What if miss a required safety stop?

[AJ]

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

No worries, I update when new software is released. I've been in IT for more than 20 years, I know how important updating software is.

 

[The Chairman]

Another great discussion. My response may surprise some people... and the caveat is: I live in the Keys.

Let me preface this by saying I don't do three minute safetystops. Mine are a minimum of five. I feel better and never feel sluggish afterwards. Longer is better in this case.

If I miss a safety stop, even after being down a hundred foot or more, I'm going back in as soon as I can. The best thing about living in the Keys, is that almost without fail, the next dive can be done at 20 to 25 ft. However, I can only remember this happening once in the last decade... I don't think it happened much before that either. I was on the Duane and was riding the NDL up. I was solo diving, had plenty of gas and a bottle of O2 slung as well. My truck had been stolen and so I was without my hat. Unfortunately, we had the invasion of the moon jellies that morning. They were mostly in the 10-15 ft zone, so I planted myself on the down line at 20 ft. Then I got hit by one on the left side of my face and moved away only to get a rather large wrap around my right ear. My safe spot was no longer safe. The next dive was ten minutes away on Crocker reef. Nice and shallow and the reef blocked the plethora of moon jellies.

 

[Jamesdclxxv]

I can see where the confusion comes from. The padi rdp states that a safety stop is required any time the diver comes up to or within 3 pressure groups of a ndl and for any dive to a depth of 30m or deeper. This seems to be in contrast to the open water course material which defines a no stop or no decompression dive as a dive that if necessary a diver could ascend directly to the surface without unacceptable risk of dcs.

However this note on safety stops seems to clear it up;

A safety stop is not required to be within the limits of most dive computers or tables decompression models. You make the stop as a prudent, conservative diver to remain well within your dive computer or table limits. A few computers and tables have a "required" safety stop. With these, because you a nearing the limits, they call it "required" to put more importance on being conservative.

 

[boulderjohn]

I can see where the confusion comes from. The padi rdp states that a safety stop is required any time the diver comes up to or within 3 pressure groups of a ndl and for any dive to a depth of 30m or deeper. This seems to be in contrast to the open water course material which defines a no stop or no decompression dive as a dive that if necessary a diver could ascend directly to the surface without unacceptable risk of dcs.

However this note on safety stops seems to clear it up;

This issue comes up on ScubaBoard regularly--how can an "optional" safety stop be "required"?

If you understand what is really meant by it, and if you try to come up with simple, clear language that explains it, you will see the problem with coming up with the right words.

There are no clear cut bright lines in diving, in part because of the limits of research and in part because we are all different people with different physical characteristics. When it comes to ascent profiles, there is a range of possibilities, and that range passes through the following levels at imprecise moments:

1. Shallow and short dives that allow immediate access to the surface with virtually no possibility of decompression sickness.
2. A bit deeper and longer--you should probably do a safety stop just to be extra sure you are going to be fine.
3. Deeper and longer still--you really should do a stop be safe--seriously.
4. You are now into mandatory decompression stops--if you don't do the stops, you are really rolling the dice.
5. If you don't do the stops, you are probably going to get DCS.
6. No stops? You are screwed!

Steps 4-6 are technical diving. Steps 1-3 are recreational diving.

 

[Neilwood]

This issue comes up on ScubaBoard regularly--how can an "optional" safety stop be "required"?

If you understand what is really meant by it, and if you try to come up with simple, clear language that explains it, you will see the problem with coming up with the right words.

There are no clear cut bright lines in diving, in part because of the limits of research and in part because we are all different people with different physical characteristics. When it comes to ascent profiles, there is a range of possibilities, and that range passes through the following levels at imprecise moments:

1. Shallow and short dives that allow immediate access to the surface with virtually no possibility of decompression sickness.
2. A bit deeper and longer--you should probably do a safety stop just to be extra sure you are going to be fine.
3. Deeper and longer still--you really should do a stop be safe--seriously.
4. You are now into mandatory decompression stops--if you don't do the stops, you are really rolling the dice.
5. If you don't do the stops, you are probably going to get DCS.
6. No stops? You are screwed!

Steps 4-6 are technical diving. Steps 1-3 are recreational diving.

Quite a good way of describing this

 

[nohappy]

I think they should use "strongly suggested" instead of "required".

 

[Trace Malinowski]

The newer you are to the sport of diving and the farther down the rungs on the certification ladder, the more you should error on the side of caution. When in doubt don't dive. As your knowledge and skills grow, the more you'll be able to understand your predicament, safe ascent strategy, and physical response to time, depth, and stops (suggested or mandatory).

DAN actually once told me to take 2 aspirin and dive deeper when I had decompression stress as the training director of an agency. They admitted they would have chambered an open water diver with like symptoms.

