Tech Diver with the 5thd-X team

[JeffG]

30/30 yes... but within the 'old' MOD

25/25.... convince me why that's a better choice than 21/35 for dives deeper than the 30/30 MOD....

I guess I a bit of a ******. To me, both 25/25 or 30/30 are solutions looking for a problem. I'd be 32% no-deco or 21/35 +deco...why even bother with the inbetween stuff.

p.s. my training is pre-non-GUE-DIR :11:

Training..Whats that?

 

[onfloat]

our max working depth for 25/25 is 130. Keeps the ppo2 in acceptable levels. It gives you %10 EAD advantage. The END is still above 100 ft.

For other standard gases 10/70 all the way to 32%, including 25/25 mixes can be accomplished with 32% on top of the helium. So if banked 32% is all that's available......

 

[JeffG]

For other standard gases 10/70 all the way to 32%, including 25/25 mixes can be accomplished with 32% on top of the helium. So if banked 32% is all that's available......

The topping off with 32% does makes sense to me, but in practice, its much ado about nothing IMO. (We never drain out tanks to zip and fill with 32%. We use a haskel and the top off with air.)

 

[onfloat]

Well you can see by the start date of the thread. I'm about on my 2nd week of this, so I still have to build some real world experience.

Dang, I hope I'm not violating some 30 day rule.

 

[Snowbear]

The 30 day rule does not apply to the class report

 

[onfloat]

The topping off with 32% does makes sense to me, but in practice, its much ado about nothing IMO. (We never drain out tanks to zip and fill with 32%. We use a haskel and the top off with air.)

I was just sitting here thinking (uh oh). Wouldn't it be possible to figure the amount of helium left in the tank, top with helium to the appropriate pressure and then top with 32%?

 

[onfloat]

The 30 day rule does not apply to the class report

Good to know. I'll try to refrain from jumping in to any more controversies.:14:

 

[JeffG]

I was just sitting here thinking (uh oh). Wouldn't it be possible to figure the amount of helium left in the tank, top with helium to the appropriate pressure and then top with 32%?

You could, but is still basically the same procedure as topping with air. The only benefit is when the tank is empty.

(Plus...a lot of places don't bank 32%)

 

[JeffG]

You could, but is still basically the same procedure as topping with air. The only benefit is when the tank is empty.

(Plus...a lot of places don't bank 32%)

Re-looking at the math. I'm wrong and onfloat is right. Add the right amount of helium and top with 32%. (still would need a Haskel)

 

[lamont]

Personally I disagree with the new MODs for *recreational* triox diving. If you're only doing 30 mins at a 1.4 ppO2 and not spiking to 1.6 on deco switches to open the O2 window, then I think the standard recreational limit of 1.4 makes perfect sense, and has a good safety record as all the RSTC-trained Nitrox divers can attest to...

The only reason to be against 1.4 is because when you start technical diving you need to keep bottom mix to 1.2 because you're likely to have longer exposures, and to immediately follow those exposures up by hitting 1.6 on deco. So I can understand where the idea comes from that the you need to practice from the beginning what you'll be doing later so that how you dive doesn't change. But at the same time GUE has gone to 80% of ATAs for the first stop for technical diving and 50% of the ATAs for the first stop for recreational diving because someone had the good sense to realize that an 80 fsw deep stop on a 100 fsw dive is pretty inane. There are a few valid differences between recreational and technical diving, and I think the max ppO2 of bottom mix needs to be added to that list.

Stepping off my soapbox now...

Oh, and if you're diving a site that is 130 fsw in the sand as a rectriox dive then 30/30 is a little bit rich, and 25/25 gets you an extra 5 mins of NDL over 21/35 which is the difference between 15 and 20 mins at 120. Granted if you hold a Tech 1 card then a 40 minute dive there on 25/25 and 21/35 doesn't really have much difference in how much you need to deco and 25/25 gets really pointless. It only seems like a useful gas if you don't have Tech 1 training, which makes it seem not very useful...