When doing the test, you heat the end of the wire first and burn off any impurities that could remain. You continue until the only color you see is the flame of the bunsen burner. You then add the sample and repeat. If the copper was the source of the flame color, then you would see this before you even loaded the sample.
But even if they don't, the plastic could still contain low amounts of PVC and plasticizer. There are so called "low PVC" or "low vinyl" flips for sale that are very dangerous IMHO. Your method is very prone to error. Not everyone has a sensitive sense of smell. I know someone who has no sense of smell - I am not exaggerating.
Look, ya wanna burn plastic on copper wires go ahead. All I'm saying is there are other methods that do work.
Not a thing, except it's too tame for my taste. I guess that's why I figured out how to make gunpowder from scratch when I was only 6, and nitro from scratch by the time I was 8. Ya see, it's sooooo much mooooooooore fun to blow things up
A fire is just a slow explosion, although there are other kinds of explosions. A professor I had in college had a great definition..."An explosion is a loud noise followed by the going away of things from where they were." One of the ones I continue to do is exploding the eyes out of a pumpkin to form a jack-o-lantern at Halloween.