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Diving is the act by which a person is immersed in a body of water, (it can be a sea, lake or river), for sport, commercial or scientific research, or for military purposes, with or without the aid of special teams.
Diving is practiced in two ways. This first is apnea (from the Greek apnoia, meaning ‘without breath’). There is also a technique known as aqualung, or snorkeling, and uses diving equipment. With equipment a diver can be independent, using scuba-also called SCUBA (an English acronym for Self Contained Underwater Breathing Apparatus) or dependent, as in a surface supply dive (SSD).
Apnea techniques and SCUBA diving belong to the category of diving for sport or recreation. SCUBA techniques, using mixed gas (Nitrox, Heliox, Trimix), and SSD are considered within the category of technical or professional diving because of both the risk and the level of preparation required by the diver that uses them.
Sport diving is generally limited to a depth of less than forty meters (although apnea can attain significant depths), while the professional diver with special mixtures can reach depths of over one hundred meters.
Apnea diving is the technique and skill in which the diver holds his breath after taking a deep breath at the surface. While this can be performed without any special equipment, the current configuration consists of a sport appropriate mask, fins, snorkel, weight, and, if necessary, a suit of thermo-insulating material.
The simplest form of diving, and the oldest used by man, it appears in various regions and cultures to exploit food sources (such as fish, crustaceans and mollusks), useful resources (algae, sponges, corals) and resources of cultural or economic value(pearls).
SCUBA diving uses the storage of air pressure in a bottle that is carried by the diver; breathing the stored air allows for a considerable time of autonomy. Besides the basic equipment, it requires an air storage bottle, a harness, and a mechanism of buoyancy. This is an integrated system of a harness and buoyancy vest called hydrostatic buoyancy vest or BCD (the English acronym for Buoyancy Compensation Device).
SCUBA diving also involves a system of valves, ballast system, tubing and nozzle(s) that make up what is called the regulator. This is the most basic, but safety standards require a number of “clocks” that allow one to know how deep one is and how the air is; i.e. depth and pressure gauges.
Sport diving (apnea and SCUBA) is a safe activity, but has risks of its own and demands a lot of responsibility on the part of its practitioners. Adequate preparation, familiarity with the equipment used, knowledge and application of security measures, a minimum of technical and physiological knowledge, and respect for aquatic organisms are the minimum conditions to smoothly carry through these activities.
Decompression chamber
The decompression chamber is an airtight chamber for the controlled increase and decrease in air pressure ((re-) compression and decompression). It is used by commercial divers after being used for proper adjustment to the atmospheric pressure in order to prevent decompression sickness (caisson disease).
The stay in the decompression chamber can be as long and deep as diving operations lasting for several hours, days or weeks. In some cases, the chambers are mounted on special ships, which are specially designed and constructed.
Particularly important is the recompression chamber to treat decompression sickness of divers who have surfaced too quickly from the depths to the surface. The diver will go as soon as possible into the decompression chamber, where they are under increased pressure from 1.7 bars of air and breathing pure oxygen (pure oxygen is toxic from a pressure bar) of 1.7.
While the pressure in the decompression chamber is slowly lowered, the high nitrogen content in the blood slowly diminishes. If this fails, a gas embolism is possible, because the nitrogen is excreted as a result of lower ambient pressure of the solution in the blood plasma into the gas phase. The resulting bubbles can clog major arteries and thereby make the tissue behind it extinct.
The Federal Teaching and Research Center in Berlin, the DLRG, operates a globally unique decompression chamber with a diving tower, where divers can collect under very safe conditions. In the context of hyperbaric oxygen therapy, decompression chambers can also find other uses, such as carbon monoxide poisoning or gas gangrene infection.
Diving Decompression Tables
Decompression tables are cards where divers can determine conditions for a writ of gas diving and decompression stops to avoid decompression problems. With decompression tables a diving identification card is considered “rectangular”, i.e. the diver is at the maximum depth from entering the water until it exits (called rectangular because it is the figure formed if is plotted in a plane where one axis is the depth and the other length). There are also complex tables for diving in stages of altitude decompression.
