Turn pressure in the recent incident [Archive] - Cave Diver's Forum

jj1987

09-09-2009, 05:17 PM

Well, I don't have a set answer, but to get the discussion going, I'll throw some numbers out there. Hopefully I don't embarrass myself doing this on the fly in an attempt to stimulate what I think could be a good discussion. These numbers are absolute minimums IMO, and wouldn't really allow for any rescue attempt if I did find the missing diver.

First question is how long does it take me to get out of the cave?
I think a typical pace is 50fpm, boosted by your flow of 20fpm, so for calculations, I'll be exiting at 70fpm.

So from 500ft-
500ft to entrance / 75fpm = 6.6 or ~7min to get me out.

Assuming I'm panic'ed and have a sac of .75 since we're planning for worst case scenario, that means I need-

.75sac*((90ftdepth/33)+1)*7min = 19.56cu ft or ~20cuft of gas to get out.

On LP104's I believe that works out to 204.5psi, and I'd add 100 to that to compensate for the regulator working pressure. Let's double the gas to get out and add 100psi to it, meaning I'd need ~500psi to get us both out.

I guess you can take a cave fill (3600), subtract 1/3 (now 2400) then subtract the gas needed to get out (now 1900psi) and assume that you could dick around for 1900psi in the given scenario, obviously a number that can change based off of the details left out.

I'm thinking of how to calculate this on the fly. I really can't thinkof a way to do this in a cave without a calculator.other than ignore flow, and assume 99ft max depth (or round do the nearest whole ATM) to keep the numbers rounded well.

Here's as close as I can come to "Battlefield Calculations"
.5sac*4 = 2.0 cufpm at depth.
distance/50 = 10min
2*10 = 20cuft

Now, add 50% of that to it's self (.75 wouldn't be something you can calculate in your head)....so 30cuft.

Now, 104's are a tank factor of 8, so 30/8= roughly 4, so you get 400psi for one diver, 800psi for two. We're off by 400psi, almost double (eek!), but this seems like something you can realistically do in your head. Subtract that from my remaining gas.

Great post, Andrew...this should get interesting.

Edit to add- Anyone is welcome to tear apart my math, no offense taken, it's an on the fly thought meant to stir conversation!

09-09-2009, 05:17 PM

I could get out on less than 500 psi, but like Crawford said, it wouldn't do much good to find him, and not be able to help him out. I thought about 1000psi, but he might be breathing fast, not to mention regulators quit working well at around 200 psi. This also assumes we have deco bottles in the cave.

rjack

09-09-2009, 05:19 PM

you're wearing steel 104/108/130s right?

fixxervi6

09-09-2009, 05:26 PM

I wouldn't know how to answer this due to uknown factors, one of them being, who is lost?

Is it my wife or is it my regular buddy? High flow, no flow?

Reason I say that is, I have kids, and the wife and I have an agreement that at least one of us has to make it back even if that means leaving the other. I hope to God it would never come to that, but its a difference of leaving behind 3 orphans or losing a wife/mother/father, its not pretty to think about at any level but its the harsh reality.

Obviously we would both give it our best shots but the extreme need to not turn 1 body recovery into a 2 body recovery is all that more important between the two of us due to kids.

09-09-2009, 05:29 PM

marinediver

09-09-2009, 05:30 PM

It depends... with the distance to the entrance in this accident, I would have stayed till somewhere around 700. But you have to think, if you are that low your buddy is going to be lower or running out. Normally I can exit from hill 400 jump on less than 100 pounds, but would we be able to do it on 700 or less with a stressed out of gass diver sucking on my tanks? Also, what about if you are scooting. I would personally stay till around 500 giving the distance and the fact that I could tow an out of gas diver out and back to deco bottles. I think it starts to get tricky farther back. How many people know just how much gas it will take them to swim from say the double domes area. I know I can swim back from there on half a stage, under ideal conditions. It all really depends on the dive, where you went, and where the problem happens and waht equipment you have on hand. You would have to think about what point you will no longer be any use to the diver you are looking for, and your own personal safety.

marinediver

09-09-2009, 05:33 PM

And how is that any different than your buddy? Either way, you stay as long as you safely can, and no longer.

I hate to sound cold or like a dick, but once you hit the point that your own safety is at risk, I am willing to bet that the lost/stuck diver is out of time and your risking your self for no reason.

El Toro

09-09-2009, 05:43 PM

If I were on the boneroom side in decent visibility I would likely keep searching until I hit 700psi if I were swimming out - 500 psi if I were scootering. I would pad a bit more depending on visibility or my deco obligation. Hopefully, given the traffic through the gallery I would pass another team and alert them to the lost diver situation. And, I wouldn't leave one of my backup lights on the line - just a cookie to let the search team know where I left off.

aainslie

09-09-2009, 05:44 PM

I said I'd shut up but... 700 PSI is more than eouugh to get two people out.

And everyone seems to be assumung a double whammy. i.e. the guy is lost AND totally out of gas, i.e. he somehow got through 1400 psi more than you.

atedeschi

09-09-2009, 05:49 PM

For a dive like that with a 10% SF of my gas plan would look like this:
(Assumming LP85s filled to 3600)
Turn psi 2000 (used 103 cu ft) gets me about 1450' into cave
Use 50 cu ft or 800psi to exit from 1450'
Which leaves me 78cu ft or 1200psi for emergencies

For this situation:
Now if am at 600' which is about half of my total distance in so I need only 400psi to exit plus my buddy so 800psi plus 200psi reserve brings me to 1000psi.

So 1000-1200psi turn pressure, assumming we have deco bottles as well.

wingman

09-09-2009, 06:10 PM

Thinking this in the cave, I’d guess I’m 500 psi in my 104’s from O2 at that point (that’s way conservative given that’s about 40 cubic feet). If I encounter my buddy (there’s a low probability of this) he would need gas as well (maybe more ) so at 1000psi I would pull out my cookie that says “I have left the cave…Bill” and break the cyalume stick that is attached to it via a piece of cave line (I’m calling this a Bosshardt Marker) and attach the assembly to the line at the point I last saw him. At the park bench in the junction room I would stop and breathe my gas down to 400 psi watching for lights back up the gold line and the bone room line. At 400psi I would head for the lips, before going through the lips I would stop and check pressure wait a few seconds for any light coming through the keyhole, no light… I would head for my deco gas at the sign (my deco gas is always at the sign as that way I always have my choice of exits).

amphipod06

09-09-2009, 06:11 PM

Andrew,

There is no option for a CCR diver there diving with an OC diver... not common, I know, but plausible (I regularly dive with an OC friend, team of 2 CCR and one OC diver) We do gas planning slightly different, based on our OC buddy and he routinely carries AL too...

Dive safe,

Celia

novadiver

09-09-2009, 06:17 PM

I would turn off my light. look around for two minutes. turn my light back on , and swim elsewhere , and repeat.

at about 550psi I would call it and leave.

aainslie

09-09-2009, 06:48 PM

Interesting... a common answer has been 1200.

Would that answer change if the separation had been by the Maple Leaf? I.e. is that answer dependent on penetration (i.e. always leave at 2/3) or based on where that location was?

fixxervi6

09-09-2009, 06:52 PM

And how is that any different than your buddy? Either way, you stay as long as you safely can, and no longer.

I'd be willing to risk my neck a little more if my wife was safe on shore, obviously there is that point of no return but this is not a hard science, there is a gray area.

Again the point becomes, at least one of us HAS to return, obviously I'm not saying, well its ok for me to push it to the point I put two bodies in a cave if its just my buddy, I'm saying if I push it to the point that I make it a double recovery, it would be a worse situation if the double recovery was me and my wife vs me and my buddy, I have plenty of life insurance to take care of the family and the kids will at least still have one parent.

Not sure how I can say it to put it into perspective for some people.

sandy

09-09-2009, 07:07 PM

Based on the following assumptions, possibly 900 psi:

1. My buddy is out of air - worst case.
2. I used 600PSI on the way in.
3. I had a deco bottle 50 to 100 feet from the surface.
4. Good viz

Our SAC rate would be higher on the exit but we could cover some ground with the flow which would result in less usage - maybe 400psi each on the way out plus 100psi to spare. Deco bottle would provide extra air if needed and reached.

I will have to check my logs but it seems like I use 1100psi going into JB but only use about 700 to 800psi on the way out with virtually no kicking - just enjoying the ride. A good poll. Next time I dive JB or the Ear, I will take some notes on distance and psi used with kicking and no kicking.

My main buddy is my brother in law so I would push the envelope on this.

aainslie

09-09-2009, 07:50 PM

Let's turn up the heat a little.

45% have said 1200 or above, but none of them have said why.

Why is exiting at 1200 or above a good idea in this case?

atedeschi

09-09-2009, 08:10 PM

i was between 1000-1200 so i voted for 1100psi, with LP85s with a flow of 20fpm therefore i figure im am exiting around 75 fpm. So for 2 divers to exit from that location it will take 1100psi, with a stressed calc rate.

My numbers would change depending on distance from exit, but I dnt think I would think of a quick method to do it for a different distance, so i might start thinking about that alil more along the lines when planning a dive. IE if say I went to 2000' max pen. then maybe i would spilt it up into 1500', 1000', & 500' or something along those lines, I would have to think about it some more.

Neptuno

09-09-2009, 08:47 PM

I'd say, that depends very much on who is my buddy there, if is a guy I have done a very few dives with and never got in some kind of dangerous situation together I'd say never less than 3x of what I need to get myself out safe, so, if it is 400psi will go to 1200, if is somebody that I know very well he can handle stress because has been entangled or in a total silt out before with me a few times, would go as far as possible, like 2x what I need to go out myself and maybe add an extra 100psi for safety

battles2a5

09-09-2009, 08:54 PM

I voted 700. For some of the simple reasons already stated, 1/3's become more and more conservative the closer you get to the entrance in a high flow cave. By the time you get back to that area of Ginnie, you have oodles of gas in reserve so you should have some time to search. I take mental note of pressure at various points on ingress, so I would look at where I am, mutliply that mental note by 2, then add a couple of hundred psi to deal with any CF's while exiting.

uncle ricky

09-09-2009, 08:57 PM

I know from experience that when I'm, uh, let's say "particularly attentive to my predicament," my SCR can easily double with zero extra effort... add to that slowing down for zero vis line following and the possibility of finding my buddy out of air... and excited too..., I figure I need to set my abort point at 8 times the gas I'd normally actually use for the exit from wherever I'm searching, so... from the Harry's Crack jump (500' to fresh air) I'd need to reserve 8 X 5 (minutes to make 500' at a leisurely pace) X .5 cfm (normal SCR) X 3 ATA (I reckon that's a bit deeper than the average depth for this run) = 60 CF, a bit less than 800 psi in 104's; or a bit less than 1000 psi in 85's. If my gauges are accurate. If there are no other delays... if, if, if.
Rick

jcr

09-09-2009, 08:58 PM

Personally, I believe that there's only one acceptable outcome to every dive, which is the safe return of both divers.

Squirrel Girl

09-09-2009, 09:00 PM

Let's turn up the heat a little.

45% have said 1200 or above, but none of them have said why.

Why is exiting at 1200 or above a good idea in this case?

Because not everyone has as good a SAC rate as everybody else. One person's panic rate is another person's everyday rate.

mfascuba

09-09-2009, 09:37 PM

I'm going to do this without a calculator, bear with me.

I know I can exit from 3000 ft on an al 80 towing a scooter (I've done it), with about no gas left when I hit deco. That's 100 psi for each 100 ft into the system, on an 80, for exiting.

I dive double 108's. Knowing that a 108 is larger than an AL80, and knowing that there are two of them (think one for me, one for him), I'll turn hard on 600 psi, if I'm 600 ft into the Devil's Cave System. This gives me enough for me and him (doubles) and margin (108's vs AL80). I also usually dive with an AL80 stage, even if I'm with somebody. This is my emergency reserve, it doesn't get touched. Absolute worst case, I turn at 600 psi, leave the AL80 with a backup light clipped to it, both clipped to the line, backup light on, where the buddy was last seen.

Remember, I've had since Friday to think about this as far as the whole scenario, but I just ran the numbers in my head now to ensure they will work. I'm also not panicking, I'm thinking it through. If I were faced with this in reality, I might stay until 350 to 400 psi, knowing I've got the 80 to get him out. After that I've got to leave though. I have a wife and two kids that I'm not ready to leave behind quite yet.

Mark

rjack

09-09-2009, 09:46 PM

I voted 700 assuming 104s and no deco gas, stages etc

I have never been to Devil's so that factored into my math. By all accounts its only a few 100 psi to exit from that point. I doubt I would know that so intimately so my number is a bit padded for 2 divers (350 each). If he showed up at 701 psi OOA we'd be blowing off deco (absent stages that can't be that much, maybe 15-20mins worth missed?)

mfascuba

09-09-2009, 09:46 PM

Personally, I believe that there's only one acceptable outcome to every dive, which is the safe return of both divers.

Reality has proven that this community suffers from several unacceptable outcomes each year. The point of this discussion is to get people to think things through ahead of time so when TSHTF the thinking part is mostly done. It's been a few years since I did my full cave (2003), and I've not given things like this much serious thought recently - I usually dive solo and am more focused on my oxygen toxicity clock than anything else. This has been a strong wakeup call for me.

Mark

Bob Cree

09-09-2009, 09:59 PM

I voted 800 before I read anything. My thinking started with a ditto on the single stage towing the scooter from 3000. Did exactly the same thing and had just a little gas to piss out when I exited - not very much though.

So I figured (no calculator) under normal calm circumstances 150 psi to exit from the Hill 400 jump + deco. Double the 150 for my stress and assume I need that amount also for a stressed and almost OOA buddy - so say 600. Now my gauge stops indicating at 250...so I kicked it up 200 to 800.

Bob

jcr

09-09-2009, 10:01 PM

Reality has proven that this community suffers from several unacceptable outcomes each year. The point of this discussion is to get people to think things through ahead of time so when TSHTF the thinking part is mostly done. It's been a few years since I did my full cave (2003), and I've not given things like this much serious thought recently - I usually dive solo and am more focused on my oxygen toxicity clock than anything else. This has been a strong wakeup call for me.

Mark

My post was not a meant to be an incidental comment but a serious answer to the question that was posted. Please re-read my post and think about its implications.

BackstageDiver

09-09-2009, 10:29 PM

My post was not a meant to be an incidental comment but a serious answer to the question that was posted. Please re-read my post and think about its implications.
from this i'm getting that you'd stay until you found your buddy no matter what. i know there are lots of people that would sacrifice themselves to save a friend/buddy/family member's life, but if you sacrifice yourself for naught, it is wasted.

BackstageDiver

09-09-2009, 10:35 PM

rjack

09-10-2009, 01:13 AM

09-10-2009, 05:49 AM

We seem to be concentrating on math, when we need to be looking at a larger picture.

There are several possiblilites in any situation. A couple not mentioned so far are:
1. What if the buddy has already left the cave?
2. If not, would it be better to go out and get help with the search, and a lot more spare gas?

What this thread really is about is getting everyone to prepare in advance. A good plan would be to discuss contingincies with your buddies before the dive.

Things like:
How long should we look, before surfacing?
Should we leave a slate/light/arrow/cookie, etc. showing where/when we exited?

