In chapter 21, the chemical leak goes from "feathery plume" to black billowing to cloud" to "airborne toxic event." Why is the naming significant?
At first, the "feathery plume" is a marvel to behold. It is likely akin to the perception of witnesses to the atom bomb who often describe the mushroom cloud as "beautiful." Like the atomic bomb, the perception of beauty becomes one of horror. The name change sounds official and scientific, but also is probaby designed to quell panic, as it is rather dull and benign in tone.
The "feathery plume" may also be a tongue-in-cheek nod to a literary classic, "The Castle of Otranto" by Horace Walpole. In this 18th century Gothic novel, a huge helmet adorned with black plumes mysteriously lands in the castle's courtyard, causing death and wreaking havoc.