Wire insulation safety

Ohhh..when Teflon gets really hot, you want to ba *far* away. Have you heard of Phosgene? Consider the flurine version; *much* worse!

the coated pan on dry heating was less than that of fumes given off by ordinary cooking oils".

The MSDS however says "During a fire, irritating and highly toxic gases may be generated by thermal decomposition or combustion." Wikipedia would not be one of my top 100 sources for toxicity data. There is a lot of reliable data on the toxicity of fumes produced by burning teflon which can be easily found, just not on wikipedia.

Usually when the contribution of wire insulation to smoke from a fire is a concern some particular standard is invoked and wire must pass the appropriate tests in order to be used. Guessing what the smoke contribution of particular compounds would be is a rather poor way to spec wire insulation IMO.

The specification we are following is from the US Army. They have more funding to pursue these tests than we do. Specifically it says PVC=No, Teflon=Yes. My guess would be that PVC is toxic at a lower temperature or in a higher lethality than Teflon.

But my original question was about irradiated polyolefin insulation. Where does that fit on the safety spectrum?

(Sure, Phosgene is manufacturered in large quantities for use in the manufacture of certain plastics, and shipped around the country in tank trucks with the standard "corrosive" placard. I did some lab testing on a phosgene compressor seal long ago, and the co-worker who installed it in the field reported that phosgene makes cigarettes taste terrible.)

I would guess that polyolefins, consisting only of hydrogen and carbon, would be fairly good as far as smoke toxicity. But this is precisely the sort of guess I don't think you should be basing design decisions on. What does the Mil-Spec say? I would expect major wire manufacturers to be able to answer questions about what insulations meet your specifications; possibly you could call Belden or your preferred wire supplier and discuss the matter with their applications engineering department.

Try burning PVC sometime. HCl will make you cry - and rust.

There's a movement afoot to get rid of PVC entirely, at least in applications where there are reasonable substitutes. Hard to believe, considering all the PVC extrusions that are all around us.

Best regards, Spehro Pefhany

I worked in a molding factory. PVC and acetal would explode if mixed and heated.

What do they know? Besides, frying pans are cold relative to the decomp temp of Teflon.

It does seem to withstand a 200C environment.

Yes, you have to purge the machine barrel with something else (eg. PE) when you are switching resins.

Best regards, Spehro Pefhany

One of our guys didn't and stuck his head over the hopper to see what was happening. He looked like he had the worst case of measles for a few weeks. Lucky it missed his eyes!

Much more complicated when you're comparing Army/AF/mil-specs with UL/ CSA or building codes.

The worst case army environment has several soldiers in a tiny tank compartment (OK, not as tiny as they used to be) filled with dozens and dozens of electronic subsystems, a turbine for propulsion, live ammo stashed in all kinds of places, and depleted uranium as the preferred projectile. I'd rather NOT HAVE A SHORT that might spark an explosion, rather than use something like PVC :-).

Note that European building codes are often different than US/Canada, and in some cases ban PVC while allowing Teflon in the same situations (risers).

Flame dynamics can be ridiculously nonlinear in response to a small change in parameters.

Tim.

If the same reservations were held to all other components in the assembly, I doubt few would be acceptible. Why the emphasis on wire insulation alone?

RL

The PVC ban applies to all components used. I have no problem finding usable components.

Interesting that PTFE is considered as ok in a fire:

"at temperatures greater than 350 deg C for emissions of noxious fluorine compounds (including HF and COF2)"

My recollection was the temperatures required were higher than this, but any chance of releasing HF is a Bad Idea.

Regards Ian

For far more than you ever wanted to know toss "wire insulation fire toxicity" to a search site / engine.