Is there any scientific evidence that safety stop decrease DCS risks?

[shurite7]

Dear all,

I've been searching for awhile but can't find any study or paper for this question. Could any one provide any reference for me?

My questions are...
3. Does anyone know why do we choose 3 meter / 5 meter (or maybe 6) as the depth for safety stop but not 7 or 8 meter? Is there any reason or story behind this? Or is it just a magic number?

Go to 53:05 in the below video that has a short answer to a question pertaining to safety stops.

The speaker does mention the SAFE program. I briefly scanned the material sometime back, but cannot find it or remember where I saw it. If anyone has a link or URL, everyone will be greatfull for the posting.

 

[BoltSnap]

I'm not a decompression scientist, but my understanding of the reasoning behind the safety stop is that it's an operational speed bump rather than any sort of calculated decompression advantage.

This is it!

 

[TMHeimer]

I'll add nothing to what previous experienced folks here have said. I do think it's interesting that from what I recall, the standard safety stop used to be at 10 feet and was changed to 15' (as pointed out) to keep the diver clear of boats and away from surge. My thought is if 10 feet was the optimal depth, that's what we really should do. Similarly, in the CPR (EFR) course they changed chest compressions to rescue breaths ratio to 30:2 for everyone, as opposed to 15:2 or 30:2 depending on whether the patient is an adult or child (I have no idea what it is now, probably changed again). This apparently was done to make it easier for the layman to remember. Probably not a real good reason.

 

[dmaziuk]

2. Allow me to re-phrase my question, if there is a time machine that I could go back to ask Haldane if safety stop helps, I thought he would say "no" because he didn't consider bubble formation during ascending. (Right...?)

But if you asked him where you should make a stop coming up from a 20-something-meter dive, he would've said 5-6 metres.

 

[Pinecube]

I'm not sure it was mentioned but I recall reading about studies done specifically on safety stops in Mark Powell's book Deco for Divers. I don't recall if the source of those studies was cited or not. The studies found that even short stops significantly reduced the amount (or was it size?) of bubbles found in divers once they reached the surface vs divers that ascended directly to the surface.
It has been a while though, I need to find where I put that book.

Similarly, in the CPR (EFR) course they changed chest compressions to rescue breaths ratio to 30:2 for everyone, as opposed to 15:2 or 30:2 depending on whether the patient is an adult or child (I have no idea what it is now, probably changed again). This apparently was done to make it easier for the layman to remember.

As an aside, the reason I was given for the 30:2 compression/breaths was that "they" (I didn't ask, I assume it's the CPR gods) found that people were taking too much time in between compression and breaths resulting in less effective CPR.

 

[doctormike]

As an aside, the reason I was given for the 30:2 compression/breaths was that "they" (I didn't ask, I assume it's the CPR gods) found that people were taking too much time in between compression and breaths resulting in less effective CPR.

 

[RyanT]

I'm not sure it was mentioned but I recall reading about studies done specifically on safety stops in Mark Powell's book Deco for Divers. I don't recall if the source of those studies was cited or not. The studies found that even short stops significantly reduced the amount (or was it size?) of bubbles found in divers once they reached the surface vs divers that ascended directly to the surface.
It has been a while though, I need to find where I put that book.

@Pinecube, you are correct. Powell provides a nice graphic to show the influence of safety stops on reducing bubble formation. I'm sitting here with the book though, and unfortunately, it's unclear what study he references. He provides a bibliography for each chapter, but doesn't make it clear which study generated the information for the graph.

 

[Sol518]

As an aside, the reason I was given for the 30:2 compression/breaths was that "they" (I didn't ask, I assume it's the CPR gods) found that people were taking too much time in between compression and breaths resulting in less effective CPR.

The deeper explanation to that is that during the pause for breaths the blood pressure would drop and it would take some compressions to build it back up the a level that was high enough to actually circulate the oxygenated blood to the body.

With fewer pauses in the compressions, there are more compressions that are effectively circulating oxygen to the brain and other vital organs.

 

[bada3003]

Dear all,

I've been searching for awhile but can't find any study or paper for this question. Could any one provide any reference for me?

My questions are...
1. Is there any experiment trying to compare the risk of DCS with and without safety stop? Or we all just assume that safety stop would help improve safety "theoretically"?

2. According to Haldane's decompression model, it would consider that it is better to dive without safety stop because divers should increase gradient between tissue pressure and ambient pressure for better off-gasing. Is that assumption correct?

3. Does anyone know why do we choose 3 meter / 5 meter (or maybe 6) as the depth for safety stop but not 7 or 8 meter? Is there any reason or story behind this? Or is it just a magic number?

The best "safety stop" is to very gradually ascend throughout the water column. That includes the last few feet where pressure differential is the highest. A safety stop is a rough approximation since ascending in such gradual manner is not always practical. If conditions allow, I always try to spend 10 minutes or so ascending from 10 feet before surfacing. Many people rush to the surface after one's dive computer clears the safety stop.

 

[doctormike]

If conditions allow, I always try to spend 10 minutes or so ascending from 10 feet before surfacing. Many people rush to the surface after one's dive computer clears the safety stop.

Wow, that sounds really dull! I think that there is a sweet spot between "rushing to the surface" and 1 FPM...