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Old 30th December 2010, 08:46 AM   #11
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As far as I could determine, Teflon releases PFIB when heated, not Phosgene. Although they are similar and are chemically related, they are not the same thing.

Now, PVC does actually release Phosgene Gas when heated between 300 and 600C; see:

Brown and Birky (1980)

... and:

Bjerre, Anders; HEALTH HAZARD ASSESSMENT OF PHOSGENE FORMATION IN GASES OF COMBUSTION OF POLYVINYL CHLORIDE USING A SIMPLIFIED METHOD OF MATHEMATICAL MODELLING; Annals of Occupational Hygiene; Oxford University Press; (1984) 28(1): 49-59.

The only references that I could find regarding Teflon and Phosgene came via unattributed allegations via nut-bar websites trying to get people to throw out their non-stick muffin pans. It was often repeated but never referenced to a citation. I attribute that to my suspicion that there are none.

My guess is that people just made the jump they wanted to make; ie similar to Phosgene equals identical to Phosgene equals Teflon is Poison, and then a call for the pitchforks and torchlit mobs.

But chemistry is funny sometimes ... a little molecule here or there and the entire nature of the chemical can change from benign to deadly, but that little molecule is still required ... this isn't "horseshoes and hand grenades" where "close is good enough".

Having said all that, PFIB is also a deadly toxin. Like a lot of things all around us every day; don't burn it and don't breathe it if you do.

The short answer is a lot simpler ... burning anything changes it chemically, and usually the result is something that if you breath enough, is toxic to fatal. So don't breathe smoke, which is itself potentially fatal, even if it's just plants from nature that are burning.
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Last edited by Johnny2Bad; 30th December 2010 at 09:16 AM.
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Old 30th December 2010, 11:07 AM   #12
SY is offline SY  United States
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Quote:
Originally Posted by Johnny2Bad View Post
So don't breathe smoke, which is itself potentially fatal, even if it's just plants from nature that are burning.
Well, hell, there goes my New Year's Eve plans.

Yes, you're correct, there's no phosgene in PTFE. Interestingly, there IS phosgene in polycarbonate (e.g., Lexan), but the chlorines are stripped off during polymerization with the notorious BPA so there's no phosgene when PC burns.

It takes a much lower temperature to get bad stuff to come out of PVC than PTFE, though, so the comparison is chalk to cheese.
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Old 30th December 2010, 12:01 PM   #13
DF96 is offline DF96  England
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I like numbers - we physicists are like that! Very boring, but instructive. Let's do a very rough calculation. Assume a speaker cable with poor dielectric (maybe PVC?). Let's assume 5m at 100pF/m, so 500pF in total. Most speaker cables will probably have lower capacitance than that. Assume an amplifier output impedance of 1 ohm (i.e. DF=8) - not very good (unless you are into valve SE). Assume that at peak bass voltage the capacitance varies by 10% due to the voltage swing across our poor dielectric - probably an overestimate. This means that the low pass filter formed by our output impedance and cable capacitance will modulate an HF signal and give intermodulation.

Do the sums (for 20kHz) and you find that the error signal is -104dB with respect to the music. I think this should be inaudible due to noise and masking. You can play with the figures and make different assumptions, but you have to have a very bad amplifier driving a long cable with very poor dielectric insulation before you get something which might be heard. My conclusion is that it really doesn't matter what you insulate speaker cables with.

It may matter what you insulate interconnects with, if they are long, your preamp has high output impedance and your main amp requires many volts of input signal. These conditions are more likely with 'high end' equipment, using something barmy like SRPP output from the preamp?
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