Drowning in three feet of water with a tube full of air

September 2, 2022 12:01 AM

The extremely high rate of tourist snorkeling deaths in Hawaii may not actually be caused by breathing in water as widely assumed, but by the lungs failing to deliver oxygen to the rest of the body (called ROPE - Rapid Onset Pulmonary Edema) leading to loss of consciousness. A combination of factors are suspected, including high breathing resistance in snorkeling masks, existing heart conditions, and recent long air travel, the three year Snorkel Safety Study concludes. In a separate study, the best indicator that the newly popular (but sometimes banned) full-face snorkeling mask was harder to breathe through was its ability to be traced to a source manufacturer (YouTube webinar).
posted by meowzilla (57 comments total)

Probably not relevant but I got a splitting headache when I went snorkeling in Raro Tonga, Cook Islands, 3 years ago.
The mask was very tight and the sea felt really pressurised. Haven't had a heart attack yet though.
posted by Narrative_Historian at 1:04 AM on September 2, 2022

I didn't know those full face masks were so controversial.
posted by Zumbador at 1:50 AM on September 2, 2022 [7 favorites]

Interesting, and a bit awkward for me personally. I’ve gone snorkeling in Honduras and Curaçao, and I’m an exceptionally poor swimmer. (I went so far as to wear a life vest in Honduras). Perhaps this was … not the best idea?
posted by Mr. Excellent at 2:17 AM on September 2, 2022 [1 favorite]

This is timely for me as I will be taking a trip to Hawaii with the fam this fall. Good to note.
posted by zardoz at 3:03 AM on September 2, 2022

Scuba and snorkel instructor here. I have had reservations about the full face masks since they came out. Snorkeling is a tough sport for many and while I appreciate trying to make an activity more accessible to all, the full face masks tend to circumvent proper training for ease of use, and introduce a major issue that can lead to fatigue and drowning.

When we teach snorkeling we teach about dead air spaces and why it's important to breathe properly through your snorkel. That means forcefully exhaling to clear as much of your last exhaled breath from the tube as possible so you breathe less CO2 on your next breath. The dead air space in a standard snorkel is pretty small but still exists. The dead air space in a full face mask is enormous. Even with a full forceful exhale (if you know to do so) there's no way you can clear as much CO2 out of your mask and breathing tube to get a clean breathe of oxygen-rich air. That means your body is already breathing less than it's required percentage of oxygen on each breath and CO2 is building up, causing fatigue, headaches, dizziness, nausea, etc. Add to that breathing shallow from swimming exertion or anxiety... AND then not being able to communicate how you're feeling to anyone around you without taking off your entire kit and exposing your face to the ocean? Recipe for disaster.

I definitely appreciate the need for them for some. Just this week I was out with a diver who has a cleft palate disorder and she needed to use one as she cannot stop breathing through her nose and can't use a standard snorkeling setup. But she has been trained properly and knows the drawbacks, symptoms to look for, and is exceptionally comfortable in the water. They have their place, but shouldn't be readily available to the general public who falsely think "oh I'm super uncomfortable in the water, this will make it so much easier!" without folks understanding what the drawbacks are.
posted by danapiper at 3:14 AM on September 2, 2022 [109 favorites]

That means forcefully exhaling to clear as much of your last exhaled breath from the tube as possible

Why forceful, rather than simply deep breaths? I can’t imagine that forcefulness makes any difference in the volume of air being expelled.
posted by jon1270 at 4:48 AM on September 2, 2022

Can you just surface every five minutes or so and take a few breaths without the snorkel/mask? Maybe blow through the snorkel to get all the dead air out?
posted by zardoz at 5:05 AM on September 2, 2022

Huh. I had no idea that snorkeling was dangerous in this way. Every time I've snorkeled it's just been a 'rent a mask and fins in a tourist area, no instruction' kind of situation. Exactly as the article says-- I would never expect that it was a real risk to drown in three feet of calmish water (without any additional extenuating circumstances.)
posted by geegollygosh at 5:07 AM on September 2, 2022 [8 favorites]

Wow, just looking at the dead air in those things makes my skin crawl. Imagine what a CO2 alarms would read out of the air inside those. I think mine would probably go into full-on screaming "get out" mode in mere seconds.

I can feel the dead air in my Dentec respirator building up through normal exertion and that's just muzzle sized.

I don't think there's any way full-face masks should be used without some kind of training.
posted by seanmpuckett at 5:22 AM on September 2, 2022 [3 favorites]

ROPE is not caused by CO2 inhalation, but by inhalation against resistance drawing bodily fluids into the lungs. The FAQ at that Snorkel Safety Study site says

WHAT ABOUT CO2 BUILDUP?

