Ontario Regulation 833 – Control Of Exposure to Biological or Chemical Agents

What This Regulation Is About 

In Ontario, many workplaces use chemical and biological products or create contaminants —from cleaning products and solvents to welding fumes and laboratory samples during work.  

Under the Occupational Health and Safety Act (OHSA), employers must protect workers from harmful exposure to these substances. 

Ontario Regulation 833 – Control of Exposure to Biological or Chemical Agents sets legal exposure limits for airborne chemical agents and describes how employers must control workers’ exposure to hazardous biological or chemical agents in the workplace. 

In simple terms, the regulation requires employers to: 

• keep worker exposure at or below the legal occupational exposure limits (OELs); and 

• use effective controls (engineering, administrative and, when needed, personal protective equipment) to protect workers. 

Understanding these duties is important for any organization that uses, stores, or generates chemical or biological agents as part of its operations. 

Occupational hygiene assessments are often the starting point for compliance. 

What Ontario Regulation 833 Covers 

Regulation 833 applies to most workplaces in Ontario that fall under the OHSA.  

Some substances are covered by separate regulations, including: 

• Designated Substances such as lead, mercury and silica – covered by O. Reg. 490/09 

• Asbestos on construction projects and in building operations – covered by O. Reg. 278/05 

For these substances, the specific regulation applies in addition to, or instead of, Reg. 833. 

Key Elements of the Regulation 

1. Occupational Exposure Limits (OELs):  

The regulation sets occupational exposure limits for many airborne chemical agents. These limits are based  mainly on the Ontario Table and the ACGIH Table of the Threshold Limit Values (TLV): 

• Time-weighted average limit (TWA): The average airborne concentration of a substance a worker may be exposed to during a normal 8-hour and 40-hour week. 

• Short-term exposure limit (STEL): the maximum airborne concentration a worker may be exposure to:
  (a) during any 15-minute period;  

(b) no more than four times in an 8-hour shift; and  

(c) with at least one hour between exposures; 

• Ceiling limit (C): The concentration that must never be exceeded at any time. 

If a substance has only a TWA (and no STEL or Ceiling) listed, the regulation also sets “excursion limits”: 

• up to 3 times the TWA for any 30-minute period; and 

• up to 5 times the TWA at any time. 

2. Assessment of Exposure:  

Employer must determine whether worker may be exposed to these agents and whether those exposures could be high enough to be harmful or to exceed the OELs. 

In practice, this usually includes: 

• identifying all chemical products used or generated 

• reviewing Safety Data Sheets (SDS) and process information 

• observing how chemicals are stored, handled and used 

• understanding which workers, tasks and areas may be exposed 

• deciding whether air monitoring is needed 

 3. Control Requirements:  

Employers must take all measures that are reasonably necessary to protect workers from exposure. Typical measures include: 

• Substitution – replacing a hazardous substance with a less hazardous one 

• Engineering controls – e.g., local exhaust ventilation, process enclosure, isolation 

• Administrative controls – e.g., limiting time in high-exposure areas, safe-work procedures 

• Hygiene facilities and practices – e.g., wash facilities, clean change areas, no eating in contaminated areas 

• Personal protective equipment (PPE) – including respirators, when other controls alone are not enough 

 When respirators are required, the regulation includes detailed requirements for: 

• choosing a suitable respirator for the substance and concentration 

• minimum protection factors 

• air quality for supplied-air respirators 

• training, fit testing and maintenance 

4. Measurement and Monitoring: 

Air sampling is often the most reliable way to check whether workers are below the OELs and exposure testing may be required to verify compliance. Air monitoring is often the most reliable way to check whether workers are below the OELs. 

When an employer carries out monitoring under Reg. 833, the regulation requires that: 

• recognized sampling and analytical methods are used (e.g., NIOSH, ISO, OSHA, IRSST methods) 

• monitoring and interpretation are performed by, or under the direction of, someone who is qualified in industrial hygiene practice 

• samples are representative of workers’ actual exposure during their normal work 

5. Training and Records:  

Under the OHSA and its regulations, employers must: 

•  inform workers about the chemical hazards in their workplace 

• explain the health effects and symptoms of over-exposure 

• train workers and supervisors on safe work procedures, controls, PPE and emergency response 

• keep records of exposure assessments, sampling results and control measures 

Employer Responsibilities in Plain Language 

In simple terms, Ontario Regulation 833/90 requires employers to: 

