Navy Adversary,
I have witnessed the RAAF F111 "dump & burn" (when they visited an Airshow at Boscombe Down some years back), the "wave" of heat could be felt easily from the crowdline
Have also been a pax in an aircraft that dumped once - glad to say we were informed by the Flight Deck when it was going to start and how long it would last (could be an alarming sight otherwise) - from witnessing the spectacular volume at which it comes out, have to say I'm surprised it dissipates so quick.
IIRC, we were told it was 40t in about 25mins (this was an L1011).
Incidentally, thought it was known as "adjusting gross weight" and not "dumping" in these politically-correct times?