When swimming underwater, we are accustomed to holding our breath. I mean, we’ll drown, if we don’t, so breath-holding is critical to our survival in the water.
But, the moment you put on SCUBA gear and dive beneath the surface, you need to throw all of those reflexes out the window. When you’re SCUBA diving, holding your breath can be fatal…and can be even more dangerous than the infamous decompression sickness, aka “the bends”.
So what happens if you run out of air underwater? Can’t you hold your breath like usual and swim to the surface? Nope. You can’t. This isn’t about common sense; this is about physics.
In the metric system, pressure is measured in bar. Bar is a critical measurement for scuba divers because the air level on our SPG (aka submersible pressure gauge) is measured in bar. Unless, you’re American and use PSI. But, trust me, bar is MUCH easier to use.
So let’s use bar to understand how pressure increases beneath the weight of the sea.
At the surface, we are subject to one bar of pressure or 14.5 pounds per square inch. When we dive underwater, that pressure increases by one bar/14.5 PSI every 10 meters or 33 feet. That means at 10 meters we’re at 2 bar, 20 meters we’re at 3 bar, and 30 meters we’re at 4 bar.
This means that our bodies are subject to these increased pressures the deeper we dive. Just as pressure changes at high altitudes cause our ears to pop, the rapid pressure changes underwater also affect our ears and sinuses. That’s why divers are taught how to equalize the pressure in their ears, so they can descend safely.
So what does this have to do with holding your breath underwater? Well, our lungs are also subject to pressure as we descend, and as the pressure increases, they start to contract. This also happens when you’re swimming and dive deep, BUT there is a key difference.
When you hold your breath and swim underwater, you have no issues because the oxygen content in your lungs remains the same. However, when you’re SCUBA diving, you are always adding and subtracting oxygen from your lungs while inhaling and exhaling.
This is great when you’re breathing normally like you’re trained to do, but it’s not great when you stop breathing, especially if you start ascending while holding your breath.
When you ascend, your lungs and the air inside them will start expanding again as the pressure decreases. If the air expands beyond your lungs’ capacity, the air will have nowhere to go, and it can collapse or rupture your lungs.
This medical condition is called an arterial gas embolism or pulmonary barotrauma. When this happens, the results are often fatal. For this reason, it is probably the most feared scenario among SCUBA divers. However, it is very preventable. Just don’t hold your breath, especially while ascending.
Now, what happens if you run out of air and need to get back to the surface? Well, first, you should always be checking your air and have a buddy nearby to share air with in case this happens. But, if you are alone or separated from other divers, you should start your ascent immediately while slowly exhaling a very small stream of bubbles. This will flush the rapidly expanding air from your lungs as you return to the reduced pressure at the surface.
Okay. So, with all these frantic warnings and scary-sounding medical conditions, you might be a little intimated by SCUBA diving. Don’t be. SCUBA diving is a very fun and safe activity, and there’s no reason to be afraid of diving.
I made this video, so you can be a safer and better informed diver. Like any recreational activity, SCUBA diving can be dangerous, IF you deviate from your training. But, if you stick to your training and keep your buddy close, you will be just as safe beneath the sea as your are in your own home.
Hi, I’m Tidewater Teddy, and I’ve been a certified PADI Divemaster since 2014. If you enjoyed this video, please like it and subscribe to my channel! Thanks and happy diving!!!
Tidewater Teddy 