The modularization of process plants addresses the need for flexible production options in the process industry. In order to maintain the advantages of the adaptability of modular plants, an adaptation of established engineering methods and procedures to their dynamic context of use is required. This paper describes the development and the features of a demonstrator, which makes it possible to investigate aspects of modular plant topology, the design of modular process units, and the functional safety of modules and plants. During the engineering of the modules, modular planning principles are applied and evaluated with respect to the requirements for functional safety and with a strong focus on the modification of safety systems through the exchange of PEAs and FEAs. For the design and modification of the safety systems, a safety life cycle, which meets the requirements of modular automation and takes the provisions of IEC 61508 and IEC 61511 into account, is applied. Practical insights into the construction and the implementation of the distributed Safety Instrumented System as well as the Basic Process Control System are described. In addition to the validation of safety concepts related to the interconnection of Safety Instrumented Functions, the demonstrator is used to study human working environments in modular plants.