It’s just dry ice...I can’t see what could possibly present a hazard.
If mixed with certain things Dry Ice can react badly.
I won’t really say publicly but think of oil and or Anti-Freeze or another chemical.
Also, HazMat had to be called because normally the F.D. would just do a “Wash Down” but water also makes Dry Ice react not good for the situation.
Look up dry ice in a pool on YouTube…….the Crazy Russian guy did an experiment.