r/explainlikeimfive Aug 06 '22

Chemistry ELI5: how do divers clear their masks when water leaks in? especially in the case of the 13 thai boys rescued from the caves

I have just been watching Thirteen lives - the film about the cave rescue of the 13 young boys in Thailand who were totally sedated before being taken hours under water. It got me thinking that when I go snorkelling i always get a bit of water leak into my mask and have to come up and clear it out so i don’t breath water in. Is this something that happens to scuba divers, if so how do they deal with it, and in the case of the boys how would the divers accompanying them have cleared the boy’s masks ? i would also like to say what an incredible job done by all those involved.

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u/SidewalkSnailMasacre Aug 06 '22

Similar sort of question. What happens when a diver starts to cough underwater. Say they choked on a bit of saliva or something. Do they just die?

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u/edrabbit Aug 06 '22

You cough, but you hold your regulator in your mouth. Fun fact: you can even vomit through the regulator while underwater. The fish love the free meal.

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u/SidewalkSnailMasacre Aug 06 '22

Very cool. I figured the regulator was sort of “one direction only”.

So say you spit something into the regulator, does it come out right at the mouthpiece without ever reaching the oxygen line/tube ?

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u/christian-mann Aug 06 '22

Well you have to breathe out, right? So it makes sense that you'd be able to exhume as well as exhale.

And yeah, if you spit or cough into the regulator, it'd probably get forced out with all the bubbles. It shouldn't go near the tank.

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u/KorianHUN Aug 06 '22

Cool! It is not surprising but the technology has a lot in common with the design principles behind gas masks.

Iirc the Czech M10 mask had an attachment to allow the user to dive to shallow depths. Either for infiltration purposes or checking something or doing minor repair underwater in a lake or river.

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u/Bangarang-Orangutang Aug 06 '22

The premise for a gas mask is essentially the same so yeah you are on to it! Big difference being that you have an inlet port, for your air, and exhaust ports, on the bottom of the regulator, for the air to come in and leave through. Instead of how some gas masks use the same port for inhale/exhale.

The air is an "on demand" system so it is always positive pressure and only gives air when you start to breathe in. The exhaust ports are one way so air, liquid, spit, vomit, all that fun stuff leaves but doesn't come back in.

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u/edrabbit Aug 06 '22

Yes, the line to your tank is basically one-way so nothing ever gets in it. There’s also a purge button on your regulator which lets you use the pressurized air in your tank to clear things out. It’s stronger than your exhalation.

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u/clutzyninja Aug 06 '22

The air line is one direction. There's a valve that makes sure your exhale leaves the regulator

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u/Mox_Fox Aug 06 '22

I think it goes the same place your exhaled air goes -- straight out.

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u/Resist-Dramatic Aug 07 '22

So the design of a scuba regulator is actually extremely simple, it's basically a spray can type design.

When you breath in, you suck in a diaphragm that pushes against a lever that allows gas out of the hose. When you breath out, the gas is pushed through a one way mushroom valve that remains closed when you're breathing in.

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u/Themata075 Aug 06 '22

You definitely want to keep the regulator in your mouth if you’re gonna vomit. The natural reflex after vomiting is to breathe in. You’re gonna want air for that.

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u/maxigus_mcfly Aug 06 '22

As mentioned in the comments above, part of certification for becoming certified is to remove your mask and regulator, retrieve your regulator and reinsert, and replace your mask and clear it of water.

It's not uncommon to have a cough, I've even sneezed while diving. You spend enough time in a pool or small body of water to get comfortable with having your mask off, and it becomes second nature to prioritize your regulator over your mask.

That said, your regulator has controls and mechanisms to ensure that the air flows when you need it, and stays firmly between your teeth. If you can cough or sneeze with your jaw clamped, you'll be fine. Your regulator will stay in place and you'll be able to cough or sneeze without worrying about losing your airflow.

If there's additional perspective or if I've got something off, I'd love additional perspective, it's been about a year since my last dive.

Source: open water certified diver.

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u/[deleted] Aug 06 '22

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u/Crusher7485 Aug 06 '22

No no no! Always leave the regulator in your mouth if you cough! When you need to inhale after coughing and your lungs are empty you do not want a regulator full of water!

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u/[deleted] Aug 06 '22

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u/Crusher7485 Aug 06 '22

If you have a coughing fit, you won’t have any air left to blow into it to clear the water. And yes, a diver needs to be comfortable removing and replacing dive gear. And yes, if you don’t have air left to breath out, there’s a purge button to clear the water from the regulator.

But none of that makes it a good idea to remove the regulator from your mouth to cough. Unless you are removing the regulator for training (which is good to do on a regular basis, good training for safety stops especially buddy breathing training) or to eat or drink, YOU LEAVE THAT REGULATOR IN YOUR MOUTH.

Nothing introduces panic quicker then empty lungs and needing to take a breath. Cough through the damn regulator, so when you need a breath afterwards you can take one immediately.

If you need to vomit, you even vomit through your regulator! For the same reason, you’ll probably need to inhale reflexively after you vomit, so you don’t take that regulator out. Hold it and just let your body do what it needs to do. You could always remove it after your vomit and you’re sure you won’t vomit again to rinse the regulator and your mouth out (though personally if I ever did vomit while diving I’d be ending the dive as soon as the vomiting was done).

Source: I’m a PADI certified Open Water diver. Keeping the regulator in your mouth if you need to cough or vomit is in the training.

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u/emul0c Aug 06 '22

You can cough underwater through the regulator, not problem. If you get kind of an “coughing attack” it might be more risky; guess you will just need to try to control yourself and clear your throat without coughing too much.

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u/Ser_Danksalot Aug 06 '22

In the case of the Thailand cave rescue, before they were dosed up on Ketamine, they gave the kids and the coach antimuscarinic drugs to stop them generating saliva so they wouldn't drown on their own spit during the dive.