Potential Workplace Respiratory Hazards

The three most common routes for occupational exposure to toxic materials are inhalation, ingestion, and absorption. The respiratory system provides the quickest and most direct route of entry, which can be attributed to the fact that the respiratory system has a direct relationship with the circulatory system. Ingestion can occur by hand to mouth contact (i.e. smoking), and absorption can occur through the skin.

When deciding on the appropriate respiratory protection, the type of airborne contaminant must be considered. Any one of the following types of airborne contaminants may be encountered while working at Columbia University.

Airborne material can be classified into the following major categories:

  • Gas - a normally formless fluid that can occupy the space of an enclosure and which can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature. Examples of gases are ozone, carbon dioxide, carbon monoxide, and chlorine.
  • Vapor - the gaseous form of a substance which is normally in the solid or liquid state and which can be changed to these states by either increasing the pressure or decreasing the temperature alone. Vapors can diffuse into a substance in its gaseous state, which is usually a solid or liquid at room temperature. Examples of vapors are methylene chloride, toluene, and mineral spirits.
  • Dust - particulate matter generated from intrusive processes such as grinding, blasting, or mixing. Examples of dusts are wood dust, coal, and silica dust.
  • Mist - a dispersion of visible liquid particles, suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into the dispersed state, such as by splashing, foaming, or atomizing. Examples of mists are paint mists and oil mists.
  • Fume - solid particles generated by condensation of vaporized material, generally after volatilization from molten metals. Examples of a fume generating processes are welding, brazing, and smelting. Examples of fumes are lead, zinc, and iron.
  • Fibers - Fibers are solid particles with a length to width ratio of 3:1. Fibers can be found in insulation products. Examples of fibers are asbestos and fiberglass.


Toxic agents can also be classified according to the health effects they cause. These types of chemicals can be classified as irritants or asphyxiants. Irritants are corrosive in action and can cause inflammation of mucous membranes. They can also stimulate changes in the respiratory process such as increasing resistance to airflow.

Irritants are subdivided into two categories; primary and secondary:

  • Primary Irritants - Affect the upper respiratory tract. Form non-toxic end products, which cause no systemic health problems.
    • Examples: Hydrochloric Acid (HCl), Sulfur dioxide (SO2), and Ammonia (NH3)
  • Secondary Irritant - Cause initial mucous irritation and produce toxic systemic effects due to their absorption on lung tissue.
    • Examples: Chlorine (Cl2), Bromine (Br2), and Ozone (O3) affect the upper and lower region of the respiratory tract while, Nitrogen Dioxide (NO2), phosgene (COCl2), and arsenic trichloride affect the terminal regions of the lung.


Asphyxiants are substances that have the capability to deprive living tissues of oxygen and are classified into simple and chemical.

  • Simple Asphyxiants - are usually physiologically inert gases that act by accumulating in sufficient quantities to prevent an adequate amount of oxygen to body tissues. Asphyxiants are often associated with confined spaces and other forms of vessel entry.
    • Examples: acetylene (C2H2), carbon dioxide (CO2), ethane (CH2), methane (CH4), helium (He), hydrogen (H2), and nitrogen (N2).
  • Chemical Asphyxiants - are able, through their individual or unique toxic action, to render the body incapable of utilizing oxygen.
    • Examples: carbon monoxide (CO), hydrogen cyanide (HCN), and hydrogen sulfide (H2S)

Carbon monoxide combines with hemoglobin to form carboxy-hemoglobin (COHb), which interferes with oxygen transport to tissues and removal of CO2 from tissues.

Carbon Monoxide

Carbon monoxide combines directly, rapidly, and firmly with the hemoglobin molecule (which is the molecule that transfers oxygen to bodily tissue), forming a new compound called carboxyhemoglobin, which cannot perform the usual function of hemoglobin. It is an odorless, colorless gas that is generated during incomplete combustion. Carbon monoxide can also be present in confined spaces and is always a consideration during the assessment of workplace hazards.

Hydrogen cyanide inhibits cellular respiration.

Hydrogen Sulfide blocks cellular oxidation at the respiratory center, thereby stopping breathing.


Contaminants in the workplace can also be in the form of fibers. These agents, if present at high concentrations, can cause fibrosis or scarring in lung tissue. These changes occur over a long period of time depending on the fiber type. Examples of these agents are: silica, asbestos, and coal dust.


Another potential workplace hazard is sensitizers. These substances cause an allergic reaction in sensitized individuals. Chemicals called histamines are released in the body in response to exposure to these substances. Symptoms can include constriction of the breathing passage and difficulty in breathing. 

Examples of sensitizing agents include: Toluene-2, 4-diisocyanate (TDI) and Methylene bisphenyl isocyanate (MDI).

Oxygen Deficient Atmospheres

Upon assessing any respiratory protection issue the presence or lack of oxygen is of great importance. Confined spaces may present oxygen deficient or oxygen rich atmospheres and should never be entered without proper training and air monitoring.