DIR- Generic Marked stages filled with lower O2?

[inquis]

Another angle... The MOD of my 50% bottle is 80 ft because I dive at altitude. However, I switch to it at 70 ft and use a 70 ft MOD sticker because I also dive at sea level. (So does everyone in the team.) Is it bad that we're using "mismarked" bottles? I don't think so, it's just a more conservative PO2 than 1.6.

 

[SpeedyJ]

My guess is the urge to do this is strongest at the start of your tech diving addiction. At that point, you likely only have one rigged cylinder, and I could see the urge of getting a few practice ascents in with a cylinder topped up at the closest shop or at a quarry as opposed to hitting up a tech shop for a proper fill.

These days I just keep a couple cylinders with 32% in them marked appropriately, and would likely recommend the same to a new tech diver. If I want to practice for a class or test weighting, I'll just grab one of those. Beyond not worrying about swapping stickers, it keeps my O2 clean tanks away from busy shops that may not have the best fill station hygiene. After all, isn't acquiring more tanks off craigslist and marketplace part of the hobby?

 

[Pavao]

I've been hesitant to respond, but some of the above sounds similar to using a color-coded regulator to ID the gas in a tank. I think everyone would agree that's a bad idea, but isn't equating a 21m MOD sticker to 50% kind of the same thing?

No, the MOD sticker is “permanent”, that’s what makes the cylinder a DEDICATED cylinder. Regs go on and off every time the cylinder is used, a dedicated cylinder only sees one gas gets put on it, if it isn’t, it needs to be fixed.

The analysis tape on the neck is the authoritative identifier. The diver should be referencing that

No, tape on neck identifies the cylinder was verified gas matches MOD sticker of dedicated cylinder after filling, if gas didn’t match, it needed be addressed. A large MOD sticker is much easier to reference, specially from afar by your buddy.

 

[AeroSpartacus]

On top of everything else mentioned here, consider the possibility of thinking you put a lower O2% gas into one marked high but actually didn't. If you're going to put a sticker at all, stick to what it says (and re-verify anyway)

 

[justinthedeeps]

I think this topic highlights another issue with an emphasis on over-standardization of equipment, gases and protocols, particularly when it is overdone in the names of "consistency," "unification," "clarity," and "efficiency."

Some agencies seem to have created a culture of overemphasizing their approach and standards so much that it has warped people away from simpler, safer, more logical, and more correct processes that already existed.

Obviously, the cylinder labeling should always be re-considered and then correctly expressed before every dive, and immediately after gas analysis. If the exact type of sticker or label is a hangup, this is a perilous descent into over-conformity. The only rules are simple: it should be clearly visible, accurate for the next dive, and not fall off. (Many tape/marker combos can satisfy these requirements.)

The MOD shown on the cylinder can reflect more than just the oxygen content of the gas. The MOD depth on the cylinder should indicate the actual maximum depth that you plan for the gas to be used on the actual next dive(s). This obviously can change, even if the gas doesn't.

For an air diluent on a CCR dive, the MOD of ordinary air is now considered to be 40m (130') or even 35m, because of gas density. Its MOD should be labelled that way in this context. Maximum Operating Depth

ppO2 is only one of multiple things that could factor in. Dive plan could also factor in. Dive conditions and dive plans might influence the gas parameters you consider safe at planned depths. There is also gas density, and END, if that matters for the dive.

"Fixed permanent stickers" sounds like a recipe for mistaken assumptions, confusion above and below water, and accidents, should the parameters of the dives change, as in the example given originally

 

[rjack321]

No, the MOD sticker is “permanent”, that’s what makes the cylinder a DEDICATED cylinder. Regs go on and off every time the cylinder is used, a dedicated cylinder only sees one gas gets put on it, if it isn’t, it needs to be fixed.

There is no single gas that everyone agrees on that goes into a 100, 120, 150, or even a 200 bottle.

Past 20 and 70, the MOD =/= and particular gas although it's usually just no more than 2 options. 120 is 35/25 for some folks and 30/30 for others for instance. 150 is 21/35 for some and 25/25 for others. 190 is usually just 21/35... The disparities are real.

 

[crofrog]

There is no single gas that everyone agrees on that goes into a 100, 120, 150, or even a 200 bottle.

Past 20 and 70, the MOD =/= and particular gas although it's usually just no more than 2 options. 120 is 35/25 for some folks and 30/30 for others for instance. 150 is 21/35 for some and 25/25 for others. 190 is usually just 21/35... The disparities are real.

As long as it’s agreed upon in the standards you’re diving in it doesn’t really matter than it doesn’t align between gue / utd.

The team needs to be on the same gasses.

 

[rjack321]

As long as it’s agreed upon in the standards you’re diving in it doesn’t really matter than it doesn’t align between gue / utd.

The team needs to be on the same gasses.

I agree - I'm just saying the while you can fairly reliably expect a 70ft bottle has 50% (mostly), the expectation that the 120 bottle on the shop floor has X/Y contents is even more erroneous

 

[Pavao]

There is no single gas that everyone agrees on that goes into …

Yes, this is true. I think the issue lies on “everyone”, meaning not everyone follows the same standards, and if everyone has their own set of standards, then that’s not much of a standards. I follow standard gas practices, if someone comes along using best mixes, it’ll be reasonable to expect our bottles won’t line up.

Past 20 and 70, the MOD =/= and particular gas although it's usually just no more than 2 options. 120 is 35/25 for some folks and 30/30 for others for instance. 150 is 21/35 for some and 25/25 for others. 190 is usually just 21/35... The disparities are real.

I have 100’ bottles with different mixes, but it’s either 30/30 or 32%. 35/25 and 25/25 does not exist in my inventory. 21/35 I think is the weird one as it can mean two things depending on weather it’s a bottom mix or a deco/travel mix.
Again, I think the issue is in defining the standards, as it gets broaden, then at some point it ceases to exist.

To your point, actually a bit beyond that in how bad things can get, I was once lining up to dive with two other guys as part of a cert upgrade, ending the phone call I asked what we were diving in terms of gases, I think I’ve said something like, are we bringing our 70 bottles? To which the guy answered “yes”. I showed up with 50%, they showed up with 70% lol.

 

[OTF]

• Analyze and properly label your cylinders every day before diving.
• My AL40 has a MOD 70 sticker on it. When it is full of air I put a piece of tape over the sticker.