All resins give off toxins when burned.
Urethanes give off, for example, traces of cyanide gas above 325.
Methacrylates under pyrolysis give off 2-methylpropanol, butane, and benzene… all bad stuff.
But if you guys are WELDING, you are already exposing yourself to ridiculously hazardous fumes.
You Ought to invest in an activated charcoal Fume Extractor system that comes with a flexible gooseneck hose you can position at the site of the weld to vacuum up fumes and run them thru the filter.