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Basic Cave Diving: A Blueprint for Survival (1986) [pdf] (nsscds.org)
77 points by wallflower 6 months ago | hide | past | web | favorite | 43 comments

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"

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.

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.

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

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."

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

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.

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.

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

> 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.

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.

Based on what I know about cave diving, it seems both terrifyingly dangerous and also just plain terrifying. Just this image is enough to put me off forever: http://i.imgur.com/7Vr7F1r.jpg

I watched a cave diving documentary a few years ago about finnish divers that lost a couple of friends while diving. The film was about the rescue of the bodies and is called "Diving into the unknown". After watching that, the dangers of cave diving were quite clear. Highly recommended for people interested in the subject

Detailed BBC article about that accident and recovery, the same accident on which "Diving into the Unknown" is based: https://www.bbc.com/news/magazine-36097300

Also recently on HN, "British divers at heart of Thai cave rescue among best in world": https://news.ycombinator.com/item?id=17448311 (the British divers in the Thai cave rescue also attempted a recovery in the accident for Diving into the Unknown, and stopped because it was too difficult.)

I am very interested in learning about the project management/logistics of the operation in the cave.

You have the personnel, who speak different languages, and of variable ability.

There are tasks to accomplish such as laying supply lines, placing cylinders, finding the boys, accompanying lesser trained divers.

There are supplies to manage, food, water, equipment.

I suppose armed forces specialize in planning these types of operations. Most other project managers have more of a luxury of time. I just am amazed about how they put this together. I hope they put together a report afterwards, because people need to learn an awful lot from this.

Somehow it's easier. In hard times only the truly competent lead. In peace times, the incompetents want to lead. They want to have a title, not to lead actually.

That’s not accurate. There is no shortage of poor decision making in war. I just finished Arnhem by Antony Beevor which is about Market Garden. There is a complete fiasco if you want one, and there are unlimited other examples.

Are there any armed forces doing cave diving - I know that US SEALs and UK SBS (and others) do a lot around diving but cave diving would looks like a specialism that wouldn't have much direct military relevance?

I've read in some articles that there are no military divers specialized in cave diving. Experienced private cave divers are of more help here.

Well, a so called former Thai Navy SEAL died during this rescue operation, so I guess they are.


I'm sure special forces are incredibly tough and very skilled - I was just wondering whether there would be any reason for them to train in the skills relevant to cave diving.

Wreck salvage. It's not quite the same skillset as cave diving, but wrecks have many very similar hazards.

Of course, the most dangerous person is someone who thinks they know what they are doing.

There was a news story in 2004 or so, where a team of british soldiers got stranded in a cave in Mexico. To assist with local efforts, two brits flew out - one of whom, civilian firefighter Richard Stanton, was also one of the two brits who found the kids in Thailand.

While there may have been other reasons not to send a military presence to assist (I recall it being a rather messy situation as it was), it seems clear we know exactly where the expertise is here, and don't let silly 'special forces' bravado get in the way of getting the job done.

Since there is a considerable risk of panic here, do you think that the rescuers will either pre-sedate the boys, or have sedatives on them to administer if they panic?

Is there any sedative available which calms you down without also reducing your cognitive/motor capabilities?

I'm not sure the children's cognitive abilities are particularly relevant, as blunt as it sounds. It's not like in the last 2-3 days they've trained them to a level beyond the Thai SEAL who didn't make it.

Panicking is almost the worst thing that could happen here. Someone flailing around is a threat to their own apparatus, their rescuer's apparatus, and at best depletes their own oxygen much faster.

It sounds incredibly cruel, but I'd completely understand if they opted for a doped deadweight. I'd also completely understand if they didn't advertise such details until they're certain it was successful. Having the whole world watching adds some political tightropes.

I know almost nothing about cave diving, but I can't imagine sedating the people being rescued would be a good idea. Is sedating people in cave diving emergencies a normal thing?

In one of the TV interviews a cave rescuer talked about a rescue where an inexperienced diver was restrained whilst being brought out of a tunnel. Given the distances involved here it would seem unlikely they would sedate them.

