"Bullseye's introduction of liquid oxygen as a fuel"

FYI, oxygen isn't a fuel, it's an oxidizer. The fuel is the part that the oxygen binds to, typically a hydrocarbon.

Introducing oxygen would have two effects. First it allows the fuel to burn hotter but it also introduces a greater oxidizing condition to the melt which I assume is being done to either enhance the color or to speed up the melt. It's expensive to do so it is not being done casually. I'm still waiting to see when the discussion about fluorine and lead will hit the conversation. It's certainly easy to see in the air quality charts when the chrome melts and the cadmium melts were taking place. That would be true of the Arsenic/Lead melts as well. I can't draw conclusions from the statements about air quality being degraded with chrome on days when there were no melts beyond simply observing that "Dust Settles"