Air Refills Mixing With NITROX Gas Remains...

[MXGratefulDiver]

Seems the opposite of common sense to me. More a case of passing the blame. I'm far happier with the end user being solely responsibly for knowing what he is using and the proper usage.

It is common sense.

The mixer should analyze the cylinder to assure that the mix came out within a percentage point of what the user requested.

The user should analyze the cylinder to know, and mark, the mix that's in it.

Personally, I think any cylinder that's rented from a shop that mixes nitrox should be analyzed before it's used ... humans make mistakes, and breathing a cylinder with a different mix than what you think is in it can have catastrophic consequences if you're planning a deep profile. For the few seconds it takes to put an analyzer on the tank and assure that you KNOW what you're breathing, seems like common sense to me that you'd want to take that simple precaution.

When did they drop this stuff from the basic Nitrox curriculum anyway?

... Bob (Grateful Diver)

 

[MXGratefulDiver]

I certainly agree that you should analyze, but there maybe situations where you can't. One of the dive shops that I frequent sells Nitrox, but doesn't have an analyzer available for public use. You have to take their word for it that you have 32%. Ironically, they then ask you to sign a log book and put in the mix and MOD. I can sometimes be a smart ***** so I sign the book and put Unknown for both mix and MOD, just to make a point.

That's asking for trouble ... I would never, ever, EVER take a cylinder out of a shop without analyzing the contents for myself. If they wouldn't let me use their analyzer, I'd want to watch while they do it.

... then I'd avoid that shop like the plague afterward ...

... Bob (Grateful Diver)

 

[hvulin]

you can always go for a gas blender course and then you'll fully understand how and what to do (to get to whatever ppO2 you are trying to get to)

 

[DeepSeaExplorer]

you can always go for a gas blender course and then you'll fully understand how and what to do (to get to whatever ppO2 you are trying to get to)

Yep... I know how to mix and would never accept a PP fill without testing. My ability to mix helps me estimate the O2% on top-offs and understand the criticality of the need for testing.

However, banked mixes where the content of the bank HAS been tested, but outside your presence, may be a different issue. When it comes to banked mixes, I occasionally get a funny look when I ask to test 32% premix. I've even been told, "It's premix. Why do you need to test it?" However, when dealing with premix, and a shop that pumps a lot of gas, and knows what they are doing, I can and do accept it.

My only point is that there are some dives and circumstances where testing is either not possible, or due to using a mix well below the MOD, not completely necessary. If you're not exceeding the mod, then you can work with the mix and estimate the amount of bottom time fairly accurately. But, it's a judgement call and I am certainly not recommending not testing.

 

[MXGratefulDiver]

"It's premix. Why do you need to test it?"

Well, I can think of two reasons ...

1. I didn't see them mix it.
2. I didn't see them putting that mix into my tank.

In either case, I'm not willing to take someone else's word for it. I want to make sure I know what I'm breathing.

My only point is that there are some dives and circumstances where testing is either not possible, or due to using a mix well below the MOD, not completely necessary.

Guess I'm just having a hard time imagining what those circumstances might be. Even if you don't own an analyzer, any shop that's selling nitrox must have an analyzer handy. It takes about 10 seconds to analyze a tank. Perhaps it's not necessary ... but isn't even a remote risk worth 10 seconds of your time to mitigate?

... Bob (Grateful Diver)

 

[DeepSeaExplorer]

Guess I'm just having a hard time imagining what those circumstances might be. Even if you don't own an analyzer, any shop that's selling nitrox must have an analyzer handy. It takes about 10 seconds to analyze a tank. Perhaps it's not necessary ... but isn't even a remote risk worth 10 seconds of your time to mitigate?

... Bob (Grateful Diver)

Gettting a top-off at a shop that doesn't sell Nitrox and thus doesn't have an analyzer and transfilling at home.

 

[Scubakevdm]

Gettting a top-off at a shop that doesn't sell Nitrox and thus doesn't have an analyzer and transfilling at home.

I would test it.

 

[Colliam7]

That's not done in the UK? Or rather, I should ask, where is that not done?

Although some shops make you sign a fill log its not a legal requirement. The responsibility is solely on the person requesting and buying the gas for verifying its contents and use. (You don’t need cards to buy gas either by law although some places annoyingly ask for them). I personally like it that way - responsibility should always lie with the end user.

