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Here's the rest of the e-mails I was referring to.
-Dave
To All:
FYI - I've worked with a number of metal alloys in my experience in PVD
films. Titanium is the only metal thus far that I've seen ignite when
exposed to atmosphere after exposing from an ultra-clean environment.
To prevent this ignition the PVD chambers are slowly brought up to
atmospheric pressure and then allowed some time to "soak" (30 minutes)
at atmospheric pressure before opening the chamber. To date the only
benefit that I'm aware of for Ti Vs. Chrome plated brass is weight. In
my case a reduction of weight at the regulator means an increase on my
weight belt. This does not compensate for the difference in cost
between reg's. If anyone has any other proven claims/benefits of the Ti
reg' over the std. I'd be glad to hear about it. The whole point of
this message is that when safety is a concern, go with the traditional
proven standards when selecting equipment not the latest fad or gimmick.
Cheers.........<deleted>
<deleted> wrote:
>
> Hello all,
>
> I am not a technical diver, but was made curious about regulator materials
> and high O2 gas mixes by several discussions about Saturday's dive accident,
> so I asked someone in the diving manufacturing industry about it. This
> person's answer is below, although they wished not to be directly named.
>
> I am not intending any comment at all about the accident on Saturday; I am
> only being curious about materials and high O2. The answer I received was
> fairly interesting, so I am passing it along. If anyone has different or
> additional information, please pass it along. Let's just please avoid making
> this personal for the guy last Saturday (especially since we don't know the
> details). Thanks.
>
> <deleted>,
>
> Your deductions are by and large correct. In summary:
>
> Titanium has a low threshold for ignition. About 17 times lower than
> aluminum, and 285 lower than brass. Which means that it burns easily. In the
> ASTM standards related to flammability and sensitivity of materials for
> oxygen-enriched atmospheres, it is classified as a material 'avoided for
> hazardous oxygen service'.
>
> So say that you have a brass regulator with a nitrox kit, i.e. Viton o-rings
> and O2 compatible HP seat. Nothing should happen. However, circumstances
> might arise that will make either the o-ring or the seat ignite. If that
> happens, they will burn releasing heat of combustion. As this is directly
> proportional to the mass of material involved, it is not much. The brass
> will not ignite. But now there is no more seal in the first stage, pressure
> builds up in the second stage which automatically discharges: freeflow. The
> only issue here is that viton releases toxic fumes when it burns. So
> depending on when and where this happens, the diver may feel the
> consequences of that (though I cannot quantify them). Again, it is very
> unlikely for this to happen with the nitrox kit.
>
> So say that you use a brass regulator with standard HP seat and o-rings.
> Depending on the percentage of O2 in the mix, it may and it may not ignite.
> If it does, same result as above, however EPDM (material used in all our
> non-viton o-rings) does not release toxic fumes. So the chances of
> combustion are higher, but the consequences less severe. Our company's
position
> in this matter is that for anything above 23.5% O2 you should use a nitrox
> kit.
>
> Now say that you use a titanium regulator. Even if you use a nitrox kit, it
> may ignite. Because when you first open the valve, the regulator goes from
> 14.7 psi (ambient) to about 120psi (intermediate pressure with open piston)
> to about 3000-3500 psi when the piston closes in on the seat. This sudden
> compression generates heat. Titanium, having the lowest threshold for
> ignition, does not take much heat to ignite, more so in presence of so much
> oxygen. So now you have the spark, the fuel (titanium) and the oxidizer (the
> O2 in the tank). So combustion is going to take place. The main difference
> between this scenario and the one with a brass regulator is that now the
> heat of combustion is related to the entire mass of the first stage, which
> is far more than that of the seat itself. Yes, the metal is now burning.
>
> If you now do this without a nitrox kit, it is even worse. Because you don't
> need to reach the threshold for the titanium to ignite, it is sufficient to
> reach that for the seat to ignite or one of the o-rings. The heat generated
> by that could be sufficient to start the fire in the titanium.
>
> So, I hope this answers your questions. Keep in mind that I don't intend to
> portray myself as a materials expert, these are just very simple and obvious
> considerations given the existing literature on materials.
----------------------
This message was sent to me by one of my cooworkers, also
concerned
with the titanium regulator issue at hand! Now it turns out, even
aluminum
regulators prove to be a hazard when used with high pressure O2! The
gravity
of this situation seems to be increasing!
<deleted>--
> -----Original Message-----
> From: <deleted>
> Sent: Tuesday, June 06, 2000 2:10 PM
> To: <deleted>
> Subject: RE: regulator materials and high O2 mixes
>
> FDA Recalls Emergency Oxygen Regulators
>
> The FDA has documented 16 fires in aluminum-bodied medical regulators, and
> with NIOSH, issued a Public Health Advisory in February 1999. The fires
> resulted in severe burns to eleven Emergency Medical Technicians and
> patients. Several were catastrophic burnouts consuming large sections of
> the regulator's components and bodies. One exceeded fifty percent loss of
> the regulator and also resulted in ignition of the attached aluminum
> cylinder yielding a longitudinal split and burn-through of the cylinder
> wall.
>
> Several ignition mechanisms were consistent with the evidence, including
> particle impact on the inlet filters or flow control orifice,
> contamination in gauge ports, and adiabatic compression ignition of the
> main seat. Particle impact has been most often implicated, and testing has
> found up to 300 particles entrained in the flow stream when the cylinder
> valves are opened while the cylinders are horizontal.
>
> The Alert warns about the use of aluminum in high-pressure oxygen
> regulators and recommends replacement with brass-bodied regulators. Also,
> FDA and NIOSH have expressed interest in ASTM G-4 developing a
> positive-ignition test standard to evaluate the ability of oxygen
> regulators to tolerate those ignition mechanisms normally present in
> oxygen systems. G-4 has assigned a Task Force to look into this. G4N
>
> This article came from here:
> http://www.wstf.nasa.gov/oxcompat/newslett.htm
>
> Note: titanium and aluminum have the same autocombustion temps in
> hyrozine/air evironments at one atmosphere.
> 644 degrees F.
>
<deleted>
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