Shaking the fizzy bottle ... ooo 000 OOO

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Shaking the fizzy bottle ... ooo 000 OOO

Postby Jason » Fri May 01, 2009 6:28 am

(taken from other thread)

I've been wondering about the possibility (after reading another thread and remembering some of the medical sections in dive Mags) of a Diver receiving the bends after a very conservative dive profile to 30metres with no strenuous activity involved. I know people still get bent after doing everything right and we are still unsure as to why ' :?: '. But this is a rare occurance I must add.
When asked by non-divers about such a thing as being 'bent', other than asked about sharks, us Divers mention that we take things slow when ascending becasue we have to offload the nitrogen in our explain it better - we do this 'like opening a fizzy bottle slowly' so the nitrogen bubbles don't enlarge as if out of control so to speak. The slower the ascent = the less bubbles are left to contend with until none at all.
But I can't help but think about that all important 5mtr Safety Stop for 3mins. Sometimes I've found myself at the 5m safety stop and there is a bit of a swell going so I've got to contend with a bobbing up and down safety stop. Now I've never experienced anything extreme - only a difference of just a few metres up or down when bobbing. But I do know that a few times of this I have emerged onto the boat not feeling the best - this though I have to consider I have a bias towards being motion sick anyway (can't even watch people on carnival rides without feeling a bit green in the gills :mrgreen: ). I do know though that there have been people who aren't as motion-sickness prone as me who have found themselves 'bobbing' at 5mtrs for 3 mins after a conservative dive, who have ended up slightly to mostly bent. Maybe dehydrates like alcohol might contribute, right down to the very popular coffee before a dive - but in the other thread, the person stated that they only drink water before diving.
:arrow: So I'm wondering if the safety-stop situation of bobbing up and down (with or without a rope or deco bar to hold onto) sort of 'shakes the bottle' up and somehow re-ignites the nitrogen bubbles in our system even if it is just a minor shake-up but enough to make a difference :?:
Just drifting along with whatever is current.
Currently I'm reading : The Art of Innovation by Tom Kelley.
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Re: Shaking the fizzy bottle ... ooo 000 OOO

Postby Andy » Fri May 01, 2009 6:55 am

A mildly informed opinion only, but yes.... any variation in stop depth is going to have a possible affecct on nitrogen bubbles in the body,

Whether it's measureable/discernable is a different question.

Again, just my opinion.... but if a metre or two variation at 5m is going to have an affect, then you're stopping too shallow (on a "normal" dive). I don't think the value of a 5m stop is really controlling bubbles, it's about stopping and hving control in the last 5m of the ascent.

Whilst controversial (in some senses), a good deep stop helps prevent bubbles forming (maybe).... you just need to find a definition of a "good deep stop", not so easy on the internet.
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Re: Shaking the fizzy bottle ... ooo 000 OOO

Postby ScubaDog » Fri May 01, 2009 9:23 pm

A safety stop is just that - to increase safety by remaining under 1.5bar (ish) of pressure for just a wee bit longer. A 4.5 - 7m stop for 3 - 5mins has been shown to decrease the risk of DCI in recreational diving - thats the consensus. But if the conditions are swelly, do the stop deeper or omit the stop altogether.

On deep stops - I think I remember reading that there is some slim evidence that they may in some circumstances increase DCS - go figure. Watched a DAN conference podcast with 5 experts and all give 5 different answers to the same question. To paraphrase somebody "never in the history of mankind, has so much, been said by so many, who know so little - the internet" And I include myself in this :-)

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