Type I Bends Hit in Chuuk

[Charlie99]

48m/160 50min

Nitrox 50 Segment revised profile was performed like this:
21m/70 4min (switch to Eanx 50)
18m/60 3min
15m/50 3min
12m/40 3min
9m/30 4min (or 2:2 with Backgas Break)

What I wanted to do was this:
21m/70 7min (switch to Eanx 50)
18m/60 6min
15m/50 6min
12m/40 6min
9m/30 7min (4:3 Backgas Break)

Or better yet, a S-Curve Sequence:
21m/70 9min (Eanx 50 switch)
18m/60 9min
15m/50 3min
12m/40 3min
9m/30 6min (3:3 Backgas Break)

So all in all for the Nitrox 50 Segment, only 17 to maybe 20 minutes total time was spent; it should have been at best an optimal 30 minutes!

Did your buddy ever explain how he came up with his deco plan?

At the 6m/20 O2 switch, I was going to signal my Buddy to do a 30 minute Oxygen Segment, with the sequence 10:5:10:5 (i.e. 10min on O2:5min Backgas Break etc.) with an nice slow 1m/min or 3'/min ascent to surface on Oxygen. He immediately signs back at me a 12:6 sequence, so I think to myself, "Great . . .I'll just signal an additional 12 minute period on O2 after the 6 minute Backgas Break.

Am I correct in assuming that the 12:6 sequence that your buddy signalled is consistent with already executed EAN50 stops of 20 minutes; while your desired 30 minute total O2 was inconsistent with what had been done? Or asked another way .... it seems like calling for a 30 minute O2 stop should have set off alarm bells in your buddy. Correct?


You give two possible EAN50 plans, calling the S-curve plan starting with 9 minutes the better plan. Why did you initially signal for a 7 minute 70' stop instead of the "better" 9 minute stop of the S-curve plan. Was this do to a difference in training in on-the-fly deco calculations between you and your buddy? Was your avoidance of the S-curve plan because of the additional complications of planning?

------------------------------------

What was the originally agreed upon deco plan for the dive? Did you agree on specific numbers, or just that you'd figure it out on the fly?

 

[Kevrumbo]

Yes . . .he mistakenly re-did the revised deco profile based on the 30min bottom time, rather than the extension to 50min. I think he got confused between the original plan of 54m/180' for 30min vs the extended bottom time at a less deeper depth of 48m/160' for 50min. In-other-words, looking back in hindsight --he reverted back to the original 30min bottom time as reference rather than using the actual elapsed bottom time of 50min

I decided not to do the S-curve segment, because my buddy and his group are of the current set of divers who refrain from doing S-curves anymore (which seems to be in vogue in the tech world these days) --and essentially keep the profile in that range more linear. . .

 

[Rick Murchison]

... with potential pathological bubbles still residing in my circulatory system. . .

...one of the reasons that treatment should begin as quickly as possible is that when the nitrogen bubbles expand, they can move organs/tissues etc. out of the way of the bubble and cause damage. When the bubble reduces, the hole left by the bubble and the resulting negative consequences can remain. Karl said that if treatment is begun immediately, the chances of permanent damage is reduced

