Mo. Rev. Stat. § 292.380
All employers engaged in carrying on any process or manufacture or labor referred to in section 292.310, shall provide and maintain adequate devices for carrying off all poisonous or injurious fumes from any furnaces which may be employed in any such process or manufacture or labor, and shall also provide and maintain adequate and efficient facilities for carrying off all injurious dust, and the floors in any room or apartment where such work or process is carried on shall be kept and maintained in a smooth and hard condition, and no sweeping shall be permitted during working hours except where the floor in such workshop is dampened so as to prevent the raising of dust; and all ore, slag, dross and fume shall be kept in some room or apartment separate from the workrooms occupied by the employees, and all mixing and weighing of such ore, slag, dross or fume shall be done in such separate room or apartment, and all such material shall be dampened or covered before being handled or transported by employees.
§ 292.380, RSMo
RSMo 1939 § 10219