Section 120. Every such wheel shall be fitted with a hood or hopper of such form and so placed that the particles or dust produced by the operation of the wheel or of any belt connected therewith shall fall or will be thrown into such hood or hopper by centrifugal force; and the fans or blowers shall be of such size and shall be run at such speed as will produce a volume and velocity of air in the suction and discharge pipes sufficient to convey all particles or dust from the hood or hopper through the suction pipes and so outside of the building or to a receptacle as aforesaid. The hoods or hoppers shall be so constructed and the suction pipes and connections shall be suitable and efficacious and such as shall be approved by the attorney general.