Descend to Decompress???

[danvolker]

i guess we first would have to distinguish between recreational diving and tec diving. in recreational diving you clearly shouldn't experiment with the whole inwater decompression since you do not have the training needed as an all overruling fact, secondly you would not know how deep you can/have to go to start offgasing appropriately (since therefore you would need to have a deco-schedule or a computer telling you this) and as a last point you most likely would not have the right mix of gases available (since you would certainly not be able to climb on the boat, get an other nitrox-tank and redescend in the short amount of time you mentioned).

since i just did my tec- and trimix-course (read my article about it on my website if you're interested about my thoughts on the experience) the emergency-scenarios for cases like that may include redescent and decompressing on different gases on different deco-schedules from the ones you planned for in the first place. again, these are EMERGENCY-scenarios for TEC diving qualifications and have to be considered COMPLETELY independently from what ever you have been taught in any recreational diving course so far!

by far the best choice would be the one where you go back to the boat, tell what just happened and get the highest possible amount of O2 (ideally pure oxygen) and get to the nearest chamber to have yourself checked.

Not to mention, if a diver with the ascent problem was to take the huge amount of time ( many minutes you dont have) required to get back on the boat, switch tanks, and jump back in, there is almost no possible way this would happen in the narrow little window you have prior to when hypersaturation will occur. If you have to get back on the boat, you are going to need to stay there, unless you are mixed gas/tech certified and have plenty of 100% O2. And even then, this would only be in extreme cases in areas where a chamber was too far away. Once the hypersaturation has begun, the bubbles and rapidly increasing levels of inflammation are going to make the re-descent and re-compression far more dangerous.

 

[Thalassamania]

The "site" command can very helpful in google, try something in this form:

site:scubaboard.com decompression surface asymptomatic

 

[danvolker]

It seems to me like all the good discussion topics have been done so many times now, that there is not that much left to argue about....

Is it my imagination, or are SB members getting dangerously close to agreeing on too many topics?

 

[Thalassamania]

If the problem is a blown "safety" stop, it can be ignored, it is a non-issue, never return to the water to "make up" omitted "safety" stops.

If the problem is a blown required decompression stop and the diver is asymptomatic, then the diver can return to water withing 5 minutes, the procedure for omitted decompression may be followed.

If the problem is a blown required decompression stop and the diver is symptomatic, then diver should be placed on oxygen and transported to the nearest chamber as quickly as possible.

Only when the problem is a blown required decompression stop resulting in a symptomatic diver, and it is not possible to transport, should IWR be attempted, and then only when an operation is prepared, equipped and drilled for IWR.

 

[DevonDiver]

If the problem is a blown "safety" stop, it can be ignored, it is a non-issue, never return to the water to "make up" omitted "safety" stops.

If the problem is a blown required decompression stop and the diver is asymptomatic, then the diver can return to water withing 5 minutes, the procedure for omitted decompression may be followed.

If the problem is a blown required decompression stop and the diver is symptomatic, then diver should be placed on oxygen and transported to the nearest chamber as quickly as possible.

Only when the problem is a blown required decompression stop resulting in a symptomatic diver, and it is not possible to transport, should IWR be attempted, and then only when an operation is prepared, equipped and drilled for IWR.

That's pretty definitive...

I'm still kinda interested in the issue of blown 'rec-deco' though (rather than blown 'safety stop'). The issue being; fast ascent from recreational dives (within no-deco limits of time/depth) - which can be considered to be 'decompression' - where a constant, controlled ascent rate is exceeded, rather than a mandatory stop blown.

 

[RetroBlader]

First of all, I want to thank all for the discussion so far. As a still-very-green rec diver, with way too many months of involuntary surface interval to kill until I can dive again, reading Scubaboard daily is not only a coping mechanism for me, but also helps immensely in my effort to become a better diver.

So, what I'm about to say is said with no disrespect whatsoever towards the much more experienced members....

We are discussing missed safety stops/descending following a rapid ascent. First, by definition, a safety stop is not required by any stretch of the imagination for recreational dives. Therefore, missing one incurs no penalty, therefore, descending following a missed one serves no purpose.

I'm betting that you can't find a computer manufactured after 2005 that, if it gives you an ascent lockout for too rapid of an ascent will ever let you clear that alarm by going back down. Uwatecs beep but don't lock up. Suuntos and Mares give you a audible warning, and if you ascend above the mandatory stop depth, lock up and don't clear for a significant penalty. My Shearwater grins and gives me an easily ignored red blinky light, which I'd pay twice as much for if I didn't already have one. I hate racket underwater.

My Suunto Zoop is definitely manufactured after 2005, but still:
- assigns what it calls a "Mandatory" safety stop when one ascends too fast ("ascent rate exceeds 12 meters/min [40 ft] momentarily or 10 meters/min [33 ft] continuously")
- penalizes if one misses such a stop
- is willing to clear that penalty if one re-descends within 3 minutes

(The manual, printed in 2009, is still available online here.)

If you ascend
above the Mandatory Safety Stop ceiling, a downward
pointing arrow will appear and a continuous beeping
starts (Fig. 3.14.). You should immediately descend to,
or below, the Mandatory Safety Stop ceiling depth. If
you correct this situation at any time during that dive,
there are no affects on the decompression calculations
for future dives.

If you continue to violate the Mandatory Safety Stop,
the tissue calculation model is affected and the dive
computer shortens the available no-decompression
time for your next dive. In this situation, it is recommended
to prolong your surface interval time before
your next dive.

As you can see, missing this kind of (still non-deco) stop will incur a penalty -- albeit an artificial one imposed by the dive computer -- in having less time on the next dive.


I agree that in rec diving, a Safety Stop is recommended but not mandatory. Even Suunto agrees -- missing what it calls a "Recommended" Safety Stop (incurred whenever a dive goes over 10 meters) will incur no penalty.

