Trimix and Nitrox second dives

[scott laddiman]

I would like to know peoples views on doing a 60M to 70M Trimix dive in the morning followed by a Nitrox 30M dive in the afternoon using a high Nitrox mix for deco on both dives.

Do you think this is Ok or should it be one deep dive a day?

Comments please.

[Nigel Hewitt]

I would like to know peoples views on doing a 60M to 70M Trimix dive in the morning followed by a Nitrox 30M dive in the afternoon using a high Nitrox mix for deco on both dives.

This sounds like a pretty normal day's diving. People only start gripeing when the tides mean it would be easier to do them the other way round.

[scott laddiman]

:=I would like to know peoples views on doing a 60M to 70M Trimix dive in the morning followed by a Nitrox 30M dive in the afternoon using a high Nitrox mix for deco on both dives.

This sounds like a pretty normal day's diving. People only start gripeing when the tides mean it would be easier to do them the other way round.


I should mention I was directing this to Open Circuit Divers.
I have heard thoughts that one deep dive a day is enough.
I have my own views but was interested in others opinon.

With VR3's letting you do mutiple dives regardless of what gas.

Remember all the talk about being a bit 'savy' and not jumping in regardless of what your old Aladin said.

Are we going to see an increase of mutiple Trimix dives in a week or will we stick to one dive a day?

I know there is experimentation on using Trimix even for shallow dives i.e. less than 40M & CC can use it all the time but offset the He with 1.3 PPo2

[Nigel Hewitt]

>>This sounds like a pretty normal day's diving. People only start gripeing when the tides mean it would be easier to do them the other way round.

>I should mention I was directing this to Open Circuit Divers. I have heard thoughts that one deep dive a day is enough.

That's pretty much what I was thinking about. We'd do a second dive to use up that expensive third (or more) we brought back from the first dive as most shops would only trimix fill from empty. In fact it was when I started puting in deep stops and padding profiles that I started to feel like a second dive (unless I was feeling seasick).

>I know there is experimentation on using Trimix even for shallow dives i.e. less than 40M & CC can use it all the time but offset the He with 1.3 PPo2

Agreed. I use 18/40 dil as standard because that's what's in the bottle and buying a third tank for air would be more expensive than using 'mix in the pool tonight.

[scott laddiman]

Interesting.... Yeah I know I would have all this hassle if I was on CC.......!

The reason I asked the question is I am on an Expedition to Norway in May and after researching the wrecks, I see there is some in the 55 to 60M range. They are all mostly on a sloping rock face so typically starts at 10M and goes down to 50 ,60 ish sometimes.

I will be doing repetative Nitrox diving with 50 or 60% as deco but fancied 3 or 4 dives on Helium to get the deeper ones.

Hence my question about a second dive after a Trimix one.

Most agency's discourage a second dive after a deep Trimix one but I know it goes on and seems to be getting the 'norm'??

[David Walker]

I should mention I was directing this to Open Circuit Divers.
I have heard thoughts that one deep dive a day is enough.
I have my own views but was interested in others opinon.

I don't use it myself, but dive with a lot who do. Out on the club RIB just on a weekend if they're doing a deep trimix dive they'll usually just do the one dive that day.
They're all off up to Mull this week though, will be doing a lot of deep stuff, and are planning two dives a day, so obviously not opposed to the idea.

Just depends how you feel I suppose - as long as your trimix quals don't limit you to one dive per day then if you feel happy doing it then go for it.

David

[Ben Field]

I would like to know peoples views on doing a 60M to 70M Trimix dive in the morning followed by a Nitrox 30M dive in the afternoon using a high Nitrox mix for deco on both dives.

Do you think this is Ok or should it be one deep dive a day?

Comments please.

HI have done a couple of trips where we've done one 65-70mtr dive a day for 6 days without problems but never with second dives... (Remember if its the ONLY dive you are more inclined to hang out the deco just to be on the safe side... seeing as you've not got to prepare for anything in the afternoon)

Whereas in Scapa and similar locations I've done a week of 50m (30-40min BT and 20+ min deco) followed by afternoon 30m (40-50min BT and 10+ min deco) for 6 days which is almost certainly a greater risk.