The standard *open water* plan is to look for one minute, and then go to the surface. Maybe there needs to be a similar plan for *all* cave divers. It would be terrible to die looking for a buddy that was already out of the cave.

cavemark

09-10-2009, 06:42 AM

I'm not going to die in the process of doing a search for a buddy that may not be in the cave anymore. I had to assume that if I had been in long enough to breath down to an absolute final turn pressure then I will have deco (not much if it was a first dive, but could be 20min on a second dive). If by some chance I do find him and he is totally freaked out and is almost out of gas then we both have to use what is left in my tanks. I have to figure he will probably be breathing twice as much as me, at least until we get to 20ft. I just swam into Ginnie at a rate of about 500psi/1000ft. I'm not going to reduce that for exit flow if I'm under stress which means 250psi for me, 500psi for him and 250psi for both of us for deco.

I need to change my answer to 1,200psi. (LP85s)

Of course if I had Al with me, and I often do even on buddy dives, that would change.

Mark

Doppler

09-10-2009, 08:03 AM

Interesting grown-up question.

Off the top of my head figure is about 900 - 1000 psi. Many reasons for this and all have been stated already.

Not an experience I have had and therefore impossible to answer with anything but a WAG.

Tegg

09-10-2009, 08:35 AM

1000psi

You may get to the O2 you left and it may be empty... no point bending yourself and causing two issues from one.

Especially if vis was reduced greatly in the cave from said missing buddy...

tflaris

09-10-2009, 08:49 AM

Let's turn up the heat a little.

45% have said 1200 or above, but none of them have said why.

Why is exiting at 1200 or above a good idea in this case?

Sitting in front of your PC debating your answer is much easier to do than when you are in a system while separated from your buddy or in a possible silt out situation separated from your buddy.

I answered 1200 psi because in sprite of the distance and in spite of the flow I do not believe that either party would be at their best of sac rates in this situation.

If my buddy was lost I would be activiely looking that means entering the silt out area or back tracking futher into the system to find them. I feel my anxiety level would be higher and reflected in my SAC rate.

I feel my buddy would be experiencing the same and would also be reflected in his or her SAC rate.

You may not be 500-700' from exit when you find them. Maybe they went the wrong way on the main line or the wrong way into a side tunnel when they thought they were on the main line.

In order to save someone else you must be able to save yourself.

MORGAN

09-10-2009, 09:12 AM

In order to save someone else you must be able to save yourself.

Yup. 30 years ago in the fire academy I learned Rule #1: "Do not add to the number of victims."

I put 1000 psi. I know that I can get out comfortably from the Hill 400 jump on less than 500 psi in my LP95's. Doubled it to account for elevated SAC rate, possibly having to share gas, and other unforseen events. This may not be enough.

I tried not to overthink it or do any complex calculations - just came up with a quick answer as I would have to in the event.

I do keep track of my gas use on exit from various landmarks in caves I commonly dive, so I have a pretty good idea of how much gas I need to exit from a particular spot. I ought to put these "gas consumption exiting from X" numbers on a list so that I can refer to them in my dive planning more frequently - as it is now they are scattered through my logbook.

Lots of food for thought on this thread.

Mike

uncle ricky

09-10-2009, 09:13 AM

Something I just thought of to further this discussion: what if you calculate an absolute last ditch turn pressure waiting for a lost buddy, and at the very last instant, find your buddy? His tanks are empty and he has found salvation on your back (or sides or w/e). In both of your excitements, breathing rate increases, and on the way out, you determine that you won't have enough gas to get both of you out alive. What do you do?

Bonus question: reverse roles. You've been lost, you're out of air and your buddy appears with less than enough for both of you. Same question.I'm reminded of a "what if" session with Chuck Yeager soon after he'd broken the sound barrier. One young pilot kept adding "but what if this happened, or what if that happened" to the problem. Finally Yeager said "some day you'll just have to kiss your ass goodbye."
---
One tenet of safety planning is that the more decisions you can make during the planning stage, with the benefit of time to mull things over and to do the math and to consider possibilities, the better. Then all you have to do when the situation hits underwater is to follow the decision you've already made.
The original question posed here is a great case in point, and an opportunity to consider developing some "rule of thumb" to apply to the problem: What is my abort gas supply if I'm looking for my buddy? For me, that's four to eight times the gas I need for a normal exit - double for my buddy, double again for the "excitement" factor, and if visibility is shot, double again for that. Now at first blush that sounds like a lot of gas, but let's take a look...
If I know I normally use 200 psi to make it out of JB (on a normal flow day) from the first "T," then my abort gas from the "T" would be between 800 and 1600 psi, depending on visibility. Let's take the worst case and set it at 1600 - so I leave the "T" at 1600, and head out - but unless I've made the decision that it would be better to go for help than to wait longer, I don't go out. I'm only going to use a fraction of the gas I have reserved while exiting alone and under control, so for every foot I proceed along the exit I'm adding time to my ability to wait for my buddy. So, if I set my next wait point at halfway out (between the first & second breakdowns), I'd arrive there with 1500 psi and could now wait until I reach my new abort gas of 800 psi... bottom line is that my "retreat" from my original search point (if I'm keeping myself under control and breathing at my normal rate) can be at an eighth my normal exit speed, and I can keep gas in the cave - albeit at a diminishing distance from the exit - for a long time indeed.
Rick

crawford

09-10-2009, 09:52 AM

The standard *open water* plan is to look for one minute, and then go to the surface. Maybe there needs to be a similar plan for *all* cave divers. It would be terrible to die looking for a buddy that was already out of the cave.

Yep, this question reminded me of the story, I think I read it in "The Last Dive" where a father and son got separated in a shipwreck, the son went directly back to the boat, and the father died (supposedly) looking for the son while he was sitting safely at the surface.

uncle ricky

09-10-2009, 10:17 AM

...250psi for both of us for deco... Let's take a look at deco vs life saving decisions here.
There's a lot of gravy in most deco schedules.
Are you in a remote area all alone? Or are you somewhere there's a reasonable chance that if you surfaced and hollered "give me some gas!" you'd get some, and could use the old Navy way of deco? (like Ginnie)
Unless I've got a pretty horrific deco obligation and I'm in a remote area, I'm not figuring that into an abort gas calculation with a lost buddy. If he's already exited he'll have gas for me when I get there, eh?
:)
Rick

aainslie

09-10-2009, 10:21 AM

Thanks everyone for participating. This is turning interesting. It does seem like the most conservative turn would be about 1200 (very few put higher numbers) and few put 500.

I'll give my number at this point. I put 500 assuming I was using my 108's - I'd up it to 700 on 85's. Let me try to explain why. The following scenarios could occur:

1) You never find him. In which case 500 is plenty to exit - comfortably double (at least on my SAC/swim rate. My SAC sucks but I move fairly fast). Try it one day - youll be surprised how little gas you use from that point to the exit.
2) You find him with gas. Also not a major problem.
3) You find him, out of gas, exactly at 500. The thing to realise is that this has an infinitesimally small probability. Remember what I said earlier - a lost buddy drill has two participants. It's unlikely that s/he is even more stressed than you. So unless they had a pretty catastrophic gas loss (~1000 psi) this is unlikely.

Sure, I'm playing a probability game, but all of life is a probability game. So I'd ignore the OOA AND lost scenario simultaneously as too improbable. I understand that these type of events will induce correlation, making their joint probability far higher than the product of the independent probabilities, but I still think it's too low to be a major factor.

So now we come down to other issues -

High SAC? Yeah, it's possible. I can certainly see someone increasing to (say) 800 for that reason alone.

Low vis? GIve me a break! In the absolutely worst siltout I've seen in Ginnie (which I created, I ahve to admit), the vis dropped to about 3 or 4 feet. If you need to slow down for 3 ft vis, you need to practice low vis exits more. This should NOT be an issue

Deco? Get surface O2, and/or go to a chamber. This small deco obligation is unlikely to hurt you that badly.

So... 500 psi is dangerously low. But death is a pretty irreversible scenario.

All this is while sitting comfortably in my armchair. Underwater I doubt I'd be this level headed. I suspect I'd get the hell out of Dodge at the higher number - i.e. 800. But that's what these exercises are for - to think it through when you have the luxury of time in order to know what to do when the actuality happens.

I think the really important issue is, in a cave that you dive frequently, it REALLY helps to know how many psi you use per 100 ft of exit. This can be a real lifesaver in an emergency.

jcr, your answer sounds cute but it's intellectually lazy and ambiguous simultaneously. What's your number? And I hope to God you're not suggesting suicide. It's just stupid to go so low that a solo exit becomes infeasible.

uncle ricky

09-10-2009, 10:25 AM

This question brings up one of the reasons I like three man teams for caving. If a buddy gets lost (or stuck, or whatever), the remaining two can send one for help immediately.
Rick

aainslie

09-10-2009, 10:28 AM

This question brings up one of the reason's I like three man teams for caving. If a buddy gets lost, the remaining two can send one for help immediately.
Rick

It reminds ME of why I like solo. This becomes a non issue!

LCF

09-10-2009, 10:45 AM

Andrew, I just want to thank you for, once again, starting a really good, though-provoking thread which elicited a number of interesting answers. And thank you to Rick, for one of the best ones. Threads like this are why reading bulletin boards is worth the time I spend doing it.

uncle ricky

09-10-2009, 10:48 AM

It reminds ME of why I like solo. This becomes a non issue!Yes, yes, solo... I remember that... never forget the day it changed... 'bout three years ago... I'd had trouble clearing an ear, and sent the other two on ahead into Hole-in-the-Wall (Merritt's Mill Pond). Finally got my ears cleared & headed on in, with the idea that I'd meet 'em and join 'em on their way back out. It was the usual milky water for Hole, so I was sticking pretty close to the line, easing on in, when my little pea brain began to think, "Rick, you're nearly 60; if you have some 'event' right now you'll drift off the line, they'll never see you, and your dumb ass will die, and the Lovely Young Kat will be really pissed off at you!"
Quit solo caving then and there.
In another decade you may reconsider, too :)
Rick

novadiver

09-10-2009, 10:50 AM

WOW, 65% would bolt with 1000psi or more. I guess you really can't trust most divers to watch your back. Hell a few would even try , and would bolt with 2400 psi.

In doubles no less

aainslie

09-10-2009, 11:05 AM

WOW, 65% would bolt with 1000psi or more. I guess you really can't trust most divers to watch your back. Hell a few would even try , and would bolt with 2400 psi.

In doubles no less

I woudn't condemn these people. Remember, this is pretty much what the agencies teach. Well, tehy really don't teach anything when it comes to lost buddy turns... but it's not surprising that people use high numbers, especially if they're just out of training.

It'd be nice if agencies spent a little more time on this.

novadiver

09-10-2009, 11:13 AM

I woudn't condemn these people. Remember, this is pretty much what the agencies teach. Well, tehy really don't teach anything when it comes to lost buddy turns... but it's not surprising that people use high numbers, especially if they're just out of training.

It'd be nice if agencies spent a little more time on this.

1/3 as a rule of thumb is fine for safe penetration (given the flow is right) but the reserve 1/3 is for emergencies. I realize it's important to stress not letting one fatality turn into two , but I'd feel like crap if I got out of the water with 1500psi and my buddy didn't make it home.

That's just the way I feel about it. Everybody has the right to make their own decision

Oister

09-10-2009, 11:15 AM

I can’t remember if I picked 1800 or 1200 my choice one the fly in like 15 seconds with no calculator was 1600 psi. maybe I would of pushed it who knows till you have to leave your buddy. Maybe this is a drill should be included in class the leaving your buddy part. The rules say anything under 2400 is in violation of the rule of thirds but what is that reserve for? I would think this would include searching for a buddy.
The one thing I did not see mentioned was now YOU are a solo diver in my mind that requires at least some reserve. Because we all know “things are going to happen”
My next cave dive with a buddy we will include lost buddy turn pressure. I for one do not want anyone dying looking for me.

WOW, 65% would bolt with 1000psi or more. I guess you really can't trust most divers to watch your back. Hell a few would even try , and would bolt with 2400 psi.
In doubles no less Watching your back and dying for you are to different things. What happens when your playing hero suck your tanks down to 900psi looking for your buddy on the way out all your thinking is I have to get out to save my buddy and 2 things go wrong on your way out do you still have enough gas? Did I mention your buddy lost you looked till he hit 1500 then swam to get help for you.

ScubaBob-Squaretank

09-10-2009, 11:54 AM

I figure 600 lbs should be more than enough for myself, and my buddy should we meet on the way out. By about 700 lbs I would be really watching my gauge and checking the vis out.

aainslie

09-10-2009, 12:18 PM

1/3 as a rule of thumb is fine for safe penetration (given the flow is right) but the reserve 1/3 is for emergencies. I realize it's important to stress not letting one fatality turn into two , but I'd feel like crap if I got out of the water with 1500psi and my buddy didn't make it home.

That's just the way I feel about it. Everybody has the right to make their own decision

You know, with respect, that's NOT a good answer. A generic rule like "use your spare third" just doesn't cut it IMHO. It's too little in this case, and way too much in other cases.

It's still important to reserve double the gas that you need to exit. If you go down to 1/3 in a no flow cave on a straight in swim, that's just nuts (it's why no flow caves are so damn dangerous IMHO). There were two big differences here: 1) high flow, 2) they weren't very far in.

If I'd been at the coathangers I'd have left with nearer 1000-1200. If I was in Mexico in a passage with no other exits and we'd done a straight swim to 1/3, and I then lost him, I would spend very little time looking before exiting.

The safe exit pressure is highly context dependent.

LCF

09-10-2009, 12:23 PM

My agency did address this in detail. As I've said elsewhere, I think, I was taught to take "snapshots" on the way into the cave, so I know at a given point that it took me "x" minutes to get here, and I used so many psi. That way, if I have to do a search, I double the gas it took for me to get where I am and subtract that from what I have (on the idea that I may need some gas to extract my buddy). I can then search using thirds on what I have. I WAS taught to assume the person I find may be out of gas, or nearly out of gas, and that I have to have enough gas to get him and me back to the start point of my search, and then out of the cave, and that may be too conservative. But we did go over this, and we were expected to do the gas calculations when we did the lost buddy drill.

novadiver

09-10-2009, 01:08 PM

You know, with respect, that's NOT a good answer. A generic rule like "use your spare third" just doesn't cut it IMHO. It's too little in this case, and way too much in other cases.

It's still important to reserve double the gas that you need to exit. If you go down to 1/3 in a no flow cave on a straight in swim, that's just nuts (it's why no flow caves are so damn dangerous IMHO). There were two big differences here: 1) high flow, 2) they weren't very far in.

If I'd been at the coathangers I'd have left with nearer 1000-1200. If I was in Mexico in a passage with no other exits and we'd done a straight swim to 1/3, and I then lost him, I would spend very little time looking before exiting.

The safe exit pressure is highly context dependent.

Maybe this will clear things up.

500 feet back , and I wouldn't turn at thirds.

1800 feet back , and you're damn Skippy I,m turning.

Just because a diver is separated doesn't mean their lost. If you're close to thirds .they should be close to thirds also (tanks and sacs being equal, and all that pre dive stuff)

BabyDuck

09-10-2009, 01:42 PM

mike o'leary addresses it in class. his take is that the reserve 1/3 is for emergencies, whatever the emergency may be. it's not necessarily your buddy's gas (though it might be used for that) and 1/3 isn't necessarily enough for every contingency, but it's where we start. if you're doing lost buddy, check your gauge and decide how much gas you're gonna spend looking. if you're doing lost line, look until you're dead.

another instructor addressed the 'very low on gas & coming out on my tanks' scenario. he wanted us to think about isolating, especially if the other person is really excited & huffing like a freight train.

what would i actually do? dunno, but i've thought about it. i certainly plan on raising my baby. if on that day it means i start moseying out at 1000psi, so be it. it would suck, but i'd live with it.

