Titanium regs and nitrox don't mix??? True or False

[Diver0001]

From what I was told at a seminar it's not a problem until you go past 40%,

In laboratory conditions using a catalyst and within the parameters found on the inside of a 1st stage titanium can be made to sponaneously combust with lower than 40% O2.

In practice the only titanium reg I know of that caught fire was on stage of deco gas.

There was also an incident a couple of years ago with a rebreather that caught fire. IIRC someone said that it was fitted with titanium regs too....

In any case it's clear that titanium is poor choice of materials for high O2 environments.

R..

 

[Diver0001]

So the conclusion I'm reaching is that if I want to dive Nitrox, I probably want to avoid anything with titanium in the 1st stage (too expensive anyways).

However, titanium in a 2nd stage, where the pressure is much lower (no more than 220psi in recreational diving), is fine, and I can safely enjoy holding less weight in my mouth. But it would be totally unsuitable for use in technical diving with trimix and heliox (not a concern for me, though).

Am I jumping to the wrong conclusion?

I'm trying to decide between Atomic M1 (titanium parts in second stage) and Atomic B2 (all titanium 2nd stage) for recreational diving. Mostly with 32% Nitrox, but I can't completely eliminate the possibility of diving air if I plan to go deeper than 90-100 ft.

That's correct. Pressures in the 2nd stage are too low to cause spontaneous combustion and typically the titanium on the 2nd stage is used on hte outside of the housing anyway. It's just for the bling bling.

R..

 

[Diver0001]

There are three things that are needed to start a fire: oxygen, fuel and heat. Using a titanium reg with nitrox gives you two of the three. The third could come from heat caused by the shockwave of 3000 psi air hitting a wall in the 1st stage or trying to pass though the restriction in the HP port.

Actually I think the heat is formed by the rapid oxidation of the material. The same effect (spontaneous combustion) can be seen by exposing phosphorus to air, for example. Most people saw this in their highschool chemistry classes

R..

 

[cyklon_300]

I was aware of that one in San Diego. It was on a 80% tank.

posted shows the cylinder stickered as OXYGEN.

So, is it a separate incident or did the guy just not know how to proper label his bottle...?

 

[boydski]

posted shows the cylinder stickered as OXYGEN.

So, is it a separate incident or did the guy just not know how to proper label his bottle...?

I think Dave was right about the content being 80%. It is a fairly common practice to fill an Oxygen deco bottle with oxygen to ~2100 psi (which is the most you can get out of an Oxygen supply cylinder), and then add air to bring the pressure up near 3000 psi. This results in about an 80% mix, which is similar (deco wise) to 100% and just as dangerous.

I guess he was going for quanity rather that quality, and I do believe you are discussing the same incident.

 

[boydski]

I'm trying to decide between Atomic M1 (titanium parts in second stage) and Atomic B2 (all titanium 2nd stage) for recreational diving. Mostly with 32% Nitrox, but I can't completely eliminate the possibility of diving air if I plan to go deeper than 90-100 ft.

I use both M1 and B2 regulators, and they both work fine for recreational nitrox mixes. The M1 is actually rated by atomic for mixes up to 80% because the first stage is Monel. I use an M1 as my primary, and also on my 50% deco bottle (but not on my Oxygen bottle). Given the choice between an M1 or B2, I'd pick the M1, but you'll be happy with either regulator.

 

[Bearded Diver]

Glad I read this. Really was thinking of getting a titanium reg. Thanks for the useful info everyone

 

[IslandKraut]

Interesting discussion. Aircraft engine pylons use mostly titanium, and most of the internal compressor and turbine blades are made from titanium ... Also help me out here:

Titanium burns at 4.4 bar of partial pressure?
I have seen Atomic regs with titanium bodies and HP plugs.
With Air at 20% O2 and 200 bar would hit the reg with 40 bar of PP O2 on the high pressure side, which is factor 10 of the stated ignition point. At 40% Nitrox you're at factor 20.
I am surprised that we don't see Atomic regs blow up more often.

That said, I can see there being a much larger step with 2100PSI of pure O2...
I suspect in the fire case there was probably some grease involved.

 

[IslandKraut]

But ... from the

Journal of the Less Common Metals​

Volume 3, Issue 5, October 1961, Pages 367-378

A study of metal ignitions I. The spontaneous ignition of titanium​

A study of metal ignitions I. The spontaneous ignition of titanium

Spontaneous ignition of massive shapes of titanium can occur at room temperature when a fresh, oxide-free metal surface is exposed to oxygen under pre…

www.sciencedirect.com

Spontaneous ignition of massive shapes of titanium can occur at room temperature when a fresh, oxide-free metal surface is exposed to oxygen under pressure. Such a surface can be produced by the rupture of a titanium specimen under tension. If these surfaces are exposed to oxygen pressure in excess of 350 p.s.i.g. spontaneous ignition of the sample occurs. With dilute oxygen, using helium or steam as a diluent, higher pressures are required for ignition.

Spontaneous ignition at various concentrations of oxygen was investigated and the effect of temperature on ignition limits was also determined. The hypothesis is suggested that only those metals whose oxides are soluble in the metal will ignite spontaneously and ignition will occur only if the initial reaction is vigorous enough to raise the surface temperature to the melting point of the metal or an eutectic.

--

I guess if the regulator experiences a catastrophic failure under pressure (such as a crack), and such new surface then is clean, and exposed to O2, and the failure added enough energy to melt the top layer of metal, then I suppose a fire could happen.

 

[tursiops]

Many membrane systems dont meet oxygen compatible gas standards.

Why would they need to? They don't ever see pure O2....