Acsent Rates

[Juz]

Originally Posted by nickb

Gotta link Juz?

To be fair, I have not looked at this in much depth as I have found slower ascent rates work for me, so no real reason to change.

DAN Divers Alert Network : Deep Stops: Can Adding Half the Depth of A Safety Stop Build in Another Safety Margin?

The last table (very bottom of page):
Table 4: Fast Tissue Saturation and Bubble Scores after the Different Dive Profiles

This seems to indicate, and was wholeheartily supported by Bob Cole and a hyperbaric Doctor at a lecture I attended recently, that a 10m/min ascent rate is better than either faster or slower.

Juz

[GLOC]

Originally Posted by Juz

This seems to indicate, and was wholeheartily supported by Bob Cole and a hyperbaric Doctor at a lecture I attended recently, that a 10m/min ascent rate is better than either faster or slower.

I haven't read the article because the firewall won't let me, but between which depths and what BTs does 10m/min apply?

60m to the surface at 10m/min after 20mins, f*ck that!!

30m to the surface at 10m/min after 40mins, same as above

10m/min from depth to first deep stop[1], I can handle that.

[1] deep stop based on what works for you but probably somewhere between 80% and 65% ATA depending on what your training has told you, what depths you are going to and what physiological experiences you have had in the past.

[And]

Originally Posted by milldog

However there is a limit to where you off gas and on gas and there are formula's for this the 10m/min is based on the navy tables; and is the maximum rate of ascent that should be used, (these are fit young marines) however by slowing the accent rate to 6 or 7m/min with give the gases more time to circulate to the pulmonary system and off gas it also reduces the size of the bubble formation and gives (in my case) better results. Now i know that there is a fine line between off gassing and on gassing and this is border line for on gassing of the muscular and tendons but good for the off gassing of tissues and bubble growth keeping them as small as possible for as long as possible during deco is a good thing, it will increase the off gassing, also i have introduced light finning on stops to help with the circulation and off gassing.

however if you look at the other end of the scale some doctors will tell you to add the bottom time decent time and the time it takes to reach the deep stop to all count as bottom time to be truly safe (this i class as over cautious) but again it's another theory of deco and thats all it is at the moment best used theory's

My understanding of the reason why we would ascend at 10 m/min, or even faster at the beginning of the ascent is because the pressure differential is lower, so the offgassing even in the faster tissues is below any bubble creating type threshold. By slowing this down you do not really get any benefit, indeed, some people have increased the speed of the 65 to 45 (% of ata's) stops from 3m/min to 6m/min as they felt the additional time at those depths were producing 'niggles'.

Although we tend to bandy around terms like compartments and slow/fast tissues, these are very over simplified attempts to explain what is a very complex process, such that I am not sure we can really observe objectively whether the deco has been good or bad, and at what stage one deco profile was better than another, as you have no real measurable data available, unless you get bent. Even then you are not forced to know you are bent until you are told to walk in a straight line with your eyes closed three days later and fall over, some of the symptoms being that hard to distinguish. You also have no idea when the offending bubble or bubbles were formed, what they consisted of, and which particular tissue 'compartment' they damaged. We only know that a chamber and O2 can help fix the damage done.

With regard to the practice of counting some of the ascent time in the deco time, then I have done that, and it has worked (in as much that I didn't get bent), as I have not been able to guarantee that I can ascend initially at a rate as fast as 10m/min (such as Ressel) but I have started the bottom time at a predetermined depth, rather than starting it at the surface. Realistically though, these are just ways of manipulating the plan to fit how conservative or not you want the deco to be, and this is why some of us will use an 'average depth' measurement, but even then, which type of average will you use and what factors will you use to manipulate it, the possibilities being near endless.

My opinion, after a bit of a ramble, is that I do not think that changing the initial ascent rate from 10m/min to 6m/min is a particularly good thing to do, and I do not think we are clever enough (as a collective of divers) to determine precise results of individual dives or that the measurement system (how do I feel today?) is objective enough to come up with a solution which works for everyone.

Andy

[GLOC]

Good post Andy.

[milldog]

Andy

answered your post via PM

Graham

[PW1664]

Originally Posted by And

My understanding of the reason why we would ascend at 10 m/min, or even faster at the beginning of the ascent is because the pressure differential is lower, so the offgassing even in the faster tissues is below any bubble creating type threshold. By slowing this down you do not really get any benefit, indeed, some people have increased the speed of the 65 to 45 (% of ata's) stops from 3m/min to 6m/min as they felt the additional time at those depths were producing 'niggles'.

