In this article we describe current and future technologies for ensuring the safety of the operators maneuvering a Skill-Assist working in an automobile final assembly process. It proposes a method that allows a Skill-Assist to detect operation slip from a sequence of an operator's hand motion trajectory data represented using hidden Markov models (HMM). The method can also determine either safety- or productivity-oriented control policy throughout two-way interpretation of the belief structure. A workability improvement process that comprises a fault-warning (FW) safety-preservation (SP) space policy and teaching data renewal subprocesses allows for optimal reconstruction of the policy determinant observation space and HMMs. Some experimental results are shown to demonstrate the effectiveness of both the control policy determination and the workability improvement process.