Cheaping out on Trimix - travel gas

[barth]

A couple of months ago we were diving with a lot of gue divers. Most of the divers were tech 1 oc divers. They were using a set of doubles with ean32, 21/35 stage and oxygen stage.

I was in a team of gue ccr divers. We had a dpv and a oxygen stage.

After visiting 2 wrecks at 35 meter the oc divers were switching from their trimix stage to backgas. It was really a mess, the tech 1 divers could not handle 2 stages and dpv. They were loosing their buddies, bouyancy was screwed up.

Adding more gear doesn’t always solve problems…

 

[KenGordon]

A couple of months ago we were diving with a lot of gue divers. Most of the divers were tech 1 oc divers. They were using a set of doubles with ean32, 21/35 stage and oxygen stage.

I was in a team of gue ccr divers. We had a dpv and a oxygen stage.

After visiting 2 wrecks at 35 meter the oc divers were switching from their trimix stage to backgas. It was really a mess, the tech 1 divers could not handle 2 stages and dpv. They were loosing their buddies, bouyancy was screwed up.

Adding more gear doesn’t always solve problems…

Does tech 1 teach a stage plus deco gas? Or were they making it up as they went along?

 

[CptTightPants21]

Does tech 1 teach a stage plus deco gas? Or were they making it up as they went along?

Tech 1 is only one bottle. There is actually a Tech 1+ (called Tech 60) which incorporates two bottles, but that class is a 1 or 2 day workshop and not many people take it. Like the official 30 min deco limit, tech 1 divers slightly increase the equipment and dive times once they go out into the real world.

 

[lermontov]

A couple of months ago we were diving with a lot of gue divers. Most of the divers were tech 1 oc divers. They were using a set of doubles with ean32, 21/35 stage and oxygen stage.

I was in a team of gue ccr divers. We had a dpv and a oxygen stage.

After visiting 2 wrecks at 35 meter the oc divers were switching from their trimix stage to backgas. It was really a mess, the tech 1 divers could not handle 2 stages and dpv. They were loosing their buddies, bouyancy was screwed up.

Adding more gear doesn’t always solve problems…

what do they use the 21/35 stage for? extra gas or bottom gas?

 

[CptTightPants21]

what do they use the 21/35 stage for? extra gas or bottom gas?

I imagine it is a version of "cheaping out" on helium. They do the bulk of the dive on helium and switch to the 32% for portion and the ascent up to their deco. Means they only have to refill an al80 with trimix and not all their backgas.

Not a bad strategy for 35m. I would just dive that on nitrox, but if you wanted to at least play a little homage to GUE's position on helium below 30m this would be a way to do it.

 

[Jack Hammer]

Tech1 is one deco gas, no stages. A lot of GUE divers also have certs from other agencies. As above I imagine the stage was to minimize helium usage and only for the deeper portion of the dive while the 32% was for for the shallower portions.

 

[rjack321]

Tech 1 is only one bottle. There is actually a Tech 1+ (called Tech 60) which incorporates two bottles, but that class is a 1 or 2 day workshop and not many people take it. Like the official 30 min deco limit, tech 1 divers slightly increase the equipment and dive times once they go out into the real world.

Tech1+ is a 25 dive post class workshop add on to use a bottom stage (still only one deco gas)
Tech60m was a 2 deco gas course (50% and O2) with a 60min deco limit that straddled tech1 (one bottle) and tech2 (3 bottle) courses.

 

[Wibble]

When diving with backgas, a bottom stage cylinder and one deco stage cylinder, how do you mitigate the failure of the deco cylinder?

The benefit of diving with two deco stages is you can extend the bottom time such that you’ve enough backgas to get to the second switch should the lean deco gas fail, or fully deco out on the lean deco gas should the rich deco gas fail.

 

[KenGordon]

When diving with backgas, a bottom stage cylinder and one deco stage cylinder, how do you mitigate the failure of the deco cylinder?

The benefit of diving with two deco stages is you can extend the bottom time such that you’ve enough backgas to get to the second switch should the lean deco gas fail, or fully deco out on the lean deco gas should the rich deco gas fail.

Team deco gas. These people are big on the Team.

I am also confused about the charging model for the gas. Does it cost less if I buy it in an Ali80 compared to a twinset? Do they dump the gas in the twinset and charge for a complete fill?

 

[CptTightPants21]

When diving with backgas, a bottom stage cylinder and one deco stage cylinder, how do you mitigate the failure of the deco cylinder?

The benefit of diving with two deco stages is you can extend the bottom time such that you’ve enough backgas to get to the second switch should the lean deco gas fail, or fully deco out on the lean deco gas should the rich deco gas fail.

Your buddy's deco gas. When diving with one deco gas you also have the reserve in your back gas

Team deco gas. These people are big on the Team.

I am also confused about the charging model for the gas. Does it cost less if I buy it in an Ali80 compared to a twinset? Do they dump the gas in the twinset and charge for a complete fill?

Depends on a number of factors, but ultimately it is a about limiting up front expenses and reducing the amount of trimix that needs to get dumped.

The shop might have some trimix tanks always banked and it would allow for being charged by the cuft from the first breath, but in my experience it is not the most common practice--shops unwilling to keep sets of doubles unutilized until someone needs trimix. Easier to just create a fresh batch of trimix when a customer asks for it, charge for the full initial fill, and then charge for the top ups after.

If a diver who only owns one of two sets of doubles puts trimix in their tanks, they have to either make a set of doubles just for trimix or the helium will get diluted out and consumed as they continue using the set for none trimix purposes.

Draining an AL80 (or nearly draining it) leaves ~5cuft of gas in the tank. Lets say that is 3 cuft of helium that might be wasted.

Coming up from a deco dive you will have around 1100 psi in a set of doubles. That is the potential to waste 25 - 40 cuft of helium.