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 upon the facts they find in a workplace.

Carbon monoxide is a poisonous gas that has no:

  • colour
  • odour
  • taste

It is a by-product of the incomplete combustion of any material containing carbon (for example, wood, oil, kerosene, diesel fuel, propane, liquefied petroleum gas or natural gas).

Health effects

If you or someone you know may have carbon monoxide poisoning seek fresh air immediately and call 911.

Carbon monoxide is often called “the silent killer,” because it gives no clear signal that it is present.

The warning signs of carbon monoxide exposure include:

  • headache
  • faintness
  • dizziness
  • confusion
  • nausea
  • irregular heartbeat

Never ignore these warning signs when working, especially when using fuel-burning equipment or where work involves processes that may be a source of carbon monoxide. Carbon monoxide poisoning can occur when carbon monoxide builds up in your bloodstream and replaces oxygen. Carbon monoxide poisoning can cause loss of consciousness and even death. Workers who have been exposed to carbon monoxide should seek immediate medical attention.

Sources in the workplace

All fuel-burning equipment powered by propane, gasoline or diesel emits some carbon monoxide, including:

  • car, truck and forklift engines
  • generators
  • air compressors
  • power washers
  • power concrete trowels
  • chain and chop saws
  • boilers
  • kilns
  • heaters

Processes, such as welding, foundries, coke ovens and metal hardening, can also be a source of carbon monoxide exposure.

Carbon monoxide tends to build up in pockets, in poorly ventilated areas of workplaces. This can happen even in semi-enclosed workplaces, where tarps and plastic sheeting are used for shelter.

Summary of legal requirements and precautions

Occupational Health and Safety Act

The Occupational Health and Safety Act (OHSA) sets out the general duties of workplace parties, describes ways of dealing with workplace hazards and provides for enforcement by the Ministry of Labour, Immigration, Training and Skills Development where compliance is not achieved voluntarily. The general duties for employers, supervisors and workers may apply to protect workers from the hazards of carbon monoxide poisoning. The following are some examples of employers’ and supervisors’ general duties under the OHSA, as well as examples of precautions that may be reasonable depending on the circumstances.

Maintenance

Poorly maintained equipment usually emits more carbon monoxide.  Employers must ensure that the equipment they provide is maintained in good condition. Depending on the circumstances, this may include:

  • making sure that fuel-burning equipment is maintained to minimize carbon monoxide in exhaust emissions
  • checking engine operation
  • conducting carbon monoxide emission tests

Employers should follow the manufacturer’s equipment manuals, instructions and/or recommendations and may be required to do so depending on the OHSA regulation that applies.

Information and instruction

The OHSA requires employers to provide information, instruction and supervision to a worker to protect their health or safety. Depending on the circumstances, this may include instructing workers on how to read a carbon monoxide monitor and what to do if the alarm is activated.

Reasonable precautions

The OHSA also requires employers and supervisors to take every precaution reasonable in the circumstances for the protection of a worker.

Depending on the circumstances, reasonable precautions may include:

  • not leaving equipment running when not in use
  • installing or using air-monitoring devices where potential sources of carbon monoxide exist (for example, direct reading meters or personal monitors equipped with audible and visible alarms, detector tubes, dosimeter tubes, badges)

Regulations

Regulation 833 — Control of Exposure to Biological or Chemical Agents

In addition to the general duties in the OHSA, which may apply to the hazard of carbon monoxide poisoning, there are several regulations that contain requirements specifically related to the hazard. For instance, Regulation 833 — Control of Exposure to Biological or Chemical Agents sets out rules for measuring airborne concentrations of biological or chemical agents, including carbon monoxide, to which a worker may be exposed in the workplace.

Where Regulation 833 applies, section 3 requires employers to take all measures reasonably necessary in the circumstances to protect workers from exposure to a hazardous biological or chemical agent because of the storage, handling, processing or use of the agent in the workplace. The measures required by section 3 must include the provision and use of:

  • substitution of the agent
  • engineering controls
  • administrative controls, including work practices
  • hygiene facilities and practices
  • in certain circumstances, personal protective equipment

Without limiting the generality of section 3, under section 4 of Regulation 833 employers musttake the above measures to limit the level and duration of worker exposure to hazardous biological or chemical agents, including carbon monoxide, in accordance with the rules set out in that section.

