I've seen this image a bunch of times and i always wondered what it really was about - thank you!

I never would have guessed that.

I'm guessing that the material they're warning about would be galvanized steel. Apparently the fumes are extraordinarily toxic, and there's fuck all that can be done once you've inhaled it. Also, chemically treated steel/metals can have residue that is toxic once heated to extreme temperatures... and again, little to no treatment once you're exposed.

I've seen it many times and it only clicked mere seconds before i read your comment.