The changeability of modular process plants implies the need for fundamentally new safety strategies: Since Operators must implement safety measures, assistance systems are needed to enable the operator to execute safety engineering tasks. We analyze the operator tasks during build up and re-configuration of flexible production systems in the process industry. Based on a state-of-the-art analysis of conventional safety engineering tasks, requirements to assist operators by a technical system are derived. We designed an assistance system and a module self-description to enable operators to implement the safety related interconnection of modules. To prove our concept, we successfully implemented the technical concepts in a demonstration plant. By implementing measures that are conducive to operators, we have been able to maintain their role as the most flexible resource in modular plants.