Respiratory Hazards in the Workplace

Exposure Assessment

Respiratory protection should never be used either as a primary solution or as the only solution for controlling employee exposure to harmful airborne contaminants. Rather, respirators supplement engineering and administrative controls and work practices when they are not adequate to control worker exposure to airborne contaminants to safe levels.

To identify the appropriate type and level of respiratory protection, employers must conduct an exposure assessment of their workplace. The purpose of this is to identify the types of air contaminants present and the levels of exposure to these substances to select the appropriate respirator when respiratory protection is necessary.

Air contaminants can exist in several forms that are dependent on their identity, how the exposure is generated, and its physical form or state of matter. These include particulates, gases and vapors.

Human lungs


Particulates constitute the most common type of air contaminant in occupational settings and include dusts, fibers, mists and fumes. Dusts are generated during the handling, crushing, grinding, detonation, impact and decrepitation (breaking apart by heat) of solid materials and have a general range of particle sizes ranging from 0.1 to 25 micron (1/25,400 inch) diameter. The health consequences of dust exposure by inhalation depend on the dust particle size and the toxicity of the material from which the dust is generated. Some dusts that are known to produce hazardous health effects include those from beryllium, raw cotton, inorganic lead, nickel, cadmium, chromium and silica.

A fiber is a particle that has a length-to-diameter ratio of 3 to 1 or greater. In the workplace, exposure to fibers can arise from asbestos-containing materials and man-made mineral fibers (MMMF, also referred to as synthetic vitreous fibers (SVF)) such as refractory ceramic fibers, fiberglass (glass wool and glass filament) and mineral wool (rockwool and slagwool).

A fume is formed when volatilized particles condense in air during operations such as welding, brazing and torch cutting. Fume particulates generally have a particle diameter that is less than 1 micron. In most cases, the hot vapor reacts with oxygen in air to form the oxide. Examples include iron oxide fume, zinc oxide fume and chromium (VI) oxide.

Mists are suspended liquid droplets generated by the condensation of liquids from vapor back to liquid or by breaking up liquid into a dispersed state, for example, by atomization or splashing. Mists are often found in electroplating and pickling operations.

The size of the particulate determines what part of the respiratory system will be affected. Particles that have a diameter of 10 microns or greater will be deposited in the upper regions of the lungs and will not impact the alveolar (gas exchange) region of the lungs. These are referred to as non-respirable particles. Particulates that are less than 10 microns in diameter are small enough to reach the alveolar sacs of the lungs in great quantities.

With the exception of fibers, the concentration of particulates in air is expressed in terms of milligrams per cubic meter (mg/m3). The measured concentration of airborne fibers, especially for asbestos fibers, is expressed in fibers per cubic centimeter (f/cc).

Gases and Vapors

Hazmat Awareness Training Online vapors are normally in a liquid state at normal temperature and pressure. Vapors can be returned to the liquid state either by lowering the temperature or by increasing the pressure.


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