Abstract: An improved fault simulation environment is described in this paper, and details of its faulting capability are presented and tested. The versatility of our fault simulator in handling different fault models by adding new activity functions to our modeling structure such as n-terminal bridge faults is shown. We use our TUFTsim simulator, which is based on concurrent simulation algorithms to efficiently fault simulate large networks, and the Multiple List Traversal [9] mechanism handles the propagation of concurrent elements through the topology. Results on some of the ITC '99 Benchmarks [1] are shown based on the stuck-at and logical bridge fault models. The use of the bridge fault in combination with the stuck-at model does not depreciate the simulation efficiency.