Jay

09-10-2009, 03:10 PM

Well, for all you folks who said 500psi all I can say is "are you f----- nuts?" :) :)

More politely I would say that I think 500 psi is dangerously low. Too much can happen.

I have been in two situations where I left the cave with a whole lot less gas then I would ever be comfortable with. And no, it was not "Gee, let's see how much gas I use swimming out of this nice clear high flow cave with no stress."
Yes I had plenty to get out, but the stress level sucks. I couldn't imagine adding a lost buddy into the mix.

Ask your buddy this the next time you talk about a lost buddy drill. "Would you want me to risk my own life by going down to 500 psi (or x psi) waiting for you?"
Based on my experiences I would never ask or expect someone to go that low waiting for me.

For you guys that would, good luck to you, and I mean that from the bottom of my heart.

jj1987

09-10-2009, 03:16 PM

Jay

09-10-2009, 03:35 PM

I didn't see anything wrong with your math, I just think there is much less safety factor then I would be comfortable with. Too much can happen, SAC's and math can go out the window. In that scenario I would have a number of closer to 1000 in my head, but it would all depend on the moment.

Crap, I would fail a student who surfaced from a 30 foot OW dive with less then 500 psi in his 80. :)

My main point was to ask your buddy how much you should keep. It might be funny if he decides he is keeping much more then you would. :)

deepdiverbob

09-10-2009, 03:44 PM

I apologize if this has been addressed, and I missed it, but does diving sidemount change anything? Would you breath down one tank, and leave at thirds on the second tank? I have zero side mount experience, and maybe my questions proves that. I am just curious.

Now its time for me to go vote.

Edit:
I voted 700. I was using the area of the Hill 400 jump as the point of where we became seperated, because this was generated in response to the tragedy last week. I think my turn pressure would obviously change based on dive plan, and actual area of separation.

rjack

09-10-2009, 03:49 PM

I apologize if this has been addressed, and I missed it, but does diving sidemount change anything? Would you breath down one tank, and leave at thirds on the second tank? I have zero side mount experience, and maybe my questions proves that. I am just curious.

Now its time for me to go vote.

Breath down waiting or exit earlier and leave gas on the line? I don't dive sidemount and wouldn't dive with someone who wanted to do a quick solo jaunt down some tunnel while I waited either.

Mart

09-10-2009, 03:51 PM

I think most agencies teach not to break thirds when looking for a lost buddy.

What is your definition of thirds? If you define it as "leave one third of your starting pressure untouched" it would leave nothing for a search after turning the dive. Define it as "always leave twice the amount of gas needed to exit" it leaves nothing for a search at the turning point.

Jay

09-10-2009, 03:52 PM

I apologize if this has been addressed, and I missed it, but does diving sidemount change anything? Would you breath down one tank, and leave at thirds on the second tank? I have zero side mount experience, and maybe my questions proves that. I am just curious.

Now its time for me to go vote.

I am a proponent of long-hose-on-one tank SM diving ( Treat a buddy OOA incident as you would on BM, any cave diver should be able to that in their sleep) And I look at buddy-breathing as the extreme air sharing scenario, so no I wouldn't recommend sucking one dry. I would make sure the long hose one was left for my buddy.

Good discussion question though.

Slüdge

09-10-2009, 03:53 PM

Well, for all you folks who said 500psi all I can say is "are you nuts?"

I can get out from the Hill 400 jump on 100psi. That leaves 400psi for my buddy. :smt102

jj1987

09-10-2009, 03:54 PM

Define it as "always leave twice the amount of gas needed to exit" it leaves nothing for a search at the turning point.
It leaves quite a bit at Ginnie. It leaves almost nothing at peacock. It's not enough at peacock 3.

I think that's what Andrew wanted us to think about when replying...

aainslie

09-10-2009, 04:02 PM

It leaves quite a bit at Ginnie. It leaves almost nothing at peacock. It's not enough at peacock 3.

I think that's what Andrew wanted us to think about when replying...

Yup. Location and flow matter, a lot.

But unless we spend time measuring our swim and consumption rates, and thinking about this outside the water, it's hard to know when we are at double the gas needed to exit.

Mart, I like the idea of "double the gas to exit". It's a mantra for me. At least when no stages enter... stages complicate things a bit.

jj1987

09-10-2009, 04:07 PM

Yup. Location and flow matter, a lot.

But unless we spend time measuring our swim and consumption rates, and thinking about this outside the water, it's hard to know when we are at double the gas needed to exit.

Mart, I like the idea of "double the gas to exit". It's a mantra for me. At least when no stages enter... stages complicate things a bit.
Well, you saw how much rounding really screwed up a true "rock bottom" on the fly from my first post in this thread. Andrew Georgitsis published a GREAT pdf with "Battlefield Calculations", that came with his Intro to tech dvd, but I think it's copyrighted, so I can't post it...not that it helps here, but it really got me thinking about how simple a little forethought can make a LOT of diving math :?

Surely there has to be a better way than a complete guess....Any ideas? Anyone?

Steve Clark

09-10-2009, 04:18 PM

rjack

09-10-2009, 05:11 PM

I don't know the details of the incident, but personally (Cave 1 + 20dives, 10 in Devil's) :

Usual drill stuff, cover the light and look. Have a good look around with the light for a failed buddy light, search locally up and down the line for a couple of minutes. Leave the line on a arrow/spool if there is a good reason to suspect where they've gone (silt?/a line).

Then....I'd have a good think and triple check that's it's not me that's 'lost'. Do I really know where I am, and 100% certain of exit direction. If my buddy is only as experienced and just vaguely familiar with the cave like me, I'm just as likely to be the confused one.

Cave 1 penetration limits at 2/9ths (3rds after resevering a 3rd, turn at 2800psi), I'd consider leaving at 2800psi and definately at 2400. Then prompt exit, wetnotes to any entering teams, leave the reel, raise alarm at surface. No divers around to enter, tell the staff and maybe go back into the Gallery and hang-out with spare gas.

Have I lost the plot?

Steve

GUE Cave1?

Leaving at 2400 you end up at the surface with ~2000-2200psi depending.

The GUE Cave1 I took has you guesstimate the amount of gas needed to exit and double that. Keep looking until you hit that pressure. If you are looking further into the cave that number rises until you get to your original turn pressure. If you are not at your point of maximum penetration or you have alot of flow helping you exit it can be alot less. For some people in this location/circumstance as little as 500psi to exit. Assuming they didn't find their OOG buddy at the last instant they reach the surface with 300-400psi. That's alot less than you chose to exit with.

icestac

09-10-2009, 05:11 PM

Cave 1 penetration limits at 2/9ths (3rds after resevering a 3rd, turn at 2800psi), I'd consider leaving at 2800psi and definately at 2400.

WOW! I mean to each there own and all, but you've got an eternity of gas in there. Isn't the whole point of the reserve to handle emergency situations?

Jeff

Steve Clark

09-10-2009, 05:54 PM

Yes, an open-minded GUE Cave 1 diver.

I've now read some the incident report/speculation. All a bit academic given that myself and buddy wouldn't be deliberately leaving the mainline.

So in answer to the actual question asked : I wouldn't be doing the dive.

For a novice team, losing your buddy on the mainline in a silt-out? Given that they are also likely to have a massive reserve of gas are you not just adding to the problem searching/hanging around for 60min+ until the very last minute (2 x exit gas)?

Thought provoking discussion, learning a lot about the options. Thanks.

Steve

jcr

09-10-2009, 07:13 PM

jcr, your answer sounds cute but it's intellectually lazy and ambiguous simultaneously. What's your number? And I hope to God you're not suggesting suicide. It's just stupid to go so low that a solo exit becomes infeasible.

Not lazy or suicidal, just hoping that divers will think about what this really means. Planning when to leave my buddy in the cave seems like planning to fail. Of course, I would quit searching and exit at the last possible moment but I refuse to lend credibility to this notion of planned abandonment with a number.

Based on some of the numbers that have been thrown out more people than realize it are diving solo.

rjack

09-10-2009, 07:26 PM

Based on some of the numbers that have been thrown out more people than realize it are diving solo.

If I had this conversation with a new-to-me buddy and they were thinking a number 1000psi or greater I'd really have a hard time wrapping my head around their committment to "us"

jj1987

09-10-2009, 07:31 PM

Planning when to leave my buddy in the cave seems like planning to fail.
Do you wear a seat belt?

icestac

09-10-2009, 07:58 PM

Do you wear a seat belt?

Amen!

aainslie

09-10-2009, 08:00 PM

Not lazy or suicidal, just hoping that divers will think about what this really means. Planning when to leave my buddy in the cave seems like planning to fail. Of course, I would quit searching and exit at the last possible moment but I refuse to lend credibility to this notion of planned abandonment with a number.

Based on some of the numbers that have been thrown out more people than realize it are diving solo.

Lots of words. No actions.

At some point YOU NEED TO PICK A NUMBER, like it or not. And if the first time you start thinking about this is when it happens, you'll either commit unintended suicide or leave ridiculously early and blame yourself later.

I don't even know what your last sentence means.

Anyway, go your own way. Your sort of laziness is why the "standards" ahve barely been changed since Exley. It's pretty sad.

JS1scuba

09-10-2009, 08:47 PM

Assuming a lazy travel to the first 600 feet I would have used 40 cuft. Now I will need from this point out 80 cuft plus a small functionality reserve so let's call it 95 cuft from this point out.

My tank set started with 295 cuft (LP 108s to 3600) so at this moment I am at 250 cuft --(3100 psi) i will need to be back to this start/exit point with no less than 95 cuft (1200 psi) (if I find him back here) this leaves me with 155 cuft to go look - so i play this by 1/3rds and only use 50 cuft to go look and then turn back.

It's essentially a new set of 1/3rds of the gas AFTER having 2x + the exit gas from the point where I start the search from.

If I find the lost diver within the 50 cuft I have alloted and he's empty I have enough of gas to get us out. If I find him and he still has gas then we are both in the same situation and we come out with plenty of gas. If I don't find him then I have plenty of gas to get out and can then get some help.

As much as I can take into consideration the exit flow it's a variable change that is best left off the table. So i won't consider it in the exit scenario.

Since I mostly wreck dive this is how I would approach it on a wreck as well. Though we do have some other techniques there that are not applicable here.

Interesting discussion.

Cheers
JDS

DA Aquamaster

09-10-2009, 09:17 PM

Generally, I dive in a two person team with Marci who shares a basically identical SAC and swimming speed. We are pretty well matched, fairly fast in the water and have fairly good SAC rates, so we tend to penetrate farther on backgas than would be desireable for a two person team if one of us had a catastophic gas loss near thirds.

So I usually carry a buddy bottle to add what amounts to another team member's reserve "third". In the event we were separated with me carrying a buddy bottle, I'd expect Marci to not use more than her reserve third looking for me and to even leave a few hundred psi early in a no flow or low flow cave to ensure she gets out if breathing a bit harder due to stress. She is after all the baby mama.

If the situation were reversed, I have an extra third from the buddy bottle to use in the search, so I could stay quite awhile. Alternatively, I could leave the buddy bottle with enough gas left in it to exit along with its extra light on the line at the point where I turn, depending upon what made the most sense in the given scenario.

In a high flow cave, the buddy bottle may get taken along, but then again you can exit on a lot less than the third you entered on. In that case (which is the situation for the poll) I could easily exit Ginnie on half what I entered on, so lets say I need 600 psi to exit safely. But...what happens if a diver stays until he or she is at 600 psi and then the lost diver finds them but is basically out of gas? Talk about a shitty situation to be in.

There is no sense in two people dying, and it goes to the heart of issues like isolating during a gas share when you get to the point that half your remaining gas is just enough to get you out, and the buddy is hoovering it for all he's worth. In that case, it sounds heartless, but it makes sense for the donating diver to isolate and the hoover buddy is going to have an uncomfortable final moment when he goes dry in the event the team does not come upon another diver to help him exit. It's a tough world. It's also a strong argument for 3 person teams, buddy bottles, or very conservative gas planning.

But in the given scenario, (two person team, high flow cave, no extra stage) I am likely to start a withdrawl from the cave at a bit less than twice the gas I need to exit (1000 psi perhaps) since a total OOA encounter with the diver is less likely. I'll exit slowly however with the flow and continue to recalculate and pause so that I don't retreat any faster than the available exit gas from that point times two. It keeps me in the cave longer so that if the buddy was finally exiting low on gas and would have otherwise still have been a few hundred feet short of exiting, I may still be there when needed.

mfascuba

09-10-2009, 09:39 PM

My post was not a meant to be an incidental comment but a serious answer to the question that was posted. Please re-read my post and think about its implications.

I did seriously consider the content when I responded, I stand by my initial reply. The facts are that our community suffers losses each year from various causes, some preventable, some not. A person that has a fatal medical event under the water would be just as dead if it happened behind the wheel of their car. From a traffic statistics point of view that would also be unacceptable, but it still happens.

As far as the solo stuff, I mostly dive solo, and when I dive with a buddy I follow thirds on back gas, plan to air share if needed, and carry a stage that I don't touch, just like I do when I dive solo, just in case. An AL80 doesn't get in the way or create any drag if properly rigged, and can be the deciding factor between outcomes. I made that decision a long time ago, and have never regretted carrying an extra bottle with me, even when I came out of a multiple stage dive with a full one. As has been stated, it's important to think these things through now so it's one less thing to mull over in your head in the event that things get very bad.

The original post asked for an exit pressure based on a very specific set of conditions, in a very specific cave. I stand by my response, and would like to see what number you come up with - really, I'm curious (this is not a "call out", just an enquiry). If you keep your number to yourself, no problem, it's a deep topic.

Mark

DogDiver

09-10-2009, 09:42 PM

jcr

09-10-2009, 09:59 PM

Anyway, go your own way. Your sort of laziness is why the "standards" ahve barely been changed since Exley. It's pretty sad.

This reminds me why I typically avoid these forums. There's always someone that thinks they have all the answers and resorts to ad hominem attacks when challenged.

chimie007

09-10-2009, 10:42 PM

There's always someone that thinks they have all the answers

You are right.... and I think you are the "someone".

Andrew is known for speaking his mind but to his credit he started one of the best/useful thread we have seen here in a few weeks for sure.

What about you tell us what you would do in the presented scenario ? You don't have to but then why posting as you did earlier if you didn't want to bring something constructive... maybe you do have something to say but you didn't explain well for sure.

skip

09-11-2009, 12:15 AM

Quote: "Yes, yes, solo... I remember that... never forget the day it changed... 'bout three years ago... I'd had trouble clearing an ear, and sent the other two on ahead into Hole-in-the-Wall (Merritt's Mill Pond). Finally got my ears cleared & headed on in, with the idea that I'd meet 'em and join 'em on their way back out. It was the usual milky water for Hole, so I was sticking pretty close to the line, easing on in, when my little pea brain began to think, "Rick, you're nearly 60; if you have some 'event' right now you'll drift off the line, they'll never see you, and your dumb ass will die, and the Lovely Young Kat will be really pissed off at you!"
Quit solo caving then and there.
In another decade you may reconsider, too :smile:
Rick "

I'm nearly 60 and solo cave dive way more than buddy dive. And the viz is rarely better than 10 feet. My wife says if I die in a cave she will never forgive me and bury me in a suit and tie (she'd have to buy it first). I don't see what age has to do with it. I am far more comfortable solo than with a buddy or buddies. I typically dive sidemount with a stage, three tanks redundancy and always run a continuous guideline to the surface. any "event" may be certain death, but a buddy along won't change that. Maybe I'm missing something, but as I get older I think I get riskier. Hell, I've had a long good life so dying now is no big deal. But I am a cautious diver, spend more time planning than diving, and always dive the plan. No health issues, no meds, so an "event" would be like fate. I fear driving on the interstate more than solo cave diving.

