Long Island is an eighty-mile (nearly 130km) long island in the Bahamas that is split by the Tropic of Cancer. The island is only about four miles (6km) wide, but a road spans most of the length. Long Island is about 165 miles or 265 kilometres southeast of Nassau. Some of the main settlements are Clarence Town, Deadman's Cay, Simms, Salt Pond(Home of The Annual Long Island Regatta), Stella Maris and Scrub Hill. Long Island is one of the Districts of the Bahamas and is known as the most scenic island in the Bahamas.

The island originally was called by the Arawak name "Yuma". It was rechristened "Fernandina" by Christopher Columbus on his first voyage in 1492. Archaeological evidence shows that the Lucayan Taíno tribe settled on Long Island, as they did throughout the Bahamian chain of islands. After the demise of the Lucayans, who were carried as slaves to Hispaniola and Cuba, there was no large settlement until the arrival of the Loyalists.
The Loyalists were people mainly from New England and New Jersey who fled the American Revolution. Numerous Loyalist families settled on Long Island, some setting up cotton plantations and other raising cattle and sheep. The plantations flourished for only a few years and, by the time of the abolition of slavery in 1834, most of them had collapsed and been abandoned. There are many ruins from this era today, the majority of which are overgrown by bush. There are also remains of some of the houses built after slavery, which are usually small and built of stone. Originally they had thatched roofs; today, most are shingled. The descendants of these families continue to be widespread on the island. The population of Long Island is roughly 4,000 inhabitants.

Part of the economy is based on tourism and farming, but fishing dominates the economy. The inhabitants grow peas, corn, bananas, and pineapples, and they raise small livestock such as pigs, chickens, goats, and sheep. Some cattle are raised for export. Tourists enjoy sailing, fishing, scuba diving, snorkeling and relaxing on fine beaches and exploring its distinctive landscapes, which consist of rugged hills and crashing waves along the Atlantic east coast, with more tranquil waters on the west coast.

Cape Santa Maria Beach is listed in the top most beautiful beaches in the world and Dean's Blue Hole is the world's deepest Blue Hole dropping to a depth of about 660 feet.

Scuba diving
Scuba diving is swimming underwater, or taking part in another activity, while using a scuba set.By carrying a source of breathing gas (usually compressed air),the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in snorkeling and free-diving, and is not hindered by air lines to a remote air source. The scuba diver typically swims underwater by using fins attached to the feet. However, some divers also move around with the assistance of a DPV (diver propulsion vehicle), commonly called a "scooter", or by using surface-tethered devices called sleds pulled by a boat.

For the history of diving, see timeline of underwater technology.

Etymology
The term SCUBA arose during World War II and originally referred to United States combat frogmen's oxygen rebreathers, developed by Dr. Christian Lambertsen for underwater warfare.Today, scuba typically refers to the in-line open-circuit equipment, developed by Emile Gagnan and Jacques-Yves Cousteau, in which compressed gas (usually air) is inhaled from a tank and then exhaled into the water. However, rebreathers (both semi-closed circuit and closed circuit) are also self-contained systems (as opposed to surface-supplied systems) and are therefore classified as scuba.

Although SCUBA is an acronym for "self-contained underwater breathing apparatus", usage is mainly as a normal word "scuba", it has become acceptable to refer to scuba as "scuba equipment" or "scuba apparatus" — an example of the linguistic RAS syndrome.

Types of diving
Scuba diving is still evolving, but general classifications have grown to describe various diving activities. These classifications include:

Commercial diving
Military diving
Naval diving
Police diving
Professional diving
Recreational diving
Rescue and recovery diving
Scientific diving
Technical diving
Cave diving
Cavern diving
Deep diving
Ice diving
Wreck diving

Physiological issues

Breathing underwater
Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices.

Early diving experimenters quickly discovered it is not enough simply to supply air in order to breathe comfortably underwater. As one descends, in addition to the normal atmospheric pressure, water exerts increasing pressure on the chest and lungs — approximately 1 bar or 14.7 psi for every 33 feet or 10 meters of depth — so the pressure of the inhaled breath must almost exactly counter the surrounding or ambient pressure in order to inflate the lungs.

By always providing the breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and virtually effortlessly, regardless of depth.

Because the diver's nose and eyes are covered by a diving mask; the diver cannot breathe in through the nose, except when wearing a full face diving mask. However, inhaling from a regulator's mouthpiece becomes second nature very quickly.

Open-circuit
The most commonly used scuba set today is the "single-hose" open circuit 2-stage diving regulator, coupled to a single pressurized gas cylinder, with the first stage on the cylinder and the second stage at the mouthpiece.This arrangement differs from Emile Gagnan's and Jacques Cousteau's original 1942 "twin-hose" design, known as the Aqua-lung, in which the cylinder's pressure was reduced to ambient pressure in one or two or three stages which were all on the cylinder. The "single-hose" system has significant advantages over the original system.

In the "single-hose" two-stage design, the first stage regulator reduces the cylinder pressure of about 200 bar (3000 psi) to an intermediate level of about 10 bar (145 psi) The second stage demand valve regulator, connected via a low pressure hose to the first stage, delivers the breathing gas at the correct ambient pressure to the diver's mouth and lungs. The diver's exhaled gases are exhausted directly to the environment as waste. The first stage typically has at least one outlet delivering breathing gas at unreduced tank pressure. This is connected to the diver's pressure gauge or computer, in order to show how much breathing gas remains.

