Nitrox: Should I be worried?

[Snoweman]

I know Tres Pelicanos has an analyzer. I don't know if they have two. I think we had to chase down their other boat to get an analyzer from it.

 

[uncfnp]

The reality for Cozumel is that a lot of nitrox divers do not analyze their tanks. The risk is low, the fill stations use membrane and not partial pressure. I would not dive a tank filled with partial pressure that I did not analyze.

 

[Rob9876]

I know Tres Pelicanos has an analyzer. I don't know if they have two. I think we had to chase down their other boat to get an analyzer from it.

So with them you do your analysis on the boat? I'm also new to Nitrox, and diving with them soon.

 

[tmassey]

So with them you do your analysis on the boat? I'm also new to Nitrox, and diving with them soon.

Here’s the question: do you want to find the problem while a stack of tanks is within easy reach, or do you want to find the problem when you’re limited to asking if there’s any extra tanks on the boat? Which may or not be what you expect — or even need?

I don’t care who the operator is: I would strongly recommend you do any analysis before you put the tanks on the boat, let alone before the boat leaves the dock.

Edit to add: I guess if the tanks are *only* on the boat, you may not have a choice. The point is: as *early* as possible.

 

[Snoweman]

Yes. You can test your tank if you want to. I dive air on my deep dive and EAN 36 on my second dive. I use the remaining air on the first tank to calibrate the analyzer before testing the EAN 36 tank.

 

[Snoweman]

Here’s the question: do you want to find the problem while a stack of tanks is within easy reach, or do you want to find the problem when you’re limited to asking if there’s any extra tanks on the boat? Which may or not be what you expect — or even need?

I don’t care who the operator is: I would strongly recommend you do any analysis before you put the tanks on the boat, let alone before the boat leaves the dock.

I don't know if any of the shops have a CO analyzer. Analyzing the tank on the boat means that I will adjust the computer EAN setting before the dive. I dive air first, so I don't worry about having EAN 36 (or greater) on the deep dive by accident.

 

[jgttrey]

Yes. You can test your tank if you want to. I dive air on my deep dive and EAN 36 on my second dive. I use the remaining air on the first tank to calibrate the analyzer before testing the EAN 36 tank.

If you are confident that your first cylinder was air. Calibrating off dry air from a cylinder is better practice if you are confident that it is, in fact, air. Otherwise, I'd rather calibrate to ambient. If I'm subsequently off by a percent or two because of humidity or whatever, it's immaterial.

Better to analyze before you depart the dock, but that's often hard and not a deal breaker. If the mix isn't what its supposed to be, just figure out the new MOD and stay above it. A couple of percent off, no big deal. But, I have received cylinders that were 10% too rich in Mexico before and that is material. Diving to 100' on EAN 42 is no bueno, as they say. So, yes, know what you are breathing.

 

[uncfnp]

So with them you do your analysis on the boat? I'm also new to Nitrox, and diving with them soon.

Yes. The tanks are already loaded on the boat and the regulator will be connected. If you are doing it yourself make sure you have the air flow set before you place the analyzer to the valve. I read the second tank first then use the purge on the my reg connected to my first tank to run a gentle flow through the mouthpiece then get my reading there. Another more cautious way is to use the valve to give just a gentle flow while depressing the purge. Of course you could also just disconnect the regulator.

The only time the boat did not have one was a rental for the shop. But as with Snoweman, they managed to track one down. Now we just carry our own.

 

[lionfish-eater]

If divers are concerned about o2 content of tanks they are told have nitrox, why aren't they equally concerned about tanks that they are told have air? If mistakes can be made with nitrox fills, why can't similar mistakes be made with tanks that are "supposed" to contain air.
Makes sense to analyze all tanks if one is concerned about exceeding mod's.
Makes no sense to say, "I dive air so I don't need to analyze my tank.

 

[Joneill]

Yes, you’re being paranoid. Bad air can happen on just regular air. Smell the air when you pre-breathe your reg. Does it smell weird? Ask for another tank.

As for nitrox, check to see ahead of time if there’s an analyzer on the boat. If not, dive regular air.

While diving foul/off odor gas is certainly a bad idea, smelling gas is not a very reliable test for bad gas! CO is odorless and potentially lethal at depth at relatively low concentrations. I typically analyze every tank I dive with my own Cootwo to ensure I know what I'm diving (air or nitrox) and that CO levels are not a concern.