Phosgene gas a chemical weapon used in WWI is also a potential byproduct but I am unsure of the quantity that would be generated. It appears that those involved are aware of the potential and are monitoring those levels as well. I don't currently see any data that suggest that phosgene gas is of immediate concern but that may change with more data. If it is an issue it would have likely dissipated by now and may only be an issue in the upper atmosphere. I have never dealt with phosgene gas so I am not super confident on how it interacts or dissipates in the environment.