BT BB 19a(17) :משום דלא דמי האי היזיקא להאי היזיקא רישא היזיקא דמתונא סופא היזיקא דהבלא‏ : because this damage is unlike that damage. The former part (of the Mishna deals with) damage caused by wetness, the latter part with damage caused by vapor
See the entire entry for hyzq n.m. damage