. ; Dive Flag : used by a boat to indicate that it has 'divers down'. Comes in two versions: the international (international code letter flag 'A', ) and the American (red flag with white diagonal, ), introduced by Ted Nixon in 1956. Boats must maintain a minimum distance away from the flag. Personal water craft pose a hazard to divers, and sadly few operators do know what a dive flag is. Some believe it is turn marker. If you observe a personal water craft operating to close to a dive flag contact the lake patrol. ; Hard Hat diving: A term for commercial divers. Refers to a modern fiberglass helmet or the old style brass helmet tethered divers wear. ; Dive club: a group of people with an interest in SCUBA diving ; Navy SEAL: A highly trained military diver ( ) ; Frogman: A slag term for scuba divers ; Fire Diving: An urban legend about a diver who is scooped up by a plane/chopper and dropped on a forest fire led someone to build a web site for the fictitious sport of Firediving

Training and Certification

Becoming a scuba diver requires training. Dive training organisations can be found throughout the world, and in very large numbers in popular dive spots. A good dive training organisation will always offer courses to the standard of a recognised certification organisation, such as those listed below. Many dive shops in popular holiday locations offer courses that can teach you to dive in a few days, and can be combined with your vacation.

Initial training can be broken down into three phases.

Upon completing the course the student is issued a certification card.

Many of the activities mentioned above require additional training to be done safely.

Certifying dive organizations include:

Other organizations:


External links

Popular locations for SCUBA diving

Equipment Manufacturers

Equipment used in scuba diving

  • Mask
    • non purge
    • purge valve
    • single lens
    • split lens
    • full face - the diver in the first photo is wearing an AGA full face mask
    • other category
      • hard hat
  • Fins
    • modern fins come in many shapes and colors
    • open heel type
  • Snorkel
    • used by divers when swimming at the surface, worn on the left side of the mask.
    • some modern snorkels have drain valves to aid in the removal of water from the snorkel tube
  • Weight Belt
    • A nylon web 2" wide that holds the weights (some belts can be filled with lead pellets as weights.) and features a quick release buckle. Belts come in many color with yellow or black being the most popular.
  • Weights - used to offset positive buoyancy.
    • Lead is the most common material used
    • 1, 2, 3, 4, or 5 pound blocks with holes to thread the weight belt through
    • Many modern BCD's have weight pockets with quick release buckles

A diver in a pool wearing a full face mask from AGA and a twin 6 liter 300 bar tank rig.

  • SCUBA tank
    • A hollow cylinder that holds compressed air with an on/off valve at the top.
    • Typically filled to somewere the range of 18.6 to 30.0 MPa (2700 to 4300 psi, or 200 to 300 bar)
    • Some countries require a burst disk installed in the valve that prevents pressures exeeding approx. 15% above working pressure.
    • Tanks should only be filled with air from a reliable source (dive shop)
    • Never fill a tank with oxygen unless it has been certified for pure oxygen use.
    • Contaminated air at depth could be fatal
    • Common sizes - materials for scuba tanks
      • 80 cubic feet - Aluminum - most common size used
      • 63 cubic feet - Aluminum
      • 72 cubic feet - Steel
      • 50 cubic feet - Aluminum
      • 30 cubic feet - Aluminum "pony bottle"
      • 13 cubic feet - Aluminum "bailout bottle"
      • 100 cubic feet - Aluminum
      • 120 cubic feet - Steel
      • Twin 80's - Two 80's with a manifold that connects them. Twin tanks are typically used in technical diving.
      • Most countries requires tanks to be checked on a regular basis. This usually consists of an internal visual inspection and a hydrostatic test. In the United States, an visual inspection is required every year, and a hydrostatic every five years.

  • Buoyancy Control Device BCD or BC
    • Modern BCDs are the jacket model that is worn like a vest. Looking a little like a lifejacket, they allow the diver to change his buoyancy while under water by adding or releasing air.
    • Low pressure inflator
      • a hose on the left side of the jacket that allows air to be added or released from the jacket. The inflator should be held higher than the jacket to release air.
    • Over pressurization valve
      • A spring loaded valve that prevents the jacket from holding too much air, can also be used to rapidly dump air from the jacket
  • Backpack
    • Holds the tank in place
    • Modern Buoyancy Control Devices have the backpack built into the unit.
  • Regulator
    • Attaches to the SCUBA tank, reduces the tank pressure to ambient pressure.
All modern regulators consists of two stages. The first stage attaches to the tank and reduces the tank pressure to aprox. 1 MPa obove ambient pressure. This intermediate pressure gas is lead through a hose to the second stage witch in turn reduces the gas pressure to ambient pressure.
    • Double hose style
Earlier models of regulators had the two stages combined into one. Air was supplied to the diver via a large corrugated hose to the divers mouth piece. Exhaled gas returned via a second hose back to the regulator where it was released into the water.

  • Underwater Compass
Works just as the "dry" versions. Often worn on the forearm, just as a clock.

  • Under Water Time Piece
    • Waterproof Watch to keep track of time
  • Air pressure gauge
    • Used to monitor the tank pressure
    • Connects to the first stage of the regulator.
  • Depth Gauge
    • Used to monitor depth
  • Console
    • a plastic or rubber box that holds the air pressure gauge and the depth gauge, typically worn on the left hand side of the diver
  • Dive Computer
    • Watertight computer with LCD display showing the amount of time the diver can remain underwater while staying inside decompression sickness safety limits
    • Most fit into the console or into a wrist mount

Movies that feature Scuba Diving

Scuba Magazines