Couple of nits here... except in extreme cases where nitrogen titres are so high in the tissues that they keep dumping enough into the bloodstream to continue to form bubbles, circulatory bubbles don't hang around much; they're filtered out and offgassed pretty quickly in the lungs. It is the bubbles in the tissue that are harder to reduce, and crushing them promptly is important to stop the ongoing damage. DCS bubbles are tiny; they don't "move organs," and they don't leave "holes" per se as they resolve. If they are crushed immediately by recompression and adequately offgassed without regrowing the damage is usually minimal, if noticeable at all.
There are a couple of important mechanisms for damage we need to consider:
(1) if bubbles do form in the arterial bloodstream, they can cause tiny emboli in the capillaries and tissue necrosis will occur downstream of the bubble. Depending on the tissue's ability to tolerate an absence of oxygen, this damage can occur in a matter of a few minutes (neurons), or it can take many hours or even days (bone). The longer the bubble remains the greater the chance that a clot will form and even recompression won't restore bloodflow to the affected tissue. Once the tissue's dead the damage can be permanent.
(2) bubbles in the tissues are detected as foreign bodies, and can also cause tiny rips and tears, ... not really that big a deal by itself, but as the body reacts to those bubbles bad things happen. Because the body "thinks" these bubbles are invaders, it attacks with a range of weapons, some of them toxic to the very tissue the body's trying to protect. Swelling can cause bloodflow problems as well and exacerbate the problem, to say nothing of hindering the gas transport needed to get rid of the excess nitrogen. The longer the bubbles remain the more damage occurs.
These phenomena help explain the delayed onset of DCS symptoms in many cases, and also the importance of not delaying treatment.
It also reinforces the efficacy of returning to a blown deco stop immediately and completeing it (plus a little) if possible.*

... I decided not to do the S-curve segment, because my buddy and his group are of the current set of divers who refrain from doing S-curves anymore (which seems to be in vogue in the tech world these days) --and essentially keep the profile in that range more linear. . .

I'm not a great decompression theorist, but I do have three or two years as a practitioner... those who dive with me know that I'll add time shallow at the drop of a hat - sometimes a lot of time. As "vogue" comes and goes, I find myself more and more interested in the plankton in the top 20' of the water column
Rick

*this is a topic for another discussion...

 

[Rick Inman]

Thanks for the post, Kev. This kind of discussion makes people think and reevaluate their own diving, and is just the kind of subject that can help others avoid a hit.

You do enough dives, you will inevitably have in-water deco disagreements with your buddy. Our team agrees to go with the most conservative, regardless of who is leading the deco (of course "conservative" could be up for debate on the mid-range stops, but that's another kettle of fish).

Every move to travel to the next stop is signaled, and there must be team agreement. No one is a blind follower. That is the power of the team: Multiple minds. Leading the stops doesn't mean controlling them. The team controls the stops, the leader just leads them. And we default to the most conservative.

So say if I want to extend my (OUR) 30' stop for 2 more minutes, when the leader signals the move, I would signal to stay two more minutes, and the team would signal back agreement. After the 2 additional minutes the leader would signal the move. I wouldn't take over the leadership, just request the additional time.

A request for a more conservative profile is non optional for the team, unless someone has a problem and has to expedite their exit (again, another kettle of fish).

My normal dive buddies are younger than me, and they are more logical and tend to follow deco profiles by the numbers. I am older and have a tendency to go by "how I feel". That nagging little sensation might have me requesting another 5 mins on O2.

No one has ever denied my request for more time, and I am absolutely sold on team diving. But if I ever felt I really wanted more time and my buddy insisted on moving, he would be moving without me (unless he was moving because of some issue).

I have also blown off deco early. One time my buddy and I were doing our 20' and had literally 2' of muddy dark vis. We had both our SMB's up, and we started hearing boats right above us. We realized that we had managed to land right in front of the boat ramp. We had about 3 mins remaining, and I felt great, so I put my mask a few inches from his so he could see me, and he at once read my mind and nodded and gave the thumb and we exited.

One thing I really believe about deco is that it is measuring with a micrometer, marking with chalk and cutting with an ax. If I am cutting with an ax, I usually prefer to leave some room for error.

 

[Rick Murchison]

... Our team agrees to go with the most conservative, regardless of who is leading the deco ... there must be team agreement. ... The team controls the stops, ... I would signal to stay two more minutes, and the team would signal back agreement. After the 2 additional minutes the leader would signal the move. ...

