Ask HN: Could big rubber pipes save the Thai cave boys?

[jakobov]

I'm wondering if large rubber-like pipes could be used to make crawl-able tunnels through the submerged areas of the cave?

Divers would carry the rubber pipes through the cave such that both ends are above air, the water would be pumped out of them, and then the boys would just need to crawl through the pipes.

If a suitable type of pipe could be found/made this seems like a good solution.

What does everyone think?

[simon_acca]

Interesting, I don't see any "first principles" reason why this couldn't be done, except for some bend radius that might be just too tight [0]. Also the pipe would have to be made of something more solid than rubber to overcome the water pressure (it's not much but it's still there).

From a risk management point of view however this solution seems a bit reckless, as a rescuer you never want to cause more damage/hazard than what's already present and this untested solution could fail in some catastrophic ways. What to do if the pipe becomes punctured? How do you rescue somebody that becomes stuck for whatever reason? (think also psychological factors)

If you compare this to just waiting a few months and walking out you might conclude that it's not worth the risk.

https://www.theguardian.com/world/ng-interactive/2018/jul/03...

[eesmith → simon_acca]

Such a pipe would have to be placed with water inside, then pumped out once its installed. Why? Because it takes a lot of force to put an air-filled tube through water.

I see no way that such a pipe could be deployed. Even without buoyancy issues, there will be a lot of friction from the cave walls, and going around bends. The force can't come from simply pushing it it, as anything flexible enough to bend around curves will also crumble from the pushing force.

If I read it right, the pipe would need to be 6 meters deep in some points in the cave. As you might recall from Star Trek IV The Voyage Home, the transparent aluminum scene, the whale tank needed 6" of Plexiglass. If I use the "Aquarium Thickness Calculator (xls)" from http://www.sdplastics.com/aquaria1.html and plug in 200 inches (for about 6 meters), then it says it would need 16 inches of Plexiglass.

You might shave that down, with better materials that don't need to be clear, but, as The Guardian points out elsewhere, there isn't much room: "Parts of the cave system are reportedly so narrow that Thai Seal teams and the volunteer rescue divers had to remove their own breathing apparatus to get through"

Furthermore: "It’s about 11 hours – six on the way from the entrance to where the kids are and five on the way back"

Who will guide the pipe at it goes through the route? Once the pipe has gone through one of those constrictions, can anyone else get by? If the pipe blocks the route, then what?

And, how long would it take to lay such a pipe?

[simon_acca → eesmith]

To eliminate some of the raised issues, particularly around the forces acting during the installation, the conduit could be assembled from sections, in the guise of HVAC ventilation shafts[0].

With that said, I won't add any further speculation since mechanical/materials engineering is really not my area of expertise. Someone knowledgeable could provide insight on: what material (steel?) is suitable for such a task and what are processes for watertight bonding performed underwater (welding?).

0: https://bigreddog.com/wp-content/uploads/2016/02/Ductwork-1-...

[eesmith → simon_acca]

There is no need for a materials engineer. We can look to existing structures which hold water to get an idea.

Above ground pools use 1/8" steel for about 1-1.5 meters of water depth. (Eg, https://www.answers.com/Q/How_thick_is_a_swimming_pool )

Pressure is linear with depth, so 6 meters would require about 1/2" of steel.

HVAC ducts like you pointed to are about 1/40". (Based on numbers I see at https://www2.iccsafe.org/states/newyorkcity/Mechanical/PDFs/... ).

[simon_acca → eesmith]

I just pointed at hvac ducts to illustrate the kind of tech I was referring to (pipes assembled from small sections), wasn’t suggesting that actual hvac pipes should be used

[eesmith → simon_acca]

Ahh, I see. I misunderstood.

Your model, I think, is that the divers would lay at least 1km of 1/2" thick steel pipe, from the far end backwards (since otherwise there's no way to get the segments to the end). Call it 1cm for easy of calculation.

Steel is 8g/cubic centimeter. Assuming the divers can carry 20kg (which seems large), each segment is at most 25 cm long. That's at least 4,000 segments, each to be welded. Assuming it takes 5 minutes per weld, that's 13 days of non-stop work. And I am assuming that the welding equipment doesn't need to be moved in.

As Johnny555 pointed out elsewhere in these threads, the divers are having problems putting in a communications cable, which is much smaller and more flexible.

[simon_acca → eesmith]

Thanks for doing the math, looks plausible to me. Just for the argument sake, since there seem to be logistical problems (hey, Hanoi is not that far away, right?) to the whole solution: you could carry out several non-adjacent welds in parallel and then join these segments together, that would speed things up.

The data cable seem to have water damage problems, something that would not be a concern here it seems.

[eesmith → simon_acca]

How do the divers get to the non-adjacent welds if the pipe blocks their way?

How are they supplied?

Why should we assume that the require equipment won't also suffer from water damage? Eg, "around small passages" might mean the cable scraped against the wall, causing water to leak in.

BTW, it seems the critical section is under 5 meters of water, not 6 as I thought, and is 70cm across.

And it seems one of the divers just died. If that's an indication of the mortality rate, then imagine how many might die building a tube.

[Johnny555]

Note that they had issues just pulling a simple communications cable, I can't imagine that a 2ft diameter rubber tube is going to be easier.

However, attempts to install the cables have been unsuccessful so far, Maj. Gen. Bancha Duriyaphan said. One cable suffered water damage as divers transported it "around small passages." Teams are attempting to take in a new one.

https://www.cnn.com/2018/07/04/asia/thai-cave-rescue-intl/in...

[aaang]

I was thinking this too. Wide PVC plumbing pipe with joints for the angled sections, just for the water filled sections. The person is wrapped, arms up, and pulled at speed through the pipe via a rope attached to some kind of harness attached to the waist, legs and feet.

[simon_acca]

Elon Musk seem to think this is an option worth exploring: https://twitter.com/elonmusk/status/1015105500105412610

[cimmanom]

AFAIK, there's no path through the tunnel that would allow one end to be brought through while keeping it above water.