The occupational exposure limits (OELs) in parts per million (ppm) for carbon monoxide (as set out in the 2017 American Conference of Governmental Industrial Hygienists (ACGIH) Table) are:

  • time-weighted average (TWA): 25 ppm (TWA means the time-weighted average airborne concentration of a biological or chemical agent to which a worker may be exposed in a work day or work week)
  • 30-minute excursion limit: 75 ppm (exposure shall not exceed 3 times the TWA for any period of 30 minutes)
  • ceiling excursion limit: 125 ppm (exposure shall not exceed 5 times the TWA at any time)

Where Regulation 833 applies, subsection 7.2(1) requires employers to protect workers from exposure to a hazardous biological or chemical agent, including carbon monoxide, without requiring them to wear and use a respirator, unless subsection 7.2(2) applies.

Subsection 7.2(2) requires employers to provide — and workers to wear and use — a respirator appropriate in the circumstances to protect the workers from exposure to the agent if:

  • substitution of the agent is not reasonable or not practical, and
  • the engineering controls required by Regulation 833 are:
    • not in existence or not obtainable
    • not reasonable or not practical to adopt, install or provide because of the duration or frequency of the exposures or because of the nature of the process, operation or work
    • rendered ineffective because of a temporary breakdown of the controls, or
    • ineffective to prevent, control or limit exposure because of an emergency
  • An employer who provides a worker with a respirator must comply with the requirements in sections 9 to 13 of Regulation 833.

Regulations for workplace sectors

Specific regulations may also apply to your workplace if it is:

  • an industrial establishment
  • a construction project
  • a mine or mining plant
  • a health care or residential facility

The following are examples of requirements in regulations made under the OHSA that may apply to protect workers from carbon monoxide poisoning.

Industrial establishments

Sections 127, 128, 130 and 138 of Regulation 851 — Industrial Establishments include the following requirements:

  • Adequately ventilate an industrial establishment by either natural or mechanical means so that the atmosphere does not endanger the health and safety of workers.
  • Provide replacement air to replace air exhausted, in accordance with certain requirements.
  • Train a worker who may be exposed to a biological, chemical or physical agent, such as carbon monoxide, that may endanger a worker’s safety or health, in specified topics.
  • Protect a worker by mechanical ventilation so their health and safety is not endangered where the worker is likely to be exposed to an atmosphere at atmospheric pressure with an oxygen content of less than 19.5%. If it is not practicable to do so, the worker must be protected by air supplied breathing equipment,so their health and safety is not endangered.
Construction projects

Sections 46, 47, 49 and 93 of Ontario Regulation 213/91 — Construction Projects include the following requirements:

  • Adequately ventilate a project by natural or mechanical means in certain circumstances, including if a worker may be injured by inhaling a noxious gas, vapour, dust, fume or from a lack of oxygen. If it is not practicable to provide natural or mechanical ventilation, respiratory protective equipment suitable for the hazard must be provided to and used by the worker.
  • Only operate an internal combustion engine in an excavation, building or other enclosed structure if there is an adequate supply of air for combustion and either:
    • exhaust gases and fumes from the engine are adequately discharged directly outside to a point sufficiently remote to prevent the return of the gases and fumes
    • there is adequate natural or mechanical ventilation to ensure that exhaust gases and fumes from the engine will not accumulate in the excavation, building or structure
    • Note: This section of the Construction Projects Regulation does not apply to an internal combustion engine operated in a tunnel, although other provisions of the regulation may be applicable depending on the circumstances (see, for example, section 316).
  • Where an internal combustion engine is operated in an excavation, building or other enclosed structure, the space must be tested for airborne concentrations of carbon monoxide to ensure that the concentrations do not exceed OELs determined in accordance with section 4 of Regulation 833. A competent worker must carry out this testing according to a written testing strategy developed by the employer in consultation with the joint health and safety committee or health and safety representative, if any. Note: this section of the Construction Projects Regulation does not apply to an internal combustion engine operated in a tunnel, although other provisions of the regulation may be applicable depending on the circumstances (see, for example, section 316).
  • A fuel-fired heating device must not be used in a confined or enclosed space unless there is an adequate supply of air for combustion and adequate general ventilation.
    • A fuel-fired heating device that generates noxious products of combustion, such as carbon monoxide, must discharge those products of combustion outside the building or structure in which the device is located.
  • Maintain all vehicles, machinery, tools and equipment in a condition that does not endanger a worker.

