SCUBA is an acronym standing for "Self Contained Underwater Breathing Apparatus". SCUBA is used commercially (e.g. oil rig divers) and recreationally by divers all over the world.
The 'standard' open circuit kit used by the majority of recreational divers consists of:
- A stability jacket (stab jacket)/ BCD (buoyancy compensating device).
- A cylinder of an appropriate gas (usually compressed air).
- Two stage regulator (steps down the high pressure air to allow breathing.
- Face mask.
- Weight belt -lead filled (rocks can be used in an emergency ;o)).
- Diving suit (only if the water is chilly).
Advances in diving overcoming natural barriers
Many advances in SCUBA technology
ahs been made throughout the years
, however a lot of the groundwork of today’s technology was developed pre 1900's.
These technical advances
are mainly based around combating the problems faced by the foreign underwater
environment. After getting past the problem of breathing
underwater, the main problem becomes the gas
within our bodies becoming compressed
. When the pressure increases, more gas becomes dissolved
in to the blood
, potentially leading to conditions
such as nitrogen narcosis
, oxygen poisoning
and of course the bends
Associated Diving Medical Conditions
- Bends - When at depth, the divers body is under a great deal of pressure that allows more gas to dissolve in to the blood than at the surface. As the diver comes up the gas comes back out of solution, if this happens too quickly the blood will 'fizz' with these bubbles causing the bends. A recommended ascent rate is 18 meters / 60 feet per minute. These gas bubbles can block blood vessels causing muscle spasm, paralysis and death. An appropriate treatment is to recompress the diver and very gradually decompress them, hence the hyperbaric chamber was invented.
- Nitrogen Narcosis - Nitrogen makes up approximately 79% of the air we breath. When the amount of nitrogen dissolved within the tissues reaches a certain threshold, it takes on narcotic qualities. The diver can become disorientated and in extreme cases delusional; this is not fatal, however can cause the diver to make stupid mistakes leading to fatality. An appropriate treatment is administering pure oxygen which helps to flush out the nitrogen.
- Oxygen poisoning - Oxygen makes up approximately 21% of air and obviously is essential to breathing underwater (vital in breathing anywhere really). It acts in a similar way to nitrogen in that it dissolves under pressure but unlike nitrogen, it does not lead to a 'sleepy' feeling. When oxygen reaches a partial pressure of around 0.5 it becomes an irritant, when a partial pressure of roughly 1.6 (6 meters deep) it becomes toxic to the central nervous system and can be fatal. There is no treatment for oxygen poisoning.
Gas mixes used in diving
Compressed air is the standard gas breathed underwater, however it is not the only one. For instance Nitrox
is a gas mix with a reduced nitrogen concentration
to combat nitrogen narcosis. This is achieved by increasing oxygen
, which unfortunately increases the chance of falling prey to oxygen poisoning which can be fatal. Another gas mix is Helox
; in this mix some of the nitrogen is replaces with helium
to reduce narcosis
effects. Helium is a non-reactive
gas and as such has almost no chemical
effect on the body; also helium will contribute to the bends to a lesser degree than nitrogen can. Any gas mix diving is a specialist field requiring extra equipment
(especially Helox diving). As such gas mixes tend used by professional or commercial divers, however 'technical' (techies) recreational divers use these mixes to increase their bottom time or maximum depth for the sake of pushing back the limits
History of SCUBA pre-1900
There has been evidence
, in one form or another, stretching back for thousands of years. Most of this is indirect
evidence e.g. mother of pearl ornaments, or legends
. Sponge diving
is known to be a very old tradition, spanning back as far as ancient Greece
. An interesting story of mans early underwater adventures comes from Greece, this tells of Scyllis, a sailor in a battle around 500 B.C.
"During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I. When Scyllis learned that Xerxes was to attack a Greek flotilla, he seized a knife and jumped overboard. The Persians could not find him in the water and presumed he had drowned. Scyllis surfaced at night and made his way among all the ships in Xerxes's fleet, cutting each ship loose from its moorings; he used a hollow reed as snorkel to remain unobserved. Then he swam nine miles (15 kilometres) to rejoin the Greeks off Cape Artemisium".
Humans have been intrinsically linked to being underwater, ever since we came in to the world of air following our birth. Many scientists have suggested that at some level we still remember what it was like to be ‘underwater’ in our mothers womb.
As the story above illustrates, a snorkelling approach was an early attempt to sustain time spent underwater. There is however certain problems in this approach which limit depth. If a man is at a depth of 10 meters, he will experience pressure from displacing the water surrounding him and more importantly, the water above him. At 10 M, this translates to your lungs being subject to twice the pressure than experienced at the surface. The pressure inside your lungs will be equal (near enough) to the outer pressure; so the deeper you go the harder it is to breathe air at surface pressure. So a long snorkel is not the way to go!
Another approach could be to take a big bag with you; the problem is you will asphyxiate quickly. Also as you go deeper the air comes under pressure and is compressed, so wont last as long as on the surface.
An extension of this idea is the diving bell. Records of this thought stretch back almost as far as breath holding dives. In 332 BC the Greek philosopher Aristotle relates a story of Alexander the Great using a ‘diving bell’ in the siege of Tyre in his book "Problemata".
Around the 16th century people began to use diving bells, following their official introduction in 1530. This was a large metal structure shaped like a bell, which trapped an air pocket inside it and could be lowered to a certain depth, acting like an underground cave
for divers. The breath holding diver
could then use it as a base of operations until the air became stale and having to swim to the surface. This idea was expanded on latter in 1650 when Von Guericke designed the first working air pump
, which allowed surface air techniques such as the diving bell and hardhat deep sea diving.
In the 1500's Leonardo da Vinci drew the earliest known designs for scuba gear in his "Codex Atlanticus". This was a combined breathing and buoyancy unit, unfortunately (like many of his inventions) it was never put in to use.
