So why is it a bad idea to go back to do a safety stop if you blow it?

[ianr33]

Yes, 80-20 is useless for deco. The master himself said so long ago

<< The 80/20 mix is in fact totally useless and contraindicated as a deco gas. At thirty feet it is only a 1.52 ppo2 (the real 1.6 ppo2 gas would be 84/16) and as such does not either provide the right oxygen window, nor does it does it work as well as pure oxygen without an inert gas at any depth. The gas mixing in your lungs has already lowered the effective ppo2 enough to prevent spiking at 20 feet anyway with the use of pure oxygen - in other words, we are dealing with a simplistic misunderstanding here, or "old wives tale" that is typical in diving.>>

The Bakers Dozen - 13 reasons why we do not use 80/20 by George Irvine

 

[divermike1011]

I agree with DanVolker, at least for myself. I'd have a hard time recommending it to a new diver who didn't immediately understand what to do. Still, if you understand the risks you can make your own informed decision.

Michael

 

[Brascan]

to add to this topic just a bit, in a re-compression chamber you are able to receive proper doses and be monitored by the doc of meds given (ie blood thinners) as well as be monitored for arterial blood gases and so fourth. It in itself is reason enough to head to your nearest Hospital with the proper gear to treat. That being said, there are some instances where it is impossible due to location or time constraints. But as every diver should know......plan your dive anddive your plan.......

 

[danvolker]

There is another issue as well. I am NOT talking about lung overexpansion injury...this thread was just about what should be done if a rapid ascent from 130 feet were to occur.

It is my contention, that provided the diver exhaled like a thinking diver during the ascent, that zero damage would exist in the first minute at the surface, even if he/she had been at 130 for 10 minutes...it takes more than a minute for the bubbles to begin forming. Let's assume a 10 minute bottom time.

So you have this diver that still has no injury, and the Agency position is to absolutely CAUSE them to become bent, by scaring them into staying on the surface. If they are fortunate enough to have pure O2 on the boat, the DCS may not be that severe, but the issue is, why cause a chamber ride, and the potential for damage to vascular system and nervous system, etc, when there is an extremely strong probability that the diver could avoid all the injuries, by just going back down to 60 feet, then doing the slow ascent with a couple of minutes of stop time on each 10 feet they go back up.
If someone on the boat could get them O2 for the 20 foot stop, there would be virtually no chance that this diver would sustain DCS.

Ask the saturation divers....they routinely do a huge sat dive, and can hop out of the water after a quick ascent, but get into a recompression chamber to do normal deco in...all without any symptoms having occurred prior to the recompression chamber, because hypersaturation IS NOT immediate..you do have a minute or so.

Back in the mid 90's, I was on A TEK dive with a bunch of friends and an english guy we knew --the English guy was using a brand new doubles BC. In those days before helium, these deep air dives were handled differently than today's trimix dives...On 280 foot dives like this one, after we all re-assembled after the 25 minute bottom time on the wreck, we wanted to massively cut more deco obligation we would get if we ascended slowly to 100 feet...so we did Blow and Go...A full inflation of the BC, and a rocket ride to 100 feet, where you fully dump the bc, then stay there for e few minutes, then begin the slow ascent and then staged deco stops..
On this dive, the Eglish guy's inflator dump failed...I and one other diver saw the failure occurring as he tried desparately to dump at about 140 feet -- the other buddy and I completely dumped, and grabbed the guy, and tried to swim him down....Unfortunately, the bs BC was one of those monster lift bc's. with like 100 pounds of lift. In about 5 more seconds, so fast we did not even imagine this was happening, we were at the surface. This, after a 280 foot dive with a 25 minute duration.
In the first instant after I realized I was on the surface, I recalled the Navy Deep diving info on rapid ascents and how long it would take for hypersaturation to occur. I still felt totally normal, though a bit nervous as you might imagine....I told the english guy to stick his knife in the bc, and I and the other buddy swam instantly back down to 100 feet, follwed by the English guy. We did a fairly normal 100 to 50 foot slow ascent, then the normal 10 foot increment stops from 50, then 40, then 30, then at 20 ft we went on full O2.
We got out, and felt like kids on their junior prom -- in other words, no pain and elated after the dive.
So I have the three of us, with a far more severe rapid ascent scenario that virtually anything a recreational diver would ever experience, getting zero issues on going back down....Had we listened to the "conventional wisdom" of the training agencies on this, we would have waved frantically for the boat, radioed for help, and potentially died on the boat of DCS far too severe for the pure O2 to mitigate on the surface.

