Three years later. Full-time disinfection and sterilization personnel are trained in professional knowledge once or twice a year, and the pressure vessel employment certificate is trained once every three years, which is valid for three years. The knowledge of disinfection and sterilization is constantly updated and improved, so new knowledge and technology should be trained once or twice a year. The employment certificate of pressure vessel is valid for three years, and a new employment certificate must be replaced after every three years of training.