Molten State KNO3 used in Ion exchange Chemical glass Tempering

I have read that Potassium Nitrate (KNO3) in a motlen state of about 450 Celcius is used in the ion exchange of aluminosilicate glass (that is glass wher some alumina, Al²O³, replaces silica) to make Gorilla Glass (i.e., chemically tempered glass). I had a question regarding the toxicity of the fumes relased by the KNO3 during this process. My question is three fold (1) are the fumes released by Potassim Nitrate alone in a molten state toxic? (2) Somewhere else I had come accross that the only air born by product KNO3 in a molten state is oxygen, is this true? (3) Does the ion exchange of Potassium Nitrate with aluminosilicate glass, occuring at 450 Celcius, have any other byproducts that can be released in the process?

Thanks