Holding your breath while scuba diving, especially during ascent, can rupture your lungs. As you rise toward the surface, the air in your lungs expands according to the decreasing water pressure. If your airway is closed, that expanding air has nowhere to go, and the delicate air sacs in your lungs can tear. This is one of the most dangerous injuries in scuba diving, and it can happen after ascending from as little as 4 feet of depth.
Why Depth Changes Make Air Expand
Water pressure increases as you go deeper. At the surface, the air in your lungs is at one atmosphere of pressure. At 33 feet (10 meters), it’s compressed to half its surface volume because the pressure has doubled. When you breathe from a scuba tank at depth, you’re inhaling air that matches the surrounding water pressure. That air fills your lungs at a volume that feels normal underwater.
The problem starts when you ascend. As the water pressure drops, that air expands back toward its original volume. If you’re breathing normally, the expanding air simply exits through your mouth and nose. But if you hold your breath, close your throat, or even swallow at the wrong moment, the expanding gas is trapped. Your lung tissue stretches beyond its limits, and the walls of the tiny air sacs (alveoli) can tear open.
This is why the number one rule taught in every scuba certification course is to never hold your breath. Even during a normal, controlled ascent at the recommended rate of 33 feet per minute, a closed airway turns routine physics into a medical emergency.
Where the Escaping Air Goes
When lung tissue tears, air escapes into the body. Where it travels determines which type of injury you get, and some are far more dangerous than others.
- Into the chest cavity (pneumothorax): Air leaks between the lung and the chest wall, causing the lung to partially or fully collapse. You’ll feel sudden chest pain, shortness of breath, rapid shallow breathing, and a racing heart. In the worst case, a tension pneumothorax builds pressure that compresses the heart and major blood vessels, leading to circulatory failure.
- Into the space around the heart (pneumomediastinum): Air migrates to the central chest area. This can cause substernal chest pain, coughing, shortness of breath, voice changes, and difficulty swallowing. Sometimes a doctor can hear a distinctive crackling sound synced with the heartbeat. Many cases are mild and some people feel no symptoms at all.
- Under the skin (subcutaneous emphysema): Air tracks upward into the neck and throat area. You may notice a feeling of fullness, voice changes, difficulty swallowing, or a sensation like something is stuck in your throat. Pressing on the skin over the affected area produces a crackling feeling, like bubble wrap under the surface.
- Into the bloodstream (arterial gas embolism): This is the most immediately life-threatening outcome. Air bubbles enter torn blood vessels in the lungs and travel through the arteries to the brain, heart, or other organs.
Arterial Gas Embolism: The Greatest Risk
When air enters the bloodstream and reaches the brain, the result closely mimics a stroke. Bubbles block blood flow in multiple areas simultaneously, which is why symptoms often affect several parts of the body at once rather than following the pattern of a typical stroke that damages one region.
Symptoms almost always appear within 10 minutes of reaching the surface. The most common initial signs are loss of consciousness (39% of cases), confusion (37%), and dizziness (30%). About 27% of affected divers develop paralysis on one side of the body. Visual disturbances occur in 21%, headache in 20%, and seizures in 11%. Because the bubbles scatter through different blood vessels, a diver might simultaneously have trouble speaking, lose coordination, and experience vision problems.
Without treatment, an arterial gas embolism can cause permanent brain damage or death. The standard emergency treatment is a hyperbaric chamber, where high pressure forces the gas bubbles back into solution in the blood. Getting the diver on 100% oxygen as quickly as possible buys critical time by helping shrink the bubbles and restore oxygen delivery to affected tissues.
Why 4 Feet of Water Is Enough
One of the most counterintuitive facts about this injury is how little depth it takes. According to the Divers Alert Network, ascending just 4 feet while holding a breath of compressed air from a scuba tank can tear the air sacs in your lungs. The greatest relative pressure change happens in the shallowest water. Going from 33 feet to the surface doubles the volume of air in your lungs, but so does going from just a few feet to the surface in proportional terms. Many divers instinctively feel safer in shallow water, which makes this one of the most dangerous misconceptions in the sport.
This also means the final portion of every ascent is the riskiest. Divers who remember to exhale during a deep ascent but hold their breath in the last few feet near the surface are still at serious risk.
How Divers Prevent Lung Injuries
The fix is straightforward: breathe continuously. You don’t need to forcefully exhale the entire time. Normal, relaxed breathing cycles keep your airway open and allow expanding air to escape naturally. During emergency ascents, divers are trained to exhale slowly and steadily, sometimes making a humming or “ahh” sound to ensure the airway stays open without dumping all their air at once.
Ascending slowly also matters. The current industry standard, used by most dive computers and training organizations, is a maximum ascent rate of 10 meters (33 feet) per minute. A slower ascent gives your body more time to off-gas safely and reduces the pressure differential your lungs face at any given moment. Even with continuous breathing, rocketing to the surface increases risk.
Certain pre-existing conditions can increase vulnerability. Lung cysts, scarring from previous infections, asthma with air trapping, or even a bad chest cold can create pockets where air gets trapped during ascent regardless of breathing technique. This is why dive medical screenings ask about respiratory history.
What a Lung Injury Feels Like After a Dive
Symptoms range from subtle to catastrophic depending on where the escaped air ends up. A mild pneumomediastinum might feel like vague chest discomfort that you could easily dismiss as muscle strain. Subcutaneous emphysema produces that strange crackling under the skin of your neck, which is hard to mistake for anything else once you know what it is.
A pneumothorax hits harder: sharp chest pain, difficulty breathing, and a sense that something is seriously wrong. A tension pneumothorax escalates rapidly into a cardiovascular emergency. An arterial gas embolism is often the most dramatic, with sudden neurological collapse that can look identical to a stroke to bystanders.
Any chest pain, breathing difficulty, voice changes, neurological symptoms, or unusual skin sensations after a dive should be treated as a potential lung expansion injury. Symptoms appearing within the first few minutes after surfacing are the strongest red flag, but some presentations can be delayed slightly. Emergency oxygen at the highest available concentration is the critical first response while arranging transport to a medical facility with hyperbaric capability.