Building up to a deep dive

[John Touhig]

This question is really prompted by a documentary I saw last night on Nat. Geo. About a cave diving expedition in New Zealand. The two divers concerned were looking to push the depth limit in a cave system down to 75m on air. They spent the first week building up to the big dive. This got me thinking about the way we each approach our diving. Do you build up to a big dive, if so why?

One of things the program stated that there is no scientific evidence to back up the fact that you can build up a tolerance to narcosis by undertaking a number of progressively deeper build up dives.

I can see the benefit, especially at the start of a new season, to build depth progressively to refresh skills that might not have been used over the winter but is there any real physiological benefit? Or is it purely psychological?


John

[vulcan]

Originally Posted by John Touhig

One of things the program stated that there is no scientific evidence to back up the fact that you can build up a tolerance to narcosis by undertaking a number of progressively deeper build up dives.

Maybe it's just like there isn't scientific evidence for many things; Homeopathy is one, no scientific reason why it should work, but for some it appears to work, is that psychological?

I prefer to think it's to do with the fact we don't understand it YET. A hundred years ago we had little or no grasp of the physics/mechanics of DCS and what caused it, nowadays we can scientifically explain it. Maybe in the future there will be an explanation for why building up works.

I for one build up to a deeper dive, and if I have a lay off for any length of time, again, always start shallower. Call me old fashioned but touch wood, it's kept me out of harms way so far.

[Janos]

Don't get me started on the subject of homeopathy

But anyway, whether or not Narcosis is reduced by build-up dives, if you have done a series of build-up dives then your general diving skills are going to be that little bit sharper, and you are also going to be better practiced at dealing with the effects of Narcosis.

Janos

[nigelH]

Originally Posted by John Touhig

Do you build up to a big dive, if so why?

No.
Because I don't see an advantage.

I do regular skill practises but I don't let that dictate my diving schedule. I certainly would not add the risk of a deepish dive to a planned deep dive. I might break something on the build up and have to miss the one I want to do. I reason there is more risk being in the water for no reason.

Seasickness is another matter. I'll drive the boat and not even plan to get in the water because I know that that helps develop the sea-legs.

[NotDeadYet]

The events of the documentary, if its the one I'm thinking of, happened a few years ago before trimix was widely available/accepted.

I remember there was a study on how narcosis adaptation works. Their findings were not that your brain was getting used to it, instead they found it was more like what happens in stroke victims. Brain functions get routed through different pathways to avoid the narc'd bits, thereby making them slower, less capable of complex tasks and less efficient. Basically, your brain learns to switch into a downgraded mode.

To be honest, no I don't work up to deep dives. Trimix makes that unnecessary. Since I started diving on a rebreather, apart from <25m dives, I use mix all the time. I'd rather do 5 decent dives than 4 work up dives for 1 not very productive dive. 75m is fairly shallow/average for current trimix diving, it's pretty every day stuff.

My own experience is that if you eliminate narcosis then diving in 70m isn't much different to diving in 7m. Use a rebreather and you eliminate the other major factor, time pressure. So no, I don't do build up dives. I don't stop during the winter either so have never felt the need to work back into it.

[John Touhig]

Originally Posted by NotDeadYet

The events of the documentary, if its the one I'm thinking of, happened a few years ago before trimix was widely available/accepted.

Yes its the same one. The program suggested that the fact that one of the divers had only done 4 dives in the run up to the deep push could have been a factor in his drowning.

[Juz]

I think build up dives do help with narcosis, be it psychological or physiological I don't know. If nothing else, we know that stress makes narcosis worse and if you're only making a 5m jump then your personal stress level is likely to be much lower than if you were making a 25m jump.

I do tend to 'stay built up' tho by continuing 50+ m dives throughout the winter. I book onto lots expecting to get a few and I've had some great deep dives off the South Coast in Nov and Dec!

Failing that I would take to the lakes once every 3-4 weeks through the winter to keep my skills and kit up to speed.

Juz

[Narked@50]

Originally Posted by John Touhig

The two divers concerned were looking to push the depth limit in a cave system down to 75m on air.

For me this is just silly, especialy in a cave, hope they don't have kids.

Originally Posted by John Touhig

One of things the program stated that there is no scientific evidence to back up the fact that you can build up a tolerance to narcosis by undertaking a number of progressively deeper build up dives. John

I don't think you can build up a tolerance as such, but I think you can handle the effects better when you have experience of them.

So I only go to around 50m, and generaly practice a couple of 40-50m dives prior so my deco procedures are in place and I know what I'm doing.

James

[db8us]

It is the same with drunk driving.
If you are an alkoholic at least you do a "Bit" better.
That should not justify doing things in the first place.

[Tim Ingmire]

I'm with Juz on this one, knowing that you can do stuff helps to reduce anxiety and in turn reduces narcosis.