How SCUBA Diving Works

Podcast Transcript

SCUBA diving is a popular activity that has recreational appeal and commercial uses.

Most people who have never gone SCUBA diving think that it is just a matter of breathing air out of a tank when you are underwater. However, there is a lot more to it.

In fact, solving the problem of underwater breathing wasn’t solved until after humans discovered artificial flight and split the atom.

Learn more about SCUBA diving, its history, and how it works, on this episode of Everything Everywhere Daily.

If breathing underwater was nothing more than getting air to someone one who is below the surface, then some equivalent of SCUBA diving would have been invented centuries earlier.

There were stories from Ancient Egypt of people hiding below the surface of the water who used reeds as a snorkel.

In the 18th century, there were experiments where people underwater were hooked up with air hoses and air was fed down to them via hand pumps.

So, yeah, believe it or not, the fundamental problem wasn’t getting air down to someone in the water. The main problem was pressure.

We don’t tend to think much about pressure because we really never notice it from where we sit on the surface of the Earth. The pressure coming from the atmosphere is in equilibrium with the pressure inside of us.

However, the Earth’s atmosphere actually has a lot of pressure. You might have seen experiments where someone heats up an oil drum that is open at the top, then they seal it and cool it off.

As the air inside cools down, it reduces the pressure inside the drum, and eventually, it is crushed by the power of the atmosphere’s pressure.

You also might have noticed pressure changes if you’ve been at a high altitude or flown in an airplane and you’ve had a headache or you’re ears would pop.

Just as the atmosphere has pressure, water exerts even more pressure.

If you go down just 10 meters or 30 feet below the surface of the water, the pressure is twice what it is at the surface.

When the pressure increases, it becomes very difficult, actually near impossible, to breathe air which is at 1 atmosphere of pressure. The pressure on your lungs from the water would prevent you from breathing in the air at a much lower pressure.

In a submarine, here I’ll refer you to my previous episode, the solution is just to create a very strong container that can withstand the outside pressure.

Early diving bells just used the fact the air pressure will equal water pressure when an enclosed space full of air is submerged with the opening at the bottom. If you remember back to my episode on the Brooklyn Bridge, that was what they used and it was extremely dangerous and caused all sorts of problems.

Systems with air hoses and diving helmets were in use in the 19th century, but those had inherent dangers as well. The supply of air had to be delivered in real-time, and if anything happened, the air would be immediately cut off.

The ability to store compressed air in cylinders came about in the early 20th century, and there were early attempts at using them to breathe underwater.

The big breakthrough, and the creation of the basic system we use today, occurred in France during World War II.

Two men, Jacques Cousteau and Émile Gagnan developed a system of air regulators that made it possible to breathe compressed air underwater.

Gagnan was an engineer and Cousteau was an explorer and a sailor.

Here I’ll explain how the system works.

Most people think that you just breathe air directly out of a cylinder when you are diving. That would be impossible because the pressure of the air inside the cylinder is usually around 200 atmospheres of pressure.

Breathing from it directly would be like drinking from a firehose.

What the regulator does is regulate the pressure of the air as it comes out of the tank.

A SCUBA system will have two regulators. The first stage regulator is attached to the tank. What it will do it allow air to come out and reduce it to an intermediate pressure, usually around 9 ½ atmospheres of pressure. Still, too much pressure to breathe directly.

The second stage regulator is what goes in your mouth. This takes the intermediate pressure air and lets you breathe it in at whatever the ambient water pressure is.

That last bit is really the key point. Just as you don’t notice pressure on the surface because the pressure in your lungs is at equilibrium, so too does a SCUBA regulator keep the pressure in your lungs at equilibrium with your surroundings when you are underwater.

This is why the deeper you dive, the more quickly you will exhaust your air supply. You are breathing it in at a higher pressure, so there are more total air molecules you are breathing in every breath.

Likewise, the regulator in your mouth will also vent air out into the water whenever you exhale. This is called an open-circuit system. A closed-circuit uses something called a rebreather which lets you reuse oxygen you exhale, but those are almost never used in recreational SCUBA diving.

A regulator will also always have a gauge attached so you can see the pressure in your tank as well as a backup second stage regulator in case you or your diving partner are having problems with theirs.

It is a very elegant system that just works. I’ve known people who have literally vomited into their regulator and it managed to expel everything into the water and kept working. I don’t recommend that, but it just shows how robust a regulator can be.