Attention has been given to the possibility that CO2 accumulation in the mask/snorkel and then the blood causes the snorkeler to become unconscious. CO2 buildup is not a physiologically viable explanation of snorkel-related drownings.

posted by nicwolff at 5:58 AM on September 2, 2022 [9 favorites]

zardoz, without a solid place to stand, it can be difficult for n00bs or poor swimmers (like me!).

My wife & I went to the Caribbean this spring, and everyone said how great the snorkeling is: a short walk down the beach to a public "park" full of fish & coral, super clear water -- totally awesome! So we ordered a few masks from Amazon and brought along the ones that fit best.

I found it impossible to keep my mask sealed to my face, and I kept returning to the shallows to fix it because I didn't want to accidentally kick or stand on any corals under me. (My CPAP masks don't fit well, at the best of times: I think I've got a non-standard skull. And clearly my breathing mechanism is suspect, too.)

But no one selling masks warned us about this, no one at the resort mentioned it when they loaned us flippers, no sign at the beach mentioned it, and none of the tourism web sites mentioned it -- just like geegollygosh writes, above. I had seen articles warning of the dangers of full-face masks with integrated snorkels, but I figured we were safe when the snorkel was separate.

It never occurred to me what the actual danger was from, and no article described it the clear way that danapiper does in this thread.
posted by wenestvedt at 6:00 AM on September 2, 2022 [5 favorites]

I thought 128 deaths was pretty shocking, when I read it. Never heard about this before.

I mean, no one wants to die while trying to enjoy a vacation.
posted by tiny frying pan at 6:18 AM on September 2, 2022 [14 favorites]

Don’t think that 100% of those people are snorkeling. The reason it’s a focus is that it’s a leading cause of preventable death in visitors- worth a PSA I think.
posted by q*ben at 6:20 AM on September 2, 2022 [5 favorites]

So out of 17,000,000 tourists 128 died, giving us an utterly over-the-top, unbelievable, startling enormous, bone-chilling, spine tingling death rate of .000752941%.

I mean sure if you put it that way, snorkeling is not as dangerous as cancer, heart disease, or driving a car, but these are still preventable deaths, and Departments of Health should do things exactly like this, identifying clusters of deaths and looking into common factors and trying to prevent them.
posted by entropone at 6:20 AM on September 2, 2022 [21 favorites]

(The snorkeling safety study linked in the post seems to show over 100 snorkeling deaths, so...not sure the metrics here but have no reason to doubt it)
posted by tiny frying pan at 6:24 AM on September 2, 2022 [1 favorite]

Why the fuck would you jokingly minimise any number of preventable deaths? What the hell, Metafilter.
posted by seanmpuckett at 6:27 AM on September 2, 2022 [32 favorites]

I'm grateful for this post. Although I don't anticipate an opportunity to snorkel soon, I would have jumped at using a mask, which I hadn't heard of till now. When I did snorkel, I had a lot of trouble blowing forcefully enough to empty the tube, to the point where I would have to bob up and empty it manually, and I never could dive down without problems. Together with constant fogging, it really made the experience difficult. I can imagine how easy and fun a mask would seem.
posted by Countess Elena at 6:36 AM on September 2, 2022 [2 favorites]

Why forceful, rather than simply deep breaths?
When I did snorkel, I had a lot of trouble blowing forcefully enough to empty the tube

The first thing I taught the kids was to say TWO! into the tube as loudly as you can to purge the water out before inhaling.
posted by JoeZydeco at 6:53 AM on September 2, 2022 [7 favorites]

MetaFilter: I think I've got a non-standard skull. And clearly my breathing mechanism is suspect, too.
posted by Splunge at 6:53 AM on September 2, 2022 [7 favorites]

I cannot imagine how one clears (de-fogs) a full face mask.

Also: in my youth these (which were popular at the time) we’re also fitted with little floats on the ends of the snorkels that sealed the mask if the wearer ducked down for a breath-hold dive. These were famous for not easily re-opening, requiring a sharp breath out before they’d pop open. There were good reasons people at the time stopped using them.
posted by Insert Clever Name Here at 6:55 AM on September 2, 2022 [4 favorites]

I don't see the CO2 buildup in the body as the direct cause of deaths, but symptoms of CO2 buildup can cause issues that could lead to drowning or distress in some people. I'm by no means an expert but know first hand how much a CO2 headache can completely ruin your day, even when you know exactly what's going on. I can only imagine how it might affect someone new to or inexperienced in snorkeling.
posted by danapiper at 7:00 AM on September 2, 2022 [3 favorites]

JoeZydeco that "TWO" method is exactly how I teach it. It sends the water and some of the dead air out, clearing the tube for your next breath. You're never going to get all of it out but that's why simple tubes are best. Smaller airspaces are better.

The other key is to hold your breath until your ready to take the next one, that way you've got a full breath to blow the water out, then immediately inhale thru the cleared tube, and if a wave splashes in between breaths, you've got another lungful of air to blast it out with.

