To tackle emerging challenges related with traditional safety training for practitioners that work onboard trains in society; for this research, we developed an immersive virtual safety training environment with Immersive Virtual Reality technology. We employed the Action Design Research (ADR) approach to design an Alpha prototype in close cooperation with end-users and software developers. The end-users were train operators and safety trainers at a train operating company in Sweden known as SJ. Two research cycles were executed to develop and evaluate the prototype. Consequently, by following the ADR method, we developed and proposed four design principles for immersive virtual safety training environments: (1) Design for Virtual Safety Realism, (2) Design for Virtual Boundary Crossing, (3) Design for Virtual Multimodal Feedback, and (4) Design for Virtual Touchpoints and Collaborative Reflection.