Adding to a safety stop

[Doppler]

...

But then again spreading grape jelly on your mirror keeps elephants out of your bedroom.

Yep, that about sums up the situation regarding ways to keep DCS at bay.

Sounds like you already have a good handle on things.

No need to make your life too complicated judging by the profiles you are diving. Would suggest slowing your ascent to about 3 metres per minute for the last six metres of your travel to that safety stop, hanging there for those extra few minutes, and then a very slow final ascent back to the surface.


All the best.

 

[Diver0001]

Hi,

Looking at the deco tables, if you just go over the NDL, it looks like you have a 2 or 3 min stop at 10ft.

I'm in good physical condition, but my age is 56. I've never had any issues with DCS, and I never get real close or go over the NDL. Recreational diving only.

My question is: If I do my 3 min safety stop, at 15-20ft, and then hang at 10 for another 2, am I doing anything meaningful to reduce any chance of DCS similar to an increased "safety factor", or am I just wasting time? I usually have plenty of air left.

Thanks!

At 6m and shallower in a recreational context you can extend your safety stop indefinitely without *increasing* your risk of DCS. Therefore, the obvious conclusion is that 3min is a minimum recommended time, not a maximum time. There is no practical maximum time. If you want to stay longer for whatever reason, go for it.

As for whether or not it will *decrease* your DCS risk, I'm not sure. My assumption is that if 3min helps then 5min will help at least as much. This is obviously a game of diminishing returns.

R..

 

[igor p]

igor,

I think we might be misunderstanding one another. If you perform a deep stop and the computer adds decompression on the shallow end, it's telling you that you have taken on inert gas at your deep stop, which is defeating the purpose. Am I reading your post correctly?

Best regards,
DDM

Hi DDM,

Yes you understood correctely.
If the deep stop will be of correct length nearly no shallow time will be added - not seen on your computer.On the other side you need to know any time under water ongasses some tissue. If not other the slowest one usualy ongass even on 3 m stop. So any additions do ongas additionaly some tissue.
At the deep stop some (fast) tissue offgas and some (slower) tissue ongas.

Adding deep stops does cost more shallow time usualy. Correct are very short deep stops that do not add much to shallow time.

If this is defeating the purpose I do not want to judge. For me more safety is not. I think it is not the purpose to exit water fast but safe.
So addind deep stop and if necesary some time shallow and being safer I think is not defeating the purpose.

Sure, here we went out of topics, that was adding or not some time to safety stop. I would agree with Steve and what he wrote - so yes, why not.

Best

Igor P

Sorry for typing errors. Sent from my PAP4500DUO using Tapatalk 2

 

[Duke Dive Medicine]

Hi DDM,

Yes you understood correctely.
If not other the slowest one usualy ongass even on 3 m stop. So any additions do ongas additionaly some tissue.
At the deep stop some (fast) tissue offgas and some (slower) tissue ongas.

I don't know that you can generalize like that. Are you assuming the tissues are in series?

Best regards,
DDM

 

[doctormike]

Correct are very short deep stops that do not add much to shallow time.

If this is defeating the purpose I do not want to judge. For me more safety is not. I think it is not the purpose to exit water fast but safe.
So addind deep stop and if necesary some time shallow and being safer I think is not defeating the purpose.

Sure, here we went out of topics, that was adding or not some time to safety stop. I would agree with Steve and what he wrote - so yes, why not.

Yes, it is a bit off topic, but lots of new divers read these threads, so it's probably worthwhile to address the topic of deep stops a bit, since it was brought up and differing opinions were offered.

I think that you are saying that you advocate deep stops, but short ones so that don't add much to the overall required decompression time (correct me if I am wrong). Of course, if you are adding a stop that actually increases the time that your computer says that you need to spend underwater, then by definition you are doing a staged decompression dive, so the new divers should understand that.

Are you stating that a good general approach to a staged deco dive is to add a deep stop to your planned profile, but a short one that only adds a little to your run time because you feel that this will reduce the risk of DCS? Or more accurately, reduce bubble formation, since the actual risk of DCS is so low that you need very large study populations to see a difference in DCS rates. I don't think thats a well established protocol.

 

[igor p]

From theory of saturation and desaturation of tissue, the tissue ongass when its inert partial pressure in tissue is lower than inert partial pressure in inhalled gass and offgas when the partial pressure of inerts in tissue is higher than partial pressure of inerts in inhaled gas.

So based on this you can know that ascending and arriving at certain stop slowest tissue will probably not jet ongass enought for inerts partial pressure to be higher than prartial pressure of interts in inhaled gas so it will be still ongassing, and fast tissue will probably be offgassing as its partial pressure of inerts will probably still be higher than the partial pressure of inerts in inhalled gas.

Tissue are not in series but in paralel based on Haldane decompression theory.

Sorry for my bad english, as it is not my mother language!

Best regards,

Igor P

---------- Post added March 13th, 2015 at 06:42 AM ----------

Hi DrMike,

I think you understood most of what I wrote correct. But only with a difference that I do advocate using software to plan staged decompession and not ad hoc adding stops. Or if you add addhoc some sort of stop you need to folow tha computer you use so that if you added too much time it tells you that you need to stop in shallows too.

