Air v's trimix

[richieoflynn]

Hi everyone,

Let me just start by saying I'm not tech trained or have I ever dived trimix so to those who know, this is probably a straight forward question. I saw advertised in Ireland a dive being organised for people who dive twinsets on air to go to a wreck in 55m.

I put some figures through V planner to see what kind of deco profiles I would get by using air with 50% and 100% O2 for deco mix and 18/45 with the same deco mixes.

I got the 18/45 as being the GUE standard mix for this type of dive from this forum. Is this correct ?

The main question I have is that appart from the obvious benifit of breathing helium to reduce narcosis, why are the deco profiles and in water times very similar ? My thinking was that if some of the nitrogen was replaced by helium then the deco profile would be shorter. Does helium have similar off gassing properties as nitrogen ? Can somebody please explain this to me

Thanks,

Richie.

[Rob Dobson]

Narcosis is the reason for using 18/45 in that range, not the deco obligation.

Helium on gasses much quicker than nitrogen but it off gases quicker too. So your deep stops become more important.

Overall the times may be similar but the stops would be in different places as the profile would be a different shape.

If you're looking at doing this sort of thing then don't try and learn it on the internet; find a good instructor and do the training.

Dive safe.

[david_1]

Quote: (Originally Posted by richieoflynn)

a dive being organised for people who dive twinsets on air to go to a wreck in 55m.

55 meters on air in clear warm water might of been considered ok in the past.
but 55 meters inside a wreck in our green cold water is never going to be fun let alone very safe....

[Jack]

Richie, as Rob said, the profile would be different with an S curve. Deeper stops and more than on air.IMHO its a non runner air to that depth. Air is for tyres!! I know :D
ps. decoplanner is worth the money.

[richieoflynn]

Hi lads,

Thanks for the info.

Rob & Dave : Don't worry, I'm not trying to find out how to do this on the internet. Hopefully, I'll be continuing my training the GUE way and with a bit of luck get to do Tech 1 this year. I remember (just about) doing a dive to 48m on air a couple of years ago and lets just say it was an eye opener. I've made some serious decisions with my diving since then, one is never to dive deep air again. To be honest, I don't understand why anyone would want to do it but hey, you can't tell some people.

Jack : Thanks also and thanks for the pm. I will certainly get a copy of decoplanner.

Thanks lads,

Richie.

[lizardland]

For a lot of people, a 55m wreck on air is an acceptable proposition because a 55m wreck will probably mean 48-52m average depth. Some of the club systems teach and allow air diving to 50m, some of the tech training agencies do to. Despite what you may read on this and other fora, the "trimix at 30m" mindset is very much in the minority in the real world of diving.

I did my first air dive in 3yrs a couple of weeks ago (28-30m average) and I was narced out of my tree (I even managed to swim in the opposite direction from the wreck). After diving on helium on every dive regardless of depth for so long I'm now more convinced than ever as to how shallow it will hit you.

Good luck to them, people do it every day and nothing bad happens but it's out of my comfort zone.

[Cyrille]

Quote: (Originally Posted by richieoflynn)

Hi everyone,

I saw advertised in Ireland a dive being organised for people who dive twinsets on air to go to a wreck in 55m.

I put some figures through V planner to see what kind of deco profiles I would get by using air with 50% and 100% O2 for deco mix and 18/45 with the same deco mixes.

I got the 18/45 as being the GUE standard mix for this type of dive from this forum. Is this correct ?

Hi Richie,

Let me give you my point of view. Being a CMAS 3* diver, I am qualified to dive 65 meters on air in France, which I did for about 8 years. I explored those magnificent shipwrecks such as "LE TOGO", "LA DROME", "LE MIQUELON" and many more, without forgetting some nice walls like the "IMPERIAL DU LARGE" in Marseilles.

All with a 15L cylinder on my back. This is the norm out there.

Then 2 years ago I read the book from JJ and decided to change my configuration and move to full DIR.

I enrolled in a DIR training (NAUI NTEC) which I successfully passed and pursued with a TDI/CMAS Normoxic Trimix course last october in Cavalaire, France.

My first Trimix (Tx 20/30) dive take place on "LE TOGO", this shipwreck I dove many times with air & ease before. My equipment was somewhat different: double 12, stage cylinders, dry-suit, argon, etc.

I realized that:
1. my mind was clearer than with air (with air I always thought I did not have a problem with narcosis!)
2. I could recall many details from the wreck
3. one buddy had a problem with his inflator; we saw it and solved it with ease on the spot

Changing the gas... but not changing the shiprwreck.... and yet it was a totally different dive.

Then I went on with the training and successfully completed it. I enjoyed then several dives in the 70m range with some buddies using Tx18/40. During on of those dives, on the dive boat there was a Belgian couple preparing to dive on air what we were ready to dive on Tx: le Tombant des Corailleurs. They planned 15min at 55m, we planned 20min at 70m.

When we returned to the dive boat we saw the belgium diver, Luc, on the boat. He was complaining about back problems and was put immediately under O2. He was then transferred into the care of the emergency services.

Air diving is always the easiest way to dive, but nowadays not the safest.

After a Tx dive I feel much less tired than I was before with air.

So as far as I am concerned: I am using Nitrox most of the time, and Trimix only when I plan to exceed 40m.

Kind regards.

Cyrille

[richieoflynn]

Thanks again guys for the feedback.

I have to admit, I did a 48m dive last March on a sub and can't remember jack. It was hell scary. I had this darkness closing in around my vision, a really strange taste in my mouth like I had licked a 9V battery. I was really cold on the ascent and especially on the deco stop. I guess a good example of how not to dive ! Enough to put me off any sort of deep air for good.

I think also that here in Ireland, I don't know too many places where you can get trimix and most people mix there own AFAIK. Probably leaves some people with the decision of spending a shed load of money on mixing gear or just dive on air. Probably a huge factor in choosing deep air.

Richie.

[keri.lewis]

Richie

For home/small volume use it doesn't have to be too expensive - as long as you can get He from a supplier.

Check out this thread - Mixing Gas

Ignore the bit about shop-set-ups and it shows some nice home-made set-ups that would service a team of divers very well. If you get a friendly dive centre (that does Nitrox to make sure the supply is clean) they might let you top up if you sign enough disclaimers..

Good luck on the hunt - I am expecting to build a blending panel myself in the next couple of months.. if I get the time.

[lizardland]

Quote: (Originally Posted by Cyrille)

After a Tx dive I feel much less tired than I was before with air.

Even after shallowish air dives (20-30m) I was always wiped out afterwards, I often had to pull over on the drive home for some sleep. After doing the same dives on helium all the way I don't have any fatigue at all.