occupational health image, people working, factory environment

Occupational Hygiene

Occupational hygiene (also called industrial hygiene) is concerned with both the preservation of good health and the prevention of diseases in workplace settings. It is the discipline of anticipating, recognizing, evaluating, and controlling occupational health hazards.

Practically, an occupational hygienist has the skills to protect workers’ health and well-being. The word “hygiene” comes from the Greek goddess, Hygieia, who represented the preservation of good health and prevention of disease.

There are many different types of hazards that are present in the workplace. The main categories include: biological, chemical, ergonomic, physical and process hazards. Occupational hygienists are experts in biological, chemical, and physical hazards.

Occupational Exposure Limits (OELs) are the levels of acceptable exposure over a length of time (usually 8 hours/day or 40 hours/week) for chemical or physical hazards. OHCOW routinely references certain OELs, including international best practices, legislation, and standards, with the intent to support the most protective workplaces. Referenced OELs include:

  • Best practices pertaining to the ACGIH TLVs (threshold limit values) and various international health-based protective OELs;
  • Legislated OELs for Ontario, which are called TWA (time-weight average limits):   regulated by R.R.O. 1990, Reg. 833 : Control of Exposure to Biological or Chemical Agents; and by O. Reg. 490/09 : Designated Substances; and
  • Legislated OELs for federal workplaces, where the Canada Occupational Health and Safety Regulations SOR/86-304 have mostly adopted the ACGIH TLVs.

OHCOW has developed an OEL Adjustment Tool  to account for irregular shifts. Users can choose to select the Ontario-legislated OELs or the more protective health-promotion OELs.

In cases where there are exposures to multiple chemicals or agents that target the same organ in the body, the effect of each chemical will be at least additive. There are ways to address additive effects, complex mixtures, as well as synergistic effects. Contact OHCOW for assistance at any time.

OHCOW also offers other tools that assess, calculate, and characterize specific types of hazards like silica exposure and heat/cold stress:


OHCOW’s Occupational Hygienists participate in interdisciplinary teams working on the following cluster investigation projects. These projects monitor the health hazards of worker groups and help affected communities.

  • Neelon
  • Peterborough
  • Dryden
  • Ventra/Pebra
  • McIntyre Powder Project (MPP)
  • Rubber workers

Clinical Occupational Hygiene

OHCOW’s occupational hygienists offer a unique service to Ontario workers. Occupational hygienists investigate past occupational processes and occupational exposures as a part of an interdisciplinary occupational health team. They review work history and safety data sheets (SDS, formerly MSDS), and speak directly with the injured worker and their colleagues. Additionally, they search the published occupational exposure monitoring results and databases, and complete systematic searches of peer-reviewed published occupational hygiene and epidemiological studies. Based on the exposure data and occupational epidemiology, the occupational hygienists produce retrospective exposure reports outlining the probable risks of developing occupational diseases. Occupational health teams use their reports to make a collective assessment of the degree to which a worker’s health condition is work-related.

OHCOW’s occupational hygienists participate in Joint Health and Safety Committees  to resolve workers’ health concerns, with the goal of supporting safe and healthy workplaces where worker concerns are addressed.

They also respond to inquiries  about occupational exposure and occupational disease, and are available to explain hazards and suggest ways to reduce risk. Common topics include: indoor air quality, noise, asbestos, heat stress, cold stress, VGDF (vapours, gases, dusts, fumes), diesel exhaust (DE), irritants and allergens, solvents, metal dusts and fumes, and any other workplace chemicals, biological agents, or physical agents.

Some of the methods used by occupational hygienists can be technically challenging, requiring expertise to master. However, OHCOW strives to provide workplaces with simple tools and techniques to enable  hazard assessments. For instance:

  • Simple rules such as knowing the odour threshold of a chemical (if there is one) can help workers estimate the degree of exposure and associated hazard.
  • Having to speak in a raised voice to be heard at an arm’s length away is an indicator of excessive noise exposure.
  • Various checklists, charts and rules of thumb can help those without formal expertise to identify exposures of concern.

OHCOW's hygiene services are available to anyone who has a workplace exposure question, and to any workplace needing assistance with an occupational health concern. Individual services can be accessed by contacting the clinic (no referrals required). Workplace assistance is available to Joint Health and Safety Committees that provide a written request (signed by the JH&SC Co-Chairs) to the clinic.

For queries please contact us at ask@ohcow.on.ca

Steps in Occupational
Hygiene Practice:

Anticipating, recognizing, evaluating, controlling