In the spring and summer, enclosed parking garages are often cleaned using gas-powered pressure washers to remove the deposits that have accumulated over the winter months. In 2014, seven workers were treated for carbon monoxide (CO) poisoning and one died after using gasoline-powered pressure washers in poorly ventilated underground parking garages.

Locations and sectors

Gas-powered pressure washers are used in many industrial workplaces that are provincially regulated.

Hazard summary

Carbon monoxide is often called “the silent killer,” because it gives no clear warning to its victims. It is an invisible gas with no taste or smell and it will not cause any unusual feeling in the nose, mouth or throat as it is breathed in. The first effects that can actually be noticed are headache and faintness. A worker who does not know about carbon monoxide poisoning may ignore these early symptoms or think a minor illness is coming on. But continuing exposure can cause confusion, loss of consciousness and even death. Often there is little time before workers experience symptoms that inhibit their ability to seek safety. Use of the equipment without incident sometimes gives the workers a false sense of safety, and workers have been poisoned on subsequent occasions.

Employers must ensure that supervisors and workers know about the dangers of carbon monoxide when using gas-powered pressure washers.

Carbon monoxide monitoring is recommended to ensure that workers are not exposed to the hazard of carbon monoxide poisoning. The work area must be well ventilated to ensure adequate protection of workers. Fans should be used to bring in fresh air.

Most problems occur due to inadequate equipment maintenance, inadequate ventilation and workers not being provided with the necessary information on hazards associated with the use of gas-powered pressure washers.

Workers who can be affected by carbon monoxide of gas-powered pressure washers are operators and others who are in the vicinity during and after use. Carbon monoxide can accumulate quickly in enclosed work areas or poorly ventilated areas, increasing the risk of carbon monoxide poisoning.

Carbon monoxide interferes with the ability of red blood cells to carry oxygen. Exposure to this toxic gas at high concentrations (more than 1,200 parts per million [ppm]) is considered to be immediately dangerous to life and health (IDLH)footnote 1. Gas-powered washers can emit carbon monoxide levels well in excess of 2 per cent or 20,000 ppm.

Suggested precautions

If possible, electric-powered or battery-powered pressure washers should be used in place of gas-powered pressure washers. To prevent an electrocution hazard, the equipment must be safe to use in wet environments.

If gas-powered pressure washers are used:

  • The manufacturer’s specifications for the equipment should be followed.
  • Ensure equipment is maintained in good condition to minimize exhaust emissions of CO.
  • Equipment should not be left running when it is not in use in the workplace.
  • Learn to recognize the symptoms and signs of CO overexposure: headache, nausea, weakness, dizziness, visual disturbances, changes in personality and loss of consciousness. Any of these symptoms and signs can occur within minutes of starting the equipment.
  • Where possible, run the high-pressure washer line into the workplace from the outside; that is, place the pump and power unit of the high-pressure washers outdoors. Make sure that the power unit is placed away from air intakes so that engine exhaust is not drawn indoors where the work is being done or where others are present. The same steps should be taken if compressed air is used: place the gasoline-powered compressor outdoors and away from air intakes so that engine exhaust is not drawn indoors.
  • To avoid electrocution hazards, consider the use of tools powered by compressed air if they are available and can be used safely in wet environments.
  • Personal CO monitors should be used where potential sources of CO exist. These monitors should be equipped with audible alarms set at 25 ppm CO to warn workers when concentrations are too high.

Employers should:

  • Use equipment that allows for the placement of gasoline-powered engines outdoors at a safe distance from air entering the workplace.
  • Monitor the worker for CO exposure to determine the extent of the work area hazard.
  • Ventilate the work area to minimize the introduction of CO-contaminated air.
  • If possible, substitute with less hazardous equipment. Use electric tools or tools with engines that are separate from the tool and that can be located outside and away from air intakes.

Workers should:

  • Learn to recognize the warning symptoms of CO poisoning.
  • If experiencing any symptoms, immediately turn off equipment and go outdoors or to a place with uncontaminated air and report the situation to the supervisor.
  • Stay away from the work area until the equipment has been deactivated and measured CO concentrations are in compliance with the Regulation 833.

