The dust removed in the filters may be classified as poisonous, infective, obstructive, or irritating and may originate from an animal, vegetable, mineral, or metallic source. Industry produces many deleterious fumes and dusts, for example, those emanating from grinding, polishing, dyeing, gilding, painting, spraying, cleaning, pulverizing, baking, mixing of poisons, sawing, and sand blasting. This dust must be filtered out of the air because of its effect on health and efficiency, to recover valuable materials, to save heat by reusing filtered air, and to prevent damage to equipment and products in the course of manufacturing.
