Are People backing away from VPM?

[Taliena]

I use buhlmann, gf's differs a little bit (in the range 35/85 and 40/80). I tried some dives with vpm-b+2 and was tired after that dives (on oc and cc). When I used a vpm-b+3/80 on a ccr dive to over 330 ft with almost 3 hours deco, I was fit after the dive.
I won't use a vpm-b+2 for a deep long dive, I won't take the risk. Maybe there is no real risk and is it between my ears, but do what you think you have to do.
Deepstops: I do some, but most times I prefer a slower ascent. Most times deepstops are a sort of feeling where I do them.

My caveinstructor told me he don't trust vpm, too agressive. He always use for dives over 450ft a 40/80. Of course again a theoretical aproach, but maybe some truth in it?

 

[Vegan Shark]

Which agencies are using deep stops, and which no longer recommend them?

 

[Diver0001]

In a recent thread, some of the participants talked about problems with VPM. (See posts 126-132.) Here are a couple of the quotes:

...

I had not heard anything about this before that thread. I thought I would start a new discussion here instead of buried on the back pages of an another unrelated thread. Does anyone have any information related to this?

Well.... What I think happens a lot with these kinds of discussions is what I call the "believers" and "non-believers" effect.

Why would a discussion about problems with VPM come up in a discussion about RD? Because the RD "believers" feel a need to substantiate why they have made the choices they did. Likewise, in a discussion about VPM people would point out that while some divers will get bent using any protocol, that RD has a number of problems, including a steady stream of bent divers.

None of this needs to be based in facts. Facts are not interesting to "believers" and "non-believers". Sounding persuasive is.

As for VPM. My personal experience is that you (a) need to really think through the settings you use and (b) that it is generally more conservative than my computer because of the "bucket" profile effect that tables have. Bucket profiles almost always give longer deco times than the computer. For me, Vplanner (which is what I use) for planning, is a good enough tool. and just like any tool, you should keep your brain engaged.

R..

 

[LiteHedded]

Which agencies are using deep stops, and which no longer recommend them?

gue is still teaching them but there more like pauses. very abbreviated. this is what the nedu guys are doing themselves as well. slow your ascent, sure, but dont STOP

 

[PfcAJ]

What gue is teaching comes out to be a "variable ascent rate". Much like how a 10fmp rate is achieved by short stops, you can do 20fpm and 15fpm the same way. They're "stops" but only as an aid to attain a certain ascent rate.

 

[shoredivr]

This is all extremely interesting and thanks for posting the links

 

[Michael Guerrero]

I think a significant issue when discussing a deep stop approach and a Buhlmann approach is what actions people believe affect conservatism.

For example, if you believe that straight Buhlmann (100/100) is too aggressive, you have three options to try and make it safer. You can lower the GF lo, the GF Hi, or both. So which of these actually adds conservatism? To know that, we have to know why people get bent with 100/100. Is it primarily the fast compartments or slow compartments?

If you lower the GF lo, you will add conservatism for the fast compartments, but you will increase tissue-loading of the slow compartments (a la deep stops) which the NEDU and Italian results seem to indicate is sub-optimal. You could keep the GF lo at 100, and lower the GF high, which will mean that your first stop will be what we consider rather shallow, though perhaps perfectly fine, and then you'll proceed to extend all of your stops above the first and away from the theoretical critical supersaturation point. This will tend to favor the slow compartments over the fast ones. Does this add conservatism?

If you lower both, you're trying to get some of both, but are they complementary or contradictory? The Pyle stop is basically the same principle as modifying your GF lo or slowing your ascent, but it doesn't change the entire deco profile as dramatically as a GF lo setting does. The profiles using the Pyle stop actually show lower VGE than either a Buhlmann or deep stop approach, but the sample sizes for these studies are small.

What I find interesting from these studies and another Italian study on trimix divers is that the highest VGE scores were from profiles that were least favorable to the slow tissues. Likewise, the highest instances of type 2 DCS, the one we should be scared of, were from those same profiles.

It would seem to me that if you want to reduce the amount of VGE you get, and reduce the risk of a type 2 hit, then you want to protect the slow compartments. You protect the slow compartments by lengthening the shallow stops. Food for thought.

 

[Ayisha]

...The DIR peoples stop waaaay too deep (80% of ATAs is nuts). The overall profiles sometimes end up being like 10/125 though (too abbreviated on the shallow end according to buhlmann)...

Not sure about the rest of the DIR world, but doesn't GUE teach that the first stop should be at 50% rather than 80%?

 

[PfcAJ]

Not sure about the rest of the DIR world, but doesn't GUE teach that the first stop should be at 50% rather than 80%?

Depends on the profile and it depends on what you call a "stop".

Rec profiles transition from a 30fpm ascent rate to a 10fpm ascent rate at 50% of the depth.

Compare that with a T2 profile which might start a 10fpm rate at 75%, then a 5fpm rate at 50% of the depth till the 1st gas switch. Those ascent rates pretty much mirror what 20/85 puts out for stops before the 1st gas switch.

 

[bradells]

Not sure about the rest of the DIR world, but doesn't GUE teach that the first stop should be at 50% rather than 80%?

GUE Min Deco (aka NDL diving) is 50% of your Max or Average depth (depending on what depth you start you ascent) at 9m/min (30fpm).


The articles that I have bookmarked on Decompression Ratio Ascents (to avoid Organizations Ascent Naming to confuse things) - (The Decompression Curve - George Irvine) states 80% ATA for ascent to the first stop.

I've also read other places the 80% ATA figure with 50% of depth for ease of internal math. It's always noted (in those articles) that 80% ATA <> 50% Depth, but is 'close enough' for a first stop (paraphrasing).

BRad