Problem in Using Common Diving equipment
A mask is needed to give the diver adequate vision under water. The mask usually covers the eyes and nose, and it seals by pressing on the cheeks and forehead with a soft rubber edge to prevent entry of water. The nose must be enclosed in the mask so that the diver can exhale into it to allow equalization of the pressure between the mask and the water environment. It should be possible to block the nostrils without disturbing the mask seal, to allow the wearer to perform a Valsalva manoeuvre. Full facemasks that cover the mouth as well as the eyes and nose, or helmets that cover the entire head, are more commonly used by professional divers and Commercial Divers.
However, the first time when people fit in the mask, visual field limitation and difficulty in breathing with month in and out with the nostril being covered will be a great surprise. All masks cause a restriction in vision to about one-third of his normal visual field. The restriction is most marked when the diver tries to look down towards his feet and can be a danger if the diver becomes entangled. The more nervous beginner finds the visual restriction worrying often fearing that there is a predator lurking just outside his vision. The visual field varies with the style of mask and the diver need to master a technique of expulsion of water from the mask. If it is not learned, a leaking mask can become a major problem. Adjustment failure will lead to choking, aspiration and the worse one ：panic；, lost of self-control.
As the facemask have one fifth to quarter contact area over our facial area, the possibility of contact allergic eczema will happen even newer material used in the manufacturing of the mask.
A snorkel is used to provide method of maintaining a free airway for diving. The typical snorkel is a tube; about 40cm long and 2cm in diameter to reduce anatomical dead space of breathing, with a U bend near the mouthpiece. A mouthpiece is fitted to allow the diver to grip the tube with his teeth and lips. The tube is positioned to lead past the ear so that the diver can breathe through the tube while he floats on the surface looking down. Any water in the snorkel can be expelled from the snorkel before inhaling. All snorkels impose a restriction on breathing some snorkels can restrict the maximum breathing capacity to about 70% of normal. These problems all add to the difficulties of a diver who may be struggling to cope with waves breaking over him (and into his snorkel) and a current that may force him to swim hard. Attention has been given to temporomandibular joint pain associated with long periods of snorkel and regulator mouthpiece use.
Fins, or flippers, are mechanical extensions of the feet. Fins allow the diver to swim faster and more efficiently, and free his arms for other tasks. The fins are normally secured to the feet by straps or moulded shoes. Various attempts have been made to develop fins that give greater thrust with special shapes, valves, and controlled flex and miracle rubber. Divers often get cramps, either in the foot or in calf, with fins that are the wrong size, or if they are out of training. The loss of a fin may also cause problems for a diver if he has to swim against a current.
Self-contained underwater breathing apparatus (scuba) is the basic life-support system for the recreational divers. Open-circuit scuba enables the diver to remove high-pressure gas from a cylinder through a regulator, which reduces the breathable gas to ambient pressure and moves it into the lungs on inhalation and into the water upon exhalation. The exhaled gas forms into bubbles and creates noise. Closed-circuit breathing apparatus also reduces the high-pressure gas, usually oxygen, to ambient pressure in a counterlung or bag. The gas is inhaled from the counterlung and exhaled back into the counterlung, passing through a carbon dioxide and water vapour filter on the way. The volume in the counterlung is maintained by the addition of high-pressure oxygen to replace the oxygen, which has been metabolized. The SCUBA equipment includes gas cylinder, regulator and breathing apparatus.
The compressed gas cylinders or ：tanks； used in diving is available in a variety of sizes generally ranging from 50cu.ft (1.4m3) to 100cu.ft (2.8m3). Pressures commonly range from 2250 psi (15.5 MPa) to 3500 psi (24.1 MPa), although there is a trend towards higher pressures. Tank buoyancy not only increases as the gas is depleted, but also varies initially from 2-3kg positive to 3-5 kg negative. This rather wide disparity in tank sizes and pressures will result in the possibility poor buoyancy control. Uncontrolled rapid descent resulted in barotrauma while, uncontrolled rapid ascent liable to decompression sickness.
