I read online that you could melt plastic shopping bags(made from ldpe) using a pot illed with oil and form them into a mold. I tried it, using a respirator, and it worked. They said in the instructions that since the plastic is being melted, and not burned, that fumes are not given off. Are they? And are they dangerous?

LDPE MSDS

Any fumes given off (if at all) will be classed as organic vapour, so you should make sure your respirator cartridges comply with this. Obviously, working outdoors will minimise the risk to anyone else in the house, including animals. I would also wear goggles to gaurd against any vapours or hot oil splashes. The technique which uses oil does not appear to give off fumes but you never know. The important thing is that you protect yourself in any case. I've smelted hot melt and pour vinyl rubbers in my line of work and those fumes are quite dangerous, despite what others might say. But I deal with organic vapours on a daily basis. Just make sure your respirator is up to the job. You should also test it for air tightness each time you put it on by placing the palm of your hand over the filter and breathing in sharply, to collapse the rubber face piece. If there are leaks, you'll feel them. Hope this helps.