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Diving injury and illness

Diving and snorkelling activities  expose participants to a wide range of potential hazards which can lead to a  range of injuries and illness.

The aquatic environment is non-respirable and  creates changes that are:

  • physical  – pressure, gas laws, temperature, noise and light
  • physiological  – effects of pressure, decompression illness, barotraumas, gas toxicity,  drowning, medical fitness
  • psychological  – experience, training, competence, behaviour, panic
  • task  or environmental related – marine animals, trauma, use of plant, vessel  movements, entrapment, currents, visibility.

Persons conducting diving or  snorkelling businesses (PCBUs) should ensure they understand fully any hazards  and risks and apply risk  management principles to controlling exposures  to eliminate or minimise risk as far as is reasonably practicable.

Key diving injuries and illnesses include:

  • medical conditions
  • drowning
  • decompression illness
  • barotrauma
  • contaminated air
  • nitrogen narcosis
  • panic
  • hypoxic blackout

Medical conditions

Many diving and snorkelling incidents involve the  participant suffering a medical condition that may be made worse by the diving  activity and environment. Key medical conditions include:

  • cardiac  conditions (e.g. heart disease or high blood pressure)
  • respiratory  illnesses and injuries (e.g. asthma, pneumothorax and congestion)
  • conditions  that may result in a loss of consciousness (e.g. epilepsy and diabetes).

It is important that all participants are aware  of risks posed by relevant medical conditions and that they advise the PCBU  before entering the water. In some cases medical advice or assessment may be required before a person can participate  in the diving or snorkelling activity.

Businesses that are conducting diving or  snorkelling for persons with medical conditions should take steps to minimise  these risks. Requirements  vary depending on the activity being conducted. For  example a snorkeller may be provided with a flotation device and taken on a  guided tour where extra supervision can be provided.


Water is non-respirable and inhalation of water  may lead to drowning syndromes resulting in injury or death. Diving and  snorkelling activities aim to give participants a view into the underwater  world without compromising respiratory activity. Ensuring participants are in medically fit, have appropriate equipment, are properly trained and experienced and are not left behind are all ways of minimising these risks.

Drowning may result whenever a person becomes  incapacitated in water (e.g. through fatigue, panic or another injury). PCBUs  must ensure that divers and snorkellers are supervised and also that they have efficient and effective  systems, personnel and equipment for rescue, first aid and evacuation.

Decompression illness

Decompression illness can result when excessive amounts of nitrogen in the  body start to form bubbles in blood vessels and tissues as the diver ascends.  The bubbles can cause tissue damage and block blood vessels, obstructing blood  flow to vital organs.

Symptoms include:

  • mental dullness
  • fatigue
  • pins and needles (prickling and  itching)
  • pains in the joints and muscles
  • numbness
  • headache
  • weakness
  • dizziness and nausea.

Decompression illness can arise after any diving, even when diving has been  carried out within the limits of standard decompression tables or computers. If a diver displays  symptoms, appropriate first aid should be provided and medical advice sought.


Barotrauma is injury brought about by pressure differences  causing changes in volume in air spaces in the body. Examples of air spaces at  risk of barotrauma include the ears, sinuses, lungs and the face-mask cavity.

During descent external pressure may become greater than  the pressure within air spaces. For example, if a diver cannot or does not  equalise the ears during descent, then a perforated eardrum can result.

When a diver ascends, the external pressure may become  less than the pressure within an air space. If the diver does not exhale on  ascent and/or makes a rapid ascent, their lungs will expand as the volume of  gas increases. This can result in lung tissue being overstretched and tearing  with gas escaping into surrounding tissues or the bloodstream. If the gas  enters the bloodstream, it may lead to arterial gas embolism which can result in  death, stroke or other neurological conditions.

As the greatest pressure changes occur near the surface,  the diver is most at risk of barotrauma within the first 10 metres.

Contaminated air

Breathing gases for divers must not be  contaminated. Even small amounts of contamination can affect divers and the  effects of most contaminants increase with the depth of the dive. Possible contaminants  include carbon monoxide and oil. Contaminants can cause a range of injuries and  illness including, convulsions, loss of consciousness and death.

Compressor systems must  be correctly designed, installed and operated to minimise risks of  contamination. Gases must be regularly tested to monitor contaminant levels and  a current test certificate should be available for each compressor.

Air is primarily composed of oxygen and nitrogen.  Even these gases can have serious effects on a diver's health when breathed at  depth See below for more information about the effects of nitrogen.

Nitrogen narcosis

Nitrogen narcosis can result from breathing nitrogen under  pressure. It acts like a drug and affects individuals differently. Nitrogen  narcosis affects reasoning, judgement, memory, perception, concentration and  coordination. It may lead to over confidence, anxiety or panic. Survival  instincts and responses may be suppressed. If the dive is uneventful, the  narcotic effects of nitrogen narcosis may not be evident. A diver failing to  follow instructions or the dive plan, or being inattentive to buoyancy, air  supply or buddy signals may be suffering from nitrogen narcosis.

