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It's surprising to see such an article #1 in HN ... right after a long weekend of cave diving training! It's a sport that requires a lot of preparation, planni

It's surprising to see such an article #1 in HN ... right after a long weekend of cave diving training! It's a sport that requires a lot of preparation, planning, risk estimation and counter-measures. My hobby cave dives are nothing like such explorations, but the principles are the same. In the end, when you go diving, the level of risk is close to 0: one regulator may fail (risk around 1/100 if well checked), two won't fail during the same dive (risk of two failures 1/100 x 1/100 = 1/10000 which is negligible--if I got the figure right, I didn't double check! EDIT: it's rather 1/1000 x 1/1000 = 1/1.000.000). And we use two independent air tanks, and with air reserves managed with one regulator fault in mind, as well as the 'little' panic induce by the regulator fault. That's called the 1/4 rule, we use it in France in FFESSM diving organisation.

elcapitan 10y ago
I guess that depends on how you think about risk - if it's about some probability of an unfortunate event, or maximum unavoidable damage in case of that event. A 1/10000 chance of certain death doesn't sound like something I'd like to take.
- wazari972 10y ago
  > A 1/10000 chance of certain death doesn't sound like something I'd like to take. (maybe I was a little bit off, it's more likely that the risk of failure is 1/1000, so sum is 1/1.000.000) but the point is, it's more risky to drive back home after the weekend than to recreational cave dive, especially with dive fatigue!
  - elcapitan 10y ago
    > it's more risky to drive back home after the weekend than to recreational cave dive, especially with dive fatigue! I think that's the same issue with risk assessment and mixing up probability and impact: A problem when driving home is not a 100% certain death sentence, and it is not something you could not mitigate. You can drive slower, try to avoid dangerous streets etc. And even in the event of an accident you have systems that might save you (airbag etc).
  - chimprich 10y ago
    You have more risks than just reg failure though. Losing your line, line snapping, floods, rockfall, silt bank collapse, getting physically stuck, just to name a few. Based on the number of cave divers and the number of cave diver deaths over the past few years I would say your odds of dying on a cave dive are far, far higher than driving home. I think if you believe that you are more at risk driving then you haven't assessed the risks accurately. I speak as an experienced caver with several cave diving friends.
  - crispyambulance 10y ago
    These kinds of risk calculations are perhaps useful for insurance companies, but for individuals doing a "dangerous" sports there is more to the risk than merely probability. In particular, with something like cave diving and mountain climbing the "bad" outcome is going to be death of the individual or their friends and it will likely be the result of a series of bad decisions under stress (each of which makes the situation more dire) rather than an exceedingly rare multiple systems failure.
- grecy 10y ago
  > A 1/10000 chance of certain death doesn't sound like something I'd like to take. Your chance of certain death is 1. It's only a question of when.
  - thaumasiotes 10y ago
    Some people consider that question fairly important.
- beefield 10y ago
  https://en.wikipedia.org/wiki/Transportation_safety_in_the_United_States https://en.wikipedia.org/wiki/Transportation_safety_in_the_U... More than one death per 100 million miles gives worse than 1:10 000 odds per 10 000 miles. If you do not want to take 1/10 000 death risks, you would need to limit your lifetime car travels to way less than 10 000 miles.
  - elcapitan 10y ago
    As I said below, this is not comparable. 1 death in 100M miles means most likely stupid behavior leading to an accident. That's pretty ok. You can mitigate that risk. Don't drink and drive. Don't drive when tired. Don't drive too fast, avoid fast streets/highways (where most of the accidents happen). This is different from a setting where something you can't influence at all can fail and then kill you. The probability of the traffic accident is conditional pretty much on the individual case. Having said that, I don't own or drive a car ;)
    - Scarblac 10y ago
      > Don't drink and drive. Don't drive when tired. Don't drive too fast, And particularly, don't share roads with any drivers doing any of the above.