Regulators are used to reduce high-pressure air to the ambient level, where a slight negative pressure on a demand valve will provide the diver a full breath with minimal resistance. Regulators have evolved to the point where the breathing characteristics of a well-maintained regulator will rarely require more than 1.5 in (3.8 cm) of differential pressure to activate the flow of air into the lungs. Exhalation pressure is usually about 1 in (2.5 cm) of water in most modern exhaust valves. These differential pressures are increased as the diver goes deeper and the density of the gas increases and more water pressure is placed against the diver's chest. It is important to recognize that the flow demands placed on the regulator by the diver・s breathing pattern will play an important role in establishing the amount of resistance the diver will encounter.
Thermal protection is needed in cold water or on prolonged dives to minimize the risk of hypothermia. The protection is normally provided by insulated clothing which reduces heat loss. The most common protection is a wet suit, made from air-foamed neoprene rubber. The water which leaks into spaces between the suit and the diver soon warms to skin temperature. Foamed neoprene has similar insulation properties to wool felt. Its effectiveness is reduced by loss of heat with water movement, and increasing depth. Pressure decreases insulation by reducing the size of the air sacs in the foam; at 30 metres, the insulation of a wet suit is about a third of that on the surface. The compression of the gas in the foam also means that the diver's buoyancy decreases as he goes deeper. He can compensate for this if he is wearing a buoyancy vest. If he is not, he needs to consider reducing his weights, but this will mean he is too buoyant when he is closer to the surface. The buoyancy and insulation of a wet suit decrease with repeated use. The other common form of thermal protection is the dry suit. This is watertight and has seals round the head and hand openings: openings with waterproof seals to allow the diver to get into the suit. The dry suit allows the diver to wear an insulating layer of warm clothes. A gas supply and exhaust valve are needed to allow the diver to compensate for the effect of pressure changes on the gas in the suit. The gas can come from the scuba cylinder or a separate supply. The diver needs training in the operation of a dry suit or he may lose control of his buoyancy. This can lead to an uncontrolled ascent when the excess of gas expands, speeding the ascent. If the diver tries to swim down, the excess gas may accumulate round his legs. Then it cannot be vented off through the exhaust valve; the excess gas can also expand the feet of the suit and cause the diver's fins to pop off, so he can find himself floating on the surface with the suit grossly overinflated.
Besides, heat can also be supplied to a diver to help him keep warm namely external heat supply used more often in commercial divers. The most commonly used systems include hot water pumped down system or ．hot water suit・ to the diver in hoses; various chemical and electrical heaters are available.
Buoyancy Compensators or Buoyancy Aid
This consists of an air-filled bag attached to the SCUBA, or an inflatable jacket, called an ABLJ (adjustable buoyancy life jacket) or BCD (buoyancy control device) worn by the diver. It allows the diver to adjust his buoyancy or bring him to the surface and support him. The ability to change buoyancy allows the diver to hover in the water and adjust for any factor that causes his density to increase (e.g. picking up some object on the bottom). A buoyancy compensator with a reduced maximum lift is needed in cave and saturation diving because, in these situations, it may be dangerous to ascend. The best buoyancy compensators can be inflated from the SCUBA or a small separate air bottle which can also be used as an emergency air supply. A vent valve is fitted so the diver can reduce buoyancy by venting gas from the compensator. Divers can lose control of their buoyancy while ascending - as the diver starts to ascend the gas in the vest expands, so the lift increases and the rate of ascent increases. This may lead to the diver imitating a leaping whale and an air embolism may result from the rapid ascent. The second problem is that the diver surfaces when he should have stopped for decompression.
Even the most up to date scuba equipment weight over 10lb which is very heavy to most of the lady and novice divers. More user friendly or ergonomic design in the scuba equipment is necessary to avoid accidental lost of regular or fatigue after diving against current.