Scuba diving

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 air in order to allow the diver to breathe air during the immersion.

The first known use of air tanks is in Italy, 15th century: Leonardo da Vinci affirmed in his Atlantic Code (Biblioteca Ambrosiana, Milan) that systems were used at that time to artificially breathe under water, but he didn't 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 brought 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 Halley's ones (yes, the astronomer), in 19th century August Siebe[?] invented a sort of apparatus but still not completely independent of external air. His studies were perfected by the Frenchman Cabirol and later, more incisively, by Rouquayrol[?] and 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 Le Prieur[?] invented another apparatus, better developed 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 apparatus 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 mines 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, 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 with the apparatus co-invented by Jacques Cousteau and Emile Gagnan and named Aqua-lung.

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The maximum safe depth[?] for normal scuba gear with normal air in the tank is certainly within the 50 metres, 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 at eventually 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.

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 in a severe respect of safety rules. Any accident in water, even the "lightest" one, can bring to death.

Some say that it could be possible to learn how to tolerate narcosis (allegedly, same as with alcohol), but disconcerting doubts cannot allow this statement to be released so easily without at least the mention that nothing and no one can seriously ensure that you will be able to reach again the surface if a similar accident happens, effective known rescues generally having depended on highly hazardous and quite randomised factors.

If Enriched Air Nitrox is used, additional serious risks come from oxygen toxicicity[?]. Breating 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 msw 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.

There are certification agencies for learning to scuba dive, most of them attentively focusing on physical traning and deep scientific learning well before starting water activities.

Scuba diving requires practice and a certain amount of experience before entering water without an instructor (or a professional assistant). Even experienced divers should never dive alone, but instead have a companion (or more) in sight.

Major deadly risk factors include:

• Vertical speed (descent and ascent)
• Lung problems
• Running out of air (often due to secondary factors such as getting trapped by nets, rocks inside caves, etc)

Major diving diseases include:

• Embolia[?]
• nitrogen narcosis
• Tympanum damage[?]

Bends, or "the chest disease", regards mainly early times of underwater activities, and was related with "the aeronauts' disease"; both diseases are forms of embolia.

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Certifying dive organizations include:

• PADI - Professional Association of Diving Instructors (http://www.padi.com/ )
• NAUI - National Association of Underwater Instructors (http://www.naui.org/ )
• GUE - Global Underwater Explorers (http://www.gue.com/ )
• ACUC - American and Canadian Underwater Certifications (http://www.acuc.ca/ )
• BSAC - British Sub Aqua Club (http://www.bsac.com/ )
• CMAS - Confederation Mondiale des Activites Subaquatiques (http://www.cmas2000.org )
• SSI - Scuba Schools International (http://www.ssiusa.com/ )

See also: Scuba News (http://www.HavenWorks.com/scuba)