I understand that breathable air behaves differently underwater due to higher ambient pressure, and that for some reason it causes bubbles in your blood vessels if you ascend too quickly. But I couldn’t understand why that is.
Additionally, given the same supply of air tank, why is it the case that if you are living in a underwater habitat, then you can dive for longer hours as opposed to someone who came down from the surface?
In: Biology
The lungs have a membrane which allows gasses to pass through but not blood. So any gas can freely pass between your blood stream and the air in your lungs. The reason for this is that any oxygen in the air can freely enter the blood stream and be carried away to the cells and any carbon dioxide that have been dissolved into the blood will be released into the air. But the process is not limited to those gasses but any gas in the air will dissolve into the air, although usually in smaller quantities.
When you dive under water you increase the pressure. This means that your lungs need more air to fill the same volume which increase the amount of oxygen and nitrogen in your lungs. Oxygen is actually toxic in large concentrations and if the concentration is high enough even nitrogen is toxic. So divers usually change the mixture and might even use another gas like helium to pressurize with. But all these gasses will dissolve into the blood stream. And since there is much more gas in the high pressures there will be more gasses dissolving into your blood. This is not a big problem as it does not really take up any space in the blood stream and is relatively harmless. The problem is when you try to ascend back to normal pressures. A commonly used demonstration is when you open a pressurized soda bottle and see all the bubbles form in the soda as the dissolved gasses comes out of the solution. This is pretty accurate as to what is happening in your blood if you ascend too fast. The solution to this is to spend more time when heading for the surface so that the dissolved gasses will slowly get out of your blood stream through the lungs.
The problem to this is that it takes a lot of time. Especially if you have been working at deapths for some time and allowed a lot of gasses to dissolve into your blood. If you go deep enough you will often spend more time and oxygen ascending then actually working on the bottom. The solution to this is satturation diving. You use a diving bell which can keep the pressure at the same level as the deapths you are working at. But when the diving bell is closed it can be raised to the surface and even connected to other pressurized habitats where the divers will be living with their blood satturated with gasses under pressure at all times. This allows a team of divers relative comfort and the ability to go to and from the work site without having to spend a lot of time depressurizing between dives. These dives often takes place far out to sea so when the work is done they have a lot of time as they head back to land when they can slowly release the pressure in the habitat so the gasses that is dissolved in the divers blood have plenty of time to get out throug the lungs. It is a very dangerous job though as any issues with the equipment might release all the pressure at once killing the divers either by the strong winds created and related debris or by having all the dissolved gasses in their blood release from the blood. So today most deep sea dives is done exclusively using robots.
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