Deep Stops Increases DCS

[C Dub]

I watched the presentation linked above, and I could not stop thinking "that must be what was happening to Kevrumbo..."

I know Kev, they were using was AIR.......but still....just saying....

If you're integrating the information from the NEDU study and are concerned about type II hits, then remember ...

... the deep schedule produced a rate of DCS II cases that was 94% more than the shallow schedule.

... the deep schedule produced a rate of DCS I cases that was 287% more than the shallow schedule.

... the deep schedule produced a hit rate that was 223% more than the shallow schedule.

 

[UWSojourner]

Then as a practical application, best compromise & precaution, extend your O2 Deco profile to ameliorate the above risk as indicated by the NEDU Study (which btw did not use any hyperoxic Deco Gases at all, only just using inefficient Air Decompression). Otherwise risk a vestibular or Neuro/Fast tissue hit by omitting Deep Stops . . .do you understand?

I'm sure you know this Kevrumbo, but I just want to use your post to point out something important ... Decompression is NOT over once you surface.

We ALL decompress on air. Unless you spend substantial time on the loop or on your O2 bottle after you surface you are decompressing on air. And part of the problem I think the NEDU study has highlighted is that heavy emphasis on deep stops (when compared to a shallower first stop profile with the same runtime) ends up dropping you onto shore carrying more inert gas in your tissues all of which is going to be treated with air.

So while I certainly agree that efficient in-water use of gases is wise, how you decompress in the water is only preparing you for a pretty critical period of decompression once you surface -- which almost always is executed breathing air. The NEDU study wasn't flawed in some way just by using air; we all decompress that way.

I've reposted the prior chart with comments to be clear where air decompression is taking place.

 

[Ayisha]

So does anyone have a link to Dr Doolette's presentation at the GUE conference a few weeks ago or was it about the same as the presentation that you linked to from last year, UWSojourner? Just wondering if anything specific to GUE was mentioned by Dr Doolette at the conference...

 

[Kevrumbo]

UWSoujourner, I understand that as well from experience. The typical "Expedition Profile" (i.g. Pete Mesley's seven to ten dive day Bikini Atoll or Truk Lagoon charters), is one deep dive 45m to 66m for 90min to 180min Total Run Time; then a three hour surface interval; and finally a last dive of the day to depth ranges 24m to 39m for 90-200min TRT. For myself on Open Circuit, these dives usually on Air or 20/20 with Nitrox 50 & O2 for deco gases (i.e. bottom mixes with high fractional inert N2).

If you don't clean up those slow tissues efficiently and effectively after the first deep dive of the day -especially over consecutive dive days- you will have significant residual inert gas loading that will put you at greater risk for a type I DCS event later on during the week. This is why I now favor surfacing GF's of 60% or less with a prolonged Oxygen Deco Profile at 6m with a slow 0.5m/min final ascent; minimum 3 to 4 hour SIT to somewhat check & relieve the CNS O2 exposure; and the same surfacing or better GF than 60 (per the Petrel Computer GF99 readout) for the final dive of the day.

For this upcoming return to Truk 18Jan - 08Feb, I might take a day-off after three consecutive days of two deco dives per day, or even just only do one deco dive a day. . .

 

[rjack321]

Kevin, if you are following the ratio deco prescription for "deep stops" your low GF is about 5 to 10 and if you do the requisite amount of O2 time your high GF is about 85. Obviously you can do more time shallow and apparently you are, but do you know your surfacing GF high?

Instead of skipping dives or doing some arbitrary amount of extra O2 time, how about raising your low GF and lowering your high GF? 30 or even 40 GF low and 60 to 70 GF high would integrate current knowledge about surfacing gas loads and (relative) risk far better than whatever AG taught you 5 or 6 years ago.

 

[ajduplessis]

If I understand how Kev dives, he is more likely to extend time shallow rather than reducing it.

---------- Post added January 4th, 2015 at 08:51 AM ----------

So does anyone have a link to Dr Doolette's presentation at the GUE conference a few weeks ago or was it about the same as the presentation that you linked to from last year, UWSojourner? Just wondering if anything specific to GUE was mentioned by Dr Doolette at the conference...

search youtube, or go back a couple pages in this thread

 

[Kevrumbo]

Kevin, if you are following the ratio deco prescription for "deep stops" your low GF is about 5 to 10 and if you do the requisite amount of O2 time your high GF is about 85. Obviously you can do more time shallow and apparently you are, but do you know your surfacing GF high?

Instead of skipping dives or doing some arbitrary amount of extra O2 time, how about raising your low GF and lowering your high GF? 30 or even 40 GF low and 60 to 70 GF high would integrate current knowledge about surfacing gas loads and (relative) risk far better than whatever AG taught you 5 or 6 years ago.

Of course you can set the pre-dive conservative overall Buhlmann GF's to any arbitrary Lo/Hi value you want (i.g. 30/80 per AG's latest experimental test paradigm versus RD; or 40/70 as Simon Mitchell recommends). The real-time actual surfacing GF99 readout from the Petrel Computer can be as you programmed it pre-dive, or alternatively even lower for a greater degree of conservatism --I've actually surfaced with the Petrel showing 45 after a extended & long O2 profile over & added to a requisite RD profile to 51m for 50min on Air bottom mix, with an initial Lo/Hi GF's of 30/85 to start on the Petrel.

And for the health & sake of Truk Dive Guides, it's always a considerate practice to give them a day-off after several consecutive days of deep deco dives. Also it was their application of very long extended 6m O2 or 50% deco profile clean-ups with a few days off between guiding dives which influenced me to adopt the practice as well.

Note: the Truk Stop Hotel Dive Staff are the only dive operators who will actually guide OC & CCR diver clients on traverse penetrations of the deeper wrecks (45m to 67m) in the lagoon/atoll, and actually do the entire required deco profile along with the clients -i.e. Other dive guides on single tank from Blue Lagoon or any of the Liveaboards will only "escort" you down and then quickly depart back to the upline & ascend to their safety or deco stop.

 

[Freewillow]

Apparently Dr Doolette presentation is from the Rebreather Forum 3.0 - May 18, 2012. Wasn't the question relating to a newer presentation at the GUE from a few weeks ago?

 

[Ayisha]

So does anyone have a link to Dr Doolette's presentation at the GUE conference a few weeks ago or was it about the same as the presentation that you linked to from last year, UWSojourner? Just wondering if anything specific to GUE was mentioned by Dr Doolette at the conference...

search youtube, or go back a couple pages in this thread

You mean the post before mine that I addressed? That video was from 2012 and I asked the person who posted the link if they knew if there was a video posted from Dr Doolette's presentation a few weeks ago. I haven't seen it yet or heard if anything specific to GUE was mentioned... as I stated in that post you quoted.

 

[PfcAJ]

The best most prudent compromise to practically apply from the NEDU Study & discussion, is to do the Deep Stops, and extend out the O2 profile at 6m such that you have a surfacing Gradient Factor of 60% or less (per the readout of a Petrel Computer upon surfacing from your O2 deco stop) --to ensure inert gas elimination from those Slow Tissues. This is especially warranted if you're doing multiple deco dives per day for a week or more -and I would also recommend taking a day-off/break after three consecutive days of multiple deep deco dives per day. . .

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