There is no exception that the general occupational hazards of workplace including fire , electricity shocks and noise hazards during the process of gas tanks filling can occur in the diving industry. However, there are number of specific physical health hazards which are limited to diving and are due to pressure changes. Although increased pressure exerts no mechanical effect on the tissues of the body per se, since liquids and solids are relatively incompressible, a pressure gradient develops when equalization is failed within our body cavities such as the middle ear, paranasal sinuses and the lung.

Dysbarism of ascent (Decompression) and decent (Compression) known as barotrauma are commonly happened to divers.

Five conditions must be present for barotrauma to occur

(1) There must be a gas-filled space. Most of the body is fluid and not compressible. However, any gas-filled space naturally present within the body (sinus) or next to the body (face mask) can damage the body tissues when the gas volume changes as described by Boyle's Law.

(2) The space must have rigid walls. When the walls are elastic like a balloon, there will be no damage done by gas compression or expansion until the volume change surpasses the elasticity of the walls or vessels.

(3) The space must be enclosed. If any substance (with the exception of blood in the vessels lining the space) were allowed to enter or leave the space as the gas volume changes, no damage would occur.

(4) The space must have vascular penetration (arteries and veins) and a membrane lining the space. This allows the blood to be forced into the space and exceed the elasticity of the vessels to compensate for the change in pressure.

(5) There must be a change in ambient pressure.

It is important to note that barotrauma will not normally occur in divers who have normal anatomy and physiology, and who are using properly functioning equipment and correct diving procedures. The predominant symptom of barotrauma is pain. Other symptoms such as vertigo, numbness, or facial paralysis may be produced depending on the specific anatomy.

Narcosis involves confusion, impaired judgement, and a sense of well-being. Divers find it difficult to concentrate or to reason, and may not be able to remember what they are supposed to do or have already done. Performing even simple tasks is difficult. The signs of narcosis are:

· Loss of judgement or skill

· A false feeling of well-being

· Lack of concern for job or safety

· Apparent stupidity

· Inappropriate laughter

An uncontrollable desire of the diver to laugh, and a tingling and vague numbness of the lips, gums and legs are symptoms reported by divers who have experienced nitrogen narcosis. Divers may display abnormal behaviour such as removing the regulator or swimming to unsafe depths without regard to decompression sickness or air supply. There is no specific treatment for nitrogen narcosis; the diver must be brought to shallower depths where the effects are not felt. Experience, frequent exposure to deep diving, and training may enable divers to perform air dives as deep as 180-200 fsw. The performance or efficiency of divers breathing compressed air will be impaired at depths greater than 180 fsw. The greater the depth the greater the partial pressure of nitrogen and the larger the amount of this gas which will be absorbed by the body. This excessive amount of dissolved nitrogen produces a sense of dizziness like that which follows drinking alcohol. Just like the effect of alcohol there is great individual variation to increasing nitrogen pressure. Prevention of mishap depends on being aware of the danger and recognising early signs (i.e. giddiness and a sense of euphoria) and maintaining communication with the surface and buddy diving.

A water temperature of approximately 91˘XF (33˘XC) is required to keep an unprotected, resting man at a stable temperature. The unprotected diver will be affected by excessive heat loss and become chilled within a short period of time in water temperatures below 72˘XF (23˘XC). As his body temperature falls, the diver first feels uncomfortable, and then, as his body tries to increase heat production in the muscles, shivering begins. If cooling continues, his ability to perform useful work becomes seriously impaired; his sense of touch is dulled and his hands lose dexterity. As shivering intensifies, it brings on a general lack of co-ordination and a SCUBA diver may experience difficulty keeping his mouthpiece in place. He soon loses his ability to think clearly and finds it increasingly difficult to concentrate. At extremely low temperature or with prolonged immersion, body heat loss will reach a point at which death will occur. Appropriate dress can greatly reduce the effects of heat loss, and a diver with proper dress can work in very cold water for reasonable periods of time.

Inhaled gases are heated in the upper respiratory tract. More energy is required to heat the denser gases encountered at depth. Thus, heat loss through the respiratory tract becomes an increasingly significant factor in deeper diving. In fact, respiratory shock can develop if a diver breaths unheated gas while making deep saturation dives at normal water temperature. The body's ability to tolerate cold environments is due to natural insulation and a built-in means of heat regulation. The automatic, cold-induced vasoconstriction lowers the heat conductance of the superficial layer and acts to maintain the heat of the body core. Unfortunately, vasoconstrictive regulation of heat loss provides only a narrow range of protection. As circulation and heat loss increase, the body temperature falls, and may continue falling, even though heat production is increased by shivering.

