Live Aboard and Risk of DCS

[DepartureDiver]

I didn't realize there were so many more layers to consider on a long dive trip. Where does one get VPlanner or some of this other software?

Here's one place. Enjoy your new journey.

 

[rcohn]

As to the live aboard question, there may be evidence of "bubble resistance." I do not believe there is anything published on this yet. This is a theory as to why there is a low incidence on the live aboards. Basically, if you do a lot of diving over many days, it becomes harder to get bent. There are no algorithms that I know of that assume this. A subcategory of PDE, the professionals study, is exploring this among other things in Pros (OWIs and DMs) in Mexico and S.A.

(This is not to be construed as the DAN, USN or Duke University opinion, but mine, based on what little I have seen and know.)

Alex
2003 DAN intern
PADI/NAUI Instructor

I'm aware of the bubble resistance possibility. My question is why did DAN just reemphasize the take a day off in the middle of the trip? See: http://www.divernet.com/news/stories/DAN270404.shtml

The PDE data looks good. DAN is going to publish an article about Stacking the Dives which Ill look forward to reading. It sounds like it may be an issue with diving to the limits.

The problem is outline in an article titled Stacking the dives
"Repetitive, multiday diving represents profiles that may have been 'outside the envelope', or beyond the set limits, in which tables now in use [in modern dive computers] were developed. Diving the limits of any table or computer can increase the risk of getting bent." The problem is outline in an article titled Stacking the dives
"Repetitive, multiday diving represents profiles that may have been 'outside the envelope', or beyond the set limits, in which tables now in use [in modern dive computers] were developed. Diving the limits of any table or computer can increase the risk of getting bent."

Ralph

 

[sharkbaitDAN]

I'm aware of the bubble resistance possibility. My question is why did DAN just reemphasize the take a day off in the middle of the trip? See: http://www.divernet.com/news/stories/DAN270404.shtml


Ralph

I don't know why they did that. The evidence, based on the 2004 Injury Report, suggests most DCS hits in the first three days of diving. It looks like about 75% of DCS I hits and 64% of DCS II hits (p.60). It is more stratified when looking at number of dives. Numbers seem to go down until the 6th dive of a series, and then goes up through dive 20 (p.61). That's a big range of dives, and could take a person as little as two days to be in that range. I've done more than 6 dives in two days plenty of times while working. I'll have to find the actual DAN recommendation to see what it says about a mid-week break before I comment on it.

Alex

 

[HammerNoMore]

I don't know why they did that. The evidence, based on the 2004 Injury Report, suggests most DCS hits in the first three days of diving.

It's probably like the "you're more likely to have an accident within 5 minutes of your house" statistic. It's not that it's more dangerous there, it's just where people spend most of their time.

Only avid divers diver 5 or more days on a trip. Most of the vacation divers dive 1 or 2. I'd say if you're seeing 60-70% on the first 3 days that 60-70% of divers don't dive more than 3 days... That also includes the large groups of:

1. Cruise shop divers
2. Weekend divers
3. People who took a hit on the first 3 days and didn't make it to days 4+ (ok not so large a group).

James

 

[Dr Deco]

Hello Readers:

Repetitive Dives

This is a question without a solid answer. Some evidence indicates that individuals become resistant as the dive week progresses. Some Doppler studies indicate that the number of detectable bubbles increases as the week moves along. I am not aware that this question has been resolved to date.

Micronuclei Generation

In my opinion, the most worrisome process involved in repetitive diving is the question of tissue bubble formation. This naturally is minimized by slow ascents, safety stops, and not nucleating yourself by strenuous activities (such as climbing into the boat with full gear).

Several replies noted that the time for off gassing should only be a few hours. This is true if all nitrogen remains dissolved. Should tissue microbubbles form to any appreciable extent, the nitrogen is in the gaseous form and will exit the bubble very slowly. During a dive, dissolved nitrogen can diffuse into a microbubble, and, with each dive, it can be “pumped up.”

Clear, this is not a desirable situation and can ruin your dive vacation. :icosm12:

Dr Deco :doctor:

 

[DepartureDiver]

Several replies noted that the time for off gassing should only be a few hours. This is true if all nitrogen remains dissolved.

Dr. Deco,
While I haven't confirmed this, apparantly GUE is claiming that the way in which they do their deco allows them to be clean in a few hours where they can ignore residual gas issues for a repetitive dive. Assuming they don't do anything post dive to generate more muclei, what are your thoughts on this?

 

[Saturation]

Dr. Deco,
While I haven't confirmed this, apparantly GUE is claiming that the way in which they do their deco allows them to be clean in a few hours where they can ignore residual gas issues for a repetitive dive. Assuming they don't do anything post dive to generate more muclei, what are your thoughts on this?

