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

[UnixMarine]

He is not saying the reference spoke about safety stops. He is trying to extrapolate deco theory into safety stops. His point is that the static safety stop (15' give or take 5') is not always ideal. You would surface with less nitrogen saturation if you maximized your M factor (maximum super saturation) in order to maximize off gassing.

That being said. For a recr recreational dive, doing deeper stops, you would be ongassing your slow compartments and offgassing your fast compartments which would end up needing more time at a shallow depth to off gas and would not be ideal

 

[boulderjohn]

He is not saying the reference spoke about safety stops. He is trying to extrapolate deco theory into safety stops. His point is that the static safety stop (15' give or take 5') is not always ideal. You would surface with less nitrogen saturation if you maximized your M factor (maximum super saturation) in order to maximize off gassing.

That being said. For a recr recreational dive, doing deeper stops, you would be ongassing your slow compartments and offgassing your fast compartments which would end up needing more time at a shallow depth to off gas and would not be ideal

People like to point out that during a safety stop, you are decompressing while stopped, so that makes it a decompression stop. That is true enough, but there is a big difference.

• When doing a decompression stop, the algorithm you are using to control your dive has determined that there is a significant risk of DCS if you were to ascend directly to the surface. It requires you to stop at a certain point to allow for further decompression.
• When doing a safety stop, the algorithm you are using to control your dive has determined that there is a NO significant risk of DCS if you were to ascend directly to the surface. It suggests that you stop along the way to allow for further decompression--just to be extra safe.

In both cases, the depths at which you stop are somewhat arbitrary. You say that "the static safety stop (15' give or take 5') is not always ideal." That is true of decompression stops as well. That ideal is, in fact, constantly changing as your tissues off-gas. A decompression algorithm tells you to stop at a certain depth for a certain amount of time and then go to the next shallower allowed depth. The truth is you would be better off going part way up to that depth before that. That would be far, far too complicated, so you are given specific depths for your stops.

If you are trying to find the exact, precise, perfect depth for a suggested, non-mandatory, just-to-be safe safety stop, you are seriously overthinking this.

 

[leadduck]

Besides DCS, if novice divers were taught to always bolt straight to the surface from 60fsw then we'd see a lot more barotrauma accidents and ruptured eardrums. Doesn't really matter at what depth exactly you stop, 15fsw is fine.

 

[Blasto]

If you are trying to find the exact, precise, perfect depth for a suggested, non-mandatory, just-to-be safe safety stop, you are seriously overthinking this.

I have to diverge on the reasons for the safety stop. While it has been introduced for reasons of safety, my personal reason for doing it is not to feel like crap after the dive.

I noticed I don't feel the usual reduced energy and earlier onset of sleepiness after multiple long no-deco dives if I do a couple minutes at 5m followed by 5-6 at 3m, or dive a computer set to GF 30/30 or less. The extra 3m stop is logistically easier to do with buddies following different algos.

DCS is not a binary thing, you don't "get it" or "not get it". You get some amount of tissue damage after every dive, at some point that damage produces symptoms, and at a further point these symptoms get pronounced enough to count as DCS. I prefer to reduce my damage to the logistically achievable minimum, well within asymptomatic range, rather than just to 0 risk of DCS.

Thus, for me, it's a deco stop (that can be skipped if necessary). It's not risk avoidance driving it, but simple desire to feel better. It certainly differs for everyone.

 

[Neilwood]

As @boulderjohn says, there is a big difference between deco stop and safety stop.

Whatever algorithm you pick, it gives a "line in the sand" (NDL) where it calculates that you are at significant risk of DCS.

When you dive you can choose two options:
1) Go beyond the theoretical line at which point you are in to deco stop territory - fail to do the stop at your peril and increasing risk of DCS.
2) Stay on the "safe" side of NDL and any stop you are doing is purely padding your ascent and making you even more safe. Whether that padding is at 10, 15 or 20 ft is a relatively moot point. I suspect that 15ft was picked as a number that translates easily between imperial and metric and is easy to hold in nearly all conditions.

If we want to be absolutely exact with regards to ascents, I suspect the theoretically perfect ascent would not even had stops but would follow the constantly changing window at which you are achieving maximimal off gassing but staying within safe supersaturation levels. That would be far too difficult for what I would suspect would be 99.99% of divers so stops are inserted at convenient points to make it easier for divers.

 

[Addicted2H2O]

You guys took a fairly simple question and essentially turned it into a college course discussion. OP....I'd set it for 20 ft and call it good. My Atomic Cobalt II is set at 15 and it starts the timer once I reach that depth. It counts down as long I'm somewhere between 15-20 ft. Once I descend past the 20 ft mark it stops counting until I get back up into that window. I wouldn't make it a habit but I have made an ascent from about 60 ft without a safety stop (by accident) and was just fine afterward. Again I certainly wouldn't make a habit of it, but like others have said I think if you practice a slow ascent rate you can probably do without a safety stop altogether. But take my advice for what you paid for it.

 

[Snoweman]

People like to point out that during a safety stop, you are decompressing while stopped, so that makes it a decompression stop. That is true enough, but there is a big difference.

• When doing a decompression stop, the algorithm you are using to control your dive has determined that there is a significant risk of DCS if you were to ascend directly to the surface. It requires you to stop at a certain point to allow for further decompression.
• When doing a safety stop, the algorithm you are using to control your dive has determined that there is a NO significant risk of DCS if you were to ascend directly to the surface. It suggests that you stop along the way to allow for further decompression--just to be extra safe.

In both cases, the depths at which you stop are somewhat arbitrary. You say that "the static safety stop (15' give or take 5') is not always ideal." That is true of decompression stops as well. That ideal is, in fact, constantly changing as your tissues off-gas. A decompression algorithm tells you to stop at a certain depth for a certain amount of time and then go to the next shallower allowed depth. The truth is you would be better off going part way up to that depth before that. That would be far, far too complicated, so you are given specific depths for your stops.

If you are trying to find the exact, precise, perfect depth for a suggested, non-mandatory, just-to-be safe safety stop, you are seriously overthinking this.

What about when my computer wants a five minute safety stop and not three minutes?

 

[doctormike]

If you are trying to find the exact, precise, perfect depth for a suggested, non-mandatory, just-to-be safe safety stop, you are seriously overthinking this.

Preach it, brother!

 

[Saniflush]

What about when my computer wants a five minute safety stop and not three minutes?

Well you signal to your computer that you are heading on up and to come on when they finish their other two minutes. Duhhhh.

 

[boulderjohn]

What about when my computer wants a five minute safety stop and not three minutes?

Some people prefer to do 5 minutes. Apparently some computer programs do, too. If my computer algorithm said to do a 5 minute safety stop, I think I would do a 5 minute safety stop.