Might be a stupid question but.....

[boulderjohn]

I just now came upon this thread. I thought I would relate a true story from a few years ago just for consideration. (I am doing this from memory, and I may have a couple minor and unimportant parts wrong.)

Diver A was planning a big dive, and in preparation, he deposited at least one AL80 n the cave. He had not yet begun the planned big dive.

Two of his friends who knew his plan, Divers B and C, went on an unrelated dive of their own, using scooters. During their exit, the two took a wrong turn and ended up in a tunnel that was inappropriate for scooters--too narrow and silty. They silted it out completely and were stuck. The rearmost of the two eventually worked his way out and decided that the best way to save his friend was to exit as quickly as possible and summon a rescue team. He took off.

The other diver eventually managed to extricate himself, and he started for the exit. He knew he did not have enough gas to make it. He headed for where he knew diver A had stashed a tank and picked it up. He was breathing from that when he encountered the rescue team near the entrance.

 

[_Ralph]

1/3 of 2/3?...2/9ths?

Yes, harder to do the math that way...

_R

 

[Wstern5]

I just now came upon this thread. I thought I would relate a true story from a few years ago just for consideration. (I am doing this from memory, and I may have a couple minor and unimportant parts wrong.)

Diver A was planning a big dive, and in preparation, he deposited at least one AL80 n the cave. He had not yet begun the planned big dive.

Two of his friends who knew his plan, Divers B and C, went on an unrelated dive of their own, using scooters. During their exit, the two took a wrong turn and ended up in a tunnel that was inappropriate for scooters--too narrow and silty. They silted it out completely and were stuck. The rearmost of the two eventually worked his way out and decided that the best way to save his friend was to exit as quickly as possible and summon a rescue team. He took off.

The other diver eventually managed to extricate himself, and he started for the exit. He knew he did not have enough gas to make it. He headed for where he knew diver A had stashed a tank and picked it up. He was breathing from that when he encountered the rescue team near the entrance.

That’s a lot to unpack

 

[lostsheep]

Yes, harder to do the math that way...

Care to elaborate on this one? I agree the math is harder, but it's not rocket science. 1/6=.17 , 2/9=.22

Is someone teaching this?

I'm just a lowly 1/6 intro cave diver so bear with me

 

[lermontov]

I just now came upon this thread. I thought I would relate a true story from a few years ago just for consideration. (I am doing this from memory, and I may have a couple minor and unimportant parts wrong.)

Diver A was planning a big dive, and in preparation, he deposited at least one AL80 n the cave. He had not yet begun the planned big dive.

Two of his friends who knew his plan, Divers B and C, went on an unrelated dive of their own, using scooters. During their exit, the two took a wrong turn and ended up in a tunnel that was inappropriate for scooters--too narrow and silty. They silted it out completely and were stuck. The rearmost of the two eventually worked his way out and decided that the best way to save his friend was to exit as quickly as possible and summon a rescue team. He took off.

The other diver eventually managed to extricate himself, and he started for the exit. He knew he did not have enough gas to make it. He headed for where he knew diver A had stashed a tank and picked it up. He was breathing from that when he encountered the rescue team near the entrance.

im assuming diver A found out about the used gas before they started ?

 

[drk5036]

So this is kind of a facetious question, but if we are dropping tanks just for the heck of it, why not just keep some emergency tanks dropped every x feet throughout the cave system? Like fire extinguishers in a public building? Pay for the upkeep with park entrance fees?

 

[boulderjohn]

im assuming diver A found out about the used gas before they started ?

The whole things was a rather big deal, so, yes.

 

[_Ralph]

Care to elaborate on this one? I agree the math is harder, but it's not rocket science. 1/6=.17 , 2/9=.22

Is someone teaching this?

I'm just a lowly 1/6 intro cave diver so bear with me

First 1/3 is purely reserve, then take a 1/3 of the remaining 2/3... a little more gas for the first level of cave diving, but still lots of gas in reserve for the first level of cave diving.

Keeps the same ‘math’ (thirds) throughout your cave diving... (rather than 1/6th, or 1/2 a 1/3rd)

Some organizations teach this way instead of 1/6ths


_R

 

[halocline]

I believe that the 1/6 rule for cavern and intro divers is not a gas planning limitation, its a penetration limitation. Basically the rule is saying "at your level of experience you should never penetrate more than 500PSI on AL80 doubles" or whatever your tanks are. This is why you can go to 1/3 on a single tank (although diving with a single tank in an overhead is rightfully pretty well obsolete). It's also why you can do an intro level training dive with a full set of doubles, turn at 2500PSI (using AL80s as an example), exit with 2000PSI, and do another training dive on the same set, turning this time at 1500PSI. You still keep a minimum planned exit reserve of 1/3 your tanks' capacity. There is a lot of confusion about this particular rule, I believe.

Whether or not diving to 1/3 penetration is conservative enough or not is an entirely different conversation.

 

[Capt Jim Wyatt]

I believe that the 1/6 rule for cavern and intro divers is not a gas planning limitation, its a penetration limitation. Basically the rule is saying "at your level of experience you should never penetrate more than 500PSI on AL80 doubles" or whatever your tanks are.

Yes that is the reason that 1/6 rule exists at the intro/apprentice level.