There is some truth and supportive medical evidence for their procedures, but it needs to be tested. Their success hinges on the FF issues:

1] they dive with substantial amounts of helium in nearly all their mixes, including recreational dives; He mobilizes faster than N2, it not only is blown off faster post dive, whatever residuals dissipate rapidly once on the surface ... breathing air the gradient for He is substantial. At issue is surfacing with a low enough tension to preclude bubbling. Therefore, the only issue in repetitive dives is the residual N2 and the time needed to offgas same

2] the use 02 to accelerate offgassing and this changes the picture substantially


3] In general, its rare to do more than 3 technical dives daily, and two are typical. Consider, each dive is 2 hours long, and the SI between each is best at 3 hours. The effect of the residual N2 for most of the standard GUE bottom gases, is small. Even via Vplanner modeling you will see a small, almost neglible increase in the profile of a second dive to identical depths if you can make at least a 2-3 h surface interval.

In planning such a dive, the table used would be the long, 102 minute version, which could be used throughout the entire profile. As technical divers know, the secondary issues here are the racking up of OTU with each dive, but not the residual inert gas. In this example, the table is an aggressive nominal table, properly done the diver would choose the right conservatism for the conditions.


V-Planner 3.40 by R. Hemingway, VPM code by Erik C. Baker.

Decompression model: VPM-B

DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 200ft (2) on Trimix 15.0/55.0, 100ft/min descent.
Level 200ft 28:00 (30) on Trimix 15.0/55.0, 1.06 ppO2, 55ft ead, 72ft end
Asc to 130ft (32) on Trimix 15.0/55.0, -30ft/min ascent.
Stop at 130ft 0:40 (33) on Trimix 15.0/55.0, 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (34) on Trimix 15.0/55.0, 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 1:00 (35) on Trimix 15.0/55.0, 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 2:00 (37) on Trimix 15.0/55.0, 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 3:00 (40) on Trimix 15.0/55.0, 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 4:00 (44) on Trimix 15.0/55.0, 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 2:00 (46) on Nitrox 50.0, 1.56 ppO2, 32ft ead
Stop at 60ft 3:00 (49) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 4:00 (53) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 5:00 (58) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 7:00 (65) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 26:00 (91) on Oxygen, 1.60 ppO2, 0ft ead
Asc to sfc. (91) on Oxygen, -30ft/min ascent.

Off gassing starts at 162.4ft

OTU's this dive: 113
CNS Total: 80.9%

181.8 cu ft Trimix 15.0/55.0
29.3 cu ft Nitrox 50.0
25.2 cu ft Oxygen
236.3 cu ft TOTAL


DIVE PLAN #2
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 200ft (2) on Trimix 15.0/55.0, 100ft/min descent.
Level 200ft 28:00 (30) on Trimix 15.0/55.0, 1.06 ppO2, 55ft ead, 72ft end
Asc to 130ft (32) on Trimix 15.0/55.0, -30ft/min ascent.
Stop at 130ft 0:40 (33) on Trimix 15.0/55.0, 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (34) on Trimix 15.0/55.0, 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 2:00 (36) on Trimix 15.0/55.0, 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 2:00 (38) on Trimix 15.0/55.0, 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 3:00 (41) on Trimix 15.0/55.0, 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 3:00 (44) on Trimix 15.0/55.0, 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 3:00 (47) on Nitrox 50.0, 1.56 ppO2, 32ft ead
Stop at 60ft 2:00 (49) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 4:00 (53) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 6:00 (59) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 8:00 (67) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 34:00 (101) on Oxygen, 1.60 ppO2, 0ft ead
Asc to sfc. (101) on Oxygen, -30ft/min ascent.

Off gassing starts at 162.4ft

OTU's this dive: 132
CNS Total: 131.9%

182.3 cu ft Trimix 15.0/55.0
32.0 cu ft Nitrox 50.0
32.9 cu ft Oxygen
247.2 cu ft TOTAL


DIVE PLAN #3
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 200ft (2) on Trimix 15.0/55.0, 100ft/min descent.
Level 200ft 28:00 (30) on Trimix 15.0/55.0, 1.06 ppO2, 55ft ead, 72ft end
Asc to 130ft (32) on Trimix 15.0/55.0, -30ft/min ascent.
Stop at 130ft 0:40 (33) on Trimix 15.0/55.0, 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (34) on Trimix 15.0/55.0, 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 2:00 (36) on Trimix 15.0/55.0, 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 2:00 (38) on Trimix 15.0/55.0, 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 3:00 (41) on Trimix 15.0/55.0, 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 3:00 (44) on Trimix 15.0/55.0, 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 3:00 (47) on Nitrox 50.0, 1.56 ppO2, 32ft ead
Stop at 60ft 2:00 (49) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 4:00 (53) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 5:00 (58) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 8:00 (66) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 36:00 (102) on Oxygen, 1.60 ppO2, 0ft ead
Asc to sfc. (102) on Oxygen, -30ft/min ascent.

