This article is about designing a custom biosafety cabinet (BSC) for laboratory equipment that requires primary containment. The article explains how to determine if the equipment needs to be placed inside a custom BSC, the critical discussion points for custom BSC design, the physical placement of the custom BSC, and the considerations for performance testing and field certification. The risk assessment and overall process to design a custom BSC involves many considerations, including the equipment's dimensions, sensitivity to vibrations, operating temperature requirements, electrical requirements, and need for connection to utilities, as well as the location of associated equipment and the custom BSC's ability to contain aerosols. The custom BSC aims to provide adequate containment, functionality, and access to the equipment, be located in the lab where it can properly function, connect to utilities, and be field certified with the equipment inside. The article emphasizes the importance of consulting with safety experts from the start of the design process.