B.1.8.1 Introduction

Most professional inshore divers work on underwater construction projects, in fish farming, shellfish harvesting, rescue diving, diving instruction and marine research. In addition, diving takes place on merchant or cruise ships allows inspection for damage beneath the water line, in a water hull survey, cleaning of the hull and security inspections. Offshore divers are traditionally engaged in diving related to the offshore oil industry. This often involves work from a diving support vessel and divers may be engaged in complex diving operations in cooperation with an oil drilling platform.

Diving implies working below sea level and incurs physiological effects from increased ambient pressure and breathing a gas mixture that is different from normal air. Divers also meet challenges such as varying sea states, from calm to waves several meters high, gale force winds, currents and a wide range of temperatures. Diving operations are technically complex and the underwater environment poses a high risk of fatal or serious accidents. Contamination of the breathing gas with chemical substances during diving has been observed both inshore and offshore. Divers may be exposed to many hazards like polluted water and occupational carcinogens. [1].

Each dive consists of a compression phase (from sea level to bottom), a bottom phase (often the working level) and a decompression phase. To minimise risks form decompression dive tables are used to give information on the recommended decompression time in relation to the depth and duration of the dive. There are a variety of dive tables, dive time calculators and dive computers available.  There are tables designed specifically for recreational diving, and other tables for professional diving and for diving in the Navy.

Recreational, scientific and rescue divers normally carry their own compressed air supply, self-contained underwater breathing apparatus – SCUBA, and are independent of a surface supply during the dive. Professional divers in shallow waters down to 50 metres will normally get their breathing gas from the surface and normal air or oxygen-enriched air is usually the preferred breathing gas. In more complex professional diving operations, especially deeper dives, saturation diving with the breathing gas mixture contain helium (Heliox) is recommended. Short duration ‘bounce dives’ to depth may be used, where tissues do not have time to become saturated with the gas mixture used, but this technique can be hazardous. Saturation dives, where the diver’s body becomes saturated with the breathing gas at a constant depth and ambient pressure are normally used for work at depth.  This allows the diver to stay at the bottom phase of the dive for several days, living in a chamber and leaving it to work, often in a diving bell.  It requires a decompression phase lasting for several days.

B.1.8.2 Health requirements

Good health is required in order to be a professional diver and strongly recommended for recreational divers. The certificate for a professional diver last for one year. The medical examination and assessment of divers are based on fitness criteria and considerations of health risks of diving. People suffering from cardiac disease, type I diabetes, asthma and epilepsy should not dive. There are some variations between different national guidelines regarding the specific health requirements for professional diving[1] [2].

There are no formal health requirements for recreational divers but a health check is recommended for the divers own safety. Generally, recreational diving depths are limited by the training agencies to a maximum of between 30 and 40 meters, 100 and 130 feet, beyond which a variety of safety issues such as oxygen toxicity and nitrogen narcosis significantly increase the risk of diving using recreational diving equipment and practices. Specialized skills and equipment for technical diving are needed.

B.1.8.3 Health risks


Barotrauma may occur if air is trapped within a closed body compartment during the ascent from a dive. Barotrauma of the inner ear, sinuses or in the root canals of teeth will cause pain. Inner ear barotrauma may also be associated with burst ear drum (tympanic membrane rupture), vertigo and loss of hearing. If the hearing does not improve, the diver should seek referral to an Ear Nose and Throat (ENT) specialist. Pain in the cheeks, between the eyes, alongside the nose and in the upper teeth may indicate barotrauma of the sinuses. A nasal spray and alternating hot washcloths and ice packs on the cheeks may help to open drainage pathways and provide relief.

Barotrauma to the lungs primarily occurs if the diver holds their breath during an ascent, after breathing compressed air at depth. An obstruction trapping gas within a section of the lung will effectively make that portion of the lung fail to deflate. The obstruction may be caused by mucus accumulated in the lung passages due to a respiratory infection or asthma. Over pressurization of the lungs can cause pulmonary capillaries and alveoli to rupture, mixing blood and air in the lungs and leading to coughing blood (). The symptoms develop rapidly and tend to be dramatic. The situation is most serious if air enters the bloodstream and causes an arterial air embolism. This can lead to a wide range of symptoms in the central nervous system and vascular system, for example dizziness, personality change, paralysis, loss of consciousness and death.

Other consequences of lung barotrauma may be pneumothorax, mediastinal emphysema and subcutanous emphysema.

The priorities of care are to monitor and restore airway, breathing and circulation, administer oxygen and rapidly transfer the diver to a medical facility if possible.


