Health & Safety

Information Bulletins · Inadequate Ventilation and High CO2 Levels



Inadequate Ventilation and High CO2 Levels

Does your room feel stuffy? Do you feel fatigued or become dizzy during the work day? Do you regularly get headaches at your work location?

These symptoms have a variety of causes (ergonomics, lighting or noise) but could indicate an indoor air quality problem due to inadequate ventilation.
In an office building, a minimum supply of 10 litres per second of outdoor air per person is recommended by ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) but measuring airflow is complicated.

Inadequate ventilation can lead to the build-up of small amounts of contaminants which are difficult to identify and test, so carbon dioxide (CO2) levels are used as an indicator of adequate ventilation in a room. Carbon dioxide is released by combustion of fuels and every time we breathe. It is normally measured at 300-350 ppm (parts per million) in the atmosphere. The legal exposure limit is a TWAEV (time weighted average exposure value) of 5000 ppm which will unlikely be reached outside of heavy industry (Regulation 833 Control of Exposure to Biological or Chemical Agents). Levels of 600-800 ppm are typical in office environments. Guidelines suggest CO2 levels do not exceed 1000 ppm (700 ppm above outdoor levels), the ASHRAE action level. Some individuals are sensitive to CO2 levels as low as 600 ppm so action may even be warranted at lower levels.

The Joint Health and Safety Committee (JHSC) can make recommendations to improve the ventilation if there is an obvious problem. If the employer does not believe there is a ventilation problem, the JHSC can recommend indoor air testing for CO2 and any other suspected contaminants be done to ensure exposure values are not being exceeded. If the employer refuses, the Ministry of Labour can be called.
Testing should be done throughout the day to show fluctuations and should show the worst case scenario. A JHSC member may be present at the beginning of every workplace test and OSSTF recommends that this is requested.

  • If levels are above outdoor levels before the room is occupied each morning there is definitely a problem with the ventilation system, or possibly the problem can be alleviated if the ventilation is left on longer in the afternoon/evening or throughout the night.
  • Be aware of the way the room is ventilated. Turning off the ventilation because it is noisy or blocking the ventilator to control temperature or drafts can lead to inadequate ventilation. A unit ventilator allows for adequate fresh air intake and is not just necessary for heating and cooling.
  • Be sure there is air movement at both the supply and the return (using a short ribbon) and that they are adequately spaced apart to promote air circulation.
  • HVAC (Heating, Ventilation and Air Conditioning) systems in older buildings may not have been designed to today's standards. The employer does not necessarily have to redesign the ventilation system but does have to maintain the ventilation system in place.
  • To be properly maintained ventilation units need to be rebalanced, filters should be changed regularly and dampers should remain open to allow for some outside air to be brought in if possible. Appropriate maintenance records should be made available to the JHSC.
  • Buildings made in the 1970s were often built airtight and without windows to open in order to save energy. Ventilation in these building and in interior rooms of any building is regularly a concern since there is rarely any air exchanged through drafts if the ventilation system is not working properly.
  • Be sure any renovations include ventilation plans for any subdivided rooms.
  • Leaving a door open to the hallway, leaving a window open a crack, or opening windows for a few minutes a couple of times a day can alleviate problems if the employer has taken all other actions possible to maintain adequate ventilation.
  • Plants can help reduce carbon dioxide levels and produce oxygen but generally not to a significant amount and if they are not properly cared for can become sources for mould growth.

Improving ventilation rates can eliminate high CO2 levels and prevent other contaminants from accumulating. Employees should not have to suffer from headaches and fatigue.

Relevant Legislation

Occupational Health and Safety Act
25. (1) An employer shall ensure that, 
      (b) the equipment, materials and protective devices provided by the employer are maintained in good condition;

Industrial Establishments Regulation 851
127. 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. R.R.O. 1990, Reg. 851, s. 127.

128. (1) Replacement air shall be provided to replace air exhausted. 
       (2) The replacement air shall, 
(a) be heated, when necessary, to maintain at least the minimum temperature in the workplace specified in section 129; 
(b) be free from contamination with any hazardous dust, vapour, smoke, fume, mist or gas; and 
(c) enter in such a manner so as,
      (i) to prevent blowing of settled dust into the workplace,
      (ii) to prevent interference with any exhaust system, and
      (iii) not to cause undue drafts.
      (3) 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. R.R.O. 1990, Reg. 851, s. 128.

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