What is your personal "Helium" Depth?

[macado]

question

Is there any particular reason or big difference you guys choose 21/35 over 25/25 if you are diving 45m, I use 28/22 for 40m and 25/25 for 45m and 25/30, TDI Helitrox limits anyway the maximum too 20% He @ 45m, but I guess not to much people follows that, because we prefer to keep the END lower.

A few reasons. One is flexibility for me.. 25/25 would be a fairly useless mix for me unless I am absolutely sure that I'm only going to be diving 150' or shallower (~45m). Sometimes mooring break, wrecks get blown out. I've been on plenty of charters where 150' wreck has broken mooring or is blown, our next option is a wreck at 165' (50m). Suddenly my 25/25 mix is not the best option.

Ignoring helium content and ENDs, the difference in runtimes diving 25% of O2 verus 21% of O2 is negligible. Sure 25% is "best" mix for 150' (45m) but you don't really save much deco by using 25 over 21.

A lot of people are taught to keep the working portion of their dive at or below 1.4ppO2. I like to keep my working portion of the dive at ~1.2-1.3ppO2 on open circuit (To be clear, I have no problem running at 1.4 and above, I just choose to keep this much lower depending on the dive). Becomes even more important to keep this lower on a rebreather but I won't get into that.

Example: 21/25 vs. 25/25 using 50% as deco gas.

35 minutes at 150ft (21/25) with 50% GF 45/80
Runtime: 81 minutes

35 minutes at 150 (25/25) with 50% GF45/80
Runtime: 77 minutes

So I save 4 minutes of deco by using 25/25? Obviously these profiles can manipulated many ways (adding/changing deco gas, changing deco model or gradient factors, etc) but I just wanted to illustrate one example of why I try to use standard mixes over best mixes.

 

[exposure]

Dont have the standard in front of me, I think the problem is that he is not a PADI trimix instructor.

Most probably. I have the same problem

 

[manni-yunk]

As many have posted -on my CCR, I have Helium at any depth...even a 50' dive.

On OC - anything 100' or deeper, I have some sort of mix (but I barely dive OC these days)

 

[Remy B.]

A few reasons. One is flexibility for me.. 25/25 would be a fairly useless mix for me unless I am absolutely sure that I'm only going to be diving 150' or shallower (~45m). Sometimes mooring break, wrecks get blown out. I've been on plenty of charters where 150' wreck has broken mooring or is blown, our next option is a wreck at 165' (50m). Suddenly my 25/25 mix is not the best option.

Ignoring helium content and ENDs, the difference in runtimes diving 25% of O2 verus 21% of O2 is negligible. Sure 25% is "best" mix for 150' (45m) but you don't really save much deco by using 25 over 21.

A lot of people are taught to keep the working portion of their dive at or below 1.4ppO2. I like to keep my working portion of the dive at ~1.2-1.3ppO2 on open circuit (To be clear, I have no problem running at 1.4 and above, I just choose to keep this much lower depending on the dive). Becomes even more important to keep this lower on a rebreather but I won't get into that.

Example: 21/25 vs. 25/25 using 50% as deco gas.

35 minutes at 150ft (21/25) with 50% GF 45/80
Runtime: 81 minutes

35 minutes at 150 (25/25) with 50% GF45/80
Runtime: 77 minutes

So I save 4 minutes of deco by using 25/25? Obviously these profiles can manipulated many ways (adding/changing deco gas, changing deco model or gradient factors, etc) but I just wanted to illustrate one example of why I try to use standard mixes over best mixes.

I'm talking about planned dives, not deeper than 45m, it seems that you save a little time and money by using 25/25 vs 21/35, and it will be a little easier to mix as well, that is the reason I ask what make you guys choose 21/35 over 25/25, am I missing something ?

I never heard about standard mixes, I was in the impression that the Best Mix is better, of course trimix is what ever the diver chooses to dive and can afford.

it is obvious that if you go deeper than 45m then you need to adjust your PPO by reducing the O2%

 

[victorzamora]

I'm talking about planned dives, not deeper than 45m, it seems that you save a little time and money by using 25/25 vs 21/35, and it will be a little easier to mix as well, that is the reason I ask what make you guys choose 21/35 over 25/25, am I missing something ?

Mixing 21/35 is a piece of cake. Fill helium to 35% of your tank, top off with EAN32.
Mixing 25/25 is a piece of cake. Fill helium to 25% of your tank, top off with EAN32.

21/35 is a little bit more flexible in that it lets you dive deeper. Let's say you use Trimix on any dive deeper than 40m (130ft). 25/25 is only good for an additional 6m. If you use 21/35 instead, it would be suitable for 17m of your trimix diving. It's just one less bracket of depth.

 

[Remy B.]

then you are actually not planning your dives nor diving your plan.

Mixing 21/35 is a piece of cake. Fill helium to 35% of your tank, top off with EAN32.
Mixing 25/25 is a piece of cake. Fill helium to 25% of your tank, top off with EAN32.

that is for 10L tanks correct ?, will that apply for other size and pressure tanks, what is your accuracy doing those mixes ?