And yea, those floating water stopper things at the top? The less moving parts the better.
posted by danapiper at 7:06 AM on September 2, 2022 [14 favorites]

Well this is certainly giving me something to think about ahead of any future snorkelling trip. Plus my cardiac nurse warning me about cold water shock. Plus a guy my age (51) getting cold water shock in 28C water jumping into Lake Garda recently (about two weeks after I jumped into Lake Garda). Generally I snorkel in much lower temperatures (17-18C here currently), so its on my mind.

Following the link "newly popular" in the FPP, the first hit looks like it has a swastika printed on the nose part of the mask. Seems like a bit of a design booboo.
posted by biffa at 8:05 AM on September 2, 2022

This wasn't my experience with snorkeling at all.

No. I almost drowned snorkeling in Mexico, not Hawaii.

Man, fuck snorkeling. Least relaxing thing ever.
posted by DirtyOldTown at 8:16 AM on September 2, 2022 [12 favorites]

I have one of those full face masks. They have exhalation valves at the bottom of the mask, so in theory your CO2 goes out immediately. The area around your mouth is sealed off with intake valves so that the dead space is much smaller.

All the valves are simple silicon flaps that can only move one way. Given omnipresent sand on virtually everything on the beach, it's not hard to imagine that some sand buildup in the wrong place would cause the mask to catastrophically fail. And I found it impossible to remove the mask quickly while standing in my living room while breathing normally. In a panic situation, it might as well be welded to your head.

I didn't use the mask or even bring it on my trip, because it would have taken up about a quarter of my total luggage space.
posted by meowzilla at 8:20 AM on September 2, 2022 [2 favorites]

If I’m snorkeling and doing any exertion I will typically just slowly exhale out of the side of my mouth, rather then out of the snorkel.

If there would be any place to put a check valve in a snorkel it would be at the bottom, to make it work like a SCUBA regulator.
posted by snuffleupagus at 8:21 AM on September 2, 2022 [1 favorite]

Every time I've snorkeled it's just been a 'rent a mask and fins in a tourist area, no instruction' kind of situation.

The one time I tried it--circa age 18 or so--that was what I got. "Here, figure this out for yourself." I had no clue, I was afraid to use the thing, I wasn't sure at what level to even swim so I didn't go too far down and choke myself on water. And now, this. I don't think I'd ever try it again.
posted by jenfullmoon at 9:29 AM on September 2, 2022

So out of 17,000,000 tourists 128 died, giving us an utterly over-the-top, unbelievable, startling enormous, bone-chilling, spine tingling death rate of .000752941%.

That's the death rate for all Hawaii tourists who die snorkeling...that's not the same thing as the death rate while snorkeling. I'd guess only a fraction of total tourists to hawaii snorkel, making that number easily an order of magnitude or more off.
posted by JauntyFedora at 9:29 AM on September 2, 2022 [9 favorites]

I haaaated snorkles when I was a kid. I was told the TWO! thing. I tried and tried and tried because it was what you were supposed to do, but my snorkel was effectively a decorative thing I wore because I was told to.

Then, once, when I was an adult, I went out with some friends and they suggested we go snorkeling. I was like, "that sounds awful!" and they were like "just give it a try, we think you'll like it!" and then we got out there and they handed me a life vest and all of a sudden, snorkeling worked and was fun.
posted by aniola at 9:38 AM on September 2, 2022 [8 favorites]

There’s another factor that might make snorkeling more difficult than novices might expect:

At sea level, every portion of our bodies is subjected to an air pressure of 14.7 pounds per square inch--a considerable load, but one which we are not even conscious of because the pressure within our bodies is maintained at the same level as the air pressure around us.

This pressure of 14.7 pounds per square inch is the same as that existing at the interface of the air and the water at the swimming pool's surface. However, once we submerge ourselves in the pool, pressure from the surrounding water increases at the rate of an additional 0.433 pounds per square inch for every foot which we descend, although the air pressure in the hose remains the same as at the surface. This means that, at a depth of two feet, the confining pressure on the rib cage (assuming about two square feet of surface area for an average chest) totals about 250 pounds! Accordingly, inhaling would be roughly equivalent to trying to take a deep breath with a sumo wrestler sitting on your chest. It can only be surmised that Gary Cooper must have used a very short reed and very shallow water for this trick.

If for snorkeling we estimate that the part of your body which moves in and out as you breathe is about a foot below the surface, and has an area of one square foot instead of two, that means the muscles which allow you to inhale are working against 60+ pounds more opposing force than they usually do with every breath you take.

That has to be tiring in a way which most people who haven’t snorkeled have had very little experience with, and once you've been snorkeling for a while, those muscles probably can’t exert anything like their maximum force anyway.

