Regarding the courtyard of a cemetery, Beis Shammai say that one standing in it remains clean so long as there’s a space of four cubits (about six feet); Beis Hillel say four handbreadths (about 12”). If a beam was used as a cover for a grave, whether it was standing upright or lying on its side, then only what’s opposite the opening of the grave is rendered unclean. If the end of the beam was used as the grave cover, then only up to four handbreadths is rendered unclean in a case where one intends to cut the beam. Rabbi Yehuda says the entire beam is connected.
Regarding a jar full of a ritually clean liquid and sealed with a tightly-fitting lid that was used as the cover of a grave, one who touches it contracts seven-day impurity but the jar and the liquid remain clean. If an animal was used as a grave cover, one who touches it contracts seven-day impurity. Rabbi Meir says that anything possessing the breath of life doesn’t convey impurity by being used as a grave cover.