Scuba divers ascend slowly because ascending too quickly can cause serious injury or death. Slow ascents decrease the risk of decompression illness by allowing the body to eliminate excess nitrogen. Rapid ascents may also cause lung rupture with collapse (pneumothorax) and reverse ear squeeze.

Scuba diving is a popular activity that is appealing to many, it is also an activity that requires proper training to maintain safety.  Each year, approximately 200 people die worldwide as a result of scuba diving accidents. Knowing how to dive correctly is essential.

While it may seem like fun to give a firm push from where you are diving or to kick quickly to the surface, the result can be painful and even life-threatening.  In this article, you will learn why scuba divers ascend slowly to the surface. 

What Happens to Your Body When You Dive? 

Aside from ensuring you have the proper gear for scuba diving, the ascent is one of the most critical parts of scuba diving that does not leave much room for error.  Your body has several physiological reactions when your scuba dive. Among these are build up of nitrogen in tissues due to breathing pressurized air and changes in volume of air pockets in body due to pressure difference from the surface.

These natural effects of breathing compressed air at depth can result in unintended consequences under certain conditions. Two of the most common ailments experienced by scuba divers are decompression illness and squeezes.  A more rare event called a pneumothorax (sudden rupture of lung lining with air leak and lung collapse) can also occur. Each of these is due to sudden changes in pressurization of the body. (Source: American Family Physician)

Descending 

As you dive down, the pressure of the water increases dramatically. The pressure increase depends on whether the water is freshwater or saltwater.  As you descend into the water, the air in your body is significantly compressed.  As depth increases, each breath from your air tank includes more air volume to offset the higher external pressure. When you ascend, the air expands because pressure decreases. (Source: Abyss Ocean World)

If you have ever been at the bottom of a swimming pool, you have likely felt the pressure in your ears and lungs.  This pressure is magnified during a dive. The scuba gear you wear helps to offset the pressurization effects on the air you are breathing; however, the changes on your body are still apparent and need to be kept in mind throughout the dive. 

It is also a common misconception that the gear helps your body not to be “crushed” by the water pressure.  This is not true.  The gear helps you to stay warm and protected while monitoring the amount of air and time you have left for your dive. 

Equalize early and often on descent. Ascend slowly to allow air to exit the ears

A couple of dangerous situations that can happen during a dive are:

  • Crushed by water pressure: Descending into the ocean or any body of water for that matter will exert an increased pressure on your body.  As you descend, the pressure increases and forces the air out of your lungs, thereby causing them to cave in. (Source: Sciencing)  This doesn’t occur anywhere near recreational scuba diving depths.  This is avoidable by not holding your breath at depth. Your regulator will supply you with the correct volume and pressure of air to prevent this, unless you’re thinking about trying to dive to the Titanic! (Spoiler-you can’t.)
  • Squeezes: One common problem that can occur during descent is called a squeeze.  This occurs when the pressure changes and affects both your mask area and inner ears.  There is extreme pain associated with this ailment, but it usually heals on its own with time. Learn to properly equalize on descent, and ascend slowly to allow pressure to decrease before you feel pain.

When the squeezes occur, the pressure causes your face mask to suction against your face.  If you have ever experienced a suction cup on your skin, you likely know how much it pulls at your skin.  The face mask pulls at the skin around your eyes, which can cause bruising to occur.  In a severe situation, blood vessels in your eyes may even be impacted. (Source: Ocean Scuba)

You avoid ear squeezes by equalizing as you descend. You avoid mask squeezes by exhaling a small amount of air through your nose as external pressure builds. If you experience ear pain on ascent, descend to the point where the pain goes away, and try swallowing your saliva a couple of times. You can gently equalize to open your Eustachian tubes, but don’t add much air or you magnify the problem. You can also try rolling sideways to reposition the trapped air.

This is called a reverse squeeze, and it is miserable if you ascend all to the surface without trying to correct it first. Only one of us has ever experienced this, but she felt bad for 24 hours with severe pain for the first 6 hours.

Why is it Vital to Ascend Slowly?

A scuba tank contains compressed air, not oxygen as commonly believed. Air contains 71% nitrogen, which is inert and goes unnoticed when breathing at the surface. But inhaling it under pressure results in a gradual build up of excess nitrogen in various tissues of the body.

Decompression Illness

One of the most critical moments during a dive is the ascent to the surface.  This is the part of the dive that requires careful calculation and patience.  If a diver ascends or comes to the surface too quickly, they may face serious consequences, one of which is decompression illness, often referred to as the bends. 

  • Bends (decompression sickness): The bends occur when the excess nitrogen in tissues expands too rapidly for your body to eliminate it. This excess nitrogen can form bubbles in joints, many different tissues, and the blood stream. Bubbles in blood vessels can be carried to vital organs and cut off the blood supply. Heart attacks, strokes and death can occur.

The bends affect many parts of your body.  Typically, when a diver is suffering from the bends, they will notice weakness or numbness in the arms and legs, dizziness, vomiting, or even losing consciousness.  This is a medical condition that needs to be treated by a physician, as it can affect your entire circulatory system, including your heart. (Source: E-Medicine Health)

The current world record for the deepest dive ever is held by Ahmad Gabr. In 2014, Gabr took 12 minutes to descend to 1090 feet, backed by a team tracking him and helping him switch tanks when needed as I describe here.