The author of the linked page discovered that he couldn’t take even one breath through a two foot tube in a swimming pool.
posted by jamjam at 9:58 AM on September 2, 2022 [5 favorites]

I visited Hawaii as an 18-year-old. I had relatives who'd rented a condo for a month, and I flew out to spend a week.

I grew up around water: inland lakes and Lake Michigan. I'd snorkeled in all of them, and also had made it through the Red Cross Junior Lifeguarding course at around age 12. I still know various, probably outdated or superseded, survival tips, like how to make your shirt and/or pants into a flotation device, how to handle waves coming toward you when you're floating, and so on. I vividly remember the test where we had to go in the water fully clothed including shoes, and tread water for some very high number of minutes (probably 10, but it felt longer in blue jeans and sneakers) while demonstrating the skills we'd learned.

I had a great time snorkeling in Hawaii. I loved that you could be standing in water not even up to your waist, and when you put your masked face under, there were tropical fish right there . It's a very happy memory.

I also went body-surfing in Hawaii, in waves the likes of which I had never seen before. One of them tore off my one-piece swimsuit. Another tossed me around like I was in a washing machine. Maybe those were the same wave.

The snorkeling was OK for me. I knew how to clear my tube and de-fog my mask, and I was using my own (cheap but familiar) gear from home. But I reckon I was never closer to drowning than I was while body-surfing in waves I had no business being in.

I did not even know there were full-face snorkeling masks. I'm no genius, and can't say, "Oh, it's so obvious they're a bad idea," but a thing that stands out for me is how much the straps are like my CPAP mask straps (I even once tried a full-face CPAP mask). That's obviously harder to get out of than a traditional snorkeling mask, though my CPAP mask has quick-release buckles at each side of the lower edge of the mask, and if I need to, I can get it off easily by opening one of them and pulling it off. But I'm very familiar with my mask—-I've been using the same model for most of the 15 years I've had it. I don't see that on the full-face snorkeling masks, and it's easy for me to imagine an inexperienced person whose mask is, say, filling with water due to a poor seal, really struggling to get the darn thing off.

I could be wrong—-maybe I just can't see them in the pictures.

When I learned to skydive 30+ years ago, we spent half our training day in parachute harnesses hanging from the ceiling of a pole barn. Over and over we practiced the movements to cut away a parachute that hadn't opened properly, and then deploy the backup chute. I still remember it vividly.

You look down at the cutaway handle, a D-ring, on your right upper chest ("Look down! Don't fumble around! Look at the release handle!"), put both thumbs through it, and then quickly straighten both arms. Then you look ("Look! Look at the handle!") at your left upper chest and do the same with the release lever for the backup chute.

I see from googling that parachute harnesses have different kinds of releases now. But the cutaway is still on the right, the backup chute release is still on the left, and safety videos still emphasize, "Look at what you're doing!" and "Pull that thing like you're punching someone!"

"Look at what you're doing" is a lesson that has served me well over the years. I only ever jumped out of an airplane once, on a static line that opened my chute for me, and I botched the landing a bit. But I'm glad I did it, and even gladder I trained to do it.

I will write a thing someday about how being strapped into the parachute harness was part of my awakening as a lover of bondage, as well.
posted by Well I never at 11:35 AM on September 2, 2022 [14 favorites]

My parachuting digression was to contrast how hard we were made to practice what to do in an extremely unlikely life-threatening situation, versus the "Here's your snorkel and mask! Have at it!" process for ocean snorkeling.

That said, I just looked it up, and malfunctions in parachutes seem to happen 1 in 1000 jumps, which seems like a lot. Not sure I like those odds when death is on the line.

Deaths occur once in about 167,000 jumps. So it is riskier than snorkeling. Still, when a prudent equipment choice and a bit of training could prevent unnecessary deaths, one should make prudent equipment choices and undergo a bit of training.
posted by Well I never at 11:49 AM on September 2, 2022 [3 favorites]

The author of the linked page discovered that he couldn’t take even one breath through a two foot tube in a swimming pool.

I also saw characters hiding with hollow reeds in any amount of action scenes and comic books. I thought you would just have to be tough and lucky to make it work. Knowing swamps as I do, I think it would probably be better just to hide your whole body in tall grass and cane, and avoid leaving giant sucking footprints on your way into the water.
posted by Countess Elena at 12:09 PM on September 2, 2022 [3 favorites]

I also saw characters hiding with hollow reeds in any amount of action scenes and comic books. I thought you would just have to be tough and lucky to make it work.

Yeah, that always bugged me, too. Also most reeds that I've known aren't hollow all the way through, and even if you had time to prep some kind of breathing straw it would almost surely collapse or crack from the water pressure.

I remember trying to breath through a garden hose in a swimming pool as a kid and learning very quickly why it doesn't work. For one it's just impossible for your lungs and diaphragm to overcome the water pressure at any depth below a couple of feet, and for two you're just rebreathing increasingly stale air trapped in the tube.

