Safety stop/Deco stop .Whats the difference?

[Dr. Lecter]

Personally, I don't like how deco is taught to most OW students. they're given a lot of rules to follow and very seldom do they understand the reasoning behind the rules. I make it a point to discuss reasons when stops should be blown off. I also cover tissue groups and why I do a full five minute precautionary stop. I don't have a problem with deco theory being discussed in the basic forum.

Fair enough, and I can agree with the fact that most rec courses do a poor job with explaining deco/NDL distinctions.

The best plans are fluid and change according to how the dive progresses.

Yes and no. The best plans are well-considered and exacting, while the best planners are willing to adapt their plan to the dive within the bounds of the original plan. Without meaning to dog tom's specific dive further, I'll suggest that Get into the water, find it's colder than anticipated, and shorten the BT accordingly knowing the hang is going to be even worse? Good adaptation. Same thing but decide to go ahead with the original plan and then ditch the last 10:00 of deco because you had to adapt the plan or freeze to death? Bad adaptation.

 

[tomfcrist]

But a blanket statement from a ing instructor in Basic Scuba that "deco isn't exactly mandatory" based on that fact that he once blew off a stop and was OK? Nope, not letting that one pass without a BS tag.

Feel Free to throw the BS flag.....The fact remains that there are times when blowing a deco stop is an acceptable option. Im not telling anyone that deco stops arent needed, but that under certain circumstances they can be put aside. It comes down to time critical risk management, and having the knowledge to make that decision when need be. Why are we taking this off the topic? Answer this for me: Is a safety stop a deco stop? And to clarify that, is the point of a safety stop not to allow time to offgas prior to finishing your ascent? Is Decompression occuring on all dives? If your answer is yes, then we can agree that my initial point that all dives are deco dives and all safety stops are deco stops is reality.

 

[victorzamora]

That's really not what he said.

His exact words were: "deco stops arent mandatory"
The point should be made that "deco stops aren't mandatory given very extreme circumstances," I agree. However, I think that point should be made in a tech-level class (AN/DP or Tec40). Rec-only divers shouldn't be reaching deco anyway, and they definitely shouldn't be deciding to just blow-off deco. Both getting a deco requirement and ignoring it are tech-level decisions.

Is it? I did a dive where the top was 80+F and 48F on the bottom. I had an ice cream headache the entire dive.

You didn't control the temperature, but you decided to go/stay below the thermocline (first choice) AND you decided to continue the dive (second choice). Those are still choices.
Sidenote: this is actually a REALLY safe way of diving as gas [-]profusion[/-] perfusion is lower at depth and higher on your stops....so you're absorbing less and off-gassing more.

 

[tomfcrist]

This is absolutely untrue, unless you're simply using grammar to be "technically" correct. Yes, technically, you "decompress" during all dives as you attained a higher nitrogen loading than what is considered saturation at your altitude. However, a "deco dive" in the common vernacular refers to dives where the NDL was breached and you have an obligatory deco stop according to that algorithm.

You need to think outside the box a little more. Can you get bent doing a 100' dive and ascending rapidly? Heck yes you can.....therefore your "slow" ascent.......is a deco technique.

 

[Dr. Lecter]

"

Originally Posted by tomfcristAnd all dives ARE deco dives......whether you like it or not...its a fact.
"
This is absolutely untrue, unless you're simply using grammar to be "technically" correct. Yes, technically, you "decompress" during all dives as you attained a higher nitrogen loading than what is considered saturation at your altitude. However, a "deco dive" in the common vernacular refers to dives where the NDL was breached and you have an obligatory deco stop according to that algorithm.

In one technical sense, he's correct. You on gas and off gas during all dives. The difference isn't just the terms NDL or deco obligation and time/depth on a chart, it's about how much you've on gased during the dive. At least theoretically, within NDLs you haven't saturated any tissues: go straight to the surface and they shouldn't (heh) cause DCS even given that extreme pressure change. As you cross into deco, at least one type of tissue/compartment has taken on so much gas that without stopping at various points along the ascent, they're too saturated to handle the low, low pressure of 1 ATA.

"

Originally Posted by tomfcristAnd all dives ARE deco dives......whether you like it or not...its a fact.
"
This is absolutely untrue, unless you're simply using grammar to be "technically" correct. Yes, technically, you "decompress" during all dives as you attained a higher nitrogen loading than what is considered saturation at your altitude. However, a "deco dive" in the common vernacular refers to dives where the NDL was breached and you have an obligatory deco stop according to that algorithm.