    - beefield 10y ago
      Well, I would argue that in most so called extreme sports the mitigatable (is that a word?) risks play relatively much larger role than in traffic. You can't mitigate a drunken driver colliding with you, but it is precisely you who makes the knots in the climbing rope and packs your parachute correctly. And, given so small probabilities, even if you tell yourself that you are mitigating the risk by not drinking&driving, it is virtually impossible for you to know that you do not have some other habit that increases your death probability to the average levels or above. Are your reaction times slower (or faster) than other peoples? Do you hitch a hike always in a car that is properly taken care of? Etc. And if you do not own a car, your lifetime cycling quota in the US cycling environment is less than 2 000 miles[0]. Even less mitigating other peoples' mistakes than in a car. [0] http://www.mrmoneymustache.com/2013/06/13/bicycling-the-safest-form-of-transportation/ http://www.mrmoneymustache.com/2013/06/13/bicycling-the-safe...
- chimprich 10y ago
  Do you eat bacon? If so your chances of getting colorectal cancer are likely increased by a fair bit more than 1/10000.
  - elcapitan 10y ago
    No, I don't eat bacon.
  - junto 10y ago
    Just of of interest of that all cured ham or is there something sorbian about bacon particularly?
- scythe 10y ago
  His independence assumption is wrong. If one regulator fails, you return to the surface ASAP. That leaves much less time for the second regulator to fail, and a smaller conditional probability.
- anro 10y ago
  Gear failures is almost never a big part of cave accidents. But lack of training and following established best practices is a big part of cave diving deaths. (Actually cave diving used to have better statistics than regular recreational scuba diving. ) In this case I do think the accident could have been avoided by following the established best practices they all knew.
hjalle 10y ago
Sounds fairly high with a regulator failure rate of 1%, especially if it is well checked, isnt it?
samwilliams 10y ago
Take 100 divers, each performing 100 divers in their lifetime. One of those people will encounter double regulator failure. I am not a diver, so I am not sure whether this is a definitely fatal scenario. However, if that is the case it would imply that 1% of divers that perform 100 dives will die from this one mode of failure. Given that I am sure there are many other ways that one could die in submerged caves like these, as the people in the article did, I imagine that the actual 'lifetime probably' of death in frequent cave divers is much higher.
- philbarr 10y ago
  I ran out of air once, which obviously has the same effect as "double regulator failure" and I was fine. If you have failures like this you're taught to share air with your "buddy".
  - eggy 10y ago
    I worked for 5 years, and part of my job was inspecting, maintaining, and making emergency repairs on underwater hydraulic and electrical systems aside from the structural work. Running out of air in recreational diving is one thing, but in the tight, dark spaces of a cave, or under a moving piece of machinery it is another. The one guy, Huotarinen, in the article died while trying to switch mouthpieces, and he was an experienced cave diver, not recreational diver.
    - anro 10y ago
      He died at 130m stuck in a tight restriction, breathing a rebreather and after many attempts on freeing him self he died when he tried to switch to bailout gas. The reason why he didn't manage to do such an easy task is most likely related to the fact that he had been breathing heavily from the rebreather and because of that most likely suffered from hypercapnia (to much Co2)...
- lamontcg 10y ago
  With 2 dives and 4 regulators on the team, it takes 3 failures to reduce the whole team down to 1 regulator -- and even then there's ways to survive and get out of the cave. So more like 100^3 to start with, and then the failure rate in practice is lower than that (I've done 200 cave dives and I've had 1 failure -- and I know many other cave divers with similar levels of experience that have had none).
simplemath 10y ago
It's an incredible hobby, to be sure. But it's also verifiably one of the more dangerous sporting activities known.
blubb-fish 10y ago
1/1000 x 1/1000 only holds for two independent events. If the gear production and preparation is linked personally, locally, informally, productively ... then the probability of the backup device also failing is larger than 1/1000 if the main one failed.

