According to articles I have read the rescuers are taking 4 boys at a time and then resting and doing it again the next day. Why are they only taking 4 out at a time? The articles say they have 30 experienced cave divers and plenty of oxygen tanks. Are they only using the best divers or do they only do 4 at a time in case something goes wrong?
There’s only so much room and it can take four-six hours to get them out.
They’re doing a fine job under difficult and dangerous circumstances. They’re doing it as quickly and as safely as they can.
There’s more to it that just guiding the boys. For example, there’s resting places along the way where they swap oxygen tanks. Someone has to bring in fresh tanks to those spots, which means more dives. And there’s only so many dives a diver can make in one day.
AIUI, the dives are pretty shallow and short in duration; I would be surprised if decompression sickness is a major concern. Even if it is a concern, the long breaks between dives (which are dictated by many other logistical issues as outlines in Iggy’s excellent post, linked to by Bone) would provide adequate decompression time.
Each boy is escorted out by a diver in front and a diver in back. Stuff has to be staged so that the whole group can make it out OK. Much of the dive has to be done single file, and if too many boys are set up like this, a panic by one boy could cause a chain reaction for boys behind him, putting them in mortal danger. They were all in pretty bad physical shape, too, when they were first discovered. They hadn’t had enough food. They had to get in better shape, learn how to scuba dive, and a protocol for leading them out developed. Given that a Thai Navy Seal guy died already doing a set-up dive tells us that this is a pretty dangerous thing to do.
Mental decompression is another limiting factor. The guys escorting the kids underwater absolutely cannot make a mistake, and they’ll know what their limits are, seeing as they are the best the world has to offer. The cycle that’s been established of very roughly half a day active rescue, and half a day re-provisioning by other teams seems to be working so far.
My son explained it aloud last night as being the Saturn V rocket problem (or really any rocket) in that by adding more weight (another player), the amount of fuel (support divers) grows exponentially rather than marginally (i.e. with 90 divers getting 4 people out, evacuating 1 more doesn’t add just one more rescuer but rather 2… plus 3 sets of air tanks plus 3 people to carry them plus 3 to support the tank carriers plus surface support). And at some point you just can’t put more people through some of the tunnels! There are additional divers going in and out with medical supplies and food and oxygen for the chamber itself.
But if we just take the 90 rescue divers plus 4 rescuees, there are places where there are 184 swimmers going past lots of points in 10? hours. Few airports hit that amount of traffic and they have lots more visibility. Coordinating 184 swims is complicated- and there has already been one death.
Most decompression algorithms provide for indefinite dive time at depths as shallow as encountered in the cave so that is not a concern. The limit is usually shallower than about 23ft (7m) to have indefinite bottom time. And only extremely long dives (4+ hours or so) at such a shallow depth would incur a decompression obligation. Overall, it is not a concern in this situation as max depth is apparently only about 5 meters.
Others referred to my prior post in that other thread discussing the logistics. Also the oxygen levels in the cave may be a limiting factor as putting enough workers in the cave to stage enough cylinders to pull all the trapped boys at once might drop the O[sub]2[/sub] levels to dangerous levels. :eek:
And a point in favor of doing it slowly is that communication is a HUGE concern and a major reason to use the same rescuer divers who have proven successful so far.
The kids are also in poor shape. They are likely taking the fittest out first. Giving the rest time to get up to speed for the trip. Some may be having a harder time with the dive training as well. So they will be given extra time and experience. So they will be calmer during the extraction. Not everyone can do SCUBA. There are mental aspects that can render a person incapable of it. They would be very likely to panic and maybe die. It is possible that some other means of rescue might be required for some of the people.
On top of all the other valid things already pointed out.
Further to being incapable of SCUBA use.
I personally have a problem with a spastic constriction of the throat that can happen with the tiniest bit of saliva or other thing somehow triggering it. When it happens, I can barely breath in, but can exhale.
I have learned to deal with it. But it is still quite terrifying to me and very much those who are witnessing it.
I have snorkeled a few times. And overall I enjoy it. But am always quite tense. I have decided to never SCUBA dive. I think I could do the self control to get through an instance of it while submerged. But I do not wish to test that.
Interesting decision. Must have been a hard one. I guess the doctor felt that there would be no improvement with the fresh supplies being brought in. Those kids must be in real bad shape.
To elaborate on this, working from a limited air supply requires discipline. pacing yourself and your breathing are critical. I have no experience with SCUBA but I have a bunch with its cousin firefighting SCBA gear. I discovered during training that I can suck down a tank in a matter of minutes under heavy exertion. Even a smaller kid can panic and use up his air very quickly.
Even if the kids were in good health, the tiny size of some of the passageways is an issue. This isn’t a US 4 lane freeway. I’ve read that at one point, the cave is so small that the divers have to take their tanks off to get through it. There is no room for two way traffic. So all the resupplying has to be done before the rescue divers enter. The logistics and timing has to be amazing. I’m very impressed with what I have heard of the operations.
It took about 22 hours to get the 33 Chilean miners up in their one-person cage. They didn’t have to worry about swimming, breathing apparatus or anything other than getting into a 21-inch cage.
Getting out a dozen 12-year olds who didn’t even know how to swim, much less wear SCUBA gear, out through 4 km of flooded caves, after one highly trained rescuer had already died in the attempt, in just two days, seems pretty impressive.
Not to diminish the rescue or rescuers in any way, but only part of it required SCUBA gear. Apparently, once through the much-discussed underwater bottleneck, a great deal of the journey was wading.