However, rec divers can inadvertently get themselves into trouble (or at least into the grey zones) by ascending too fast, or by staying at depth past the allowed NDL time (by not paying attention to his/her computer and/or depth). I think this is what DevonDiver refers to as "rec-deco".

As I learned in another thread shortly after my recent Cozumel trip, even the most conservative/vigilant rec diver can sometimes run into a down-current and end up much deeper than planned. After he/she manages to escape, he/she may ascend too fast or spend too much time at depth and incurred a deco obligation.

It is therefore worthwhile to discuss what one should do in such situations, which one is much more likely to encounter than "real IWR".


Again, Suunto gives 3 minutes for the diver to re-descend if he/she ascends above the ceiling depth for an inadvertently acquired deco stop (page 26):

If you ascend above the ceiling during a decompression
stop, a downward pointing arrow will appear and
a continuous beeping starts (Fig. 3.18.). In addition,
an error warning Er reminds you that you have only
three minutes to correct the situation. You must immediately
descend to or below the ceiling.

If you continue to violate the decompression, the
dive computer goes into a permanent Error Mode. In
this mode the instrument can only be used as a depth
gauge and timer. You must not dive again for at least
48 hours (see also section 3.8. “Error Conditions”).

Then on page 36:

During this three-minute period the Er
warning is shown and the audible alarm beeps. After this, the dive computer will
enter a permanent Error Mode. The instrument will continue to function normally
if you descend below the ceiling within this three-minute period.

On the Zoop website I found an updated version (Aug 2011) of the Zoop manual, but it still presribes the same 3-minute limit to re-descend after a missed deco stop in order to prevent a permanent Error Mode.



Of course, after reading this thread if I have any DCS symptoms at all, I will NOT go back down, and will instead get oxygen at surface and try to find the nearest chamber.

However, if I'm completely symptom-free, still have plenty of air in my tank, and there are no hungry sharks around, I might be very tempted to redescend to 15 ft for a few minutes to appease my Suunto....

:shocked2:

 

[danvolker]

First of all, I want to thank all for the discussion so far. As a still-very-green rec diver, with way too many months of involuntary surface interval to kill until I can dive again, reading Scubaboard daily is not only a coping mechanism for me, but also helps immensely in my effort to become a better diver.

So, what I'm about to say is said with no disrespect whatsoever towards the much more experienced members....






My Suunto Zoop is definitely manufactured after 2005, but still:
- assigns what it calls a "Mandatory" safety stop when one ascends too fast ("ascent rate exceeds 12 meters/min [40 ft] momentarily or 10 meters/min [33 ft] continuously")
- penalizes if one misses such a stop
- is willing to clear that penalty if one re-descends within 3 minutes

(The manual, printed in 2009, is still available online here.)



As you can see, missing this kind of (still non-deco) stop will incur a penalty -- albeit an artificial one imposed by the dive computer -- in having less time on the next dive.


I agree that in rec diving, a Safety Stop is recommended but not mandatory. Even Suunto agrees -- missing what it calls a "Recommended" Safety Stop (incurred whenever a dive goes over 10 meters) will incur no penalty.

However, rec divers can inadvertently get themselves into trouble (or at least into the grey zones) by ascending too fast, or by staying at depth past the allowed NDL time (by not paying attention to his/her computer and/or depth). I think this is what DevonDiver refers to as "rec-deco".

As I learned in another thread shortly after my recent Cozumel trip, even the most conservative/vigilant rec diver can sometimes run into a down-current and end up much deeper than planned. After he/she manages to escape, he/she may ascend too fast or spend too much time at depth and incurred a deco obligation.

It is therefore worthwhile to discuss what one should do in such situations, which one is much more likely to encounter than "real IWR".


Again, Suunto gives 3 minutes for the diver to re-descend if he/she ascends above the ceiling depth for an inadvertently acquired deco stop (page 26):



Then on page 36:



On the Zoop website I found an updated version (Aug 2011) of the Zoop manual, but it still presribes the same 3-minute limit to re-descend after a missed deco stop in order to prevent a permanent Error Mode.



Of course, after reading this thread if I have any DCS symptoms at all, I will NOT go back down, and will instead get oxygen at surface and try to find the nearest chamber.

However, if I'm completely symptom-free, still have plenty of air in my tank, and there are no hungry sharks around, I might be very tempted to redescend to 15 ft for a few minutes to appease my Suunto....

:shocked2:

I think it is good you studied up on how these computers work, if you are intending to use them.....On the other hand, many of the best tech divers would never consider using a computer in anything other than guage mode, and much prefer the understanding of tables, ratio deco, etc.
Whether computer or tables, these are both statistical models, and are not necessarily directly related to YOU and the way YOU on-gas and off-gas. This is why understanding beyond just the manual of the computer can be of benefit.

Then again, if you are just doing normal recreational profiles, there is so much slop and fudge factor built in, that it can be quite a challenge to hurt yourself.

 

[RetroBlader]

On the other hand, many of the best tech divers would never consider using a computer in anything other than guage mode, and much prefer the understanding of tables, ratio deco, etc. [...] This is why understanding beyond just the manual of the computer can be of benefit.

Yes, I intend to pick up Deco for Diver at some point.
(Deeper into Diving costs quite a bit more, so will have to wait until later....)

Then again, if you are just doing normal recreational profiles, there is so much slop and fudge factor built in, that it can be quite a challenge to hurt yourself.

Having seen lots of rec divers (many with much more diving experience and/or certification levels than me) doing all kinds of "wrong" things, and still walked away from their mistakes with no apparent ill effect, I think you are right!

However, that should not stop me from trying to understand diving and becoming a better diver while dry, right?

:cool2: