The ´Safety Stops´Debate.

[Mal Bridgeman]

Thanks for the views so far...

Safety stops a good for a number of reasons, all already covered, but divers must know enough theory to properly assess risk.

This is the point. I am not advocating wholesale that people abandon safety stops....just that divers should understand enough about what they are doing to realise the stop is optional and therefore under certain circumstances, like the ones I described, they might consider not doing them.

Doing the optional stop is an added level of safety which I think everyone advocates and supports ....but....it is not the case that missing a safety stop is somehow cavalier or wrong.

Rgrds
Mal

[MattS]

Mal, like so many things it comes down to assessing risk. Unfortunately deco is not a simple subject and you are not going to find simple rules. I certainly would not disagree with what you are teaching though.

Doing the optional stop is an added level of safety which I think everyone advocates and supports ....but....it is not the case that missing a safety stop is somehow cavalier or wrong.

This does depend on what you happen to think about bubble theory. The safety stop has nothing to do with the dissolved gas that the recreational tables/computers model, it is really about bubble control.

I am sure you must have done the cola bottle experiment to show how decompression works for dissolved gas. Well try it again but this time once you have opened the bottle, without getting cola all over you, pour the coke into a glass. Lets look at what happens. Removing the cap from the cola bottle proves that it is safe to ascend to atmospheric. But as you pour the cola into a glass, a froth forms which increases all the time you are pouring. The height of the froth depends on how fast you pour the cola, but the only way to stop the growth and prevent the froth overflowing the glass is to stop pouring. Now have a look at what is going on inside the froth - some of the smaller bubbles are joining with other smaller bubbles making bigger bubbles.

So here is a potential mechanism for a so called unearnt bend. Just like when pouring the cola, throughout an ascent bubbles are produced in the blood stream. The faster you ascend the faster these bubbles are produced. The further you ascend the greater the quantity of this micro-bubble 'froth'. Usually this froth is filtered by the lungs but if you ascend too far too fast you can overwhelm the lungs the same way a cola froth eventually overwhelms the glass by overflowing. The more of this froth that is about, the greater the chance of microbubbles coalescing into a bigger DCI provoking super bubble.

The theory is not as clear cut as I just made it but the research coming out of DAN is pointing at the above explanation as I understand it. It explains why bends can happen well within dissolved gas limits (coalescence) and how lung function is a factor in decompression. It also accounts for a super-slow ascent rate not reducing bubble growth to the same extent as a faster mean ascent rate with a brief stop. If this is the case then deep stops are simply safety stops for deco-divers.

So to summarise.

Missing a safety stop can be considered wrong as it is intended to control a completely separate process to the one which says you can make a direct ascent (dissolved gas). To be as affective as possible safety stops should be brief (3 minutes) and completed above 5m - otherwise they add to the dissolved gas problems on subsequent dives. Safety stops are a mandatory requirement for no decompression dives on some tables including the PADI RDP and Buhlmann. You can miss the 3 minute countdown on a Vyper without error but you will get penalised with shorter limits and longer stops on subsequent dives.

When deciding whether to forgo a safety stop, you have to think what the alternatives are. After regaining control subsequent to a rapid ascent, I would need a very compelling reason to miss a safety stop. If a diver was close to panic and was not calming down, I would ignore it. If I saw a diver shivering on a safety stop I would cut it to a minute - same applies for drifting away from surface cover - but I always carry a DSMB.

YMMV

[onthetrain]

very interesting thread. My policy is that I tend to do the safety stop even if not required. As someone mentioned earlier, in warm water it's a real pleasure pootling about for ages in shallow water watching the pretty fishies. I like watching the phosphouresance on UK night dives, but it aint much fun in no visible refernce dives where you have nothing to do but make faces at your buddy.

I think it's good practice to build in the safety margin. Obviously different tables & computers build in ever larger margins of safety. One of the guys in my branch worked out a spread sheet showing the differences and we worked out that on some computers you could miss 20 mins of stops and still be inside the BSAC 88 tables :-)

[Clare]

Now I'm straying into something I haven't before on this board - an opinion about diving - runs away and hides.

As I was the diver referred to who stopped for a safety stop when out of air at stoney, I thought it best if I clarify a few things.

First, I was not technically out of air, I switched to my buddy's air source when I felt the reg starting to be hard to draw on. I was aware when I started my ascent that air was tight and had already decided that if there were any problems in sharing air then I would kick for the surface from 6m if and when I felt resistance from the reg. I had not exceeded no decompression limits, nor had I exceeded a 10 meter ascent rate.

The fact that Steve and I were able to share air allowed us to maintain the stop for the full time allowed. You are absolutely right to suggest that it was not necessary - and this an option I was aware of throughout. As it was, I have discussed this with Steve and we both felt that it was useful for us to know that we had remained calm and in control throughout - making sensible and well considered decisions in the given circumstances.

For info, I breathed the reg down on the surface and there was probably about a minutes worth of air in it - far too close for comfort. Several valuable lessons learned on this dive - mainly if you are going to breath your cylinders down on a dive to do a weight check - don't cut it too fine

[dry suit diver]

I think Clare summed it up quite well , we were both aware that it wasnt completely neccesary but we did it to avoid the 'coke bottle' effect of smaller bubbles forming into larger bubbles.
A couple of further points ,at the depth we were at CESA was an option if my gas had run out which it didnt and was nowhere near to running out completely (100 bar at start of ascent and 60 Bar on exit).

As dives go it probably wasnt one of the best i have done but we learnt things from it and I was pleased to know that I stayed calm and did not panic which could have caused problems.