 

[PfcAJ]

then you are actually not planning your dives nor diving your plan.

Mixing 21/35 is a piece of cake. Fill helium to 35% of your tank, top off with EAN32.
Mixing 25/25 is a piece of cake. Fill helium to 25% of your tank, top off with EAN32.

that is for 10L tanks correct ?, will that apply for other size and pressure tanks, what is your accuracy doing those mixes ?

Applies for all tanks.

 

[rjack321]

A few reasons. One is flexibility for me.. 25/25 would be a fairly useless mix for me unless I am absolutely sure that I'm only going to be diving 150' or shallower (~45m). Sometimes mooring break, wrecks get blown out. I've been on plenty of charters where 150' wreck has broken mooring or is blown, our next option is a wreck at 165' (50m). Suddenly my 25/25 mix is not the best option.

Ignoring helium content and ENDs, the difference in runtimes diving 25% of O2 verus 21% of O2 is negligible. Sure 25% is "best" mix for 150' (45m) but you don't really save much deco by using 25 over 21.

A lot of people are taught to keep the working portion of their dive at or below 1.4ppO2. I like to keep my working portion of the dive at ~1.2-1.3ppO2 on open circuit (To be clear, I have no problem running at 1.4 and above, I just choose to keep this much lower depending on the dive). Becomes even more important to keep this lower on a rebreather but I won't get into that.

Example: 21/25 vs. 25/25 using 50% as deco gas.

35 minutes at 150ft (21/25) with 50% GF 45/80
Runtime: 81 minutes

35 minutes at 150 (25/25) with 50% GF45/80
Runtime: 77 minutes

So I save 4 minutes of deco by using 25/25? Obviously these profiles can manipulated many ways (adding/changing deco gas, changing deco model or gradient factors, etc) but I just wanted to illustrate one example of why I try to use standard mixes over best mixes.

I'd use 21/35 for that dive. Cause if for whatever reason (high tide, was told the wrong depth by someone, its a wall and a whaleshark swims by down there etc) I end up at (e.g. 52m) I don't want to be on 25% O2. 21/35 gives more flexibility there.

If the site I'm diving has a known bottom, I've done it before or whatever I will go with 25/25. But max is more like 40m for that gas.

I would not use only EAN50 for 35 mins of OC deco. If you lose it you're in deep trouble with over 70mins of backgas deco to do. For deco times >30mins I would bring an al40 of 50% to keep my 'rock bottom' moderate and O2 to get the slow tissues offgassing better. That way if I lose one deco gas I can modify the plan and still have something to accelerate the deco with

 

[macado]

I'm talking about planned dives, not deeper than 45m, it seems that you save a little time and money by using 25/25 vs 21/35, and it will be a little easier to mix as well, that is the reason I ask what make you guys choose 21/35 over 25/25, am I missing something ?

I never heard about standard mixes, I was in the impression that the Best Mix is better, of course trimix is what ever the diver chooses to dive and can afford.

I already explained this in my above post, as did others that replied.

Best mix "can" be better but standard mixes provide greater flexibility and greater ranges for when dive plan may have to change for whatever reason. If you're absolutely sure that you're never going to end up deeper than 150ft (45m) then there is nothing wrong with your gas choice.

21/35 versus 25/25. Little benefit to "best" mix in this example when a standard mix has a greater range. Run a dive plan and compare both of those mixes, you should see very little difference in runtime/deco.

In some places in the world you cannot always assume your dive plan is going to end up at same dive site, things change, weather changes.

Some dive sites that are reported as a depth of 150ft could actually be 155-160ft. I've seen it plenty of times. Maybe depth was taken at low tide or you have an extreme high tide. Maybe you're diving a wall and end up deeper than 150ft. Just a few examples.

Some people like to utilize standard mixes for certain depth ranges. GUE, for example does this. If the entire team/group is diving the same gas, it makes dive planning easier then trying to accomodate everyone's best mix.
Feet Meters Gas
10-100ft 3-30m 32% or 30/30
110-150ft 33-45m 21/35
160-200ft 48-50m 18/45
210-250 ft 63-75m 15/55

A scenario: You blend a best mix of 25/25 for a 150ft (45m) wreck. Unfortunately perhaps the wind/conditions aren't good so you motor over to another site that is more sheltered unfortunately that dive site is 160ft. Everyone else on the boat is using 21/35 but you. Do you sit on boat?

 

[macado]

I would not use only EAN50 for 35 mins of OC deco. If you lose it you're in deep trouble with over 70mins of backgas deco to do. For deco times >30mins I would bring an al40 of 50% to keep my 'rock bottom' moderate and O2 to get the slow tissues offgassing better. That way if I lose one deco gas I can modify the plan and still have something to accelerate the deco with

Yes, completely agree. For stuff deeper than ~150ft I typically sling two deco gases (50% and O2). I was just using one deco gas as an example in my dive plan above to show that a runtime with backgas of 25/25 or 21/35 is not very different.