An important property in a sensor network is the mon- itoring of temporal changes of hazardous situations such as forest fires. Rescue groups need to be aware of dy- namic changes that affect their rescue efforts. In this paper, we discuss a sensor network model that provides a good abstraction of geometric and topological fea- tures of a dynamically changing sensing environment. This model enables efficient path planning and naviga- tion using localized algorithms. We propose a dynamic medial axis model that represents shapes and changes of shapes in a geometric space. We develop distributed algorithms to capture the dynamic network topologies. Dynamic medial axis allows rescue teams to find a short path to safety in a changing environment. We show that our dynamic medial axis algorithms provide good ap- proximations to the true medial axis and our routing scheme generates short and safe routes. The simula- tion results show that the routes found by our scheme are near-optimal.