O2 analyser is a must or not????

[Scared Silly]

We recently bought our own analyzer. For much of the same reasons others have pointed out, history usage, sensor, etc. While on a live-a-board which had two, ours was in our locker all the time so we never had to search around for one to use. That said buying one was not a high priority as we have been using nitrox for over five years.

One reccomemdation on buying one - I prefer analyzers where sensor is inside the unit. We had a sticky valve that at first was not providing enough gas that when turned blew the sensor apart.

 

[rsdancey]

The question is not really should you own an analyzer or not, but can you get the tank analyzed after it has cooled and had time to thoroughly "mix" after filling.

A lot of places will put an analyzer on a tank right after they fill it, but the O2 % that results is often substantially higher or lower (say +/-5%) than the actual percentage. It's a good quick way to make sure the tank does have enriched air in it, but not a good way to know what the true mix is for diving.

You should analyze your tanks personally, regardless of what the fill station says is in the mix, they're not the ones taking it under water - you are. If you typically drop your tanks off to be filled and pick them up the next day, and the fill station will let you use their analyzer, you're probably fine to check the mix at pick up and label the tanks at that time.

For the saftey margin involved, and the convenience, I found that owning my own analyzer was well worth the minimal expense.

Ryan

 

[RonFrank]

The key is to analyze the mix before diving it. How that happens is up to you.

My shop as at least three analyzers, so when I pick up the tanks, I can always analyze them.

On a boat if you are planning on diving Nitrox either 1) make sure you analyze tank before loading it on the boat, or 2) Make sure the boat has one, and it works.

This is one reason some like to own. They don't run the risk of getting on a boat only to find that the Nitrox analyzer batteries are dead, and you have to call the dive.

 

[Scared Silly]

A lot of places will put an analyzer on a tank right after they fill it, but the O2 % that results is often substantially higher or lower (say +/-5%) than the actual percentage.

When you are adding gas to a bottle the mixing is pretty much instantaneous due the nature of the flow of the gas into the bottle as such I would say this is nothing but an urban ledgend. The few times I wanted a particular mix and mixing it myself I have been able to hit it with in less than an percent each time. I.e started with air in the bottle, added 100% O2, then topped it off with air. Each time I measured it with in a minute of topping it off and as I said got the percentage I wanted.

If you want to see it for yourself and do not have access to filling your own bottle try the following: go into a closed room, near one corner put a pile of fine dirt, turn on your shop vac and blow the dirt. Within a few seconds the room will be filled with dust.

 

[Dive-aholic]

There's no "additional mixing" that takes place in the tank after the fill. It happens during the fill. If there were additional mixing, then you wouldn't be able to take the tank from the shop right after filling. It would be too dangerous if the mix were off. Nitrox mixing is supposed to result within 1% of the requested mix. Even 1% is too much though. I prefer less than .5%.

As for owning your own analyzer, when I first got Nitrox certified, I didn't own one, but I also didn't dive Nitrox very often. I now dive Nitrox almost exclusively and do own my own analyzer. I will also probably be building a 2nd one this summer. It's a nice thing to have when you're diving it all the time. Even though I do mark the mix, I like to verify right before the dive, especially my deco mixes. So basically, figure out how often you'll be diving Nitrox and decide whether it's worth it or not to buy the analyzer.

 

[rsdancey]

I get my tanks filled with 32% every week.

Every week, the mix "at the store" right after filling is off. I've used my analyzer and their analyzer on site; same mix readout. Usually analyzes at about 37%.

Wait an hour (or put the tanks into a cold water bath for 10 minutes and give them a good shake & roll) and the mix returns to exactly what it should be: 32%.

I think there's a message here in the archives somewhere from a diver who scoffed at the whole "not mixed" thing for years, then finally ran into a situation where it happened to him. Careful mixing, analyzer reports unexpected O2%. The LDS owner said "roll the tanks around for a few minutes, then anaylze it again." - Our Hero laughs at the guy, who says "no really, do it", so Hero decides "what the hell", and afterwards the mix analyzed as expected.

The gas in your tanks is at a different pressure and temperature than the gas coming in from the fill station. If you're not doing blended fills, but doing partial pressure, then you're adding gasses that aren't identical to the tank mix either. Why is it so surprising that these new gasses don't "mix" instantly with the pre-existing tank gas?

Ryan

 

[Dive-aholic]

A 5% discrepancy? That's interesting. I get PPB fills on a regular basis. I analyze before I leave. I analyze right before the dive. The reading is always within .5%, usually less. And I don't roll my tanks, especially not the doubles. Do you really think rolling a tank is going to mix air? Like I said, if you had to wait for the air to mix, then you wouldn't be able to take your tanks right after they're filled. When I get my tanks filled, I bring them in, watch them get filled, and leave with them right after analyzing them. No "mixing" time required.

 

[DepthCharge]

When you are adding gas to a bottle the mixing is pretty much instantaneous due the nature of the flow of the gas into the bottle as such I would say this is nothing but an urban ledgend. The few times I wanted a particular mix and mixing it myself I have been able to hit it with in less than an percent each time. I.e started with air in the bottle, added 100% O2, then topped it off with air. Each time I measured it with in a minute of topping it off and as I said got the percentage I wanted.

If you want to see it for yourself and do not have access to filling your own bottle try the following: go into a closed room, near one corner put a pile of fine dirt, turn on your shop vac and blow the dirt. Within a few seconds the room will be filled with dust.

This is true of Nitrox.Trimix however is a different story................

 

[Charlie99]

A 5% discrepancy? That's interesting. I get PPB fills on a regular basis. I analyze before I leave. I analyze right before the dive. The reading is always within .5%, usually less. And I don't roll my tanks, especially not the doubles. Do you really think rolling a tank is going to mix air? Like I said, if you had to wait for the air to mix, then you wouldn't be able to take your tanks right after they're filled. .

I'm just a nitrox user, not a blender, but I've seen this whole discussion (and the related trimix discussion) often enough that I believe that there is more than just urban legend involved.

As another poster has mentioned, there have been several credible reports of this sort of thing happening. It seems to correlate with extremely slow air topoffs that leaves the gases stratified --- most commercial fill stations aren't willing to take forever to fill a tank and they add the air topoff fast enough that it does a good job of mixing the gases.

 

[E Rick]

Thank's to all of you!!!! Really help me to make my mind... I'll buy an O2 analyser!!!