who developed an apparatus to breathe compressed air underwater

An early diving dress using a compressed air reservoir was designed and built in 1771 by Sieur[10] Fréminet from Paris. He conceived an autonomous breathing machine equipped with a reservoir, dragged behind the diver or mounted on his back.[11][12] Fréminet called his invention machine hydrostatergatique and used it successfully for more than ten years in the harbors of Le Havre and Brest, as stated in the explanatory text of a 1784 painting.[13][14]

Scuba set

self contained underwater breathing apparatus

A scuba set is any breathing apparatus that is carried entirely by an underwater diver and provides the diver with breathing gas at the ambient pressure. (Scuba is an anacronym for self-contained underwater breathing apparatus.) Although strictly speaking the scuba set is only the diving equipment which is required for providing breathing gas to the diver, general usage includes the harness by which it is carried, and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge, and in the looser sense it has been used to refer to any diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface supplied diving systems, and is allowed by the relevant code of practice.

Two basic functional systems of scuba are in general use:

Within these systems, various mounting configurations may be used to carry the scuba set, depending on application and preference. These include back mount, which is generally used for recreational scuba and for bailout sets for surface supplied diving, side-mount, which is popular for tight cave penetrations, sling mount, used for stage-drop sets, decompression gas and bailout sets where the main gas supply is back mounted, and various non-standardised carry systems for special circumstances.

The most immediate risk associated with scuba diving is drowning due to a failure of the breathing gas supply. This may be managed by diligent monitoring of remaining gas, adequate planning and provision of an emergency gas supply carried by the diver in a bailout cylinder or supplied by the diver's buddy.

The word SCUBA was coined in 1952 by Major Christian Lambertsen who served in the U.S. Army Medical Corps from 1944 to 1946 as a physician.[1] Lambertsen first called the closed circuit rebreather apparatus he had invented "Laru", an (acronym for Lambertsen Amphibious Respiratory Unit) but, in 1952, rejected the term "Laru" for "SCUBA" ("Self-Contained Underwater Breathing Apparatus").[2] Lambertsen's invention, for which he held several patents registered from 1940 to 1989, was a rebreather and is different from the open-circuit diving regulator and diving cylinder assemblies also commonly referred to as scuba.[3]

Open-circuit-demand scuba is a 1943 invention by the Frenchmen Émile Gagnan and Jacques-Yves Cousteau, but in the English language Lambertsen's acronym has become common usage and the name Aqua-Lung, (often spelled "aqualung"), coined by Cousteau for use in English-speaking countries,[4] has fallen into secondary use. As with radar, the acronym scuba has become so familiar that it is generally not capitalized and is treated as an ordinary noun. For example, it has been translated into the Welsh language as sgwba.

A diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater. Scuba provides the diver with the advantages of mobility and horizontal range far beyond the reach of an umbilical hose attached to surface-supplied diving equipment (SSDE).[5]

Unlike other modes of diving, which rely either on breath-hold or on breathing supplied under pressure from the surface, scuba divers carry their own source of breathing gas, usually compressed air,[6] allowing them greater freedom of movement than with an air line or diver's umbilical and longer underwater endurance than breath-hold. Scuba diving may be done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface supplied diving equipment for main gas supply when this is practicable. Surface supplied divers may be required to carry scuba as an emergency breathing gas supply to get them to safety in the event of a failure of surface gas supply.[5][7][8]

There are divers who work, full or part-time, in the recreational diving community as instructors, assistant instructors, divemasters and dive guides. In some jurisdictions the professional nature, with particular reference to responsibility for health and safety of the clients, of recreational diver instruction, dive leadership for reward and dive guiding is recognised and regulated by national legislation.[8]

Other specialist areas of scuba diving include military diving, with a long history of military frogmen in various roles. Their roles include direct combat, infiltration behind enemy lines, placing mines or using a manned torpedo, bomb disposal or engineering operations. In civilian operations, many police forces operate police diving teams to perform "search and recovery" or "search and rescue" operations and to assist with the detection of crime which may involve bodies of water. In some cases diver rescue teams may also be part of a fire department, paramedical service or lifeguard unit, and may be classed as public service diving.[8]

There are also professional divers involved with underwater environment, such as underwater photographers or underwater videographers, who document the underwater world, or scientific diving, including marine biology, geology, hydrology, oceanography and underwater archaeology.[7][8]

The choice between scuba and surface supplied diving equipment is based on both legal and logistical constraints. Where the diver requires mobility and a large range of movement, scuba is usually the choice if safety and legal constraints allow. Higher risk work, particularly in commercial diving, may be restricted to surface supplied equipment by legislation and codes of practice.[8][9]

There are alternative methods that a person can use to survive and function while underwater, currently including:

A scuba set is characterized by full independence from the surface during use, by providing breathing gas carried by the diver. Early attempts to reach this autonomy from the surface were made in the 18th century by the Englishman John Lethbridge, who invented and successfully built his own underwater diving machine in 1715.

The Frenchman Paul Lemaire d'Augerville built and used autonomous diving equipment in 1824,[15] as did the British William H. James in 1825. James' helmet was made of "thin copper or sole of leather" with a plate window, and the air was supplied from an iron reservoir.[16] A similar system was used in 1831 by the American Charles Condert, who died in 1832 while testing his invention in the East River at only 20 feet (6Â m) deep.

The oldest known oxygen rebreather was patented on June 17, 1808 by Sieur Touboulic from Brest, mechanic in Napoleon's Imperial Navy, but there is no evidence of any prototype having been manufactured. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver himself and circulating in a closed circuit through a sponge soaked in limewater.[17][18]

After having travelled to England and discovered William James' invention, the French physician Manuel ThÃ©odore Guillaumet, from Argentan (Normandy), patented in 1838 the oldest known regulator mechanism. Guillaumet's invention was air-supplied from the surface and was never mass-produced due to problems with safety. The oldest practical rebreather relates to the 1849 patent from the Frenchman Pierre Aimable De Saint Simon Sicard.[19]

None of those inventions solved the problem of high pressure when compressed air must be supplied to the diver (as in modern regulators); they were mostly based on a constant-flow supply of the air. The compression and storage technology was not advanced enough to allow compressed air to be stored in containers at sufficiently high pressures to allow useful dive times.

By the turn of the twentieth century, two basic templates for a scuba had emerged; open-circuit scuba where the diver's exhaled gas is vented directly into the water, and closed-circuit scuba where the diver's carbon dioxide is filtered from unused oxygen, which is then recirculated.

The first important step for the development of scuba technology was the invention of the demand regulator. In 1864, the French engineers Auguste Denayrouze and Benoît Rouquayrol designed and patented their "Rouquayrol-Denayrouze diving suit" after adapting a pressure regulator and developing it for underwater use. This would be the first diving suit that could supply air to the diver on demand by adjusting the flow of air from the tank to meet the diver’s breathing and pressure requirements. The system still had to use surface supply, as the cylinders of the 1860s would not have been able to withstand the necessary high pressures.

The first open-circuit scuba system was devised in 1925 by Yves Le Prieur in France. Inspired by the simple apparatus of Maurice Fernez and the freedom it allowed the diver, he conceived an idea to make it free of the tube to the surface pump by using Michelin cylinders as the air supply, containing three litres of air compressed to 150 kilograms per square centimetre (2,100 psi; 150 bar). The "Fernez-Le Prieur" diving apparatus was demonstrated at the swimming pool of Tourelles in Paris in 1926. The unit consisted of a cylinder of compressed air carried on the back of the diver, connected to a pressure regulator designed by Le Prieur adjusted manually by the diver, with two gauges, one for tank pressure and one for output (supply) pressure. Air was supplied continually to the mouthpiece and ejected through a short exhaust pipe fitted with a valve as in the Fernez design,[20] however, the lack of a demand regulator and the consequent low endurance of the apparatus limited the practical use of LePrieur’s device.

Le Prieur's design was the first autonomous breathing device used by the first scuba diving clubs in history - Racleurs de fond founded by Glenn Orr in California in 1933, and Club des sous-l'eau founded by Le Prieur himself in Paris in 1935.[21] Fernez had previously invented the noseclip, a mouthpiece (equipped with a one-way valve for exhalation) and diving goggles, and Yves le Prieur just joined to those three Fernez elements a hand-controlled regulator and a compressed-air cylinder. Fernez's goggles didn't allow a dive deeper than ten metres due to "mask squeeze", so, in 1933, Le Prieur replaced all the Fernez equipment (goggles, noseclip and valve) by a full face mask, directly supplied with constant flow air from the cylinder.

