Kids trapped in a cave 25

[3DDave]

Not a result of engineering, but one that might benefit from it.

The kids soccer team is trapped in a cave. From the graphic on the news it seems there are several pools that have sealed off the exit path. The children are supposed to be unable to swim, though I don't know that that is a special limitation. More concerning is that using scuba equipment might be too complicated for them; not only are they not familiar with it, the water they will move through is so murky that they would essentially be blind, deaf, and unable to communicate so that even guides would be unable to help them escape.

There is no immediate problem for them; they are now supplied with food and water and medical care. They have been without food for a week and will take a while to recover from that.

However, there is no known time at which the water will recede from the cave. I expect that there is insufficient pumping capacity to offset the rate at which it can be replenished. On the news they estimated weeks to months before the cave might dry enough.

Since they are in the cave, the passage was certainly large enough to get in and so there should still be enough room to get out. In particular full-sized adults have made the journey.

A thought occurs to me that it should be possible to pull corrugated tubes through each of the pools and then pump those out. If the ends are above water, there should be no replenishment beyond minor leaks for the pumps to offset. Using these the children should be able to crawl out, and will have light and audible communications to guide them.

The water is apparently only 16 feet deep at most, so the pressure can't exceed 8 psi. Anchorage will be required to keep it from shortening axially, but that should be a few hundred pounds to be useful.

I would estimate that a 24 inch diameter would be enough. I'm thinking of construction as is used for ventilating manholes, possibly with stronger wire.

If the tube obstructs the path for the adults, then they can wait the few days while the tubes are placed, the children escape, and then the tubes can be retrieved. If they are anchored against the cave roof by buoyant forces, they can be flooded again and then pulled back out.


Does this seem like a feasible way out?

 

[IFRs]

Why don't they use rebreathers - for the experienced divers?

 

[3DDave]

The experienced divers did use rebreathers. But those use CO2 soaks to remove the CO2 and still require an O2 source to make up for consumed oxygen. They benefit from the inability (thank goodness) of human lungs to absorb 100% of the oxygen on each breath, which is wasted in conventional scuba gear to get rid of the CO2, but that doesn't mean they have unlimited capacity. They also benefit that no gas needs to be expelled from the system; the nitrogen (or helium??) inert bulk is just recycled (but there is a second tank of diluent to make up for losses) and O2 added as required to be converted to CO2 and absorbed. So they are great if bubble production is a problem, like sneaking explosives or assassins onto heavily guarded boats. Or probably drugs into the rudder wells of ships. They are also good in letting a given size cylinder allow the diver stay underwater for longer.

However - humans are really bad at detecting low oxygen levels. In fact they can't. Really, it's worse than can't. Some start feeling euphoric and think that it's better and then they pass out and soon die. What people can detect is CO2 levels which causes gasping for breath, but O2 needs an independent monitor and that monitor needs to be monitored by the diver consistently. Which is why rebreathers are typically used only by people with the experience/habit/ability to remember to look at the monitor even in the face of life-threatening distraction, because if the O2 is not being replenished, they will feel really good about themselves and they they will die - if no one else notices and helps them. When diving, in the dark, in a cave, that would be, no one helps them; even buddy diving because the buddy can't see the monitor all the time.

To be fair, electronics have been developed to do the monitoring, control, and alerting the diver about the rebreather gas condition, but it's still a great deal more risk than a tank with a differential pressure regulator.

Another, big problem with rebreathers is that there is a large diameter hose to and from the absorbant. It has to be large because the air is moved by the user's diaphragm and restriction will tire the diver. This hose needs to be flexible and will be quite buoyant because of the diameter and therefore easier (because there are two sides) to snag. Regular scuba uses a small high pressure hose that is relatively a lot tougher. Snagging won't cut it, just pulling the regulator loose from the diver's mouth (reaching back to the tank to find the hose and reel in a displaced mouthpiece is Diving 101, so it's an annoyance. Likewise re-placing and clearing a flooded face mask.) I expect rebreather hoses to be cut resistant, but they would be too inflexible if they were as tough as high-pressure hoses are.

Finally, it looks like rebreathers are larger; essentially the diver has lungs to process the CO2 out and the rebreather has a "lung" to absorb the CO2 in addition to the oxygen and diluent tanks. In regular diving one could just trail a series of air tanks and as each is depleted, swap to the new one using a spare hose and regulator. The farther the diver goes and the more tired they are, the less they are carrying. Circumstances will favor a constant drag that starts smaller vs a variable drag.

If I had to get through small gaps, surrounded by sharp rocks, I'd rather go with a smaller diameter metal tank with a small, tough hose than trying to get an external artificial lung with a big loop of hose through the opening. OTOH, like the first diver, if I had no idea just how far was required, I'd go with the system that gave the longest range.

Finally, I doubt there is any good way to tandem a rebreather. With one tank and two regulator lines the lead diver can keep an eye on the supply for both parties no matter the experience of the second diver.