I never tried that one again.

Scuba rigs overcome this by using compressed air to force your lungs to inflate, as do forced air surface fed systems.

I used to do a little snorking and skin diving when I was younger, and it was always impressive and kind of scary how difficult it could be to breath even just on the surface. If you tried to breath while upright underwater, that extra foot or two of depth made it even more difficult.

Well this is certainly giving me something to think about ahead of any future snorkelling trip. Plus my cardiac nurse warning me about cold water shock.

The last time I jumped off a dock into Puget Sound on a really hot summer day I probably came real close to cold water shock issues. I was aware of the issue, I grew up surfing and swimming and I'm a strong swimmer, I know how to float and tread water and used to do it in the open ocean basically all day when body surfing.

I'm not sure if I'll ever do that again. I mean I was fine and not having a bad time, but I definitely learned that I'm not as strong as a swimmer as I used to be, the cold water shock took my breath away in a major way, and I just wanted to get out of that freezing cold water as fast as possible.

Though I did jump back in about a dozen times that day and was having a blast. It was fun to be able to jump off the dock, swim to the beach and run right across the street to my friend's bar soaking wet and shoeless, grab a beer on the patio, and then run right back out to the dock to do it again and generally feeling and acting like a kid again.

Granted this kind of thing is normal in warmer places with touristy beach bars, but in the PNW it's a rare treat.
posted by loquacious at 1:15 PM on September 2, 2022 [5 favorites]

++ glad to learn from this post, thank you meowzilla, and danapiper for the added info.

I knew from caving that most drownings happen in less than 3 feet of water; to me that meant most drownings involved some external factor (eg concussion) making it difficult to do simple things like stand up, more than the challenge of water itself. Makes sense that CO2 is an added factor, though I hadn't considered the extras of wearing fins, and the need to take a mask off while in the water.

The article mentioned the difficulty a lifeguard faces in figuring out which of the 50 face-down mostly inert snorkelers haven't moved in the last 30 seconds. The hard-to-spot aspect reminded me of how drowning doesn't quite look like you might expect, either.

I have snorkeled in Hanauma Bay. We rented full-face masks from the shop on the beach. We thought the masks were great, and we should get some! Maybe not now.
posted by Dashy at 1:43 PM on September 2, 2022 [4 favorites]

I actually know someone in their 30s who died in exactly this way in Hawaii, while snorkeling in shallow water. Totally healthy and fine one minute, comatose and brain dead in the ICU the next. Their stunned parents flew in from abroad to give the OK to remove life support and left with their child’s remains. Needless to say, no one was held responsible, not the mask manufacturer, nor the rental place. It was an unnecessary tragedy, and put me off snorkeling forever.
posted by Atrahasis at 2:39 PM on September 2, 2022 [4 favorites]

Atrahasis, what a heartbreaking trip for their parents. It feels wrong to hit the plus to favorite your comment, even though I appreciate you sharing it.

As a former resident of Honolulu, I remember the frequent media coverage of tourist injuries and fatalities in the ocean and the mountains. Never turn your back to the ocean.

The infographic of ocean drownings (2010-2019) from the study shows the difference between residents and non-residents in the activities leading to the drowning. Opihi picking is one of the locals only activities. There's even a Ka‘au Crater Boys song that goes

Gotta fill up your bag, with the yellow and black
Keep your eye on the wave, don`t ever turn your back
Opihi man in the sun. Opihi man grab your bag and run
Opihi man another swell is coming your way

posted by spamandkimchi at 3:29 PM on September 2, 2022 [11 favorites]

If there would be any place to put a check valve in a snorkel it would be at the bottom, to make it work like a SCUBA regulator.

I've owned several snorkels designed like this. The diaphragm eventually stiffens and they wind up leaking a bit when closing. I either put up with a bit of collected water at the bottom or covering the top of the snorkel with my hand and giving it a sharp exhale blast to clear it.

Ultimately, as a SCUBA diver, I stopped keeping my snorkel on my mask (where it could tangle with kelp---I did a lot of cold water dives in Monterey/Carmel CA) but instead kept it handy in a pocket on my drysuit leg or dive vest (if in warm water). Good for emergencies.
posted by Insert Clever Name Here at 4:34 PM on September 2, 2022 [2 favorites]

Wow, in a startling coincidence I saw this post about 30 minutes after finishing a swim in Honaunau Bay on the Big Island. I say swim because out of convenience we bought some swim goggles and have enjoyed the waterscape that way (snorkeled another day). To be honest although I miss having fins I don't especially miss the snorkel itself. I've rented snorkel gear many times and apparently was lucky that the first time I learned was on a snorkel trip where they actually gave real instructions on how to breathe through it. As I lay face down on the water this morning, not moving, it crossed my mind that it would be difficult for an observer to know whether I was dead, unconscious, or just watching the fish - apparently not a ridiculous thought after all. I can't imagine trying to snorkel without knowing how to swim well - that sounds so terrifying.
posted by weirdly airport at 5:50 PM on September 2, 2022 [2 favorites]

