ELI5- Why is it dangerous for a scuba diver to ascend too quickly?

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ELI5- Why is it dangerous for a scuba diver to ascend too quickly?

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Your body needs to adjust to the pressure change between the surface and the large depths divers might travel down to. Our body isn’t just a solid mass and so has air pockets inside, and these need to be released slowly and not put into a frenzy due to a rushed dive.

The deeper you go in water, the more pressure is applied to your body. Your body have a good amount of gas inside of its tissues and that gas is compressed by that pressure. If you go up too quickly, that gas expand too fast to escape the inside of your tissues and that expansion can create damage to those tissues.

If you go up slowly, the gas have time to escape as it expand, causing no damage. Sometime, you might need to do decompression stop, meaning you need to stay for some time at different depth to leave enough time for gas to escape. The more time you spent at depth and the deeper you go, the longer you need to take to get to the surface. At some depth/amount of time it can last several hours.

Effectively, you get a condition commonly called “the Bends”, but is properly known as decompression sickness.

Basically, the oxygen tanks used by divers have compressed air which includes nitrogen gas. With the higher pressure exerted by the water below a certain depth, that nitrogen gas gets absorbed into the body’s tissues.

When you ascend out of that pressurized underwater environment, and the pressure decreases, the nitrogen begins to form little bubbles in your body.

These bubbles can cause an excruciating amount of pain and can require medical treatment. Hence why planning and self-discipline when you dive is key — if you take the proper amount of time to ascend to the surface, you won’t get the decompression sickness, and you’ll feel fine.

Or course, there are exceptions to this rule and there’s far more to it than that basic little outline I gave. But generally, that’s the simplest way to describe it. In extreme circumstances it can be fatal, though this is rare. Nevertheless, I’ve talked with divers who had it, and they highly recommend never attempting to get the bends, unless it’s an emergency situation. Even then, it’s dangerous.

I didn’t see it mentioned, but it’s nitrogen gas that causes the issues seen in the bends.

Substituting helium for nitrogen can help prevent decompression sickness, and allow for deeper dives, but it is a lot more expensive.

After breathing pressurized air (at depth) there are 2 major problems.

1: For anyone, you can’t hold your breath while ascending because your lungs will pop as the air expands (there’s less pressure at the surface than underwater). So go slowly enough to breathe out thoroughly.

2: For some few highly-qualified divers, who go deep & long, they might need to make stops at certain depths and hang there just breathing to let the excess nitrogen come out of the blood & be breathed away. Not doing this can cause nitrogen bubbles in… let’s say “inconvenient places”… Inside a blood vessel, so blood can’t pass. Inside a joint. Inside the spine (nerve bundle). It’s painful & damaging.

Dissolved gasses in your blood emerge as bubbles from solution due to the effects of rapid decompression, which in turn is caused by too quick of a reduction in external pressure as you rise quickly from deep water to shallow water. Known as compression sickness or the bends. Just like when you open a carbonated beverage.

These gas bubbles can wreak havok on your lungs and venous systems through gas embolism and cause central nervous damage leading to paralysis, coma and even death.

For the ELI5 answer, rising quickly does to your body what opening a can of soda does. Gas you breathe under pressure suddenly has much less pressure and comes out of your tissue like bubbles in a soda and causes damage.

It’s important to note that if you are snorkeling or free diving, you can rise as fast as you want because you weren’t breathing air under pressure.

Imagine a bottle of sprite when you first open it, the gasses that are absorbed in the soda spontaneously turn to bubbles when the pressure inside the bottle drops. By rising too quickly underwater, this same phenomenon can happen in your blood/tissues. Bubbles in your blood kills you.

Ascending too quickly from a depth can cause excess nitrogen from your oxygen cylinders to get absorbed more quickly by the blood due to the high pressure. More the pressure, more is the solubility of a gas. Too much nitrogen in the blood would mean too little oxygen is reaching your lungs and nitrogen bubbles will block your blood vessels a condition called “The Bends”.

as you dive, the pressure increases 1 bar (1 atmosphere) for every 10M of depth. so as you go down you have more pressure on you. with that, you have gasses in your body being compressed and you are breathing air that is compressed. so air pockets, and existing air in your body will change in volume as pressure changes. because scuba tanks are generally filled with air and not pure oxygen, there’s about 71% nitrogen that usually would go unnoticed if breathed at the surface. but because you’re breathing it compressed and under pressure, it will build up an excess amount in various tissues in your body. as you ascend, if you do it too rapidly, it’ll expand from the tissue faster than your body can absorb it, causing a buildup that can form nitrogen bubbles in joints and the blood stream making it so the bubbles will disrupt the supply of blood to major organs.

TLDR: nitrogen is breathed and compressed in the body, building up. if you rise too fast, it’ll expand in your body and can create nitrogen bubbles that will disrupt vital blood flow, causing heart attacks, stroke and death.

source: certified open water diver