Scuba Diving · 12:50pm Apr 25th, 2018
The deeper you go, the harder it gets.
You're supposed to be certified in order to scuba dive, but rather than covering the dizzying array of organizations and qualifications you can get, I'll mostly focus this blog on the how of diving.
People have always tried to go where they shouldn't. In order to stay underwater, diving bells were first conceived in the early AD years. Aristotle mentioned them.
The old-timey Bioshock-style diving suits with air supplied from the surface were pioneered in the late 1700s.
The first scuba systems came along in the mid-1800s, but it wasn't until around WWII that what we think of as modern systems appeared. SCUBA stands for Self-Contained Underwater Breathing Apparatus. Pretty straightforward. The most common setup consists of an air tank and some way to breathe from it.
A rebreather is a special system that recycles the air and scrubs it. It can provide a longer breathing time and doesn't emit bubbles, but is more complicated and expensive. In digging into the history of diving, I was surprised to learn that rebreathers were actually invented parallel to scuba, not as an evolution.
A standard scuba system is usually broken down into a few common parts.
The first stage connects to the air tank and converts what could be as much as 3000 psi of pressure into something more manageable. The second stage is the mouthpiece, where you breathe. The octopus is an extra mouthpiece to let someone else breathe in an emergency and is usually brightly colored. The low pressure hose connects to an inflatable vest so the diver can control their buoyancy. The console consists of pressure gauges at minimum, but fancy systems can incorporate a computer.
A dive computer uses air pressure, air mixture, dive depth, and time to give you a wide range of information including safe limits for depth and time. Some even have games.
As I stated way back at the start, diving begins easy but gets progressively more difficult the deeper you go. A basic certification usually qualifies you to dive to about 60 ft / 18 m. At this depth, you're under almost three times the normal surface pressure. For short periods at this depth, you can return to the surface immediately with no ill effects.
But for safety purposes, you probably shouldn't. Read on.
The problem comes when nitrogen builds up. Considering that regular air is about 21% oxygen and 79% nitrogen, you can imagine how this happens. The deeper you go, and the longer you stay there, the more nitrogen builds up. When you're under more pressure, you have to breathe more air from the pressurized tank to compensate. It feels like taking a regular breath, but the air is more dense. This also means the deeper you go, the less time your tank lasts.
When you have a lot of nitrogen buildup and subsequently come to the surface and depressurize, nitrogen can bubble out of your blood. This is known as the bends, and it can kill you if severe enough. This is why divers return from depth slowly, decompressing gradually, and make safety stops for a few minutes below the surface. Passing a few minutes' time is where the computer games come in.
After finishing a dive, you should wait a while before diving again to let the nitrogen dissipate. How long? There are tables and charts that show you for X depth and Y time, you should wait additional time Z before diving again.
But a good dive computer will do the math for you.
All this gets way more complicated - and dangerous - once you go past 60 ft / 18 m. Your required decompression time goes up, but you also get into weird problems like narcosis. At certain depths, the air you breathe becomes dense enough that it begins to have an effect similar to drunkenness. Needless to say, deep underwater is a bad place to lose judgement. Additionally, there's the problem of oxygen toxicity. Under enough pressure, oxygen can cause problems like seizures. For these reasons, going past about 130 ft / 40 m is not advised while breathing regular air.
What can you breathe besides air? Nitrox is fairly common. It has a greater percentage of oxygen than the 21/79 mix of regular air. Most commonly, about a 32/68 mix. Nitrox causes less nitrogen to build up, so you can dive for a longer period and with less waiting between dives. However, because of the aforementioned oxygen toxicity problem, you can't dive as deep with nitrox.
Other, more exotic gasses are used to dive deeper. Common kinds are trimix or heliox. These replace some or all of the nitrogen with helium or another inert gas.
Is there a way to get more bottom time? Here we come to saturation diving. The US Navy SEALAB experiments in the 1960s were some of the first efforts to spend long periods in the deep. Essentially, you live at pressure. SEALAB was lowered into the water and pressurized to the same pressure as the water around it. All the divers had to do was just go outside. You don't have to decompress if you never come up headtap.gif
Interestingly, astronauts have been involved. Scott Carpenter spent time in SEALAB II. Here's a video of him breathing heliox and trying to talk to President Johnson.
And here's a video of Chris Hadfield also underwater.
This blog just scratches the surface of some of the effects of diving. Actually doing it takes about a week to get certified with classroom time and actual diving. Math is involved.
As of this writing, I have made 11 dives for a total of about six and half hours of bottom time. My longest ever dive was fifty minutes, on a fairly shallow profile. This gives you a little idea of how long a tank of regular air usually lasts. Different people breathe air at different rates. I'm sort of midrange. My wife somehow uses more than me. Diving instructors usually use less, having trained themselves to do so.
The most surprising thing about diving is how weird it doesn't feel. Other than maybe your ears, it's hard to tell that the depth is changing. This is why you have to be careful to constantly check your instruments and stay within your limits.
Most divers require 8-12 pounds of weight to reliably sink in seawater, which can be overcome by inflating the buoyant vest. Weights are generally lead blocks carried on a quick-release belt.
It's cool that diving is a sport where they recommend you carry a knife.
Ohey, I remember these blogs!
Neat stuff, TNaB.
Pretty interesting. At some point I would like to go diving, but just don't have time or the money to do so.
That reminds me I need to watch the latest episode of Amanchu.
Always a pleasure to read your blogs
You know what’s harder than scuba?
Commercial diving
Greetings form block SS-114#44 in the Gulf of Mexico my man
4847268
Neat. Anything to add?
That screenshot still has me thinking about the whole "bathing in human blood" part. Is there something you're not telling us to our faces? Are you screaming to get out inside because you're stuck in the psyche of a serial killer? PM me if you need help, man. You know I've got your back.