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Airborne Contaminants: Defining the Terms

- November 5, 2014 by Glen O'Rourke, ALCM (View all posts by Glen)

Airborne contaminants can present a significant threat to your team’s health and safety. When determining which control measures to use to protect you and your workers from airborne contaminants, its important to first identify and understand them.  In part one of a two-part series, I will review the five basic airborne contaminants, and the forms in which they may be present.

Dust: A solid particle ranging in size from 0.1 to 25 micrometers in diameter.  Dust may be formed when a solid substance is ground, crushed, drilled, cut, detonated, or otherwise handled.  In addition to being a possible inhalation hazard, airborne combustible dusts may present an explosion hazard.

Fume: Solid particles, usually less than one micrometer in diameter, that are formed when a solid volatilizes.  Fumes are most commonly from metals when those metals are exposed to extreme heat during operations such as melting (as in a foundry) or welding.  The fume can be the metal itself or an oxide of the metal formed by a reaction of the metal with oxygen in the air.  As an example, fumes of Zinc and Zinc Oxide (which can produce toxic effects when inhaled) are released when galvanized steel is subjected to welding or flame cutting.

Vapor: The form of a substance produced through evaporation (at normal temperature and pressure).  Vapors are formed when a substance naturally volatilizes from a liquid or a solid.  Flammable liquids (such as gasoline) produce vapors that are hazardous for two reasons: because they can burn when ignited and because they produce toxic effects when inhaled.

Mist:  A finely divided liquid suspended in air.  Liquids may become mists by breaking up in to a dispersed state by splashing or by condensation of vapors back in to the liquid state.  Mists can be produced in metal cutting operations (such as sawing and milling) when liquid is used for cooling and lubrication at the point of operation.

Gas: Formless fluid that will continue to expand and occupy space until it is confined by an enclosure.  (Physically speaking, the molecules are unrestricted by cohesive forces.)  Carbon monoxide, such as that produced by burning fuel in an internal combustion engine, is an example of a hazardous gas.

Now that I have identified the five basic airborne contaminants and their forms, you can use this information as a foundation when developing proper control to protect your people from the hazards associated with those contaminants.    Check out Part 2 of this blog to learn more about the hazards present.


Plog, Barbara A. (1988). Fundamentals of Industrial Hygiene. (3rd ed.) Chicago, Illinois: National Safety Council.