What if miss a required safety stop?

[Miyaru]

.....but my question is that what if i accidentally exceed 30m in a dive (say 31m) and I also miss safety stop as PADI RDP required (but I'm not in deco), what should I do after the dive?
....

The only thing that happens when you go deeper, is that your NDL becomes shorter.

If you miss a safety stop, you off-gassed less nitrogen at the ideal depth. The RDP is based on surfacing without a safety stop (above 30m). With a safety stop, the SI for your next dive is probably shorter, but there's no reliable data to support this, so stick to the table. Diving the near limit of the RDP (greyed and black boxes) strongly recommends a safety stop.

PADI does a fair job in explaining the theory about NDL in recreational diving, but I always spend an extra hour of theory during the Open Water course on this subject.
Exceeding the NDL does not harm you, nor does exceeding the maximum depth for recreational diving.
Not knowing what to do if this happens, is what might get you injured.

Getting entangled at +30m/+100ft could result in exceeding your NDL, getting caught in a downcurrent might take you deeper than you planned.

In the first case, the guideline of staying 8 minutes at 5m (less than 5 minutes exceeding the NDL) and 15 minutes at 5m (more than 5 minutes exceeding the NDL) should in general be save enough to get you healthy back to the surface. Use the advised time on the surface of 6 or 24 hours to check for any signs and symptoms of dcs.

In the second case, the RDP won't help you unless you put it in your bcd and you can check during the dive how much shorter your NDL has become.
The RDP does not go beyond 42m. At that depth, you only have 8 minutes bottom time and you used 2 or 3 minutes to descend to that depth. Going deeper means less time and will inevitably result in a deco obligation. To dive safely beyond the recreational depth, you need additional knowledge. And a good instructor!

Computers have become fairly cheap over the last decade. The manual will tell you what your computer will do in case you exceed the NDL. Read it! And understand it.
An ascent time of 9 minutes with a ceiling of 3m does not mean go immediately to 3m and stay there for 9 minutes. There's a difference between ascent time and stop time.


Just ask yourself - if you are often diving near or on the recreational limits, why not extend your knowledge and skills?

 

[rhwestfall]

There is no such thing as a "required safety stop". It is either "required", as in the case of exceeding NDL and having to do staged decompression, or a "safety stop" where a cushion is put into place as theory on what is happening is still not really known to be accurate and the physiology of divers is significantly different as a whole group than the original "Navy Diver"..

The words that are put into play are purely "legal-ease", and as such insulate the agency.....

If using a PDC, it likely should account for this, as well as your SI to give you a plan for your next dive. If on tables, I'd likely add a little padding in my next plan. There are multiple ways to do this.

YMMV

 

[Neilwood]

I have to agree with the people suggesting a read of Mark Powells book "Deco for Divers" - really sheds a lot of light on what is really a murky subject (even the deco professionals agree that they don't fully understand deco). What deco theory as it stands at the moment is a best guess which fits most people (no guarantees of not getting bent even if you do follow it 100%). The adage of measure with a micrometer, mark with chalk and cut with an axe comes to mind. Your computer will come up with an exact NDL/deco schedule but how close it is to your DCS limits are on that particular day, no-one actually knows (unless you happen to be part of a clinical trial in DCS).

With that in mind, I would suggest that a blown safety stop should not be a huge issue however that comes with a few caveats:
1) The ascent rates to me are almost as important as the stop - too fast and you go outside the model you are using (be it PADI RDP, SSI, RGBM, VPM-B etc).
2) If you blow the stop, keep a close eye on your health and advise others to keep an eye on you as well. If you feel any symptoms of DCS, get treatment asap. If you feel unusually tired, extend your SI accordingly ( unusual tiredness might be a sign of nonclinical DCS).

 

[boulderjohn]

What if your computer does not do safety stops like Shearwater Petrel 1?

This will sound like I am quibbling over language, but I actually have a serious point: no computer does safety stops; safety stops are done by divers.