I don't think doing ONE trimix dive followed by ONE nitrox dive is an issue what is- is doing it more than one day in succession (ie- where you have a much shorter surface interval before the second gas dive (not 22-24hours but 15-17hours) You might be safer doing three dives every two days and planning on that basis?

On the other hand some major expeditions have done mulitple gas dives per day... it just depends how serious/complicated you want to make things?

Of course all of this is under the caveat to your emergancy planning, nearest pot, amount of O2 on board etc. I don't know what Recompression services are like where your going but you need to temper the reisk if the backup is lacking or along way away.

[nick kay]

Interesting - all I can find in BSAC's safe diving practices is:
- Deepest dive first - no argument there
- Max 20mins deco per day
- Monitor CNS/UPTDs

The TDI "Entry Level Trimix" notes state
"In general, repetitive dives using trimix or heliox are not recommended unless the diver has received and understands significant additional training in special table considerations"

I seem to remember in some - either BSAC or TDI publication/course notes an item referring to one 40m+ dive per day, but can't find the reference

[Ben Field]

I seem to remember in some - either BSAC or TDI publication/course notes an item referring to one 40m+ dive per day, but can't find the reference

I think if you are planning to do a gas dive and nitrox dive daily then perhaps its outisde the remit of Entry level Trimix training and into the Adv Trimix area- for the necessary understanding of repeat diving on mix etc?

I've heard the 1x 40m+ dive /day thing too but can't remeber where, again in this senario I think you are well outside certainly BSAC club diving regulations.

[nick kay]

:=I seem to remember in some - either BSAC or TDI publication/course notes an item referring to one 40m+ dive per day, but can't find the reference

I think if you are planning to do a gas dive and nitrox dive daily then perhaps its outisde the remit of Entry level Trimix training and into the Adv Trimix area- for the necessary understanding of repeat diving on mix etc?
>> Was just pointing out that there is a caveat - though I have no idea what the "significant additional training in special table considerations" means???
>> However, the reference refers to multiple Trimix/Heliox dives - I guess, even if its a weak mix
>> Surely a 50m Trimix dive in the morning, followed by a (say) 30m Nitrox (no deco) with (say) 70% deco in the afternoon is "Entry Level"???
>> Not sure why I should be "penalised" for a 23/23 mix at 50m against an air diver?
>> Can probably see an argument if the dive is hypoxic.

I've heard the 1x 40m+ dive /day thing too but can't remember where, again in this senario I think you are well outside certainly BSAC club diving regulations.
>> Yes, but if you're "diving BSAC", on a branch trip for example, then you're "governed" by BSAC safe diving practices
>> If its not a BSAC organised dive, then (potentially) different "rules/guidance" apply

[scott laddiman]

>> Yes, but if you're "diving BSAC", on a branch trip for example, then you're "governed" by BSAC safe diving practices
>> If its not a BSAC organised dive, then (potentially) different "rules/guidance" apply


Yeah and I wonder how BSAC's preferred dive Insurance company would think about it? I know they cover down to 75M on Trimix but if stepping outside ''rules/guidence'' they may take a strong view!!

It seems as if we are working on 'common sense rule' for example 1 x 70M + dive a day or maybe 1 x 50M Trimix dive and 1 x 20M Nitrox a day, but with the increase of Trimix repetative diving this is going to be interesting to follow!

I wonder if the 40M+ is a rule or guidence? !!

[nick kay]

1. BSAC insurance is to cover "what you do to others"

2. Private dive insurance covers against specific risks and probably has a statement like "whilst diving within the limits / safe guiding practices of the training organisation"

2a. If its a BSAC dive, then specific rules / guidance / recommendations apply (I'd hate to end up in a situation where I was trying to argue to an insurance company / coroners court the diference between those)

2b. If its not a BSAC dive, and you're multi-agency trained, then depends which agency you're diving under...

[John Williams]

1. BSAC insurance is to cover "what you do to others"

2. Private dive insurance covers against specific risks and probably has a statement like "whilst diving within the limits / safe guiding practices of the training organisation"

2a. If its a BSAC dive, then specific rules / guidance / recommendations apply (I'd hate to end up in a situation where I was trying to argue to an insurance company / coroners court the diference between those)

2b. If its not a BSAC dive, and you're multi-agency trained, then depends which agency you're diving under...