EDIT: "Mr [Peter] Dennis also said he thought the boys would have been lightly sedated by a doctor who joined them in the chamber, to prevent them from panicking during the journey out." From the BBC live reporting webpage.

I posted this because, of course, of the ongoing rescue operation but more for the helicopter pilot-like checklists to stay safe and stay alive. I understand that recommendation #4, #7, and #8 are practically nil'd in the case of the Thai rescue operation (cold iced coffee-like water and the untrained, not-in-great-health kids).

It reminds me a lot about how methodical planning and preparation can help prepare for a better outcome, especially when problems occur. Particularly, the part of how they practice buddy breathing and hand signal communication before going into the real depths reminds me of the proverbial testing before you are ready to "go live in production" (without life/death consequences, just 'revenue' of course). I won't belabor the metaphor but there is something that can be learned from those who go into some of the riskiest situations that a person can put themselves into precisely by "de-risking" as much as possible. For example, the probability of all three lights failing is a fraction of a percent. In a non-silt situation, having a light fail is equivalent to becoming blind.

If you are like me, this X-Ray Mag site below is a fascinating armchair way to read about the small world of cave divers. I know that the closest I will ever get to cave diving is with a full-immersive VR experience when the great, great grand-children of Oculus arrive. My scuba-loving friends all called it at open water night diving. Even wreck diving was regarded with awe. Cave diving was like being an astronaut.


Also, the accident reports are NTSB-level in their analysis.


The "Ten Recommendations for Safe Cafe Diving"

1. Always use a single, continuous guideline from the entrance of the cave throughout the dive.

2. Always use the "third rule" in planning your air supply (this means 1/3 to go to where you want to go, 2/3 to return and for emergencies)

3. Avoid deep diving in caves

4. Avoid panic by building up experience slowly and being prepared for emergencies

5. Always use at least three lights per diver

6. Always carry the safest possible scuba.

7. Avoid stirring up silt.

8. Practice emergency procedures with your partner before going diving, and review them often.

9. Always carry the equipment necessary for handling emergencies, and know how to use it.

10. Never permit overconfidence to allow you to rationalize violating recommended safety procedures.

> Cave diving was like being an astronaut.

At age 16 (or so), I dived into an undersea cave in Sardinia, pretty much completely unprepared.

I had scuba gear, but only a "waterproof" flashlight (read: not a proper diving lamp by any means), no line, no backups, no nothing. Just a teenager's sense of invincibility.

It was almost literally otherworldly, floating through bone-white passages full of strangely shaped rocks, and being so palpably close to my own fate.

It was also very scary for reasons both objective (I knew it was monumentally stupid going in) and imagined (the darkness beyond the cone of your lamp is full of sharks, giant kraken, and Cthulhu).

I turned around after five minutes. On the way back, noticed a fork in the cave. Had a horrible sinking feeling and cursed myself for not looking back on the way in. Picked a path at random, and apparently picked right.

It was the best experience I never want to repeat again.

Are those accident reports publicly available online? The site you linked seems to have a one line summary of each accident but no link to further details.

The IUCRR maintains a few public incident reports at http://www.iucrr.org/. Look under the"Accident Analysis" heading on the left.

At least ten years ago, when I went through cave training, incident reports were a significant fraction of the curriculum between Apprentice and Full Cave certifications. If you weren't in the overhead, you were reading about people who didn't make it back and figuring out how to structurally reduce the risk of suffering the same specific misfortune.

No, sorry. I linked that site in error. That site only has reports available for NSS members. The only accident reports that I have read have come from googling "accident analysis + cave diving" or "aquacorps + accident analysis".

For example the Aquacorps archives on archive.org


Would thoroughly recommend reading "The Last Dive: A Father and Son's Fatal Descent Into the Ocean's Depths Paperback" by Bernie Chowdhury. It features the author of this pdf, Sheck Exley quite extensively.

1. Reconsider whether you actually need to dive into this cave...

That's pretty much the first line of the standard warning sign you see underwater: https://pbs.twimg.com/media/CkwjzltUUAEjHvV.jpg


Wow, depth blackout is scary

Though the best prevention for accidents still seems to be: don't get into a cave without training (and even then!)

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