In 1942, during the German occupation of France, Jacques-Yves Cousteau and Émile Gagnan designed the first successful and safe open-circuit scuba, known as the Aqua-Lung. Their system combined an improved demand regulator with high-pressure air tanks. Émile Gagnan, an engineer employed by the Air Liquide company, miniaturized and adapted the regulator to use with gas generators, in response to constant fuel shortage that was a consequence of German requisitioning. Gagnan's boss, Henri Melchior, knew that his son-in-law Jacques-Yves Cousteau was looking for an automatic demand regulator to increase the useful period of the underwater breathing apparatus invented by Commander le Prieur,[22] so he introduced Cousteau to Gagnan in December 1942. On Cousteau's initiative, the Gagnan's regulator was adapted to diving, and the new Cousteau-Gagnan patent was registered some weeks later in 1943.[23]

In 1957, Eduard Admetlla i Lázaro used a modified version of the Aqua-Lung made by Nemrod and broke the world record by descending to a depth of 100 metres (330 ft).[24]

The alternative concept, developed in roughly the same time frame was the closed-circuit scuba. The body consumes and metabolises only a small fraction of inhaled oxygenâ€”the situation is even more wasteful of oxygen when the breathing gas is compressed as it is in scuba systems underwater. The rebreather therefore recycles the exhaled oxygen, while constantly replenishing it from the supply so that the oxygen level does not get depleted. The apparatus also has to chemically remove the exhaled carbon dioxide, as a buildup of CO2 levels would result in respiratory distress and hypercapnia.

The first commercially practical closed-circuit scuba was designed and built by the diving engineer Henry Fleuss in 1878, while working for Siebe Gorman in London.[25][26] His self contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with (estimated) 50-60% O2 supplied from a copper tank and CO2 scrubbed by rope yarn soaked in a solution of caustic potash; the system giving a duration of about three hours.[26][27] Fleuss tested his device in 1879 by spending an hour submerged in a water tank, then one week later by diving to a depth of 5.5 metres (18Â ft) in open water, upon which occasion he was slightly injured when his assistants abruptly pulled him to the surface.

His apparatus was first used under operational conditions in 1880 by the lead diver on the Severn Tunnel construction project, who was able to travel 1,000 feet (300Â m) in the darkness to close several submerged sluice doors in the tunnel; this had defeated the best efforts of hard hat divers due to the danger of their air supply hoses becoming fouled on submerged debris, and the strong water currents in the workings.[26]

Fleuss continually improved his apparatus, adding a demand regulator and tanks capable of holding greater amounts of oxygen at higher pressure. Sir Robert Davis, head of Siebe Gorman, perfected the oxygen rebreather in 1910[26][28] with his invention of the Davis Submerged Escape Apparatus, the first rebreather to be made in quantity. While intended primarily as an emergency escape apparatus for submarine crews, it was soon also used for diving, being a handy shallow water diving apparatus with a thirty-minute endurance,[28] and as an industrial breathing set.

The rig comprised a rubber breathing/buoyancy bag containing a canister of barium hydroxide to scrub exhaled CO2 and, in a pocket at the lower end of the bag, a steel pressure cylinder holding approximately 56 litres (2.0 cu ft) of oxygen at a pressure of 120 bars (1,700 psi). The cylinder was equipped with a control valve and was connected to the breathing bag. Opening the cylinder's valve admitted oxygen to the bag at ambient pressure. The rig also included an emergency buoyancy bag on the front of to help keep the wearer afloat. The DSEA was adopted by the Royal Navy after further development by Davis in 1927.[29]

In 1912 the German firm Dräger developed their own version of standard diving dress with a self-contained gas supply from a rebreather with the circulation driven by an injector.[30]

During the 1930s and all through World War II, the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the first frogmen. The British used the Davis apparatus for submarine escape, but they soon adapted it for their frogmen during World War II. Germans used the Dräger rebreathers,[31] which were also originally designed as submarine escape sets and only adapted for use by frogmen during World War II.

The Italians developed similar rebreathers for the combat swimmers of the Decima Flottiglia MAS, especially the Pirelli ARO.[32] In the U.S. Major Christian J. Lambertsen invented an underwater free-swimming oxygen rebreather in 1939, which was accepted by the Office of Strategic Services.[33] In 1952 he patented a modification of his apparatus, this time named SCUBA. Although he coined the most common English word used for autonomous open-circuit diving equipment, Lambertsen did not invent that equipment.[34] After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away the presence of the divers.

Air Liquide started selling the Cousteau-Gagnan regulator commercially as of 1946 under the name of scaphandre Cousteau-Gagnan or CG45 ("C" for Cousteau, "G" for Gagnan and 45 for the 1945 patent). The same year Air Liquide created a division called La Spirotechnique, to develop and sell regulators and other diving equipment. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed to the U.S. Divers company (the American division of Air Liquide) and later sold with La Spirotechnique and U.S. Divers to finally become the name of the company, Aqua-Lung/La Spirotechnique, currently located in Carros, near Nice.[35]

In 1948 the Cousteau-Gagnan patent was also licensed to Siebe Gorman of England,[36][verification needed] when Siebe Gorman was directed by Robert Henry Davis.[37] Siebe Gorman was allowed to sell in Commonwealth countries, but had difficulty in meeting the demand and the U.S. patent prevented others from making the product. This demand was eventually met by Ted Eldred of Melbourne, Australia, who had been developing a rebreather called the Porpoise. When a demonstration resulted in a diver passing out, he began to develop the single-hose open-circuit scuba system, which separates the first and second stages by a low-pressure hose, and releases exhaled gas at the second stage. This avoided the Cousteau-Gagnan patent, which protected the twin-hose scuba regulator.[38] In the process, Eldred also improved performance of the regulator.[citation needed][clarification needed] Eldred sold the first Porpoise Model CA single hose scuba early in 1952.

Early scuba sets were usually provided with a plain harness of shoulder straps and waist belt. The waist belt buckles were usually quick-release, and shoulder straps sometimes had adjustable or quick release buckles. Many harnesses did not have a backplate, and the cylinders rested directly against the diver's back. The harnesses of many diving rebreathers made by Siebe Gorman included a large back-sheet of reinforced rubber.[citation needed]

Early scuba divers dived without any buoyancy aid.[39] In emergency they had to jettison their weights. In the 1960s adjustable buoyancy life jackets (ABLJ) became available. One early make, since 1961, was Fenzy. The ABLJ is used for two purposes: to adjust the buoyancy of the diver to compensate for loss of buoyancy at depth, mainly due to compression of the neoprene wetsuit) and more importantly as a lifejacket that will hold an unconscious diver face-upwards at the surface, and that can be quickly inflated. It was put on before putting on the cylinder harness. The first versions were inflated with a small carbon dioxide cylinder, later with a small direct coupled air cylinder. An extra low-pressure feed from the regulator first-stage lets the lifejacket be controlled as a buoyancy aid. This invention in 1971 of the "direct system,"[citation needed] by ScubaPro, resulted in what was called a stabilizer jacket or stab jacket, and is now increasingly known as a buoyancy compensator (device), or simply "BCD".

Scuba sets are of two types:

Both types of scuba set include a means of supplying air or other breathing gas, nearly always from a high pressure diving cylinder, and a harness to attach it to the diver. Most open-circuit scuba sets have a demand regulator to control the supply of breathing gas, and most rebreathers have a constant-flow injector, or an electronically controlled injector to supply fresh gas, but also usually have an automatic diluent valve (ADV), which functions in the same way as a demand valve, to maintain the loop volume during descent.[citation needed]

Open-circuit-demand scuba exhausts exhaled air to the environment, and requires each breath to be delivered to the diver on demand by a diving regulator, which reduces the pressure from the storage cylinder and supplies it through the demand valve when the diver reduces the pressure in the demand valve slightly during inhalation.

The essential subsystems of an open-circuit scuba set are;[citation needed]

Additional components which when present are considered part of the scuba set are;

The buoyancy compensator is generally assembled as an integrated part of the set, but is not technically part of the breathing apparatus.

The cylinder is usually worn on the back. "Twin sets" with two low capacity back-mounted cylinders connected by a high pressure manifold were more common in the 1960s than now for recreational diving, although larger capacity twin cylinders ("doubles") are commonly used by technical divers for increased dive duration and redundancy. At one time a firm called Submarine Products sold a sport air scuba set with three manifolded back-mounted cylinders.[citation needed] Cave and wreck penetration divers sometimes carry cylinders attached at their sides instead, allowing them to swim through more confined spaces.

Newspapers and television news often describe open-circuit scuba wrongly as "oxygen" equipment.

Constant flow scuba sets do not have a demand regulator; the breathing gas flows at a constant rate, unless the diver switches it on and off by hand. They use more air than demand regulated scuba. There were attempts at designing and using these for diving and for industrial use before the Cousteau-type aqualung became commonly available circa 1950. Examples were Charles Condert dress in the USA (as of 1831), "Ohgushi's Peerless Respirator" in Japan (a bite-controlled regulator, as of 1918), and Commandant le Prieur's hand-controlled regulator in France (as of 1926); see Timeline of diving technology.

This system consists of one or more diving cylinders containing breathing gas at high pressure, typically 200–300 bars (2,900–4,400 psi), connected to a diving regulator. The demand regulator supplies the diver with as much gas as needed at the ambient pressure.

This type of breathing set is sometimes called an aqualung. The word Aqua-Lung, which first appeared in the Cousteau-Gagnan patent, is a trademark, currently owned by Aqua Lung/La Spirotechnique.[40]

This is the first type of diving demand valve to come into general use, and the one that can be seen in classic 1960s television scuba adventures, such as Sea Hunt. They were often use with manifolded twin cylinders.