elcapitan 10y ago

I guess that depends on how you think about risk - if it's about some probability of an unfortunate event, or maximum unavoidable damage in case of that event. A 1/10000 chance of certain death doesn't sound like something I'd like to take.

wazari972 10y ago
> A 1/10000 chance of certain death doesn't sound like something I'd like to take. (maybe I was a little bit off, it's more likely that the risk of failure is 1/1000, so sum is 1/1.000.000) but the point is, it's more risky to drive back home after the weekend than to recreational cave dive, especially with dive fatigue!
- elcapitan 10y ago
  > it's more risky to drive back home after the weekend than to recreational cave dive, especially with dive fatigue! I think that's the same issue with risk assessment and mixing up probability and impact: A problem when driving home is not a 100% certain death sentence, and it is not something you could not mitigate. You can drive slower, try to avoid dangerous streets etc. And even in the event of an accident you have systems that might save you (airbag etc).
- chimprich 10y ago
  You have more risks than just reg failure though. Losing your line, line snapping, floods, rockfall, silt bank collapse, getting physically stuck, just to name a few. Based on the number of cave divers and the number of cave diver deaths over the past few years I would say your odds of dying on a cave dive are far, far higher than driving home. I think if you believe that you are more at risk driving then you haven't assessed the risks accurately. I speak as an experienced caver with several cave diving friends.
- crispyambulance 10y ago
  These kinds of risk calculations are perhaps useful for insurance companies, but for individuals doing a "dangerous" sports there is more to the risk than merely probability. In particular, with something like cave diving and mountain climbing the "bad" outcome is going to be death of the individual or their friends and it will likely be the result of a series of bad decisions under stress (each of which makes the situation more dire) rather than an exceedingly rare multiple systems failure.
grecy 10y ago
> A 1/10000 chance of certain death doesn't sound like something I'd like to take. Your chance of certain death is 1. It's only a question of when.
- thaumasiotes 10y ago
  Some people consider that question fairly important.
beefield 10y ago
https://en.wikipedia.org/wiki/Transportation_safety_in_the_United_States https://en.wikipedia.org/wiki/Transportation_safety_in_the_U... More than one death per 100 million miles gives worse than 1:10 000 odds per 10 000 miles. If you do not want to take 1/10 000 death risks, you would need to limit your lifetime car travels to way less than 10 000 miles.
- elcapitan 10y ago
  As I said below, this is not comparable. 1 death in 100M miles means most likely stupid behavior leading to an accident. That's pretty ok. You can mitigate that risk. Don't drink and drive. Don't drive when tired. Don't drive too fast, avoid fast streets/highways (where most of the accidents happen). This is different from a setting where something you can't influence at all can fail and then kill you. The probability of the traffic accident is conditional pretty much on the individual case. Having said that, I don't own or drive a car ;)
  - Scarblac 10y ago
    > Don't drink and drive. Don't drive when tired. Don't drive too fast, And particularly, don't share roads with any drivers doing any of the above.
  - beefield 10y ago
    Well, I would argue that in most so called extreme sports the mitigatable (is that a word?) risks play relatively much larger role than in traffic. You can't mitigate a drunken driver colliding with you, but it is precisely you who makes the knots in the climbing rope and packs your parachute correctly. And, given so small probabilities, even if you tell yourself that you are mitigating the risk by not drinking&driving, it is virtually impossible for you to know that you do not have some other habit that increases your death probability to the average levels or above. Are your reaction times slower (or faster) than other peoples? Do you hitch a hike always in a car that is properly taken care of? Etc. And if you do not own a car, your lifetime cycling quota in the US cycling environment is less than 2 000 miles[0]. Even less mitigating other peoples' mistakes than in a car. [0] http://www.mrmoneymustache.com/2013/06/13/bicycling-the-safest-form-of-transportation/ http://www.mrmoneymustache.com/2013/06/13/bicycling-the-safe...
chimprich 10y ago
Do you eat bacon? If so your chances of getting colorectal cancer are likely increased by a fair bit more than 1/10000.
- elcapitan 10y ago
  No, I don't eat bacon.
- junto 10y ago
  Just of of interest of that all cured ham or is there something sorbian about bacon particularly?
scythe 10y ago
His independence assumption is wrong. If one regulator fails, you return to the surface ASAP. That leaves much less time for the second regulator to fail, and a smaller conditional probability.
anro 10y ago
Gear failures is almost never a big part of cave accidents. But lack of training and following established best practices is a big part of cave diving deaths. (Actually cave diving used to have better statistics than regular recreational scuba diving. ) In this case I do think the accident could have been avoided by following the established best practices they all knew.

hjalle 10y ago

Sounds fairly high with a regulator failure rate of 1%, especially if it is well checked, isnt it?

samwilliams 10y ago

Take 100 divers, each performing 100 divers in their lifetime. One of those people will encounter double regulator failure. I am not a diver, so I am not sure whether this is a definitely fatal scenario. However, if that is the case it would imply that 1% of divers that perform 100 dives will die from this one mode of failure. Given that I am sure there are many other ways that one could die in submerged caves like these, as the people in the article did, I imagine that the actual 'lifetime probably' of death in frequent cave divers is much higher.

philbarr 10y ago
I ran out of air once, which obviously has the same effect as "double regulator failure" and I was fine. If you have failures like this you're taught to share air with your "buddy".
- eggy 10y ago
  I worked for 5 years, and part of my job was inspecting, maintaining, and making emergency repairs on underwater hydraulic and electrical systems aside from the structural work. Running out of air in recreational diving is one thing, but in the tight, dark spaces of a cave, or under a moving piece of machinery it is another. The one guy, Huotarinen, in the article died while trying to switch mouthpieces, and he was an experienced cave diver, not recreational diver.
  - anro 10y ago
    He died at 130m stuck in a tight restriction, breathing a rebreather and after many attempts on freeing him self he died when he tried to switch to bailout gas. The reason why he didn't manage to do such an easy task is most likely related to the fact that he had been breathing heavily from the rebreather and because of that most likely suffered from hypercapnia (to much Co2)...
lamontcg 10y ago
With 2 dives and 4 regulators on the team, it takes 3 failures to reduce the whole team down to 1 regulator -- and even then there's ways to survive and get out of the cave. So more like 100^3 to start with, and then the failure rate in practice is lower than that (I've done 200 cave dives and I've had 1 failure -- and I know many other cave divers with similar levels of experience that have had none).

simplemath 10y ago

It's an incredible hobby, to be sure. But it's also verifiably one of the more dangerous sporting activities known.

blubb-fish 10y ago

1/1000 x 1/1000 only holds for two independent events. If the gear production and preparation is linked personally, locally, informally, productively ... then the probability of the backup device also failing is larger than 1/1000 if the main one failed.