 

[MXGratefulDiver]

Back in the mid 90's, I was on A TEK dive with a bunch of friends and an english guy we knew --the English guy was using a brand new doubles BC. In those days before helium, these deep air dives were handled differently than today's trimix dives...On 280 foot dives like this one, after we all re-assembled after the 25 minute bottom time on the wreck, we wanted to massively cut more deco obligation we would get if we ascended slowly to 100 feet...so we did Blow and Go...A full inflation of the BC, and a rocket ride to 100 feet, where you fully dump the bc, then stay there for e few minutes, then begin the slow ascent and then staged deco stops..
On this dive, the Eglish guy's inflator dump failed...I and one other diver saw the failure occurring as he tried desparately to dump at about 140 feet -- the other buddy and I completely dumped, and grabbed the guy, and tried to swim him down....Unfortunately, the bs BC was one of those monster lift bc's. with like 100 pounds of lift. In about 5 more seconds, so fast we did not even imagine this was happening, we were at the surface. This, after a 280 foot dive with a 25 minute duration.
In the first instant after I realized I was on the surface, I recalled the Navy Deep diving info on rapid ascents and how long it would take for hypersaturation to occur. I still felt totally normal, though a bit nervous as you might imagine....I told the english guy to stick his knife in the bc, and I and the other buddy swam instantly back down to 100 feet, follwed by the English guy. We did a fairly normal 100 to 50 foot slow ascent, then the normal 10 foot increment stops from 50, then 40, then 30, then at 20 ft we went on full O2.
We got out, and felt like kids on their junior prom -- in other words, no pain and elated after the dive.
So I have the three of us, with a far more severe rapid ascent scenario that virtually anything a recreational diver would ever experience, getting zero issues on going back down....Had we listened to the "conventional wisdom" of the training agencies on this, we would have waved frantically for the boat, radioed for help, and potentially died on the boat of DCS far too severe for the pure O2 to mitigate on the surface.

... or maybe ya just got lucky.

But yeah ... if you've got the chops to be doing 280-foot staged deco dives, you've got options that the typical recreational diver probably shouldn't be considering. And I do think it's gonna be a situational-dependent decision, based on the person's skills and available resources. What I do know is this ... if I'm sending a diver back down with an O2 bottle, I'm going with him ... just in case things don't go according to plan ...

... Bob (Grateful Diver)

 

[DevonDiver]

Why would you go on O2 if you missed a totally OPTIONAL stop?

My assumption, within this theoretical and very generalized discusssion, would be that the diver who missed the stop, probably did so due to a lack of buoyancy control. Such an event, would probably be twinned with an excessively fast/uncontrolled ascent.

It really boils down to the dive profile; taking into mind the factors of max/ave depth, bottom time and ascent speed. Saw-tooth profiles and 'heavy' square profile dives make a safety stop more prudent. Dive history has to be considered also - repetitve dives, especially deep ones, play a role in the decision. As would any clinical history of DCS that the diver might have. Coupled with a fast ascent, they could (IMHO) make the use of precautionary O2 a wise decision.

A safety stop is optional for recreational dives, but that is also based upon a pre-defined ascent speed being adhered to. If the ascent speed is violated, then the safety stop becomes more critical as a factor to mitigate risk of DCS. I, personally, think that safety stops should be treated as mandatory if ascent speed is violated for a significant portion of the ascent. Many dive computers are programmed to treat the stop as mandatory under those circumstances.

 

[boulderjohn]

This is actually a controversial topic. TDI, for example, teaches that one should indeed go back down and do omitted deco,within certain parameters.

Yes, 80-20 is useless for deco. The master himself said so long ago

<< The 80/20 mix is in fact totally useless and contraindicated as a deco gas. At thirty feet it is only a 1.52 ppo2 (the real 1.6 ppo2 gas would be 84/16) and as such does not either provide the right oxygen window, nor does it does it work as well as pure oxygen without an inert gas at any depth. The gas mixing in your lungs has already lowered the effective ppo2 enough to prevent spiking at 20 feet anyway with the use of pure oxygen - in other words, we are dealing with a simplistic misunderstanding here, or "old wives tale" that is typical in diving.>>

The Bakers Dozen - 13 reasons why we do not use 80/20 by George Irvine

And this is also very controversial. It focuses on the O2 window effect. GUE has backed off from that as a deco concept. (I base that on an email exchange I had with JJ recently. They continue to plan RD deco curves as before based solely on the fact that it has worked in the past, not because of the now discredited O2 window theory.) UTD has also recently backed off from the O2 window theory, and I base that observatrion on what AG said when I took my RD class from him.

When I did 5 weeks of trimix diving in FL this spring, every diver on every boat used 80% for their final deco gas. The local dive shops banked it. Somebody thinks it's OK.

 

[Jaydubya]

Oxygen windows, 80% vs 100%, omitted decompression stops. Hey, isn't this the basic scuba forum?

 

[Centrals]

And this is also very controversial. It focuses on the O2 window effect. GUE has backed off from that as a deco concept. (I base that on an email exchange I had with JJ recently. When I did 5 weeks of trimix diving in FL this spring, every diver on every boat used 80% for their final deco gas. The local dive shops banked it. Somebody thinks it's OK.

Having deco on the 50 and 100 over last 10yrs and without any incidence. I would be very reluctant to try anything new unless supported by very sound scientific study.

 

[JazzeD]

The thread and agency's are talking about safety stops and not going down.

If you blew your Deco stop of course you would go if you could.