Chemicals are counter-intuitive. People don't have a good match for looks-scary to is-scary.
I watch the Checmical Safety Board incident report videos from time-to-time. The most common killer in chemical plants? Carbon monoxide: odorless, colorless, tasteless, and simply displaces oxygen. You climb into an enclosed space, have just enough time to realize something's wrong (maybe) before you pass out, and never wake up. The methyl isocyanate that killed in Bhopal rolled along the ground creating a silent blanket of death.
A giant black plume climbing into the cloud layer is scary looking but in no way correlated, one way or another, with the actual risk to public safety. Made for great 6 o'clock news footage, but the followup story really is just "Clean the soot off your house and maybe check your basement for any chemical that rolled away before it burned."