Do you know what happens to your lungs when you take a breath and dive in with your mask and snorkel or what happens to the lungs of professional free divers who can stay underwater for minutes at a time on just one breath? What about when you take scuba gear with you and breathe compressed air throughout the dive? Two completely different processes are at play in each case and they show how truly amazing the human body is.
If you take a breath of air and dive in to admire the beauty of the underwater world, technically you are a free diver. Free diving has become a serious sport in its own right. Professional free divers train extensively to be able to hold their breath for prolonged periods of time, to control their mind and body underwater. However, the principle is the same – even if you are not a professional free diver and simply decide to dive in to a couple of metres for a few seconds with a mask and a snorkel, your body undergoes the same transformations as those of a professional free diver. One of these transformations is what happens to your lungs.
Your lungs fill up with air when you take a breath. Under pressure air, like any other gas mix, compresses (imagine squeezing an air balloon). The same happens to your lungs when you dive in on one breath: at 10 metres of depth the surrounding i.e. ambient pressure is twice the pressure on the surface, meaning that your lungs will squeeze to half their original size. When you go down to 20 metres, they will squeeze to 1/3rd of their original size, to 30 metres – 1/4th, to 40 metres – 1/5th, and so on.
So how is it that a free diver’s chest does not get crushed under so much pressure given that his or her lungs occupy just a fraction of space they did on the surface? This is because as soon as a diver’s body is submerged under water the Mammalian Diving Reflex sets in, one of the adaptations of which is called the Blood Shift effect. A free diver’s blood shunted from the extremities travels to his/her chest cavity and occupies the empty space. Unlike gases, liquids are not compressible under pressure. Have a look at this amazing free diving video: Guillaume Nery’s, a French free diving champion’s Free Fall into the Blue Hole.
Unlike in free diving, scuba divers’ lungs are not squeezed under pressure. Why is that? The reason is that scuba divers breathe compressed air. A typical scuba diving cylinder is filled with a gas mix (regular air or Enriched Air Nitrox in recreational diving) pressurized to 200 ATM (atmospheres) or BARs. Regulators that scuba divers use are designed to supply them with air from the cylinder at ambient pressure, for example, at 2 BARs at 10 metres, 3 BARs at 20 metres, 4 BARs at 30 metres, and so on. This means that with every breath a scuba diver takes, he or she takes in breathing gas that fills up their lungs at ambient pressure, allowing the lungs to remain the same exact size as on the surface.
The only caveat is that the deeper a scuba diver descends, the denser the compressed breathing gas becomes and the more of it the diver takes in with each breath. On deep dives scuba divers consume much more breathing gas than they do at shallower depths. It is for this reason that the number one rule of scuba diving has always been and always will be: Never Hold Your Breath! If a scuba diver ascends from 40 metres to the surface while holding their breath, his or her lungs will expand to 5 times their regular size on the surface. For your own entertainment, check out Ahmed Gabr, Egyptian special forces soldier, who has achieved a Guiness world record scuba dive to a whopping 332.35 metres (1,090.3 feet). Have a look at his Deepest Scuba Dive Training Video.
We hope you found this article entertaining and informative. Stay tuned for more!