What affect does pressure have on divers?
We’ve looked at how pressure works in both the air and underwater in the pressure lab, but is the body affected by the underwater pressure experienced in a dive? This is one of the most important aspects of underwater diving and is important to the safety and well–being of the diver.
Have you ever noticed when you go up in an airplane or drive up into the mountains that your ears “pop?” Our ears have a space in them that is filled with air. If we change our altitude, the pressure exerted on us changes (just like the pressure changes the deeper in the water you go). The reason we experience this “popping” is due to the fact that gases are compressible. Basically that means there’s space in between the molecules and it’s possible to squeeze them closer together. This closeness of molecules is known as density.
Let’s suppose you take a cup and invert it so that it catches air and dive underwater with it. As you descend, you notice that at 33 feet down (2 ATA) the container is only half full now. No air has escaped, so where has it gone? The air has become compressed by the surrounding water pressure. The air in our container is twice as dense as it is at the surface. Likewise, if you blew up a balloon and took it down, it would shrink to half its original size by the time you reach 33 feet of depth.
Now, what if you were at a depth of say 66 feet (3 ATA) and you inflated a balloon. If you released it, what do you think would happen? It would float to the surface, of course, but what about the size of the balloon? Remember that the air you put into the balloon is under pressure and is three times as dense as it would be at the surface. It's compressed. As the balloon ascends, the pressure decreases, the balloon expands, and might eventually burst! This takes us to an important rule of diving: Never Hold Your Breath!
If a diver held their breath while ascending from depth, their lungs would expand just like the balloon and eventually burst, causing serious injury or death! However, if a diver continues to breath normally as they ascend the expanding air will simply escape with each breath.
This brings us to an important concept known as Boyle’s Law. It states:
“If the temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure.”
This explains our cup, balloon, and diver examples given above.
Find Out More:
- Explore some advanced uses of Boyle’s Law
- Learn About Tanks and Regulators
- Find out about Robert Boyle at Britannica Online.
Lesson design by Lucas Gillispie.