Article from COMEX Scientific Director on rebreathers, decompression and Penny Glover

Hello Mike,

I would point out some errors is the paper you reference.

The paper mentions VPM-B, when in fact the dives shown are old original VPM - hence the comparisons are not valid as described. I have emailed the author several times asking for, and suggesting corrections. That was a year ago now, but none have been amended.

I strongly disagree with any suggestions that CDM is in any way authoritive, binding, or superior to real deco models. Simply put; The CDM 18 is not a deco algorithm, and it is not a deco model. Its a collection of the longest possible times and simple timing formula, taken from an assortment of real deco models. Many have been validated in their own right. But making a matrix of the longest possible time from each one... not a valid model. CDM further appears to be fitted with hand crafted formula to make it produce a desired result in the deeper sections.
Does the CDM 18 have any basis for its own existence? Can it be considered an authoritive source of data? I don't believe so. CDM relies only on the simple principle "more deco time is alway better than less". At no point does it recognize sufficient deco on any one model or deco approach. It claims all deco models a failure, because they do not align with its combined, hand fabricated - longest possible time approach. I don't believe this kind of simplistic approach and test have a valid place.


On a different note.. for the really deep dives your doing - I recommend all the safety factors you can afford. However, lets not confuse desired deco, safety deco, cautious deco, with required deco. At the very deep depths, personal preference plays a big part. Some do a VPM-B/E straight out of the box, some even a straight VPM-B. Others want / need more.

Regards

...whats the rush?

Hello All,
<snip>Your serve...regards...Mark

Hi Mark,
I wouldnt really bother normally posting but I would like to comment on your post as its potentially full of nonsense
<snip>explosive decompression.

Caught your eye before it did mine, thanks Phillippe.

Mark LE8, you might want to make an effort to keep your posts civil.
Besides Phillippes link you may want to have a look at our TOS
Also, an intro post would be nice so those of us who don't know you
have an idea who the hell you are.
Welcome to Rebreather World (for now anyway)

Hello All

The paper you mention was very upto date when it was written Ross - We are not your publicists! .........<snip>

Why on earth do you still have conservatism settings that reflect the ...........<snip>


Your serve...
regards...Mark

I'll try to answer your questions briefly Mark:

The paper says "Draft". The info I provided (many attempts) was to correct the errors and misrepresentations in the paper ... nothing changed.

The VPM model and revisions are clear and straight forward. The criteria and plans are consistent - the many updates are for program features - not model changes. Many people find their own level of conservatism and satisfaction: some enjoy more, some want less. There are only three varieties of VPM - read more here:
http://www.rebreatherworld.com/49933-post12.html


VPM-B is used successfully by many every day - here are some recent deep CCR dives on VPM-B.

Cedric Verdier 201m - initial report here:
http://www.rebreatherworld.com/showthread.php?t=4880

Dave Shaw 270m - sadly Dave is not with us - his report here:
http://www.deepcave.com/images/Boesm...h_Oct_2004.pdf

Dave's report clearly says VPM-B, but I see on your web site Mark, your have this dive listed as a CDM? Is this another error Mark?


Regards

Hi Mark,

I wouldnt really bother normally posting but I would like to comment on your post as its potentially full of nonsense

I hope people realise that 10/125 for arguements sake gives significantly less deco than say 30/65. Neither GF is relevant though. The GF becomes only relevant when matched against a specific profile.

60metres for 20 mins at 10/125 would save you 10-15 minutes and probably still be within tolerable (pain wise)exposures. However if you use the same GF on 60 for 60mins then you will be effectively shaving over an hour of the stops and this is a huge amount relative to the total (Im fully aware that the % is the same-despite the creme de menthe )

25% off of 20mins shallow stop is 5 mins = no obvious bends and possibly even within realms of safety
The same 25% of 120mins shorter in the shallows however is 40mins. Missing this time may still give no apparent symptoms (pain) but you may have heard of osteonecrosis?

My point was, that stating various GF's is often detrimental to safety considering you might actually want ruined bones and others not. Something that MIGHT work again and again is 30/75 (air based) or 20/65 (helium) - again it is worth noting that GF's are not transferable between software packages, compare like for like and see

The same is true of with all the bubble model nonsense planners - relatively short duration dives can have 25-50% of the shallow stop time shaved without an obvious need for a wheelchair. When you do something larger though this same 50% can have an effect likened to lets say...explosive decompression.