1. Identify all hazardous biological or chemical agents that workers may be exposed to. 
2. Review and assess processes and tasks to understand how workers may be exposed. 
3. Decide whether air monitoring is needed, and if needed, arrange occupational hygiene monitoring. 
4. Compare results to the legal exposure limits (OELs) and any excursion limits. 
5. Control exposure so that worker exposure stays at or below the OELs. 
6. Provide and maintain ventilation and other engineering controls where needed. 
7. Use administrative controls and safe-work procedures to reduce exposure. 
8. Provide appropriate PPE and respirators, and ensure workers are trained and fit-tested where required. 
9. Keep records of assessments, test results and control measures. 
10. Review and update controls when processes, materials or work conditions change, or when OELs are updated. 

Even workplaces that appear “low risk” such as warehouses, laboratories, maintenance shops, office buildings and food-processing facilities – can fall under this regulation if workers may be exposed to airborne chemical agents. 

The First Step: Occupational Hygiene Assessment 

A comprehensive occupational hygiene assessment is often the best way to determine whether your workplace is meeting the requirements of Ontario Regulation 833. 

What It Involves 

An assessment typically includes: 

• a walkthrough of the workplace to review processes and materials 

• identifying Similar Exposure Groups (SEGs) – workers who do similar tasks and have similar exposure patterns 

• a qualitative exposure assessment to identify where higher exposures may occur 

• air sampling and laboratory analysis where needed to measure worker exposure 

• checking existing controls (local exhaust, general ventilation, isolation, housekeeping) 

• practical recommendations to improve controls, training and procedures 

• documentation that can be used to show due diligence to the Ministry of Labour, Immigration, Training and Skills Development (MLITSD) 

Workplace Exposure Compliance Checklist 

Use this checklist as a starting point to see how closely your workplace aligns with Ontario Regulation 833. 

Step	Compliance Action	Status
1	Identify all chemical agents used, handled, stored or generated in your workplace	☐
2	Review processes and tasks to understand how and where workers may be exposed	☐
3	Group workers into Similar Exposure Groups (SEGs) where appropriate	☐
4	Decide whether air monitoring is needed and, if needed, carry out sampling using recognized methods	☐
5	Compare monitoring results to Ontario’s OELs and any applicable excursion limits	☐
6	Implement or improve engineering and administrative controls to reduce exposure	☐
7	Provide appropriate PPE and, where respirators are needed, maintain a compliant respiratory program	☐
8	Train workers and supervisors on hazards, controls and safe-work procedures	☐
9	Maintain records and review assessments and controls on a regular basis	☐

If any of these steps are incomplete or uncertain, THEM’s occupational hygiene specialists can help you develop a clear, practical and compliant plan. 

Next Steps for Employers and Safety Leaders 

Protecting workers from exposure to hazardous agents is: 

• a legal requirement under the OHSA and Reg. 833 

• a key part of responsible risk management 

• good for worker health, retention and productivity 

Whether you manage a manufacturing facility, a warehouse, a healthcare setting, a laboratory or a commercial building, it is important to: 

• Understand which chemical agents are present. 
• Check whether worker exposure might exceed Ontario’s OELs. 
• Put in place effective controls and keep them up to date. 

By starting with an occupational hygiene assessment and acting on the findings, you can: 

• reduce workplace risk and address liability 

• improve employee health and confidence 

• strengthen compliance with Ontario’s exposure limits 

• support long-term environmental, health and safety (EHS) performance as well as company’s sustainability 

Why Partner with T. Harris Environmental Management Inc. (THEM) 

T. Harris Environmental Management Inc. has over 45 years of experience in occupational hygiene and exposure control. 

Our team includes certified industrial hygienists and occupational health and safety professionals who provide one-stop cost-effective services: 

• tailored air monitoring and sampling programs aligned with Reg. 833 and recognized standards 

• clear, data-driven and reasonably practicable recommendations on engineering controls, work practices and PPE 

• support in developing and reviewing Respiratory Protection Programs that align with the respirator requirements in Reg. 833 (selection, fit testing, breathing air quality, training) 

• training and policy support to help your organization understand and meet its legal duties 

THEM’s occupational hygiene services help you: 

• identify risks early 

• reduce exposure and incidents in a cost-effective way 

• recommended sustainable solutions 

• support long-term worker health and safety 

• demonstrate due diligence and regulatory compliance 

Take the first step toward a safer workplace. Request an Occupational Hygiene Assessment →