[Andy Phillips]

Imported post

Hi,

Got a bit of a question, I followed a bit of a thread on divernet, made a somewhat facile remark, and then wondered;

Why O2 clean, it can't possibly be the fact that the kit will spontaneously burst into flames, it just can't - surely

So why, does the O2 break down the seals, please if there is omeone out there who knows let me know, the next stage is the library and it's just to quiet in there

 

[John Gulliver]

Imported post

"Why O2 clean, it can't possibly be the fact that the kit will spontaneously burst into flames, it just can't - surely"
As I understand it, that's exactly why. Any traces of oil in your cylinder are liable to cause combustion/explosion in contact with high concentrations of O2. The same applies to ordinary rubber o-rings. The risk is obviously greatest in connection with filling. There was a fire  in connection with filling nitrox at a dive centre not far from where I live about a year ago. Once the oxygen is diluted with air to below 50%, the risk is negligible, I believe. Which is why it is not considered necessary to clean BC inflators, for example.

(Edited by John Gulliver at 11:38 am on Dec. 8, 2002)

 

[Dr Stevil]

Imported post

I won't say anything about the "does oxygen break down the seals" bit here and now as oxygen chemistry is a complex topic, and my interest centres more on oxygen biochemistry.
I'll put something on the "Dive Medicine" forum in the near future, that way the science nerdiness is kept out of the mainstream forums.

Hopefully it may be of some general interest to all as oxygen is often referred to as a "double-edged sword" ie we all need it to live but it is also the thing which makes us grow old and die.
Chee-az
Steve

 

[Dominic]

Imported post

You obviously haven't heard about the titanium DV which spontaneously caught fire when used with Nitrox...

 

[Hobby]

Imported post

The above resonses to your post are quite correct Andy,things can just go...bang!Have a look at these 2 links,they should clear things up for you,if not come back ad shout!Take care,Hobby.
  http://www.mindspring.com/~divegeek/oxclean.htm
  http://www.scubadiving.com/training/science/nitroxfire/

 

[Andy Phillips]

Imported post

Hi,

A lesson to us all.

One of the guy's I work with is an analytical chemist, so, I come into work, and start moaning on about how I can't belive this about O2. Right say's John I'll prove it.

Well, we have an O2 cylinder in the office, John goes home and comes back with a big glass jar with a water lock inlet.

In goes an O ring with a bit of three in one on it, and we happily start fill in the jar with O2 ------ BANG ------

No jar, big cuts on my hand and a strange shakey feeling in my stomach.

Next time I will Blo**Y well listen.

Andrew

 

[Andy Phillips]

Imported post

Hello,

Thought I would add a little addendum to this for those who have any interest, the last post was put up about 10 minutes after I attempted to blow myself to kingdom come.

Once the other two had finished wetting themselves with hysterical laughter we worked a couple of things out.

The O2 cylinder has a flow control, the jar we used had a capacity of 2L, it was set at 2L per min and ran for about 2 mins before going off, (just about the point I was going to say, so you see I'm right) we made a guesstimate that it was about 90% O2, also, the reason why I didn't get so hurt was pretty obvious when you think about it, it imploded not exploded, the O2 had gone, nothing left and the jar just wasn't strong enough.

So, I'm off to get all my regs etc cleaned by a professional, I shant ask anymore stupid questions either - not.

Andrew

 

[Driftwood]

Imported post

I've posted on this subject before and contrary to popular belief, aluminium, titanium and even brass can spontaneously combust in the presence of high FO2 at sonic flow....

Don't belive me?

See The Firefighter Incident or The EMS Incident or TI Reg fire

    Titanium alloys are totally resistant to all forms of atmospheric corrosion regardless of pollutants present in either marine, rural or industrial locations. Titanium has excellent resistance to gaseous oxygen and air at temperatures up to 370°C (700°F). Above this temperature and below 450°C (840°F), titanium forms colored surface oxide films which thicken slowly with time. Above 650°C (1200°F) or so , titanium alloys suffer from lack of long-term oxidation resistance and will become brittle due to the increased diffusion of oxygen in the metal. In oxygen, the combustion is not spontaneous and occurs with oxygen concentration above 35% at pressures over 25 bar (350 psig) when a fresh surface is created.

Causes of O2 fires.....

Adiabatic (isentropic) compression of the oxygen. When oxygen is rapidly compressed, it gets hot. The temperature of oxygen can rise to 1688 degrees F if it is quickly compressed to 2000 psi, hot enough to ignite seals or contaminants within the device. This is why it is recommended that cylinder valves be opened slowly.

A particle larger than 100 microns moving at high speed within a pressurized oxygen system may ignite upon impact and could cause the material, which it strikes to start burning.

Heat generated by the friction of materials rubbing against each other - rare.

Acoustic resonance - rare.

Nice eh? Just remember that next time you play wit' Devil Gas. Please accept my apologies as I can't find the link for the theoretical combustion limits for Al and brass....

 

[Dr Stevil]

Imported post

Incidentally, I once (long time ago) saw a video where a diamond was burnt in pure O2, think it was ambient pressure too

 

[Dominic]

Imported post

Hey, I saw that once.
Drop a white-hot diamond into a vat of liquid oxygen, and hey presto, you've just produced some amazingly expensive CO2!

 

[Tim Ingmire]

Imported post

</span>

Quote[/b] ]Quote: from Dominic on 2:19 pm on Dec. 10, 2002
Hey, I saw that once.
Drop a white-hot diamond into a vat of liquid oxygen, and hey presto, you've just produced some amazingly expensive CO2!

<span =''>

Hey I wonder if the wife would go for that instead of diamond earings?  

"Here darling, I've got you some CO2 made from Diamonds".

 

[Jay]

Imported post

Nah - stick the the trusty pearl necklace mate. Always a winner I find!