The paper presents the design and usability evaluation of an interactive virtual reality (VR) application for visualizing smoke propagation in large indoor spaces. The application visualizes smoke dynamics derived from computational fluid dynamics simulations and aims to provide a more intuitive and exploratory means of interpreting simulation results compared to traditional post-processing tools. The paper investigates whether immersive VR improves the perception of smoke behavior in complex environments and supports the verification and validation of smoke-extraction system designs. A usability study was conducted with participants of varying levels of experience in VR and smoke-extraction system design. User interaction data, task completion metrics, observations, and post-study questionnaires were collected to assess usability, learnability, and perceived usefulness. The results indicate that VR enables clearer perception of smoke movement, airflow direction, and temperature distribution, and supports exploratory interaction with simulation data. While novice VR users initially experienced difficulties with basic interactions, all participants were able to complete the tasks, and overall usability ratings were high. Domain experts highlighted the potential of VR as a complementary tool to physical smoke tests, particularly for early-stage design evaluation.