I’m terribly skeptical of this at this point. Me too, but you have to admit that, based on past experience, when the Russkies decide to have an industrial disaster, they don't screw around!
The environmental record of the USSR was a catalog of horrors (something the greens never mention, of course). Lots and lots of really nasty stuff is haphazardly strewn all over Russia in "out of sight out of mind" sites which have undoubtedly deteriorated since the collapse of the Soviet Union. Widespread fires can easily cause a lot of this material to become airborne and therein lies the problem.
Clearly this warrants close monitoring. Embassy staff evacuations may be exaggerated but they can't be concealed if true.