triox vs. trimix?

[Brian of Aquanauts]

Apologies.

We recommend that GUE divers carry enough gas for the greater of minimum gas, and the amount required if the next gas source is lost. In general minimum gas is the greater of the two figures.

Minimum gas is the absolute minimum volume of gas required for
2 divers
at a safe ascent rate
including all deco stops
using a stressed breathing rate
to get the next available gas source

So our procedures do take account for lost buddies but it doesn't really happen. However we do calculate and carry the gas supply needed to safely take 1 diver to their next gas source.

What do the other agencies recommend about gas for your dive buddy if he were to suffer a catastrophic gas loss?

[NotDeadYet]

Originally Posted by Brian of Aquanauts

Apologies.

I'm thick skinned so no need. Some would say that the "skinned" part is unnecessary

Minimum gas is the absolute minimum volume of gas required for
2 divers
at a safe ascent rate
including all deco stops
using a stressed breathing rate
to get the next available gas source

So our procedures do take account for lost buddies but it doesn't really happen. However we do calculate and carry the gas supply needed to safely take 1 diver to their next gas source.

What do the other agencies recommend about gas for your dive buddy if he were to suffer a catastrophic gas loss?

What I got taught sounds not dissimilar to the above only with some faffing time added in on the bottom as well to sort stuff out. That was IANTD circa 1994 and the instructor I was using was one of the founding members of IANTD UK who had been trained under Billy Deans (as to why that was relevant, a lot of Capt Billy's standard procedures found their way into the WKPP & prehistoric DIR). What's in the manual I don't know because they were never well known for being exhaustive but that's more or less what we had to plan our dives for (and IIRC we did quite a few dives where the deco bottle was "failed"). We weren't taught the sharing deco gas procedure GUE uses but we were taught not to leave a buddy on an extended stop if a deco bottle fails. If one of you is on an extended schedule then both of you is. When I first read about the GUE procedure I thought it made a hell of a lot more sense and started using that. Thankfully, outside of training I've only once had a complete, unsalveageable deco gas reg failure and once lost a bottle completely

[IanDennis]

Originally Posted by Brian of Aquanauts

What do the other agencies recommend about gas for your dive buddy if he were to suffer a catastrophic gas loss?

In the event of a catastrophic gas loss then goto back up schedule and use what's available. If planned out then there should be back gas available - in which case double the deco stops. If other divers are present then once they have completed their stops have them swap over deco bottle and complete the appropriate revised stop. The team stays together and sorts out the problem. If other divers not prescent then BG and yellow blob for additonal deco gas (assuming that its available).

Obviously divers under stress are going to increase their breathing rate and both gas matching and rule of thirds rely upon maintaining a constant breathing rate. Stress management is important as is training and practice and determining the capabilities of the team. Whilst divers should be self sufficient, the final outcome of this sort of situation may depend upon a co-ordinated team effort.

For deco gas then we typically plan required amount then multiply by 1.2 to have "adequate" reserves- adequate being a relative term. Personally an Ali 80 fits the bill quite nicely.

Ian

[Brian of Aquanauts]

Originally Posted by IanDennis

For deco gas then we typically plan required amount then multiply by 1.2 to have "adequate" reserves- adequate being a relative term. Personally an Ali 80 fits the bill quite nicely.

Ian

Why 1.2 specifically? There must be a reason behind why that particular number was chosen.

I use 1.5 as that's the required amount for 2 people to deco out on 1 bottle, and for the bottle to have an adequate reserve in case of loss of the next bottle.


(re re faf time, we have the same, minimum 1 minute ti deal with the emergency, i often allow 2).

[IanDennis]

Brian- planning in a slightly different way- not looking at a team deco requirement- we are multiplying personal requirements by 1.2 to compensate for anything that might increase our own level of respiration and also to have a reserve should the diver goto the next greater schedule. Once a diver has completed this schedule then teammate may use remaining gas.

Its a minimum and at triox level no extra gas is included for buddy as there should be sufficient BG available to complete the deco.

I would completely agree that for deeper dives carrying more gas is a very good idea in order to have a greater reserve.