All the stages of this type of regulator are in a large valve assembly mounted directly to the cylinder valve or manifold, behind the diver's neck. Two large bore corrugated rubber breathing hoses connect the regulator with the mouthpiece, one for supply and one for exhaust. The exhaust hose is used to return the exhaled air to the regulator, to avoid pressure differences due to depth variation between the exhaust valve and final stage diaphragm, which would cause a free-flow of gas, or extra resistance to breathing, depending on the diver's orientation in the water. In modern single-hose sets this problem is avoided by moving the second-stage regulator to the diver's mouthpiece. The twin-hose regulators came with a mouthpiece as standard, but a full-face diving mask was an option.[citation needed]

Most modern open-circuit scuba sets have a diving regulator consisting of a first-stage pressure-reducing valve connected to the diving cylinder's output valve or manifold. This regulator reduces the pressure from the cylinder, which may be up to 300 bars (4,400 psi), to a lower pressure, generally between about 9 and 11 bar above the ambient pressure. A low-pressure hose links this with the second-stage regulator, or "demand valve", which is mounted on the mouthpiece. Exhalation occurs through a rubber one-way mushroom valve in the chamber of the demand valve, directly into the water quite close to the diver's mouth. Some early single hose scuba sets used full-face masks instead of a mouthpiece, such as those made by Desco [41] and Scott Aviation [42] (who continue to make breathing units of this configuration for use by firefighters).

Modern regulators typically feature high-pressure ports for pressure sensors of dive-computers and submersible pressure gauges, and additional low-pressure ports for hoses for inflation of dry suits and BC devices.[citation needed]

Most recreational scuba sets have a backup second-stage demand valve on a separate hose, a configuration called a "secondary", or "octopus" demand valve, "alternate air source", "safe secondary" or "safe-second". The idea was conceived by cave-diving pioneer Sheck Exley as a way for cave divers to share air while swimming single-file in a narrow tunnel,[citation needed] but has now become the standard in recreational diving. By providing a secondary demand valve the need to alternately breathe off the same mouthpiece when sharing air is eliminated. This reduces the stress on divers who are already in a stressful situation, and this in turn reduces air consumption during the rescue and frees the donor's hand.[citation needed]

Some diver training agencies recommend that a diver routinely offer their primary demand valve to a diver requesting to share air, and then switch to their own secondary demand valve.[43] The idea behind this technique is that the primary demand valve is known to be working, and the diver donating the gas is less likely to be stressed or have a high carbon dioxide level, so has more time to sort out their own equipment after temporarily suspending the ability to breathe. In many instances, panicked divers have grabbed the primary regulators out of the mouths of other divers,[citation needed] so changing to the backup as a routine reduces stress when it is necessary in an emergency.

In technical diving donation of the primary demand valve is commonly the standard procedure, and the primary is connected to the first stage by a long hose, typically around 2Â m, to allow gas sharing while swimming in single file in a narrow space as might be required in a cave or wreck. In this configuration the secondary is generally held under the chin by a loose bungee loop around the neck, supplied by a shorter hose, and is intended for backup use by the diver donating gas.[43] The backup regulator is usually carried in the diver's chest area where it can be easily seen and accessed for emergency use. It may be worn secured by a breakaway clip on the buoyancy compensator, plugged into a soft friction socket attached to the harness, secured by sliding a loop of the hose into the shoulder strap cover of a jacket style BC, or suspended under the chin on a break-away bungee loop known as a necklace. These methods also keep the secondary from dangling below the diver and being contaminated by debris or snagging on the surroundings. Some divers store it in a BC pocket, but this reduces availability in an emergency.

Occasionally, the secondary second-stage is combined with the inflation and exhaust valve assembly of the buoyancy compensator device. This combination eliminates the need for a separate low pressure hose for the BC, though the low pressure hose connector for combined use must have a larger bore than for standard BC inflation hoses, because it will need to deliver a higher flow rate if it is used for breathing.[citation needed] This combination unit is carried in the position where the inflator unit would normally hang on the left side of the chest. With integrated DV/BC inflator designs, the secondary demand valve is at the end of the shorter BC inflation hose, and the donor must retain access to it for buoyancy control, so donation of the primary regulator to help another diver is essential with this configuration.[citation needed]

The secondary demand valve is often partially yellow in color, and may use a yellow hose, for high visibility, and as an indication that it is an emergency or backup device.

When a side-mount configuration is used, the usefulness of a secondary demand valve is greatly reduced, as each cylinder will have a regulator and the one not in use is available as a backup. This configuration also allows the entire cylinder to be handed off to the receiver, so a long hose is also less likely to be needed.

Some diving instructors continue to teach buddy-breathing from a single demand valve as an obsolescent but still occasionally useful technique, learned in addition to the use of the backup DV, since availability of two second stages per diver is now assumed as standard in recreational scuba.[citation needed]

There have been designs for a cryogenic open-circuit scuba which has liquid-air tanks instead of cylinders. Underwater cinematographer Jordan Klein, Sr. of Florida co-designed such a scuba in 1967, called "Mako", and made at least a prototype.[citation needed]

The Russian Kriolang (from Greek cryo- (= "frost" taken to mean "cold") + English "lung") was copied from Jordan Klein's "Mako" cryogenic open-circuit scuba. and were made until at least 1974.[44] It would have to be filled a short time before use.

A rebreather recirculates the breathing gas already used by the diver after replacing oxygen used by the diver and removing the carbon dioxide metabolic product. Rebreather diving is used by recreational, military and scientific divers where it can have advantages over open-circuit scuba. Since 80% or more of the oxygen remains in normal exhaled gas, and is thus wasted, rebreathers use gas very economically, making longer dives possible and special mixes cheaper to use at the cost of more complicated technology and more possible failure points. More stringent and specific training and greater experience is required to compensate for the higher risk involved. The rebreather's economic use of gas, typically 1.6 litres (0.06 cu ft) of oxygen per minute, allows dives of much longer duration for an equivalent gas supply than is possible with open-circuit equipment where gas consumption may be ten times higher.[citation needed]

There are two main variants of rebreather — semi-closed circuit rebreathers, and fully closed circuit rebreathers, which include the subvariant of oxygen rebreathers. Oxygen rebreathers have a maximum safe operating depth of around 6 metres (20 ft), but several types of fully closed circuit rebreathers, when using a helium-based diluent, can be used deeper than 100 metres (330 ft). The main limiting factors on rebreathers are the duration of the carbon dioxide scrubber, which is generally at least 3 hours, increased work of breathing at depth, reliability of gas mixture control, and the requirement to be able to safely bail out at any point of the dive.[citation needed]

Rebreathers are generally used for scuba applications, but are also occasionally used for bailout systems for surface supplied diving.[citation needed]

The possible endurance of a rebreather dive is longer than an open-circuit dive, for similar weight and bulk of the set, if the set is bigger than the practical lower limit for rebreather size,[45] and a rebreather can be more economical when used with expensive gas mixes such as heliox and trimix,[45] but this may require a lot of diving before the break-even point is reached, due to the high initial and running costs of most rebreathers, and this point will be reached sooner for deep dives where the gas saving is more pronounced.[citation needed]

Until Nitrox, which contains more oxygen than air, was widely accepted in the late 1990s,[46] almost all recreational scuba used simple compressed and filtered air. Other gas mixtures, typically used for deeper dives by technical divers, may substitute helium for some or all of the nitrogen (called Trimix, or Heliox if there is no nitrogen), or use lower proportions of oxygen than air. In these situations divers often carry additional scuba sets, called stages, with gas mixtures with higher levels of oxygen that are primarily used to reduce decompression time in staged decompression diving.[43] These gas mixes allow longer dives, better management of the risks of decompression sickness, oxygen toxicity or lack of oxygen (hypoxia), and the severity of nitrogen narcosis. Closed circuit scuba sets (rebreathers) provide a gas mix that is controlled to optimise the mix for the actual depth at the time.

Gas cylinders used for scuba diving come in various sizes and materials and are typically designated by material — usually aluminium or steel, and size. In the U.S. the size is designated by their nominal capacity, the volume of the gas they contain when expanded to normal atmospheric pressure. Common sizes include 80, 100, 120 cubic feet, etc., with the most common being the "Aluminum 80". In most of the rest of the world the size is given as the actual internal volume of the cylinder, sometimes referred to as water capacity, as that is how it is measured and marked (WC) on the cylinder (10 liter, 12 liter, etc.).[citation needed]

Cylinder working pressure will vary according to the standard of manufacture, generally ranging from 200 bar (2,900 psi) up to 300 bar (4,400 psi).

An aluminium cylinder is thicker and bulkier than a steel cylinder of the same capacity and working pressure, as suitable aluminium alloys have lower tensile strength than steel, and is more buoyant although actually heavier out of the water, which means the diver would need to carry more ballast weight. Steel is also more often used for high pressure cylinders, which carry more air for the same internal volume.[citation needed]

The common method of blending nitrox by partial pressure requires that the cylinder is in "oxygen service", which means that the cylinder and cylinder valve have had any non-oxygen-compatible components replaced and any contamination by combustible materials removed by cleaning.[47] Diving cylinders are sometimes colloquially called "tanks", "bottles" or "flasks" although the proper technical term for them is "cylinder".[citation needed]

The scuba set can be carried by the diver in several ways. The two most common basic mounting configurations are back-mount, and side-mount, and back-mount may be expanded to include auxiliary side-mounting, including bungee-constrained low profile side-mount, and the less compact sling-mount or stage-mount arrangement.

