Why do people add a few minutes to their last deco stop?

[boulderjohn]

Yes. It was measure of VGE, but the time chosen for the stop was arbitrary as best I can tell, and both of them showed a reduction in VGE, but is 5 minutes better than 3, is 10 better than 5? is 20ft better than 15? Those parameters were not tested.

That, in general, is the problem with testing NDL ascent profiles--too many options. The studies that claimed a benefit to deep stops on NDL dives suffered from the same problem--you added to the ascent time and found an improvement, but you did not show that the depth at which it was added was beneficial. Is it possible that adding that time to the shallow stop would have had an even greater benefit?

 

[boulderjohn]

The one study that I keep coming back to personally is the one that showed that saturation divers on air at less than 20 feet could safely ascend directly to the surface--all saturated tissues were within M-values. To me that is pretty simple. If I am above 20 feet, any tissues that are above m-values will eventually drop to a safe level, and the tissues that are still on-gassing cannot go too far.

For me, that means the traditional safety stop depth makes sense. I cannot possibly stay too long, and staying a little longer might help in some cases.

 

[JMarc]

The one study that I keep coming back to personally is the one that showed that saturation divers on air at less than 20 feet could safely ascend directly to the surface--all saturated tissues were within M-values.

Do you have a more complete reference for this one? I'm interested in reading it.

Thanks

 

[boulderjohn]

It was cited in a recent SB thread--perhaps the one @tursiops recently linked. I am in a motel in the middle of a multi-day trip and about to hit the road.

 

[dmaziuk]

The one study that I keep coming back to personally is the one that showed that saturation divers on air at less than 20 feet could safely ascend directly to the surface--all saturated tissues were within M-values. To me that is pretty simple. If I am above 20 feet, any tissues that are above m-values will eventually drop to a safe level, and the tissues that are still on-gassing cannot go too far.

Note, however, that M-values is where the model's statistical likelyhood of clinical DCS is encoded. I.e. saturation dives to/above no-limit depth are only as "safe" as the model's target incidence of DCS.

 

[BRT]

I disagree. Having a healthy fear of something that you like doing is good, doesn't mean you should stop. I see it in my kids. One is fearless, and he'll push the envelope. I have another that is way more cautious, has some fear, and knows his limitations. Which one do you think is more likely to get hurt?

What's that saying, there are old divers and there are bold divers, but there are no old bold divers.

Pretty much all divers are old divers.

 

[TrimixToo]

Pretty much all divers are old divers.

Hey! I resemble that remark!

 

[twistypencil]

I've just found the oft-cited article about optimizing your Shearwater for GF99 and SurfGF. As someone who is *not* a tech diver, only doing rec, I was interested to learn about these and have added them to my "homescreen" so I can pay attention to them and see how they impact things.

However, I'm wondering why I wouldn't want to just set the highest conservative GFhi value (in rec mode, you can pick 'low', 'med', 'high' or 'custom')? It seems like that would mean the computer would suggest I do more of a "safety stop" and from reading this thread, it seems like more people are doing longer deco because of their SurfGF values suggest it might be better to be more safe, or to remove decompression stress.

I'm about to go on a liveaboard and dive at least three dives a day for 12 days. Because I'm getting older, and beer is harder to recover from these days, I'll be using Nitrox for most of those dives to reduce the build-up of fatigue and stress with repeated dives. That makes me think setting my GFHi to 'high' (which would result in a lower GFhi value, but more conservativism) might be a good idea.

Is the only draw-back my dive gets shorter, and I spend more time hovering at safety stop?

 

[tursiops]

I've just found the oft-cited article about optimizing your Shearwater for GF99 and SurfGF. As someone who is *not* a tech diver, only doing rec, I was interested to learn about these and have added them to my "homescreen" so I can pay attention to them and see how they impact things.

However, I'm wondering why I wouldn't want to just set the highest conservative GFhi value (in rec mode, you can pick 'low', 'med', 'high' or 'custom')? It seems like that would mean the computer would suggest I do more of a "safety stop" and from reading this thread, it seems like more people are doing longer deco because of their SurfGF values suggest it might be better to be more safe, or to remove decompression stress.

I'm about to go on a liveaboard and dive at least three dives a day for 12 days. Because I'm getting older, and beer is harder to recover from these days, I'll be using Nitrox for most of those dives to reduce the build-up of fatigue and stress with repeated dives. That makes me think setting my GFHi to 'high' (which would result in a lower GFhi value, but more conservativism) might be a good idea.

Is the only draw-back my dive gets shorter, and I spend more time hovering at safety stop?

No, your safety stop length does NOT change when you change your conservatism/.GFHi; all that changes is your NDL gets shorter.
You can set the safety stop to be 3, 4, or 5 minutes.
You can also set an ":adaptive safety stop" that forces 5 mions rather than 3 if you go to 100 ft or more, or your NDL drops below 5 minutes at any point during the dive.
I think you'll find that High Conservatism (GFHi=75) does nto cut your NDL that much, espeically if you are uding Nitrox anyway (always a good idea).

 

[boulderjohn]

it seems like more people are doing longer deco because of their SurfGF values suggest it might be better to be more safe, or to remove decompression stress.

Some people are also doing shorter safety stops or no safety stops when their SurfGF numbers suggest there is no need for them.