No offense, but to say that buddy diving is the only way to dive, at any age, sounds to me like depedent diving, not independent diving.

oops, this thread is about psi to search for lost buddy...sorry for the hijack.

-skip

Meister481

09-11-2009, 12:44 AM

I can get out from the Hill 400 jump on 100psi. That leaves 400psi for my buddy. :smt102

That's my take. 100 for exit, 100 for lost deco gas, 200 exit for buddy=400 doubled for bad vis/ problems/ my safety margin. 800 PSI in this situation. Maybe less/more depending on the consumption of the individual involved. Leave slate/wetnotes with a strobe and any gas I can leave. If I find him on the surface with 2000psi in his tanks it's going to get ugly. :mad:

Andrew is known for speaking his mind but to his credit he started one of the best/useful thread we have seen here in a few weeks for sure.

What about you tell us what you would do in the presented scenario ? You don't have to but then why posting as you did earlier if you didn't want to bring something constructive... maybe you do have something to say but you didn't explain well for sure.

It's nice to see a thought provoking thread about dive planning/safety. I'd love to see more responses. Getting people to rethink what they consider appropriate is a good thing.

Honestly, how many people here have thought this through before tonight? I have but not to this level.

09-11-2009, 03:37 AM

I've been in a couple of similar scenarios in which a buddy went into a passage that was best left to one diver. Both scenarios played out just fine. I never broke 1/3s and we both came out alive. However, the first time had me thinking about what I would do if he didn't come out and how long I would wait. It was a question I couldn't answer right then and one I think I could only answer when I see that magic number appear on my SPGs. Now, that particular incident had us 5000' back in the system in new passage that we were lining. We had 2 stage bottles each waiting for us and neither of those had been breathed down to 2/3s by either of us. In that situation, I probably would have taken it down to 1000', knowing we could still get back to our stage bottles on that, even if he was out of air which wasn't going to be likely. But I also know that when SHTF both of us slow down our breathing. It hasn't always been this way for me, but I've learned to condition myself so this happens. I never even had any thoughts like this during the other incident, but we were also much closer to the exit, less than 250', and I always carry lots of tanks in my van.

So, that being said, in this particular situation, I'd have 800 in one of my bottles for my buddy. I'd take my own bottle down to 300. I could exit on less, but I'd be worried about the accuracy of the SPG at that low of a pressure.

mfascuba

09-11-2009, 06:17 AM

sounds to me like depedent diving, not independent diving.

That is a profound statement. In my OW class they made the point that just because you had a buddy didn't mean that you were to depend on them - you were there to assist the buddy in case they had an emergency. I don't think many cavers "depend" on their buddy, as much as enjoy a dive with another person. If folks go into a cave with the mindset that "he's here to help me" instead of "I'm here to help him", it fosters a dangerous mindset.

Two people prepared to assist is better than two people ready to be rescued.

Mark

MORGAN

09-11-2009, 07:36 AM

...this notion of planned abandonment...

In the event, the more you've thought about and planned for how to manage such a situation, the more likely you are to have a good outcome for both you and your buddy. Which I think was aainslie's point in starting this thread.

Mike

icestac

09-11-2009, 07:56 AM

Well the correct answer is 2400 or 2/3's period. It woudnt do you or your buddy any good if you find him or her with no gas in their cylinders and you have used up more gas then the two of you need to exit.

I would say fair enough if you had reached maximum penetration and it was going to take you a third to get back out (we'll ignore the flow in Ginnie for the sake of argument). Is you answer still the same in THIS situation where you are 500ft from the exit?

Cheers,
Jeff

BabyDuck

09-11-2009, 08:24 AM

yes, ken, i was going to post the same as jeff. it's fine if that's your answer from hill 400 *or* past olson, but i think my answer might be different from different spots.

and that third third is reserve for emergencies. i would think lost buddy counts as an emergency and would use it - maybe not every breath of it, once again depending on where i am in what system, but i would come out of the water with less than 1200 in my tanks, that's for sure.

but i'm not picking on you. i'm glad you're here. to be honest, the first reports from this had me wondering how old you were, so i'm happy to see your words!

uncle ricky

09-11-2009, 09:56 AM

... I don't see what age has to do with it... It's those pesky age-related facts.
The chances of having some debilitating event increase exponentially with age.
You're not as strong or as limber as you used to be, and it'll only get worse.
"Old age and treachery will beat youth and skill every time" only goes so far. We're great at accomodating - especially us adventurous guys - and we're way younger than our contemporaries who aren't testing their limits on a regular basis, both mentally and physically. But, hard as it is to admit, the simple fact is that our strength, endurance, mental accuity, elasticity etc are on the decline, and it is statistically more likely with every passing day that we'll need a buddy's assistance with something.
It'll probably hit you at a friend's funeral.
Just last month a 58 yr old co-worker "in perfect health" had a sudden stroke... had he been on a solo dive he'd have died right there. As it was, he at least had a few days consciousness to say goodbye and tie up a few loose ends before drifting off permanently.
I've already made the decision to make no more solo cave dives or wreck penetrations or spear fishing excursions, and my solo open water diving's been curtailed to the "solo in a group" concept.
I'm not telling anyone not to solo dive, but when you decide to do it, just make sure you are accepting the real risk and aren't denying the increasing statistical probability that as you age you're more likely have a surprise debilitating event. If that ever happens on a dive, you don't come back by yourself - either a buddy drags you out, possibly alive, or the recovery team does.
Rick

jj1987

09-11-2009, 10:09 AM

Well the correct answer is 2400 or 2/3's period. It woudnt do you or your buddy any good if you find him or her with no gas in their cylinders and you have used up more gas then the two of you need to exit. Then you have a double fatality. Follow the lost buddy training rules then exit the cave. I dive with my son and daughter and we have discussed the issues. Mom would have a tough time if one of us didn't return, but I can't even imagine how she would cope if both of us didn't return. Hope I never have to make such a decision. Safe diving. Ken
I would say fair enough if you had reached maximum penetration and it was going to take you a third to get back out (we'll ignore the flow in Ginnie for the sake of argument). Is you answer still the same in THIS situation where you are 500ft from the exit?

Cheers,
Jeff

I would have a very tough time leaving my family member at 2400psi, especially 500ft in, considering that's enough gas to get us out from almost waaaay back in the cave.

During the flood when there was almost no flow, a buddy and I swam to around 3500ft using 2 stages and cave filled 104's. It still took slightly LESS gas coming out than going in, since we picked up the pace a bit to beat deco obligation. Using 1/2+200 on each stage, and 1000psi penetration for backgas, that means we used about 145cu ft of gas. At 2400psi, you've got 188cu ft of gas AND you have flow.

rjack

09-11-2009, 12:40 PM

I would have a very tough time leaving my family member at 2400psi, especially 500ft in, considering that's enough gas to get us out from almost waaaay back in the cave.

Similarly, I would have a really hard time explaining to someone's wife or husband that I surfaced early with 160-180cf of gas (e.g. leaving at 2400psi) while their loved one drowned.

NWGratefulDiver

09-11-2009, 01:19 PM

During the flood when there was almost no flow, a buddy and I swam to around 3500ft using 2 stages and cave filled 104's. It still took slightly LESS gas coming out than going in, since we picked up the pace a bit to beat deco obligation. Using 1/2+200 on each stage, and 1000psi penetration for backgas, that means we used about 145cu ft of gas. At 2400psi, you've got 188cu ft of gas AND you have flow.
Over the years I've noticed that when I hurry I tend to use more gas going from point A to point B ... not less. Although I can get there in less time, my breathing rate picks up ... often considerably.

How is it any different in a cave?

I can see the deco obligation thing as legitimate, but I would think that if you're trying to get the most "miles per gallon" you'd be better off heading out at a reasonable pace so as to keep your breathing rate as relaxed as possible.

... Bob (Grateful Diver)

jj1987

09-11-2009, 03:10 PM

Over the years I've noticed that when I hurry I tend to use more gas going from point A to point B ... not less. Although I can get there in less time, my breathing rate picks up ... often considerably.

How is it any different in a cave?

I can see the deco obligation thing as legitimate, but I would think that if you're trying to get the most "miles per gallon" you'd be better off heading out at a reasonable pace so as to keep your breathing rate as relaxed as possible.

... Bob (Grateful Diver)
Well, you do all your looking around going IN instead of out. In a high flow system I typically look around a lot more in the way out, but when the flow is reduced to almost nothing, I try to keep them proportional (adding time as I build reserves) or the exit faster. Just like we all learned in Gym class, running on the inside of a track is a shorter distance than running along the outside...apply that to caves. Swimming 2 stages is easier once they get light. I think there's several ways to make up time on the way out of a cave. I would also guess that level of fitness effects how fast you can exit a cave and not raise your sac as well, but haven't tested it...I don't notice any increase in breathing when I pick up the pace.

Plus, taking it slow out of a cave that has almost no flow when you're diving to 1/3rds really isn't an option, you're COMMITTED to exiting at least as fast as you entered. Reserves build up exponentially as you exit, but I can't do that math in my head, so I'll wait a few 100ft to start slowing it down even when not trying to beat a deco requirement.

LCF

09-11-2009, 03:10 PM

Bob, I don't know about you, but my SAC rate isn't horribly different between a leisurely cruise and steady, relaxed swimming -- but my rate of progress is. Now, if I get past a comfortable, steady rhythm and start to HURRY, that's a different story.

We were taught, being trained in Mexico, to go in moseying and come out at a steady, brisk clip. I simply can't see a difference in gas consumption between in the inbound and outbound legs (unless there is some flow, and even then it is small). However, if I'm chasing Kirk with his long legs and big fins, THEN I see my SAC rate go up, because I exceed what's comfortable.

NWGratefulDiver

09-11-2009, 05:20 PM

Bob, I don't know about you, but my SAC rate isn't horribly different between a leisurely cruise and steady, relaxed swimming -- but my rate of progress is. Now, if I get past a comfortable, steady rhythm and start to HURRY, that's a different story.

That's what I meant ... if I get going at a clip more than about 50 fpm (excluding the effects of "flow") I notice a rapid increase in consumption rate, and the Law of Diminishing Returns kicks in pretty quick ...

... Bob (Grateful Diver)

09-11-2009, 09:07 PM

Plus, taking it slow out of a cave that has almost no flow when you're diving to 1/3rds really isn't an option, you're COMMITTED to exiting at least as fast as you entered. Reserves build up exponentially as you exit, but I can't do that math in my head, so I'll wait a few 100ft to start slowing it down even when not trying to beat a deco requirement.

This is why diving to 1/3s is more risk than it's worth. I almost never dive to 1/3s and I almost always take my time exiting. I would rather see and learn the cave on the way out because that's the cave I need to know in an emergency. You should never COMMIT yourself to having to exit at least as fast as you entered.

aainslie

09-11-2009, 09:20 PM

Reserves build up exponentially as you exit

Well... linearly really:)

But it IS exponential-ish in terms of the percentage needed to exit, exploding at infinity AS you exit.

Let's say there's no flow and you turn at thirds. You have double the gas needed to exit at that point. Halfway home, you've used 1/3+1/6 = 1/2 and you need 1/6 - you now have 3* the gas you need. 3/4 of the way, you have 5/12 left and you need 1/12 - you have 5* the gas. It really explodes from there.

James et al, good points. One thing I don't see most instructors stressing is that shared gas exits MUST be as fast as normal exits if they're to be successful. Same with lights out. And shared/lights out... man, it's hard to keep up 50 fpm! Which once more points to putting in a fudge factor BEYOND having twice the gas needed to exit. Bogaerts really drilled this one into me when I spent a weekend learning from him.

fixxervi6

09-12-2009, 12:05 AM

...... One thing I don't see most instructors stressing is that shared gas exits MUST be as fast as normal exits if they're to be successful. Same with lights out. And shared/lights out... man, it's hard to keep up 50 fpm! Which once more points to putting in a fudge factor BEYOND having twice the gas needed to exit. Bogaerts really drilled this one into me when I spent a weekend learning from him.

O'Leary stressed this to my class, and my intro instructor did as well, so I know at least some instructors do.

Just another reason for me to take my time going in vs going like a bat out of hell in no flow caves

NWGratefulDiver

09-12-2009, 11:14 AM

One thing I don't see most instructors stressing is that shared gas exits MUST be as fast as normal exits if they're to be successful. Same with lights out. And shared/lights out... man, it's hard to keep up 50 fpm! Which once more points to putting in a fudge factor BEYOND having twice the gas needed to exit. Bogaerts really drilled this one into me when I spent a weekend learning from him.

My instructor stressed it ... in fact, he nearly dragged my ass out on a shared air exit just to make sure I got the message.

The more I read and learn about this stuff, the more certain I become that I chose the right instructor ...

... Bob (Grateful Diver)

ScubaBob-Squaretank

09-12-2009, 12:23 PM

The chance of two people making it out of a cave in little flow is probably very slim, if they are at a maximum turn point using the thirds rule. By the time you get everything back under control, including your breathing rate back to normal. Hopefully you havent ruined the vis by then. You better light a fire under your #%* to get out.
Bob Klauck

DA Aquamaster

09-12-2009, 01:27 PM

O'Leary stressed this to my class, and my intro instructor did as well, so I know at least some instructors do.

Just another reason for me to take my time going in vs going like a bat out of hell in no flow cavesSame with Marci and I. He made the point that you have to be fast and if leaving as fast as you entered may not happen for any of a number of reasons, you better have more gas. He is the person who brought it home to us that having good SAC rates and fast swim rates with resulting deep penetrations, but only a two person team placed us at elevated risk if a catastophic gas loss occurred. He suggested taking a stage with an extra back up light add some of the reserve resources that would be provided by a third team member in addition to conservative gas plans.

LCF

09-12-2009, 01:36 PM

My instructors repeatedly stressed that thirds ISN'T conservative, and works best with teams of three. We were also taught in Mexico to do our lollygagging on the way in, and that, once you turn, you have one purpose, and that's to exit expeditiously. That was not stressed as hard in my Florida class, for what I suppose are kind of obvious reasons. But the riskiness of thirds was, and we were strongly encouraged to be more conservative in many cases.

Mart

09-12-2009, 02:55 PM

I like the idea of "double the gas to exit". It's a mantra for me.

For me it is the basis of all gas calculations in a non-emergency situation. Of course to be modified according to team size, familiarity with the cave, flow etc.
In an emergency (like a lost buddy) I would violate the double rule and use one third to half of my extra gas for the search.

Bob Cree

09-13-2009, 10:23 AM

Yup. Location and flow matter, a lot.

But unless we spend time measuring our swim and consumption rates, and thinking about this outside the water, it's hard to know when we are at double the gas needed to exit.

Mart, I like the idea of "double the gas to exit". It's a mantra for me. At least when no stages enter... stages complicate things a bit.

Use thirds in outflow caves and certainly you are good to go. For me, double the gas to exit is not enough, and in fact you contradict yourself.

Case in point - a no flow cave with only one exit - double the gas is the same as diving thirds. So double the gas is your mantra contradicts your statement(s) elsewhere that this is dangerous and NOT conservative enough.

If double the gas (thirds) is not enough, then what I would like to know is what would you consider safe in a no flow cave?

Might make a good poll.