Most common for recreational diving is the stabilizer jacket harness, in which a single cylinder, or occasionally twins, is strapped to the jacket style buoyancy compensator which is used as the harness. Some jacket style harnesses allow a bailout or decompression cylinder to be sling mounted from D-rings on the harness. A bailout cylinder can also be strapped to the side of the main back-mounted cylinder.[citation needed]

Another popular configuration is the backplate and wing arrangement, which uses a back inflation buoyancy compensator bladder sandwiched between a rigid backplate and the main gas cylinder or cylinders. This arrangement is particularly popular with twin or double cylinder sets, and can be used to carry larger sets of three or four cylinders and most rebreathers. Additional cylinders for decompression can be sling mounted at the diver's sides.[citation needed]

It is also possible to use a plain backpack harness to support the set, either with a horse-collar buoyancy compensator, or without any buoyancy compensator. This was the standard arrangement before the introduction of the buoyancy compensator, and is still used by some recreational and professional divers when it suits the diving operation.[citation needed]

Surface-supplied divers are generally required to carry an emergency gas supply, also known as a bailout set, which is usually back-mounted open circuit scuba connected into the breathing gas supply system by connecting an interstage hose to the gas switching block, (or bailout block), mounted on the side of the helmet or full-face mask, or on the diver's harness where it can easily be reached, but is unlikely to be accidentally opened. Other mounting arrangements may be used for special circumstances.

Side-mount harnesses support the cylinders by clipping them to D-rings at chest and hip on either or both sides, and the cylinders hang roughly parallel to the diver's torso when underwater. The harness usually includes a buoyancy compensator bladder. It is possible for a skilled diver to carry up to 3 cylinders on each side with this system.[citation needed]

An unusual configuration which does not appear to have become popular is the integrated harness and storage container. These units comprise a bag which contains the buoyancy bladder and the cylinder, with a harness and regulator components which are stored in the bag and unfolded to the working position when the bag is unzipped. Some military rebreathers such as the Interspiro DCSC also store the breathing hoses inside the housing when not in use.[citation needed]

Technical divers may need to carry several different gas mixtures. These are intended to be used at different stages of the planned dive profile, and for safety reasons it is necessary for the diver to be able to check which gas is in use at any given depth and time, and to open and close the supply vaves when required, so the gases ate generally carried in fully self-contained independent scuba sets, which are suspended from the harness at the diver's sided. This arrangement is known as stage mounting. Stage sets may be cached along a penetration guideline to be retrieved during exit for convenience. These are also sometimes called drop tanks.

In most scuba sets, a buoyancy compensator (BC) or buoyancy control device (BCD), such as a back-mounted wing or stabilizer jacket (also known as a "stab jacket"), is built into the harness. Although strictly speaking this is not a part of the breathing apparatus, it is usually connected to the diver's air supply, to provide easy inflation of the device. This can usually also be done manually via a mouthpiece, in order to save air while on the surface, or in case of a malfunction of the pressurized inflation system. The BCD inflates with air from the low pressure inflator hose to increase the volume of the scuba equipment and cause the diver gain buoyancy. Another button opens a valve to deflate the BCD and decrease the volume of the equipment and causes the diver to lose buoyancy. Some BCDs allow for integrated weight, meaning that the BCD has special pockets for the weights that can be dumped easily in case of an emergency. The function of the BCD, while underwater, is to keep the diver neutrally buoyant, i.e., neither floating up or sinking. The BCD is used to compensate for the compression of a wet suit, and to compensate for the decrease of the diver's mass as the air from the cylinder is breathed away.[citation needed]

Diving weighting systems increase the average density of the scuba diver and equipment to compensate for the buoyancy of diving equipment, particularly the diving suit, allowing the diver to fully submerge with ease by obtaining neutral or slightly negative buoyancy. Weighting systems originally consisted of solid lead blocks attached to a belt around the diver's waist, but some diving weighting systems are incorporated into the BCD or harness. These systems may use small nylon bags of lead shot or small weights which are distributed around the BCD, allowing a diver to gain a better overall weight distribution leading to a more horizontal trim in the water. Tank weights can be attached to the cylinder or threaded on the cambands holding the cylinder into the BCD.[citation needed]

Many closed circuit rebreathers use advanced electronics to monitor and regulate the composition of the breathing gas.[citation needed]

Rebreather divers and some open-circuit scuba divers carry extra diving cylinders for bailout in case the main breathing gas supply is used up or malfunctions. If the bailout cylinder is small, they may be called "pony cylinders". They have their own demand regulators and mouthpieces, and are technically distinct extra scuba sets. In technical diving, the diver may carry different equipment for different phases of the dive. Some breathing gas mixes, such as trimix, may only be used at depth, and others, such as pure oxygen, may only be used during decompression stops in shallow water. The heaviest cylinders are generally carried on the back supported by a backplate while others are side slung from strong points on the harness.[citation needed]

When the diver carries many diving cylinders, especially those made of steel, lack of buoyancy can be a problem. High-capacity BCs may be needed to allow the diver to effectively control buoyancy.[citation needed]

An excess of tubes and connections passing through the water tend to decrease swimming performance by causing hydrodynamic drag.[citation needed]

A diffuser is a component fitted over the exhaust outlet to break up the exhaled gas into bubbles small enough not to be seen above the surface the water, and make less noise (see acoustic signature). They are used in combat diving, to avoid detection by surface observers or by underwater hydrophones, Underwater mine disposal operations conducted by clearance divers, to make less noise,[48] to reduce the risk of detonating acoustic mines, and in marine biology, to avoid disruption of fish behavior.[49]

Designing an adequate diffuser for a rebreather is much easier than for open-circuit scuba, as the gas flow rate is generally much lower.[citation needed] An open-circuit diffuser system called the "scuba muffler" was prototyped by Eddie Paul in the early 1990s for underwater photographers John McKenney and Marty Snyderman; the prototype had two large filter stones mounted on the back of the cylinder with a hose connected to the exhaust ports of the second-stage regulator. The filter stones were mounted on a hinged arm to float 1 to 2 feet (30 to 60Â cm) above the diver, to set up a depth-pressure-differential suction effect to counteract the extra exhalation pressure needed to breathe out through the diffuser. The scuba muffler was claimed to cut the exhalation noise by 90%.[50] Closed circuit rebreathers proved more useful in letting divers get near sharks.[51]

Gas endurance of a scuba set is the time that the gas supply will last during a dive. This is influenced by the type of scuba set and the circumstances in which it is used.

The gas endurance of open-circuit-demand scuba depends on factors such as the capacity (volume of gas) in the diving cylinder, the depth of the dive and the breathing rate of the diver, which is dependent on exertion, fitness, physical size of the diver, and experience among other factors. New divers frequently consume all the air in a standard "aluminum 80" cylinder in 30 minutes or less on a typical dive, while experienced divers frequently dive for 60 to 70 minutes at the same average depth, using the same capacity cylinder, as they have learned more efficient diving techniques.[citation needed]

An open-circuit diver whose breathing rate at the surface (atmospheric pressure) is 15 litres per minute will consume 3 x 15 = 45 litres of gas per minute at 20 metres. [(20 m/10 m per bar) + 1 bar atmospheric pressure] × 15 L/min = 45 L/min). If an 11-litre cylinder filled to 200 bar is to be used until there is a reserve of 17% there is (83% × 200 × 11) = 1826 litres available. At 45 L/min the dive at depth will be a maximum of 40.5 minutes (1826/45). These depths and times are typical of experienced recreational divers leisurely exploring a coral reef using standard 200 bar "aluminum 80" cylinders as may be rented from a commercial sport diving operation in most tropical island or coastal resorts.[citation needed]

A semi-closed circuit rebreather may have an endurance of about 3 to 10 times that of the equivalent open-circuit dive, and is less affected by depth; gas is recycled but fresh gas must be constantly injected to replace at least the oxygen used, and any excess gas from this must be vented. Although it uses gas more economically, the weight of the rebreathing equipment means the diver carries smaller cylinders. Still, most semi-closed systems allow at least twice the duration of open-circuit systems (around 2 hours) and are often limited by scrubber endurance.[citation needed]

An oxygen rebreather diver or a fully closed circuit rebreather diver consumes about 1 litre of oxygen corrected to atmospheric pressure per minute. Except during ascent or descent, the fully closed circuit rebreather that is operating correctly uses very little or no diluent. A diver with a 3-litre oxygen cylinder filled to 200 bar who leaves 25% in reserve will be able to do a 450-minute = 7.5 hour dive (3 litres × 200 bar × 0.75 litres per minute = 450 minutes). This endurance is independent of depth. The life of the soda lime scrubber is likely to be less than this and so will be the limiting factor of the dive.[citation needed]

In practice, dive times for rebreathers are more often influenced by other factors, such as water temperature and the need for safe ascent (see Decompression (diving)), and this is generally also true for large-capacity open-circuit sets.[citation needed]


where do lymph vessels join the circulatory system

Rhythmic contraction of the vessel walls through movements may also help draw fluid into the smallest lymphatic vessels, capillaries. If tissue fluid builds up the tissue will swell; this is called edema. As the circular path through the body's system continues, the fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); both ducts drain into the circulatory system at the right and left subclavian veins. The system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a secondary circulatory system.

