There's a massive difference between HDPE (which is a hydrocarbon) and PVC (which contains chlorine and is awful to burn). Might be some plasticizers in the mix

There's a massive difference between HDPE (which is a hydrocarbon) and PVC (which contains chlorine and is awful to burn). Might be some plasticizers in the mix as well, but mostly they're just H, C, and O. Cl makes the real nasty stuff. Rocket fuels can have some pretty nasty stuff in them as well, of course...