It's a good day for gas blending

[Hickdive]

Just finished my first practical exam for my gas blending course. I had to mix 6 bottles of 50%, 3 with O2 and air and 3 with O2 and 32% in 30 minutes..

So you didn't have to fill against the clock? Fair enough; that's not what you wrote though.

However, your attitude to oxygen fill speeds suggests strongly to me that your blending course either didn't cover or didn't emphasise the hazards of oxygen. For a fire you need oxygen, fuel and heat. You've got the first two in spades and, filling at the rates you must be using, you're adding the third. Cooling the cylinder body does nothing to control the heat generated in the cylinder valve as oxygen flows through the restriction of the HP orifice and over the HP seal.

Whether you are 'comfortable' with the speed or if you've seen others fill faster is neither here nor there. Frankly, I wouldn't be standing in any shop if I saw you filling so quickly in it. I suggest you re-visit your training materials and re-read the part on oxygen fires and filling rate. If your training materials don't mention these issues then I suggest you get your money back on the course.

 

[NAM001]

Im not doing trimix mixing, although I can...... I just do nitrox.

Try this: Take 2 tanks and do identical partial pressure trimix blends in each. But do one with the tank standing vertically and the other lying down. Then immediately take a reading from each. No way they will be the same. When I blend my large storage bottles that I can't lay down, it takes a long time before the reading stabilizes at each step. It has a lot to do with entropy. And I use a digital infrared temp gauge to make certain that temp change doesn't enter the equation.


iPhone. iTypo. iApologize.

 

[dbulmer]

Hickdive,

I'm doing a blender course at the moment and I shuddered at his first post
(To the OP: From your original post I drew the same conclusiions as HickDive).

You have small cylinders with fast filling rates hitting the valves.

Although DSAT and TDI cover adiabatic compression - I prefer Vance Harlow's description of adiabatic compression in his book Oxygen Hackers Companion as I feel it reads more naturally than the content in the DSAT and TDI manuals. Harlow's book is good but gets better when you read it alongside an agency manual.

The point I'm trying to make is that the agency course materials describe adiabatic compression in very broad terms - the instructor is expected to fill in the practical details. (As I'm at the start of my blending journey I have bugger all credibility but I am amazed at how poor the course materials are - there's good infomation in there but the presentation is poorly structured and I wish there was a lot more on the practical side)

Ultimately it's down to the instructor - now where have we heard that before?

 

[ScoobaChef]

Ok guys, I accept the criticism and will reevaluate my methods.But dbulmer brings up a good point about the instructor.This is my first time blending, but I have been dealing with pure O2 for over a year. Over that time, a number of people across several shops have taught me or used the same method of filling and handling.Not saying it's right or wrong, but how many times do you need to get the same answer before you believe it's correct.

 

[Wookie]

Proper fill rates into scuba cylinders is all the more critical because there is no way to make the teflon seat of a scuba cylinder O2 resistant, much less O2 compatible. Take it from someone who has burnt up 2 of them, and blessedly we caught the result in a "sniff test" before sending the diver to 60 meters with teflon combustion products in his rebreather O2 cylinder. A O2 fire in a scuba cylinder is no way to make friends or long term customers in the dive business. The 50 PSI/Min fill rate is based on O2 cylinders with brass valve disks and seats. Not the fill rate based on scuba cylinders with brass seats and teflon disks.

 

[dbulmer]

Ok guys, I accept the criticism and will reevaluate my methods.But dbulmer brings up a good point about the instructor.This is my first time blending, but I have been dealing with pure O2 for over a year. Over that time, a number of people across several shops have taught me or used the same method of filling and handling.Not saying it's right or wrong, but how many times do you need to get the same answer before you believe it's correct.

You're ahead of me mate -

The most important part of learning is to be able to say "I know that I do not know" - Socrates

That's where I am right now.

 

[NAM001]

That is the main benefit of formal training. The ability to sort out what is correct and what is common practice which is most often wrong. The list of fine points seams endless. When you foloow the rules there is a great amount of room for error without setting the bomb off. There are some aspects that are the main/ high percentage aspects of an accident. HIgh fill rate is one of them, if not the main one. BTW i say this not to belittle you but to support you learning the proper ways of doing things. Its not rocket science and is safe so long as you dont smoke next to the main rocket booster.
I mean " That woud be really dumb" for real for sure.

Ok guys, I accept the criticism and will reevaluate my methods.But dbulmer brings up a good point about the instructor.This is my first time blending, but I have been dealing with pure O2 for over a year. Over that time, a number of people across several shops have taught me or used the same method of filling and handling.Not saying it's right or wrong, but how many times do you need to get the same answer before you believe it's correct.