So the described problem here - breathing against resistance causing fluid to enter the alveoli from the body itself - is interesting.
Does this happen to people in corsets? People with heavy dogs that sleep on their chests? People buried in sand?
If not why not?
posted by Acari at 7:07 PM on September 2, 2022

Fainting in corsets is a thing.
posted by aniola at 7:46 PM on September 2, 2022

Metafilter: Fainting in corsets is a thing.
posted by MrVisible at 8:15 PM on September 2, 2022 [1 favorite]

There's some evidence for it in avalanche victims, but I guess most of them die of other, more obvious reasons and it's not really investigated: Mechanism of death in avalanche victims
posted by meowzilla at 8:39 PM on September 2, 2022

Is fainting in corsets just general lack of oxygen, or this specific issue? I know that just because I've never heard of ROPE before, that doesn't mean it's there kind of thing that gets missed, but I'm still curious.

I can't picture edema looking like a faint, but maybe?

Now I'm just picturing an experiment now with the test subjects all in Temple Grandin's hug machine or something and the ethics review board denying permission with prejudice.
posted by Acari at 8:45 PM on September 2, 2022

breathing against resistance causing fluid to enter the alveoli from the body itself - is interesting.
Does this happen to people in corsets? People with heavy dogs that sleep on their chests? People buried in sand?

None of those situations cause a differential in air pressure... I think. Those situations would cause your muscles to strain to expand your chest, but you're still breathing in the same pressure air that exists in the environment around you - the air pressure facing the membranes in your lung is the same.

In the case of the snorkel, the air you're breathing - that column of air inside the snorkel - is at a lower pressure because you're sucking on it against the resistance from valves and the height of the column of air in the snorkel itself.

HAPE (high altitude pulmonary edema) is a similar thing, where ascending to high altitude exposes you to low pressure air that also draws fluid out from the lungs. The study itself mentions that there might be a link between recent, prolonged air travel - which exposes travelers to lower air pressure. It could cause minor injury in the lungs which then makes you more susceptible to ROPE.
posted by xdvesper at 11:43 PM on September 2, 2022 [5 favorites]

Ultimately, as a SCUBA diver, I stopped keeping my snorkel on my mask (where it could tangle with kelp---I did a lot of cold water dives in Monterey/Carmel CA) but instead kept it handy in a pocket on my drysuit leg or dive vest (if in warm water). Good for emergencies.

I'm curious about the logic of this and why a snorkel is useful for emergencies while SCUBA diving to the point that you'd retrieve it from a pocket or wear one on your mask at all?

If you're close enough to the surface that you can use a snorkel and you're not dealing with decompression sickness or the bends, wouldn't you just rather surface and breathe without a snorkel?

I guess it's easier to breathe without having to tread water and you can just so deadman's float and save your energy, but I figured that's what inflatable life vests or buoyancy compensators are for?
posted by loquacious at 12:22 AM on September 3, 2022 [2 favorites]

Thanks, xdvesper! Your first sentence was all I needed. Makes way more sense from that perspective which I just needed help to see
posted by Acari at 6:04 AM on September 3, 2022

There can be chop that can make it hard to breathe bobbing on the surface, while festooned with clumsy SCUBA gear restricting your movement, a steel tank on your back (presumably now empty) and the regulator first stage behind your head. Being on the surface is not like being even a few feet down, and the BCD (vest) doesn’t float you quite so vertically as a life vest.

You can tread water that way and paddle around a bit, but you’re not swimming any distance like that, as you might conceivably have to do in a dive emergency. Especially with the BCD fully inflated.

Some shore divers will also use them while swimming out to the reef, etc, to conserve the tank.

I keep mine in the big BCD front pocket too, I hate having it wiggling my mask strap as I swim, ruins your streamlining.
posted by snuffleupagus at 8:29 AM on September 3, 2022 [4 favorites]

The simplest snorkel is just a J-shaped tube whose lower end you put in your mouth. If it's longer than 12 inches it's too long. The idea is to keep your face and mask in the water so that you can see below you and still breathe. Your head is supposed to be on the surface. Your face is in the water. The back of your head isn't submerged. You're floating on the surface. I think the issue of trying to inhale against pressure is a red herring. When you're face down floating in the water at the surface there is no effective pressure differential to cause a problem. Of course if you're two feet underwater trying to breathe through a long tube that's a difference scenario. It's practially impossible and you will indeed put your lungs under some significant strain trying it. But that's not what's happening when you're snorkelling.

