To investigate the electrostatic discharge phenomenon and ignition hazard in a silo during powder loading, a three dimensional simulation of the electric field distribution was performed. Experimental data on the specific charge and powder surface geometry of polypropylene powder （about 800 kg） continuously loaded into a full-scale silo was used. Evaluation of the effects of the surface geometry of deposited powders, powder loading amount, and pipe length on the electric field distribution clarified the conditions that increase the electrostatic hazard. The discharge hazard inferred from the time variation of the electric field strength was almost consistent with the number of high-energy surface discharges observed in the experiment. Furthermore, since the size and distance or angle to the grounding material of the powder bed surface affect the electric field at each location, it is essential to understand these changes for electrostatic safety management in powder loading processes.

The purpose of this study was to investigate ways to prevent oral indium exposure due to indium adhesion to the interfaces of respiratory protective devices. Methods: The amount of indium adhered to the face and factors that may increase the amount of indium adhered were measured and discussed. Fourteen measurements were conducted. The number of workers at the same site grinding wet indium tin oxide （ITO） targets was 41 measured. The amount of indium adhered to the face of the Powered air-purifying respirator （PAPR） protective device used at the start and end of the work, the indium exposure concentration, the indium concentration in the interface, and the leak rate （％） of the respiratory protective devices at the start and end of the work were measured. The amount of indium adhering to the interface of the powered airpurifying respirator used at the start and end of the work, the indium exposure concentration, the indium concentration in the interface, and the leak rate （％） of the respiratory protective devices at the start and end of the work were measured. The values of each measurement item were divided into quartile groups, and the amount of indium deposition was compared among the groups. Results: The higher the exposure concentration, and the higher the leak rate before the start of work, the more the amount of indium adhered tended to increase. Conclusions: In order to reduce the amount of indium adhering to the interface of respiratory protective devices in contact with the workerʼs face, it is necessary to reduce the exposure concentration and ensure that respiratory protective devices are worn securely and without leakage before work begins.