In extreme static pressure conditions, reducing speed may not be enough to prevent reverse rotation. Alternatively, it may not be conducive for system operation during hot swap. More consideration may need to be placed on design implementations which prevent air from flowing backwards through a hot swapped fan. The best design method requires obstruction of airflow from entering the inlet side of the fan with a temporary or permanent blockage. A Louver system, pictured above, can be added to any fan with the implicit function of preventing back flow. Louvers should be designed to allow airflow through the fan normally when the fan turns on but will prevent reverse airflow as it is installed into a chassis. Alternatively, this process can be done manually by blocking the inlet side with a rigid barrier that can be removed after the fan has reached full speed. This barrier could be a sheet of metal or a plastic insert designed to perfectly cover the fan opening.