Every employer in this state to which sections 292.300 to 292.440 apply shall provide for and place at the disposal of the employees so engaged, and shall maintain in good condition without cost to the employees, working clothes to be kept and used exclusively by such employees while at work and all employees therein shall be required at all times while they are at work to use and wear such clothing; and in all processes of manufacture or labor referred to in this section which are productive of noxious or poisonous dusts, adequate and approved respirators shall be furnished and maintained by the employer in good condition and without cost to the employees, and such employees shall use such respirators at all times while engaged in any work productive of noxious or poisonous dusts.