This paper presents a practical case for safety assessment of bulk supply substations (BSS) and traction supply substations (TSS) in Taipei Rail Transit Systems (TRTS). For a substation grounding system to be safe, the maximum touch-and-step voltages should not exceed postulated safety criteria. The safety criterion in IEEE Standard 80 is defined in terms of permissible body current. The permissible body current is then translated into the permissible touch-and-step voltages. Since the mesh voltage is usually the worst possible touch voltage inside the substation (excluding transferred potentials), the mesh voltage is used as the safety criteria. In other words, safety assessment of an ac substation grounding system in TRTS is referred to a procedure by which the mesh and step voltages are computed and compared to the maximum permissible (safe) touch-and-step voltages. Computation results for the orange line at O19 station are presented.