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

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.

Last updated
05 December 2016