Ascent rates - normoxic Trimix on OC

[Caracis]

Question for tech divers out there. Consider dive to 65m on 18/45, 15 min bottomtime + descent, with EAN50 and Oxygen as deco gas, all open circuit. What are your ascending rates. I am a bit conflicted between what I was taught, read, etc. Like info 9m per mi up to first deco stop, to some extremely allow ascent (when offgasing slow to 3m per minute, after 1st deco stop slow to 1m per minute). So there are big discrepancies, “old” divers say things differently lot of times then some”younger” ones. Could not I am wondering what each system teaches, what are personal approaches and if someone has EBM/ peer reviewed articles. Mind you: open circuit, not CCR, because I am not there yet. As anesthesiologist I would like to do things based on evidence based and not eminence based
Petr

 

[Rayk]

Your first deco stop depth and duration of your deco stops will be dictated by your gradient factors. It is a compromise between safety and efficiency that you need to decide.

A deco planner can help by simulating a dive on different settings to see how GF choices effects deco plan and total run time.

 

[Caracis]

Your first deco stop depth and duration of your deco stops will be dictated by your gradient factors. It is a compromise between safety and efficiency that you need to decide.

A deco planner can help by simulating a dive on different settings to see how GF choices effects deco plan and total run time.

I am not solving issue of stops. I am resolving ascend rates…. GFL will decide my lowest, yes, but what ascend rate to 1st stop and what between them. I a, considering 6-7 m per minute till 1st deco, 3 m per min between deco, last at 6 m and then 1m per min to surface with surface rest

 

[inquis]

Much will depend on your/team skills. Early on, the guys I dove with could only achieve 5 m/min.

These days, I plan my gas for 6 m/min to the first stop, 3 m/min up to 3 m, and 1 m/min from 3 m. (4-5 mins to surface from a last stop of 6 m)

However, I try to get to the first stop as fast as I can while being certain of stopping. I see no point in further on gassing with a slow ascent from the bottom. I would have no issue with a 20+ m/min rate below 30 m. The pressure reduction per m ascent when deep is relatively low.

 

[Caracis]

Much will depend on your/team skills. Early on, the guys I dove with could only achieve 5 m/min.

These days, I plan my gas for 6 m/min to the first stop, 3 m/min up to 3 m, and 1 m/min from 3 m. (4-5 mins to surface from a last stop of 6 m)

However, I try to get to the first stop as fast as I can while being certain of stopping. I see no point in further on gassing with a slow ascent from the bottom. I would have no issue with a 20+ m/min rate below 30 m. The pressure reduction per m ascent when deep is relatively low.

Thank you, my thought process was the same. In MultiDeco 7m per min till 1st stop, then 3 per min and 6 min last 6 m

 

[PfcAJ]

The deco program you’re using will have a parameter for the ascent rate. I think you’ll be hard pressed to find any real data regarding ascent rates to the 1st deco stop.

30fpm seems to work, and that’s the default setting of most decompression programs.

 

[Kendall Raine]

Question for tech divers out there. Consider dive to 65m on 18/45, 15 min bottomtime + descent, with EAN50 and Oxygen as deco gas, all open circuit. What are your ascending rates. I am a bit conflicted between what I was taught, read, etc. Like info 9m per mi up to first deco stop, to some extremely allow ascent (when offgasing slow to 3m per minute, after 1st deco stop slow to 1m per minute). So there are big discrepancies, “old” divers say things differently lot of times then some”younger” ones. Could not I am wondering what each system teaches, what are personal approaches and if someone has EBM/ peer reviewed articles. Mind you: open circuit, not CCR, because I am not there yet. As anesthesiologist I would like to do things based on evidence based and not eminence based
Petr

I use 10 m/min up to the 20’ (100% switch) then slow down to 1 -2 m/min. I will often stay at the 20’ for as much as 50% of the 10’ time before hitting the 10’ and then 1-2m/min to surface. Extending the 20 is “old style” and I have no empirical support (e.g. comparative Doppler) for this other than no hits for me and regular dive buddies (n=~2,000) and Doppler grades 1-2.

 

[Nick_Radov]

No one has done controlled experiments on this so you're not going to find any hard data. Most divers target something like 9m/30ft per minute for planning the ascent from the bottom to the first real deco stop, and then progressively slow down.

In practice the initial ascent rate from the bottom is often dictated by more practical concerns. Like if you have to send up an SMB when leaving the bottom then you can only wind up the spool so fast. Or if it's a DPV dive from shore then the seafloor only slopes up at a certain angle. Just make sure you account for this in gas planning.

 

[Moerae]

Like if you have to send up an SMB when leaving the bottom then you can only wind up the spool so fast.

We typically "ride" the SMB off the bottom (holding tension on the spool or reel so you get dragged up with the SMB). You can kind of alternate keeping/releasing tension on the spool/reel with your hand to control speed.

Makes a huge difference on getting to that first stop.

(Note: Requires practice and confidence/competency in controlling your buoyancy during ascent, especially on CCR and/or with a drysuit).

 

[Imla]

What you want to achieve is to get to your first decompression stop as expediently as possible to start offgassing and avoid ongassing of slower tissues during the ascent.
GUE operates with standard ascent rate of 9m/min up to first stop, while adjusting ascent speed to team control, and recommends 1m/min from 6m up after decompression has cleared. If you need to slow down ascent speed, you also need to be aware of any potential ongassing happening in slower tissues on the way up. (As per GUE SOP v3.0 and GUECCR SOP)


Slower ascentspeeds can be similied to "adding deep stops/lowering GFlow". This was all the hype a few years ago, but newer research (i wish I could cite them, but it is quarter past midnight... couldnt be bothered) does indicate that deep stops do more harm than good. You basically end up ongassing some tissues while offgassing others.

Anaesthesiatip: keep an eye on ETSevo/Des/Iso during "ascent" from anaesthesia. Especially in long lasting procedures (Whipples for example) where the patients body is more or less in quilibrium both in fast and fatty tissues, you will see a first significant drop of gas in ET when the high flow O2/air flushes the patient. This will be the easy offgassing compartments. Blood and muscle. Not until these are offgassed enough will the fat release the gas (anaesthesiagas OR nitrogen in diving) into blod/muscles. You can see this is a shortlasting spike in ETSevo/Iso/Des after the first drop. This can be quite significant.
Think of your ascent from a decompressiondive in the way you consider the patients "ascent" from a general anaesthesia with gas.