All comments on this thread have been taken on board and where appropriate, will be used in future.


The last Dive did need a stop as it was the last dive of a day with 20-25metre dives unfortunately my p!ss poor gas planning meant I had to cut it short.

[Janos]

Now I'm straying into something I haven't before on this board - an opinion about diving - runs away and hides.

As I was the diver referred to who stopped for a safety stop when out of air at stoney, I thought it best if I clarify a few things.

First, I was not technically out of air, I switched to my buddy's air source when I felt the reg starting to be hard to draw on. I was aware when I started my ascent that air was tight and had already decided that if there were any problems in sharing air then I would kick for the surface from 6m if and when I felt resistance from the reg. I had not exceeded no decompression limits, nor had I exceeded a 10 meter ascent rate.

The fact that Steve and I were able to share air allowed us to maintain the stop for the full time allowed. You are absolutely right to suggest that it was not necessary - and this an option I was aware of throughout. As it was, I have discussed this with Steve and we both felt that it was useful for us to know that we had remained calm and in control throughout - making sensible and well considered decisions in the given circumstances.

For info, I breathed the reg down on the surface and there was probably about a minutes worth of air in it - far too close for comfort. Several valuable lessons learned on this dive - mainly if you are going to breath your cylinders down on a dive to do a weight check - don't cut it too fine

I don't mean to come across all preachy, as
a) anyone who's dived with me knows what my in water skills are like
and
b) I made a similar mistake myself last year

But I think in your situation I would now skip the safety stop and get on the surface. Unless, you are really, really, really comfortable with the situation (and perhaps with the 6m shelf below you) then I would head straight to the surface. Read the incident reports and you will read several cases of people 'recovering' from a situation only to lose contact and for the casualty to sink back down (especially in an OOA situation as you can't inflate your suit / BCD) I can't recall a case where people died as a result of missing a safety stop.

Again, I really don't mean to be all preachy as I made a similar (what I believe to be) mistake early last year, and lost control of my buddy. Fortunately he went up not down. As I say: taught me a lot.

Laters,
Janos

PS - I personally wouldn't do a weight check at the end of a 20m-25m dive, but would instead do one in shallow water where there's no danger if something goes wrong.

Laters,
Janos

[dry suit diver]

I don't mean to come across all preachy, as
a) anyone who's dived with me knows what my in water skills are like
and
b) I made a similar mistake myself last year

But I think in your situation I would now skip the safety stop and get on the surface. Unless, you are really, really, really comfortable with the situation (and perhaps with the 6m shelf below you) then I would head straight to the surface. Read the incident reports and you will read several cases of people 'recovering' from a situation only to lose contact and for the casualty to sink back down (especially in an OOA situation as you can't inflate your suit / BCD) I can't recall a case where people died as a result of missing a safety stop.

Again, I really don't mean to be all preachy as I made a similar (what I believe to be) mistake early last year, and lost control of my buddy. Fortunately he went up not down. As I say: taught me a lot.

Laters,
Janos

PS - I personally wouldn't do a weight check at the end of a 20m-25m dive, but would instead do one in shallow water where there's no danger if something goes wrong.

Laters,
Janos

Janos , I dont feel you are being preachy at all and the last posting of mine shows that I had ample air left in the tank to inflate my BCD and support Clare whilst she orally inflated her wings bladder, just like they taught us on the OW course, no thinking about what to do, just doing it which pleased me because i always thought i wopuld panic in an emergency situation but didnt
We all make mistakes and as somebody once said to me ,the only bad mistakes to make are the ones where you dont learn from them.

[MattS]

We all make mistakes and as somebody once said to me ,the only bad mistakes to make are the ones where you dont learn from them.

I am a firm believer that if you walk away you did not do it wrong!

You have provided a very good justification for how you acted. You can feel comfortable about not being thought of as complete idiots. Now what would be really good is if you can come up with a couple things that could have been done better. This is harder than justifying what you did as you have to first admit that you did not act perfectly.

So we have established that you did not do anything wrong, but how could you have done things better?

[dry suit diver]

I am a firm believer that if you walk away you did not do it wrong!

You have provided a very good justification for how you acted. You can feel comfortable about not being thought of as complete idiots. Now what would be really good is if you can come up with a couple things that could have been done better. This is harder than justifying what you did as you have to first admit that you did not act perfectly.

So we have established that you did not do anything wrong, but how could you have done things better?

Better gas planning for my last dive , should have binned it but didnt and I am not going to slag off another buddy in public , on the board but Clare knows what went on on the last dive and suffice to say it was not Clares fault.
First dive is Clares call.

[Paul Oliver]

Thanks for the views so far...



This is the point. I am not advocating wholesale that people abandon safety stops....just that divers should understand enough about what they are doing to realise the stop is optional and therefore under certain circumstances, like the ones I described, they might consider not doing them.

Doing the optional stop is an added level of safety which I think everyone advocates and supports ....but....it is not the case that missing a safety stop is somehow cavalier or wrong.

Rgrds
Mal

Hi Mal

A very good thread and a point of view i very much support, we see with the scenarios and events that are covered that you have to make decisions based on THAT SPECIFIC DIVE, Janos, Gledders and Dry Suit have all learned lots and i think their experiences and the fact they are prepared to talk about them and review their actions is top stuff and a learning curve for everyone, not just them.

Mark's point on "How could we have done it better" is also very relevant and something that should never be omitted from a Dive or Incident review. I do this on a regular basis (not quite every dive) and their is always something to do better.

Again, top thread Mal.