Diving on air at or beyond 30 metres significantly  increases the risk of nitrogen narcosis. Nitrogen narcosis can develop when  diving in shallower depths, but is less likely to be evident, that is, a diver  may not be aware that he or she is affected by nitrogen narcosis and/or it may  not be evident to an observer. Safe  diving beyond 30 metres requires an awareness of the increasing risk of this  condition and its symptoms, and the practices required to reduce the symptoms  and the associated likelihood of an accident. Nitrogen narcosis is directly  related to diving at depths and diminishes as a diver ascends to shallower  water. If a diver begins to be affected by nitrogen narcosis, then immediate  ascent to shallower depths, taking into account decompression requirements, is  required.

Factors  known to increase the effects of nitrogen narcosis include:

  • fatigue  or heavy work
  • anxiety,  inexperience or apprehension
  • the  diver feeling cold
  • poor  visibility
  • carbon  dioxide excess
  • recent  alcohol intake or use of sedative drugs including sea sickness medications or  marijuana.


Studies have implicated panic as a contributor to many  diving-snorkelling/snorkelling deaths. As panic develops, anxiety increases and a person  diving-snorkelling/snorkelling reduces his or her capacity to think rationally and may  focus on only one act or goal while forgetting about other important  requirements. For instance, a panicky diver might focus on reaching the surface  but forget to exhale during ascent.

Factors  which can play a role in the development of panic include:

  • equipment  problems such as low air and ill-fitting equipment
  • environmental  hazards such as cold water, deep diving, marine animals and poor visibility
  • personal  factors such as fatigue, medical or physical unfitness, seasickness, alcohol  intake, inexperience, excessive general anxiety, phobias, diving accidents,  dizziness or disorientation
  • inadequate  instruction and training of person diving-snorkelling/snorkelling.

Effective explanation and training in relation to all relevant aspects of diving can help minimise the  likelihood of panic. Additionally, it is important for a person  diving-snorkelling/snorkelling to know his or her limitations and to stay within these.

While the person displaying anxiety and lack of confidence may be readily  noticed and can be more thoroughly trained, more carefully monitored, given  more assistance or advised not to engage in diving-snorkelling/snorkelling, also at risk is  the overconfident person diving-snorkelling/snorkelling who is out of touch with, or concealing  his or her real capabilities and concerns.

Hypoxic blackout ('shallow water blackout' of  snorkellers)

Where a person holds their breath on the surface, the irresistible urge to  breathe is initiated mainly by a rise in CO2 levels and to a lesser extent  by a fall in arterial O2. If a person's arterial O2 levels drop below a critical level, hypoxia will develop and the person will  suddenly lose consciousness and 'blackout'.

The term 'shallow water blackout' is often used to describe this condition  but is also used to describe a condition associated with closed circuit  rebreathers. Hence the expression 'hypoxic blackout' is used here.

In recreational  snorkelling, there are two causes  for this condition that can affect a 'breath hold diver' who leaves the surface  with a single breath. They are hyperventilation and ascent. These conditions  may occur concurrently or independently.

Hyperventilation occurs when the person takes repeated deep breaths before  descending. This affects the relative balance of CO2 and arterial O2 and can reduce the person's urge to breathe. It is a condition that is  independent of depth and has been recorded in swimming pools.

Hypoxia of ascent occurs when the person descends to depth. There the  elevated partial pressure of O2 is sufficient for the person whilst  they remain at depth, but falls rapidly to critical levels as the person  ascends. This condition is more prevalent in persons who train to extend their  breath hold and who dive deep, such as competitive breath hold divers, spear  fishermen and photographers. Deaths have been recorded in depths from 3 m to 30  m.

PCBUs conducting recreational snorkelling should  provide advice to prospective snorkellers who intend to breath hold dive that  covers:

  • The risk posed to breath hold divers  of hypoxic blackout that may lead to unconsciousness, drowning, serious injury  or death.
  • This risk is increased significantly  for breath hold divers who hyperventilate by taking repeated deep breaths  before descending or who do deep dives. Consequently divers are strongly  advised not to hyperventilate.
  • Experienced breath hold divers are at  particular risk in that they have the ability and technique to do long and deep  dives.
  • Breath hold divers should always dive  in buddy pairs where one buddy remains on the surface and observes the other  buddy whilst they are diving (one up, one down).
  • Breath hold divers using weight belts  should be carefully weighted to ensure that they are neutrally buoyant whilst  at the surface. The weight belts should have a quick release mechanism and  divers should be familiar with its operation.

Lookouts,  snorkelling supervisors and snorkelling guides should be aware of which  snorkellers intending to breath hold dive and provide them with additional  levels of supervision.