While air is obviously the big problem with diving, it isn’t the only problem.

Most of what you have on you when you are diving, especially in salt water, will float. Your body will want to float, your air tank floats, and if you are wearing a wetsuit, that too will float.

The question then is how do you manage to dive when everything you have is trying to make you float?

The answer is lead weights.

If you go diving somewhere, part of your gear will usually be a weight belt. You will put lead weights on the belt and the amount of weight will usually depend on your weight. The bigger you are, the more weight you usually need.

This still doesn’t really solve the problem, however.

Once you dive down, you don’t want to sink to the bottom either. You want to be able to control your buoyancy. In the 1960s, the first vests were developed that let you do just that.

Basically, inside the vest, there are air bladders that attach to your air tank. You can control the bladder by pressing a button that will either inflate or deflate the bladder depending on what you need.

It is something you need to adjust as you dive because the deeper you go, the more the increase in pressure will squeeze the air bladder, reducing its volume, and hence its buoyancy.

These are usually called BCDs or buoyancy control devices. Once you get the hang of how to use it, you can literally hover in the water, neutrally buoyant.

The other big issue, probably the biggest issue, is safety. You might be thinking that the biggest safety concern when diving is running out of air.

To be sure that is something to keep an eye on, but that really isn’t the biggest threat. Problems with air supply almost never happen, and if you are diving with someone else, then you can easily use their backup regulator and get to the surface.

The big danger when SCUBA diving, and the thing they will always hammer home when you are learning how to dive, is decompression sickness, aka the bends.

This happens when you return to the surface too quickly when you been down too deep.

If you remember in my Brooklyn Bridge episode, the bends caused multiple injuries and deaths during its construction because people would go from a high-pressure environment to a low-pressure environment quickly.

The nitrogen in your body can literally turn into bubbles. The deeper you dive, the more time you have to take to get to the surface.

The deepest dive I ever did was about 45 meters or 150 feet in Papua New Guinea. We went down to see pygmy seahorses. We went directly down, and then spent the rest of the dive slowly coming back up to the surface.

That is why the limit for recreational SCUBA diving is given as 40 meters. Once you get below that point, you enter the realm of technical diving.

To give an example, the world’s record for the deepest dive using SCUBA equipment was set in 2014 by an Egyptian army officer named Ahmed Gabr. He is an incredibly experienced diver who spent years preparing for this dive.

He went down to a depth of 1,090 feet, four inches, or 332 meters.

The amazing thing is that he went from the surface down to that depth in just 12 minutes. Coming back up, however, took him 15 hours.

For most recreational diving you do, the standard rule is to make a safety stop at 5 meters for 3 to 5 minutes at the end of every dive. If you dive deeper, you might need an extra stop.

The vast majority of dives will use plain old compressed air. However, sometimes it might be possible to use special mixes like Nitrox.

Normal air is about 78% nitrogen and 21% oxygen. Nitrox mixtures will have more oxygen. This is primarily to offset the effects of what is called Nitrogen narcosis, which is a lightheadedness that can be experienced at depth. It isn’t designed for extremely deep water dives.

There are other mixtures for very technical dives such as Heliox, which is a mixture of helium and oxygen.

I actually got nitrox certified back in 2007 in Palau, and then I think I actually used nitrox one time after that because it is almost never available or necessary.

The amount of time you can dive is of course dependent on the amount of air you have. How long your air lasts will depend on several things including how deep you dive, how exerted you are, and how big you are. Men tend to have larger lung capacities and go through air faster than women.

The average for me tends to be about 45 minutes, but that can vary. I’ve had dives as short as 30 minutes, mainly because I wasted so much air trying to stay buoyant with a massive underwater camera, and I’ve had dives that almost lasted an hour because it was a very shallow dive and we never went below 10 meters.

If you are interested in learning how to SCUBA dive, it isn’t hard. There is a short certification course that can often be done in 3-4 days and much of that is classroom material which can be done separately. If you go on vacation somewhere, you can often get certified at a resort, and there are often dive shops in most decent-sized communities.

You don’t really even need to invest in any equipment. Dive shops will almost always have everything you need.

Diving is pretty much down to a science now, and if you are interested in seeing more than the 30% of the Earth which is land, it is really your only option.