Some common decompression tables are:
Tables of the U.S armed
Buhlmann tables (special for use in mountain lakes, altitude 600 meters)
BSAC 88 Tables
PADI tables
DCIEM Tables
French Navy tables (tables MN90)
Tables FMAS
There is currently alternatives to traditional decompression tables:
Dive computer: monitor has the advantage of diving at the time, not only the ballot planned by generating a dive plan and increasing the time instant background (against the profile generated rectangular tables).
Tables generated by computer programs that fit the diver’s plan and the gas mixture to breathe.
Decompression at the time (DOTF: Deco on the Fly) is a method for determining the profile of decompression needed swiftly and successfully without the help of tables or a computer. It is taught in advanced courses taken by diving GUE instructors.
Also known as radio decompression because it uses a known required decompression point and relates it to the specific depth and bottom time. The decompression obligation changes in fixed increments in relation to the point chosen according to changes in depth and bottom time.
Free Diving
Called free diving, it is basically diving using your own breath and no outside oxygen supply. The diver breathes before the dive and only uses this breath. The period between inhalation and exhalation is known as apnea. Apnea diving is the oldest and most primitive form of diving.
In the Stone Age apnea divers collected, for example, mussels, sponges and fish beads and hunted with spears. Nowadays, free diving is a leisure activity, but also operated as a performance and/or extreme sports. In the leisure sector it is primarily used to explore the underwater world. In competitive sports, however, it is increasingly sought by targeted trainers for longer apnea times, distances and depth of services.
Breathing is usually an involuntary process that can be controlled consciously. While the untrained are barely able to suppress their respiratory irritation over a long period, the duration of apnea performance for an expert is limited by the amount of oxygen in the blood. If the partial pressure of oxygen in the blood in an individual is at its limit, the diver falls unconscious. The respiratory irritant is not caused by decreasing oxygen, but by rising carbon dioxide content of blood simplification.
Conscious breathing or hyperventilation before diving does not lead to an increase in oxygen supply, but to a reduction of carbon dioxide in the blood. Depending on the duration and intensity, they will lead to a delayed respiratory irritation. In particular, the beginner is not able to recognize the signs of this impending impotence.
It attacks those affected usually suddenly and without warning. If the breathing holes of the person concerned are not placed within a short time above the water surface, or drowning accidents can be the consequence (shallow water blackout). Therefore, the protection of the divers will play a particularly important role.
Dives are made by at least two people, and is generally mutually assured. In this way, accidents are very unlikely. The accident rate during apnea diving is therefore – except”no limit” diving – very low. A rapid loss of consciousness without experienced assistance is a life-threatening situation. There is an acute danger to life!
Physical effects of diving
These rules have an accurate, physical influence in the body of a diver and bring a range of mechanical and biochemical effects to consider.
A 1970 American study found that sport diving was (per hour of activity) ninety-six times more dangerous than driving an automobile. A 2000 Japanese study found that each hour of recreational diving was between thirty-six and sixty-two times more risky than driving one automobile. Still, specialists consider diving one of the safest activities in the world.
The physical model of the human body
The human body is composed of matter in its three basic phases (solid, liquid and gas). The only structure is the rigidity of the skeletal system, which has the mechanical function of supporting the other organs and tissues (mainly muscles and with the help of these, viscera).
The body parts directly attached to the skeleton (like most of the muscles) retain their relative position; the components that are “free” or little associated with the skeleton (as the abdominal viscera) maintain their position by balance of forces.
Then there is the respiratory system, which consists of sacs and ducts representing its own organs and tissues with gas phase excellence. The blood tissue is the most important liquid phase of the body. Finally, all other tissues (muscle and viscera) have the consistency of the meat itself, and are more or less firm and deformable.