After needing just 12 minutes for the descent, he had to take 15 hours to ascend slowly enough to avoid the risks of decompression illness (Interesting Engineering.)

Reverse Ear Squeezes

If the diver ascend too quickly, the air pressure in the middle ear will cause the ear drum to bulge outwards. This is called a reverse squeeze, and it is very painful. My daughter experienced this in Bonaire and had to skip the next few dives.

  • Reverse Ear squeezes: As you descend, the pressure on your eardrums increases. Divers offset that by adding air to the part of the ear behind the eardrum; the middle ear. This is connected to your throat by a small tube (Eustacian tube). Divers can force air through it during descent by closing mouth and nose and trying to exhale. On ascent, this air has to naturally move back through to your throat as it expands.

You can try to fix this by descending slightly until the pain disappears, and then swallow a few times to open the Eustachian tube. If this doesn’t work, you can tilt head with the painful side down and try again. Or go a little deeper and try both.

As a last resort, descend a little further very carefully equalizing to reopen the tube. Then ascend even more slowly with the affect ear tilted up. Keep in mind your dive time, depth, air supply and dive profiles for the day as you do this.

Rupture of lung with air leak (pneumothorax)

The lungs are constantly changing pressure with each breath. They are also the most affected part of the body when external environmental pressures change, such as when ascending to great heights or diving to different depths. Since water is denser than air, pressure changes in the body occur in much shorter distances. At 33 feet, the body experiences twice the pressure felt at the surface.

  • Pneumothorax: Another potentially life-threatening complication from a rapid descent. The lungs are lined by a thin layer of tissue connect their walls to the chest wall. This layer moves with breathing. If pressure in the lungs suddenly increases, a hole can develop in this layer, allowing air to leak from lung. This occurs in chest injuries, sudden pressure change environments and sometimes without any cause at all.

When a pneumothorax occurs on the surface, the effects can range from nothing at all to severe breathing problems and cardiac arrest. The hole that forms can allow air to build up between layers such that the lung is compressed. Or it may continue to leak causing the hole to enlarge and the lung to collapse away from the chest wall. This means it won’t expand when you try to breath.

If it occurs suddenly underwater due to rapidly increasing pressure, the effects are magnified quite a bit. Once it has occurred, it requires emergency treatment, preferably by trained doctors or EMTs in an ambulance or hospital. There are cases where lives have been saved by inserting a small sharp needle into the chest to allow re-expansion. But if done incorrectly, it leads to greater collapse and worsening condition.

When a pneumothorax occurs or is suspected, the diver needs to continue ascent as safely as possible, preferably with assistance, and then get immediate medical attention. In the image below, you see that the right lung has ruptured and pulled away from the side wall of the chest. The dark area represents air in the lining of the lung, while the collapsing lung is whiter because it doesn’t have enough air to expand it.

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An example of pneumothorax from the author’s personal case files. Not a diving injury.

How Do You Ascend Safely?

When a diver begins their ascent, it needs to be carefully planned and executed.  It is recommended that an ascent take place in two different stages that are carefully timed and monitored by the diver.

Stage 1 of the Ascent (Decompression Stop)During this stage of the ascent, the goal of the diver is to reach a safe ascent zone.  This means they are ascending from a deep dive location and will need to stabilize halfway to the surface. This decompression stop allows the body to reacclimate to the changing pressure gradually. It is recommended that a diver not ascend more quickly than 30 feet per minute. (Source: Scuba Diving) If you have been on an extremely deep dive, you may have more than one stopping point before reaching the surface. 
Stage 2 of the AscentThis is the final stage of the ascent and a time to be extra cautious.  It may be tempting to rush to the surface when you can see it just above you; however, you need to continue a slow and steady ascent. It is crucial to slowly release air pressure during this final phase of the ascent to ensure you are correctly depressurizing. 

(Source: Dive Training Magazine)

How Do You Track Your Ascent?

Most scuba divers use a dive computer to track their dive times and frequency and decompression status. The dive computer provides the diver with information regarding the time left for a safe dive as well as the depth they have reached.

Determination of safety stops, time between dives, time spent at each depth, required surface break, and more are tracked. (Source: Oyster Diving) The safety of your ascent will be dependent upon the tools you use as well as the communication you have with your dive partner. Your depth gauge and dive watch or computer are used in tandem. If you aren’t using a computer, then you will rely on manual dive tables to track these things.

The entire time a diver is making the ascent to the surface, they should consult their dive computer as well as their diving partner to ensure they are ascending at a safe rate and leaving enough time for the dive to be completed safely.

Why Can Snorkelers Ascend Quickly?

Snorkeling is much different than scuba diving because it involves swimming at the surface of the water.  They inhale air at surface pressure, and as they descend the air is compressed. When they ascend, it expands only back to the original volume taken in before descent. Therefore, snorkelers do not need to worry about the speed of their ascent.  Snorkelers aren’t taking in pressurized air that can expand on ascent or release higher amounts of nitrogen into the tissues.

Final Thoughts

Scuba diving is a favorite activity for many people around the world.  While fun and exciting, it requires thorough training to execute a safe and successful dive.  The two bookends to a successful dive are the descent and ascent.  By following safety precautions and ascending slowly with dive stops along the way, you will ensure an enjoyable – and safe – dive.