I was not trying to paint a gloom and dome type scenario. This was information that was new to me and I found it interesting which sent me on a search for more information. I am well aware of the risks of simply accepting something like that at face value without verification. I think you will agree that informed desicion making is important.

Urban myth, perhaps when pushed to the extreme or exagerated. However, the manufacturers themselves warn of the danger:

I forgot which site I copied this from otherwise I would post the reference:

<quote>
There is a remote risk of sustaining chemical burns from Viton® O-rings if they are burned or otherwise exposed to temperatures above 600ºF. Viton® begins to decompose above 600ºF, yielding some nasty compounds including hydrogen fluoride. In the presence of water vapor, this can produce hydrofluoric acid, an extremely corrosive mineral acid which causes severe burns to exposed skin. Proper protective gear should be warn when dealing with burned Viton®. There is no danger in dealing with cured Viton® used within the rated temperature range.
</quote>

For our use in our small engines the risks are minimal to non existent but it is nice to be aware of the risks so as not bury our heads in the sand.

I'll keep using Viton O Rings but now I am aware of any potential risk if used beyond their rated specs.

In any respect the other information on O Rings I found most useful and as the subject of O rings and specs turns on this forum from time to time I hoped that would be useful to others as well.

cheers, Graham