Better to safety stop at 10 or 20 if...

[Blasto]

The science is for deco stops, not safety stops. NEDU 2011 that showed Buhlmann working the best over deep-stop models.

In absence of evidence to the contrary, the default assumption would be that safety stops influence deco stress in the same way as planned deco stops.

 

[Compressor]

Current science indicates the optimum stop distribution to be at GF.low=GF.high.

What does this mean?

TO original operator asking question: Right around 20 feet it starts counting down. I keep my depth above 10 and close to 15 but if I have to I will go a bit deeper to say 18 feet. You are decompressing at roughly 1.5 ATA so its good.

 

[boulderjohn]

The science is for deco stops, not safety stops. NEDU 2011 that showed Buhlmann working the best over deep-stop models.

In absence of evidence to the contrary, the default assumption would be that safety stops influence deco stress in the same way as planned deco stops.

I am very familiar with the studies. I have no idea how they would specifically affect the decision of the depth of a safety stop.

 

[Blasto]

I am very familiar with the studies. I have no idea how they would specifically affect the decision of the depth of a safety stop.

If you were to pick a perfect depth for the deco stop, you'd treat it as a deco stop with very low GF. The optimum depth for that (within the limitation of only a single depth) wouldn't always be the same.

 

[lv2dive]

I’m with @boulderjohn and @Compressor - I’m really not understanding what sure you are saying at all. I am not aware of any implications (much less direct correlations) from recent studies related to safety stop depth.

If you were to pick a perfect depth for the deco stop, you'd treat it as a deco stop with very low GF. The optimum depth for that (within the limitation of only a single depth) wouldn't always be the same.

 

[eelnoraa]

how about 1 minute at each?

 

[KenGordon]

The science is for deco stops, not safety stops. NEDU 2011 that showed Buhlmann working the best over deep-stop models.

In absence of evidence to the contrary, the default assumption would be that safety stops influence deco stress in the same way as planned deco stops.

NEDU 2011 (the deep stops study) did not consider any Buhlmann profiles.

 

[KenGordon]

Those are the only choices.

I just got the Perdix dive computer and the two options to set the safety stop are at 20’ or 10’.

I usually stop at 15’ so it’s kind of a moot point but I was wondering if you can’t stop at 15’ for some reason, is it safer to stop deeper or shallower?

(I don’t know, say a whale was in your way between 30’ and 4’. I know whales are taller than 26’, but this is a skinny hypothetical whale.)

And if you have thoughts on which is a better setting, do let me know.

On a few dives look at the GF99 number and the coloured bar chart of tissue saturation.

GF99 is a proxy for risk. What does the “GF99” display value mean? - Shearwater Research

You will probably notice that the GF99 peaks as you reach the surface. The idea of the safety stop is to keep that peak low and so the ongoing surface risk exposure low.

A shallower safety stop, of the same time, will result in a lower surfacing GF99, but you will probably arrive at that stop with a higher initial GF99.

For a regular air/mild Nitrox dive, conditions allowing, you are probably best to stop at 6m and gradually ascend to 3m over a minute and then wait a couple of minutes before gradually surfacing. Some agencies say to take five minutes for the final ascent from the last stop to the surface and if you can do that your peak GF99 with be much better controlled.

Short of going directly to the surface, the worst plan is to do a stop at 6m and then ‘pop’ directly to the surface. Popping up up from 3m is not so bad but still to be avoided.

Personally I set the computer to 3m but basically do the stops at 5m and then slowly ascend. Note that if you do this your Time To Surface will be wrong if you have real stops.

 

[boulderjohn]

If you were to pick a perfect depth for the deco stop, you'd treat it as a deco stop with very low GF. The optimum depth for that (within the limitation of only a single depth) wouldn't always be the same.

The only study you cite is not about recreational diving, did not involve Bühlmann, and did not involve GFs.

But I will bite.

Let's say I do a square profile dive to 76 feet for 32 minutes on air. Where do your calculations say I should do my safety stop?

 

[hammet]

Ten feet is the ideal stop. However, conditions, such as high waves, are not always conducive for this. Therefore, the twenty foot choice is a better option. The fifteen foot stop is a simple compromise and usually works well. For some people, fifteen feet is easier to maintain buoyancy than ten feet.

When did someone decide 10' is 'better' than 15'?
Pretty sure padi still says 15 on their plastic RDP tables.