In accordance with the latest NSF/ANSI Standard 49, BSCs shall be field certified at the time of installation and annually thereafter; when replacing HEPA/ULPA filters; when maintenance or repair of internal parts is needed; and after relocating the cabinet to a new room or facility. You should consider more frequent certification for particularly critical applications such as BSL-2+ operations and work involving sensitive cell cultures. Field certification ensures the unit continues to meet the design criteria, as established by NSF/ANSI and the BSC manufacturer, thus confirming environmental, personnel, and product protection. Based on the results of the tests performed during field BSC certification, the following may be required: filter replacement/repair, airflow adjustments, and/or various parts replacement.