I recently had my first scuba dive. And the other instructor here was referring to something that is related to air Embolism as I overheard, that one should not surface too rapidly after a deep dive. I could only hear it that it could prove fatal as well.
I know what is Embolism, but i have no wisdom about how the embolism would be introduced when a diver gets to the surface rapidly. Please shed some light here..


2 Answers 2


An embolism in a medical context refers to any large moving mass or defect in the blood stream. An air embolism is an air bubble trapped in a blood vessel. When an air bubble travels along an artery, it moves through a system of blood vessels that gradually become narrower. At some point, the embolus will block a small artery and cut off the blood supply to a particular area of the body.

For example, when a person scuba dives with compressed air, they take in extra oxygen and nitrogen. The body uses the oxygen, but the nitrogen is dissolved into the blood, where it remains during the dive. As one swims back toward the surface after a deep dive, the water pressure around decreases. If this transition occurs too quickly, the nitrogen does not have time to clear from the blood. Instead, it separates out of the blood and forms bubbles within tissues or blood. It is these nitrogen bubbles that cause decompression sickness.

For venous air embolisms, death may occur if a large bubble of gas becomes lodged in the heart, stopping blood from flowing from the right ventricle to the lungs. However, experiments in animals show that the amount of gas necessary for this to happen is quite variable, and also depends on several other factors, such as body position.

  • Your answer is only partially correct :-) I think you need to re-write the 2nd paragraph. You are referring here to partial pressure of the gasses. Which might cause a condition know as Decompression Sickness, this does not just influence the blood and actually could affect you irrespective of the speed of your ascent. There are several good articles on the internet around DCS & AGE. Divers Alert NEtwork would be the best resource but even Wikipedia has a nice summary: en.wikipedia.org/wiki/Decompression_sickness
    – AquaAlex
    Commented Aug 19, 2014 at 12:05

Here is an interesting article on wikipedia to give overview of pressure related injuries. Dysbarism

Embolism in diving would most likely refer to Arterial Gas Embolism (AGE) and the internet is full of articales on AGE, DCS, Baurotrauma etc.

But to give you a quick laymen overview of the issues related with rapid ascents while scuba diving.

In scuba diving we breath gas (in most cases air, but could be Oxygen, Nitrox, Helium, Heliox, etc) under pressure. This means for every breath of air we take the volume will be same as at the surface but the density would be higher. For instance when we are 10m deep in sea water we will breath twice the amount of air which means same volume but double density.

If I now did a rapid ascent while holding my breath or if some obstruction like flem was present in a part of my lung the gas would expand (based on boyle's law) causing a rupture of the lung this can be small or large.

The air in the lung can now enter the arteries and could end up blocking blood flow to the brain, the heart muscle, etc. which will cause heart attack or stroke. If a larger rupture happens we could also have air entering the chest cavity which could cause lungs to collapse.

DCS/Decompression Sickness is different this could happen whether you did a slow or rapid ascent, as this is based on how much gas was absorbed into your body (blood, bone, muscle, etc) And DCS could take several hours to affect you after the dive where as AGE would effect you immediately and normally be much more life threatening.

Please read DAN's article: Decompression Illness: What Is It and What Is The Treatment?


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