This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations and should not be used as or considered legal advice. Health and safety inspectors apply and enforce these laws based on the facts they find in the workplace.


An occupational hazard is a thing or situation that can harm a worker. Occupational hazards include:

  • safety hazards that cause accidents and physically injure workers
  • health hazards that can make a worker sick, varying from health effects like a headache or skin rash to a fatal occupational illness, such as cancer

Occupational illness is defined in section 1 of the Occupational Health and Safety Act (OHSA). It includes an occupational disease for which a worker is entitled to benefits under the Workplace Safety and Insurance Act, 1997.

A workplace hazard only represents a potential to cause harm. Whether it actually causes harm will depend on the circumstances. For example, if the hazard is exposure to a chemical, the harm will depend on factors such as the toxicity of the chemical, the exposure amount, the exposure route, and how long a worker is exposed.

Hazards can be rated according to the severity of the harm they cause. Some hazards have the potential to cause a critical injury or death.

Lean about the hazards specific to workplace sectors and strategies to deal with those hazards:

Anticipate and recognize, assess and control hazards and evaluate controls

There is a four-step process for dealing with workplace hazards. Hazards must be:

  1. Anticipated and recognized – this involves both anticipating (before a hazard is introduced into the workplace) and identifying a hazard and determining if there is a possibility of workers being affected by it.
  2. Assessed – if there is a possibility of workers being affected by the hazard, it must be assessed for its potential to cause harm.
  3. Controlled – if the hazard identified may cause harm to a worker, the hazard must be controlled.
  4. Evaluated – to assess if a control is effective and the hazard is adequately controlled or eliminated

Hazard recognition is an important role of the joint health and safety committee.

The anticipation/recognition, assessment and control of hazards the general duty of employers under OHSA section 25(2)(h). However, some regulations also have specific requirements for dealing with hazards. Examples include:

This page describes the general approach to controlling hazards in the absence of requirements in specific regulations. Employers must be aware of the regulatory requirements that apply to their workplace and follow them as part of the process to address hazards.

Control can be applied at the source of the hazard, along the path between the source and the worker, or at the worker. Control at the source is preferred.

Health effects from exposure to workplace hazards

Workplace health hazards can cause a variety of health effects on the body, with many having specific adverse effects on a specific part of the body such as the lungs, skin or liver.

For a hazardous substance to have an adverse effect on the body, it is important to consider how exposure occurs. Most hazardous substances come into contact with or enter the body through inhalation (breathing them in) or contact with the skin (where the hazard can be harmful to the skin at the point of contact and/or can be absorbed through the skin to cause problems elsewhere in the body). It is also possible that exposure leading to health effects can occur through ingestion (swallowing a hazardous substance) either directly or via transfer from contaminated hands.

For some hazards, there can be two different types of effects:

Acute effects

Acute effects are adverse effects on the body that happen shortly after exposure to a hazardous substance. Some examples of common symptoms that can occur shortly after hazardous exposures include headaches, difficulty breathing and vomiting.

Some hazardous substances produce symptoms and effects that can be life-threatening with no early warning signs that exposure is occurring (such as with carbon monoxide poisoning). Since these kinds of symptoms occur quickly after exposure, hazardous exposure should be anticipated and pre-emptively controlled. This is an example of recognition and assessment used to prevent exposure from happening in the first place.

Chronic effects

Chronic effects differ from acute effects in that they happen when exposure is at a low level but is repeated regularly over a prolonged time period. Chronic effects, such as asbestosis, mesothelioma or lung cancer, have no immediate warning.

Both short and long-term worker exposures can be controlled by following the prescribed occupational exposure limits (OELs).

Managing risks posed by hazards

Removing occupational hazards is the preferred option for improving worker protection. In some cases, it may be necessary to manage the risks that hazards pose.

Difference between a risk and a hazard

A hazard involves the potential for a material or situation to cause harm. Risk is the probability, or chance, that the hazard will actually harm someone. For example, a welder’s risk of developing lung effects from welding fumes is much higher in a poorly ventilated shop (high risk) than in a well-ventilated shop (low risk).

The consequences of exposure to some hazards may be so severe that, even if there is little chance of a worker being exposed, the risk is so great that extreme precautions must be taken to mitigate even that small possibility.

Methods of control

The best methods of controlling exposure to a particular hazard will depend on what the hazard is. These methods follow the ‘hierarchy of controls’ and are placed from the most preferred method first to the least preferred method last. In general, methods of control can be placed in five categories:


Substitution includes:

  • the use of a less hazardous material
  • a change in the process equipment used
  • a change in the process itself

Care must be taken to ensure the substitution actually results in less hazardous conditions.

Engineering controls

These are methods of designing or modifying plants, processes and equipment to minimize workers' exposure to the hazard. Examples of such controls are:


Isolation is a method of limiting exposure to those employees who are working directly with the hazard, often by enclosing them within a containment structure. While isolation will reduce the risk to those outside the isolated area, it should include appropriate controls to ensure that those within are not faced with an increased exposure to the hazard.


Ventilation is most important for the control of airborne hazards. It involves removing air from the workplace that contains a hazardous contaminant and replacing it with uncontaminated outside air. There are two types of ventilation:

  • local exhaust: this type of system can capture a contaminant where it is generated and remove it before it is dispersed into the work environment
  • general dilution: this type of system uses ventilation that regularly replaces the air in the entire workplace to safely dilute contaminants

Administrative controls

These are things like job rotation schedules, work-rest cycles and timing of maintenance procedures, which can be used to limit the amount of time individuals are exposed to a hazard. 

Hygiene facilities and practices

Controls in this category include:

  • washing hands after handling material and before eating, drinking or smoking
  • avoiding touching lips, nose and eyes with contaminated hands
  • no smoking, drinking, chewing gum or eating in the work areas

Personal protective equipment (PPE)

PPE includes items like:

  • respirators
  • hearing protectors
  • safety clothing
  • protective clothing

PPE can reduce a worker's exposure but must be used properly to be effective. Use of PPE is considered the last line of defense in controlling exposure and should only be relied on if neither substitution nor engineering controls are reasonable, practical, or effective.  

Evaluating controls

After controls are in place it is important to find out how well they are working. Evaluation may include:

  • conduct regular follow-up evaluations to confirm that controls have been implemented as planned and are consistently followed throughout the workplace
  • discussing the effectiveness of controls with workers and listening to their suggestions for improvement
  • reviewing incident reports

Laws and regulations

Regulations made under the Occupational Health and Safety Act (OHSA) may be sector, work or hazard specific. Legal requirements governing exposure to various safety hazards can be found in the sector-specific regulations under the OHSA, which apply to the following sectors:

Certain types of hazardous work are covered by their own regulations:

Health hazards are either covered by the sector-specific regulations or separate hazard-specific regulations, including:

Legal requirements for personal protective equipment (PPE)

PPE should be provided to workers wherever there are health or safety risks that cannot be adequately managed in other ways. PPE can reduce or prevent a worker's exposure to a health hazard in the workplace. PPE includes:

  • respirators
  • hearing protectors
  • protective clothing
  • footwear
  • face and eye shields

In some cases, the regulations specifically address the use of PPE to protect workers when other control are inadequate. For example:

  • section 7.2(2) of the regulation respecting the Control of Exposure to Biological or Chemical Agents, R.R.O. 1990, Reg. 833, requires respirators to be provided when engineering controls are not practical
  • sections 9 to 12 of the regulation set requirements for the selection, use and care of respirators and other elements of a Respiratory Protection Program
  • section 2 of the Noise regulation, O. Reg. 381/15, sets out the requirements for protecting workers from exposure to hazardous sound levels