DIR- Generic Marked stages filled with lower O2?

[Nick_Radov]

What is the current thinking on filling stage tanks with an FO₂ lower than that normally indicated by the MOD sticker? Like I've seen divers do training and skills practice with stages marked "70" (ft) or "21" (m) but filled with 21% or 32% instead of 50%. This is totally safe from a maximum operating depth perspective: the tank can be breathed at 70ft without exceeding any limits. But if you accidentally bring that stage on a real tech dive you'll have a bad day.

 

[Badger7]

I'm not chiming in as an expert here or claim to be up on the "current thinking", but this is something I've questioned as well, and I really don't like the idea of it. Looking to tag onto this thread and see if there is any concensus. If a bottle is labeled for a standard gas with a specific MOD, filling it up with "whatever" and diving it improperly labeled sounds like an accident eventually waiting to happen.

I've done this. I have an al40 clearly labeled with a 70 foot MOD stickers for 50% O2. I've brought it with as a pony filled with 32% on a few dives. I had a roll of white gaffers tape in the truck, so I stuck a strip of the tape over both MOD labels so I didn't need to peel the stickers off and replace them later. I wrote my gas analysis on the gaffers tape covering the mod stickers with a sharpie. That felt like a reasonable compromise to me, and easily peeled off when the tank was emptied and refilled, revealing the original mod stickers.

As a check/balance, before starting any dive (tec or rec), each tanks contents should be analyzed by the diver personally that same day regardless, so an O2% variation "surprise" shouldn't ever happen if adhering to best practices.

 

[LFMarm]

Not changing MOD stickers based on actual O2 content is lazy.

I want to know what gas I and team have in the tanks so I rather make new handwritten stickers after the pre-dive gas analysis.

 

[steinbil]

If I remember correctly, I think my Tech instructor made a point of telling us always to mark the bottles correctly and not to start down the road of filling a MOD21-bottle with air or 32%, since the labeling is such an integral part of one of the most important protocols for safety on a tech dive - the gas switch. Once you start deviating "just for this practice dive" or "since it's only 32%" you're headed for a slippery slope of sacrificing the integrity and trust you have in the MOD-labels. At least that was my interpretation.

If you don't want to pay for extra stickers, I think @Badger7's suggestion to to cover the MOD-sticker with gaffers tape and a handwritten MOD for practice purposes is reasonable. Personally, I just use 50% for practice, since I get cheap fills locally.

 

[Nick_Radov]

I think that people use standard MOD stickers because they are nice and very easy to read prints and as you say conservative from MOD perspective. Personally I don't like this practice –

Then why are you in the DIR forum? It's not safe to do a gas switch without a large, clear MOD sticker on the stage.

I want to know what gas I and my buddies in the tanks so I rather go for handwritten stickers with the actuals from my pre-dive gas analysis.

Obviously we also have handwritten stickers with the actual gas analysis attached to the tank neck when filled, and verified on the day of the dive. There shouldn't be any need to restate that here.

 

[LFMarm]

It's not safe to do a gas switch without a large, clear MOD sticker on the stage.

Fully agree. I use large, clear MOD stickers on all tanks, they are just not as nice as the ones you can buy from a shop.

 

[LFMarm]

Obviously we also have handwritten stickers with the actual gas analysis attached to the tank neck when filled, and verified on the day of the dive. There shouldn't be any need to restate that here.

What I meant it that I write on the MOD stickers the actual MOD of the gas after analysis. I have no doubt that everyone using the standard printed stickers is also doing the gas analysis.

 

[rjack321]

What is the current thinking on filling stage tanks with an FO₂ lower than that normally indicated by the MOD sticker? Like I've seen divers do training and skills practice with stages marked "70" (ft) or "21" (m) but filled with 21% or 32% instead of 50%. This is totally safe from a maximum operating depth perspective: the tank can be breathed at 70ft without exceeding any limits. But if you accidentally bring that stage on a real tech dive you'll have a bad day.

The only folks I see doing this are people practicing for a T1 class. In which case the stickers are just put on prematurely in a "look cool" sense. My preference would be to just leave the sticker off. But in reality, I haven't ever heard of this being an issue because the pre-T1 students only have 1x Al40 anyway and treat it like gold and nobody else is touching it lol. Net... I know of no actual mix-ups where it's been a problem.

This is not to discount the double fatality in FL where the kids were breathing hypoxic mixes in the pool unsupervised and died.

 

[NothingClever]

Cylinder marking should accurately reflect the contents.

I can’t think of a good reason why we (technical divers) should overlook this.

I carry a roll of 2” black electrical tape and a white paint marker for this.

ETA: My deco tanks are clearly marked with proper decals for 21m and 6m along with my name for PID in advance of a switch. Having to put another gas in them would be an emotional event so to speak.

 

[rjack321]

Cylinder marking should accurately reflect the contents.

I can’t think of a good reason why we (technical divers) should overlook this.

I carry a roll of 2” black electrical tape and a white paint marker for this.

Sure but someone who just bought their first al80 or al40 stage doesnt have to stress about the marking when they aren't even fully trained to use it yet. They can paddle around in modest nitrox depths for a dive or two with stage marked with masking tape just fine. Heck the UTD people were advocating not marking bottom stages at all at one point (which I totally disagree with)