Lymphatic vessel

In anatomy, lymphatic vessels (or lymph vessels or lymphatics) are thin-walled, valved structures that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscles, and adventitia that bind the lymph vessels to the surrounding tissue. Lymph vessels are devoted to the propulsion of the lymph from the lymph capillaries, which are mainly concerned with absorption of interstitial fluid from the tissues. Lymph capillaries are slightly larger than their counterpart capillaries of the vascular system. Lymph vessels that carry lymph to a lymph node are called afferent lymph vessels, and those that carry it from a lymph node are called efferent lymph vessels, from where the lymph may travel to another lymph node, may be returned to a vein, or may travel to a larger lymph duct. Lymph ducts drain the lymph into one of the subclavian veins and thus return it to general circulation.

Generally, lymph flows away from the tissues to lymph nodes and eventually to either the right lymphatic duct or the largest lymph vessel in the body, the thoracic duct. These vessels drain into the right and left subclavian veins respectively.

The general structure of lymphatics is based on that of blood vessels. There is an inner lining of single flattened epithelial cells (simple squamous epithelium) composed of a type of epithelium that is called endothelium, and the cells are called endothelial cells. This layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous; it leaks easily.[1] The next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening (contracting) or relaxing alter the diameter (caliber) of the lumen. The outermost layer is the adventitia that consists of fibrous tissue. The general structure described here is seen only in larger lymphatics; smaller lymphatics have fewer layers. The smallest vessels (lymphatic or lymph capillaries) lack both the muscular layer and the outer adventitia. As they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, and then smooth muscles.

The lymphatic conducting system broadly consists of two types of channelsâ€”the initial lymphatics, the prelymphatics or lymph capillaries that specialize in collection of the lymph from the ISF, and the larger lymph vessels that propel the lymph forward.

Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis (propulsion of the lymph due to alternate contraction and relaxation of smooth muscle), valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation.[2]

The lymphatic circulation begins with blind ending (closed at one end) highly permeable superficial lymph capillaries, formed by endothelial cells with button-like junctions between them that allow fluid to pass through them when the interstitial pressure is sufficiently high.[3] These button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF. There is another system of semilunar (semi=half; lunar=related to the Moon) valves that prevents back-flow of lymph along the lumen of the vessel.[3] Lymph capillaries have many interconnections (anastomoses) between them and form a very fine network.[4]

The lymph capillaries drain the lymph to larger contractile lymphatics, which have valves as well as smooth muscle walls. These are called the collecting lymphatics.[2] As the collecting lymph vessel accumulates lymph from more and more lymph capillaries in its course, it becomes larger and is called the afferent lymph vessel as it enters a lymph node. Here the lymph percolates through the lymph node tissue and is removed by the efferent lymph vessel. An efferent lymph vessel may directly drain into one of the (right or thoracic) lymph ducts, or may empty into another lymph node as its afferent lymph vessel.[4] Both the lymph ducts return the lymph to the blood stream by emptying into the subclavian veins

The functional unit of a lymph vessel is known as a lymphangion, which is the segment between two valves. Since it is contractile, depending upon the ratio of its length to its radius, it can act either like a contractile chamber propelling the fluid ahead, or as a resistance vessel tending to stop the lymph in its place.[5]

Lymph vessels act as reservoirs for plasma and other substances including cells that have leaked from the vascular system and transport lymph fluid back from the tissues to the circulatory system. Without functioning lymph vessels, lymph cannot be effectively drained and edema typically results.

The afferent lymph vessels enter at all parts of the periphery of the lymph node, and after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. It carries unfiltered lymph into the node. In doing this they lose all their coats except their endothelial lining, which is continuous with a layer of similar cells lining the lymph paths.

Afferent lymphatic vessels are only found in lymph nodes. This is in contrast to efferent lymphatic vessel which are also found in the thymus and spleen.

The efferent lymphatic vessel commences from the lymph sinuses of the medullary portion of the lymph nodes and leave the lymph nodes at the hilum, either to veins or greater nodes. It carries filtered lymph out of the node.

Efferent lymphatic vessels are also found in the thymus and spleen. This is in contrast to afferent lymphatic vessels, which are found only in lymph nodes.

Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.


who composed the music for the force awakens

Star Wars: The Force Awakens â€“ Original Motion Picture Soundtrack is the film score to the 2015 film of the same name composed by John Williams with Williams and William Ross conducting, and Gustavo Dudamel appearing as a "special guest conductor". The album was released by Walt Disney Records on December 18, 2015 in both digipak CD and digital formats.[1][2]

Star Wars: The Force Awakens (soundtrack)

In July 2013, Williams was confirmed to be writing the score.[3] The music from the first two trailers for the film was reworked from earlier compositions.[4][5][6] Williams began working on the score in December 2014 and by June 2015, he had been through most of the film reels, working on a daily basis.[7][8] In May 2015, Williams said he would reuse themes from the previous films, such as those for Luke, Leia and Han, in ways that "will seem very natural and right in the moments for which we've chosen to do these kinds of quotes. There aren't many of them, but there are a few that I think are important and will seem very much a part of the fabric of the piece in a positive and constructive way." He said that working with J. J. Abrams was similar to the process he went through with George Lucas in the earlier films.[9]

Recording sessions for The Force Awakens began on June 1, 2015 at the Sony Pictures Studios' Barbra Streisand Scoring Stage in Culver City, with William Ross conducting most of the music.[10][11] Williams attended the sessions and conducted the remainder of the recordings.[12][13] He called the recording process “very luxurious,” with 12 sessions scattered over a five-month period between June and November. The score was recorded by a freelance orchestra—making it the first live-action Star Wars soundtrack not to feature the London Symphony Orchestra[14]—with sessions continuing on and off over that five-month period. The 85-piece orchestra[15] recorded 175 minutes of music, although nearly an hour of that was discarded, modified, or rerecorded as Abrams re-edited the film. The theme for Snoke was recorded by a 24-voice men’s chorus. Gustavo Dudamel conducted the opening and end title music for the film at Williams' behest.[16] The last recording session took place on November 14, 2015.[6][7][17]

Leading up to the release of The Force Awakens multiple music streaming services began offering users Star Wars-themed playlists.[18] "Streaming platforms didn't exist for the [previous] movies, so that's something that we'll be rolling out, along with character-driven playlists with sounds and dialogue from the movie," said Ken Bunt, president of the Disney Music Group. "People love to hear dialogue and sound effects, so we're working on some ideas now that will incorporate some of that into playlisting."[19] Upon its release, the soundtrack for The Force Awakens became available to stream via Spotify.[20]

The musical score has received critical acclaim. James Southall of Movie Wave said, "The new themes are great, hearing the old ones again is wonderful, the action music is remarkably energetic and the musical storytelling as vibrant as ever. It’s just so good hearing Williams return to this universe."[23] Jørn Tillnes of Soundtrack Geek said, "The fact is that this score is not even close to the classic trilogy and it struggles with the prequel trilogy as well. I don’t know if it's the weakest in the saga. Time will tell. What I do know is that it's one of the best scores I've heard in a while."[26] uDiscover gave the score a positive review, saying, "The expansive, dramatic passages are as full-bodied as one would hope for a film as epic as The Force Awakens, but the attention to detail within the score – and the exquisitely recorded performance – make the results a subtle and engaging listen."[27]

Jonathan Broxton of Movie Music UK praised the score, saying, "Even when you look at it objectively, what John Williams has achieved with this score is nothing short of remarkable. He has written five new themes, two of which – 'Rey's Theme' and the 'March of the Resistance' – are wonderfully memorable, and can stand shoulder-to-shoulder with the already bulging cache of memorable themes within the Star Wars universe."[28]

It was nominated for Best Original Score category at 88th Academy Awards and lost to Ennio Morricone's score for The Hateful Eight.

The soundtrack debuted at number five on the Billboard 200 chart for the week ending November 26, 2015, with 100,000 album-equivalent units, of which 94,000 were pure album sales. It marked the highest debut for a score-only soundtrack since 1999, when The Phantom Menace placed at number 3. Additionally, it is the sixth Star Wars soundtrack in the main Star Wars film series to reach the top ten; only the Return of the Jedi soundtrack failed to reach top ten, peaking at number 20 in 1983.[29] The album has sold 206,000 copies in the US as of April 2016.[30]

All music composed by John Williams.

Credits adopted from Allmusic:[31]

Additional music featured in The Force Awakens:[32]


which industry has the highest fatality rate on an annual basis

The majority of occupational deaths occur among men. In one US study, 93% of deaths on the job involved men,[4] with a death rate approximately 11 times higher than women. The industries with the highest death rates are mining, agriculture, forestry, fishing, and construction, all of which employ more men than women.[5] Deaths of members in the military is currently above 90% men.[6]

Occupational fatality

An occupational fatality is a death that occurs while a person is at work or performing work related tasks. Occupational fatalities are also commonly called “occupational deaths” or “work-related deaths/fatalities” and can occur in any industry or occupation.

Common causes of occupational fatalities include falls, machine-related incidents, motor vehicle accidents, electrocution, falling objects, homicides and suicides. Occupational fatalities can be prevented.