Rebreather
Main article: Rebreathers
Less common, but becoming increasingly available, are closed and semi-closed rebreathers.Open-circuit sets vent off all exhaled gases, but rebreathers reprocess each exhaled breath for re-use by removing the carbon dioxide buildup and replacing the oxygen used by the diver. Rebreathers release few or no gas bubbles into the water, and use much less oxygen per hour because exhaled oxygen is recovered; this has advantages for research, military, photography, and other applications. Modern rebreathers are more complex and more expensive than sport open-circuit scuba, and need special training and maintenance to safely use.

Gas mixtures
For some diving, gas mixtures other than normal atmospheric air (21% oxygen, 78% nitrogen, 1% other) can be used, so long as the diver is properly trained in their use. The most commonly used mixture is Enriched Air Nitrox, which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the likelihood of decompression sickness.

Several other common gas mixtures are in use, and all need specialized training. Oxygen with helium and a reduced percentage of nitrogen is known as trimix, for example.

In cases of technical dives more than one cylinder may be carried, containing a different gas mixture for a distinct phase of the dive, typically designated as Travel, Bottom, and Decompression. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times.


Injuries due to changes in air pressure
For a full list, see Diving hazards and precautions
Divers must avoid injuries caused by changes in air pressure. The weight of the water column above the diver causes an increase in air pressure in any compressible material (wetsuit, lungs, sinus) in proportion to depth, in the same way that atmospheric air causes a pressure of 14.7 pounds-force per square inch (101.3 kPa) at sea level. Pressure injuries are called barotrauma and can be quite painful, in severe cases causing a ruptured eardrum or damage to the sinuses. To avoid them, the diver equalizes the pressure in all air spaces with the surrounding water pressure when changing depth. The middle ear and sinus are equalized using one or more of several techniques, which is referred to as clearing the ears.

The mask is equalized by periodically exhaling through the nose.

If a drysuit is worn, it too must be equalized by inflation and deflation, similar to a buoyancy compensator.


Effects of breathing high pressure gas

Decompression sickness
The diver must avoid the formation of gas bubbles in the body, called decompression sickness or 'the bends', by releasing the water pressure on the body slowly at the end of the dive and allowing gases trapped in the bloodstream to gradually break solution and leave the body, called "off-gassing." This is done by making safety stops or decompression stops and ascending slowly using dive computers or decompression tables for guidance. Decompression sickness must be treated promptly, typically in a recompression chamber. Administering enriched-oxygen breathing gas or pure oxygen to a decompression sickness stricken diver on the surface is a good form of first aid for decompression sickness, although fatality or permanent disability may still occur.


Nitrogen narcosis
Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in divers who breathe high pressure gas at depth.The mechanism is similar to that of nitrous oxide, or "laughing gas," administered as anesthesia. Being "narced" can impair judgment and make diving very dangerous. Narcosis starts to affect the diver at 66 feet (20 m), or 3 atmospheres of pressure. At 66 feet (20 m), Narcosis manifests itself as slight giddiness. The effects increase drastically with the increase in depth. Jacques Cousteau famously described it as the "rapture of the deep". Nitrogen narcosis occurs quickly and the symptoms typically disappear during the ascent, so that divers often fail to realize they were ever affected. It affects individual divers at varying depths and conditions, and can even vary from dive to dive under identical conditions. However, diving with trimix or heliox prevents narcosis from occurring.


Oxygen toxicity
Oxygen toxicity occurs when oxygen in the body exceeds a safe "partial pressure" (PPO2).[2] In extreme cases it affects the central nervous system and causes a seizure, which can result in the diver spitting out his regulator and drowning. Oxygen toxicity is preventable provided one never exceeds the established maximum depth of a given breathing gas. For deep dives, (generally past 130 feet / 39 meters) "hypoxic blends" containing a lower percentage of oxygen than atmospheric air are used. For more information, see Oxygen toxicity.

Refraction and underwater vision
Water has a higher refractive index than air; it's similar to that of the cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye's crystalline lens to focus light. This leads to very severe hypermetropia. People with severe myopia, therefore, can see better underwater without a mask than normal-sighted people.

Diving masks and diving helmets and fullface masks solve this problem by creating an air space in front of the diver's eyes.The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34% bigger and 25% closer in salt water than they actually are. Therefore total field-of-view is significantly reduced and eye-hand coordination must be adjusted.

(This affects underwater photography: a camera seeing through a flat window in its casing is affected the same as its user's eye seeing through a flat mask window, and so its user must focus for the apparent distance to target, not for the real distance.)

Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic and custom corrective lenses are available for some two-window masks. Custom lenses can be bonded onto masks that have a single front window.

A "double-dome mask" has curved windows in an attempt to cure these faults, but this causes a refraction problem of its own.

On rare occasions, commando frogmen use special contact lenses instead, to see underwater without the large glass surface of a diving mask, which can reflect light and give away the frogman's position.

As a diver changes depth, he must periodically exhale through his nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles which only cover the eyes do not allow for equalization and thus are not suitable for diving.

Controlling buoyancy underwater
To dive safely, divers need to be able to control their rate of descent and ascent in the water.Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as the diving weighting systems, diving suits ( Wet, Dry & Semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy.When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth.

The downward force on the diver is the weight of the diver and his equipment minus the weight of the same volume of the liquid that he is immersed in; if the result is negative, that force is upwards. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, shrink as the diver descends, and expand as the diver ascends, creating unwanted buoyancy changes. The diver can inject air into some diving suits to counteract this effect and squeeze. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.