Viton vs Nitrile O-rings...

[dinogep]

Although I (clearly) don't know either way, phosgene does sound like a more reasonable byproduct than phosphine.

As far as I know nor viton, nor epdm or nitrile contains chlorine in its main composition. So phosgene is probably out, too.

[Puffer Fish]

Couv, You are way too kind. Your knowledge of oxygen and O-rings is rapidly exceeding mine.

It was Phosgene...and degradation of any Chlorine containing compound, in the presence of Oxygen can produce it, as well as several similar nasty compounds. The floride version of that compound is also not any fun.

Is it a danger in SCUBA? Well, no. First because Viton is a fluoropolymer and second because the rate it degrades is so slow. if I was in the plant that made viton, and there was a fire, I would try to leave very quickly.

Also, I know you know this, but Viton is not a single compound, it is a family of them, and they have lots of different properties.

The down side to Viton has been that it is just an ok elastamer...repeated compression and release will damage the material much faster than say EPDM...the upside is that it is far more O2 resistant. That down side happens to make it much better for things like tank valve O-rings and not as good for valve O-ring (although replacement is easy). When talking different materials, durometer numbers do not tell the whole story regarding extrusion issues, as viton is much harder to extrude versus EPDM of the same durometer.

Aircraft, by the way, have very different requirements for their static O2 delivery systems, and one would be advised to not try and copy them. (although the military view makes more sense to me, but the materials are very difficult to get in our world)


Due to the dynamic nature of SCUBA equipment and the need for frequent replacement, I don't see any reason to not use a good Viton O-ring, but people sure to like to play with their equipment.

....here we go again. I'll leave it to Puffer Fish to explain the advantages and disadvantages of FKM, EPDM, etc in the different applications mentioned here as he is indeed a true expert. But time and time again I see the statement, "for oxygen systems the aviation industry uses Nitrile/NBR/Buna N, etc." I've never worked in General Aviation so I cannot say for sure what puddle jumpers use, but on the military and commercial aircraft I've worked on I can say that most GOX (gaseous oxygen) system connections are metal on metal. The flexible seals I have come across in O2 systems have been Teflon or MS9385 (Mil Spec) which is Silicone! Military O-Ring MS9385 Mil Spec O-Rings

I cannot post proprietary info, but here is a PDF file I found online for a Boeing 737 O2 system just downstream of the bottle.
http://www.aerosup.com/Document/35/B...-35-PART-2.pdf

Scroll down to page 57 item 55

I also don't know where this business of phosgene (or was it phosphine) gas came into these discussions. If FKM o-rings produce a toxic gas, it would have to be at a temperature high enough for me to believe one would have bigger problems.

Cheers,

Couv

[akdeepdiver]

Although I (clearly) don't know either way, phosgene does sound like a more reasonable byproduct than phosphine.

What is your deffinition of reasonable? Phosgene gas is one of the chemical weapons that was used in WWI. Had a great track record for battlefield casualties.

[Puffer Fish]

What is your deffinition of reasonable? Phosgene gas is one of the chemical weapons that was used in WWI. Had a great track record for battlefield casualties.

I believe "reasonable" in this case refers to what compound could by made by degrading O-rings. Under the right conditions, they could degrade to make some Carbonyl difluoride (the fluoride version of Phosgene)..but not from normal room temperature use.

Phosgene was also used (when I was a kid, a very long time ago) to kill insects for collections. Some rubber bands, some carbon Tetrachloride and you get phosgene. Why it was important for grade school kids to learn how to make Phosgene is still unclear to me, but it was a very common practice.