Bob

Mart

09-13-2009, 10:27 AM

So double the gas is your mantra contradicts your statement(s) elsewhere that this is dangerous and NOT conservative enough.

Double the gas is the baseline. In a team of three it might be OK, team of two not. Familiar cave or new one, perfect visibility or bad, restrictions, new buddy(s), all these factors and more need to be taken into account.

Bob Cree

09-13-2009, 11:19 AM

Double the gas is the baseline. In a team of three it might be OK, team of two not. Familiar cave or new one, perfect visibility or bad, restrictions, new buddy(s), all these factors and more need to be taken into account.

So given a no flow one exit system you have dove before with normal vis and no significant restrictions. You dive with a buddy you have dove with before, are comfortable with and they have similar or better experience in the system. Would you go more conservative than thirds and why?

Would it be prudent to turn 100 or 200 psi before thirds to account for the elevated stress and associated additional gas use in the event of a serious problem at max penetration?

Bob

Mart

09-13-2009, 11:23 AM

You dive with a buddy

Team of two I would not dive thirds.

aainslie

09-13-2009, 10:54 PM

Use thirds in outflow caves and certainly you are good to go. For me, double the gas to exit is not enough, and in fact you contradict yourself.

Case in point - a no flow cave with only one exit - double the gas is the same as diving thirds. So double the gas is your mantra contradicts your statement(s) elsewhere that this is dangerous and NOT conservative enough.

If double the gas (thirds) is not enough, then what I would like to know is what would you consider safe in a no flow cave?

Might make a good poll.

Bob

Good point Bob. Like thirds, doubles is a STARTING point. Both then need to have an extra reserve added.

LCF

09-14-2009, 01:35 AM

Well, are you guys talking about diving thirds in no flow as a matter of course, or in the event of a buddy separation? I'd possibly do things to look for my buddy that I wouldn't plan into a routine dive.

Jay

09-14-2009, 11:08 AM

As Kelly pointed out in the other thread, besides health issues all the divers who died had one thing in common.

They ran out of gas.

I would never fault anyone who wants to be a little more conservative and would have an issue with divers who want to be less conservative.

There have been some very good divers, likely better and more experienced then anyone on this thread who died because they ran out of gas.

Do you think some of them were using alternative methods of determining their turn pressure????

atedeschi

09-14-2009, 02:19 PM

As Kelly pointed out in the other thread, besides health issues all the divers who died had one thing in common.

They ran out of gas.

I have a question about this statement. Yeah they ran out of gas but does that really mean it is because of poor planning? I mean say if a turned the dive and I lost the line some how on the way back and I can not find it? It not because poor gas planning its cause of not having a line. Or what if I do find the line and make it 500' from the entrance, people say well empty tanks poor gas planning, when it could have been other things. It just like when you bring the body up from death cause of death embolising, well yeah no ****. IDK its just something that bothers me when it may not be always the case.

09-14-2009, 02:51 PM

Well, the really sad part is they don't *all* run out of gas. There have been several cases of accident victims with gas remaining. Several reasons for this, Ox tox, stuck (and can't get to regulators), and something called "deep water blackout".

Jay

09-14-2009, 03:32 PM

I have a question about this statement. Yeah they ran out of gas but does that really mean it is because of poor planning? I mean say if a turned the dive and I lost the line some how on the way back and I can not find it? It not because poor gas planning its cause of not having a line. Or what if I do find the line and make it 500' from the entrance, people say well empty tanks poor gas planning, when it could have been other things.

Maybe it's not related to poor planning 100% of the time, but for those cases you stated, the team should have planned for enough gas. The extra gas is for emergencies other then OOA situations. Searching for the line, exiting in poor vis, etc.

Distance, visibility, increased chance of silting, syphon. You should have enough gas reserved to deal with all those scenario's. If divers put themselves in a situation where those events could occur and they do not have enough gas to deal with it, then yes, that is piss poor planning.

Jay

09-14-2009, 03:33 PM

skip

09-14-2009, 05:35 PM

for those that do run out of gas is it possible that the reg leaked it out after death? bodies are not found for many hours, enough time for a leaky purge?

-skip

09-14-2009, 07:43 PM

for those that do run out of gas is it possible that the reg leaked it out after death? bodies are not found for many hours, enough time for a leaky purge?

-skip
Most regs won't do that, but there are a few with unbalanced 1st stages that free flow worse as the tank pressure gets lower. I don't think it is very likely, though.

aainslie

09-14-2009, 08:25 PM

Let's hop back to the data collected in this exercise. Let me point out a couple of things that jump out:

1) The biggest peaks occur at round numbers, namely 1800 ("exit at half"), 1200 ("exit when you've used another third") and 1000 ("exit when you hit 3 digits"). None of these answers have anything to do with the circumstances, i.e. whether you're 600 ft or 1200 ft into the cave.

2) Overall the distribution is remarkably flat. What I mean by this is there is NO agreement amongst participants. There is no peak around a particular number or in a particular region. 16% say 1800 or more. 22% say 1200 to 1800. And 19% are willing to go below 700. The closest we have to a peak is the group of 41% who would leave somewhere between 800 and 1100. This shows that whatever else, there is no clear metric for people to decide how to handle emergencies like this.

3) The good (actually I should say great, really) news is, over half the divers took into account the location of this issue, and were willing to dip into their gas and at the very least do some sort of "thirds" recalculation. This means that a good body of divers would have radically increased their chances of pulling off a rescue. And I think it's easy to show empirically (by swimming out from 600 feet in and measuring your consumption) that only a serious hoover would compromise their safety - i.e. by exiting with less than double the gas needed - by dropping below 1200 at that point.

This is a bit of an embarrassment to our community, quite frankly. It'd be nice if we spent more time thinking about this, and thinking about ways to exit safely... but not too safely.

I encourage someone with a lot more experience and credibility than me to write an article in either the CDS or NACD journals about this issue, and suggesting a solution. If one of you don't I might just be tempted to do it!! And we don't want that, do we, Ken, FW, Kelly et al?

DA Aquamaster

09-14-2009, 08:28 PM

Most regs won't do that, but there are a few with unbalanced 1st stages that free flow worse as the tank pressure gets lower. I don't think it is very likely, though.You are correct. With an unbalanced first stage you are in effect talking only about unbalanced "flow by" piston designs as no one has actually made an unbalanced diaphragm first stage in at least 30 years.

A flow by piston first stage is a downstream design so as the tank pressure falls, the downstream assitance provided by the tank pressure drops, making it harder to lift the seat off the orifice. Consequently, the second stage is more likely to freeflow with a full tank and is much less likely to freeflow with low tank pressure.

The reverse is true with an unbalanced diaphragm design as the seat is upstream of the orifice rather than downstream, so the seat gets more assitance to open as the tank pressure drops - but again they have not been made for at least 30 years as it is really easy and inexpensive to just balance the seat carrier.

rjack

09-14-2009, 09:34 PM

This is a bit of an embarrassment to our community, quite frankly. It'd be nice if we spent more time thinking about this, and thinking about ways to exit safely... but not too safely.

Wholeheartedly agree. What is being currently being taught for lost buddy searches?

The concept of recalculating gas needed to exit, doubling it and having a new exit pressure was discussed in my intro course. IIRC when we did a lost buddy drill in my full course we were expected to have recalculated and our instructor queried us on how much gas were were expecting to use.

alias

09-14-2009, 11:17 PM

Overall the distribution is remarkably flat. What I mean by this is there is NO agreement amongst participants.

What did it mean when two people chose the same number? Did they agree/have same strategy? Was their plan as sane/insane?

For example, what does it tell you that you and I both chose 500PSI (I did not btw). I assume you know Devil's intimately, dive with another (at least) Full Cave buddy, carry something like 108s, and have deco bottle waiting for you in cavern. You know exactly what it takes you to get to the point that has been discussed, and how much you need to get 1 or 2 divers out.

Then again I am Intro diver, I’ve been to Devil’s couple of times and on LP85s it takes me 500 PSI (not as good fills as yours!) to get to the Keyhole (putting that reel in is a beotch!) On 1/6ths I have never been as far as the accident site. When looking at the poll options, I was not counting on having extra bottle on the way out. I tried to imagine what it would take me to get out from that point if something like this happened on my first visit there. (I at least had the advantage of having dived in flow something everybody who answered the poll probably hadn’t!) Now would my choosing 500 PSI mean we agreed on rescue/gas strategy?

I would not put much weight on the numbers and distributions. You do not even know who responded. The thread was the valuable thing.

aainslie

09-14-2009, 11:20 PM

alias

09-14-2009, 11:25 PM

Your hypothesis only makes my argument stronger.

If people ALSO differ in their reasons for giving the SAME number, that further makes the point that there is no consensus, and definitely ath tehre is no common basis in our training for how to handle this situation.

But you are missing all the people who agree but put down different numbers :D It's just that you do not know that 3 people who answered 1100 agree with 4 who answered 800 and 2 who answered 600 plus 1 who put down 1800

LCF

09-15-2009, 12:12 AM

Andrew, you are right. There seems to be no consensus on how to select a pressure on which to turn, or what variables affect the calculation. This thread has been excellent at making people think about the subject, and at pointing out the fallacies in some of the reflex answers. If there can be any agreement among people with enough experience to have some authority, an article would clearly be of benefit.

Arctic Mike

09-15-2009, 08:23 AM

Well, I finally picked a number. This one has taken a whole lot of thought. I hope never to have to be in this situation but here is my conclusion. I need about 200 lbs. of back gas to exit the system from the Hill 400 jump. I'll probably be breathing a little heavier because of the situation. My normal dive buddy has a slightly higher SAC rate than I have. He will probably be breathing a little heavier as well. We normally would have left deco bottles just back of the sign so I am counting on these as well. I picked 800 lbs. This is definitely enough for my exit, and will be real close if I find him in an OOA condition. Leaving alone would be one of the toughest decisions I would ever have to make.

This thread has been a huge thought provoker! Thanks Andrew!

Jay

09-15-2009, 10:06 AM

BTW, when you are thinking about your turn pressure, don't overestimate your own abilities.

There is not a posthumous medal of honor for cavediving.
Though Parker Turner probably deserved one.

aainslie

09-15-2009, 10:25 AM

Jay,

You've posted several times in this thread, yet never actually given a pressure.

So... what's yours?

Jay

09-15-2009, 10:42 AM

Jay,

You've posted several times in this thread, yet never actually given a pressure.

So... what's yours?

I said it would probably be closer to 1000 then 500 in my very first post. An exact number? I wouldn't know until I am there.
Yes, there is probably enough information based on this exact scenario in this exact spot to hazard a guess, which I did. But it's just a guess till you are in those fins.

JMHO, but the really low numbers seem too much of the 'hero' chest beating for my comfort.
And the really high numbers seem pretty unsupportive.
The discussion has been very good though, with a lot of thought provoking ideas.

aainslie

09-15-2009, 11:00 AM

I said it would probably be closer to 1000 then 500 in my very first post. An exact number? I wouldn't know until I am there.
Yes, there is probably enough information based on this exact scenario in this exact spot to hazard a guess, which I did. But it's just a guess till you are in those fins.

JMHO, but the really low numbers seem too much of the 'hero' chest beating for my comfort.
And the really high numbers seem pretty unsupportive.
The discussion has been very good though, with a lot of thought provoking ideas.

If you can't pick a number on dry land with days to think about it, how are you going to pick one underwater? Ultimately you have to commit to ONE number. And it will be only one of many things being processed by your brain. You're likely to get it highly wrong if you can't do it in the warmth of your home, either going high (say 1000) or low (say 500). At a very high SAC rate of 1 cfm in overblown 85's there's about 30-35 or so cu ft difference between those pressures, which is about 8-10 more minutes of searching at that depth. At a good SAC rate of 0.5 cfm it could be as much as 20 minutes. That's a gigantic difference.

THIS is the sort of planning that I feel is missing in many divers' thinking. And if one's thinking is sloppy above water, it's going to be dismal underwater.

Jay

09-15-2009, 11:52 AM

Andrew,

I know your intentions are to try to rethink some of the gas management rules
and "show your work" like back in math class and that is very admirable and thought provoking.

Why do you have to demand someone give you a meaningless exact number in a hypothetical situation?
You of all folks should realize that the discussion is more important then having a number tattooed on your forehead. You have these thought provoking discussions all the time.

Yes I am sure I could get out of there fine on less then 500 lbs, but of course I am not not going to commit to that number because I am not there.

Some folks posted their work for their calculations and gave good reasons, others may have done their work off line and picked their number. Some of it was pretty detailed.
Say someone picked 700 lbs. Now they just happen to be in ALMOST the exact situation. In their excited state do you think they will remember how they came up with that number and be able to adjust it for the slightly different situation?
Probably not all of them. So that number is stuck in their heads and something may be just a little different and they don't adjust for it and they don't make it.

A lot of divers read these threads and a lot of them do not have the experience or the abilities of some of the others. They may be unable to do ANY gas calculations in that situation.
Unfortunately some divers can be influenced into thinking "well if HE can get out on that amount, I can too"
It is too common that cave divers overestimate their abilities. I am not saying you are, but it is a sad fact many do. I have come across it too often to not encourage everyone not to.

I would feel much more comfortable if folks picked higher numbers and then adjusted them downward as actual events fell more in their favor.

ScubaBob-Squaretank

09-15-2009, 12:23 PM

I guarantee, that most everybody will be checking how much air it takes to get out from various points of the cave on there next dive.
Bob Klauck

aainslie

09-15-2009, 01:06 PM

Bob,

Thanks for that. You are pointing out the KEY number needed to REALLY understand how low you can safely go.

Let me suggest a procedure:

1) In caves you dive often, work out your gas consumption in PSI per 100 feet. So for example, look at your SPG as you pass th 500 ft marker and again as you get to your deco stop (go to the log in Ginnie, not the eye, as that's what you'd do in an emergency - which btw is a good reason to leave your dec cylinder at the beginning of the gold line, not in the eye). Divide by the hundreds of feet travelled (in our example, divide by 5). That tells you the gas consumed when relaxed per 100 feet. You should redo this in wildly different caves. Ginnie and Cow are reasonably similar, for example, so there's not that much mileage in redoing it for each.

2) Now work out the fudge factors you want to add. I'd suggest the following:
- Multiply by 2 so that you have a reserve for your buddy.
- Multiply by a number between 1 and 2 as a panic and contingency factor. This is going to be the hardest one to come to agreement on.
- Multiply your gas consumption by the product of these.

So for example, let's say it took you 200 PSI in your doubles to go 500 feet (I'm just picking an arbitrary number). Divide by 5 - that's 40 psi per hundred feet. Let's pick a panic factor of 1.5 - so you multiply this by (2*1.5), i.e. 3, to get 120 psi.

So our estimate is, it takes you 120 psi per 100 feet in full blown panic while buddy breathing.

Now let's remember also taht regs stop working at a certain pressure. Let's be super conservative and call it 200 psi. You need to add that in.

So - let's say you're at 600 feet in. You will need:

6 * 120 + 200

Or 920 psi. Round it up to 1000 psi.

This is an absolute maximum. If you are willing to cut into either the fudge factor, or the reserved gas, you can go substantially lower. The most insane calculation is based on 40 psi:

6 * 40 + 200 = 440 psi

So it's insanity to go below 440 psi.

An admission - these are based on my OWN numbers, i.e. I run at about 40 psi per 100 ft when exiting. When I started this exercise, I said that I'd only exit at 500 psi. I now think that this is nuts. In a dire emergency I would leave using a factor of 2, i.e. assume 80 psi per 100 feet. From 600 ft in that's 680 psi - round up to 700 psi.

