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Carbon monoxide exposure from heaters in outdoor dining spaces

What is the potential risk?

As weather becomes colder, employers may wish to enclose outdoor spaces and supply heat using space or portable heaters. Many types of heaters are available, including wall and ceiling models, stand-alone floor heaters, and table heaters. They can be supplied by natural gas, propane, or electricity (infrared heaters). Using combustion heaters (e.g., propane or natural gas) in enclosed spaces can expose workers to carbon monoxide (CO) gas.

CO is a toxic, odourless, invisible gas that comes from incomplete combustion of any carbon-containing material (e.g., wood, coal, oil, kerosene, gasoline, diesel fuel, natural gas, or propane). Victims of CO poisoning cannot see or smell the gas, so they don’t realize they are in danger.

CO interferes with the ability of blood to carry oxygen to tissues, most importantly the brain. The effects of CO poisoning vary from person to person and depend on the amount and length of exposure. The symptoms of CO poisoning include:

  • Headache
  • Feeling very tired
  • Nausea
  • Confusion
  • Dizziness

Other symptoms may include shortness of breath, chest pain, and loss of coordination. These effects become more severe the longer you are exposed and may lead to collapse, coma, and death at the highest CO concentrations.

Which workplaces may be at risk?

All restaurants, bars, or other outdoor dining venues with unventilated enclosed outdoor spaces that use a separate heating system may be at risk. If you intend to enclose your outdoor space and supply supplementary heat using propane or natural gas units, you must consider the risk of carbon monoxide exposure.

How can I reduce the risk in my workplace?

As an employer, you need to know if there is the potential for CO exposure in your workplace. It’s your responsibility to regularly inspect your workplace, and to ensure that your safety procedures and practices control the risk.

The best way to reduce the risk of exposure to CO when heating enclosed outdoor spaces is to use electric heaters, rather than natural gas or propane. Enclosing outdoor spaces also reduces natural ventilation.

When considering heating an outdoor dining space, you should do the following:

  • Avoid using gas or propane heaters. Most manufacturers state that these heaters should never be used in an enclosed area.
  • Design your dining space carefully:
    • Avoid completely enclosing the space
    • Position the walls in order to avoid a “wind tunnel” effect
  • Make sure you include proper fire and electrical safety measures (e.g., keep heaters away from combustible materials and exits).

The following sections of the Occupational Health and Safety Regulation are most relevant to this risk.

  • Section 5.54 requires the following:
    • If a worker may be exposed to an air contaminant (including CO) in excess of 50% of its exposure limit, an exposure control plan must be implemented.
    • Because CO is a designated substance under the Regulation, exposure must be kept as low as reasonably achievable.
  • Section 5.2 requires the following:
    • If a worker may be exposed to a biological agent designated as a hazardous substance in the Regulation that could cause an adverse health effect, written procedures must be prepared and implemented to eliminate or minimize the risk of exposure to the biological agent.
    • This information must be clearly communicated to the worker.

Where can I find resources?

Publication Date: Jul 2021 Asset type: Risk Advisory Reference: RA 2020-05