At the end of a dive on which you want to do a safety stop, you arrive at that depth and then do a 3 minute stop or a 5 minute stop or whatever your heart contents. If you are old school, diving with a watch and tables, you look at your watch and count off minutes. If you are using a computer, you will find that some computers are programmed to count down a 3 minute stop, and other computers don't do that and instead have you count off the number of minutes you want on your own, as if you were using a watch.

It's not up to the computer--it's up to you.

 

[kelemvor]

What if your computer does not do safety stops like Shearwater Petrel 1? Am I in violation or can I dive again that day? Furthermore, on several occasions different computers gave different advice on safety stops in my teams. What to do then?

I prefer to base my descion on tables, knowledge and agreed deco strategy within my team. Not relying on computers with very different often unknown algorithm's. So would I be worried if my computer complains about a missed safety stop? Nope, I have a plan when I dive.

Eh? My petrel 1 handles optional safety stops. It says the words "Safety stop" right on the screen and starts the countdown that I configured it to use for a safety stop.

Maybe you need a firmware upgrade or something.

Also, shearwater leaves the "can I dive again later that day" up to the diver. You can if you want, and the computer will calculate nitrogen loading on your subsequent dives - including any needed decompression stops that might result from your decision. There really is no "can't dive", it just might be a deco dive rather than a no deco dive. What it doesn't do is "lock out" so that if you decide to do a subsequent dive you're left guessing. Better to have the computer assist with calculations when they start to get harder rather than give up on you.

In my ow classes, safety stops were always called "optional safety stops" which in my opinion is far less ambiguous. It's optional. If it's not an optional stop then it's a decompression stop rather than a safety stop. Those were called mandatory decompression stops. Having different kinds of safety stops seems like a recipe for confused divers. That said, I'm no instructor.. it just seems like a bad way to describe the things to me.

 

[boulderjohn]

Eh? My petrel 1 handles optional safety stops. It says the words "Safety stop" right on the screen and starts the countdown that I configured it to use for a safety stop.

I think it is possible that the Petrel 1's did not originally come with a recreational mode, so it is possible you may need a firmware update. That countdown will also not appear if you have it in technical diving mode. I go back and forth between technical diving and recreational diving, and I don't bother putting it in recreational mode. I figure that as old and addled as my brain may be, I can still do the math it takes to add three minutes to the time when I arrived at the stop.

 

[AJ]

This will sound like I am quibbling over language, but I actually have a serious point: no computer does safety stops; safety stops are done by divers.

Exactly what I wanted to point out. It's the diver who is ultimately in control, not the computer. At least it should be that way.

Eh? My petrel 1 handles optional safety stops. ....Maybe you need a firmware upgrade or something.

No upgrade required, I run my Petrel in Tech mode. It gives advice about deep stops, but no safety stops. It's fine with me. I know how to ascend properly in a controlled manner doing more stops than just one safety stop.

 

[boulderjohn]

No upgrade required,

Just as an FYI, if you have not upgraded the firmware, you should. There were some flaws that have been fixed.

 

[Lorenzoid]

Is my recollection correct that the "standard" 3 minute safety stop has its origins in a study in which participants did different stops at different depths, and bubbles in the blood were measured by Doppler ultrasound? It might have been in conjunction with ascent rate, too. If I recall, they decided that a 3-minute safety stop achieved a good balance between time and bubbles.

 

[boulderjohn]

Is my recollection correct that the "standard" 3 minute safety stop has its origins in a study in which participants did different stops at different depths, and bubbles in the blood were measured by Doppler ultrasound? It might have been in conjunction with ascent rate, too. If I recall, they decided that a 3-minute safety stop achieved a good balance between time and bubbles.

I am quite sure you are talking about a study published (I think) in 2002 by a man named Morroni. (I may have misspelled it--going from memory.) Your description matches what he did. He compared both ascent rates and safety stops, determining that safety stops were more important than ascent rates.

This was, however, well after safety stops had been established parts of recreational diving. The PADI study that led to the RDP and included safety stops was done in the early 1980s, and it, too, used Doppler bubble imaging.