Live Aboard and Risk of DCS

[glbirch]

Just my theory, but I think dnhill's question is based on the assumption that on a liveaboard you tend to do more diving in a week (4 to 5 dives/day)than you do at a land based resort(usually 3 dives/day or so?) So what he's asking could be more like "Over a period of time, does the overall risk of DCS increase as the dives/day increase even if you stay within no-deco limits as indicated by your charts or computer?"

 

[dnhill]

Yes glbirch that was my basic question. I have a diving buddy that stated that he did not want to do a liveaboard because he read "somewhere" that the basic "eat, sleep, dive" of a liveaboard is much more conducive to DCS. I do under the basic theories of decompression sickness, but having a science degree, I tend to want to use documented studies to help with my arguments. Sorry for my inarticulate question to begin with.

dnhill

 

[MechDiver]

Ok, that makes a bit more sense.

Also, I don't have any dive planning software to simulate what my nitrogen loading might be, that was something I thought I only needed if/when I ever moved into deco diving.

The trip I am going on is to Roatan in Nov. I understand it is possible to do 30 dives in five days. If that's not a significant number of repetitive dives, I don't know what is.

Deco diving is somewhat equivalent to doing muliple dives in a short period of time. IMO, the only way to dive multiple dives in multiple days is by using dive planning software (VPlanner is a good one) that will show the buildup of both nitrogen and microbubbles (did not go there ScubaRon as it was already getting too techy for the thread), OR by using a ***good*** computer that you trust along with another means to check where you are.
Most liveaboards like to take a "day off" midway through the trip for surface stuff. Purpose? Offgassing. And this has nothing to do with being on a boat. If the shore diving lends itself to multiple dives, then there is effectively no difference.

There are lots of things that affect this stuff: depth, time, gas used, SI, etc. etc. Tables, again IMO, cannot handle this style of diving without a great deal of knowledge on the part of the user.

Sorry my other post was confusing to some.

MD

 

[Wijbrandus]

MechDiver, thanks for that info. I'll look into some of that stuff. I'm just a rookie diver, I can handle my altitude diving, and that's about the extent of it. 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?

DNHill, sorry if I hijacked your thread and took it somewhere you didn't need to go.

 

[rcohn]

The basic eat sleep dive of a liveaboard is often a more relaxed schedule with less running around and exertion than a shore based dives. Liveaboards take great pains to insure sufficient surface intervals, and plenty of fluids are available. Shore operations may do two tank trips with shorter SI to fit a schedule, the diver is more likely to be carrying his/her gear and setting it up/breaking it down daily. Liveaboard divers are generally well aware of the risks of the heavy dive schedule (maybe more experienced in general?) and may keep the profiles more conservative, and the after dive partying more restrained (actually minimal drinking on all liveaboard I've done). On every liveaboard I've done all divers are in bed early. Divemasters can keep a much closer eye on their divers. Nitrox is frequently used on a liveaboard to reduce the risk.

I believe most liveaboards have very good safety record. It's hard to keep customers happy if you must steam back to port (more then 24 hours for some boats) with an injured diver. I would be very interested in seeing how liveaboard stats compare to shore based, it's not obvious to me that thay are less safe.

Ralph

 

[pismodiver]

DAN's 2004 DCI report finds that the liveaboard divers in the Project Dive Exploration study have the lowest incidence of DCS (page 43)

 

[dnhill]

Thanks for the above information. This is the type of thing I was looking for. I appreciate the opinions and explainations.

dnhill

 

[rcohn]

Interesting, thanks.

I'm actually impressed how well the liveaboard divers do. Many of the profiles come from the Nekton and that is a 5 dive per day trip. There have been so many strong opinions on proper diving proceedures expressed over the years with so little evidence to back them up. It looks like DAN's Project Dive Exploration may finally be yielding some real data about diving practices and resulting injury rates.

It's also interesting how high a percentage of hits are found at Scapa Flow.

Ralph

 

[miketsp]

I believe the statistics may well get distorted by the type of diving on live aboards.
I have done a few live aboards with some real diving fanatics, you know the only limit is how fast the on board compressor can fill the cylinders, but even then the dive profiles tended to be un-aggressive on average. Normally the boat anchors somewhere protected for the night so the dusk dive, the 1st night dive, the 2nd night dive and the dawn dive are done in relatively shallow waters. Out of the 3 or possibly 4 daytime dives rarely has more than one been deep.
In contrast, my none live-aboard outings tend to have more aggressive profiles. If you are only doing 2 dives in the day you make the most of them.

Food for thought - why the recent trend to an increased NO-Fly recommendation of more than 12 hours after multiple dives on multiple days even when the tables or computer may show you with 0 residual Nitrogen in much less than 12 hours ?

 

[sharkbaitDAN]

Hey, I'm new to the board, but worked on PDE, so might be able to offer some insight.

Food for thought - why the recent trend to an increased NO-Fly recommendation of more than 12 hours after multiple dives on multiple days even when the tables or computer may show you with 0 residual Nitrogen in much less than 12 hours ?

One big reason for this is that it has actually been studied. Dan and USN are doing the Flying after Diving study which has produced longer time to fly intervals than were traditional. The old recomendations came from Navy rules where they wanted to be able to fly divers out quickly. They had access to chambers on many boats and bases. The 12 hour time limit was not based on any real empirical evidence, opther than most divers were ok.

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