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[danvolker]

Sheck was using mixed gas on that dive. However, there are many reports of dives to 300 feet on air. He went to Mexico in the 70s and dive some very deep caves. I believe he used air for these 300 foot explorations.
The book "Submerged", by Daniel Lenihan, talks about that trip. He says that he was diving to around 250 feet and Scheck was going down to about 300.

Apparently Sheck started his dive with air for the first 400 feet, and then switched to a helium mix that would give him an end that would feel like air at 300 feet deep at the target depth.....As George indicated, this was one of many very bad mistakes that Sheck knew better than doing....The problem was that where this was, and for the gear they were using, the deep air part was an "expedient" solution--or so it seemed to Sheck and Bowden.
I also believe there was a major problem with the borrowed BC Sheck was using, not getting him enough lift, and this could easily have contributed to OxTox and or a big CO2 buildup as he would have attempted to swim upwards to slow his descent--or even from the hanging on to the line....Just the CO2 buildup alone ( forgetting Ox Tox issues) could have been enough to cause the narc to have become overwhelming.

My understanding was they had terrible support, gear choices were absolutely ridiculous, and some of this may have had to do with the kind of record Bowden wanted them to make( relative to past records).

Can you even imagine not having considered buoyancy and depth and the lift potential needed by the BC? And then that the "borrowed BC was old and cra*py ?

Also...Sheck was known to get quite impaired by air dives to 300, and that he preferred the trimix alternative for sharper mental function.
His preferences on one side of this, and the expedience of Bowden's record desires and compromises on the other....

---------- Post added March 16th, 2014 at 12:25 PM ----------

Sheck was using mixed gas on that dive. However, there are many reports of dives to 300 feet on air. He went to Mexico in the 70s and dive some very deep caves. I believe he used air for these 300 foot explorations.
The book "Submerged", by Daniel Lenihan, talks about that trip. He says that he was diving to around 250 feet and Scheck was going down to about 300.

---------- Post added March 16th, 2014 at 09:03 AM ----------


He certainly new better, since he also experience HPNS on a previous dive to Africa. That really bothers me. Why did he push that depth after already having huge problems at a lesser depth?

This might be a better question for DCBC, but I am thinking that the HPNS and the nervous issue it represents, caused Sheck to decide the that narc from high nitrogen, might be "better" for him..less debilitating, than running with the low nitrogen mix he had experienced HPNS with in the past??????....Part of the issue was the understanding of HPNS that they had then, and of deep air, etc....

 

[boulderjohn]

Also...Sheck was known to get quite impaired by air dives to 300, and that he preferred the trimix alternative for sharper mental function.

That is consistent with what Gilliam told me. Despite what you have heard in other posts about his remarkable tolerance for narcosis, Gilliam said the opposite. He said Sheck had trouble with it and would go as deep as the rest of them on their deep dives because of it.

 

[DCBC]

That is consistent with what Gilliam told me. Despite what you have heard in other posts about his remarkable tolerance for narcosis, Gilliam said the opposite. He said Sheck had trouble with it and would go as deep as the rest of them on their deep dives because of it.

Perhaps you might relate your personal experience John. I didn't dive with Sheck past 230 FSW, so I can't really say how he acted at deeper depths. On most days I'm fine to 200' or so, but start to come unglued around 250'. I'm an accident waiting to happen past that. If your hearsay is true, having trouble at 300' isn't something that's completely unexpected. No one is unaffected by Nitrogen at 300 FSW.

 

[boulderjohn]

Perhaps you might relate your personal experience John. I didn't dive with Sheck past 230 FSW, so I can't really say how he acted at deeper depths. On most days I'm fine to 200' or so, but start to come unglued around 250'. I'm an accident waiting to happen past that. If your hearsay is true, having trouble at 300' isn't something that's completely unexpected. No one is unaffected by Nitrogen at 300 FSW.

What Gilliam said was his ungluing came before the ungluing of the others going beyond 300 feet, and he would stop his descent before them.

My personal experience with deep air is quite limited. I was at 180 exactly once, with 15 minutes bottom time, and the only clear impairment was not being able to remember some stuff. I have a lot more experience at some shallower depths, with only minor noticeable issues.

 

[DCBC]

What Gilliam said was his ungluing came before the ungluing of the others going beyond 300 feet, and he would stop his descent before them.

John, my comments are restricted to my personal experience. What Bret's observations are, I can't say. Considering Sheck's demise (and for the sake of Mary Ellen and the rest of his family), I can't see any advantage of spreading hearsay of any of Sheck's alleged shortcomings. Perhaps I'm overly sensitive about this, as I believe that if you don't have something good to say about the dead; don't say anything at all.

