As an approach to cope with rising volatility of sales markets and increasingly shorter development cycles, process industries are expecting much from the concept of modularization. However, a topic that is still rarely focused in this context is safety. Therefore, this paper is focused on the expected challenges of engineering functional safety including the architectures of safety instrumented systems, and the requirements of modularization. Possible architectures are presented and discussed in relation to the requirements of functional safety in modular process plants.