Dive Health & Safety
Lung overexpansion and arterial gas embolism: why you never hold your breath
As you ascend, the air in your lungs expands. If it can't escape — because you hold your breath or rush to the surface — it can rupture lung tissue. Air can then enter the arteries (arterial gas embolism) and block blood flow to the brain. Symptoms usually appear within 15 minutes of surfacing and need immediate medical treatment. Breathe normally and ascend slowly.
By 71 Guardians · Published 19 Oct 2026
How does a lung overexpansion injury happen?
Gas in the lungs grows as the water pressure falls on the way up. If you don't breathe out enough, DAN explains, the expanding air may rupture lung tissue — pulmonary barotrauma.
What are the signs of arterial gas embolism?
Symptoms typically appear within 15 minutes of surfacing and can include loss of consciousness, confusion, convulsions, bloody froth from the mouth or nose, and weakness or paralysis. It needs immediate medical treatment — give oxygen and call emergency services.
How serious is it?
In DAN's review of 964 diving deaths, emergency ascents were involved in 30% of cases, and among those, arterial gas embolism was the cause of death in 54%.
How do I prevent it?
- Never hold your breath while scuba diving.
- Ascend slowly — DAN cites the U.S. Navy rate of 9 metres (30 feet) per minute — and watch your computer.
- Vent your BCD gradually as you rise, and keep your weights secure.
- Monitor your air so you never need an emergency ascent.
Frequently asked questions
Why do instructors say 'never hold your breath'?
Because expanding air on ascent can rupture the lungs if it can't escape.
Can it happen in shallow water?
The largest pressure change is near the surface, so breathing normally matters on every ascent.
Questions before you dive with us?
Message our team on WhatsApp — we're divers in Hurghada and happy to help.
Chat with us on WhatsAppSources
- How to Avoid Rapid Ascents and Arterial Gas Embolism — Divers Alert Network (DAN)
- Emergency Ascents: Managing the Risks — Alert Diver — Divers Alert Network (DAN)