Peter Avila • 7 months ago

HOW SCUBA WORKS | Why Can’t We Just Use a Long Hose?

Scuba diving takes us into a stunning world where we experience thrills, majesty and beauty that is very often beyond what we had once been able to comprehend. But while the ocean supports the largest diversity of life on our planet, we aren’t one of them. It can’t support our lives. When we go into that world, we must bring life support with us.

Yet, we are not entirely outsiders to that world. With a composition of 80% water and a salty bloodstream, the human body is like a sack of ocean. Like the ocean, we’re non-compressible. That’s why we can dive to great depths and great pressures without getting crushed.

In this series of articles, we’ll explore how diving works. You might be amazed by how your body works and by how you can work together with it so that you can come back to safely enjoy the wonders of another world again and again.

Of course, we have to take air with us when we dive, but how complicated does it have to be? Why can’t “life support” simply be a long hose with one end secured above the surface? Why do divers lug around those heavy, bulky tanks? Is all that really necessary?

Think about what happens when we breathe on land. As we suck air into our lungs, the air rushes in and pushes the lung walls outward, allowing the lungs to inflate. The air can do that because it has enough force. Every gas or liquid, including air, has a force that it exerts on objects it touches. We call that force pressure. Because the air entering our lungs is the same air that surrounds us, both are at the same pressure, and so the air entering the lungs can easily push back on the pressure outside the lungs and the lungs can inflate, allowing us to breathe.

Now, let’s say that we rig a long hose with one end above the surface of the water and breathe through it as we descend. As our depth increases, so does the surrounding water pressure, but the pressure of the surface air in the hose doesn’t change; it remains at surface pressure. You might see where this is going. When we try to suck air from the surface into our lungs, that air just doesn’t have enough pressure to push back on the higher surrounding pressure, and our lungs won’t inflate. It would feel like sucking on a blocked straw—no air! That’s not a good deal for anyone who enjoys the finer pleasures of breathing. (In reality, the air would never reach our lungs in the first place, because the higher water pressure would collapse the rubber hose shut. But even if we were to use a steel pipe that didn’t collapse, we still wouldn’t be able to inflate our lungs.)

To inflate our lungs, we need to breathe air at the same pressure as that of our surroundings—just like we do on land. To complicate things, the surrounding pressure keeps changing as we move up and down the water column during a dive. We need an apparatus capable of delivering air to us at whatever the ambient pressure happens to be at the time we inhale. We need a Self-Contained Underwater Breathing Apparatus (SCUBA).

A key part of the SCUBA is the regulator, a device that can lower the pressure of a gas down to the surrounding pressure. That’s down. It doesn’t know how to increase the pressure, just lower it, so it can only do its job if it has a supply of gas that is always at a pressure that is higher than the surrounding pressure. Scuba tanks carry gas (usually air) at pressures high enough to give the regulator what it needs at all times. They’re heavy on land but you barely feel them when diving.

Please be careful! As explained in this article, scuba diving requires breathing gases at high pressures. Breathing gases at high pressures comes with hazards that we can easily and safely manage with the proper training, but that can have fatal results if we don’t know what we’re doing. Only scuba dive if you are certified or under the direct supervision of an active instructor. Your safety comes first!

Read Part 2: How Does Your Body Respond to Pressure?

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