Ontario Regulation 213/91 also includes additional requirements in sections 329–331 related to ventilation in areas such as certain tunnels and shafts, and caissons and cofferdams, that may apply depending on the circumstances.

Mines and mining plants

Sections 182–184 of Regulation 854 — Mines and Mining Plants include the following requirements that may apply to protecting workers from the hazards of carbon monoxide:

  • The exhaust of an internal combustion engine installed within a building on surface must be:
    • conducted to a point outside the building
    • prevented from:
      • re-entering the building
      • entering the intake of any compressor
      • contaminating the atmosphere of another building
      • contaminating mine workings

There are also requirements related to the use of diesel-powered equipment in underground mines, including the following examples:

  • Diesel-powered equipment must not be used in an underground mine unless a Notice of diesel-powered equipment form obtained from the Ministry of Labour, Immigration, Training and Skills Development has been completed with information relating to the equipment. The completed form must be readily available at the mine site.
  • An employer must ensure that the undiluted exhaust emissions from diesel-powered equipment contain less than 600 ppm by volume of carbon monoxide.
  • Where diesel-powered equipment is operating in the workplace, an employer must ensure that a flow of air of at least 0.06 m3/s for each kW of power of the diesel-powered equipment is provided to the workplace by a mechanical ventilation system. Among other requirements, the flow of air must reduce the concentration of toxic substances in diesel exhaust emissions, which would include carbon monoxide, to prevent exposure of a worker to a level in excess of the limits in section 4 of Regulation 833.
  • An employer must test the carbon monoxide content of undiluted exhaust emissions from diesel-powered equipment to the atmosphere:
    • immediately after repairs to the engine or exhaust system or both, and
    • at routine intervals for maintenance as the manufacturer recommends or, if there is no such recommendation, at least once a month.
  • An employer must also test the volume of air flow and the carbon monoxide contents (among other substances) of the atmosphere at the request of a worker.
Health care and residential facilities

Under section 19 of Ontario Regulation 67/93 — Health Care and Residential Facilities there are requirements related to providing general indoor ventilation adequate to protect the health and safety of a worker by natural or mechanical means. Under section 20, there are requirements related to ventilation systems providing replacement air to replace air that is exhausted.

Additional resources

Although it is not incorporated into the OHSA or the regulations, workplace parties may wish to review Industrial Ventilation: A Manual of Recommended Practice for Design, 31st Edition, published by American Conference of Governmental Industrial Hygienists (ACGIH) for further information about carbon monoxide hazards. This manual recommends the following dilution rates for fuel burning vehicles, based on average operating conditions, measured in actual cubic feet per minute (acfm):

  • 10,000 acfm for a propane fuelled lift truck
  • 16,000 acfm for a gasoline fuelled lift truck
  • 10,000 acfm for an operating automobile
  • 20,000 acfm (or more) for an operating truck
  • 100 acfm/horsepower for a diesel fuelled vehicle

With respect to the operation of lift trucks indoors, the ACGIH publication suggests that the ventilation rates above apply to lift trucks that are:

  • regularly maintained (carbon monoxide in exhaust gases limited to 1% for propane fuelled lift trucks and 2% for gasoline fuelled trucks)
  • operated for less than 50% of a shift
  • less than 60 HP with 150,000 cu ft per lift truck
  • used where there is good workplace air distribution

Contact us

If you need more information, please contact us at 1-877-202-0008 on Monday to Friday, from 8:30 a.m. to 5:00 p.m., or by email at webohs@ontario.ca.

References to materials from external parties is informational only. A reference to an external document is not an endorsement that the information included is OHSA compliant.