Blow a Safety Stop? Redescend ?

[TSandM]

I believe Marroni's studies show that many of us bubble on normal receational profiles. Ascent strategies don't completely avoid bubbling; they avoid excessive bubbling and symptoms.

 

[The Chairman]

I know that a PFO exacerbates this phenomenon... but somehow, descending and giving them 5 minutes to reabsorb while they are significantly smaller just seems wise.

 

[Cave Diver]

Once on the surface we will assume there are some bubbles present on the venous side of the circulatory system that would not be able to cross over to the arterial side because of their size and remain trapped in the lungs until absorbed and dissipated.

Descending immediately after surfacing can reduce the size of the bubble to the point it can cross over to the arterial side and reexpand on the arterial side as a form of AGE. I believe this can be defined as a form of paradoxical gas embolism.
I am sure Thal can provide a more technical explanation than I.

Why We Do Not Bounce Dive After Diving in the WKPP | Global Underwater Explorers

Why We Do Not Bounce Dive After Diving in the WKPP
by George Irvine

It is OK to offgas from the tissues into the blood stream in bubble form in the later steps of decompression as it is a more efficient, faster way of getting rid of the remaining gas (by reduced pressure) than by elevated oxygen alone (which starts taking exponentially more time with greater risk). However, this depends on having a good lung filter and no shunts. All of you have been PFO tested if you are diving with us.

The correct way to ascend from the last stop is one foot per minute for the bigger dives.

The greatest potential for offgassing in bubble form is when the pressure is totally removed back to one ATA out of the water. Now you get a real shower of bubbles, relative to what was happening in the water. A good, clean deco with the foot per minute ascent reduces this dramatically. In MOST people, the greatest bubbling occurs out of the water and continues for up to four hours, not even peaking for a couple of hours. In a well vascularized, fit person like me, it is over with in 30 minutes. Don't bet on that with most of you.

In ALL people, the bubbles continue to grow in size after the pressure is off. They accumulate like gas into themselves from the surrounding blood or tissues (if there are bubbles in the tissues or injury sites) and they grow bigger. This is why you feel pain later rather than earlier if the bubbles are in joints or tissues - they get bigger before they begin to shrink. This is why what starts out as micro bubbles can get by the lungs and grow and get lodged downstream, and you get neurological symptoms later. Now here is the important part. If you understand everything I have said above, then you know that bouncing to 20 feet or whatever to pick up a bottle and immediately returning to the surface is the like giving yourself a homemade PFO: the bubbles in the venous side compress enough to get past the lungs and then will re-expand on the arterial side and lodge in the worst places, the spine and brain blood supplies. You do not want this.

If you dive after dive, stay down and let everything reset. Get the bubbles all compressed, and then deco out and ascend accordingly. I do not want support divers diving support within four hours of doing a real dive or deep support. This works out fine, since we have support activities lasting up to 18 to 24 hours and need to rotate everyone. Let me assure you that we have found this out the hard way in the past.

Parker used to get hot as hell when it would happen. In those days we had "volunteers", and they would all get bent diving to 20 feet to pick up bottles. We have also seen some severe cases of this where dives were done away from the project with no support, and the players went back for bottles later and got hammered.

Don't do it. Also, obviously, do not freedive after a dive. When you want to freedive, do that first and then go scuba diving.

 

[HowardE]

the bubbles in the venous side compress enough to get past the lungs and then will re-expand on the arterial side and lodge in the worst places, the spine and brain blood supplies. You do not want this.

Ok... So what about spending 3-5 minutes at 15-20 feet? I understand that a bounce to say - pick up a tank, is like shaking up the coke bottle, but what if you made a reasonable stop out of it?

 

[The Chairman]

More interesting...

Now define "Bigger dive" and "Immediately".

I do 5 minutes @15 fsw, and this is suggesting that I do another 15 after that to reach the surface? I don't mind the 20 minutes, but the boat captain waiting for me to get on board might have an issue with it. I get enough flack about 3 deep, 5 shallow and 1-2 to surface.

BTW, DAN's latest report suggests that the average ascent from the shallow stop is OVER 200 fpm. Yoiks!

It's obvious that we have left "basic" territory here, but unless someone has a problem with this, I would like to see more discussion.

 

[SDAnderson]

I just read a thread that kinda sideways discussed this, but there were some varying , and some conflicting opinions and no clear answer. This question was not the orignal posters topic and I didnt want to add to the hi-jacking.

If one were to blow a safety stop, should one redescend and do the safety stop (and just add a few extra minutes)?

What would a dive computer tell you to do in this situation?

Also, does scuba board have a link that gives acess to tables and charts?
Dive Computers spoil us. I would like to see a chart which showed obligated saftey stop time for varying depth and dive times.

Skipping over the PADI semantics argument, a blown safety stop is corrected for by extending your surface interval, not by returning to depth to make the time up. That practice, called in-water recompression, is seriously dangerous business. In a few - very few, very extreme - situations it may be the best option but IWR should never be considered by NDL divers.

The protocol for treating someone who might be suffering from DCS is straightforward:

• Get them out of the water and out of their gear.
• Provide BLS as needed.
• Get them on oxygen, preferably 100%, as quickly as possible.
• Contact your local EMS and DAN.
• Get them comfortable and, if prone, on their left side.
• Monitor closely for signs and symptoms of DCS - the 5 Minute Neuro exam is perfect for this situation.
• Have them update their will to include you.

OK, the last step is optional...

Could a mod fix the image size for that table that's making the page about 40' wide? Hard to read this thread.

 

[Thalassamania]

Ok... So what about spending 3-5 minutes at 15-20 feet? I understand that a bounce to say - pick up a tank, is like shaking up the coke bottle, but what if you made a reasonable stop out of it?

