As they had detailed knowledge of the Nazis' practice of mass murder, the "Sonderkommando" were considered "Geheimnisträger" – bearers of secrets. As such, they were held in isolation away from prisoners being used as slave labor (see SS Main Economic and Administrative Office). Every three months, according to SS policy, almost all the "Sonderkommandos" working in the death camps' killing areas would be gassed themselves and replaced with new arrivals to ensure secrecy. However, some inmates survived for up to a year or more because they possessed specialist skills. Usually the task of a new "Sonderkommando" unit would be to dispose of the bodies of their predecessors. Research has calculated that from the creation of a death camp's first "Sonderkommando" to the liquidation of the camp, there were approximately 14 generations of "Sonderkommando".