What is the harm to the body of long-term inhalation of gases from burning plastic?

Hello! You should check what the material of your box is, because there are many kinds of plastic, I will first introduce three kinds, there should be one of them. pvc box, generally used for some non-edible products such as packaging, don't ever heat it moreover, don't burn it, because the pvc material has polyvinyl chloride! High-temperature heating is toxic, not in contact with edible items.

PP box, most used to hold food, etc., can be used for microwave heating. It is non-toxic material.

PET box, (is the material of beverage bottles). It can be used for water, food and other packaging. But it is not heatable.

Is there any of these three? If it is PP material box you can rest assured! Because that material is the main component of polyethylene, is non-toxic, but still be careful, for fear that some black-hearted merchants with toxic materials labeled non-toxic signs! Health is important!