We might default to this protocol in really lousy vis, but as a general rule we use more of a "same day same ocean" concept, especially at the shallow stops. If I want to extend a stop, for example, I signal the rest of the team that I'm staying X minutes and wave 'em goodbye. I don't expect them to wait for me. That doesn't mean we don't keep an eye on each other and stay within easy reach (we wouldn't get two stops apart, for example, or out of sight), but we retain more personal autonomy (and responsibility) for deco profiles. This actually makes for less confusion, as I may elect to remain at a stop (especially the last one) for other-than-deco reasons (like watching the pretty fishies )
My bunch is mostly older guys with lots of time underwater... So while we have a very rigid protocol for the deep part of any deco dive - especially deep air - I guess you could say we revert to a "just keep the team informed on what you're going to do" once the last gas switch has been made.
I will add this - none of us are shy about saying "NO" if someone signals they're going to add or subtract time in a way we think's dangerous, and none of us will argue about it underwater... we all are accustomed to taking orders, and giving them
Rick

 

[orange_diver]

Yes . . .he mistakenly re-did the revised deco profile based on the 30min bottom time, rather than the extension to 50min. I think he got confused between the original plan of 54m/180' for 30min vs the extended bottom time at a less deeper depth of 48m/160' for 50min. In-other-words, looking back in hindsight --he reverted back to the original 30min bottom time as reference rather than using the actual elapsed bottom time of 50min

wouldn't this call for 55 min of deco time? seems your buddy was calling 34 min. Can you explain the discrepancy? what was agreed on the surface for your original deco plan?

seems like you needed 55 min deco (for 50 @ 160') and if your buddy had stuck to the original plan, you would have been 10 min shy instead of 20 min. big difference.

 

[Kevrumbo]

wouldn't this call for 45 min of deco time? seems your buddy was calling 34 min. Can you explain the discrepancy? what was agreed on the surface for your original deco plan?

seems like you needed 55 min deco (for 50 @ 160') and if your buddy had stuck to the original plan, you would have been 10 min shy instead of 20 min. big difference.

Original 54m/180' for 30min per Ratio Deco 1:2 at a setpoint of 60m/200' called for 50min of deco (not including deep stops).

Revised on-the-fly deco total time at 48m/160' for 50min RD 1:1 would be 55min, and was rounded-up to 60min for conservatism. . .

His only comment post-dive was that he mistakenly referenced the original 30min bottom time; I did not do an error analysis or ask any further on how he derived the schedule . . .and just left it at that.

 

[Kevrumbo]

Couple of nits here... except in extreme cases where nitrogen titres are so high in the tissues that they keep dumping enough into the bloodstream to continue to form bubbles, circulatory bubbles don't hang around much; they're filtered out and offgassed pretty quickly in the lungs. <snip>

Just a minor nit-pick on your nit-picking Uncle Ricky --sometimes circulatory bubbles due to Nitrogen or Helium (or both) cannot be filtered out in the lungs-- resulting in sub-clinical to serious DCS symptoms called the Chokes. . . ("I still had too much residual Helium in numerous microbubbles that overwhelmed my lungs' alveolar bed. . .")

[P.S. Happy New Year to All from Manila Philippines! Truk Lagoon again next week to 12 Jan. . .]

 

[Kevrumbo]

02 Jan '2009 (original incident Left Shoulder type I DCS happened 11 Oct '08):

Shinkoku Maru Wreck; max 36m/120', average 30m/100' for BT 15min; multilevel ascent, total time around 45min.

Noticed slight twinge/spasm Left Shoulder joint space on ascent from 6m/20' to 3m/10', which then resolved after spending additional three minutes at 3m/10' --no pain experienced on surfacing or afterward for rest of day.

 

[Rick Murchison]

Just a minor nit-pick on your nit-picking Uncle Ricky --sometimes circulatory bubbles due to Nitrogen or Helium (or both) cannot be filtered out in the lungs-- resulting in sub-clinical to serious DCS symptoms called the Chokes. . . ("I still had too much residual Helium in numerous microbubbles that overwhelmed my lungs' alveolar bed. . .")

"Sub-clinical" chokes? I think we're hitting a little cross purposes here. A bubble density that "overwhelms the lungs' alveolar bed" I'd certainly classify as "extreme." But you are also correct that in that case bubbles will hang around longer in the blood.
Rick