Background: On May 3, 2017, at 11:58 AM local time, an explosion occurred in the Zemestan-Yurt coal mine in Azadshahr City of Golestan Province, northern Iran, which resulted in mass casualty incident.
Materials and Methods: In total, more than 126 miners were affected. Of them, 43 miners were killed, 73 other workers who helped their coworkers were also injured and taken to the hospital, and 10 injured people received on-site prehospital medical care. Many defects in the response phase were identified in the scene management and the triage. 
Results: It seems necessary to establish a response plan for mass casualty incident, hold regular education, and plan to prepare involved units for appropriate responses.
Conclusion: These measures are the first steps needed to improve preparedness and response to a mass casualty incident.