You offgas faster at 5m depth than on the surface

[boulderjohn]

Here's a SB thread where a 3-minute stop versus a 5-minute stop was discussed: Safety Stop - 3 min or 5 min?

Thanks. I saw a reference to Andrew Pilmanis, and I knew he had done some studies that led to people wanting to do safety stops. I did a search but did not find the actual paper on it, though. All I found was that he did the study in 1974. I have a vague memory of having read that study recently, maybe even on ScubaBoard.

With that in mind, I searched ScubaBoard and found threads back in 2000 and 2001 in what was then the ask Dr. Deco forum. Dr. Deco on ScubaBoard was Dr. Michael Powell, a NASI decompression specialist who helped with the research for the PADI RDP. He referenced Andrew Pilmanis and his study, which was a Ph.D dissertation. As I read it, it was not as detailed as we might wish.

Powell was emphatic, though, that safety stops are valuable.

 

[Subcooled]

if you are hoping for the fastest off-gassing, the surface is where you want to be.

On the surace, with oxygen
Edit, again, thanks to Akimbo: At max possible depth with oxygen. Although you should remember that off-gassing DOES continue on the surface.

I am assuming that a recreational diver will not have access to oxygen during the dive. Breathing oxygen during a stop will be better than breathing air at the surface.

Yes, just as we both know, surface deco on oxygen is an option. It has also been studied by DAN.

 

[tursiops]

Thanks. I saw a reference to Andrew Pilmanis, and I knew he had done some studies that led to people wanting to do safety stops. I did a search but did not find the actual paper on it, though. All I found was that he did the study in 1974. I have a vague memory of having read that study recently, maybe even on ScubaBoard.

With that in mind, I searched ScubaBoard and found threads back in 2000 and 2001 in what was then the ask Dr. Deco forum. Dr. Deco on ScubaBoard was Dr. Michael Powell, a NASI decompression specialist who helped with the research for the PADI RDP. He referenced Andrew Pilmanis and his study, which was a Ph.D dissertation. As I read it, it was not as detailed as we might wish.

Powell was emphatic, though, that safety stops are valuable.

The Pilmanis paper is attached.

 

[boulderjohn]

The Pilmanis paper is attached.

As I posted my previous comments, I had a feeling you would be able to produce this. Thanks!

 

[Akimbo]

if you are hoping for the fastest off-gassing, the surface is where you want to be.

On the surace, with oxygen

Yes, just as we both know, surface deco on oxygen is the best option. It has also been studied by DAN.

Actually the fastest diluent removal is as deep as you can go without Oxygen Toxicity on pure Oxygen. That is generally considered 2.8 ATA/60'/18.3M in a chamber.

 

[tursiops]

Actually the fastest diluent removal is as deep as you can go without Oxygen Toxicity on pure Oxygen. That is generally considered 2.8 ATA/60'/18.3M in a chamber.

Just to be clear, it is considered to be considerably shallower if your are wet.

 

[Akimbo]

Just to be clear, it is considered to be considerably shallower if your are wet.

Agreed, I should have clarified that for newer divers. Here is a complete explanation:

Info - Oxygen Toxicity Limits & Symptoms

Oxygen Toxicity Limits & Symptoms Oxygen toxicity limits can be very confusing, especially for PPO2 (Partial Pressure of Oxygen) levels above 1.6 ATA used in chamber-based hyperbaric treatment (recompression) and decompression tables. For example, here is a chart of one of the most common DCS...

scubaboard.com

 

[RobPNW]

Seems like, in addition to slower offgassing, you would also be consuming more N2 at 5m than at the surface since the tank is still delivering under pressure. I know this is two sides of the same coin but less N2 out than at the surface and more N2 in than at the surface,

 

[Akimbo]

Seems like, in addition to slower offgassing, you would also be consuming more N2 at 5m than at the surface

Absorbing is more precise than "consuming" but this is basically the case for every dive profile, NDL through saturation.

The perplexing parts begin with the fact that different tissues, from blood to bone, ingas and outgas at different rates. It gets even more challenging because different diluent gasses also ingas and outgas at different rates

It is very common for slower tissues to still be ingassing during a decompression stop while faster tissues are outgassing.

Info - Decompression & Treatment Simplified

1: Introduction Everything should be made as simple as possible, but not simpler — Albert Einstein (paraphrased) I probably violated the "But Not Simpler" part, but I tried to include enough Hyperlinks to make amends. Clicking on them should allow any interested diver to "drill-down" as far...

scubaboard.com

 

[Subcooled]

Actually the fastest diluent removal is as deep as you can go without Oxygen Toxicity on pure Oxygen. That is generally considered 2.8 ATA/60'/18.3M in a chamber.

Damn, I was dumb. Or I forgot what I had learned. Now that you say it, it's clear. ppO2 max.
We love to have you commercial divers here.

I'm sure some tech diver could have told that too, but you are the first one to correct me.