Off gassing starts at 162.4ft

OTU's this dive: 134
CNS Total: 156.2%

182.3 cu ft Trimix 15.0/55.0
30.6 cu ft Nitrox 50.0
34.9 cu ft Oxygen
247.8 cu ft TOTAL


DIVE PLAN #4
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = Nominal

Dec to 200ft (2) on Trimix 15.0/55.0, 100ft/min descent.
Level 200ft 28:00 (30) on Trimix 15.0/55.0, 1.06 ppO2, 55ft ead, 72ft end
Asc to 130ft (32) on Trimix 15.0/55.0, -30ft/min ascent.
Stop at 130ft 0:40 (33) on Trimix 15.0/55.0, 0.74 ppO2, 29ft ead, 40ft end
Stop at 120ft 1:00 (34) on Trimix 15.0/55.0, 0.69 ppO2, 25ft ead, 36ft end
Stop at 110ft 2:00 (36) on Trimix 15.0/55.0, 0.65 ppO2, 21ft ead, 31ft end
Stop at 100ft 2:00 (38) on Trimix 15.0/55.0, 0.60 ppO2, 17ft ead, 27ft end
Stop at 90ft 3:00 (41) on Trimix 15.0/55.0, 0.56 ppO2, 14ft ead, 22ft end
Stop at 80ft 3:00 (44) on Trimix 15.0/55.0, 0.51 ppO2, 10ft ead, 18ft end
Stop at 70ft 3:00 (47) on Nitrox 50.0, 1.56 ppO2, 32ft ead
Stop at 60ft 2:00 (49) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 4:00 (53) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 5:00 (58) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 8:00 (66) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 36:00 (102) on Oxygen, 1.60 ppO2, 0ft ead
Asc to sfc. (102) on Oxygen, -30ft/min ascent.

Off gassing starts at 162.4ft

OTU's this dive: 134
CNS Total: 165.8%

182.3 cu ft Trimix 15.0/55.0
30.6 cu ft Nitrox 50.0
34.9 cu ft Oxygen
247.8 cu ft TOTAL


DIVE PLAN COMPLETE

********* WARNING & DISCLAIMER *********
This V-Planner generated dive schedule could indirectly kill you.
The author does not warrant that it accurately reflects the Varying
Permeability Model algorithms, that it won't get you bent or dead, or that it
will produce safe, reliable results. This dive schedule is experimental
and you use it at your own risk. Diving in general is fraught with
risk, and decompression diving adds significantly more risk.
Deep diving utilizing multiple gasses, including Helium, is about
as risky as it gets.

This schedule is not intended for uneducated users. V-Planner and the
decompression schedules it produces are tools for experienced mixed-gas
decompression divers ONLY. If you have not been properly trained in
mixed-gas decompression diving by an internationally recognized technical
certification agency and/or don't have a firm handle on decompression
planning and mixed-gas diving, then DO NOT USE THIS DIVE SCHEDULE.

 

[DepartureDiver]

any program that uses a half-time decay will generate low residual gas after a 3 hour surface interval ... especially when there was substantial He used during the dive. I agree that some testing is needed as well as the term that gets people in an uproar ... "validation". Just because there is a low doppler score upon surfacing does not mean that there is no residual gas in the tissues or in any stationary bubbles. Depending upon the size of any bubbles, off-gassing can decrease ... and this means a slower off-gas rate for He as well since it is also in the bubble. Imho, the biggest unknown in dive profiling is the gas elimination rates upon surfacing. It is too simplistic to simply say that since no He is in atmospheric air that is being greathed upon surfacing that the He is necessarily leaving the body faster. If it is any bubble form, this may not be true at all. If no bubbles exist (a virtual impossibility), then I would agree that there would be very little residual He after a few hours. It has been known for a while that off-gassing can be slower than in-gassing. The aggressive profiles done by some divers (while they may be "safe") leaves in my mind that post dive bubbling or residual gas can be significant.

 

[Saturation]

any program that uses a half-time decay will generate low residual gas after a 3 hour surface interval ... especially when there was substantial He used during the dive. I agree that some testing is needed as well as the term that gets people in an uproar ... "validation". Just because there is a low doppler score upon surfacing does not mean that there is no residual gas in the tissues or in any stationary bubbles. Depending upon the size of any bubbles, off-gassing can decrease ... and this means a slower off-gas rate for He as well since it is also in the bubble. Imho, the biggest unknown in dive profiling is the gas elimination rates upon surfacing. It is too simplistic to simply say that since no He is in atmospheric air that is being greathed upon surfacing that the He is necessarily leaving the body faster. If it is any bubble form, this may not be true at all. If no bubbles exist (a virtual impossibility), then I would agree that there would be very little residual He after a few hours. It has been known for a while that off-gassing can be slower than in-gassing. The aggressive profiles done by some divers (while they may be "safe") leaves in my mind that post dive bubbling or residual gas can be significant.

???

There is much to comment on the issues you raise.

Although I would disagree on so many points above, there are other superb insights in very detailed dossiers made here:

http://www.diverssupport.com/Times3.htm

and comparisons between VPM, RGBM and Departure Diver are quite interesting to say the least:

http://www.diverssupport.com/ascending.htm

Quite a large number of novel insights.

 

[DepartureDiver]

Although I would disagree on so many points above,

It would be a boring world if people agreed and there was no discussion or debate