Although we tend to bandy around terms like compartments and slow/fast tissues, these are very over simplified attempts to explain what is a very complex process, such that I am not sure we can really observe objectively whether the deco has been good or bad, and at what stage one deco profile was better than another, as you have no real measurable data available, unless you get bent. Even then you are not forced to know you are bent until you are told to walk in a straight line with your eyes closed three days later and fall over, some of the symptoms being that hard to distinguish. You also have no idea when the offending bubble or bubbles were formed, what they consisted of, and which particular tissue 'compartment' they damaged. We only know that a chamber and O2 can help fix the damage done.

With regard to the practice of counting some of the ascent time in the deco time, then I have done that, and it has worked (in as much that I didn't get bent), as I have not been able to guarantee that I can ascend initially at a rate as fast as 10m/min (such as Ressel) but I have started the bottom time at a predetermined depth, rather than starting it at the surface. Realistically though, these are just ways of manipulating the plan to fit how conservative or not you want the deco to be, and this is why some of us will use an 'average depth' measurement, but even then, which type of average will you use and what factors will you use to manipulate it, the possibilities being near endless.

My opinion, after a bit of a ramble, is that I do not think that changing the initial ascent rate from 10m/min to 6m/min is a particularly good thing to do, and I do not think we are clever enough (as a collective of divers) to determine precise results of individual dives or that the measurement system (how do I feel today?) is objective enough to come up with a solution which works for everyone.

Andy

A well considered argument;

Any reason why not to share your reply Graham?....

[milldog]

Originally Posted by PW1664

A well considered argument;

Any reason why not to share your reply Graham?....

didn't want to put Doppler graphs, cat1 scans and i cant link the videos in. there 3 years of work on notes disk and books just to much to put down, and that research into this is in the infancy due to the lack of case studies so as i said to And if you feel the need to help do a dive over 50 meters and get bent

this will increase the case studies in to this area

Graham

[PW1664]

Originally Posted by milldog

didn't want to put Doppler graphs, cat1 scans and i cant link the videos in. there 3 years of work on notes disk and books just to much to put down, and that research into this is in the infancy due to the lack of case studies so as i said to And if you feel the need to help do a dive over 50 meters and get bent

this will increase the case studies in to this area

Graham

Understood....

I always think it's very difficult to come to quality conclusions from these types of studies, especially where base data is variable and contants are limited.

The trouble is, if comments and conclusion seem to make sense or match ones prior opinons, then regardless to the stregnth of evidence we tend to agree with the outcomes.

However, very interesting stuff. and thanks for the debate..... thanks.

[thehappychappy]

Originally Posted by milldog

didn't want to put Doppler graphs, cat1 scans and i cant link the videos in. there 3 years of work on notes disk and books just to much to put down, and that research into this is in the infancy due to the lack of case studies so as i said to And if you feel the need to help do a dive over 50 meters and get bent

this will increase the case studies in to this area

Graham

So what your saying is that you've no evidence that you are willing to share but if we all want to think your some sort of god then do as you say?

Its widely known that slowly does it from 6 metres up is best practice, so you actually haven't added anything at all apart from things you wont back up?

Put your research where you mouth is for a change.

Love & Kisses Davie

X

[Gene_Hobbs]

Originally Posted by GLOC

Another point is how deep you make the first deep stop and the current GUE thinking is 80% ATA.

Also worth a read are Ross's thoughts on this topic: Decompression myths and mistakes

Originally Posted by GLOC

Do you have a list of references which people can peruse as I know that people like Janos have nothing better to do than a little scientific reading in the evenings?!!

A good starting point is this AAUS workshop. It starts with a nice history of ascent rates used in research and gives many good papers from there
AAUS Biomechanics of Safe Ascents Workshop.
Lang and Egstrom. 1990
RRR ID: 4241

DAN Ascent Rate Study - I will find our final report on this project. Sorry we have not made it more available.
DAN Divers Alert Network : Medical Research : Ascent Rate


DAN Europe Deep Stops Study 2005

A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. (Article)
RRR ID: 3804

A deep stop during decompression from 82 fsw (25m) significantly reduces bubbles and fast tissue gas tensions. (Letter, Reply, Erratum)
RRR ID: 3805

Stay tuned, there is some VERY interesting abstracts on deep stops at the UHMS meeting this year.


Use of safety stops:

INTRAVENOUS GAS EMBOLI IN MAN AFTER SELECTED OPEN OCEAN AIR SCUBA DIVES.
Pilmanis, 1974
RRR ID: 39
NOTE: This is only an abstract. A better summary of the report is in the AAUS workshop above.

Doppler Detection of Silent Venous Gas Emboli in Non-Decompression Diving Involving Safety Stops.
Uguccioni 1994
RRR ID: 3430

I could go on but it is late... Enjoy!
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