ORIGINAL: jester_s1
Plastic spinners are perfectly safe. They aren't loaded with gunpowder, and they won't explode.
I had a plastic spinner with a plastic backing plate explode while starting a .91 four stroke engine with a electric starter. The engine kicked back and a piece of the spinner back plate barely missed my head (felt it brush by my hair) and stuck in the sheet rock ceiling of my garage! I was SHOCKED on how violent it was when it came apart. If my head was 1.5" closer to the engine, I would have lost my left eye. I no longer use spinners with a plastic backing plate. Plastic cone with an aluminum back plate is the least I would recommend. I went to all aluminum after that.