wrote:
I wonder at what temperature teflon becomes hazardous?

I make my living fixing laminators that use a teflon coated heat shoe,
they run below 350 degrees most commonly under 300. if they are found
to be dangerous its time for a new job.

I used to fix machines that used methyl alcohol, that job ended when
the healt risks of methyl vapors was publicized. oddly enough its still
used today in windshield washer fluid.

but those oither machines all went to the landfill........

I can't verify this information, but here is a chart that describes
what happens to Teflon at various temperatures, FWIW:

http://www.ewg.org/reports/toxicteflon/tempgraphic.php

Keep in mind that when cooking, the "average temperature" of the pan is
not the highest temperature that is found at places in the pan where
food is absent.