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 the law based on the facts in the workplace.

Hazard summary

Workers and the public may be exposed to mould on water-damaged building materials inside buildings, and during building maintenance and repair operations. The most common types of mould are generally not hazardous to healthy individuals — but some moulds may be hazardous to certain individuals.

People who have asthma, bronchitis, hay fever, other allergies, or have a medical condition that affects their immune system are more likely to experience health effects associated with mould. The most common health effects are:

  • runny nose
  • eye irritation
  • skin rash
  • cough
  • congestion
  • aggravation of asthma

Health effects usually disappear after mould exposure stops. In most cases, workplace exposures to mould do not result in long-term health consequences. Apart from health effects from exposure, the presence of some moulds indoors can lead to the buildup of irritating byproducts and unpleasant odours.

Hazard locations

Moulds (fungi) are present everywhere — indoors and outdoors.

Any building may have mould. However, buildings that should be considered at greater risk of mould growth have a history of:

  • water leaks
  • floods
  • fires
  • problems with indoor air quality (for example poor humidity control, lack of fresh air)

Water-damaged drywall, wood materials, jute, wallpaper, and cardboard are prone to fungal growth.

All moulds need water to grow. Mould can grow anywhere there is either:

  • water damage
  • high humidity
  • dampness

Most often moulds are confined to areas near the source of water. When mouldy material becomes damaged or disturbed, mould spores can be released into the air. Exposure occurs if people inhale the spores.

Precautions

The sustained and/or extensive growth of any visible mould on the interior surfaces of a building is unacceptable. Mould growth on the interior surfaces of buildings is a risk factor for health problems.

Moisture problems (flooding, leaks, water intrusion, condensation, etc.) in buildings are the primary reason for mould growth.

If you think your workplace has a mould issue, you should take the following precautions:

  1. Assess any moisture causing problems and try to control them
  2. Clean up
  3. Remediate contaminated materials
  4. Inspect materials periodically
  5. Conduct preventive and remedial maintenance

If mould contamination is extensive, the employer should seek professional assistance from private sector consultants who specialize in mould and mould remediation.

Occupants of buildings contaminated with mould should be advised of the presence of the mould and given information on the health effects of mould.

Legal requirements

Employers are required by section 25(2)(h) of the Occupational Health and Safety Act to take every precaution reasonable in the circumstances for the protection of workers.

The Occupational Health and Safety Act places a responsibility on constructors (section 23), employers (section 25), and supervisors (section 27) to ensure the health and safety of workers. This includes protecting workers from mould in workplace buildings. Various sections of the Industrial, Construction, Mining or Health Care regulations may also apply to maintenance and remediation activities.

Resources on corrective measures, mould remediation and worker training are listed below.

Resources