Bühlmann vs. RGBM

VoiGAS

I was suprised there is no dedicated Thread for this very intense discussed Topic.
Currently I am Diving No Deco with Mares RGBM and no problem so far. NDL times are fine, once it happened that the computer locked because the NDL time was violated by one minute (and no deco stop). That was a little bit annoying but resetting the computer brought it back ( I know, I know - but it was just a minute and we dived in a group)

Now Suunto is switching to Buhlmann completely, but is it really better? I like the bubble focused approach of the RGBM

ccrhenrik

@VoiGAS

Since the last 10 years or more many studies show that bubble theory wasn’t the best for deco dives.

Have a look at the works of, amongst others,

Dr. David Doolette
Dr Simon Mitchel
Prof Mark Powell
Dr Neal Pollock

One presentation/lecture that is more than 10 years old https://youtu.be/UY61E49lyos?si=VsaEOyB-0PVMqn0W

VoiGAS

Right, but there are some things I didn’t get:

If the Bubble models are really that bad, why are gradient factors like 30/70 used to mimic them still ( see Mitchell)
Suunto reacted with the fused RGBM (2), which looks very different in the dive profile in DM5
The big problem is the deep stop. Its optional and I deactivated it

So is all the said still true today? Or was it too late and nobody trusted something with Bubble in the name anymore?

If it really would be 100% sure that Buhlmann was correct everyone would dive with GF 100/100…

Triple S

The problem is that decompression theory is nothing that can be exactly calculated. Everything is based on models tuned to data obtained via more or less trial-and-error studies. There is no model which can define an exact threshold from which on you get DCS symptoms and since there are so many unknowns and relevant factors there most likely never will be.

Buhlmann developed a model capable of defining a threshold which gives you a fair chance of not developing DCS symptoms if you don’t cross it and the question every diver needs to ask themselves is whether this chance is acceptable for them or not. If they accept the chance they use GF 100/100 but if they say the chance is too high for them, they go with GF 30/70 or something else. In that sense the model is neigther correct nor wrong, but experience shows it’s working.

I think the fact that Bubble models are dying out is because Buhlmann has become a de-facto standard in the industry and when diving together it makes sense for everyone to use the same algorithm so that they can easier synchronize their NDL or Deco times.

VoiGAS

@Triple-S You have a point here regarding the possibility to “synchronize” algorithms based on the GFs for a group. This is something thats not possible for RGBM
Regarding the 30/70 I think this isn’t State of the Art anymore. Also not 40/85 like default on the Ocean. If you really believe in the Buhlmann theory something like 100/85 would be best to avoid saturation during the first stop. But again that doesn’t seem to be possible on the most dive computers

ccrhenrik

Many, not all, who’s doing deep, helium, diving today use

GF Low 50
GF High 70-85

Some even change the GF:s during deco depending on conditions.

GF Low 50 will get you away from the deep ie eliminate deep stops.

Why are you interested in RGBM and not (the salvation of all divers) VPM?

What about GAP or DCIEM?

Interesting but not connected to this is the report from DAN regarding risks of sickness
https://youtu.be/OnorWqH9Zs4?si=Ebofmi2haEqLmwbJ

VoiGAS

@ccrhenrik Thank you for the insights! I’m interested in RGBM in special because I recently got a Suunto Eon Core and now have the option to choose between Fused RGBM 2 and Bühlman ZHL-16. Before I had Sunnto Zoop and Mares Smart Air, so always RGBM.

Hard decision. For No-Deco dives its just a little different NDL time for first and repetition dive. But I plan to try deco, so I want to know more about the options