PADI Nitrox Course Question

[HKGuns]

I'm starting the local PADI Nitrox course and I question one of the exercise answers in the course book. I think it conflicts with the text of the book and would like the views of others who have experience or are instructors.

The book states:
"If you ever need to use air in an enriched air cylinder, no problem: Take it to an enriched air fill center. They treat the fill as enriched air in all respects, including marking it EANx21."

The question:
If an oxygen service rated enriched air cylinder is filled with standard compressed air, you should:
a. refill it with enriched air very cautiously.
b. have it serviced by someone qualified to work on enriched air equipment.
c. destroy the cylinder
d. No special action is required.

I answered d based on the text above and they claim the correct answer is b.

What am I missing?

 

[pauldw]

As I understand it, the theory is that there are two kinds of air that can go into tanks: regular air from regular compressors (which is pretty clean), and air that comes from the sort of super duper clean compressors that are used to blend nitrox (and have less hydrocarbon). So, if you get a nitrox tank filled with regular air from a regular compressor, you might have just dirtied it beyond what's safe for oxygen use in the future (and would then need to have it oxygen cleaned). But if you want just air in it without oxygen enrichment, then get it run through a nitrox compressor than blends super duper cleaned air with oxygen, but you only get the air part. You might not want to say "super duper" when going to the dive shop.

 

[Barnaby'sDad]

Standard air vs. “hyper” (O2 service) air.

Your quoted paragraph is referencing hyper air, which can be added to an O2 clean cylinder.

The test question is referencing standard air, which should not be added to an O2 clean cylinder. ‘B’ is correct.

 

[HKGuns]

Thank-you both, now that makes sense. They didn't go into that level of detail in the book and they assumed I wouldn't follow their instructions of getting it air filled at a Nitrox certified shop.

 

[TMHeimer]

The rare times I have used Nitrox it was always in rented tanks filled by the shop(s). Am no expert, but believe that whether or not you can safely fill your Air tank with Nitrox may depend on what sort of blending they do at the shop compressor. I think this is what pauldw is talking about.

 

[pauldw]

After I took the nitrox class recently I had the same question, and when I found out the answer I asked all the dive shops in my state a few things about their nitrox practices including whether they offered EAN21, and some didn't think there was any such thing as EAN21. In one case, a shop instructor thought I was an idiot.* So, depending on where you are, you may have a hard time getting it.

*This time, without good reason.

 

[Barnaby'sDad]

After I took the nitrox class recently I had the same question, and when I found out the answer I asked all the dive shops in my state a few things about their nitrox practices including whether they offered EAN21, and some didn't think there was any such thing as EAN21. In one case, a shop instructor thought I was an idiot.* So, depending on where you are, you may have a hard time getting it.

*This time, without good reason.

I don’t think that many people outside of an academic setting refer to it as “EAN21.” It’s generally referred to as “O2 clean air” or “hyper air.”

Any shop that partial pressure blends is going to have hyper air.

People that are fortunate enough to live in or frequent areas where banked Nitrox is common don’t have to worry about this. In that situation...they could add banked Nitrox (ex. 32%) to any cylinder (doesn’t have to be oxygen service clean) and top it off with standard air to get down to the desired blend.

 

[Marie13]

People that are fortunate enough to live in or frequent areas where banked Nitrox is common don’t have to worry about this. In that situation...they could add banked Nitrox (ex. 32%) to any tank (doesn’t have to be oxygen service clean) and top it off with standard air to get down to the desired blend.

Yep, often get banked 32% in my non-O2 cleaned tanks. Which is nice since O2 cleaning is $50/tank.

 

[Barnaby'sDad]

Yep, often get banked 32% in my non-O2 cleaned tanks. Which is nice since O2 cleaning is $50/tank.

Yup. It’s expensive, not all shop employees that fill cylinders are rated to blend (if a blender isn’t available...I’ll just get hyper air fills), and some blenders are better than others. Ex. I got one fill that was 8% off a few months back.

 

[HKGuns]

How often do you need to spring for a $50 a pop O2 tank cleaning? Please tell me it isn't annually.