[nickb]

Originally Posted by Clare Gledhill

We dive a maximum working partial pressure of oxygen of 1.4 so I have no argument with you on that score Nick.

However, as I am sure you know, sometimes the wreck is deeper than we plan for so having a margin for error is no bad thing. I'll plan to be a bit leaner on the O2 so if I end up a little deeper for part of the dive it is no big deal. My MOD is still 1.4 but it is there for contingency not a planned exposure.

Ah fair enough, I was infering from Howard's post that you fellas were using 1.2 as the max

Work - well we never know how hard we are likely to have to work to the bottom in current are we?

I try not to do any work down there (bit like being at my desk really). If there's a current, I'll stay in the lee of the wreck, drift with it or pull my self gently along the wreck with my hands - unless you're there to tell me off for using my hands

And time. A higher exposure won't hurt you for a few minutes but when dives in the 30 metre range go over 2.5 hours (which I have done several times) you get that clock ticking.

I've never done a 2.5 hour dive. If I did, I reckon I'd be losing the will to live by then and an ox-tox would be a welcome relief Seriously though, if I had to be in the water that long, I'd wind the PPO2 back even further, especially if I was planning to deco on O2. As it is, I'm rarely on the bottom for more than an hour.

[Mark Chase]

Originally Posted by big_si

I guess the pointless debate (and sorry for straying down that road) is around deviation from standard gases? Must admit that I'm surprised that it's sometimes used by DIR divers.

On V-planner (using my settings obviously )

A 60 minute bottom time at 40m using 21/35 gives a run time of 140 mins
A 60 minute bottom time at 40m using 28/35 gives a run time of 124 mins


A 60 minute bottom time at 45m using 21/35 gives a run time of 159 mins
A 60 minute bottom time at 45m using 25/35 gives a run time of 146 mins

Bit of a saving... But not massive...

What sort of situation would it be used in?

Not stirring, just curious on the reason for the deviation.

I used triox often when I was OC and now on CCR I use it all the time.


40m dive and i want minimum deco and dont want to be narked? Easy


28/25 back gas 36 and 80 deco 60mins on the botom 36mins deco END 20m


The same dive on air would give 46mins deco. And yes i would take tow deco mix as it offers fast deco and deep bailout. The same dive on 28/25 and50% would give 47mins deco.


ATB

Mark

[IanDennis]

Morning Mark

Triox is a single deco mix course- so we would use the 50% for deco.

With a full trimix cert obviously other options are open to divers but at this level the course is about teaching the basics.

For the reduction in narcosis at 40m its ideal.

Best wishes

Ian

[Brian of Aquanauts]

Originally Posted by IanDennis

Morning Mark

For the reduction in narcosis at 40m its ideal.

Best wishes

Ian

If there were no GUE courses (and for most these aren't easily available) personally I think your tri-ox course is a WAY better option for UK diving than ADV. Nitrox and Deco, and would highly recommend it above that alternative.

Going through my TDI Instructor manual all I can find for deco gas requirements is "Cylinder volume appropriate for planned dive and student gas consumption". So TDI leave this to the instructor, do IANTD recommend your reserve amount?

[IanDennis]

Originally Posted by Brian of Aquanauts

If there were no GUE courses (and for most these aren't easily available) personally I think your tri-ox course is a WAY better option for UK diving than ADV. Nitrox and Deco, and would highly recommend it above that alternative.

Going through my TDI Instructor manual all I can find for deco gas requirements is "Cylinder volume appropriate for planned dive and student gas consumption". So TDI leave this to the instructor, do IANTD recommend your reserve amount?

Thanks Brian- I think that the course has some significant benefits over Advanced Nitrox- it gives people options about picking better gases for intermediate depths and incorporates the basic skills required to accomplish dives to these depths. A reduction in the level of Narcosis at these depths is a positive benefit over diving weak nitrox mixes in the 35-45m range.

On the Triox course we spend a lot of time discussing gas requirements and the minimum levels of reserve are determined by IANTD. Instructors do have the ability to increase these reserves to reflect the planned dive and student capabilities.

When GUE finalise their own Triox course then I am sure a number of fundies level divers would see that as the next logical step prior to the jump to Tech 1.