The German engineers were nothing if not daring. The fail factor would have been apparent long before such speeds were achieved.
The idea of using finely pulverized coal as a fuel is ingenious in several ways. The vastly increased surface area of each particle of coal dust would greatly expand the burn exposure, making it a two-fold advantage. There would be a first burn, creating two carbon monoxide molecules, both of which would reburn forming two very hot carbon dioxide molecules, with adequate oxygen supply.
Actually, finely divided cereal flour would be nearly as effective if used as a fuel in this manner, as there are conditions in which explosions have occurred in grain milling plants, if ignited by a static electric spark or the act of lighting a cigarette.
Sorta like a half assed version of black powder.
On a related note, grain silo explosions are a real thing, and there are codes having to do with ventilation of air space above the grain mound for that very reason.