Decompression illness (DCI) is a diving injury caused by gas bubbles forming in the blood and body tissues after pressure drops too quickly. Scuba divers breathe compressed gas, and the nitrogen in it dissolves into their blood during a dive. If the diver surfaces too fast, or the dive profile exceeds safe limits, that nitrogen can come out of solution as bubbles that block small blood vessels and injure tissue. Symptoms can appear within minutes or be delayed for hours, so any diver who feels unwell afterwards should be treated as a possible case until proven otherwise.
Warning Signs of Decompression Illness
- Extreme or unusual fatigue
- Numbness, tingling or pins and needles
- Headache, or pain in the joints and limbs
- Poor balance, dizziness or loss of coordination
- Reduced alertness or confusion
- Weakness or paralysis
- A skin rash or marbled skin
- Speech, vision or hearing disturbances
Do not dismiss these as simple tiredness after a dive. If a diver has any of them, begin first aid and arrange medical advice.
Decompression Illness First Aid Steps
- Check DRABC. Make sure the scene is safe, the diver is out of the water and the airway, breathing and circulation are working, following the DRABC primary survey.
- Call for urgent medical help and contact a diving emergency service or hyperbaric medicine specialist in your region, such as the Divers Alert Network, so doctors can advise on treatment and transfer to a recompression chamber.
- Give oxygen if you are trained. The best first aid is 100 per cent oxygen through a demand valve or a well-fitting high-flow mask, as soon as possible and continued until medical care takes over.
- Position comfortably. Lay the diver flat if they are comfortable. A conscious person with breathing difficulty may prefer to sit semi-reclined, and an unconscious breathing diver should be placed in the recovery position.
- Offer fluids if appropriate. A conscious, stable diver who is not vomiting can drink water or an electrolyte drink. Avoid alcohol.
- Do not use nitrous oxide. Entonox and similar gas mixtures can make bubbles larger.
- Record the details. Note the dives completed, depths, times, ascent problems, gas used, symptoms and onset, first aid given and the diver’s response, and send the dive computer and logbook with the diver.
- Plan the transfer carefully. Help move the diver to a chamber, and avoid ascent to altitude. If air transport is unavoidable, doctors will advise on a low-altitude or pressurised option.
Why Early Oxygen and Transfer Matter
Oxygen helps remove nitrogen from the body and improves oxygen delivery to tissue starved by bubbles. Recompression in a chamber then shrinks the bubbles and restores flow. The sooner treatment begins, the better the outcome, so the first aid priorities are oxygen, specialist advice and rapid transport rather than testing or waiting to see whether symptoms resolve on their own.
Preventing Decompression Illness
Plan dives within the limits of your training and dive computer, ascend slowly, make safety stops, stay well hydrated, avoid heavy exertion straight after diving and observe the no-fly interval recommended by your training agency or dive medicine specialist. Dive operators should hold emergency oxygen on site, have staff trained in its use and display emergency contact numbers on the dive boat.
Related diving injuries are covered in our guide to burst lung in divers.
Frequently Asked Questions
How soon after a dive can decompression illness appear?
Symptoms often begin within the first few hours, though some appear later, so any new symptom after diving should be taken seriously.
Can a diver go back in the water to relieve symptoms?
No. In-water recompression is dangerous and should not be attempted by untrained people. Contact a diving emergency service and arrange medical transfer.
Is decompression illness the same as the bends?
The bends is the older term for the joint pain form. Decompression illness is the broader modern term that includes joint pain, neurological symptoms and gas embolism.
References and Further Reading
- American Heart Association and American Red Cross, Guidelines for First Aid
- Divers Alert Network (DAN)
Last updated: October 2026
Prepared by: EHS Guidelines Editorial Team
This article is general educational information and is not a substitute for accredited first aid training or professional medical care. In an emergency, call your local emergency number immediately. Emergency numbers, medicines and protocols differ between countries, so follow local guidance.
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