I certainly learned something from that little bit of "show my work like back in math class". I hope I'm not the only one. I've upped my initial estimate of 500 to 700, and I now have a way of computing this going forward.

So the rule for me is simple -

distance * ave gas/100 ft * 2 + 200.

For more conservative folk it might be

distance * ave gas/100 ft * 3 + 200.

Sure, it's harder than "thirds", but it gives you a REAL number. And it's actualy easier to do than calculating thirds with a buddy - so hopefully joe average can do it.

(Well, I suppose that's screwed up my chances of an article since now I've laid it all out there...)

One last thing - learn to measure EVERYTHING. I know my average entry and exit speed. I know my average gas consumption at different points in the cave. And of course I have a pretty good sense of my SAC rate by now. I keep track of all this stuff, and it helps enormously for planning - both before the dive, and during the dive. I humbly suggest that you should too.

deepdiverbob

09-15-2009, 01:32 PM

I actually like these thought provoking threads. Makes me think of things I might not have thought of before. I just wanted to throw another thought out there on this as well.

Would your buddy have a better chance if you was at a busy cave, such as Ginnie on a weekend, or another busy time, if you left sooner and got help? A few more divers with full doubles and a decent plan could provide more time for a detailed search and rescue. Not saying this is the best idea, but it is possibly a better one for new divers who arent familiar with the system.

Second, I dont think we should stop posting information on these boards to hide it from new and/or inexperienced divers. They are going to get the information whether it be online maps of the different systems, or buying books online. At least on here, we are bringing up the fact that if you go beyond your level of training, or comfort factor, there could be lethal consequences to pay.

aainslie

09-15-2009, 01:37 PM

deepdiverbob

09-15-2009, 02:32 PM

Bob,

I think it's not a great idea. It would take someone 5-8 minutes to exit from there. Even without a safety stop, it would take him 2-3 minutes to get someone's attention. it would take them about 5 minutes to kit up, and even on a scooter, another 5 mintues to get there. That's 15-20 minutes. A long time.

And that's best case. Imagine if you exit and the parking lot is empty.

Again, not saying its the best solution for all instances. On the other end of the spectrum, as in my example, its a busy weekend, you could catch a team just getting into the water as well. But if this was a team members first trip to Ginnie, and dont really know all the different paths, it would be an option, but I agree, maybe not the best one. I just wanted to throw something else out there instead of the same argument that keeps getting hit back and forth for 12 pages.

rjack

09-15-2009, 03:29 PM

As a general rule, you are your buddy's best hope of aid. Which is a good reason to stay and search and a leave note + backup light when you finally do leave. Yes they may have already exited, if that's the case you just had a long stressful dive. If not, at least you stayed and searched as long as you could without creating a dual fatality.

jj1987

09-15-2009, 04:13 PM

...snip...
Andrew-

Why do you prefer 2*gas needed * x where X is a number between 1 and 2 instead of calculating a set amount of time? IE why not do-

2* gas needed *((max depth/33+1)*xx min) + 200psi

Seems when SHTF you'd know "ok, I have 10 minutes to fix things before we HAVE to exit", rather than knowing a 10% safety factor or whatever. 10% reserve in peacock could be 20 minutes, and that same 10% reserve in Eagles Nest could be 2 minutes... a pretty big difference in safety margin, at least time wise (my example was extreme, just to clarify what I'm saying).

chimie007

09-15-2009, 04:25 PM

As a general rule, you are your buddy's best hope of aid.

IMHO, your buddy's best hope of aid is to EXIT THE CAVE.

I would argue that 99 % of the buddy separation are just buddy separation. Not loss line, not loss gas, not tangled.... 99% of the time, both buddies are looking for each other for nothing. Each diver can exit the cave safely by themselves. This is what solo diver do every single dive. This is not a case of superman saving the poor little lost diver.

In practice, its worth searching a little as most time (again probably 99%) you will find your buddy around the corner and keep on going with the dive.

It's also worth searching just in case (very very very few times) that you could be useful to your buddy. These cases are extremely rare and probably extremely situation specific.

While I would stick around as long as possible (I answered 1000 PSI), I think statistically it could be shown that it is more risky for both divers to look for each other that long... In almost all cases, you are increasing your risk searching for nothing as in most cases your buddy is fine and just needs to exit.

aainslie

09-15-2009, 04:31 PM

Andrew-

Why do you prefer 2*gas needed * x where X is a number between 1 and 2 instead of calculating a set amount of time? IE why not do-

2* gas needed *((max depth/33+1)*xx min) + 200psi

Seems when SHTF you'd know "ok, I have 10 minutes to fix things before we HAVE to exit", rather than knowing a 10% safety factor or whatever. 10% reserve in peacock could be 20 minutes, and that same 10% reserve in Eagles Nest could be 2 minutes... a pretty big difference in safety margin, at least time wise (my example was extreme, just to clarify what I'm saying).

James,

I was looking for something simpler. If yuu remember 40 psi/100 ft for a particular cave system, you don't need to do all that depth stuff. You could calculate it for a new system BEFORE going in the water, i.e. if you know your swim speed nad SAC you could precalculate your psi/100 ft, say, in Eagle's. then once you know that it is (say) 120 psi/100 ft, now in-water your calculation is way easier.

Raphael,

I agree that an excessive search may just cause an unnecessary fatality. But going down to somewhere between 2 and 4 times the gas needed to safely exit on your own should not imperil the diver doing the searching, making it perfectly safe to look.

chimie007

09-15-2009, 04:37 PM

Raphael,

I agree that an excessive search may just cause an unnecessary fatality. But going down to somewhere between 2 and 4 times the gas needed to safely exit on your own should not imperil the diver doing the searching, making it perfectly safe to look.

I agree but people need to stop thinking that their buddy needs help. That mindset is likely to get folks to stretch their gas limits more than they should.

09-15-2009, 04:46 PM

I agree but people need to stop thinking that their buddy needs help. That mindset is likely to get folks to stretch their gas limits more than they should.
I agree, all the training organizations need to set a time limit on how long you should stay, the same way open water divers so. The 1 minute of the OW agencies is pretty short, so maybe 5-10 minutes, assuming that doesn't cut too deeply into your gas reserves.

rjack

09-15-2009, 05:05 PM

I agree, all the training organizations need to set a time limit on how long you should stay, the same way open water divers so. The 1 minute of the OW agencies is pretty short, so maybe 5-10 minutes, assuming that doesn't cut too deeply into your gas reserves.

This is way too long in some situations and way shorter than it needs to be in others. (Eagle's vs. Peacock)

If people don't have a rudimentary capacity to estimate how much gas they need to exit from a given point in a cave system they need better awareness to be in the cave at all IMHO.

aainslie

09-15-2009, 05:11 PM

I agree, all the training organizations need to set a time limit on how long you should stay, the same way open water divers so. The 1 minute of the OW agencies is pretty short, so maybe 5-10 minutes, assuming that doesn't cut too deeply into your gas reserves.

Forrest,

You're NOT agreeing with Raph. your'e suggesting a competing (and rather strange) rule.

Why is TIME a good metric?

I don't understand the need to use overly simplistic rules. 5-10 minutes is way too long in Eagle's at the point of furthest penetration, and way too short in the recent accident.

So - why is that better than my suggestion? And how did you come up with 5-10 minutes?

(Probably came out of your axiom...)

Edit - Richard, sorry, I only saw your post after I had replied.

alias

09-15-2009, 05:16 PM

IMHO, your buddy's best hope of aid is to EXIT THE CAVE.

I would argue that 99 % of the buddy separation are just buddy separation. Not loss line, not loss gas, not tangled.... 99% of the time, both buddies are looking for each other for nothing. Each diver can exit the cave safely by themselves. This is what solo diver do every single dive. This is not a case of superman saving the poor little lost diver.

I was glad to read your post because I thought this was something that could have been emphasized more during my course. During Intro it was extremely strongly hammered in that we do not search for buddy too long, and make one fatality into a double fatality, and ESPECIALLY produce a fatality out of something that needn’t be fatality at all (the original lost buddy exited first). I don’t know if the emphasis came partially from me arguing that I would look for my buddy for extended time… I know I had a lot of “buts”.

The message was clear but the delivery would have been even better if the stuff you bring up was emphasized instead of the possibility of the ‘rescuer’ dying: The fact that someone being lost does not mean they have multiple other things going wrong and are unable to help themselves.

Indeed after Bruce’s death my cave buddy and I had one of our repeat “when to bail alone” discussions. It has to do with us reminding each others that while we are both pessimists (and always expect that the minute one is alone in water they must suffer a heart attack or at least lose buoyancy control and hit their head on something solid, panic or minimum get narced), it serves no purpose to let this kind of negative thinking set the tone for the search when the way more likely scenario is that the other person is doing exactly what you are doing – looking for you, already back on the line.

We keep reminding each other that it is extremely disrespectful to assume that the other one all of a sudden possesses no skills nor sense to work out their problems and make their way out. Yes, it will be stressful situation but we have seen each other perform under stress. We have threatened all kinds of cruel things we will do to the dead body if the one who was not lost ends up overstaying and dies in the process. You got to trust your buddy or do not go in a cave with them.

It serves no purpose to immediately expect the worse if you get separated. My premise is that I will search as long as I think is safe, if I get overtly excited it’s going to be shorter time, so I try to keep myself calm assuming that is what my buddy is doing too. That will produce the best results and it’s what is most likely too. If I move on to more demanding dives, I will have to rethink but at the moment I think the scenarios that play in the minds of newer divers can be little bit over the top. Of course one has to take into account preceding events but it’s a known fact that catastrophizing does not help in problem solving situation.

karst.window

09-15-2009, 08:01 PM

Ok Andrew... I'll bite.

Let me preface this that this should not in any way be used by anyone as their gas management plan. This is merely personal opinion and is in no way an attempt to change standards. Too many variables come into play with regards to these calculations and if you are not an experienced cave diver I think they would be difficult or impossible to perform on the fly at depth with anxiety ratcheted up.

As a rebreather diver gas management becomes based upon bailout which in turn is an estimate of the gas it would take for you, or your "team" (I'm not getting into the team versus single bailout discussion) to exit safely from point of furthest penetration given a total loop failure. This "estimate" is derived from knowing your SAC rate as well as your swim rate and is system specific (obviously swim rates will differ between various cave systems).

In Ginnie I have personally exited as fast as 100 ft per minute (purposeful but not emergently) and as slow as 65 ft per minute (leisurely). For this example I will consider the more purposeful exit. So for sake of calculations...

Travel time: 100 ft per minute

For SAC calculations I use 0.7 cu ft/min to 0.8 cu ft/min. That translates to around 3 cu ft per minute at depth and is the calculation I would use in my head. Unfortunately not everyone will have the same SAC and these calculations should be based upon the diver with the HIGHEST SAC rate.

So if you are 600 feet from the exit and traveling at 100 feet/min then you will need approximately 18 cu ft for yourself to exit. I agree with others who have posted that you should expect that your buddy will have as much or less gas in their tanks if you are able to find them and you should have enough gas for both of you to exit. Thus for this calculation would be 36 cu ft.

Knowing cylinder size and volume properties, which I'm not going into here, would be crucial. Diving a set of HP 130's would give you 3600/260 = 13.85 psi/cu ft Also note that volume/pressure realationships are not exactly linear and these calcs are estimates.

If you need 36 cu ft total gas to exit then the "hard deck" turn pressure is approx. 500psi in this example. Would I go this low? Nope. This is merely a calculation and is great for means of mental masturbation but by no means should this be advocated to divers without considerable experience.

Now consider losing your buddy at the point of maximum penetration. That's a little more interesting... but it is essentially the same calculation.

Say max penetration is 2000 ft, swim rate is 100 ft/min, and gas utilization is 3 cu ft/min at depth then you need 60 cu ft/diver thus 120 cu ft total for exit. Diving HP 130's you'd have to turn at 120/260 x 3600 = 1661 So 1700 psi would be my personal absolute turn pressure in that situation.

This inherantly adds conservatism because someone could argue that it is unlikely you'd find your buddy right at the point where they would need to buddy breathe. However, if you do and you have not added that into the contingency then you're both dead.

Let me again state that in order to perform these calculations you need to know your, tank properties, SAC's AND swim rates which are likely to be altered in an emergency situation. There are just too many variables in order for me to advocate to anyone that they turn at a specific pressure. Other psychological factors would also play into the above example in that you were both already exiting, right? I would probably exit well before the absolute lowest pressure and assume I would find you on the surface. A quick cursory search (lights, silt, etc.), exit and call for help seems to me very prudent and hard to argue against. The bottom line seems to me to plan your dive, and dive your plan. Discuss contingencies with your buddies and discuss how you are going to react.

Sean

aainslie

09-15-2009, 09:20 PM

Hey Sean,

Your calcs are very similar to mine. There are basically two ways to work this out. One requires speed, depth, tank size and SAC, as you did, and which I agree with. Another is to know your PSI/100 feet in a specific cave with a specific set of tanks. This would change for each cave but there are a lot of folk who do the same cave over and over - Gnnie springs to mind. This single calculation takes all three directly into account.

So I'm agreeing entirely with your suggestion - and adding another method, usable only in caves you dive often. Which tied into Bob's point, where he says (and I hope he's right) that going forward, a lot of people will be measuring their gas consumption on exit.

jj1987

09-15-2009, 09:29 PM

Many have mentioned covering your light, but frankly, I think that's not the most effective way of finding a buddy, because it doesn't work well in a complete siltout, which in my experience, is the only time I've ever had separation with a buddy. It works very well to verify a buddy is nearby, or to see where they are in relation to you, but in my experience it breaks down in the most likely lost buddy scenario.

Rich Courtney told me a story about an OC diver who was diving with a group of rebreather divers and they became slightly separated. the OC diver's first reaction was to hold his breath and wait to hear bubbles....but wait, he couldn't! For some reason this story stuck with me through the lost buddy drills during training, and it was often difficult to run a reel towards the buddy, because you can darn near instantly hear them.....well until they start swimming around the park bench playing hide and seek, and once I catch up to them immediately become flipped upside down and unconscious, but I'll pass that off as an instructor having fun during the class :smt081

Fortunately I've only been in 3 (almost zero viz) siltouts, one in the NW corner of Ginnie, one at Royal Springs, and one on a side tunnel near the end of goldline at Madison Blue. None of them were terribly long, and they were all siltouts that the whole team saw coming. As soon as I lost viz, I consciously changed by breathing pattern so that I could hear my buddy, and it's darn effective. Fortunately all of my buddies in this case have been on the line, and we've never really been separated.

I do however think that if you're in clear water, and separated any great distance, that covering the light would be highly effective, as it's proven to be during training. However, I've been lucky enough to not have this happen yet, so I can't formulate a real world opinion.

/rant. Sorry to get off topic. It's just a story that's stuck in my mind, I doubt Rich even remembers telling it to me...but I guess since I've found it useful I thought I'd pass it along. :smt102

09-16-2009, 08:48 AM

I've experience momentary buddy separation in silt out situations, one yesterday, as it happens. We were on the same line, just separated by several dozen feet. I was behind and shielded my light every few seconds. When we were about 40' apart from each other, I could see the glow of my buddy's light. Granted, she was in clear water at that time and turned around to face my direction, but I was still in a near complete silt out. Don't discount shielding your light in silt outs. It can still work to your advantage.

aainslie

09-16-2009, 10:15 AM

James and Rob,

This has what to do with turn pressure?

Bad boys! Stay focused here!

Edit... and litehedded...