In the United States in 2006, 41% of occupational fatalities occurred during a transportation incident, 17% occurred after a worker came into contact with an object or equipment, and 15% occurred as a result of a fall.[1] The remaining 12% of deaths were the result of chemical or environmental exposures (9%) and fires or explosions (3%).[1] Lastly, 15% of all occupational fatalities are the consequences of assault and other violent acts in the workplace.

Many factors contribute to a fatal incident at work. Lack of appropriate employee training and failure to provide and enforce the use of safety equipment are frequent contributors to occupational fatalities. In some cases, employees do receive safety training, but language barriers prevent the employee from fully understanding the safety procedures. Incidents can also be the result of insufficient supervision of inexperienced employees or employees who have taken on a responsibility for which they are not properly trained. Poor worksite organization, staffing and scheduling issues, unworkable policies and practices and workplace culture can all play a role in occupational fatalities. An incident leading to an occupational fatality is generally not the fault of a single person, but the result of a combination of many human and environmental factors.[citation needed]

Although all workers are at risk for occupational fatalities, elderly workers age 65 and older are roughly three times more likely to die at work.[3] Hispanic workers die on the job at a higher rate than non-Hispanic workers. Men account for 92% of occupational deaths.[1]

Occupational fatalities are preventable. Prevention of occupational fatalities depends on the understanding that worker safety is not only the responsibility of the worker, but is the primary responsibility of the employer. Employers must train all employees in the appropriate safety procedures and maintain a safe working environment so that fatalities are less likely to occur.[7] An occupational fatality is not just the fault of the deceased worker; instead, it is the combination of unsafe work environments, insufficient safety training, and negligible employee supervision that contribute fatal incidents. As a result, it is imperative that an employer address all the potential [risk] factors at the workplace and educate all employees in safe work practices and risk awareness.

In order to perform adequate risk assessment of injuries that occur in the workplace, health and safety professionals use resources such as the Haddon Matrix. This model assesses the risks leading up to, during, and after a death in order to prevent future incidents of a similar nature. Employers and employees can learn how to identify risk factors in their work environment in order to avoid incidents that may result in death.

The regulatory organization for occupational injury control and prevention is the Occupational Safety and Health Administration (OSHA). Formed in 1970 as an agency of the United States Department of Labor under the Occupational Safety and Health Act, OSHA exists to prevent occupational injuries and deaths by creating and enforcing standards in the workplace. OSHA standards address employee training programs, safety equipment, employer record keeping and proper maintenance of the work environment. Failure to comply with the OSHA standards can result in workplace inspections and legal action including citations and fines. In very severe cases of employer misconduct, OSHA can “red flag” an operation and send the employer to legal court.[8]

To regulate the millions of workplaces in the United States, OSHA requires that all employers maintain a record of occupational injuries, illnesses and fatalities. Occupational fatalities must be reported to OSHA within eight hours of the incident. Failure to do so can result in legal action against the employer. Employers are responsible for staying current on OSHA standards and enforcing them in their own workplace. State OSHA organizations exist in twenty-eight states and are required to have the same or more rigorous standards than the federal OSHA standards. In these states, employers must abide by their stateâ€™s regulations. It is not the responsibility of the employee to stay current on the OSHA standards.

In addition to OSHA, the National Institute for Occupational Safety and Health (NIOSH) was formed under the Occupational Safety and Health Act as a federal research agency to formulate industry recommendations for health and safety. NIOSH is part of the Centers for Disease Control and Prevention (CDC) in the United States Department of Health and Human Services (DHHS). NIOSH analyzes workplace injury and illness data from all fifty states as well as provides support for state-based projects in occupational health and safety.

Under NIOSH, the Fatality Assessment and Control Evaluation (FACE) Program tracks and investigates occupational fatalities in order to provide recommendations for prevention. A voluntary program for individual states created in 1989, FACE is active in California, Iowa, Kentucky, Massachusetts, Michigan, New Jersey, New York, Oregon, and Washington. The primary responsibilities of the state FACE programs are to track occupational fatalities in their state, investigate select fatalities, and provide recommendations for prevention. As part of the prevention efforts, FACE programs also produce extensive prevention education materials that are disseminated to employees, employers, unions, and state organizations.

Nationally, the Census of Fatal Occupational Injuries (CFOI), within the U.S. Department of Labor, compiles national fatality statistics. CFOI is the key, comprehensive system in the surveillance of occupational fatalities in the United States.

Many other non-governmental organizations also work to prevent occupational fatalities. Trade associations and unions play an active role in protecting workers and disseminating prevention information. The National Safety Council also works to prevent occupational fatalities as well as provide resources to employers and employees.


how did knights follow the code of chivalry

The code of chivalry that developed in medieval Europe had its roots in earlier centuries. It arose in the Holy Roman Empire from the idealisation of the cavalryman—involving military bravery, individual training, and service to others—especially in Francia, among horse soldiers in Charlemagne's cavalry.[2][3] The term chivalry derives from the Old French term chevalerie, which can be translated to "horse soldiery".[Note 1] Gautier states that knighthood emerged from the Moors (Muslims) as well as the Teutonic forests and was nurtured into civilization and chivalry by the Catholic Church.[5]

Chivalry

Chivalry, or the chivalric code, is an informal, varying code of conduct developed between 1170 and 1220, never decided on or summarized in a single document, associated with the medieval institution of knighthood. The ideals of chivalry were popularized in medieval literature, especially the Matter of Britain and Matter of France, the former based on Geoffrey of Monmouth's Historia Regum Britanniae which introduced the legend of King Arthur, written in the 1130s.[1]

Over time, its meaning in Europe has been refined to emphasise social and moral virtues more generally. The code of chivalry, as it stood by the Late Middle Ages, was a moral system which combined a warrior ethos, knightly piety, and courtly manners, all conspiring to establish a notion of honour and nobility.[Note 2]

In origin, the term chivalry means "horsemanship", formed in Old French, in the 11th century, from chevalier (horseman, knight), from Medieval Latin

The meaning of the term evolved over time because the word chevalier was used differently in the Middle Ages, from the original concrete military meaning "status or fee associated with military follower owning a war horse" or "a group of mounted knights" to the ideal of the Christian warrior ethos propagated in the Romance genre, which was becoming popular during the 12th century, and the ideal of courtly love propagated in the contemporary Minnesang and related genres. Thus, chivalry has hierarchical meanings from simply a heavily armed horseman to a code of conduct.

The ideas of chivalry originated in three medieval works: the anonymous poem Ordene de Chevalerie, that tells the story of how Hugh II of Tiberias was captured and released upon his agreement to show Saladin (1138-1193) the ritual of Christian knighthood,[10] the Libre del ordre de cavayleria, written by Ramon Lull (1232-1315), whose subject is knighthood,[11] and the Livre de Chevalerie of Geoffroi de Charny (1300-1356), which examines the qualities of knighthood, emphasizing prowess.[12] Based on the three treatises, initially chivalry was defined as a way of life in which three essential aspects fused together: the military, the nobility, the religion.[13]

The "code of chivalry" is thus a product of the Late Middle Ages, evolving after the end of the crusades partly from an idealisation of the historical knights fighting in the Holy Land, partly from ideals of courtly love.

Gautier's Ten Commandments of chivalry are:

Though these ten commandments are often accepted to be what knights would use, they would not necessarily be what a knight actually followed in the medieval era. This code was created by Leon Gautier in 1883, long after the knight had ceased to exist in its traditional form. Chivalry in a historical sense was more of a subjective term, these laws would likely be seen as good code for a clergyman, however others would hold different ideas on what chivalry truly was.

Fans of chivalry assume, and have assumed since the late medieval period, that there was a time in the past when chivalry was a living institution, when men acted chivalrically, when chivalry was alive and not dead, the imitation of which period would much improve the present. This is the mad mission of Don Quixote, protagonist of the most chivalric novel of all time and inspirer of the chivalry of Sir Walter Scott and of the U.S. South:[15] to restore the age of chivalry, and thereby improve his country.[16] It is a version of the myth of the Golden Age.

