ABSTRACT
Fans create the pressure difference needed to make air move. The fan must be powerful enough to move enough air to protect the employee while overcoming the resistance to move that much air through the system. While the physical differences between the categories of axial and centrifugal fans are obvious and distinct, the differences among the various types within each category are mostly internal (and thus not visible) but are operationally important. Axial fans can be subcategorized into three basic types: propeller fans, tube axial fans, and vane axial fans. Centrifugal fans differ from axial fans in more ways than they are similar. The impeller of a centrifugal fan directs the air outward where the fan housing constrains and redirects the flow tangentially toward the fan outlet.