This, linked to the anatomical architecture, defines three “compartments” that are basic to consider:
Rigid boxes determined by the skeletal system: the skull (holds important gas-phase cavity-sinuses, frontal and parafrontals and partially–ear canals) and the rib cage (containing the lungs and heart).
The abdominal viscera: separated from the rib cage by the diaphragm, but with very elastic, deformable tissues.
The blood mass: liquid phase, supplying the body through vessels, but with substantial quantities into the heart and highly vascular organs (lungs and nervous system).
The diving reflex in man
Besides considering the diver’s body as a conglomeration of materials, each with its physical properties, it is necessary to explain some physiological mechanisms that trigger reflexes when submerged.
The man is essentially a land animal and therefore its physiology is completely adapted to this lifestyle. Like their fellow animals, human physiology has inherited a number of physiological response mechanisms and is systemic (non-voluntary) to the diving situation. These responses are called “diving reflex” and include:
Decreased heart rate: triggered by the increase in blood pressure.
Hypervolemia: (increased volume of blood plasma), which is offset by an increase in diuresis (increased excretion of urine).
Accessory equipment
Knife, by law is required in many countries. A knife would be used for cutting ends of abandoned drift nets that could endanger the life of the diver.
Flashlight or focus, which in the day helps the diver see dips in the rock caves or areas with low light. For night dives it is obviously essential. The lanterns are usually less powerful and require fresh batteries, while outbreaks are usually more powerful and use a rechargeable battery.
Reel, containing a very long line that allows the diver to follow it to keep orientation.
Compass: very useful for orientation underwater.
Cyalume chemical light, which is attached to the bottle or the BCD during night dives.
Underwater Slate, allowing written or graphic communication underwater.
Rattle or horn, allowing sound signals for one diver to warn another.
Inflatable buoy, which can be inflated with a compressed air bottle. It is used to mark a position, or to help remove one from heavy water.
Diving bottles
In SCUBA, buoyancy thrust is the product of negative weight and the positive momentum of the diver’s body and the vest and carry different devices; the ballast should be sufficient to provide greater positive buoyancy when the air tank is almost empty. Today more and more vests or BCD models come with integrated lead compensating for convenience. The sealing system must be robust and secure, but easily released in case of emergency.
Regulator, a first stage (which attaches to the tank), with a high pressure hose (manometer) and three “low” (intermediate pressure) ones at BCD, and two second stages and nozzles (main and secondary-or-octopus).
Besides the basic or light equipment, the equipment for SCUBA integrates the following components:
Bottle (tank) of compressed air, which is an aluminum or steel vessel containing compressed air, and has a single opening which sets a control and has attached fittings. The taps consists of a valve (type J or K), a tap that controls the opening and closing of the bottle and one or more outputs coupled to the regulator (type INT or a moth stirrup holding the regulator to the bottle, where there O-ring to maintain the seal-and DIN-that holds the regulator to the bottle by a threaded, supports higher pressures).
There are several types of bottles according to their capacity (5-18 L) and the supporting working pressure (230 bar or 300 bar).
The bottles must pass regular reviews to check the fatigue of the metal, each country having its own rules. Never exceed the load pressure or expose to high temperatures.
Jackets (BCD) or (JACKET), as the name suggests, is a vest fused to the harness that supports the bottle on the back. It has an air chamber positively buoyant at the surface and the diver can adjust buoyancy at will to compensate for the loss of momentum that occurs with depth for pressure effects (to compress the suit, the very air chamber BCD and some body cavities).
This vest has a camera or bladder that binds with a connection to the regulator valve and a nozzle to inject air directly from the bottle or for blowing through the mouthpiece and several purge valves that allow free air during the ascent which produces the reverse. It has also a pressure relief valve which ensures that the bladder does not inadvertently explode in case of overpressure during ascent. The hydrostatic vest for the diver is what the swim bladder is to the fish.
The vest includes pockets and loops to carry items needed for the diver, and the fasteners needed to keep the vest securely attached to the diver.