LiteHedded

09-16-2009, 10:20 AM

alias

09-16-2009, 10:49 AM

This has what to do with turn pressure?

Bad boys! Stay focused here!

I know things have begun to splinter from your topic. Maybe someone could start another thread about “Things you might not have learnt re: ‘Lost Buddy Search’ during your courses”, so we don’t need to stop discussing additional search tips, flagging down help and whether it’s better to stay/leave in general etc. There has been plenty of very useful info in this thread, especially for newer cave divers. Would hate to see people stop sharing their ideas that not all of us might have heard during our training and limited exposure.

09-16-2009, 02:53 PM

James and Rob,

This has what to do with turn pressure?

Bad boys! Stay focused here!

Edit... and litehedded...

Well, let's see...cover your light, find your buddy faster, turn pressure becomes a non-issue... ;)

And I do try to keep my lights focused... :)

wendellnope

09-17-2009, 02:00 PM

This has been an interesting and educational exercise. I calculated on the specifics of the hypothetical you presented. I don't represent my vote as anything but my vote. I voted 800 psi. To validate my own calculations to myself, I relied on the fact that I have made multiple silt-out (percolation) exits of 1000'+ in a Utah cave that has similar flow to Devil's Spring. About half have turned into Bump & Go exits and one was an air-sharing event due to an equipment malfunction. I have experienced multiple lost-buddy silt-out incidents in this same cave. One event was an extended search over a 250' upstream distance. Considering your hypothetical and my own experience, 800psi is my choice for this hypothetical.

Wendell Nope
www.wendellnope.com/scuba3.htm

marinediver

09-17-2009, 03:42 PM

I agree, all the training organizations need to set a time limit on how long you should stay, the same way open water divers so. The 1 minute of the OW agencies is pretty short, so maybe 5-10 minutes, assuming that doesn't cut too deeply into your gas reserves.

I think that if you need to be taught a set time allowed to search for a suspected missing diver and can't think for yourself under stress then you do not belong in a sport where your actions have the potential of life and death.

rjack

09-17-2009, 07:05 PM

I think that if you need to be taught a set time allowed to search for a suspected missing diver and can't think for yourself under stress then you do not belong in a sport where your actions have the potential of life and death.

<clapping>

aainslie

09-17-2009, 08:08 PM

Slüdge

09-17-2009, 08:19 PM

Yeah, marinediver needs to teach FW a thing or two about cave diving.

aainslie

09-17-2009, 08:26 PM

Not much commentary on the idea of getting people to know the psi used per 100 ft in a cave. i'm going to suggst some other possible uses and see if anyone can see why they apply:

1) Gas loss situations, where the gas loss is controlled - e.g. losing half your gas after isolation.

2) Solo scootering, when you lose your scooter. In particular, this is a way to determine when to turn around. I've yet to see anyone suggest a way to calculate turn pressure whenscootering solo, yet I know a lot of us do it. How might one calculate a safe turnpoint?

3) Any others you can think of? A somewhat naughty one (that'll probably get the usual suspects yelling at me) is that it gives you a way to "recalculate thirds" (doubles actually but you get the point) during a return, when you see an interesting side passage or lead.

I'll post my answers sometime tomorrow. Anyone else want to play and suggest any of the answers?

aainslie

09-17-2009, 08:34 PM

Yeah, marinediver needs to teach FW a thing or two about cave diving.

More a comment on his (lack of) tact than his skillset.

And being good at something doesn't mean being good at thinking about how to do it. I suspect Chuck Yeager would be a lousy aeronautical engineer. Conversely, Frank Whittle (who invented the jet) was probably a sucky pilot.

Which is a roundabout way of saying that FW is a) a good rebreather designer, b) a really experienced diver and c) lousy at suggesting exit rules for buddy searches.

Slüdge

09-17-2009, 08:49 PM

lousy at suggesting exit rules for buddy searches.

Really? Didn't that poll suggest that a lot of people were letting emotion keep them in the cave WAY too long? I used to cave dive with my then-girlfriend, and I guarantee if she were lost in the cave there would have been a double drowning, because I would have kept looking until I ran out of gas.

FW is suggesting a maximum "look time" to prevent said double drowning.

marinediver

09-17-2009, 09:57 PM

Yeah, marinediver needs to teach FW a thing or two about cave diving.

You know, If I got lost or separated from my dive buddy and he wasnt able to think for himself and keep a safe amount of gas to exit the cave after exhausting every effort to find me and left with 2400 pounds after looking for a "maximum time" set in some rule manual, I would be pissed especially in the distances in the recent accident . If I got out of the cave and found this out, I would hit him in the head with an AL40.

I didnt say I could teach anyone anything about diving...I am talking about thinking under stress, something everyone here seems to think is not possible.If you can not reason and think under stress then yuo should not put yourself into unnecessary dangerous situations where that ability might come in handy...example: Cave diving...

09-17-2009, 10:25 PM

aainslie

09-17-2009, 10:35 PM

Really? Didn't that poll suggest that a lot of people were letting emotion keep them in the cave WAY too long? I used to cave dive with my then-girlfriend, and I guarantee if she were lost in the cave there would have been a double drowning, because I would have kept looking until I ran out of gas.

FW is suggesting a maximum "look time" to prevent said double drowning.

Problem is, time is a dumb metric. 2 minutes may be too long if you're at thirds. 20 minutes may be too short under other circumstances.

I once waited close to Stage Rock in Ginnie just shy of 30 minutes. Admittedly I was on a rebreather (and there's a story behind this) but I waited because a) I could and b) I didn't want the other person to go looking for me.

The critical commodity isn't TIME. It's GAS. So the rule should be tied to the binding constraint, i.e. GAS.

My suggested rule (which I'm going to recap tomorrow) focuses entirely on this constraint.

Besides, women are never lost. Haven't you learned that yet? You're the one who would have been lost!

Ain't that the truth?

atedeschi

09-17-2009, 11:09 PM

1) Gas loss situations, where the gas loss is controlled - e.g. losing half your gas after isolation.
Not sure what you are looking for here but I make sure my plans allow me to exit from max distance with half loss of gas. My planning takes into account flow and swimrates. But I think you already know what Im doing for my gas planning.

2) Solo scootering, when you lose your scooter. In particular, this is a way to determine when to turn around. I've yet to see anyone suggest a way to calculate turn pressure whenscootering solo, yet I know a lot of us do it. How might one calculate a safe turnpoint?

I do not scooter but Ill give this a shot. Why not do it like on CCR? Calculate what your exit speed is swimming. Then say you wanna use a 1/3rd of your BG for scootering, therefore you have 2/3rds to use to swim out. Calculate the cu. ft capacity of that 2/3rds, then use your depth and sac and figure out how many minutes it will last you. Then take your fpm exit speed and how long the 2/3rds will last you and you can figure out how far you can be in the cave and still swim out.

Example:
Double LP85s filled to 3600psi, swim speed out 45fpm, average depth 90’, SAC = .7

Baseline = [(85cu. ft / 2640psi) * 2] = .064

3600 psi – 1200 psi = 2400 psi

Therefore we have 2400psi or 153 cu ft (2400psi * .064 = 153 cu ft) to swim out.

[153 cu. Ft / (.7 * ((90 ft / 33 ft) + 1))] * 45 fpm = 2638 ft

The turn for this dive would be at 2400 psi and you can not exceed 2600’ from the exit.
You could also figure out how fast your arm moving into the system with the scooter and calculate max distance in based on 1200psi then just add stages that you do not breath but stage on the way in. Kind of like CCR bailout planing.

aainslie

09-17-2009, 11:46 PM

rjack

09-18-2009, 12:07 AM

3) Any others you can think of? A somewhat naughty one (that'll probably get the usual suspects yelling at me) is that it gives you a way to "recalculate thirds" (doubles actually but you get the point) during a return, when you see an interesting side passage or lead.

Naughty? This was part of my full cave (GUE Cave2) class. We went and did just this on our first day after class. Although on the entry not the exit.

Enter partway on a stage
Drop stage
Explore side passage on backgas
Return to stage and switch to it
Recalculate total 1/3rds which results in new a turn psi on backgas
Continue in on stage
Drop stage at 1700psi
Continue in backgas
Thumb dive
Exiting on backgas
Pick up + breath stage
Surface

deepdiverbob

09-18-2009, 12:09 AM

.I am talking about thinking under stress, something everyone here seems to think is not possible.If you can not reason and think under stress then yuo should not put yourself into unnecessary dangerous situations where that ability might come in handy...example: Cave diving...

That all sounds good, but in my opinion, until we are actually faced with that stress, we have no idea how we will react. 99 times out of a 100, we may react cool, and do what we are suppose to. But all it takes is that other 1 time, and we wind up on the accidents forum.

atedeschi

09-18-2009, 12:12 AM

Yeah I like the psi per 100ft, i been busy i think i will go have another look at that post. As far as losing half my gas, I can exit from max distance in on one tank as long as i do not go past my turn pressure in either my tanks.

jj1987

09-18-2009, 12:42 AM

Hey Ant,

Yep... you're definitely going where i was going. But you're using the usal stuff... sac... swim speed. I'm suggesting that for a given cave, you need to know just one number - psi used per 100 ft... and then all these calcs - lost buddy, scootering solo, isolated gas losses - become easier to calculate. BTW with the isolated gas loss, my interest is, can you exit unaided? That makes the exit much more comfortable. Since one could lose MORe than 1/2 of one's gas (unbalanced sidemount, slow reactions), this would be useful to know. If you can exit unaided, you do NOT need to rely on your buddy, which makes the exit much more relaxed.
Doesn't that number change (drastically) depending on what passage you're in? I can see averaging it out for a max penetration number as you've expressed earlier.

When we start using ___ft per 100psi (or vice versa), I think you're greatly increasing the complexity of the dive beyond what's needed (I do however, think that it's a useful exercise, and realize that knowing these rules of thumbs can come in handy when SHTF). What happens if I recalculate near the entrance and exit with 500psi in backgas on a dive where my o2 fails? There's a good chance I don't have enough gas to complete the additional deco requirement to cover the non functional o2 bottle. With the Shands chamber closed at certain hours, or at remote cave locations, that has the potential to be a big deal. I guess you could always take redundant o2 bottles or something like that...and also when doing your calculations, you can calculate for the lowest flow side passage that you may decide to go down...I can see ways of planning this, but the benefits don't seem nearly as great when I start to think of how to execute it, as I'm trading an extra stage for another o2 bottle, and now have to calculate for the lowest flow rather than the stronger mainline flow, etc. Maybe I'm missing an obvious solution to the problems I've mentioned?

Seems we can plan gas failures down to an exact science with a series of what if's, but for as much time as we spend talking about gas, I haven't seen a gas failure being a cause of death in any of the accidents that I've heard about from recent years. If I thought gas failures were the biggest risk in cave diving, I'd grab a buddy bottle and go solo dive. However, mental "failures" seem to be what's killing people which is why I prefer to have a redundant brain with me. I just think that while we can slightly modify gas plans, once we start calculating doubles, and then recalculating, we open ourselves up to mistakes...not so much on land, but in the water thing seem to happen faster, which is why predive planning can be so crucial.

I guess the cliff notes here would be- I think if you're diving doubles and recalculating, you don't have one number, but a few "hidden" variables, and plenty of places to make mistakes. I have a feeling we agree on the math end of things, but disagree on how much we trust a human brain underwater.

09-18-2009, 07:17 AM

.....FW is suggesting a maximum "look time" to prevent said double drowning.
Yes, but mostly suggesting that if all divers plan to exit if seperated, the need for a long search will cease.

There is usually no reason to get seperated anyway. The lead diver stopping, will usually be all that is necessary. In a siltout, the lead diver should stop, and/or start using the Rimbach method. Maybe even turn around and exit if it gets that bad.

If exiting is the main plan for seperation, the divers will head towards the exit. The one closest to the exit should exit slowly, so his/her buddy can catch up.

09-18-2009, 07:45 AM

How about just doing some practice dives to figure this out? When I first started scootering, I started getting a little nervous the farther I went into the cave. I decided I neede to test things out, especially since I was doing a lot of this solo. I scootered back to the traffic light in JB, turned around, switched to AL and began swimming out. I pushed the scooter in front of me and even tried to intentionally breathe a little faster than normal. I got out with gas to spare. In fact, I know I can swim out from Stage Rock in JB on an 80 and still have gas to spare. Forget about the theoretical armchair calculations. Get out there and do it!

MORGAN

09-18-2009, 08:42 AM

Forget about the theoretical armchair calculations. Get out there and do it!

Empiricist! You're spoiling all the fun we're having theorizing!:)

Mike

atedeschi

09-18-2009, 10:11 AM

BabyDuck

09-18-2009, 11:32 AM

i appreciate that knowing gas used per 100ft in several different caves would be a helpful bit of info to have.

but unless they come up with underwater calculators, all this isn't helpful to me. i'm not a stupid person & understand where the numbers come from, but doing math in my head isn't an easy skill. at all. as in, i can't remember times & pressures *in class, when i know i'll be asked,* unless i get to spit them out as soon as my mouth hits the surface. once the debrief has started, those numbers are gone. i'd spend so much time with wetnotes doing the math that i'd hit my pressure and have to leave anyway. so i'll have to be much less scientific when picking a number to leave on.

i wish it wasn't true, but it is what it is.

aainslie

09-18-2009, 12:43 PM

Well, my idea is pretty empirical. It works best for caves with fairly consistent depths and flow rates. If the cave gets deeper and/or flow decreases further in then just up the factor.

OK, so the procedure is as folllows:

1) Measure your gas usage on several exits. Get an average value of gas used per 100 ft travelled. Err on the conservative side. For example, for most people in Ginnie this will be a value between 20 and 80 cu ft/100 ft -but it is important to generate your own value. Round up to the nearest decile - i.e. 20, 30, 40, 50 etc.

2) Take this value and multiply by a safety margin. Multiplying by 2 will mean that you will ahve double the gas needed to exit. Up the factor if you're at all uncertain about your dive - new equipment, new partner etc (btw this should be a generic rule for the rule of thirds too - DON't dive thirds if you ahve uncertainties, add a margin). I'd suggest using 2, 3 or 4 depending on uncertainty.

3) Let's say you calculated that you use 40 psi/100 ft, and cho chose a factor of 3. That means that you want to reserve 120 psi/100 ft. make sure that number is cast in stone - write it on a slate if necessary. Do it often enough and it'll become second nature.

4) Now is time to use it:

- Lost buddy - search until your gas hits (current dist in hundreds) * (your factor) + 200. At 600 ft, with the numbers I used above, that's 6*120 + 200 = 920 psi. Round up to 1000. That's your exit pressure.

- Scootering solo. The HARD way is to solve a set of simultaneous linear equations underwater. Ain't going to happen. The EASY way is to precalculate. So... for my scootering calculation, I'm going to use a factor of 2, i.e. keep double the gas needed to exit. That makes my factor 80 psi/100 ft. So at 1000 ft I need 800+200 = 1000. At 2000 I need 1800. At 3000 I need 2600. You might write these on a slate too. Basically if I hit thirds at about 2800 ft it's time to come home.

Rob, please note that the problem with your empirical method is that you have NOT reserved twice the gas to exit. You need at the very least to DOUBLE your empirically measured gas to determine a turnpoint. Furthermore it needs to be in two different tanks, i.e. you need 80 in the AL and 80 in backgas. The danger of your method is that you would feel happy turning at that rock with 80 cu ft when you should be turning at 160 cu ft. I don't blame you for making this mistake - after all where in the "rules" is it covered??? I guarantee you that this is what MANY of us are doing - we are allowing JUST enough in our ad-hoc calcs to exit, NOT double. "Thirds" has left us unable to handle this situation without further careful thought.

