My first thought on this question was actually Operation Gomorrah resulting in the Hamburg firestorm. However the destruction in square miles and lives lost was only about half that of the Tokyo raid. Nevertheless, the intensity of the firestorm at Hamburg is hard to imagine: A tornadic fire funnel rising up 1500 ft. above the city, with updraft winds exceeding 150 mph (Cat 5 Hurricane-level), literally sucking people off the streets and into the vortex. I've always thought of this as the most "intense" firestorm, vs. Tokyo which was twice as large, but I never considered that it was possibly as intense. Casualty estimates at Hamburg were largely just guesses, based upon the amount of ash found on the floors of subterranean bomb shelters, since individual bodies were completely consumed in so many cases. Interesting discussion, since I always thought (right or wrong) of Tokyo as being more widespread, but less intense on a per-square mile comparison.