Exhaling forcefully enough to clear the water from your snorkel when you surface is the key to not choking on your next inhale. You definitely need a sharp exhale. You should be trying to think like a whale. In a regular J snorkel, I can't believe there's enough air to create a dead zone. What's the total possible volume? A 14 inch snorkel should have a volume of about 11 cubic inches. A single breath should clear that.

I can believe that someone can drown by choking on some water and then panicking with the possible extra complication of being in shallow water and not being able to get their feet underneath them. But surely that's a risk that's not much different than swimming in open water without a mask and snorkel?

All of the above bets are off if you have a full face mask with an integrated snorkel. The increase in volume is pretty large. Suddenly there's a lot of water to clear. All of the above bets are also off if you're not a reasonably good swimmer who is comfortable enough in the water to be a bit uncomfortable. To choke a bit and not to panic and instead to get your head out of the water and cough it out. Nobody should be in open water without a life jacket, snorkelling or not, if they're not really comfortable with a situation like this.

On the plus side, if you can get comfortable with a mask and snorkel and get your face in the water you can get very calm in the water. Just submerging your face invokes the diving reflex which slows your heart rate once you get over the initial excitement. This response is something we share with our marine mammal cousins.
posted by kaymac at 12:00 PM on September 3, 2022 [5 favorites]

Just submerging your face invokes the diving reflex which slows your heart rate once you get over the initial excitement.

Relaxing while snorkeling is definitely a help but a note about the mammalian diving reflex from wikipedia (emphasis mine):

"...the greatest bradycardia effect is induced when the subject is holding their breath with their face wetted"

So wearing a mask that covers your nose and eyes while continuing to breath through the snorkel isn't likely to elicit the reflex very strongly. If I recall correctly, free divers specifically immerse their faces in the water with their eyes open before starting a dive to maximize it.
posted by Insert Clever Name Here at 7:02 PM on September 3, 2022

> Man, fuck snorkeling. Least relaxing thing ever

Hi, internet. This reminds me of a story; I'll keep it brief.

Was in Florida, did some snorkeling, it was fine. It's never as much fun as you want it to be. You can't quite breathe, your teeth and lips feel weird after a while, there's all this pressure to see cool stuff, maybe you have to dive under to see the really cool stuff, but my extra 50 pounds of blubber make me quite buoyant...

Later that day, or possibly the next, I indulged in some of my psychedelic of choice, hugged a friend who had tears streaming down his face as he watched a beautiful sunset.. then as it got dark, jumped in the water and floated on my back with my eyes closed. My god. What a sensation. "This is the exact opposite of snorkeling!" I exclaimed in joy. No need to do anything. Gently rocked by the tiny waves of the gulf. Just being.
posted by booooooze at 10:34 AM on September 4, 2022 [3 favorites]

I’ve been snorkeling a few times, and breathing is always hard for me. I float along the surface and keep just my face in the water but I think my mind see water in my face and doesn’t want to breathe. Every breath is work, forcing my lungs to breathe even though my face is in the water. I could see how that labored breathing could be a problem for some people.
posted by LizBoBiz at 12:09 PM on September 4, 2022 [1 favorite]

As an anesthesiologist and a certified diver (although it has been long enough since I dove that I would want to go through the entire course before diving again) this post pushed a lot of buttons for me. Lots of good comments, too. Anesthesiologists do a lot of work in the field of diving and altitude medicine, in large part because our daily job requires familiarity with respiratory and cardiovascular physiology, as well as the behavior of dissolved gasses in the body. The assumption that pulmonary edema plays a large role in these deaths is reasonable, but I wonder if it is overstated. For one thing, pre-existing medical conditions probably play a larger part than they are given credit for; I’ll expand on this in a second. Also they seem to dismiss the role of hypercarbia (AKA hypercapnia) rather quickly, although the anesthesiologist quoted in the first link seemed to think it is important. The term “dead space” is used frequently, but it is an important concept in respiratory physiology and refers to that part of a breath of air that does not participate in gas exchange, i.e. getting rid of carbon dioxide and taking up oxygen. This refers both to air in the nose and throat as well as air in the lungs where they aren’t functioning well for one reason or another. Many things you breathe through affect this; sometimes decreasing dead space but more commonly increasing it. This is important because you need to either breathe more air to compensate for it or the amount of carbon dioxide in your blood will increase. And getting rid of carbon dioxide is the primary driver of breathing, so most people will unconsciously increase their respiratory rate and/or volume to compensate. But of course that requires some additional muscular work, and that is on top of the additional work involved with swimming around, both of which increase carbon dioxide production. Which then requires more work of breathing and more CO2 production, and you can see the potential death spiral happening. And those full face snorkels potentially add a huge amount of dead space (in the physiological sense), making things worse. But wait, there’s more! While the effects of hypercarbia can be well-tolerated in healthy people, if you are out of shape and have heart disease (perhaps undiagnosed) they can be bad. And for a certain group of people, those with a weak right heart or poor blood flow to the right heart, the fact that elevated CO2 levels in the blood cause the pulmonary blood vessels to constrict and make a compromised right heart work harder could easily push them over the edge.