With the birth of modern historical and literary research, scholars have found that however far back in time "The Age of Chivalry" is searched for, it is always further in the past, even back to the Roman Empire.[citation needed] From Jean Charles Léonard de Sismondi:

We must not confound chivalry with the feudal system. The feudal system may be called the real life of the period of which we are treating, possessing its advantages and inconveniences, its virtues and its vices. Chivalry, on the contrary, is the ideal world, such as it existed in the imaginations of the Romance writers. Its essential character is devotion to woman and to honour.[17]

Sismondi alludes to the fictitious Arthurian romances about the imaginary Court of King Arthur, which were usually taken as factual presentations of a historical age of chivalry. He continues:

The more closely we look into history, the more clearly shall we perceive that the system of chivalry is an invention almost entirely poetical. It is impossible to distinguish the countries in which it is said to have prevailed. It is always represented as distant from us both in time and place, and whilst the contemporary historians give us a clear, detailed, and complete account of the vices of the court and the great, of the ferocity or corruption of the nobles, and of the servility of the people, we are astonished to find the poets, after a long lapse of time, adorning the very same ages with the most splendid fictions of grace, virtue, and loyalty. The Romance writers of the twelfth century placed the age of chivalry in the time of Charlemagne. The period when these writers existed, is the time pointed out by Francis I. At the present day [about 1810], we imagine we can still see chivalry flourishing in the persons of Du Guesclin and Bayard, under Charles V and Francis I. But when we come to examine either the one period or the other, although we find in each some heroic spirits, we are forced to confess that it is necessary to antedate the age of chivalry, at least three or four centuries before any period of authentic history.[18]

According to Crouch, many early writers on medieval chivalry cannot be trusted as historians, because they sometimes have "polemical purpose which colours their prose".[19] As for Kenelm Henry Digby and Leon Gautier, chivalry was a means to transform their corrupt and secular worlds.[20] Gautier also emphasized that chivalry originated from the Teutonic forests and brought up into civilization by the Catholic Church.[5] Charles Mills used chivalry "to demonstrate that the Regency gentleman was the ethical heir of a great moral estate, and to provide an inventory of its treasure".[20] Mills also stated that chivalry was a social, not a military phenomenon, with its key features: generosity, fidelity, liberality, and courtesy.[21]

According to Crouch, prior to codified chivalry there was the uncodified code of noble conduct that focused on the preudomme. This uncodified code - referred to as the noble habitus - is a term for the environment of behavioural and material expectations generated by all societies and classes.[22] As a modern idea, it was pioneered by the French philosopher/sociologists Pierre Bourdieu and Maurice Merleau-Ponty, even though a precedent exists for the concept as far back as the works of Aristotle.[23] Crouch argues that the habitus on which "the superstructure of chivalry" was built and the preudomme was a part, had existed long before 1100, while the codified medieval noble conduct only began between 1170 and 1220.[24]

The pre-chivalric noble habitus as discovered by Mills and Gautier are as follows:

The code of chivalry, as it was known at late Medieval age, developed between 1170 and 1220.[33]

Chivalry was developed in the north of France around the mid-12th century but adopted its structure in a European context. New social status, new military techniques, and new literary topics were adhered to a new character known as the knight and his ethos called chivalry.[34] The chivalric ideals are based on those of the early medieval warrior class, and martial exercise and military virtue remains an integral part of chivalry until the end of the medieval period,[35] as the reality on the battlefield changed with the development of Early Modern warfare increasingly restricted to the tournament ground and duelling culture. The joust remained the primary example of knightly display of martial skill throughout the Renaissance (the last Elizabethan Accession Day tilt was held in 1602).

The martial skills of the knight carried over to the practice of the hunt, and hunting expertise became an important aspect of courtly life in the later medieval period (see terms of venery). Related to chivalry was the practice of heraldry and its elaborate rules of displaying coats of arms as it emerged in the High Middle Ages.

Christianity and church had a modifying influence on the classical concept of heroism and virtue, nowadays identified with the virtues of chivalry.[36][37] The Peace and Truce of God in the 10th century was one such example, with limits placed on knights to protect and honour the weaker members of society and also help the church maintain peace. At the same time the church became more tolerant of war in the defense of faith, espousing theories of the just war; and liturgies were introduced which blessed a knight's sword, and a bath of chivalric purification. In the story of the Grail romances and Chevalier au Cygne, it was the confidence of the Christian knighthood that its way of life was to please God, and chivalry was an order of God.[38] Thus, chivalry as a Christian vocation was a result of marriage between Teutonic heroic values with the militant tradition of Old Testament.[26]

The first noted support for chivalric vocation, or the establishment of knightly class to ensure the sanctity and legitimacy of Christianity, was written in 930 by Odo, abbot of Cluny, in the Vita of St. Gerald of Aurillac, which argued that the sanctity of Christ and Christian doctrine can be demonstrated through the legitimate unsheathing of the "sword against the enemy".[39] In the 11th century the concept of a "knight of Christ" (miles Christi) gained currency in France, Spain and Italy.[35] These concepts of "religious chivalry" were further elaborated in the era of the Crusades, with the Crusades themselves often being seen as a chivalrous enterprise.[35] Their ideas of chivalry were also further influenced by Saladin, who was viewed as a chivalrous knight by medieval Christian writers. The military orders of the crusades which developed in this period came to be seen as the earliest flowering of chivalry,[40] although it remains unclear to what extent the notable knights of this period—such as Saladin, Godfrey of Bouillon, William Marshal or Bertrand du Guesclin—actually did set new standards of knightly behaviour, or to what extent they merely behaved according to existing models of conduct which came in retrospect to be interpreted along the lines of the "chivalry" ideal of the Late Middle Ages.[35] Nevertheless, chivalry and crusades were not the same thing. While the crusading ideology had largely influenced the ethic of chivalry during its formative times, chivalry itself was related to a whole range of martial activities and aristocratic values which had no necessary linkage with crusading.[41]

From the 12th century onward chivalry came to be understood as a moral, religious and social code of knightly conduct. The particulars of the code varied, but codes would emphasise the virtues of courage, honour, and service. Chivalry also came to refer to an idealisation of the life and manners of the knight at home in his castle and with his court.

Medieval Europe, particularly Spanish poets, were greatly influenced by Arabic literature. The literature of chivalry, bravery, figurative expression, and imagery made its way to Western literature through Arabic literature in Andalusia in particular. The famous Spanish author Vicente Blasco says: “Europe did not know chivalry, or its adopted literature or sense of honour before the arrival of Arabs in Andalusia and the wide presence of their knights and heroes in the countries of the south."

The Andalusian Ibn Hazm and his famous book “Tawq al-Hamamah” (the ring-neck dove) had a great impact on poets in Spain and southern France after the Islamic community blended with the Christian community. The Arabic language was the language of the country and the language of the high-class people. In many Christian Spanish provinces, Christian and Muslim poets used to meet at the court of the governor. One such an example is what used to take place at the court of Sanko which comprised 13 Arab poets, 12 Christian poets, and a Jewish poet. A manuscript dating back to the era of Alfonso X, the king of Castile, was found and it contained a portrait that represented the meeting of two moving poets, one Arab and one European, singing together on lute. Even more, the European poets at the time were good at composing Arabic poetry. For this reason, Henry Maro says: “The Arab impact on the civilization of the Roman peoples did not stop at fine arts only, but extended to music and poetry as well."

The influence of Arabic literature on European writers is proven by what Reinhart Dozy quoted on his book "Spanish Islam: History of Moslems in Spain", of the Spanish writer AlGharo, who deeply regretted the neglect of Latin and Greek and the acceptance of the language of the Muslims, he said "The intelligent and eloquent people are bewitched by the sound of Arabic and they look down on Latin. They have started to write in the language of those who defeated them"

A contemporary of his, who was more influenced by nationalistic feelings, expressed his bitterness when he said, “My Christian brothers admire the poetry and chivalry stories of the Arabs, and they study the books written by the philosophies and scholars of the Muslims. They do not do that in order to refute them, but rather to learn the eloquent Arabic style. Where today – apart from the clergy – and those who read the religious commentaries on the Old and New Testaments? Where are those who read the Gospels and the words of the Prophets? Alas, the new generation of intelligent Christians do not know any literature and language well apart from Arabic literature and the Arabic language. They avidly read the books of the Arabs and amass huge libraries of these books at great expense; they look upon these Arabic treasures with great pride, at the time when they refrain from reading Christian books on the basis that they are not worth paying attention to. How unfortunate it is that the Christians have forgotten their language, and nowadays you cannot find among them one in a thousand who could write a letter to a friend in his own language. But with regard to the language of the Arabs, how many there are who express themselves fluently in it with the most eloquent style, and they write poetry of the Arabs themselves in its eloquence and correct usage.”

Medieval courtly literature glorifies the valour, tactics and ideals of both Moors and ancient Romans.[35] For example, the ancient hand-book of warfare written by Vegetius called De Re Militari was translated into French in the 13th century as L'art de chevalerie by Jean de Meun. Later writers also drew from Vegetius such as Honore Bonet who wrote the 14th century L'arbes des batailles, which discussed the morals and laws of war. In the 15th century Christine de Pizan combined themes from Vegetius, Bonet and Frontinus in Livre des faits d'armes et de chevalerie.

