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Comment by breals | Hacker News Reader

I know this was posted due to the Thai cave rescue but what is discussed in this manual and what they are doing are different. Exley wrote this because scuba divers, some even experienced cave divers, were dying in cave diving accidents and landowners in Florida were closing caves or banning diving. This blueprint is more accident/incident analysis than training material. It was required reading when I got cave trained ~17 years ago.

The Thai rescue will use some of these techniques but it's whole different set of challenges they have to deal with; being in a silt out with an untrained person who hasn't eaten or slept much for almost two weeks

Sadly Exley died a few years later trying to get into the record books for "deepest cave dive" which goes again "Going too deep"

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For people who've never had the experience, it's stunning how fast a stray kick into the silt can turn the water in a cave pitch black. Like barely able to see your hand dark. Even when you're used to it most people will find it very claustrophobic.

From the surface, it's easy to say just follow the guide cables the divers have no doubt installed. Doing that in person is quite different.

The other issue is these are some calorie deprived kids probably not in shape for an extended workout. Maintaining body heat and fighting a not-particularly strong current for 10 hours is taxing for very physically fit people who haven't been food deprived. And who aren't scared out of their minds and burning through oxygen.

> For people who've never had the experience, it's stunning how fast a stray kick into the silt can turn the water in a cave pitch black. Like barely able to see your hand dark. Even when you're used to it most people will find it very claustrophobic.

For some reason reading this made me shiver in fear. I don't usually visualize scary stuff when I read it, but this did it. I know I would be scared to death if it were to happen to me.

In practice, the training is excellent and you'll have dozens of zero-visibility experiences before finishing the certification. You learn that as long as you have the line in your hand and you stuck to your gas limits, you have everything you need to make it out alive, even if it takes you twice as long to do so.

...the trick is what happens when you don't have the guideline in your hand, or something goes wrong with your equipment, or someone's tanks run out, or a diver gets lost, etc. But you train for that, too.

From the surface, it's easy to say just follow the guide cables the divers have no doubt installed

Someone asked my cave instructor, if you lose the line how long should you search for it? The rest of your life, he replied.

Probably a naive question, but why don't they hook people up to guide cables with another line or cable?

Because then you couldn’t pass a tie-off, where the line is fixed to something like a rock. Also, risk of entanglement.

why not use something like in via ferrata sets - a single easy-to-open carabiner with a short cord, attached to you. when you climb a ferrata, you clip&unclip hundreds of times, nothing particularly complicated or taxing, and in water you would need only a basic one with little resistance on the gate opening part.

you could pass along the cable holding the carabiner in one hand, not slowing you down

You could pass a tie-off if you had two carabiners, as you do in via ferrata. Don't know about the entanglement risk though... I'm not a diver but that sounds way less dangerous to me than losing the cable altogether, since worst case you could just release the carabiner

Another thing to consider is this is just a guideline - 2-3mm nylon, fixed in place often just be wrapping around a handy outcropping. If you tug on it with any force it will come loose. And then you and everyone in the cave with you are in a lot of trouble.

Another thing that guide mentions is that if the nylon guideline is cut, it will rapidly snap and retract and spool up (kind of like a fishing line).

Also I read an accident report of some divers who survived a silt out condition, they spent a lot of time carefully figuring out what direction they should follow the rope out to exit the cave in places where it has been wrapped around a stone a few times to anchor it.

Do the guide lines have any indicators that would show which way goes further into the cave and which way heads toward the surface?

Yes, triangular plastic line arrows, you can tell just by feel which way to go if you are totally silted out - provided you can find the line itself

Most popular caves have permanent lines installed with arrows every ~100 ft or so, maintained by the local community. A common convention is that the main / most navigable path through a system uses a slightly thicker, yellow nylon line (the "gold line"), while side passages tend to use thinner, white nylon. Divers are expected to bring their own reels and markers into the cave to make and mark temporary connections, for example, from open water to the gold line, or jumps from a permanent line into side passages. Reels are also useful tools for locating lost guidelines in zero visibility.

There's an overview of various line markers at https://www.tdisdi.com/cave-diving-directional-and-non-direc..., and a great photo of line arrows and a gold line / jump reel connection on Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Line_arrow.jpg

The trick is, the permanent arrows indicate the closest "exit" to the system, so if there's a 1000m cave connecting two freshwater springs, then at the 500m mark you would usually encounter two back-to-back arrows, one pointing to each exit. The trick is, if you haven't personally explored both exits, you can't be certain that they're both navigable. So if you're 750m into that system, lose visibility, and need to get out by feel, you have to find the nearest arrow and then blindly swim in the opposite direction from what it says is the exit. It's... "fun."

I grew up in Florida near some popular diving caves. One of the most memorable bits of local apocrypha was about the dead divers they pulled out.

Lost in the dark and running low on air, they would claw at the limestone ceilings of the tunnels they were trapped in until the flesh of their fingers was worn away. Even then they’d keep scratching with their exposed bones.

Never developed an interest in cave diving, myself.

I visited Nacimiento del Río Mante on a spring break caving trip to Mexico ten years ago. We were a group of dry cavers headed back from the Aquismon area. We camped by the spring and I fondly remember swimming on top at night and exploring the small amount of dry cave there. The stream of water coming up was ridiculously strong and very warm. It was a surreal feeling, looking up at the stars and moon, knowing that below your feet there was almost a thousand feet of water extending hundreds of feet below sea level. I remember thinking that Exley's depth record there felt like reaching the moon in terms of exploration.

I didn't think a silt out was relevant to this cave.

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