---------- Post added March 18th, 2014 at 08:11 AM ----------

This might be a better question for DCBC, but I am thinking that the HPNS and the nervous issue it represents, caused Sheck to decide the that narc from high nitrogen, might be "better" for him..less debilitating, than running with the low nitrogen mix he had experienced HPNS with in the past??????....Part of the issue was the understanding of HPNS that they had then, and of deep air, etc....

HPNS can affect different individuals differently and at different times. I've experienced the onset of HPNS several times during research (DCIEM) and once later during descent in Saturation. These were only mild tremors and were corrected by holding the descent rate until they subsided (although this in theory can take as much as 12 hours).

The suspected causes of HPNS are categorized into the indirect (level of PPO2, increased CO2, higher temperatures in the environment) and direct effects of pressure, such as: osmotic gradients produced by dissolving gases (fluid shifts generated from saturation gradients of Helium between rapid and slow tissues); the possible toxicology of the dillutent gas under pressure; and the direct effects of hydrostatic pressure itself. At one time, Helium Narcosis was suspected in HPNS, but as Helium doesn't penetrate the phospholipid membranes, this has been ruled-out.

After much research it appears that the rate of pressurization appears to be the major contributing factor of HPNS. In most cases HPNS only manifests itself past 600 FSW and slow descent seems to all but eliminate most HPNS symptoms.

It seems that in situations where people attempt to break records, HPNS doesn't seem to be considered as much of a danger. Some dive plans of record attempts plan a 40 FPM descent rate, but all too often a 80 or 90 FPM rate of descent is realized. Under these conditions HPNS may well result.

 

[danvolker]

John, my comments are restricted to my personal experience. What Bret's observations are, I can't say. Considering Sheck's demise (and for the sake of Mary Ellen and the rest of his family), I can't see any advantage of spreading hearsay of any of Sheck's alleged shortcomings. Perhaps I'm overly sensitive about this, as I believe that if you don't have something good to say about the dead; don't say anything at all.

---------- Post added March 18th, 2014 at 08:11 AM ----------



HPNS can affect different individuals differently and at different times. I've experienced the onset of HPNS several times during research (DCIEM) and once later during descent in Saturation. These were only mild tremors and were corrected by holding the descent rate until they subsided (although this in theory can take as much as 12 hours).

The suspected causes of HPNS are categorized into the indirect (level of PPO2, increased CO2, higher temperatures in the environment) and direct effects of pressure, such as: osmotic gradients produced by dissolving gases (fluid shifts generated from saturation gradients of Helium between rapid and slow tissues); the possible toxicology of the dillutent gas under pressure; and the direct effects of hydrostatic pressure itself. At one time, Helium Narcosis was suspected in HPNS, but as Helium doesn't penetrate the phospholipid membranes, this has been ruled-out.

After much research it appears that the rate of pressurization appears to be the major contributing factor of HPNS. In most cases HPNS only manifests itself past 600 FSW and slow descent seems to all but eliminate most HPNS symptoms.

It seems that in situations where people attempt to break records, HPNS doesn't seem to be considered as much of a danger. Some dive plans of record attempts plan a 40 FPM descent rate, but all too often a 80 or 90 FPM rate of descent is realized. Under these conditions HPNS may well result.

OK...So what you are saying is that most likely, when he was playing with his low nitrogen/more of a heliox type mix....that he was also probably doing one of the fast descents, which were often closer to 200 feet per minute....and that the bad feelings he felt were not really the helium, but bad effects from the fast descent.
There was disinformation back in those days, about what helium would do--the HPNS issue, and it sounds likely that he was going for getting the lesser of two evils with nitrogen narcosis from his chosen END, over the HPNS of the Heliox mix that would have been far more optimal. Right?

While I never got to dive with Sheck, George did dive with him a great deal, and they both liked the fast descents....and in fact, this was something I was rapidly accepting of myself--nearly all of our deep diving was done with descents at 200 feet per minute speeds, or faster--full negative drop, with swimming...and if you are using a gavin scooter, you are pointing the scooter at the bottom and running down fast----why not get the best drop possible--why make the captain have to guess how far up current for a slow drop, when we can go so fast downward that very little estimation would be required...?

