Vinyl + Heat = Dioxin ???

The translucent, yellow walls of this robotic work cell are vinyl "flash guard".

It is common practice to use tinted, vinyl sheeting to shield workers from the byproducts of weld processes.  The generic name for this product on the factory floor is "flash guard".

The problem is that "flash" is used to describe two very different weld byproducts.

One of those byproducts is the "arc flash" of MIG, TIG, drawn-arc welds and Stick welding processes.  The damaging component is UV light.  UV light can blind a person.  Some people also find that arc flash triggers migraine headaches. Flash guard is designed to shield workers from incidental exposure to UV light and the suppliers clearly state that this is it intended use.

The problem is that weld expulsion, the sparks, are also sometimes called "flash". 

Each one of those sparks is over 2700 degrees Fahrenheit.  Over time, they burn holes through the vinyl sheet.

Where does the "burnt" material go?  Mostly, it is vaporized but some of it is pyrolytically decomposed.

Studies in Europe linked the pyrolytic decomposition of vinyl with dioxin.  Dioxin is a carcinogen and is the main contaminant that made "Agent Orange" exposure a health issue.  The study states that copper is needed to catalyze the reaction. 

Weld expulsion that originates from between the sheets of steel is very low in copper.  Weld expulsion that originates between the weld cap and the surface of the work piece has significantly higher copper due to cap erosion.  Weld sparks from MIG welding also has elevated copper content because the filler wire is typically coated with a wash of copper to provide a clean, conductive surface to the gun's weld tip.

It is my unqualified opinion that use of "flash guard" to shield workers from weld expulsion/sparks is a misuse of the product and might expose them to carcinogenic, chlorine containing byproducts, i.e., dioxin and similar compounds.