4-79 type centrifugal fan ventilation for indoor plants and large buildings in general, can be used to enter the gas can also be used to export gas. Air transport for other types of gas are not spontaneous combustion, harmless, non-corrosive to steel material and the amount of gas. Gas allowed sticky substances contained in dust and hard particles is not greater than 150mg / m3. Gas temperature must not exceed 80 ℃. Fans can be made clockwise or counterclockwise rotation of two types. From the motor side of the face, the impeller rotates clockwise, called cis Tornado aircraft, to shun said impeller rotates counterclockwise, called inverse Tornado aircraft, in order to indicate the reverse.