Diving, especially when using oxygen enriched breathing gas, is associated with too much oxygen in the body fluids and organs, called hyperoxia. This may have toxic effects on the lungs and the central nervous system. Symptoms from the lungs may include chest pain, cough, chest tightness and dyspnoea with a progressive decrease in lung function as measured by vital capacity (2).  In high concentration, hyperoxia is associated with the risk of epileptic seizures (3). Often the diver does not experience any warning symptoms before seizure and therefore there is a risk of such an event being fatal.

Nitrogen narcosis

Nitrogen is narcotic when breathed under hyperbaric conditions (4).  Nitrogen narcosis is characterised by euphoria, intoxication and progressive depression of central nervous system function, see Table 1. The onset is insidious and can result in irrational behaviour, impaired judgement and a false sense of security. Although there is considerable variation in individual susceptibility, performance is impaired in all individuals and short term adaptation to the narcotic effects does not occur. Many divers believe that they can develop resistance to nitrogen narcosis with practice, but it has been shown that while habituation reduces subjective symptoms, performance remains impaired (5).

Nitrogen partial pressure (bar)

Symptoms and signs

2  - 4

Mild impairment of performance of unpractised tasks.

Mild euphoria.


Impaired reasoning and immediate memory

Delayed response to visual and auditory stimuli

Increased reaction time

4 - 6

Overconfidence and fixed thinking

Calculation errors


Impaired judgement, hallucinations

6 - 8

Laughter approaching hysteria

Talkative, occasional dizziness


Severely impaired intellectual performance

Mental confusion, impaired concentration




Hallucinations, unconsciousness, death

Table 1. Nitrogen narcosis. The effects of an increasing partial pressure of nitrogen.


Decompression illness, decompression sickness and hyperbaric oxygen treatment

Decompression illness (DCI) is caused by bubbles in the blood or tissue during or after a reduction in environmental pressure, decompression. (6). It includes two syndromes: arterial gas embolism with bubbles in the arteries most often from barotrauma and rupture of small arteries in the lungs due to the expanding gas, and the more common decompression sickness. Diving is also associated with decompression stress associated with an excess of nitrogen in the body. This causes gas micro bubbles to develop, primarily in the venous system, leading to decompression sickness (DCS). Bubbles can have mechanical, embolic and biochemical effects with manifestations ranging from trivial to fatal. Symptoms of DCS usually appear within minutes or hours after surfacing and may manifest as

  • skin rash,
  • joint pain,
  • headache,
  • fatigue,
  • hearing impairment, or
  • more definite neurological symptoms such as sensory loss or paresis in one or more limbs. 

An overload of bubbles in the heart and pulmonary arteries is severe and often fatal.

Symptoms of arterial gas embolism are similar to DCS. First aid treatment for divers with any of the above mentioned symptoms of DCI is 100% oxygen and definitive treatment is recompression to increased pressure, breathing 100% oxygen.  Hyperbaric chambers are available on diving vessels and in some hospitals. Care should be taken when transporting a sick or injured diver from a dive site to a treatment centre and ideally this should be done under pressure, and certainly not at altitude with reduced atmospheric pressure. Treatment is, in most cases, effective although residual deficits can remain in more serious cases, even after several recompressions.

B.1.8.4 Risk management

To reduce the risk of DCI divers are recommended to be well prepared for the dive and know their equipment, follow accepted dive tables, not being affected by alcohol or drugs, to be normally hydrated and never dive alone. Professional divers do not dive alone. They will have a diving partner ready to assist in case of trouble and a diving supervisor will have control of the dive from the surface.

Flying soon after diving will increase the risk of DCS due to the decrease in ambient pressure below 1 atmosphere and cause increased decompression stress and risk of decompression sickness. Divers Alert Network (DAN) guidelines suggest a minimum of 12 hours before flying to a cabin pressure of up to 2400 metres/ 8000 feet, or ascending to altitude, after non stop diving, with this increasing to 24 hours or more following dives that involve required decompression (7).

B.1.8.5 Long-term health effects

Diving may have adverse long-term health effects on the skeleton, long bones, lung function, the nervous system, inner ear and cardiovascular system (8-12).  Dysbaric osteonecrosis (DON) is associated with prolonged hyperbaric exposure and rapid decompression that cause nitrogen bubbles to enter the fatty marrow-containing shafts of long bones leading to reduction in blood flow and subsequent osteonecrosis (8). Patients may present asymptomatically, and typical radiographic findings of DON include:

  • decalcification of bone,
  • cystic lesions,
  • osteosclerotic patterns,
  • nontraumatic fractures,
  • bone islands, and a
  • subchondral crescent sign.

Although the incidence of DON has decreased significantly over the past two decades, the lack of timely diagnosis and optimal management keeps DON relevant in the orthopedic and sports medicine community.

The cardiovascular effects may result from the physiological changes associated with diving per se, or be caused by the strenuous activity performed (12).


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[2] http://www.EDTC Medical assessment of working divers – IMCA (