Pervasive computing systems provide personalized and intimate services to improve users' quality of life by integrating computation and communication into the environments. With the capability to interact with the physical world and the promise in assisting or managing aspects of users' daily lives, the requirement for safety is high and imminent. The difficulty in providing safety is the result of the dynamicity, complexity, heterogeneity and uncertainly typical in pervasive computing. After examining and analyzing worst-case scenarios of safety violation, we identify four fundamental elements whose individual safety assurances add greatly to the overall system safety. We propose safety enhancing mechanisms for each of the four elements and their interactions.