The temporal role based access control (TRBAC) models support the notion of temporal roles, user-to-role and permission-to-role assignment, as well as allow role enabling. In this paper, we argue that role hierarchies can be temporal in nature with a dynamism that allows it to have a different structure in different time intervals; and safety analysis of such extensions is crucial. Towards this end, we propose the temporal role based access control model extended with dynamic temporal role hierarchies, denoted as TRBACRH, and offer an approach to perform its safety analysis. We also present an administrative model to govern changes to the proposed role hierarchy.