Some Assembly Required - S2-E2
Corrected entry: The vampires are digging the master up and one digs w/ his hands and they begin to smoke and he says "the ground, it's consecrated, it burns." But you never see any vampires in the cemetery burning when they dig themselves out of their graves.
Correction: The Master's grave was consecrated with special rituals that Giles, Willow, and Xander performed which are more powerful than the consecration done with ordinary funeral rites. Vampires that emerge from the grave also do it quickly and explosively enough that the consecrated dirt likely never comes in contact with them.
Captain Defenestrator