In one technical sense, he's correct. You on gas and off gas during all dives. The difference isn't just the terms NDL or deco obligation and time/depth on a chart, it's about how much you've on gased during the dive. At least theoretically, within NDLs you haven't saturated any tissues: go straight to the surface and they shouldn't (heh) cause DCS even given that extreme pressure change. As you cross into deco, at least one type of tissue/compartment has taken on so much gas that without stopping at various points along the ascent, they're too saturated to handle the low, low pressure of 1 ATA.

And to clarify that, is the point of a safety stop not to allow time to offgas prior to finishing your ascent? Is Decompression occuring on all dives? If your answer is yes, then we can agree that my initial point that all dives are deco dives and all safety stops are deco stops is reality.

All dives are not deco dives in the sense that not all dives result in tissue saturation. Do not confuse on/off gassing with decompression obligations. In any event, even if I agreed that all safety stops are deco stops, I would not have to agree that all deco stops are mere safety stops. Yes, there are reasons to potentially omit deco. No, that doesn't make them optional safety stops. It makes them deco stops, about which the only simple thing one can say is that they're mandatory*

*Except in extreme circumstances you should take every chance to avoid happening at all; by extreme we more or less mean bent beats dead. YMMV.

 

[The Chairman]

This isn't about ego:

O rly? Denial: not just another river in Egypt.

If you had asked him for clarification, it would have shown that you were trying to understand what was going on during his dive. You didn't. Instead, you took a page out of GI III's cyber play book and slapped him publicly. Again, I'm just not impressed.

 

[Dr. Lecter]

O rly? Denial: not just another river in Egypt.

If you had asked him for clarification, it would have shown that you were trying to understand what was going on during his dive. You didn't. Instead, you took a page out of GI III's cyber play book and slapped him publicly. Again, I'm just not impressed.

Well goodness, I guess I've failed at life.

 

[tomfcrist]

All dives are not deco dives in the sense that not all dives result in tissue saturation. Do not confuse on/off gassing with decompression obligations. In any event, even if I agreed that all safety stops are deco stops, I would not have to agree that all deco stops are mere safety stops. Yes, there are reasons to potentially omit deco. No, that doesn't make them optional safety stops. It makes them deco stops, about which the only simple thing one can say is that they're mandatory*

*Except in extreme circumstances you should take every chance to avoid happening at all; by extreme we more or less mean bent beats dead. YMMV.

Refer to post #44.

 

[boulderjohn]

Some people (including myself) believe the safety stop was created in part due to divers routinely failing to ascend slow enough. Ascending too fast is probably the most common violation of safe diving protocol. The other part is recognition that all dives are deco and allowing for that without calling it deco or requiring additional training. KISS.

I believe that was the origin of the safety stop, but thinking on the role of safety stops in recreational diving has evolved since then. A number of research studies have shown that safety stops provide a benefit well beyond the ascent rate, and divers who ascend at what was determined to be the optimal speed (30 FPM) still benefited significantly from the stops in terms of bubble formation. The new PADI course urges students to do safety stops on almost all dives.

you're missing the point.

Take two buddy teams A and B. Team A has conservative computers, Team B liberal.

Both teams do the same dive profile, Team B holds their safety stop and surfaces, however Team A has their computer telling them to hold some extra deco stops, and they do.

Now, was Team B's dive safer, since their computers didn't go into deco?

You have two computers with two different algorithms, neither one of which has been shown to be more effective than the other. If the only difference between them is that one required a final stop at normal safety stop depth and the other didn't, then the one that did the stop had the safer dive.

According to the research mentioned above, safety stops always do some good. They are shallow enough that there is no on-gassing going on worth mentioning, so there is no harm in it. The team that exited because their computer said they did not need a stop was probably safe, but they would have been safer if they had stayed and done the stop.

Now, if you are talking about a more complicated decompression profile, that is a different question altogether. An algorithm that has you doing longer stops at deeper depths is not necessarily safer, since there will be on-gassing in the slower tissues during those stops. At some point deeper stops for too long a time should be considered additional bottom time.

 

[The Chairman]

His exact words were: "deco stops arent mandatory"

They aren't if they are contraindicated by another factor. These could include air supply, physical threats, certain injuries as well as other unforeseen events. Teaching a "zero tolerance" approach to deco for OW divers over simplifies the decisions that sometime needs to be made. I actually teach this in OW.

You didn't control the temperature, but you decided to go/stay below the thermocline (first choice) AND you decided to continue the dive (second choice). Those are still choices.
Sidenote: this is actually a REALLY safe way of diving as gas profusion is lower at depth and higher on your stops....so you're absorbing less and off-gassing more.

Dude, get real. I stayed because it was mini-season and I was after lobster. I was having FUN and I caught a 16lb 4oz monster. If only my OW instructor had taken the time to teach me deco theory.

For the record, it's perfusion and not profusion.