There was an incident of fire in the pressure reducing and metering station in a steel plant supplying high-pressure pure oxygen gas. This paper analyzes the incident and shows photographs of the damaged valves, pipes, and filter assembly. An inspection of the partially burned parts and the control-room data showing important operating parameters give insight into the chain of events. Steady and transient fluid flow and particle trajectory were analyzed with ANSYS Fluent to assess the possibility of particle accumulation and the entrainment of particles through the pipeline and enlarger. The presence of contaminant particles was ascertained by pressure-drop analysis and from experiences of similar incidents in other steel plants. Control-room data confirmed an unusually high velocity of oxygen gas that exceeded the recommended safe velocity for oxygen systems at some specific locations that simultaneously had a transient accumulation of particles. We conclude that such a condition facilitated the ignition of some particles at those locations upstream of the filter. These ignited particles were swept ahead into the filter assembly and served as the ignition source for the large number of particles that had already accumulated there. Improper cleaning, the accumulation of particles, and a large increase in the flow rate of oxygen were identified as the root causes of the fire.