In 1680 an Italian Physician, Giovanni Borelli draws a closed circuit ‘re-breather’. He shows how a bag of chemicals could be used to recycle expired air. He also drew strange footwear on the diagram which some have suggested to be the first design of fins.
"In 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Air was pumped down from the surface with the aid of manual pumps. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. By the 1830s the surface-supplied air helmet was perfected well enough to allow extensive salvage work".
Augustus Siebe (1819-1830's) was a German inventor living in England who designed a metal "open dress helmet" with the air being pumped to the diver from the surface. He latter designed the "closed dress" outfit, which sealed the hard hat in to the diver's suit.
In 1782 the Royal George sunk. She was a British ship who played a major part of the seven years war (Royal George was-"then the flag of Admiral Sir Edward Hawke when he virtually annihilated the French fleet at the Battle of Quiberon Bay".), as well as serving in Gibraltar and aiding in the capture of several Spanish ships, came back to Portsmouth for repairs. During these repairs, she came to a most unfitting end by sinking due to incompetence of the dock authorities during the fitting of a water release valve in her hull. Following this, not too surprisingly, the Naval board took over the shipyard.
In 1839 Siebes hardhat design was one of 5 designs used to salvage the Royal George from the harbour at Spithead.
Another design used in the salvage was a modified version of Charles Deanes smoke helmet patented in England in 1823 originally used for fighting fires. Charles and his brother John added a diving suit to it, attached by leather straps and marketed it. This design was used in to salvage some of the canons from the Royal George, despite its limitations. Since the helmet is not sealed in the suit, it has to be kept horizontal at all times else water enters the helmet; so no bending down underwater, if you did you would drown. Siebe latter on adapted this design by sealing it in to a rubber suit. Siebes design is the basis of future hardhat designs, including today’s designs.
The Royal George lay in 65 feet of water with 108 cannons on board. Interestingly enough, the first recorded use of the buddy system was by the Royal Engineers during this salvage. Also in the years spent (work finished in 1843) there were reports of rheumatism and cold; this could be one of the earliest reports of the ‘bends’. Following this, Siebe received endorsement from Her Majesty's Royal Navy, propelling his firm in to a prominent market position. Siebe, Gorman & Co. became the leading manufacturer of diving equipment.
Following the salvage of the Royal George, the knowledge gained went towards the first diving school being founded in 1843 by the Royal Navy.
In 1825 William James (Englishman) developed a system using compressed air tanks with a full suit and helmet. Although it was not used widely due to its limitations of depth, it is accredited as the first true SCUBA design. In 1828, Lemaire d' Augerville brought out a patent on a swim belt allowing underwater buoyancy control; hence the first "buoyancy compensator" or stab jacket was introduced.
An English merchant seaman revived the idea of the closed circuit re-breather in 1876. Henry Fleuss' self-contained system can be used in smoky or toxic environments as well as underwater capability. Fleuss was hired by Siebe-Gorman and the Siebe, Gorman & Co. company started full production of the new design. This system allowed up to 3-hour dive times at 25 feet; it was used whilst entering an underwater tunnel that was 1000 feet long and 60 feet down. Louis Boutan developed a variant of the closed-circuit system in 1892.
Ideas and Knowledge of the Underwater Environment is Expanded
"Starting in the 19th century, two main avenues of investigation - one scientific, the other technologic - greatly accelerated underwater exploration. Scientific research was advanced by the work of Paul Bert and John Scott Haldane, from France and Scotland, respectively. Their studies helped explain effects of water pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology - compressed air pumps, carbon dioxide scrubbers, regulators, etc., - made it possible for people to stay under water for long periods".
In 1836 Charles Deane published the first "how to" diving manual, following this in 1843 the Royal Navy set up the first diving school (laying the foundations for BSAC). Further technologies continue to be incorporated in to diving, an important step came in 1864 when two Frenchmen (Benoit Rouquayrol and Auguste Denayrouze) developed the first ‘demand valve’, linked to a tank containing around 250 to 350 psi.
Jules Verne published a book called "20,000 Leagues Under the Sea". This book popularises diving, capturing the public’s imagination of what could be accomplished through technological improvement. The demand valve design (Rouquayrol + Denayrouze) features in the book heavily, with reference made to the next step of design; to break the physical link between the surface and the diver.
Between the years of 1869 and 1883, New York's Brooklyn Bridge was built. At the time this was a massive engineering feat, requiring the use of new technologies and ideas. One technique used extensively made use of caissons; these were sealed wooden boxes, three stories high with air pumped in from the surface. Men would work in these caissons for hours at depth over several months. Over a period of time the workers complained of severe joint pains after they left the pressurised containers. These symptoms were researched and the results provided the foundation of "Caissons disease" or decompression sickness. It was found that this condition was caused from working in high pressure for extended periods of time; unfortunately for the workers, the initial findings were not published till after the bridge was finished. Due to the symptoms of paralysis and cramp, the New York newspapers dubbed this condition the bends.
"1880: Dr. Paul Bert, a French Physiologist, completes his work on breathing under hyperbaric (high-pressure) conditions. He recognizes that "caisson disease" is identical to problems faced by deep-sea divers, and suggested it is caused by the release of dissolved nitrogen from the bloodstream, which can be prevented by a gradual ascent to the surface. He also shows that oxygen can become toxic when breathed under pressure".
This was however not the first reported incident showing the physiological effect of the bends. In 1667, an English physicist named Robert Boyle described his observation of gas bubbles in the eye of a viper. He wrote "I have seen a very apparent bubble moving from side to side in the aqueous humour of the eye of a viper at the time when this animal seemed violently distressed in the receiver from which the air had been exhausted."