Occupational safety has a crucial role in every technological process in industry environments. Recently, smart mobile devices have become standard hardware that can help inform workers about their duties and procedures during work. In this paper, we present an augmented reality (AR) system for mobile devices as a tool for safeguarding health and safety, and the secure performance of tasks in a technological process by following virtual instructions in the workplace. In a case study, we explored the task procedures and defined the risk factors in the electro-energetics industry. Based on that, we implement a corresponding AR system that should be used to issue occupational safety and work instructions to workers during task execution. With that aim in mind, we designed a client-server architecture to project the related instructions on the screen of the mobile device, to ensure the confirmation of implementing them, as well as to keep a record of all the steps the worker performed. As an illustrative example, we present the application of the designed AR system to particular tasks in electro-energetics industrial plants.