4) The "naughty" side passage exploration rule. I'd go conservative here and use a factor of 3. At 1000 feet, I need 1400 psi - so I can go rooting around until I hit 1400, then it's time to exit. At 500, I need 800 psi. Etc etc.. Richard, I'm not sure how you recalculated thirds but I'll bet it took longer than the method that I've jsut suggested.

After a while, all these calculations will become dead easy, and it will become second nature to figure out how much you ned to safely exit from any point.

What if it's a cave you don't know? That's when SAC plus known speed helps. Ignore flow, and use a calculated factor with the following 3-stage formula (I'm doing it in 3 stages so the math is easier to follow - it can of course be simplified to a single equation):

1) Adjusted AC = (1+depth/33)*SAC (we all know this one - I'll call this AAC)

2) Consumption/100 ft = AAC*100/speed (let's call this CPHF)

3) PSI/100 ft = (fill pressure/rated pressure)*(rated volume)/CPHF

An example - I'm diving a deepish new system at 166 ft depth. I have overfilled 108's rated to 2640. My SAC is 0.6. So:

AAC = 0.6*6 = 3.6 cu ft/min
CPHF = 3.6*2 = 7.2 cu ft/100 ft

PSI/100 ft = (3600/2640)*108*2/7.2 = 41.

Round to 50. For a factor of 2 (e.g. solo scootering) use 100. For a factor of 3 (e.g. checking out stuff on the way home) use 150.

I understand that it requires some prep. But what's the current procedure for solo scooters/ oops - there isn't one. For lost buddies? Oops again.

James - this CAN be simplified and with practice CAN become second nature. Anyone who can compute dissimilar thirds can do these types of calculations.

rjack

09-18-2009, 01:01 PM

Roughly here's our "1/3rds recalculation". This is MX, AL80s for everything. No flow cave, 1 buddy. Using the stage down to 400 psi (1/2 -200, 1300psi in, 1300psi out), reserving enough backgas to exit without the stage, and 1/3rds -100 of backgas.

Enter partway on a stage
Drop stage at 2200psi
Explore side passage on backgas (400psi used)
Return to stage and switch to it
Recalculate total 1/3rds which results in new a turn psi on backgas
reserving the stage from backgas is (still) 700psi. So 2600psi remaining in backgas - 700 = 1900psi
1900/3 = 600. 600-100 for only having 1 buddy = 500 usable
New backgas turn pressure = 2100psi

Continue in on stage
Drop stage at 1700psi
Continue in backgas, 500psi used. turn at no less than 2100
Thumb dive
Exiting on backgas 500psi used exiting
Pick up + breath stage switching off backgas at 1600, stage picked up at 1700
Surface 400psi in stage, 1600psi in backgas

We had the coverage for the loss of both my and my buddies stages, or could have lost 1 backgas and 1 stage at max penetration and still exited. Was a "no-deco" dive, average 35ft depth, 140min BT. Although we did 5min stop at 20ft and 5mins at 10ft those weren't actually required.

aainslie

09-18-2009, 01:18 PM

09-18-2009, 01:47 PM

Rob, please note that the problem with your empirical method is that you have NOT reserved twice the gas to exit. You need at the very least to DOUBLE your empirically measured gas to determine a turnpoint. Furthermore it needs to be in two different tanks, i.e. you need 80 in the AL and 80 in backgas. The danger of your method is that you would feel happy turning at that rock with 80 cu ft when you should be turning at 160 cu ft. I don't blame you for making this mistake - after all where in the "rules" is it covered??? I guarantee you that this is what MANY of us are doing - we are allowing JUST enough in our ad-hoc calcs to exit, NOT double. "Thirds" has left us unable to handle this situation without further careful thought.

Andrew, I was not advocating turning with only 80cf left. My point was to present an empirical exercise in which someone actually figures out how much gas it takes to get out alive. When I do my solo scooter dives, AL comes along as a buddy I plan on never having to touch and doesn't even play a role in my gas calculations. I then plan my dive with the turn being when I've used 1/4 of my gas supply. So, during one of those typical dives, I'm using about 73.5 cf for my penetration and have 211.5 cf left to get out (108s), PLUS 80cf in AL. Yes, this is extremely conservative, especially considering I only dive sidemount so I have 3 independent bottles. But I'm also doing 4000' penetrations, and that leaves me over 4 times the amount of gas I'll need to exit while swimming. So if I lose one complete bottle (one of the big ones, not AL), I'll still have about 2.5 times the amount of gas needed to get out alive. Hopefully this clears some things up.

rjack

09-18-2009, 03:15 PM

Richard,

I'm not arguing whetehr or not recalcing thirds works. Just that mine might be simpler, with broader applications.

Admittedly I haven't handled stages yet. I need to think about that. I don't think it's too hard. You had the simplification of all Al80's so no factors were needed between the stages and backgas. That can't be done in nost of Florida.

Let me mull that over.

Sorry I was just describing a "naughty" scenario :D

As far as exit gas goes, I just try to memorize a time and a gas amount from a distinctive part of the cave (features, turns, jumps, arrows, etc). I can usually store about 6 to 8 "waypoints" per cave. On subsequent dives I can generally add 1 to 3 additional waypoints as I learn the system over time.

I don't dive beyond the point where I know the cave, which includes knowing the exit time and gas as well as the layout of the lines in the passages. I have never been to Ginnie, but I am pretty sure I wouldn't have a huge issue remembering a rough amount that I needed to exit from an area only a few 100ft inside like Harry's Crack. If I lost my buddy I'd know how much to double and buffer that amount accordingly.

I think all the 40psi vs 48psi min type stuff is over complicating this.

Meister481

09-18-2009, 08:04 PM

Problem is, time is a dumb metric. 2 minutes may be too long if you're at thirds. 20 minutes may be too short under other circumstances.

I once waited close to Stage Rock in Ginnie just shy of 30 minutes. Admittedly I was on a rebreather (and there's a story behind this) but I waited because a) I could and b) I didn't want the other person to go looking for me.

The critical commodity isn't TIME. It's GAS. So the rule should be tied to the binding constraint, i.e. GAS.

My suggested rule (which I'm going to recap tomorrow) focuses entirely on this constraint.

I'm supposing that prior to the dive, at each location, you have a solution before you hit the water. Am I correct? Each hole has it's characteristics and flow, line traps, etc. This is the solution I've chosen.

How about just doing some practice dives to figure this out? When I first started scootering, I started getting a little nervous the farther I went into the cave. I decided I neede to test things out, especially since I was doing a lot of this solo. I scootered back to the traffic light in JB, turned around, switched to AL and began swimming out. I pushed the scooter in front of me and even tried to intentionally breathe a little faster than normal. I got out with gas to spare. In fact, I know I can swim out from Stage Rock in JB on an 80 and still have gas to spare. Forget about the theoretical armchair calculations. Get out there and do it!

Done. I used some Leica Geovid's and popped out a distance of 333 yards to swim while pulling a scooter, then a scooter and a stage, then a scooter and 2 stages. I will use this info to plan the gas for a dive and then do prep dives if needed. Just when you think you've had enough, run a line a few hundred feet with tie offs and see how long it takes you by feel, towing a scooter. This still doesn't account for restrictions or any line traps you might encounter while towing your newly acquired anchor.

Well, my idea is pretty empirical. It works best for caves with fairly consistent depths and flow rates. If the cave gets deeper and/or flow decreases further in then just up the factor.

OK, so the procedure is as folllows:

1) Measure your gas usage on several exits. Get an average value of gas used per 100 ft travelled. Err on the conservative side. For example, for most people in Ginnie this will be a value between 20 and 80 cu ft/100 ft -but it is important to generate your own value. Round up to the nearest decile - i.e. 20, 30, 40, 50 etc.

2) Take this value and multiply by a safety margin. Multiplying by 2 will mean that you will ahve double the gas needed to exit. Up the factor if you're at all uncertain about your dive - new equipment, new partner etc (btw this should be a generic rule for the rule of thirds too - DON't dive thirds if you ahve uncertainties, add a margin). I'd suggest using 2, 3 or 4 depending on uncertainty.

3) Let's say you calculated that you use 40 psi/100 ft, and cho chose a factor of 3. That means that you want to reserve 120 psi/100 ft. make sure that number is cast in stone - write it on a slate if necessary. Do it often enough and it'll become second nature.

4) Now is time to use it:

- Lost buddy - search until your gas hits (current dist in hundreds) * (your factor) + 200. At 600 ft, with the numbers I used above, that's 6*120 + 200 = 920 psi. Round up to 1000. That's your exit pressure.

- Scootering solo. The HARD way is to solve a set of simultaneous linear equations underwater. Ain't going to happen. The EASY way is to precalculate. So... for my scootering calculation, I'm going to use a factor of 2, i.e. keep double the gas needed to exit. That makes my factor 80 psi/100 ft. So at 1000 ft I need 800+200 = 1000. At 2000 I need 1800. At 3000 I need 2600. You might write these on a slate too. Basically if I hit thirds at about 2800 ft it's time to come home.

Rob, please note that the problem with your empirical method is that you have NOT reserved twice the gas to exit. You need at the very least to DOUBLE your empirically measured gas to determine a turnpoint. Furthermore it needs to be in two different tanks, i.e. you need 80 in the AL and 80 in backgas. The danger of your method is that you would feel happy turning at that rock with 80 cu ft when you should be turning at 160 cu ft. I don't blame you for making this mistake - after all where in the "rules" is it covered??? I guarantee you that this is what MANY of us are doing - we are allowing JUST enough in our ad-hoc calcs to exit, NOT double. "Thirds" has left us unable to handle this situation without further careful thought.

4) The "naughty" side passage exploration rule. I'd go conservative here and use a factor of 3. At 1000 feet, I need 1400 psi - so I can go rooting around until I hit 1400, then it's time to exit. At 500, I need 800 psi. Etc etc.. Richard, I'm not sure how you recalculated thirds but I'll bet it took longer than the method that I've jsut suggested.

After a while, all these calculations will become dead easy, and it will become second nature to figure out how much you ned to safely exit from any point.

What if it's a cave you don't know? That's when SAC plus known speed helps. Ignore flow, and use a calculated factor with the following 3-stage formula (I'm doing it in 3 stages so the math is easier to follow - it can of course be simplified to a single equation):

1) Adjusted AC = (1+depth/33)*SAC (we all know this one - I'll call this AAC)

2) Consumption/100 ft = AAC*100/speed (let's call this CPHF)

3) PSI/100 ft = (fill pressure/rated pressure)*(rated volume)/CPHF

An example - I'm diving a deepish new system at 166 ft depth. I have overfilled 108's rated to 2640. My SAC is 0.6. So:

AAC = 0.6*6 = 3.6 cu ft/min
CPHF = 3.6*2 = 7.2 cu ft/100 ft

PSI/100 ft = (3600/2640)*108*2/7.2 = 41.

Round to 50. For a factor of 2 (e.g. solo scootering) use 100. For a factor of 3 (e.g. checking out stuff on the way home) use 150.

I understand that it requires some prep. But what's the current procedure for solo scooters/ oops - there isn't one. For lost buddies? Oops again.

James - this CAN be simplified and with practice CAN become second nature. Anyone who can compute dissimilar thirds can do these types of calculations.

This is all academic until tested. The numbers will change depending upon your gear configuration and exertion level. You will need to ensure you have proper deco gas and back gas in case of lost deco, keeping in mind the additional deco obligation due to slower return caused by scooter failure/siltout. If you don't run a reel in Devils and miss your deco bottle on the way out you might not die but you could get bent. These are all facets of an overall plan, it's not like the gas plan is a separate deal, it's dependent upon many factors.

Simply calculating the gas needed to swim the distance doesn't account for all factors involved in the gas plan. This is where people can get in trouble blindly following a suggested plan, IMO.

I don't have near the experience as most of you but I do enjoy the planning stage of the dive. It's a riddle that has many answers. I'm comfortable planning for 2 major failures and the rest is up to the man above.

I test my plan (on paper) against any 2 failures.

Lost vis- covers several
Lost scooter
Lost deco gas
Lost 1/2 gas
Lost fin

aainslie

09-18-2009, 09:21 PM

1) Why would you swim out in an emergency with yoru scooter? Especially if you begin to get behind schedule? Dump the bloody thing!

2) Some things are self evident. Aruithmetic as simple as the stuff I proposed doesn't need empirical testing. Sheesh.

OK, I'm done on both these threads.

For those of you who care, DON'T DIVE THIRDS. DIVE DOUBLES.

Seriously. Find ways to make sure that you reserve double or more teh gas erquired to exit under all scenarios. With stages, you might change this to reserving (n+1)/n where n is the total number of tanks (I could provide a proof of why this makes sense but I've come to realize that mathematical sophisticaion is viewed as a form of dark magic around here - so instead I'll leave it to those willing to use their noggins), i.e. with 3 tanks, reserve 1 1/2 x the gas needed to exit in EACH tank; with 4, reserve 1 1/3 - and of course use this as an absolute minimum, i.e. add a nice margin. This is a way safer rule than the conventional one of diving stages to 1/2 + 200. This is where I intended to go next, Richard, after your example of recalcing thirds with stages. I'll hold it for an article I've decided to write - assuming anyone is willing to print it. We'll see.

This has been fun. Be careful who you buddy up with. A lot of them will, to quote myself from another thread, run like a girl at the first sign of toruble. So make sure whether your'e diving with a girl (Gary comes to mind) or a real diver (Cindy comes to mind).

Burke

09-18-2009, 09:39 PM

I voted for 800 PSI for several reasons...
- I drop my stage beyond the H400 jump. So if I can swim against the flow to that point on an AL 80, I know I can make it out with the flow on 800 PSI from 104s. No math is necessary in this instance.
- I always place an O2 bottle so I don't have to deco on BG and don't need to allow anything extra for deco. I dive with O2 on every dive and a stage on most. That extra redundancy should be SOP for cave diving. In an emergency, you don't have to make it back to the entrance, but only to the first bottle, which might be 700ft in. That's a HUGE safety factor.
- With 800 PSI that close to the entrance, there's gas for a slow exit, stopping to look behind, frequently.
- If I find my buddy on the way out, more than likely he'll have about the same amount of gas as I do. We'll greet each other and make a quick exit. He's buying lunch...
- If something else happend and he needs gas, we'll share what I have and skip breathe to the exit if necessary. What else can you do at that point, turn your back on him? At what point during the exit do you say to yourself, "I'll stop looking for my buddy now because I don't have enough gas left for the both of us?" If I happen to have that stage with me, all the better...
- 800 PSI is a lot of gas in 104s, but as someone else mentioned, I've noticed that gas isn't exactly linear, meaning the 1,000 PSI going from 3,000 to 2,000 lasts longer than the 1,000 PSI from 1,500 to 500, but maybe that's just my imagination...

I agree that in most instances your lost buddy can exit by himself with no problems, and it certainly doesn't make sense to kill yourself trying to find him when he may have already exited. That said, this isn't OW diving. No one wants an additional, and unnecessary fatality, but if you're not willing to take on some additional risk to help your buddy, you need to find some other type of diving, maybe one where it's expected that you surface after one minute to look for your buddy and yell to the DM for help when you can't find him. If I got back to the surface with 1,000 PSI left and my buddy wasn't there, I would probably have to go back in, and that could be an even worse situation. I prefer to use that 1,000 where it's most effective - in the immediate area of separation.