Deep stop decompression strategies is not adding deep stops and shortening shalow sops, but if adding deep stops account for possible prolonged ongassing and adding shallow stop time if needed too. Usualy the comercial software does this, or if folowing computer adding a stop computer will account for it and add shalow time if necesary.

Adding deep stops as writen in DAN Study does relax fast tissue and lower supersaturation at depth, that lowers probably risk for spinal cord DCS, but sure we must not forget we still ongas some tissue at the deep stop so longer decompression times in total (shalow too) are required.

NEDU study did completely contrary. It shifted shalow time to deeper deepth and did not account acordingly for added ongassing with added shalow stop time. Sure there were other stressors used to generate correct circumstances that those changes showed in DCS exits.

This is my opignion on the study.

Best regards,

Igor P

 

[doctormike]

Hi DrMike,

I think you understood most of what I wrote correct. But only with a difference that I do advocate using software to plan staged decompession and not ad hoc adding stops. Or if you add addhoc some sort of stop you need to folow tha computer you use so that if you added too much time it tells you that you need to stop in shallows too.

Deep stop decompression strategies is not adding deep stops and shortening shalow sops, but if adding deep stops account for possible prolonged ongassing and adding shallow stop time if needed too. Usualy the comercial software does this, or if folowing computer adding a stop computer will account for it and add shalow time if necesary.

Adding deep stops as writen in DAN Study does relax fast tissue and lower supersaturation at depth, that lowers probably risk for spinal cord DCS, but sure we must not forget we still ongas some tissue at the deep stop so longer decompression times in total (shalow too) are required.

NEDU study did completely contrary. It shifted shalow time to deeper deepth and did not account acordingly for added ongassing with added shalow stop time. Sure there were other stressors used to generate correct circumstances that those changes showed in DCS exits.

This is my opignion on the study.

Best regards,

Igor P

Got it, I guess that's why it's controversial - very hard to get consistent data with large study groups that can be applied to a variety of dive profiles. It sounds like you are very well versed in this field. Me, I defer to DDM!

There is so much that goes into the actual risk of clinical DCS, that people who do get bent don't always have obvious profile violations (as in my own case). The human bell curve is also why there isn't always a direct correlation between bubble formation and clinical symptoms. Truly a bright line through a grey area.

I just think that it's important that new divers understand why there is a controversy, and don't just assume that doing a Pyle stop is automatically giving them a margin of safety in any given dive profile. Many new divers don't really think about ongassing, and it's not until they start tech training that they start internalizing concept of run time and the need to get off the bottom in an expeditious fashion according to plan.

 

[igor p]

Got it, I guess that's why it's controversial - very hard to get consistent data with large study groups that can be applied to a variety of dive profiles. It sounds like you are very well versed in this field. Me, I defer to DDM!

There is so much that goes into the actual risk of clinical DCS, that people who do get bent don't always have obvious profile violations (as in my own case). The human bell curve is also why there isn't always a direct correlation between bubble formation and clinical symptoms. Truly a bright line through a grey area.

I just think that it's important that new divers understand why there is a controversy, and don't just assume that doing a Pyle stop is automatically giving them a margin of safety in any given dive profile. Many new divers don't really think about ongassing, and it's not until they start tech training that they start internalizing concept of run time and the need to get off the bottom in an expeditious fashion according to plan.

Hi DrMike,

Thanks for compliment.

I agree with all you wrote. There is truly a lot of unknown in decompression science.

Lot of cases of undeserved hits are even more adding to controversy.

Sure I would advise new divers to do some research and reading about deco theory or consult their instructors before puting in practice internet advices on decompression.

Igor P

Sent from my PAP4500DUO using Tapatalk 2

 

[NAM001]

My gut feeling is that in that situation you will have a required stop as opposed to an optional/safety stop. I would expect that if you did the safety stop at 20' the 10 ft stop requirement might clear, depending how far past ndl you got. No matter what the logic used to require a SAFETY stop it is still a safety stop and can be skipped. So again the observance of the safety stop may clear the 10' 2-3 min obligated stop. Some things to look at is other dive tables. They may not have you in a past ndl situation. If you are diving with a computer and you pass, per the tables, the ndl line what does your puter say. so many algorithms and gradients and conservative factors are out there. Bottom line is that as long as you have gas and favorable water a few minutes extra is no foul.

Hi,

Looking at the deco tables, if you just go over the NDL, it looks like you have a 2 or 3 min stop at 10ft.

I'm in good physical condition, but my age is 56. I've never had any issues with DCS, and I never get real close or go over the NDL. Recreational diving only.

My question is: If I do my 3 min safety stop, at 15-20ft, and then hang at 10 for another 2, am I doing anything meaningful to reduce any chance of DCS similar to an increased "safety factor", or am I just wasting time? I usually have plenty of air left.

Thanks!

 

[Freewillow]

Good idea, the longer @ 10/15 feet the better. BUT Make sure you do not go up from this depth too fast. Otherwise, you got it right