Much of the heat loss in the trunk area is transferred over the short distance from the deep organs to the body surface by physical conduction which is not under any physiological control. Most of the heat lost from the body in moderately cold water is from the trunk and not the limbs

Exercise normally increases heat production and body temperature in dry conditions. Paradoxically, exercise in cold water may cause the body temperature to fall more rapidly. Any movement which stirs the water in contact with the skin creates turbulence that carries off heat by convection. Heat loss is not caused only by convection at the limbs but also by increased blood flow into the limbs during exercise. Continual movement causes the limbs to resemble the internal body core rather than the insulating superficial layer. These two conflicting effects result in the core temperature being maintained or increased in warm water and decreased in cold water.

Increased heat production requires an equivalent increase in oxygen consumption. The respiratory minute volume of the lungs must increase by the same magnitude.

All of these factors work against the diver. Even his bodyˇ¦s natural insulation and protective function give way to cold water. The diverˇ¦s thinking ability becomes impaired, and the effect of this impairment on the use of his hands and other motor functions may prevent him from choosing and executing the best procedures to complete a task.

While, under extremely warm water or overheated suit and air supply may possibly result in overheat of the diver. These occur more commons in commercial diving due their extreme working environments. Pre-dive heat exposure may lead to significant dehydration putting the diver at risk once he enters the water. This is especially true if a protective suit has to be worn because of marine life or contaminated water which is warm.

The two main causes of alveolar rupture are:

(1) excessive pressure inside the lung caused by positive pressure

(2) failure of expanding gas to escape from the lung during ascent

Pulmonary overinflation from expanding gas failing to escape from the lung during ascent can occur when a diver voluntarily or involuntarily breathholds during ascent. Localized pulmonary obstructions that can cause air trapping, such as asthma, thick secretions from pneumonia, or a severe cold, are other causes. The conditions that bring about these incidents are different from those that produce lung squeeze, and they most frequently occur during free and buoyant ascent training or emergency ascent from dives made with lightweight diving equipment or scuba.

The clinical manifestations of pulmonary overinflation depend on the location at which the free air collects. In all cases, the first step is rupture of the alveolus with a collection of air in the lung tissues with resulting interstitial emphysema. Interstitial emphysema causes no symptoms unless further distribution of the air occurs. Gas may find its way into the chest cavity or arterial circulation.

Occasionally, inhalation of water and fear can also trigger a spasm of the laryngeal muscles (laryngospasm) that seals the main lung passageway, and thus brings about the overexpansion of the lungs. Under these circumstances, death can occurred during ascent from depths of only a few feet.

In certain instances, the damaged lung may allow air to enter but not exit the pleural space. Successive breathing gradually enlarges the air pocket. This is called a tension pneumothorax due to the progressively increasing tension or pressure exerted on the lung and heart by the expanding gas. The symptoms become progressively more serious, beginning with rapid breathing and ending in cyanosis, hypotension, shock, and, unless corrected, death.

The increased pressure in the middle ear may also affect nearby structures and produce symptoms of vertigo and inner ear damage. It is extremely important to rule out arterial gas embolism or decompression sickness when these unusual symptoms of reverse middle ear squeeze occur during ascent or upon surfacing.

According to the ˇ§Health Hazards of Divingˇ¨ published by Labour Department in the protection of workersˇ¦ Health series , the classification of decompression sickness in Hong Kong are as the following sign and symptoms :-

1. Type I Decompression Sickness: ( Pain, Skin and Lymphatic symptoms )

Mild limb pains (ˇ§the nigglesˇ¨)

Severe limb pains (ˇ§the bendsˇ¨)

Skin mottling and irritation (ˇ§the itchesˇ¨)

2. Type II Decompression Sickness: ( Neurological and Cardiorespiratory symptoms )

Vomiting with or without abdominal pain

Vertigo (ˇ§the staggersˇ¨)

Tingling and numbness of limbs

Paralysis or weakness of limbs

Dyspnoea (ˇ§the chokesˇ¨)

Severe headache

Visual effects, flashes of light, double vision, blindness

Angina, heart pain

Irregular pulse Collapse

Coma

Death

These symptoms come on during decompression or shortly afterwards, or more rarely delayed for several hours.

Rapid ascent on decompression results in a very high incidence of decompression sickness. Prevention depends on controlling the rate of ascent and approved decompression tables should be used. The basic requirement is that the diverˇ¦s ascent should be slow enough to allow him to eliminate dissolved nitrogen from his body without bubble formation.

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Currently, both the surface-supplied and self-contained underwater breathing equipment are being used for commercial diving. Sport divers in Hong Kong are all practising self-contained underwater breathing apparatus (Scuba) of compressed air for majority of their diving. Air compressors are used to provide air to the surface-supplied system and scuba tanks of compressed gases are used to provide air in scuba diving. In the processes of Scuba tank filling ,air around the compressor is used to fill the tank after purification and dehydration. Any defect in the filtering, purification or dehydration processes may affect the quality of the filled gas and there is the possibility of toxic gases contamination due to environmental air changes. A possibility of lead exposure is likely to occur for those divers frequent handle the lead weight.