ELI5: how do divers clear their masks when water leaks in?…

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+1750 – 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.

2022-08-06 14:00:55

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  1. Well, for one, remember that scuba divers are breathing through their mouths, so a small amount of water in a mask isn’t actually a problem when it comes to breathing. But to clear a mask underwater is actually pretty simple: you inhale air from your regulator, then tilt your head back slightly, lift the bottom of the mask a bit off the face, and exhale the air through your nose. The air bubbles fill the mask and force the water out of it.

  2. For that particular rescue, if memory serves, full face masks were used. These tend to not leak as much as traditional masks and allow breathing through the nose and mouth. Additionally, water is effectively removed from the mask automatically as any water in the mask tends to end up at the lowest point, the regulator, and is ejected with each exhalation. Of course, you can get standing water if you’re on your back looking up at the surface or standing on your head but these unusual attitudes would have likely been minimized as much as possible in this case.

  3. In this rescue they used positive pressure full face mask. This means air was constantly being forced into the mask which would push out any water. Typically divers use demand valves that only uses air when you inhale. Since the boys were effectively sedated they needed to use the positive pressure as they would not be able to clear on their own.

  4. You press the top part of the mask against your forehead and exhale out through your nose. The air coming out of your nose goes up, getting trapped in your mask since you’re holding it. This displaces the water.

  5. Usually you just blow air through your nose, then flick the mask up slightly to let the water out.

    In the case of the cave rescue, I believe the boys were in full face integrated dive masks, so the chances of leakage would have been quite low. In normal usage those masks self-clear through the action of breathing, so if water is leaking in, the next exhalation pushes it out and the mask fills with air from your lungs. You then inhale a fresh lungful from your tank via the regulator in the mask.

    Source: Am diver, have used standard and integrated full face masks before.

  6. Back to OP’s original ELIFive request:

    1. Imagine starting with mask completely off your head, laying on the sand at the bottom of 15′ of water. You have a tank of air and your regulator is working.
    2. Visibility is very poor because the water but you can see shadows and shapes, so you feel around and find your mask, and get it basically oriented the correct way in regards to the top and bottom part (where there’s a space to cover your nose.
    3. Put the mask back on. It will be 100% filled with water, but no problem.
    4. Keep breathing as normal through your regulator; take a good breath, tilt your head back, use your hand to gently put some pressure on the mask, mainly the top seal across your forehead, and then breath out through your nose, into the water that is inside your mask.
    5. This air in the mask starts to displace the water. By having your head slight back, the air is rising to the front glass and the water is starting to escape out of the sides and bottom of the rubber seal.
    6. Do that once or twice, and then tilt your head back to normal upright. You should probably have at least half the water gone and you’ll eyes will now be at least mostly in the air pocket, allowing you to see.
    7. You can clear the rest of the water (say halfway up your goggles) by keeping your head in the normal upright position, applying slight pressure with your hand on the top forehead seal, and breathing out through your nose. This is enough to watch the water level leak out along the bottom seal. (the seal will kind of vibrate open-close fast as it’s both sealing on your cheeks and then blooping out some of the water).

    That’s it. This will clear 95%-100% of all the water in your mask. Note that this nose breathing into the mask will probably fog up the mask, so use that last 5% water to remove the fog by looking down, swishing that water across the glass to remove the fog, and voila.

    If it sounds panic-inducing, it can be at first, which is why they teach it in scuba class while you’re standing/sitting in the 3′ end of a clear pool. You just start doing it over and over, 30x or more, until it’s as scary as riding a bike. The loss of panic and the gain of control is one of the very best parts of learning to scuba dive. You feel like you could get out of a flooded car without freaking out, or on a deep dive and suddenly chaos happens. It’s an empowering skill to know.

    SOURCE: started scuba diving in the Red Sea in 1980 while I was hitchhiking around the world and got a job on a kibbutz in Israel.

  7. IIRC they bound the mask onto each child’s head and hoped against hope that it wouldn’t be dislodged.

    For anyone interested in this event there’s an excellent and detailed telling of the story in a 4-part podcast series called [Against The Odds](https://pca.st/episode/5d9fa0dd-cc11-415d-9cc3-161d5181162a). The podcast covers the activity in the cave and also what was going on above ground, with negotiations, competing views, etc. They follow it up with an additional episode dedicated to an interview with one of the British rescue divers.

  8. First you get a well fitting mask so it doesn’t leak too much. Second you hold the top of the mask firm to your face and exhale through your nose to force the water out. Third, with a lot of experience you learn to put a small amount of positive pressure into your nose to pure the water a little bit at a time as you dive.

    TLDR; force air out your nose while holding the top of the mask to clear water out. After many dives it becomes second nature.

  9. 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?

  10. Check out dive talk on YouTube. They have a interview with the diver that saved one of the first divers that got stuck in the cave looking for the kids. He explains basically everything about the whole ordeal and more.

  11. Tilt your head back 15-25 degrees, press the top of your mask towards your face, and then exhale through your nose; it forces the water out & your mask has little risk of getting away.

    This skill & mask recovery after a full removal is a basic dive skill required for certification.

  12. The bigger question is what do you do if you get water in your mouth?

    How do you get back to breathing without choking to death

  13. Exhale through their nose. Masks have a weaker seal at the bottom, and it flushesthe water out. Its a big harder in an inverted position.

    Masks fog up, and divers regularly apply baby shampoo or some similar eye-safe detergent to the interior to delay this. But when this fails, the masks are cracked to allow ingress of water, then flushed with an exhale through the nose.

    Source: intermediate scuba diver, 250+ dives.

  14. I watched the rescue, the docuumentey about the same incident, one of the guys said they had positive pressure masks, so any leak would push air out rather than let water in