Which mixes for trimix are better for 330 feet (100 meters)?

[Blackwood]

For 200 feet, one deco gase is enough.

I wouldn't do 200 with one deco gas.

And for 330 feet, are two deco gases not enough?

Academically (again, I don't have that kind of experience), not for me. I'd call three minimum and would entertain a bottle at 190 (if for no better reason than to cut down on my backgas reserve requirements).

 

[texdiveguy]

Which mixes for trimix are better for 330 feet (100 meters)?

I think three mixes 14/50, 30/30 and 50, is it a good idea, if the limit of ppO2 is 1.6 for the MOD?

You list TDI Trimix as a cert. on your bio., I hope you learned far more than what is represented here in this question and replies in this thread you have made. I might suggest a solid review of your previous materials and square some of the basics with your instructor. Just don't want to see you this far off from the get-go. There is a whole lot more to consider and learn when you jump from 200ft. to 330ft..

 

[nereas]

Which mixes for trimix are better for 330 feet (100 meters)?

I think three mixes 14/50, 30/30 and 50, is it a good idea, if the limit of ppO2 is 1.6 for the MOD?

I hope you're kidding?

With those mixes, you would tox about half way into your dive.

 

[nereas]

I would not do this dive.

Your bottom gas is wrong I would use 12/60 14 is way too high for 330'.


For sub 250' dives depending on the BT you should be thinking of three deco gases. For sub 300' in my book three gases are mandatory.


Your first stop is going to be at 250' ish do you really want to use 12% or even 14% from 250' to 130'??

Then you are missing 100% I do a lot of diving sub 200' in the Great Lakes and I never see anyone using less than 80% for their last gas. Most have 100%, the people using 80% are in the minority for sure.

Exactly!

 

[nereas]

For 200 feet, one deco gase is enough. And for 330 feet, are two deco gases not enough? Three deco gases are not more easy?

One deco mix is never enough. This simply would voilate the tech rule of "two of everything." With one deco mix you have NO backup, in case your deco bottle fails.

Agencies that teach to use only 1 deco bottle are seriously flawed.

Therefore 2 deco mixes is always your minimum. And you always plan to do all your deco on either one of the two bottles, in case one or the other fails. And by using both, when all is well, you shorten your deco time somewhat.

And whether you use 3 or 4 deco mixes in total is determined by your (1) MOD and (2) B/T.

You want to approximate the performance of a continuous ppO2, determined by the length of time of your total exposure to oxygen at high ppO2s (greater than 0.20) because in the range of 1.4 to 1.6 your exposure is limited, before you tox.

Thus, by introducing more deco bottles, you improve your ppO2 level, and increase your rate of off-gassing (decompression), and decrease your overall deco time, and increase your redundance, in case one or more of your deco bottles fails.

My own deco mixes are TMX 20/40, TMX 30/30, EAN 50, and 100% O2.

And depending on the B/T, the bottom mix would be between TMX 10/70 or TMX 12/70, take your pick. Run your pick on V-Planner and see what percentage of oxygen exposure is which it gives you.

Use the TMX 20/40 as your travel mix. And switch back over by 200 ft (50 m) during your re-ascent.

Then come back to TMX 20/40 when you return to 200 ft (50 m).

TMX 20/40 also makes a perfect air-break mix, every 15 mins on pure O2, for 5 mins, to ensure that you do not tox.

 

[ucfdiver]

One deco mix is never enough. This simply would voilate the tech rule of "two of everything." With one deco mix you have NO backup, in case your deco bottle fails.

Really? If a single deco bottle fails, you have NO backup?

I thought the majority of agencies taught to reserve enough backgas for 1 failed deco bottle? I don't have any training with more than 1 deco gas, but this was my understanding, as I was taught to always reserve enough backgas to deco out.

 

[grazie42]

Tomeck, it might help us give you better suggestions if you tell us what you´re going to do on the dive, what your BT will be and the water temperatures...

I´ve only been to 80mtrs/~250ft but I used 2 deco gasses for that dive and I wouldn´t feel comfortable with a PO2 of more than 1,4 in the bottom mix for a dive like this...

I´d use a bottom mix of (<)12/70 (I would want more than the 50% He you suggested and not more than 12% O2 to keep the PO2 low)
Deco gasses would be 21/35, 50 and O2...
All this is based on the assumption that you´ll be doing this in cold water where I´d do everything I reasonably can to limit in water time...

But I might choose something different if you tell us a bit more about the context of the dive...

 

[Meng_Tze]

Tomeck is okay with diving to PO2 at 1.6.

http://www.scubaboard.com/forums/technical-diving-specialties/185584-padi-dsat-3.html.

Post 103. I am not sure if he actually does on a regular basis, but doing this especially at 330ft and having significant hang time is not smart.

Running a low PO2 on the working part is safer and will give benefits later on; especially if one runs behind RT. Doing these dives I normally run 0.9 and slowly increase that as I go up the schedule.

 

[Blackwood]

One deco mix is never enough. This simply would voilate the tech rule of "two of everything." With one deco mix you have NO backup, in case your deco bottle fails.

Agencies that teach to use only 1 deco bottle are seriously flawed.

Funny post, considering:

For the sake of brevity, just remember that if you are bringing only one deco bottle, then make sure it is EAN 50 and not 100% O2.

In any case, as UCFdiver said (but you can't see since you've ignored him):

I thought the majority of agencies taught to reserve enough backgas for 1 failed deco bottle? I don't have any training with more than 1 deco gas, but this was my understanding, as I was taught to always reserve enough backgas to deco out.

I don't know about "the majority of agencies," but there are different ways to plan dives safely. You are welcome to bring two bottles to 150 feet if you want to. I'd rather bring one and reserve enough backgas that I could get out on it (doubling deco from 70 on up) should my bottle fail.

 

[Mike Edmonston]