Diving accidents

In short

Besides barotrauma and decompression sickness, covered in their own guides, several accidents can happen while diving: breathlessness, narcosis, hypothermia, drowning or loss of consciousness, poisoning. This guide explains how to prevent and recognise them, and recalls the common reflex: signal, stop exertion, ascend safely with your buddy and raise the alarm. It gives no medical advice or care procedure: when in doubt, call emergency services.

Why it matters

These accidents often start subtly, and they combine: cold encourages breathlessness, breathlessness worsens narcosis, narcosis slows reactions. Recognising them early in yourself or your buddy lets you act before the situation becomes serious. Prevention relies on simple habits.

Common contributing factors

Most of these accidents share the same factors:

• fatigue, lack of sleep, a heavy meal or no meal at all;
• cold;
• exertion, especially finning against the current;
• stress and apprehension;
• depth;
• unsuitable equipment: a regulator that breathes badly, a suit that is too tight, overweighting;
• alcohol and some medicines; discuss your treatments with a doctor.

Breathlessness

• What happens: breathing speeds up and becomes shallow; carbon dioxide builds up and keeps the breathlessness going. Underwater, denser air and the regulator make breathing more demanding.
• Prevent: fin calmly, be correctly weighted, avoid fighting the current, keep your regulator serviced, call the dive when you do not feel well.
• Recognise: feeling short of air although the cylinder still has some, rapid breathing, agitation, urge to rush to the surface.
• React: signal breathlessness, stop, hold on to something if possible, focus on breathing out, ascend a few metres with your buddy; never ascend alone and fast.

Narcosis

• What happens: nitrogen breathed under pressure has an effect similar to drunkenness. It often appears from 30 to 40 m on air, but sensitivity varies from one person, and one day, to another.
• Prevent: respect the depth limits of your level, avoid cold, fatigue and exertion, descend gradually.
• Recognise: euphoria or anxiety, difficulty reading instruments, slow reactions, fixation on a detail, unusual behaviour in your buddy.
• React: ascend a few metres; the effects usually fade quickly. Signal it and adapt the rest of the dive.

See also the deep diving guide.

Hypothermia

• What happens: the body loses more heat than it produces; core temperature falls.
• Prevent: suitable thermal protection, shorter dives in cold water, protection at the surface between dives.
• Recognise: shivering, clumsy movements, confusion; at an advanced stage, shivering may stop, which is a warning sign.
• React: signal the cold, cut the dive short, get to shelter, remove wet clothing, cover up; call for help if the condition does not improve.

See the thermal protection guide.

Drowning and loss of consciousness

• What happens: water enters the airway after panic, a loss of consciousness or losing the regulator.
• Prevent: be fit to dive, know how to recover your regulator, do not dive after a recent loss of consciousness without medical advice, stay close to your buddy.
• Recognise: a motionless diver who does not respond, regulator out of the mouth, coughing and distress at the surface.
• React: intervene according to your training, ascend, get out of the water, raise the alarm immediately.

Poisoning

Carbon monoxide in the cylinder air

• What happens: a badly placed or poorly maintained compressor can draw in exhaust fumes.
• Prevent: fill at reputable, well-maintained stations; report air that smells or tastes unusual.
• Recognise: headache, nausea, feeling unwell, often in several divers whose cylinders were filled at the same place.
• React: end the dive, call for help, keep the cylinder for analysis.

Oxygen toxicity with Nitrox

• What happens: oxygen becomes toxic to the nervous system above a certain partial pressure; the main risk is a convulsion underwater.
• Prevent: analyse your gas, set your computer, respect the MOD. The usual PPO2 limit is 1.4 bar; 1.6 bar is an absolute maximum. See the Nitrox guide.
• Recognise: visual disturbances, ringing in the ears, nausea, facial twitching, feeling unwell; they may come only moments before a convulsion.
• React: ascend above the MOD with your buddy, signal, end the dive, call for help if there are symptoms.

Decompression sickness and barotrauma

Decompression sickness and barotrauma are covered in their own guides. Remember that any abnormal sign after a dive (pain, intense fatigue, tingling, speech or vision problems) warrants an alert, even if it seems mild.

The common reflex

1. Signal to your buddy.
2. Stop exertion.
3. Ascend safely with your buddy, at a controlled speed.
4. Call for help as soon as the situation requires it (see the rescue guide).

Key takeaways

• Fatigue, cold, exertion, stress and depth contribute to most accidents.
• Breathlessness: stop, breathe out, ascend a little with your buddy.
• Narcosis: ascend a few metres.
• Nitrox: respect the MOD, PPO2 1.4 bar in normal use.
• Any abnormal sign: signal, ascend safely, call for help.

Further reading

During a Nitrox dive, the watch shows PPO2, MOD and CNS and raises an oxygen alert; it also alerts you to a fast ascent. These alerts replace neither training nor the team's vigilance. The guides on barotrauma, decompression and rescue complement this one.