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Dangers of oxygen deficiency when using asphyxiants as refrigerants

What is the potential risk?

Cooling and refrigeration are often accomplished using chemicals known as refrigerants. Many refrigerants are non-toxic, but workers who are exposed to large quantities of them may still be at risk of serious harm.

What are asphyxiants?

Asphyxiants are gases that reduce the level of oxygen available for breathing, generally by displacing normal air. The types of asphyxiants used in cooling and refrigeration include:

  • Simple (inert) asphyxiants
  • Gases that act like simple asphyxiants
  • Asphyxiants that pose other significant risks

Oxygen displacement may occur either during an unintended or rapid release of gas, or by a small and/or slow leak that allows gas to accumulate in poorly ventilated spaces over time.

Simple asphyxiants are generally colourless, odourless, and non-toxic, so there are no warning signs to make workers aware of the danger. This makes simple asphyxiants, and refrigerants that act like them (i.e., those gases with very low toxicity and/or chemical reactivity), an invisible hazard that may pose a significant risk to workers.

Some refrigerants may also be used in solid or liquid forms. Examples include dry ice, which is a solid form of carbon dioxide, and liquid nitrogen. Because those substances convert to large amounts of gas as they warm, they pose a similar asphyxiation risk to workers, especially when open to the atmosphere.

Common refrigerants that can cause an oxygen-deficient atmosphere include:

  • Butanes*
  • Carbon dioxide (gas, liquid, dry ice)*
  • Chlorofluorocarbons (e.g., dichlorodifluoromethane)*
  • Fluorocarbons
  • Ethane
  • Ethylene*
  • Helium
  • Hydrochlorofluorocarbons
  • Nitrogen (gas, liquid)
  • Propane*
  • Propylene*

*These substances are flammable at concentrations below levels expected to result in oxygen deficiency. As such, additional controls to address the risk of fire and explosion must also be implemented.

What health effects can occur at low oxygen levels?

An oxygen-deficient atmosphere (containing less than 19.5% oxygen) can cause symptoms such as rapid breathing, rapid heart rate, and fatigue. As the level of oxygen drops further, confusion, nausea, vomiting, loss of consciousness, convulsions, and/or death can occur.

In which industries might this risk be present?

Workplaces that use refrigerants in sufficient quantities to pose a risk of worker asphyxiation in the event of a leak or containment failure include the following:

  • Food and beverage processing and manufacturing
  • Cold storage facilities
  • Restaurants, bars, ice cream shops
  • Ice rinks and curling rinks
  • Ice manufacturers
  • Supermarkets
  • Workplaces using extraction processes
  • Metal fabrication
  • Laboratories
  • Oil and gas extraction and manufacturing
  • Chemical manufacturing
  • Semiconductor manufacturing
  • Health care (laboratories, cryogenic therapy)

How can the risk be reduced in the workplace?

Employers need to know if their processes use refrigerants that may pose a risk of worker asphyxiation. Performing a risk assessment will help to determine if the refrigerants used in the workplace pose a significant risk to workers.

The following measures can help reduce risks posed by asphyxiants. They follow the hierarchy of controls.

Elimination or substitution

  • Reduce operational requirements for refrigeration; decrease the amount of refrigerant used.
  • Consider replacing the refrigerant with a non- or less-hazardous substance.

Engineering controls

  • Design and install facilities and refrigeration systems in accordance with applicable standards (see resources listed below).
  • Install appropriate shut-off valves in refrigerant lines where required.
  • Ensure refrigeration rooms are provided with properly engineered ventilation.
  • Provide local exhaust ventilation for open point-source refrigerant applications (i.e., liquid nitrogen or dry ice).
  • Ensure pressure relief valves on refrigeration equipment and storage vessels are appropriately vented out of the work area.

    Note: All ventilation must be designed and installed in accordance with acceptable engineering practices.

Administrative controls

  • Oxygen monitors — Avoid entering confined or enclosed spaces where asphyxiants are present, or may be generated, without first ensuring that a breathable atmosphere is present by using an oxygen monitor.

    Oxygen monitors must be properly calibrated and maintained and should warn workers when the concentration of oxygen drops below 19.5%. The use of portable oxygen monitors (along with other protective measures) is advisable when responding to process upsets or potential leaks.

  • Worker training — Workers must be made aware of the risk posed by asphyxiants that have no warning properties. Often, fatalities involving asphyxiants include would-be rescuers who are unaware of the potential for a hazardous atmosphere.

    Workers must be trained in the proper use of monitoring equipment and emergency response procedures. Regular rescue drills, along with signage and alarm systems, keep workers alert to the presence of asphyxiants in the workplace.

    • Routine workplace inspection — Periodically inspect containers, vessels, and piping used to handle, store, and/or transport refrigerants for damage and leaks. Check equipment prior to each use; pre-use checklists may assist with this.

    • Labelling — Label storage and transport containers, vessels, and/or piping with the content name and hazard information.

Personal protective equipment

  • Respiratory protection — Educate workers on respiratory protection suitable for responding to emergencies involving asphyxiants. Air-purifying respirators will not protect workers from asphyxiation. Supplied air respirators must be used when responding to emergencies in oxygen-deficient atmospheres.

Where can I find more information?

Learn more about managing risk in your workplace.

Publication Date: Feb 2023 Asset type: Risk Advisory Reference: RA 2023-01