There are two chemicals on the list with the qualifier “fume or dust” (zinc and aluminum). What exactly is a “fume” or a “dust?”
EPA does not have a regulatory definition of a fume or a dust, but considers dusts, for purposes of reporting, to consist of solid particles generated by any mechanical processing of materials including crushing, grinding, rapid impact, handling, detonation, and decrepitation of organic and inorganic materials such as rock, ore, and metal. Dusts do not tend to flocculate except under electrostatic forces. A fume is an airborne dispersion consisting of small solid particles created by condensation from the gaseous state, in distinction to a gas or vapor. Fumes arise from the heating of solids such as lead. The condensation is often accompanied by a chemical reaction, such as oxidation. Fumes flocculate and sometimes coalesce. Further clarification on these qualifiers can be found in the Toxic Release Inventory Reporting Forms and Instructions.