These neat little tricks are survival reflexes, designed by our brain and executed automatically to save us from an immediate lethal hazard.

There’s just one catch, though: they were designed to be efficient on Earth. Not at the bottom of the Ocean. So you might want to teach your brain a new trick: how to override these 3 survival reflexes, that are sure to do a lot more harm than good, if triggered under water.

1. Holding Your Breath: a Lung Overexpansion Waiting To Happen

You are immersed in a body of water, and suddenly something goes wrong: before you realise it, you are holding your breath. The same happens if you start getting water in your regulator: breathing stops.

Because that makes sense, right? You are in difficulty in a hostile environment, plus your body might detect unproper substances within your latest inhalation. So naturally, you hold whatever « good air » is already inside your lungs, and avoid further contamination by sealing that bag shut.

Why it’s the worst idea?

Holding your breath under water is fine if you’ve filled up your lungs at the surface, and you are keeping that same breath all the way down, and back up. This is why free divers don’t suffer terrible injuries.

But the deal changes if the breath you’re holding is one you took at 10 meters-depth, and you intent to release it once you’ve broken the surface.

A bit of physics will help you get the drift. Here’s what Boyle’s Law states:

« The volume of a gas in a flexible container is inversely proportional to the absolute pressure. »

Your lungs are a flexible container, of about 5 Litres at the surface, when the absolute pressure is 1 bar. At 10 meters-depth, the pressure is equal to 2 bar. Twice as much pressure. But you don’t breathe with half your lungs as you descent while scuba diving, so what happens?

At 10 meters-depth, you still inflate your lungs up to their 5 Litres maximum capacity (because you’re inhaling air at ambient pressure, you’re just breathing in more air than you would at the surface. This is why the deeper you go, the quicker your air supply goes.)

Let’s assume you fill up your lungs at 10 meters, then shoot for the surface while holding your breath. Boyle’s Law says that pressure and volume are inversely proportional. So if from 10 to 0, the pressure is divided by 2 (from 2 to 1 bar), then the volume of the gas trapped in the flexible container (your lungs!) will be multiplied by 2 : from 5 to 10 Litres.

Can your lungs handle 10 Litres of gas? No they can’t. And since they are « a flexible container », not a solid one, they will expand, then rupture. The lungs can expand about 30% of their capacity, but not 100%. So if the volume they hold doubles, they will rupture.

This injury is called a lung overexpansion, and you do not want to experience that. It’s mostly irreversible and can be fatal.

How to avoid it?

Fortunately, it’s super easy to avoid: DO NOT HOLD YOUR BREATH. EVER. Especially NOT while ascending.

Cue your brain to that one, as there’s no other trick than NOT DOING IT.

2. Clearing Your Airways: How To Drown Quicker

So you’ve decided that breathing is safer than holding your breath (good for you!). But then you’re feeling like you’re not getting enough air. You are probably overexerting yourself, and your brain is telling you that you need to BREATHE MORE.

And because that survival reflex was intended to be triggered above water, the diagnostic is all wrong: your brain will tell you that you would be able to breathe a lot more if you got rid of all that stuff that’s obstructing your airways, like that thing against your nose, and that other thing inside your mouth.

Ditch all that, then take a great, big inspiration!

Right. This results in a surprising, but terrifying sight of a panicked diver ripping out his mask & regulator, as he shoots for the surface.

Why it’s the worst idea?

That, of course, is unlikely to end well. In lieu of the desired big gulp of air, it’s a big gulp of salt water that the lungs will get. Unless a rescue diver or a very quick-to-act buddy brings you up to the surface, and proper care can be administered as soon as possible, you’re about to become a case of drowning and/or decompression illness.

How to avoid it?

Again, the first thing you want to do is teach your brain that under NO circumstances should you be removing your regulator.

That being said, there’s another trick in store to manage this type of situation: your brain doesn’t actually react to a lack of air, it reacts to the excess of carbon dioxide.

When you are overexerting yourself, you are taking shallow breaths, and you are failing to exhale properly. It’s a downward spiral: you don’t get rid of the carbon dioxide your body is producing, so the brain detects excessive CO2, so it tells you to BREATHE MORE, so you try to inhale more, failing yet to exhale all that CO2.

The solution is easy: EXHALE! I know your brain is screaming that you need MORE AIR inside your lungs, not less, but you do though: breathe out, breathe out, and breathe out.

Do this until you can resume your slow, normal breathing pattern, with exhalations lasting 3 times your inhalations.

If the overexertion event has lasted a few minutes, you will likely be running out of air. So you and your buddy should be making a controlled ascent & exit soon.

Remember to keep exhaling abundantly as you make your slow way to the surface, regardless of what your brain might tell you: going up is the worst time to be holding air in (refer to the 1st point!)

3. The Gag Reflex : One Second Drowning Guaranteed

The gag reflex is another clever design of the body’s defence against all sorts of internal invasion. If you ingest something that can’t be digested, if your stomach is being attacked by foreign organisms, or if something is going down the wrong way, your body will defend itself by expelling the intruder efficiently.

This is why throwing up is not controllable: it happens, you let it happen, there’s no way to hold it in more than a few seconds.

You can throw up under water, because there’s no way to stop that reflex from kicking in — nor should you want to.

But under no circumstances should you remove your regulator before doing so.

Why it’s the worst idea?

No one likes to remind themselves of the last time they had to throw up, so I’ll cut down to the point: right after that happens, you take a forceful inhalation. That’s a reflex, and again, there’s no way you can stop yourself from taking that breath.

You see where I’m going with this? If you’re under water when you feel the need to vomit, and you take your regulator out of your mouth, you will inhale water right after, with absolutely no way to stop yourself.

How to avoid it?

It’s the simplest solution of all: do not take your regulator out of your mouth! You can absolutely throw up inside, it’s designed to handle that as well. It won’t be the most pleasant experience of your life, but at least, you will live to tell the tale.

Wrap it up

The key to surviving under water is to keep breathing: as long as you are connected to an air supply, nothing should go wrong. Sometimes, a technical difficulty will cut out your air, but that’s why you should never dive alone: your buddy will be there, ready to share his tank with you.

Most of the times that you feel air-deprived, you are doing this to yourself. Remember to take deep, slow breaths, and exhale for even longer periods.

Whatever might happen down there: do not take your regulator out of your mouth. I guarantee you this won’t be a solution to your breathing problem…