2a)
In a court there is no difference!

2c)
Or which one gives the insurance company the most likelyhood of NOT paying out!
If you are multi-agency trained then the court/insurers will look to which code gives the most conservative profile and argue their case from that angle...you don't get to pick and choose! (If you have received advice against it...fom any official source - then you'll be expected to hold to that advice!)

John

[matt]

If you are multi-agency trained then the court/insurers will look to which code gives the most conservative profile and argue their case from that angle...you don't get to pick and choose! (If you have received advice against it...fom any official source - then you'll be expected to hold to that advice!)

That sounds like a rather nasty can of worms!

I was under the impression that safe diving practice was relative to training. For instance it is safe for an OD to dive to 20m but unsafe to for them to dive to 30m.

Where does a PADI crossover stand? PADI say no-deco BSAC say deco.

[Andy Wade]

:=If you are multi-agency trained then the court/insurers will look to which code gives the most conservative profile and argue their case from that angle...you don't get to pick and choose! (If you have received advice against it...fom any official source - then you'll be expected to hold to that advice!)

That sounds like a rather nasty can of worms!

I was under the impression that safe diving practice was relative to training. For instance it is safe for an OD to dive to 20m but unsafe to for them to dive to 30m.

Where does a PADI crossover stand? PADI say no-deco BSAC say deco.

Surely a PADI crossover would be 'SALT'ed then trained to dive deco with their BSAC branch? Therefore they could cite the BSAC part of their training to prove they were competent to do deco.

If they just crossed over to a BSAC branch and didn't take any deco training, then dived deco, there would be an obvious failing and a liability for someone responsible for it.

Personally I can't see a problem with mixing and matching the qualifications you have that allow you to do the diving you're trained for. If you can prove you were properly trained to do that type of diving, and your insurance covers for it, there should be no problem.
Or am I being too naive?


.

[nick kay]

2a)
In a court there is no difference!
2c)
If you are multi-agency trained then the court/insurers will look to which code gives the most conservative profile and argue their case from that angle...you don't get to pick and choose! (If you have received advice against it...fom any official source - then you'll be expected to hold to that advice!)

Hi John - I rarely disagree with you, but find this problematic... I dive with a guy who is both BSAC and TDI trained (as far a i can remember...) under BSAC he has a max ppO2 of 1.4, under TDI its 1.5... If its not a BSAC dive, then surely he's trained to dive with a ppO2 of 1.5 if he wants to?

[Nigel Hewitt]

Or am I being too naive?

No you're arguing with the dive police and like most self appointed groups the goal posts will move so you must loose.

Third party insurance is for where you get it wrong and hurt somebody not when you get it right. If I stuff an oxygen reg in somebodies mouth because it is all I have but still fail to save their life their running out of gas does not suddenly become my fault. This is the UK not the USA.

Your dive plan is your call. It has no third party implications unless you are an instructor. My duty of care goes as far as doing what I can with what I have. The law is very generous with divers: "He was non-responsive but breathing so I inflated his jacket at 40m and sent him up" sounds like you've just verballed yourself for manslaughter but it goes down as misadventure time and time again.

[Sarah Gauci Carlton]

Interesting.... Yeah I know I would have all this hassle if I was on CC.......!

The reason I asked the question is I am on an Expedition to Norway in May and after researching the wrecks, I see there is some in the 55 to 60M range. They are all mostly on a sloping rock face so typically starts at 10M and goes down to 50 ,60 ish sometimes.

I will be doing repetative Nitrox diving with 50 or 60% as deco but fancied 3 or 4 dives on Helium to get the deeper ones.

Hence my question about a second dive after a Trimix one.

Most agency's discourage a second dive after a deep Trimix one but I know it goes on and seems to be getting the 'norm'??

Sounds pretty standard to me, particularly since it sounds as though these dives are likely to be multi-level so not much time actually spent at maximum depth. I think the issue will be more about how much time you want to spend in really cold water, bearing in mind that you should bump up the safety factor on the VR3 to account for slower offgassing when you are cold.
Have a good trip.
Sarah