Nitrox equipment

[Jef]

My wife and I are taking a nitrox class next week and I have been doing my pre-class reading of the text book. I was surprised last night when I read that I’m required have a nitrox analyzer and all the equipment needed to use it, cables, oxygen pure cylinder, …. I’m not ashamed to tell you I’m already going broke with all the scuba equipment my wife and I are already purchasing; we just bought dive computers last week.

My question to you folks with more experience than me, (which is probably most people on the board), is do those of you diving with nitrox really have this equipment and do you test your cylinder every time you have it filled or when renting it from a dive shop?

Quite frankly, if we have to purchase this extra equipment we may have to cancel out of this class until another time.

Forgive me if this topic has already been covered, I did a search on it and didn’t find what I was looking for.

 

[devilfish]

Jef,
Every time you dive you should annalize your own tank and record and mark it on the tank. Most resorts do have an annalizer for you to use when they do the fill. Some charter boats may not have an annilizer but that should be done at the fill station when you pick up your tanks.
As for if you must buy an annalizer, the course should provide one for students to use. You should not be required to buy one to take the course. Of course its nice to have your own.

 

[dkerr]

I don't have one of my own, but as devilfish said you need to check it at the fill station. The EANX mix can drastically affect your dive planning so you dont want to show up to the dive site only to find your mix is too O2 rich for the depth of the dive. Any shop (at least the ones I go to) that fills nitrox will have the O2 analyzer readily available.

 

[roakey]

Jef,

You should be able to either use the shop's analyzer, or witness the shop analyzing your cylinders. If you’re not planning on doing a lot of Nitrox diving, I’d just go this route because the sensors in analyzers have a limited shelf life (2-3 years) and if you’re only diving Nitrox one or two vacations a year, I wouldn’t buy one.

In terms of your cylinder, you only need it ready for oxygen service if the shop does partial pressure blending. If they use a membrane system your cylinder must be as clean as everything else (eg. not at all) for mixes up to 40%.

If you do want to buy an analyzer and you’re able to do basic soldering, build one yourself. You can build one that reads O2 % for around $100. If you want to use a multimeter and a calculator (the bare-bones approach), you can “build” one for around $60. These are just as accurate as the store bought brands, because the accuracy is in the sensor, and that you go out and buy.

For more information on building O2 analyzers and for purchasing sensors, see:

http://www.cisatlantic.com/trimix/tools.htm (search on “sensor” and “analyzer”)
http://www.airspeedpress.com/ (The Oxygen Hackers Companion has plans)
http://www.oxygenanalyzer.com/
http://oxycheq.com/index.html

The Oxygen Hackers Companion would be a good book if the Nitrox mixing process is of any interest to you.

Lastly, use the “search” function on this board to search on “Nitrox” and “Clean.” Yes, you’re going to get a ton of topics but many you’ll be able to discard with a quick glance. Others will give you far more information about Nitrox than you’ll learn in class. As a warning, some of the discussions, especially the O2 cleaning ones can get pretty, shall we say, “spirited.”

Roak

 

[landlocked]

Don't get too concerned. The way it works here. I go into the shop to pickup the Nitrox. The shop has tested the tank and logged the mixture in a log book maintained for that purpose. As I pick up the tank we test again and I enter my findings in the book. I don't have an analyzer yet and I get by just fine. I would make sure that your tank (if you have your own) and reg have the necessary o-rings and lubricant. That is about all of the must spend things. Nitrox does seem to offer sufficient benefit to justify the additional training and effort.

 

[daylight]

Jef,

Roakey gave a very comprehensive answer. I can't add much other than to emphazise what an excellent resourse Oxygen Hacker's Companion is. The writing style is straightforward and I found it clarified some of the questions I initially had. I really like Vance's common sense approach to the subject.

You will do analysis as part of your class. Initally, you can use the analyser that they use at the fill station. I bought and built the kit from Oxycheck and am very pleased with the result. The primary reason I have my own ianalyser s to give an independent check to the fill station's. If they need a new sensor or the battery is low in their analyser you'll get a different reading than they recorded. I guess it may be overkill but i feel it's worth it to do my own check. If something is off, it's easy to figure out where the error is.

I have only found one error in approximately 25 comparisons. They fill guy recorded the wrong EAN value. When I checked it with my analyser, I got a 3% different reading. We went back and checked the gas again with their analyser and got the same value I read. No harm, no foul but that's why you check it yourself.

DSAO,

Larry

 

[wrecNcaver]

When I first was certified Nitrox, I just used the analizer at the shop where I got my fills. One thing I was always taught was that you must analize the tanks yourself, even though the shop did it. This is a safety function. Better two sets of eyes then having a too rich mix and not know it. I do own my own now but that is because when I travel I know that my equipment is working properly.

 

[dc4bs]

I don't own one but my budy does so I use his.

If I'm diving when he can't go, I'll borrow it or double check the fill at my LDS before using it (they really don't mind and encourage safty first).

Remember, the %O2 from any test made soon after a fill may be off by a significant amount (you are testing whatever gas happens to be at the top of the tank). As the 100% O2 normaly gets added first it tends to sit at the bottom of the tank, the tank will read low untill it mixes with the fill gas at the top of the tank. The longer you wait after a fill the better the gas will mix in the tank if partial pressure fills are done.

That could be the answer as to why there was a 3% difference in daylights tank when he picked it up at the shop and another reason you should test one last time right before actualy using the tank whenever possible.

We have done fills, tested them, waited 30 minutes and tested again, waited a few hours and got a 3rd different result.

If you get a nitrox partial pressure fill and want use it right away, roll the tank on the floor a bit to help mix the gas before checking it.

 

[Lost Yooper]

The shop up here requires you to analyse the tank yourself, write the contents on the tank and on the shops log, then sign your life away before taking the tank out the door. It's a good policy, I think.

Mike

 

[BILLB]

Lost Yooper,

The shop I deal with allows the same operation. In fact everywhere I have dived, every shop has allowed me to analyze my own tanks. Many California boats have Nitrox fills on board and they simply allow you to analyze the tanks and log it on their form.

Analyzing your own tanks is the only way to go!