I didn't know all of this at the start. Though I understood general principles Google was my buddy in details about rebreathers. I think they predate scuba tanks / high-pressure + regulators, but I think they were out of general favor due to the much higher risk. The development of micro-electronics to monitor and control them seems to have breathed new life into their use. Long ago PADI training covers the rest. I went though training and check-out, but wasn't interested enough in finding dive locations to send in for the certification. Even so, a year later the wife and I had the fun trip to a Florida reef where the churning of the ocean in the shallow depth allowed us both to puke up our lunch and watch the fish gather around and pick off the tasty bits.

 

[itsmoked]

Don't re-breathers use electricity? What happens when Mr Battery chokes?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BrianPetersen]

They are all out!

 

[JAE]

It appears that all are out of the cave safely.

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[bones206]

It's hard to really know what went on without being there, but from my outsider perspective that rescue operation was an incredible feat of determination, sacrifice, bravery and logistics. Very inspiring.

 

[cranky108]

I think the rescue operation was a needless action. Not that they should not have been saved, but that likely they should not have been their in the first place.
So one should ask, where was the adult leadership?

At some point, I expect that the rescuers where asking if this was worth it.

Still it looks good in the press, but this still looks reckless on the part of the coach.

I guess we all need a hero, or event to remind us we are human, and not just <insert self blaming name here>.

 

[3DDave]

The first rebreathers, per Wikipedia, were an air-filled bag of lime and a determined diver. The current ones seem to use electricity only for the monitor and the solenoids, but it's easy to have a battery that lasts days to weeks for those functions. The circulation of air is from the diver breathing - as the air is squeezed out from their lungs a chamber in the back pack expands to accept the volume while the gas is directed through a CO2 absorbent. Since it is constant volume there is no net change in buoyancy. Since they are both at the same pressure there is only flow-losses to overcome. I haven't come across what they did to begin with - probably set a needle valve to bleed oxygen at a diver-adjustable rate and then maintain exhaled volume at a constant level or one that is corrected for depth. If nominal levels can be allowed to peak at 25% O2 and drop to 15% O2, that gives a system volume change of about 10% to work with.

 

[Compositepro]

With the original rebreathers the diver breathed pure O2. They are very simple, mechanically. Just an O2 bottle, a CO2 absorber and a expansion bladder in the breathing loop. But pure O2 is toxic above 2 atm. So modern rebreathers control O2 concentration versus depth in the breathing loop, using N2 or He. This requires very sophisticated sensors and computer controls and associated training because the consequence of any error is usually death without warning.

 

[dik]

At some point, I expect that the rescuers where asking if this was worth it.

It's ironic... it was exactly this type of human activity that got us out of the caves in the first place... What's the expression, "a turtle only makes progress, when he sticks his neck out."

Dik

 

[MacGyverS2000]

I wondered the same, cranky, but so far had not voiced it. These kids were so far back in the cave (miles!), and through at least one spot that was only 15" wide?! I'm either missing some huge part of the story, or these kids were not just looking to get out of the rain.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[LittleInch]

I heard a snippet that they were going to write their names on the wall of some big cave, possibly this Payatta Beach location, but then by the sounds of it, it started raining hard and they couldn't get back and were forced deeper and deeper into the cave.

You wouldn't have got me further than about 50m.... don't like confined spaces.

Remember - More details = better answers
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[LittleInch]

https://www.standard.co.uk/news/wor...claims-team-were-taking-part-in-a3884011.html

According to the bbc

"He went missing on his birthday and his parents say they are still waiting to hold his party.

According to reports, the boys went into the cave to celebrate Night's birthday. They were said to have brought treats and snacks along with them.

These supplies probably helped sustain the group in the many days spent trapped inside the cave.




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Also: If you get a response it's polite to respond to it.

 

[IRstuff]

They have names for all the spots on printed maps, so it wasn't necessarily unexplored territory, just possibly awfully bad luck.

TTFN (ta ta for now)
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[dgallup]

I think more recklessness than bad luck. There were posted signs warning not to go in during the rainy season. I applaud the rescuers, they were doing heroic work even if the kids and especially the coach, were stupid. The real shame is the Thai Navy Seal diver who died.

How long before the movie comes out?

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[JG2828]

There were posted signs warning not to go in during the rainy season.

Technically they entered the cave on June 23. I guess the rains came early this year..

 

[IRstuff]

Discovery documentary already ordered:

https://www.yahoo.com/entertainment...y-thai-soccer-team-cave-rescue-193452329.html

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[zeusfaber]

I haven't come across what they did to begin with - probably set a needle valve to bleed oxygen at a diver-adjustable rate

The earliest ones I know much about (the Proto set) used a diaphragm regulator to maintain a constant pressure drop across a fixed orifice to provide a constant oxygen flow. The bag (what you'd call a counterlung these days) had a relief valve to burp off the excess if you consumed oxygen more slowly than it was provided and there was a manual bypass valve to let you put extra oxygen in if you breathed the bag flat, and to allow you to flush inert gases out the loop (inert gases being a bit of a killer if you weren't careful).

A.

 

[Spartan5]

Incredible detail on the rescue in the New York Times:

https://www.nytimes.com/2018/07/12/world/asia/thailand-cave-rescue-seals.html

They basically immobilized the kids and carried them, floated them, slid them, zip lined them, and transported them underwater to get them out. What an operation!

 

[waross]

Thanks for that link, Spartan5.

Bill
--------------------
"Why not the best?"
Jimmy Carter