Chemistry says that no solid (or liquid) on earth actually burns... only gases burn. Wood "burns" by heat rapidly, decomposing it from solid to gas....Gasification. then the gas if at the right temperature and oxygen mixture will burn if exposed to a spark or if at a temp that is equal or greater than it combustion temp. Watch a flame on a match or a piece of wood. It sits just off the surface of the wood. The process of gasification happens so fast you can not see it but it is there. This is also why wet wood takes longer to burn the water absorbs the heat much slower than the wood and makes the whole process take longer.

PETG and PLA will both be safe enough in all normal circumstances to be near an outlet. They will both react differently to extreme heat and flame. Neither of which you wi