Which brings me to the issue of pulmonary edema. I have seen ROPE in real time in the OR (although we call it negative pressure pulmonary edema; NPPE) and it can be impressive. As already mentioned pulmonary edema results when the plasma in the blood and the fluid between the cells through the body (including the lungs) spills into the alveoli, which are the units of the lung where carbon dioxide leaves the blood and oxygen enters it. If you know what you are looking at it is very distinctive; the patient is producing pink, frothy secretions from the nose and/or mouth. But sometimes so much that it could be confused with vomit, especially to a non-medical observer. I do not know how easy it would be to differentiate ROPE from the pulmonary edema that occurs during drowning; i would be interested to learn from a deep dive into the data how many victims were described as having those classic pink frothy secretions during the initial resuscitation attempts. Based on my experiences and reading a lot about it, ROPE/NPPE develops quickly, but not so quickly that a victim would not panic while it was happening, as opposed to the silent deaths that are described. Furthermore, it takes some serious negative pressure for ROPE/NPPE to develop in most people. In anesthesia the classic scenario is a young, healthy patient who attempts to inhale with their vocal cords shut (Müller’s maneuver). I am surprised that (normally functioning!) snorkeling equipment would allow the user to generate that kind of pressure. But I can see people who aren’t young and healthy having a different presentation; once again pre-existing conditions, both known and unknown, can be important.

It is really good that people in Hawaii and Australia (and presumably other places) are looking into this. Not only can we learn how to prevent snorkeling deaths, but the knowledge may be useful in other contexts, too.
Wikipedia has a good article on hypercapnia; more technical articles on NPPE and right sided heart attacks are here and here.
posted by TedW at 1:05 PM on September 4, 2022 [10 favorites]

I've done lots of snorkeling, including in Hawaii. All of the places we went in Hawaii mentioned the supposed risks of full-face masks and no tour would allow them to be used. The issue they all mentioned was the risk of the mask filling with water and no way to clear it out by blowing as you do with a normal snorkel. Whatever the reality, I understand you can't dive down with a full-face mask and that takes away one of the most wonderful things you can do when snorkeling - diving down as far as you can, then floating slowly back to the surface watching the fish with a complete absence of effort or noise.
posted by dg at 9:59 PM on September 5, 2022 [1 favorite]

I've been a SCUBA diver for 20+ years and am pretty comfortable, including in a hairy situation where my (primary) reg failed at 90+ feet. But I'm a terrible, nervous snorkeler, and only do it for something important, like snorkeling with whale sharks. (Which I did this summer, and now don't need to do again.) Thanks for the post.
posted by cyndigo at 12:04 PM on September 6, 2022 [1 favorite]

Later that day, or possibly the next, I indulged in some of my psychedelic of choice, hugged a friend who had tears streaming down his face as he watched a beautiful sunset.. then as it got dark, jumped in the water and floated on my back with my eyes closed. My god. What a sensation. "This is the exact opposite of snorkeling!" I exclaimed in joy. No need to do anything. Gently rocked by the tiny waves of the gulf. Just being.

I am also extremely buoyant!

A couple of decades ago, I was at a Lake Michigan beach with my partner and a friend. I was floating on my back, just perfectly balanced on the surface, not having to paddle my hands or feet at all to keep my face out of the water, but with sound muffled because my ears were under the water. I closed my eyes and floated and floated and floated in the water with the warm sun beating down on me.

I got into such an altered state of consciousness that after awhile, I wasn't sure I could get myself back out. My whole body was so heavy and relaxed, my mind was so deeply calm. Eventually my partner and friends noticed I'd been floating for awhile, and they towed me into shore (not very far away) by an ankle and then buried me in the sand to re-ground me.

I remember the whole thing as being one of the most profound altered-states experiences of my life. I loved the floating, and I loved being buried in the sand.

I've never done psychedelics, but I might sometime. And I've often thought that the best way to have this experience again might be a sensory deprivation tank.

I've never been able to float so perfectly again, in any body of water. Parts of me sink, or there's just enough of a swell or waves that my face gets splashed with water. Everything just came together perfectly that day, and the people I was with were watching out for me so I didn't just drift off into the middle of the lake and drown. Being so well taken care of was part of the magic of the experience for me.
posted by Well I never at 1:06 PM on September 6, 2022 [3 favorites]

TedW, I really appreciate your comment. Thanks for the good info.
posted by Well I never at 1:10 PM on September 6, 2022 [3 favorites]