In the later Middle Ages, wealthy merchants strove to adopt chivalric attitudes - the sons of the bourgeoisie were educated at aristocratic courts where they were trained in the manners of the knightly class.[35] This was a democratisation of chivalry, leading to a new genre called the courtesy book, which were guides to the behaviour of "gentlemen". Thus, the post-medieval gentlemanly code of the value of a man's honor, respect for women, and a concern for those less fortunate, is directly derived from earlier ideals of chivalry and historical forces which created it.[35]

The medieval development of chivalry, with the concept of the honour of a lady and the ensuing knightly devotion to it, not only derived from the thinking about the Virgin Mary, but also contributed to it.[42] The medieval veneration of the Virgin Mary was contrasted by the fact that ordinary women, especially those outside aristocratic circles, were looked down upon.[citation needed] Although women were at times viewed as the source of evil, it was Mary who as mediator to God was a source of refuge for man. The development of medieval Mariology and the changing attitudes towards women paralleled each other and can best be understood in a common context.[43]

When examining medieval literature, chivalry can be classified into three basic but overlapping areas:

These three areas obviously overlap quite frequently in chivalry, and are often indistinguishable.[citation needed]

Different weight given to different areas produced different strands of chivalry:

Chivalry underwent a revival and elaboration of chivalric ceremonial and rules of etiquette in the 14th century that was examined by Johan Huizinga, in The Waning of the Middle Ages, in which he dedicates a full chapter to "The idea of chivalry". In contrasting the literary standards of chivalry with the actual warfare of the age, the historian finds the imitation of an ideal past illusory; in an aristocratic culture such as Burgundy and France at the close of the Middle Ages, "to be representative of true culture means to produce by conduct, by customs, by manners, by costume, by deportment, the illusion of a heroic being, full of dignity and honour, of wisdom, and, at all events, of courtesy....The dream of past perfection ennobles life and its forms, fills them with beauty and fashions them anew as forms of art".[44]

Chivalry was dynamic and it transformed and adjusted in response to local situation and this is what probably led to its demise. There were many chivalric groups in England as imagined by Sir Thomas Malory when he wrote Le Morte Darthur in the late 15th century,[45] perhaps each group created each chivalric ideology. And Malory's perspective reflects the condition of 15th-century chivalry.[46] When Le Morte Darthur was printed, William Caxton urged knights to read the romance with an expectation that reading about chivalry could unite a community of knights already divided by the Wars of the Roses.[47]

During the early Tudor rule in England, some knights still fought for honor and for the good, to protect women and the poor while some others ignored the ethos. There were fewer knights engaged in active warfare because battlefields during this century were generally the area of professional infantrymen, with less opportunity for knights to show chivalry.[48] It was the beginning of the demise of the knight. The rank of knight never faded, but it was Queen Elizabeth I who ended the tradition that any knight could create another and made it exclusively the preserve of the monarch.[49] Christopher Wilkins contends that Sir Edward Woodville, who rode from battle to battle across Europe and died in 1488 in Brittany, was the last knight errant who witnessed the fall of the Age of Chivalry and the rise of modern European warfare. When the Middle Ages were over, the code of chivalry was gone.[50]

Chivalry! – why, maiden, she is the nurse of pure and high affection – the stay of the oppressed, the redresser of grievances, the curb of the power of the tyrant – Nobility were but an empty name without her, and liberty finds the best protection in her lance and her sword. —Walter Scott, Ivanhoe (1820)

This Order is an institution of Chivalry, Humanity, Justice, and Patriotism; embodying in its genius and principles all that is chivalric in conduct, noble in sentiment, generous in manhood, and patriotic in purpose.

Bombers of abortion clinics in the United States "called themselves knights, their emblem was a mask they had printed on T-shirts bearing the motto 'Protectors of the Code', and their mission was to defend the ideals of chivalry".[52]

The chivalric ideal persisted into the early modern and modern period. The custom of foundation of chivalric orders by Europe's monarchs and high nobility peaked in the late medieval period, but it persisted during the Renaissance and well into the Baroque and early modern period, with e.g. the Tuscan Order of Saint Stephen (1561), the French Order of Saint Louis (1693) or the Anglo-Irish Order of St. Patrick (1783), and numerous dynastic orders of knighthood remain active in countries that retain a tradition of monarchy.

At the same time, with the change of courtly ideas during the Baroque period, the ideals of chivalry began to be seen as dated, or "medieval". Don Quixote, published in 1605-15, burlesqued the medieval chivalric novel or romance by ridiculing the stubborn adherence to the chivalric code in the face of the then-modern world as anachronistic, giving rise to the term Quixotism. Conversely, Romanticism refers to the attempt to revive such "medieval" ideals or aesthetics in the late 18th and early 19th century.

The behavioural code of military officers down to the Napoleonic era, the American Civil War (especially as idealised in the "Lost Cause" movement) and to some extent even to World War I was still strongly modelled on the historical ideals, resulting in a pronounced duelling culture, which in some parts of Europe also held sway over the civilian life of the upper classes. With the decline of the Ottoman Empire, however, the military threat from the "infidel" disappeared; the Wars of Religion in Europe spanned much of the early modern period and consisted of infighting between factions of various Christian denominations, this process of confessionalization ultimately giving rise to a new military ethos based in nationalism rather than "defending the faith against the infidel".

From the Early Modern period, the term gallantry (from galant, the Baroque ideal of refined elegance) rather than chivalry became used for the proper behaviour of upper class men towards upper class women. In the 19th century, there were attempts to revive chivalry for the purposes of the gentleman of that time. Kenelm Henry Digby wrote his The Broad-Stone of Honour for this purpose, offering the definition: 'Chivalry is only a name for that general spirit or state of mind which disposes men to heroic actions, and keeps them conversant with all that is beautiful and sublime in the intellectual and moral world'.

The pronouncedly masculine virtues of chivalry came under attack on the parts of the upper-class suffragettes campaigning for gender equality in the early 20th century,[Note 4] and with the decline of the military ideals of duelling culture and of European aristocracies in general following the catastrophe of World War I, the ideals of chivalry became widely seen as outmoded by the mid-20th century. As a material reflection of this process, the dress sword lost its position as an indispensable part of a gentleman's wardrobe, a development described as an "archaeological terminus" by Ewart Oakeshott, as it concluded the long period during which the sword had been a visible attribute of the free man, beginning as early as three millennia ago with the Bronze Age sword.[54]

During the 20th century, the chivalrous ideal of protecting women came to be seen as a trope of melodrama ("damsel in distress"). The term chivalry retains a certain currency in sociology, in reference to the general tendency of men, and of society in general, to lend more attention offering protection from harm to women than to men, or in noting gender gaps in life expectancy, health, etc., also expressed in media bias giving significantly more attention to female than to male victims (see also missing white woman syndrome).[Note 5]

Formed in 1907, the world's first Scout camp, the Brownsea Island Scout camp, began as a boys' camping event on Brownsea Island in Poole Harbour, southern England, organised by British Army Lieutenant-General Robert Baden-Powell to test his ideas for the book Scouting for Boys. Boy scouts from different social backgrounds in the UK participated from 1 to 8 August 1907 in activities around camping, observation, woodcraft, chivalry, lifesaving and patriotism.[56]

According to William Manchester, General Douglas MacArthur was a chivalric warrior who fought a war with the intention to conquer the enemy, completely eliminating their ability to strike back, then treated them with the understanding and kindness due their honor and courage. One prominent model of his chivalrous conduct was in World War II and his treatment of the Japanese at the end of the war. MacArthur's model provides a way to win a war with as few casualties as possible and how to get the respect of the former enemy after the occupation of their homeland.[57] On May 12, 1962, MacArthur gave a famous speech in front of the cadets of United States Military Academy at West Point by referring to a great moral code, the code of conduct and chivalry, when emphasizing duty, honor, and country.[58]

Miguel de Cervantes, in Part I of Don Quixote (1605), attacks chivalric literature as historically inaccurate and therefore harmful (see history of the novel), though he was quite in agreement with many so-called chivalric principles and guides to behavior. He toyed with but was never able to write a chivalric romance that was historically truthful.[59]

The Italian humanist Petrarch is reported to have had no use for chivalry.[60]


who played charlie in the darling buds of may

Franks is best known for his role as the tax inspector Cedric "Charley" Charlton in the British sitcom The Darling Buds of May, and also as Sgt. Raymond Craddock on Heartbeat.[3] He has also been a guest star in Absolutely Fabulous, Pie in the Sky, Midsomer Murders, Foyle's War, Bleak House, Martin Chuzzlewit, The Buddha of Suburbia, The Green Man and To Serve Them All My Days.[4] For the role of his character in Martin Chuzzlewit (Tom Pinch), Franks shaved off all of the hair on his head leaving wispy strands at the sides. When he was recognized in the street by fans they asked if he had done it for religious reasons.[5]

Philip Franks

Philip Franks (born 2 February 1956) is an English actor and theatre director, known to the public chiefly for his roles in British television series, such as The Darling Buds of May and Heartbeat.

Franks was born in London and is the only child of Patricia and Robert Franks. His father was a squadron leader pilot in the Royal Air Force.[1] Franks maintains that he first fell in love with theatre at age six, when his parents took him along to see a production of The Tempest. The following year, his parents were going to a production of Hamlet, and Franks insisted on going with them; at age seven, he was hooked for life.[2]

He also makes regular appearances alongside Susie Dent in the 'Dictionary Corner' on the British quiz show Countdown (having applied to be a contestant on the show before becoming better known). From December 2012 Franks will play The Narrator in the 40th anniversary UK touring production of Richard O'Brien's Rocky Horror Show.[6]

Franks is also a member of the Royal Shakespeare Company. In addition, he has directed many plays including "Kafka's Dick" and "The Kiss of the Spiderwoman" (Nottingham Playhouse); "The Cocktail Party" (Edinburgh Festival); "Rebecca" (Royal Lyceum, Edinburgh); "Hamlet" (Greenwich and tour); "Macbeth" (Sheffield Crucible) and "The Duchess of Malfi" (West Yorkshire Playhouse, Greenwich and West End); "Private Lives" and "The Heiress" (Royal National Theatre); "The White Devil" (Lyric Theatre, Hammersmith); "Nicholas Nickleby" (Chichester Festival Theatre); and "The Tempest" (Liverpool Playhouse).[4]