Mixers, blenders, roll mills, or calenders for rubber or plastics are permitted by rule, provided the following conditions of this section are satisfied. Mixers, blenders, roll mills, or calenders handling or adding asbestos shall not be eligible to be permitted by rule under this section.(1) Organic solvents, diluents, or thinners shall not be used.(2) Material in powder form shall not be added unless the mixer, blender, roll mill, or calender is vented to a fabric filter having a maximum filtering velocity of 4.0 feet per minute (ft/min) with mechanical cleaning, or 7.0 ft/min with automatic air cleaning.(3) There shall be no visible emissions.