 

[Neilwood]

The newer you are to the sport of diving and the farther down the rungs on the certification ladder, the more you should error on the side of caution. When in doubt don't dive. As your knowledge and skills grow, the more you'll be able to understand your predicament, safe ascent strategy, and physical response to time, depth, and stops (suggested or mandatory).

DAN actually once told me to take 2 aspirin and dive deeper when I had decompression stress as the training director of an agency. They admitted they would have chambered an open water diver with like symptoms.

I think it is worth expanding on this to the point that with more experience you are in a better place to know what your body is likely to feel like after similar dives therefore you know and feel anything out of the ordinary so are in more of a position to determine how "stressed" your body is (or is likely to be) for a particular dive and how carefully you need to take things.

Examples (based on a diver that is paying attention to their body and how they feel - which is something that all of us as divers should do pre, during and post dive):
1) New diver with limited dive count - feels tired and sore after every dive due to excitement and not being used to the equipment/workload but doesn't know how much of that tired feeling is decompression stress and how much is just tiredness. They need to stick to established procedures like glue (they are the unknown/unknowns) and dive conservatively.
2) Diver with a few hundred dives of various types - can better gauge how tired they should be after a particular dive so they know better how decompression stress affects them (known unknowns)
3) Divers with thousands of dives of various types - can fairly accurately determine how close they are to decompression stress on any particular dive and therefore decide on how they might change their dive profiles for future. They know the level of tiredness and or aches is/isn't normal for them so can react accordingly. They can use this to increase/decrease their conservatism or gradient factors accordingly.

Even with the experience there is always the chance of an "undeserved" hit where the diver is well within the "safe" profile but still gets DCS. This might be down to specific issues that day (dehydration, fitness, heat etc) or some underlying physical issue (undiagnosed PFO).

Using @boulderjohn 's scale, by the time you get to 3, you really SHOULD be doing a stop no matter what your computer tells you - even if it is not "mandatory". When you get to 4, you are taking big chances. By 5, you are playing at a casino where the house have loaded the dice against you and by 6 you are pretty much playing Russian roulette with a fully loaded pistol.

 

[DiverDownD3]

I think they should use "strongly suggested" instead of "required".

Funny you say that. I'm sitting in a review this week for a flight manual and we will spend 10-20 minutes arguing over how one sentence should be worded

 

[Gareth J]

As I think has been stated already.

1. The decompression profile is 'safe' without the safety stop [1]
2. Safety stops significantly improve the 'safe' profile, reducing sub-clinical DCI, therefore reducing the risk of DCI..
3. Completing a no-stop dive and missing the safety stop on a computer that 'recommends' a safety stop will result in the computer being more punitive on subsequent dives (done inside the off gassing window). [2]
4. In 3. above, it is safe to continue to dive, but the computer will be 'punishing you' for missing the safety stop by reducing subsequent NDL time.
5. Missing a 'compulsory' decompression stop will (on a recreational) dive computer, result in a lockout for 24hours. There is now a risk of dci, the amount of risk is proportional to the violation. Missing 1 min of compulsory decompression is unlikely to result in dci, missing 20 minutes of dci is very likely to result in dci!
6. Following the dive computer (or table), completing all safety stops, and ascending at the correct ascent rate is NOT a guarantee that you won't get DCI. The risk is just very low (acceptable?).
7. Padding the stop is a trick used by a lot of divers (e.g. The Chairman).[3] This is the act of adding additional decompression time to a known stop. The only issue here is padding the deeper stops increase the required time on the shallower stops and can be counter productive. However, I do think padding the shallower stop is often a good idea if conditions allow, and is obviously adding 'safety' to the profile. I will do this if I have adverse conditions during the dive, i.e. workload, stress, etc.

One of the reasons 'safety stops' are now very popular, is that it has the effect of slowing the divers ascent down. i.e. a new diver with poor buoyancy control will at least attempt to arrest the ascent to complete the safety stop.
The biggest pressure differential is that last 6m. Slowing the ascent during this part of the ascent is going to reduce the risk of DCI. Some tables state two ascent rates (i.e BSAC88's) which give an ascent rate of 15m/min to 6m or the first stop depth, then 6m/min to the surface.
Staged (fixed) depth decompression stops are a product of practicality. It was much easier to winch a diver up to a specified depth, leave him suspended there, and then winch him to a new specified depth, than attempt a sliding ascent rate dependent on of gassing. This goes back to Haldane and his original tables I believe (1908).

Gareth

[1] Safe is a subjective issue. There is always a risk
[2] If you wait long enough the computer will assume you have fully off gased and assume a new series of dives. i.e. the 24hours that a table will normally state.
[3] Padding stops on a computer, because the computer compensates if any additional decompression is subsequently required on a shallower stop. Padding a stop on a hard table is only possible at the last stop.