I am confused as to whether there is disagreement here. What I think Thal is saying is that, irrespective of law or regulation, there are common sense practices that should be followed when dealing with nitrox, which include analysis by the filling operation, and analysis by the end user. What I think String is saying is that analysis by the filling operation is not a legal or regulatory requirement in many / most (?) European countries, AND that he prefers the final responsibility to rest with the user. I don’t see disagreement. In the US it is neither a legal nor regulatory requirement (for analysis by the filling operation), as far as I am aware, although individual states may differ. But, any operation that ‘dispenses’ nitrox, and does not analyze the tank contents after filling and before delivery to the customer is an operation with poor quality control, even if all they dispense is a premixed product. And, in the US at least it is certainly common sense from the perspective of minimizing legal liability. In doing nitrox fills as a commercial endeavor, I am selling a product which may be dangerous if used improperly. I can’t prevent Joe Bozo from knowingly diving to 300 ft on a correctly filled and labeled 40% mix he got from me. But, I want to prevent Joe from unknowingly diving to 130 ft on 40% (unknowingly, because he thought it was 28%, based on a sticker I put on the tanks, incorrectly saying it was 28%, when it was actually 40%) even if he is a Bozo and didn’t analyze it himself. Yes, it is his final responsibility, but I don’t want to contribute to an accident. (OK, someone will argue that I might be contributing to a much-needed cleansing of the gene pool. But, the hassle of the aftermath isn’t worth that satisfaction.) Moreover, I want to know that I am reliably producing my product, whether by PP filling or the use of premix. I don’t think Thal or anyone else is disagreeing with String, that the end user must accept final responsibility for use. But, best practice behavior also suggests that the filling operation should want to monitor the quality of their filling process, and a very good way of doing that is to analyze each tank after filling, AND log the results.

 

[shadragon]

When I play Devils Advocate for example purposes, quoting me literally and yelling "Error" means you didn't either understand the OP or jumped to conclusions. That is not directed at any one person as the majority of responders went off-topic. In fact, we averaged one on-topic response per page.

Yes, you are supposed to analyze your tanks. That is known as the "Well, Duh..." response. Now, lets put on our imagination hats for a second, c'mon you can do it. And pretend you don't have the NITROX course. You are an OW qualified vacation diver climbing onto a dive boat or liveaboard that has NITROX on board. Not only does that put you in the majority, but it also means you don't know you should test the mix. None of the tanks have NITROX stickers. The boat uses black and green caps on the tanks to tell the difference. However, the example diver does not know that. Heck, to them a tank is a tank and they forgot to mention it during the briefing. Besides, they have not dove in 18 months and are having a hard time remembering which end of the tank the BC goes on for their SCUBA refresher. They had a group of advanced divers on the trip before and all had NITROX in the tanks. Our example diver didn't pay for the enriched air on their trip because they didn't take the course and are on a budget. They only dive twice a day anyway so why bother. So the dive boat knows this and fills your tank with air...

Now, did the boat staff purge the remaining NITROX from the tanks before filling or was the crew busy with a diesel engine or mooring issue and just topped them up at the last minute? Was the deck hand going through a break-up and not thinking straight? Was he supposed to empty the tanks, but didn't cuz he just wanted the day to end so he could go home and crack open his 151 proof?

I am going to use three very carefully chosen words here: Duty of care... Off loading the responsibility onto the diver WITH the NITROX course is probably doable. He or she knows better. However, this probably does not apply with the diver described above. That is just one example. Others who get what I was saying have mentioned equally compelling alternates (Thanks).

So back to the two questions I asked originally: Has this situation ever occurred resulting in injury? Does your local shop have procedures in place to stop this from happening?

 

[Ironman]

So back to the two questions I asked originally: Has this situation ever occurred resulting in injury?

I am not aware of documented incidents involving diver injury resulting from this situation.

Does your local shop have procedures in place to stop this from happening?

I previously cited mine / ours.

When I play Devils Advocate for example purposes, quoting me literally and yelling "Error" means you didn't either understand the OP or jumped to conclusions. That is not directed at any one person as the majority of responders went off-topic. In fact, we averaged one on-topic response per page. Yes, you are supposed to analyze your tanks. That is known as the "Well, Duh..." response. Now, lets put on our imagination hats for a second, c'mon you can do it. And pretend you don't have the NITROX course.

In fairness to the 'quoters', and those who went astray: The OP conveyed no indication that it was a 'Devils Advocate' post. You cited what was apparently a recent personal experience. The post was liberally laced with 'I' references. Your profile indicates you are a nitrox-certified diver. The conclusions that some may have drawn are not illogical. The example now cited, a non-nitrox certified OW diver, on a boat where apparently the only attributes that are used to distinguish nitrox tanks from air tanks are colored caps, is another kettle of fish altogether. Both are interesting scenarios. They are not the same, although some of the statements about procedures may be equally applicable.