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Automated external defibrillators (AEDs)

  • A heart attack is a severe, life-threatening condition that can occur even in very fit people.
  • Chest compressions are unlikely to restart someone’s heart on their own. A defibrillator is often necessary to restart the heart. The more quickly a defibrillator is used, the more chance the casualty has of surviving.
  • The more quickly a defibrillator is used, the more chance the casualty has of surviving. 
  • Defibrillators are becoming increasingly common. 
  • Several manufacturers now sell weather-resistant AEDs suitable for use in open boats, making an AED a realistic addition to a diving first-aid kit. 
  • While AED devices are simple to use, formal training to use an AED helps with understanding and practice and minimises any reluctance to use one when necessary, BSAC runs formal training in AED use, which will improve essential lifesaving skills. 

Basic life support (BLS)

  • It is a good idea to get trained in BLS.
  • Remember that your skills will degrade over time. You should practise your skills regularly. 
  • The Resuscitation Council (UK) regularly reviews and updates its recommendations on BLS. Its guidance, and consequently BSAC’s guidance, changes as a result. You can make sure that you are current and up-to-date by looking at BSAC’s BLS guidelines.
  • Current BSAC guidance for rescue breaths (RB) and cardiac compressions (CC) includes
    - In water give one minute of RB and then remove to safety as quickly as possible without further RB.
    - On land give CC/RB in the ratio of 30:2, achieving a rate of 100-120 CC/minute, using a chest compression of 5-6 centimetres.


  • Dehydration may affect your risk of decompression illness, and you should make sure that you are properly hydrated before you dive.
  • A good way to check if you are dehydrated or not is to check the colour of your urine; it should be clear.
  • Be careful about drinking large quantities immediately before a dive. This may increase your risk of immersion pulmonary oedema (see Immersion pulmonary oedema). Instead you should drink small quantities regularly and often. 
  • When you are immersed in water the body decreases the amount of blood circulating in your body. This fluid has to go somewhere and hence you may need to urinate more when diving. After a dive you will need to replace these fluids regain normal hydration.

Drugs and alcohol

  • If you are taking prescribed medication of any kind (except for the contraceptive pill), do not dive unless clearance has been given by an approved UK Diving Medical Committee referee.
  • It is unwise, and possibly dangerous, to yourself and others if you dive under the influence of any recreational drugs or under the influence of alcohol. Remember that if you drink heavily the night before, you might still be mildly drunk and unfit to dive the following day. 

Immersion pulmonary oedema (IPO)

  • IPO is a condition that can affect anyone immersed in water, including swimmers and divers. 
  • Being immersed in water can cause blood to move from your extremities to the core circulation. In some instances this can cause fluid to seep into the lungs, a form of drowning. 
  • Some underwater problems that could be indicators of the effects of IPO include
    - Divers with breathing difficulties when not exercising particularly strenuously; breathing difficulties may be indicated by rapid, uneven or heavy breathing or coughing uncontrollably
    - Confusion, swimming in wrong/random directions
    - Inability to carry out normal functions, while appearing to have to concentrate on breathing
    - Belief that a regulator is not working properly
    - Indication of ‘out of gas’ when their regulator(s) are found to be working correctly
    - Divers refusing or rejecting an alternative supply when ‘out of gas'
    - Indication of difficulty of breathing when on the surface
  • Advice from the medical experts at this time is that if you experience breathing difficulties underwater you should terminate the dive and ascend safely and exit the water. If you recognise any of the above factors in a buddy then assist them from the water as quickly as it is safe to do so. 

Medical certificates/examinations

  • Some medical conditions, or prescription drugs, are not compatible with safe diving. You therefore need to comply with the relevant medical requirements. 
  • In many cases, a self-certification form is enough. However, if you answer “yes” to any of the questions, you will need to refer to a diving doctor. Diving doctors are medical doctors who are approved by the UK Diving Medical Committee for this role. The most up-to-date self-certification form, and a list of diving doctors, are on the UK DMC’s website.
  • Even if you have a valid medical, you should make sure that you are fit to dive.

Oxygen first-aid (for diving-related injuries)

  • Oxygen is an effective first-aid treatment for all diving-related injuries including DCI, near-drowning, trauma, carbon dioxide toxicity and shock. However in cases of DCI, it is a first-aid treatment and not a substitute for recompression.
  • The only time that oxygen should not be given is if the diver is actually convulsing. In this case you should wait until the symptoms have subsided and then administer oxygen.
  • Whenever oxygen is administered medical advice should be sought and followed.
  • While dedicated oxygen administration equipment is by far the best option available, don’t forget that rebreathers and rich nitrox mixes are a source of oxygen which can also be used to treat DCI if dedicated equipment is exhausted or not available.
  • When planning to go diving, you need to think about how much therapeutic oxygen you need to take with you. This will depend on lots of factors, including how remote the site is, what depths you are diving to, what rescue facilities are available, whether the charter boat carries oxygen, and others.

Patent foramen ovale (PFO)

  • A PFO is a hole in your heart that allows blood (and bubbles) to move from the right side of the heart to the left. 
  • Around a quater of the population have a PFO. Although most PFOs are very small, the consequence for divers of having a PFO is that it can increase the risk of DCI. This occurs as a result of bubbles in the venous circulation (which would normally be filtered out in the lungs) shunting across to the arterial circulation, where they continue to expand in size. 


  • There is little medical evidence one way or the other, but there might be a risk to your baby if you dive while pregnant. Deep diving, DCI or any other diving ailment, and also recompression treatment, could all increase this risk.
  • If a woman discovers she is pregnant and has been diving during the pregnancy, she is advised to discuss her case with a BSAC Medical Referee

Work of breathing (WOB)

  • The act of breathing uses energy. When you are diving, it is harder to breathe than when you are on land, and so you use more energy and have an increased work of breathing.
  • Having a high work of breathing increases the risk of carbon dioxide toxicity and narcosis. It can also increase the risk of immersion pulmonary oedema. 
  • Inappropriate or poorly maintained equipment can increase your work of breathing. 
  • Rebreathers often have higher levels of work of breathing than open-circuit regulators.
  • At depth, the increased gas density also increases the work of breathing. The physiological effects of this become increasingly important below 40m. To reduce this risk you can use trimix to reduce the gas density.

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