As far as I know the definitive studies have not been done, but the effect has been well known for a long time. Conventional wisdom is to wait at least 10 minutes and even then to not go shallow on the subsequent bounce dive, but to go deep, ascend slowly and THEN take a 5 to 10 minute stop.

More interesting...

Now define "Bigger dive" and "Immediately".

I do 5 minutes @15 fsw, and this is suggesting that I do another 15 after that to reach the surface? I don't mind the 20 minutes, but the boat captain waiting for me to get on board might have an issue with it. I get enough flack about 3 deep, 5 shallow and 1-2 to surface.

BTW, DAN's latest report suggests that the average ascent from the shallow stop is OVER 200 fpm. Yoiks!

It's obvious that we have left "basic" territory here, but unless someone has a problem with this, I would like to see more discussion.

A safety stop of 5 @ 15 has been shown to reduce Doppler detectable bubbles, what that exactly means is open to argument.

It's not the boat captain's spinal column, so as far an I'm concerned he does not get a say. If he want's his anchor cleared after the dive he will have to have a fresh diver or to wait on me to make the bounce the way that I see fit.

Rapid ascent from a safety stop is one of the big concerns, this almost guarantees venous side bubbles (remember the blood pressure is lower on the venous side) that will be filtered and lodge in the capillaries of the lungs (this, now reduced gas exchange surface is one of the explanations for post-dive fatigue), resubmergence of even just 20 feet is (again in the general wisdom) enough to permit those "filtered" bubbles to be compressed sufficiently to move into the arterial circulation and how long till they clear, I do not know ... I too would love a definite reference.

Skipping over the PADI semantics argument, a blown safety stop is corrected for by extending your surface interval, not by returning to depth to make the time up. That practice, called in-water recompression, is seriously dangerous business. In a few - very few, very extreme - situations it may be the best option but IWR should never be considered by NDL divers.

The protocol for treating someone who might be suffering from DCS is straightforward:

• Get them out of the water and out of their gear.
• Provide BLS as needed.
• Get them on oxygen, preferably 100%, as quickly as possible.
• Contact your local EMS and DAN.
• Get them comfortable and, if prone, on their left side.
• Monitor closely for signs and symptoms of DCS - the 5 Minute Neuro exam is perfect for this situation.
• Have them update their will to include you.

OK, the last step is optional...

Could a mod fix the image size for that table that's making the page about 40' wide? Hard to read this thread.

You are confusing matters, we are discussion SAFETY STOPS. There is no procedure that I know of for an omitted Safety Stop, since they are optional to begin with.

 

[dpaustex]

Woah, folks!!!! Too many bad terms being thrown around here.

First, safety stops are recommendations. Second, some people keep calling these a "deco -stop"...quit doing that!!! If you are doing recreational diving, your are NOT doing "deco" diving. Wrong forum, wrong place. All of the charts being referenced are for "no decompression diving", which is staying within those chart limits. Again, NOT DECO!!!!

Okay, so what "should" you do? First, understand the purpose of the safety stop. Anyone remember what was taught to them in their OWD course? The safety stop is an "added safety measure of 3 to 5 minutes at 10 to 30 feet that divers should take after no-decompression dives to help reduce silent bubbles and the risk of pressure related injuries." (reference SSI manual).

Okay, first understand that the safety stop is a recommendation. Does it mean you won't get bent? No. There are too many factors involving DCS. The whole purpose of the recommended safety stop is to let the blood circulate throughout your entire body, which will help get rid of the very tiny bubbles that may (or may not) still be present in portions of your body. The idea of 3 to 5 minutes was to allow these bubbles more "contact" time with the blood to go back into solution, which will then be off-gassed through the normal respiratory cycle.

I have no idea as to going back down if you blew your stop. Would I do it? Yes, I would, with the simple understanding that if those bubbles were still there, then the increased pressure would help drive them back into solution in the bloodstream, rather than the bubbles being transported to an area of the body where they could do harm. Again, they would be off-gassed through normal respiration (with varying times, depending on a lot of factors, below). Please understand the physics of what is happening with the air bubbles, and that going back down to a safety stop depth does nothing detrimental - at all. If you have ever watched your computer during this time (it's interesting to see how they react), they often will increase the amount of time for the recommended stop (I dive Suunto's, and that's what mine tells me).

But to say that if your computer didn't "tell you" anything was wrong is a misunderstanding of the gas laws, and how the lack of a safety stop could (note the would "could") impact you. There are so many variables involved (how much residual nitrogen you have, how many repetive dives have you already done, how hydrated you are, dive depth, etc.), that it isn't something to trifle with. Computers, for the most part, have conservative dive profiles. But computers are no guarantee how an individual's own physiology will specifically impact them. Again, the safety stop is only a recommendation, not a requirement.

I have done wall dives, where we came back up so gradually (working back and forth along the face), that the safety stop was "built in" to the dive, and while the computer "triggered" the safety stop when I hit 20 feet, I just kept on swimming.

 

[Scott L]

Why We Do Not Bounce Dive After Diving in the WKPP | Global Underwater Explorers

Although I originaly read this on one of your previous posts earlier in the week it was was of great value to me and my dive buddies as we/I have on many occasion bounced after fully saturated repeatitive dives to recover dropped equipment such as spearguns, etc. I have also been guilty of free diving after a day of aggressive profiles mearly to visit buddies on safety stops and to check out their catches. SB is a wonderfull forum that has no doubt saved many from injury and perhaps death. Scott

 

[The Chairman]

Second, some people keep calling these a "deco -stop"...quit doing that!!!

Not to be the contrarian, but no. All dives are deco dives. Stops can be deep or shallow, optional or mandatory. All stops are decompression stops as we do them to avoid DCS. A safety stop is a fun way to say "optional deco stop" without giving peeps too many reasons to just skip it.