There has been an increasing popularity of industrial usage of Internet of Things (IoT) technologies in parallel to advancements in connectivity and automation. Security vulnerabilities in industrial systems, which are considered less likely to be exploited in conventional closed settings, have now started to be a major concern with Industrial IoT. One of the critical components of any industrial control system turning into a target for attackers is functional safety. This vital function is not originally designed to provide protection against malicious intentional parties but only accidents and errors. In this paper, we explore a generic IoT-based smart manufacturing use-case from a combined perspective of security and functional safety, which are indeed tightly correlated. Our main contribution is the presentation of a taxonomy of threats targeting directly the critical safety function in industrial IoT applications. Besides, based on this taxonomy, we identified particular attack scenarios that might have severe impact on physical assets like manufacturing equipment, even human life and cyber-assets like availability of Industrial IoT application. Finally, we recommend some solutions to mitigate such attacks based mainly on industry standards and advanced security features of mobile communication technologies.