Hazard summary

The owner of a small brew-on-premise wine making establishment died of asphyxiation in a carbon dioxide (CO2) enriched, oxygen deficient atmosphere. The CO2 was produced by the fermentation of wine in the tightly closed, non-ventilated basement. The store did not have any natural or mechanical ventilation and was closed at the time of the incident. Fermentation of a large number of batches of wine had begun during the previous week. Two responding paramedics were also affected by the high level of CO2 in the stairwell leading to the basement.


Wine fermentation is carried out in vented glass or plastic carboys or in buckets and the CO2 produced in the process is released into the workplace. CO2 release is greatest early in the fermentation process when fermentation is most active. In the absence of adequate ventilation CO2 can accumulate, displace oxygen and reach dangerous concentrations well in excess of the time-weighted average occupational exposure limit of 5,000 parts CO2 per million parts of air (ppm). The accumulation of CO2 can occur even in shops located on the ground floor with access to the outdoors.

Health effects

CO2 is a colourless, odourless gas that occurs naturally in air at concentrations of about 350 ppm, or about 0.04%. The primary fermentation process that produces wine also produces CO2. The volume of CO2 produced varies according to the type of wine, the composition of the juice, room temperature and the stage of fermentation. At peak fermentation the volume of CO2 produced per day may be 10 to 15 times greater than that which occurs naturally in air. Without adequate ventilation, CO2 can displace oxygen and produce an atmosphere that is both high in CO2 and low in oxygen.

CO2 is considered a simple asphyxiant, although at high concentrations it also acts as a strong central nervous system depressant. Workers exposed to CO2 concentrations greater than 2-3% (20,000-30,000 ppm) may experience rapid breathing and shortness of breath. Exposure to CO2 in concentrations greater than 4% (40,000 ppm) poses an immediate or delayed threat to life or health and can interfere with the worker's ability to escape. Exposure to CO2 in concentrations greater than 10% (100,000 ppm) can cause death within minutes.

At oxygen concentrations of 10-16% workers may experience rapid heart rate, rapid breathing, and exercise intolerance. As the concentration of oxygen decreases to 6-10%, the worker may experience nausea, collapse, and coma. Workers exposed to oxygen concentrations of less than 6% can be expected to become unconscious and die within a short period of time footnote 1

Hazard locations

The risk of oxygen depletion and elevated CO2 concentrations as a result of fermentation in brew-on-premise wine making establishments is generally not well known. When first responders entered the shop where the fatality occurred they found the oxygen concentration to be approximately 16%. This oxygen reading was taken after mechanical ventilation had begun. The oxygen concentration may have been lower at the time of the fatality. The CO2 concentration could not be measured because it exceeded the maximum detection limit of the available monitoring equipment.

In 2002, two British Columbia winery workers died after entering a fermentation vessel. The oxygen concentration in the vessel was about 16%, and the CO2 concentration was over 100,000 parts per million, or 10% footnote 2. At these concentrations either the reduced oxygen concentration or the elevated CO2 concentration would impede the ability to escape the environment and quickly cause unconsciousness and death.

Requirements under the Occupational Health and Safety Act (OHSA) and its regulations

  • An employer shall provide information, instruction and supervision to a worker to protect the health or safety of the worker (OHSA Clause 25(2)(a)). For example, information and instruction may include:
    • the health effects of CO2
    • the circumstances under which CO2 can accumulate in high concentrations
    • the limitations of mechanical and natural ventilation
    • the use, care, and maintenance of monitoring equipment and
    • emergency measures and procedures
  • An employer shall acquaint a worker or person having authority over a worker with any hazard in the work and in the handling, storage, use, disposal and transport of any article, device, equipment, or a biological, chemical or physical agent (OHSA Clause 25(2)(d)). For example, workers should be acquainted with the hazard of elevated levels of CO2 and the potential for a reduced oxygen/elevated CO2 atmosphere caused by consumption and displacement of oxygen during the fermentation process.
  • An employer shall take all measures reasonably necessary in the circumstances to protect workers from exposure to CO2 because of the storage, handling, processing or use of CO2 in the workplace (Section 3 of Regulation 833, Control of Exposure to Biological or Chemical Agents).
  • An employer shall restrict the amount and duration of a worker's exposure to CO2 in accordance with the following limits (Section 4 of Regulation 833, Control of Exposure to Biological or Chemical Agents).
    • The TWA or time-weighted average limit to which a worker may be exposed for an eight hour work day or a forty hour work week is 5,000 ppm.
    • The STEL or short term exposure limit to which a worker may be exposed in any 15 minute period is 30,000 ppm.
  • 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 of Regulation 851, Industrial Establishments).
  • Replacement air shall be provided to replace air exhausted. The replacement air shall,
    1. be heated, when necessary, to maintain at least the minimum temperature in the workplace specified in section 129 of Regulation 851, Industrial Establishments
    2. be free from contamination with any hazardous dust, vapour, smoke, fume, mist or gas and
    3. enter in such a manner so as:
      1. to prevent blowing of settled dust into the workplace
      2. to prevent interference with any exhaust system, and
      3. not to cause undue drafts. (Section 128 of Regulation 851, Industrial Establishments)
  • The discharge of air from any exhaust system shall be in such a manner so as to prevent the return of contaminants to any workplace (Section 128 of Regulation 851, Industrial Establishments).
  • Where a worker is likely to be exposed to an atmosphere at atmospheric pressure with an oxygen content of less than 18%, the worker shall be protected by mechanical ventilation so that the worker's safety and health is not endangered (Section 138 of Regulation 851, Industrial Establishments).

Recommended precautions and control measures

  • CO2 monitors equipped with audible alarms should be installed in all fermentation areas. Monitors should be set to alarm at or below the TWA. Monitors should be inspected and maintained on a regular basis as per the manufacturer's recommendations. Sensors may require frequent calibration and regular replacement.
  • CO2 concentrations in some wine making operations may exceed the maximum detection range of CO2 monitors used in indoor air quality and occupational exposure limit assessments. Some direct reading CO2 detector tubes can be used, but extreme caution should be used when approaching and assessing the environment which may have the potential to be immediately dangerous to life and health.
  • Fermentation should be conducted in areas of the workplace that are mechanically ventilated to the outdoors with provisions for replacement air.
  • First responders (police, fire, emergency medical services) should be made aware of the potential for CO2 enriched and oxygen deficient atmospheres in brew-on-premise wine making establishments, and of the need for appropriate monitoring equipment and protective equipment when dealing with emergencies in these workplaces.

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.