Trimix 1 Class

[cadet diver]

I am taking TDI Trimix 1 in 2 weeks in the Bahamas. I found out tonight from my instructor that some of the plans changed, and I am curious what other peoples beginner trimix classes were like. We are looking at profile of 200 for 15min on 21/35, and then just 50/50 for deco. Is this a pretty standard profile for the class or should I be expecting longer bottom times?

The other thing is that he said that he can't get al40s down there anymore, which he originally said that he could get. Therefore we are going to either have to bring our own bottles, or sling an al80. Has anyone ever done any deco in the Bahamas and had a similar problem before?

Thanks for any help you can provide.

 

[Bottomfeeder]

cadet diver once bubbled...
We are looking at profile of 200 for 15min on 21/35, and then just 50/50 for deco. Is this a pretty standard profile for the class or should I be expecting longer bottom times?

15 minutes sounds about right for starting out, but the gas choice for that depth is too hot/high END.

 

[chickdiver]

Cadet Diver-

The bottom time sounds about right, depending on the deco tables you are running, when I teach trmix (not TDI) I try and keep the run times (bottom time plus deco) int he 100 minute range. That gas mix is definitely hot. For example, running a dive to 190' I would teach (and use) 18/45. Also, generally when doing a one gas deco most people opt for O2 rather than 50/50. Decoing on an al80 isnt bad, but dragging it around during the dive will be less than comfortable (do NOT drop your deco gas, whatever the instructor does).

 

[MechDiver]

IANTD limits normoxic trimix (assume same as Trimix 1) to 20/29 and either single 50/50 or dual 35% and 80%. I would have to disagree with ChickDiver over the use of 100%, at least here. 50% is much more common IME.

At least to IANTD guidelines, the 21/35 fits. We did 200 fsw on 20/30.

MD

 

[chickdiver]

Mech-

Im not familiar with IANTD or TDI's standards or class structures. The difference re: 50/50 or O2 for a single deco gas may be regional? In Florida I have never seen anyone use 50/50 for a single deco gas dive.....

 

[MikeFerrara]

The IANTD Normoxic trimix class requires the use of one deco gas. The deco gas can be anything up to 100% O2. For short bottom times there won't be much of a difference in the schedule between using 50/50 and O2 but I would rather have O2. The course also requires that no dive be more than 33 ft deeper than your deepest dive to date also 200 ft is the max depth allowed in the class.

IMO, short bottom times are ok for SOME of the training dives because skills like hitting runtimes, gas switches, shooting a bag ect) mostly come in during the ascent.

 

[padiscubapro]

I have to agree with mech.. I would never use oxygen when only carrying a single deco gas.. 50/50 up in the northeast is much more common.. using 50/50 gives you more options.. better than carying a gas thats useless deeper than 20 fsw.. assuming a contingency po2 of 2.0 (must be ascending) you can bail onto 50/50 at 100 fsw if necessary.. If using a high helium bottom gas I would still use 50% oxygen but would add some helium to the gas.. I prefer not to raise the FN2 over the bottom gas when possible..
We used fixed ascent and descent lines, I plan all decos using 50/50 and calculate schedule as such, I will have o2 hanging beneath the boat on either a trapeze or on the ascent line.. The o2 is not a required decos gas so it doesn't have to be carried but if all goes well, I will switch to 100% at 20fsw, and still run my 50/50 schedule.
If I have to shoot a bag and deco away from the line I still have the necessary gas needed..

for bottom gas I would use 20/25 (130 END) or 20/35 (100 END) for a 200 fsw dive.. This keeps the END and deco times reasonable. If I remember correctly TDI allows o2 as low as 18% on its entry level trimix program.. There was no requirement prior to last year..

 

[MHK]

cadet diver once bubbled...
I am taking TDI Trimix 1 in 2 weeks in the Bahamas. I found out tonight from my instructor that some of the plans changed, and I am curious what other peoples beginner trimix classes were like. We are looking at profile of 200 for 15min on 21/35, and then just 50/50 for deco. Is this a pretty standard profile for the class or should I be expecting longer bottom times?

The other thing is that he said that he can't get al40s down there anymore, which he originally said that he could get. Therefore we are going to either have to bring our own bottles, or sling an al80. Has anyone ever done any deco in the Bahamas and had a similar problem before?

Thanks for any help you can provide.

In my view, as others have experessed, the mix is hot but more importantly it seems to me that the focus is on the wrong thing. Depth and mix aren't the key things to focus on. You haven't really described the class in great detail so it's hard for me to comment, but from what I see, going to depth before any pre-dive evaluations and skill assesment seems short sighted to me. When we run our classes we do 4 dives in the 20' range before we even consider letting a diver go to depth.. Perhaps they will do this as well, but in my view skills are more important then depth and mix..

Hope that helps

 

[O-ring]

cadet diver once bubbled...
I am taking TDI Trimix 1 in 2 weeks in the Bahamas. I found out tonight from my instructor that some of the plans changed, and I am curious what other peoples beginner trimix classes were like. We are looking at profile of 200 for 15min on 21/35, and then just 50/50 for deco. Is this a pretty standard profile for the class or should I be expecting longer bottom times?

The other thing is that he said that he can't get al40s down there anymore, which he originally said that he could get. Therefore we are going to either have to bring our own bottles, or sling an al80. Has anyone ever done any deco in the Bahamas and had a similar problem before?

Thanks for any help you can provide.

Is that your first dive for the class? In my class we are building up slowly to those kinds of depths (i.e. starting with the pool, then the quarry, then 130-140, then to 150-160, then to 190-200 for the final dives). All of our dives are using decoplanner and GUE standardized gas mixes...so for that dive we would probably run about the same bottom time as you, but would definitely knock that o2 back to 18 and the He up to 45.. That way, you can keep your ppo2 down to a nice 1.2-1.3 and your END under 100'.

 

[cadet diver]

We will be doing 6 shallower skill dives in addition to the deeper dives, with 1 deep dive a day. My instructor was the same instructor I had for my Extended Air Nitrox class, so we have already done dives to those depths on air together. I know that doesnt go along with GUE standards because of deep air and the difference in the class progression.