Quick Nitrox Question

[Dive-aholic]

The chances that someone rented an air tank from a store, then filled it someplace else with a different blend, then returned it to the shop without telling anyone about it are rather small.

However, the chances that the shop rented a tank previously with a different mix than what you are getting isn't rather small. I rented a set of doubles that had trimix in them. All I wanted was 32%. They didn't drain them, just topped them off. I didn't get 32% and did get some helium. Fortunately, I own a helium analyzer so I caught it. I trust no one but myself when it comes to diving.

---------- Post Merged at 05:11 AM ---------- Previous Post was at 05:08 AM ----------

I'm amazed at you guys. I use my hand to blow some air across the opening in my analyzer. Air is kind of readily available, and yes, it has to be moving, but not moving all that much.

While that method might be acceptable where you live, I've seen as much as a 3% difference in calibrating with dry scuba air vs atmospheric air here in humid Florida, atmospheric being lower. That 3% difference will have quite an effect on the decompression obligation of some of my longer dives.

 

[DaleC]

If one is diving so close to the limits that +/- 1% will make a difference then the error has already been made.

 

[mattoau]

If one is diving so close to the limits that +/- 1% will make a difference then the error has already been made.

Pushing the limits is one thing, but not giving a sh!t is another!

 

[DaleC]

My experience diving is that it need not be all or nothing. There is a happy medium wherein most dives can be done in relative safety without undue fixation on micromanaging the details. Analyze once, mark your tanks in a way that you don't grab someone else's and enjoy the dive. It really isn't that complicated.

 

[Dive-aholic]

If one is diving so close to the limits that +/- 1% will make a difference then the error has already been made.

I have to disagree with this. While a 1% difference might not matter much on recreational NDL dives it can make a difference in decompression dives. And no one really knows where their diving will take them. When I first started diving I had no intention of ever doing technical dives. Now I'm a cave and technical instructor. Fortunately I was taught from the beginning that getting the right mix was important. Had I been taught otherwise I might have continued with that attitude in my decompression diving and found myself in some trouble.

 

[DaleC]

I hear what you are saying but was relating my response to the subforum; advanced recreational but not technical. In this arena I think that planning dives where a deviation of +/- 1% will affect an outcome is shaving the limits too closely and has moved beyond the built in safety net inherent in rec diving.

My argument is not regarding reasonably checking ones mix (I do that myself); it is against pushing the limits of MOD's or NDL's to the edge where a buffer no longer exists. There is more danger of injury there than in errors due to the effects of humidity or tank vs fan blown air on EAN meters.

 

[arthurmnev]

The analyzer is less for you to validate shop's analyzer tech but more to avoid tank mix up and mislabeling. If a shop is well maintained, chances are their blenders will have much more dependable (and expensive) technology than what you can get fitted in your bag. Labeling and attention to who gets what tank, however, is error prone....