The first category, particulate contaminants, includes dusts, mists, and fumes. Dusts are usually the largest particles, but not all dusts can be seen with the naked eye. Mold spores, for example, are microscopic. They're released when moldy hay, silage, or grain is disturbed. Mists are suspended liquid droplets and are usually found ear mixing, spraying, and cleaning operations.
Fumes are solid particles of evaporated metal.
They're microscopic as well and are formed during activities such as welding. The second category of hazards is gases and vapors. Vapors evaporate from liquids, such as pesticides, paints, adhesives, and lacquer thinner. Gases are chemicals that are gaseous at room temperature. The third category of hazards is oxygen-deficient atmospheres.