From the description of the Wall dive George gave in the tech list post that he made, it is clear that the "plan" was going toi be a very fast descent, so that he did not waste a lot of gas having to swim horizontally --he needed to be far enough out to be over the deep drop off, and not have to swim....If his BC was not working at all, and knowing how these guys dived, he may have been falling at 300 feet per minute, and tried to arrest his descent as he began to feel either HPNS coming on, or, a dark narc---as would be expected when such a bad emotion would be going on --being upset over the BC not working, and not being in control of descent speed. could easily cause the whole "chicken little, the sky is falling" thing to begin to overwhelm you. I am glad I never had a MAJOR catastrophic failure like that at 300 feet on air....lot less at 800!!!

 

[DCBC]

OK...So what you are saying is that most likely, when he was playing with his low nitrogen/more of a heliox type mix....that he was also probably doing one of the fast descents, which were often closer to 200 feet per minute....and that the bad feelings he felt were not really the helium, but bad effects from the fast descent.
There was disinformation back in those days, about what helium would do--the HPNS issue, and it sounds likely that he was going for getting the lesser of two evils with nitrogen narcosis from his chosen END, over the HPNS of the Heliox mix that would have been far more optimal. Right?

Sheck's death didn't happen until 1994. Divers were well aware of the effects of HPNS for years prior to this. No one may ever know the sequence of events that led to the tragedy. It's suspected that HPNS, CO2 build-up, Narcosis and physical exertion each played a part.

I understand that Sheck had experienced HPNS symptoms in the past, so I'd suspect that this would be taken into consideration for subsequent dives. Sheck had lots of experience with a PPN2 over 6 ATA, so this should have been manageable. As I'm unaware of his dive profile/plan and gas choices for this dive, so it's really impossible to suggest probabilities.

While I never got to dive with Sheck, George did dive with him a great deal, and they both liked the fast descents....and in fact, this was something I was rapidly accepting of myself--nearly all of our deep diving was done with descents at 200 feet per minute speeds, or faster--full negative drop, with swimming...and if you are using a gavin scooter, you are pointing the scooter at the bottom and running down fast----why not get the best drop possible--why make the captain have to guess how far up current for a slow drop, when we can go so fast downward that very little estimation would be required...?

As you're aware, a fast decent on Air was common practice at the time. The fact that Narcosis was exacerbated by this didn't bother most of us who could 'keep it together.' Helium however is a different beast when going deep.

 

[boulderjohn]

Here is some information from the explanation of Exley's partner on the dive (Jim Bowden), found at the end of this article. It is describing his personal plan for that dive, which was on a separate line from Exley's. I would assume Exley's plan would have been similar.

1. Free descent to 300 feet on air.
2. Switch to a second travel gas (50 He, 39.5 N2, 10.5 O2) until 600 feet.
3. Switch to the bottom gas to complete the deep part of the dive (69.5 He, 24.1 N2, 6.4 O2).

The only information I have that Exley's plan was any different was that his bottom mix was 6% oxygen, meaning he would have had a little less nitrogen and a little more helium.

 

[danvolker]

Here is some information from the explanation of Exley's partner on the dive (Jim Bowden), found at the end of this article. It is describing his personal plan for that dive, which was on a separate line from Exley's. I would assume Exley's plan would have been similar.

1. Free descent to 300 feet on air.
2. Switch to a second travel gas (50 He, 39.5 N2, 10.5 O2) until 600 feet.
3. Switch to the bottom gas to complete the deep part of the dive (69.5 He, 24.1 N2, 6.4 O2).

The only information I have that Exley's plan was any different was that his bottom mix was 6% oxygen, meaning he would have had a little less nitrogen and a little more helium.

Yes...
And..Add to that all the ranting George did about this as a "Deep Air DEATH" right after the accident....I believe he was saying he thought Sheck did 400 on air..but whether 300 or 400, the Oxygen toxicity issue, plus CO2 loading would have been huge, before he ever got to the trimix--and with the rapid descent, and less than ideal bottom mix, the switch was not going to help much to fix any thing that had already gone wrong at 400 feet ( or at 300, whichever) . Remember, George had been on the phone with Sheck a lot the month before this dive..and was very pissed at Sheck just prior to it, because he did not like the deep air plans of his buddy Sheck.

 

[fjpatrum]

Not to get too in depth into the tri-mix world since I'm not likely to ever need/want it, but could someone give me a high level description of the reasons behind the choices for gas? Eg "Helium reduces Ox-Tox past 150 feet, but also has some narcotic qualities that are offset by N %" or something like that...

These discussions are fascinating but way over my head and I'm trying to glean enough information to at least try to keep up a little bit.