Print View Posted on: 02 February 2024
On May 29, 2021, two workers were inspecting and calibrating the fluorescent X-ray adhesion meter (output 50kV x 40mA) at the Nippon Steel Setouchi Works in Himeji City, Hyogo Prefecture.There are three main operations for irradiating X-rays with this device.・ Power supply to this device・ Increase the voltage and current of the X-ray tube・ Open the shutter of the irradiation window.These operations are usually performed on the control panel outside the irradiation room where the device is installed.Initially, the two workers were working on the control panel outside the irradiation room, but when the calibration sample showed abnormal measures, they entered in the irradiation room with the device on power. There is no legal requirement for this facility to have interlocks, which cut off the power supply when the irradiation room door opens.As the two workers in the irradiation room confirmed some deposits on the X-ray irradiation window of the device, one of the workers removed them with a hand tool, and the other assisted.The two workers believed that they had closed the shutter of the irradiation window when entering the irradiation room, but it was revealed that the shutter had not been closed and that the workers were exposed to the X-rays emitted from the device during the operation. On May 30, 2021, two workers were hospitalized and treated following physical complaints and erythema on their arms and faces, which are non-fatal symptoms. The two workers left the hospital by the end of December 2021.Base on the results of the biological dosimetry (measurement of the frequency of chromosomal abnormality) conducted by November 2023, the experts evaluated the exposure to 400-500 mGy for one worker and less than 100 mGy for the other worker.