Relevant legislative requirements

Occupational Exposure Limits (OELs) restrict the level and duration of worker exposure to hazardous biological or chemical agents, including carbon monoxide. They are prescribed in Regulation 833, Regulation Respecting Control of Exposure to Biological or Chemical Agents, made under the Occupational Health and Safety Act, (OHSA). The OELs for carbon monoxide are:

  • TWA (Time Weighted Average): 25 ppm. The TWA is based on an eight-hour workday, or forty-hour work week.
  • 30 minute excursion of 75 ppm.
  • Ceiling (C) excursion of 125 ppm.

Under Sections 3 and 4 of Regulation 833:

3. (1) Every employer shall 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 such agent in the workplace.

3. (2) The measures to be taken shall include the provision and use of,

  1. engineering controls
  2. work practices
  3. hygiene facilities and practices and
  4. if section 7.2 applies, personal protective equipment

4. Without limiting the generality of section 3, every employer shall take the measures required by that section to limit the exposure of workers to a hazardous biological or chemical agent in accordance with the following rules:

  1. If the agent is listed in the Ontario Table, exposure shall not exceed the TWA, Short Term Exposure Limit (STEL), or C set out in the Ontario Table.
  2. If the agent is not listed in the Ontario Table but is listed in the American Conference of Governmental Industrial Hygienists (ACGIH) Table, exposure shall not exceed the TWA, STEL, or C set out in the ACGIH Table.
  3. If the Table that applies under paragraph 1 or 2 sets out a TWA for an agent but sets out neither a STEL nor a C for that agent, exposure shall not exceed the following excursion limits:
    1. Three times the TWA for any period of 30 minutes.
    2. Five times the TWA at any time.

Under Section 25 of the OHSA:

The employer shall:

  • take every precaution reasonable in the circumstances for the protection of a worker [clause 25(2)(h)]
  • provide information, instruction and supervision to a worker to protect the health or safety of the worker [clause 25(2)(a)]
  • ensure that equipment, materials and protective devices provided by the employer are maintained in good condition [clause 25(1)(b)]

Under Section 27 of the OHSA:

The supervisor shall:

  • ensure that a worker works in the manner and with the protective devices, measures and procedures required by the Act and the regulations [clause 27(1)(a)]
  • ensure that a worker uses or wears the equipment, protective devices or clothing that the worker’s employer requires to be used or worn [clause 27(1)(b)]
  • advise a worker of the existence of any potential or actual danger to the health or safety of the worker of which the supervisor is aware [clause 27(2)(a)]
  • take every precaution reasonable in the circumstances for the protection of a worker [clause 27(2)(c)]

Under Section 28 of the OHSA:

A worker shall:

  • work in compliance with the provisions of the Act and the regulations [clause 28(1)(a)]
  • use or wear the equipment, protective devices or clothing that the worker’s employer requires to be used or worn [clause 28(1)(b)]
  • report to his or her employer or supervisor the absence of or defect in any equipment or protective device of which the worker is aware and which may endanger himself, herself or another worker [clause 28(1)(c)]
  • not use or operate any equipment, machine, device or thing or work in a manner that may endanger himself, herself or any other worker [clause 28(2)(b)]

Regulation 851, Industrial Establishments:

  • An industrial establishment shall be adequately ventilated by either natural or mechanical means such that the atmosphere does not endanger the health and safety of workers [section 127]
  • Replacement air shall be provided to replace air exhausted [clause 128(1)]
  • The replacement air shall be free from contamination with any hazardous dust, vapour, smoke, fume, mist or gas [clause 128(2)(b)]
  • A worker who may be exposed to a biological, chemical or physical agent that may endanger the worker’s safety or health shall be trained,
    1. to use the precautions and procedures to be followed in the handling, use and storage of the agent
    2. in the proper use and care of required personal protective equipment and
    3. in the proper use of emergency measures and procedures [section 130]

The 2014 changes to the Ontario Fire Code requiring CO detectors in certain locations is enforced by local fire departments under the authority of the Fire Protection and Prevention Act, 1997.


Carbon monoxide: The silent killer

Carbon monoxide resources

For more information

Workplace Safety and Prevention Services e-laws

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.