The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Tum’at Met (3:10), rules that if the body of a deceased person was burned, Heaven forbid, the ashes do not transmit the status of Tum’at Met. Therefore, it is permissible for a Kohen to be in the same room as ashes of a cremated body. Thus, for example, a Kohen may visit the Yad Vashem Holocaust Museum in Jerusalem, even though the museum has actual ashes of Holocaust victims, may Hashem avenge their blood. By the same token, a Kohen may visit the sites of concentration camps and other sites that have piles of ashes of victims. Since ashes of a deceased person do not emit Tum’a, there is no prohibition at all for a Kohen to be near these ashes.
However, a Kohen who visits such sites should ensure not to touch the ashes, given the possibility that there might be small pieces of bone among the ashes. Touching a piece of bone that is the size of a Se’ora (kernel of barley) renders one Tameh, and therefore a Kohen should ensure not to touch the ashes in these sites. Of course, it would in any event be inappropriate for anybody to touch the ashes of a deceased person.
(Based on Mamlechet Kohanim, pp. 224-225)
Summary: Although a Kohen may not be in the same room as a human corpse, he may be in the same room as ashes of a body that was burned, and thus a Kohen may visit Yad Vashem and other sites that have ashes of Holocaust victims.
