Five Air Contaminants Common In The Workplace
Air contaminants are commonly classified as either particulate or gas and vapor contaminants. The most common particulate contaminants include dust, fumes, mists, aerosols, and fibers.
Gases are formless fluids that expand to occupy the space or enclosure in which they are confined. Examples are welding gases such as acetylene, nitrogen, helium, and argon; and carbon monoxide generated from the operation of internal combustion engines or by its use as a reducing gas in a heat-treating operation. Another example is hydrogen sulfide which is formed wherever there is the decomposition of materials containing sulfur under reducing conditions.
Fumes are formed when material from a volatilized solid condenses in cool air. In most cases, the solid particles resulting from the condensation react with air to form an oxide.
Liquids change into vapors and mix with the surrounding atmosphere through evaporation.
Mists are finely divided liquid suspended in the atmosphere. They are generated by liquids condensing from a vapor back to a liquid or by breaking up a liquid into a dispersed state such as by splashing, foaming or atomizing. Aerosols are also a form of a mist characterized by highly respirable, minute liquid particles.
Vapors are the gaseous form of substances that are normally in a solid or liquid state at room temperature and pressure. Vapors are formed by evaporation from a liquid or solid and can be found where a worker would clean and/or paint as well as where solvents are used.
Dusts are solid particles that are formed or generated from solid organic or inorganic materials by reducing their size through mechanical processes such as crushing, grinding, drilling, abrading or blasting.
Fibers are solid particles whose length is several times greater than their diameter.
Air contaminants in solid or liquid state (aerosols), e.g., wood dust, welding smoke, or oil mist, are all in principle directly visible. The dispersion of those contaminants and the airflow patterns around the source may therefore be studied without any special tools. It is, however, not always possible to see the contaminant if, for example, the concentration in the air is low, the size of the particles is small, or the lighting is poor.
The fact that the contaminant can’t be seen may stem from the acceptable low level of the concentration but that can of course not be used to conclude that the control is acceptable. That conclusion depends not only on the contaminant’s toxicological qualities but on how visible it is in air. The ability to see the particles directly is also, as said above, a function of their size. Small particles, able to be transported deep into the thinner airways of the lungs, are many times also difficult to see directly.