Divers ascend slowly to prevent issues such as decompression sickness or spontaneous pneumothorax. Expanding too quickly causes nitrogen to form bubbles in the body before they can be eliminated and increases the volume of air in the lungs too rapidly to equalize properly.
Keep reading as we explain why a slow descent is essential and what it looks like.
Why Can’t Scuba Divers Come up Fast?
Scuba divers cannot come up fast because of these unwanted reactions in the body.
Understanding Boyle’s law sets the foundation for understanding these complications.
The law explains that, in a closed system where temperature and the amount of gas remain the same, the absolute pressure of a gas tends to decrease as the volume increases.
When you apply this to scuba diving, you see that the decrease in water pressure during your ascent relates to an increase in the volume of gas in your body.
This not only affects the volume of air in your lungs, but it can cause gas in other areas of your body to form bubbles that cause complications.
What Happens If You Ascend Too Quickly Scuba Diving?
Your main concerns with ascending too quickly include decompression sickness, collapsed lung, and arterial gas embolism.
Decompression Sickness
Your body absorbs excess nitrogen gas as you descend. The volume of the gas decreases the further you dive, and slowly soaks into the tissues of your body.
Following a specific rate of ascent allows your body to deal with the nitrogen efficiently as it expands. When you ascend too quickly, the nitrogen expands at a rate where it cannot be eliminated, leaving behind small bubbles in your tissues.
Not only is this painful, but it can lead to tissue death and even prove fatal. Your response to decompression sickness plays a part in this, but avoiding it is always the best course of action.
Collapsed Lung
If you ascend too quickly to equalize the pressure in your lungs, you put yourself in a position where your lung may collapse. This happens most often when holding your breath on ascent, and you may be at a higher risk if:
- Your lungs are weakened by a disease
- You have previous lung injuries
- You smoke or have sufficiently irritated your lungs
These conditions lead to the formation of blisters on your lung’s alveoli that easily rupture, even with normal pressure.
Regardless of the cause, if there is a tear in lung tissue it allows air out into the pleural space (between the chest wall and the lung). The pressure here is normally negative, meaning less than atmospheric, but the increased volume of air leads to positive pressure that pushes against the lung, pushing out more air.
Eventually, this causes the lung to collapse in on itself.
Arterial Gas Embolism
An arterial gas embolism refers to any blockage of blood to the organs. This is caused by bubbles in the artery, and it’s a leading cause of death in scuba divers.
This happens when the gas in your body forms a bubble that cannot be eliminated. When these enter arterial or venous blood, usually after pulmonary barotrauma or decompression sickness, they can travel to any organ and cause a blockage.
The bigger worries here are blockages that deprives the brain or spinal column of blood, but this can also affect your:
- Heart
- Skin
- Kidneys
The blockage usually leads to loss or impediment of function, as well as injury to the affected organs.
Why Do Scuba Divers Exhale and Rise Slowly When Ascending?
By exhaling and rising slowly while ascending, scuba divers limit the chance of the issues listed above. This may not be exciting, and it’s certainly a pain when you’re tired from your dive, but it’s a necessary safety measure.
Scuba divers also use stops at depth and near the surface to safely deal with the buildup of gas in their bodies.
Safety Stops and Deep Stops
A safety stop usually happens at 15 feet (5 meters) below the surface for a period of 3 to 5 minutes. This gives the body time to work with any additional nitrogen while still under the higher pressure of water before your final ascent.
A deep stop is usually added to dives 70 feet (21 meters) or deeper, but it changes based on your dive profile.
The Divers Alert Network notes that divers who ascended at a rate of 30 feet per minute without a safety stop ended up with fast saturation tissues at 60 percent. When the same divers had a 5 minute safety stop at 18 feet, this decreased to 35 percent. When they added in an additional deep stop for 5 minutes at 48 feet, the saturation dropped to 25 percent.
How Do You Ascend Slowly When Diving?
Your final ascent should be the slowest part of your dive. This is when the greatest pressure change per foot of depth occurs, and nitrogen and other gasses expand most quickly at this point.
By taking it slow you allow your body extra time to deal with these gasses and reduce your risk of decompression illness and other issues.
How Fast Should You Ascend While Diving?
You should never ascend faster than 30 feet (9 meters) per minute. This means it can take you a minimum of 5 minutes to ascend after your safety stop.
Preparation
Before you make your final ascent you should make sure the space above is clear of boats. If you notice anything , including a shadow, it’s best to find somewhere else to surface.
Listen for motors from boats, and either wait for them to pass or move if you hear anything.
When you’ve found your area of accent, inflate and release a surface marker so boats other people know where you are ascending.
Making Your Ascent
After your safety stop, start your ascent by kicking slowly and deflating your buoyancy control device.
Deflating your BCD prevents it from excessive expansion as the volume of gas increases. This would cause you to float too quickly. You can also slow your kicking if you find you’re moving too quickly.
Check your dive computer to make sure you’re moving at the right speed.
Surfacing
When you’re close to breaking the surface it’s best to cover your head using your free arm. You should still look for obstructions, but breaking through with your arm protects you from last minute problems like a motorboat speeding across the area.
Inflate your BCD bladder completely the moment you break surface. This helps you stay above the water while you return to the shore or your boat, and you have an easier job getting out of the water.
References
https://www.downtoscuba.com/how-to-ascend-in-scuba-diving/
https://www.omegadivers.com/why-is-ascending-slowly-important-when-scuba-diving/