Photograph of Aspergillus niger spores.Canadian Mould Guidelines
Mould in Workplace buildings


Canadian Mould Standards: Mould in Workplace buildings, Alert 20: ISSN 1195-5228, Produced by Professional and Specialized Services, Issued: December 2000. This article describes mould (or in the U.S. mold) exposure standards fodr the Canadian workplace.

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Mould in Workplace buildings

Mould 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 weakened immune systems are more likely to react to mould. The most common symptoms are runny nose, eye irritation, skin rash, cough, congestion and aggravation of asthma. Symptoms usually disappear after mould exposure stops. Most often, there are no known long-term consequences to workplace exposures.

Hazard Locations:

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

Any building may have mould. However, buildings with a history of water leaks, floods, fires and problems with indoor air quality (e.g. poor humidity control, lack of fresh air) should be considered at greater risk of mould growth. 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 water damage, high humidity or 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.


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. These moisture problems should be the focus of assessment and control efforts, followed by clean-up, remediation of contaminated materials, periodic inspections, and preventive and remedial maintenance. The Internet resources below contain detailed information. 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.

Internet Resources:

Facts About Stachybotrys Chartarum and Other Molds. Centers for Disease Control and Prevention, National Center for Environmental Health. March 9, 2000. - Centers for Disease Control and Prevention 1600 Clifton Rd Atlanta, GA 30333 800-CDC-INFO (800-232-4636) TTY: (888) 232-6348, retrieved 7/15/2014, original source:

  • Etzel, Ruth A. "Stachybotrys." Current opinion in pediatrics 15, no. 1 (2003): 103-106.
  • Green, Brett J., Euan R. Tovey, Jason K. Sercombe, Francoise M. Blachere, Donald H. Beezhold, and Detlef Schmechel. "Airborne fungal fragments and allergenicity." Medical Mycology 44, no. Supplement 1 (2006): S245-S255.
  • Green, Brett James, Detlef Schmechel, Jason Kingsley Sercombe, and Euan Roger Tovey. "Enumeration and detection of aerosolized< i> Aspergillus fumigatus</i> and< i> Penicillium chrysogenum</i> conidia and hyphae using a novel double immunostaining technique." Journal of immunological methods 307, no. 1 (2005): 127-134.
  • Green, Brett James, Detlef Schmechel, and Euan Roger Tovey. "Detection of aerosolized Alternaria alternata conidia, hyphae, and fragments by using a novel double-immunostaining technique." Clinical and diagnostic laboratory immunology 12, no. 9 (2005): 1114-1116.
  • Mitchell, Clifford S., Junfeng Zhang, Torben Sigsgaard, Matti Jantunen, Paul J. Lioy, Robert Samson, and Meryl H. Karol. "Current state of the science: health effects and indoor environmental quality." Environmental Health Perspectives (2007): 958-964.
  • Rand, Thomas G., and J. David Miller. "Immunohistochemical and immunocytochemical detection of SchS34 antigen in Stachybotrys chartarum spores and spore impacted mouse lungs." Mycopathologia 165, no. 2 (2008): 73-80.
  • Schmechel, Detlef, Janet P. Simpson, Donald Beezhold, and Daniel M. Lewis. "The development of species-specific immunodiagnostics for< i> Stachybotrys chartarum</i>: The role of cross-reactivity." Journal of immunological methods 309, no. 1 (2006): 150-159.
  • Vesper, Stephen J., Manju Varma, Larry J. Wymer, Dorr G. Dearborn, John Sobolewski, and Richard A. Haugland. "Quantitative polymerase chain reaction analysis of fungi in dust from homes of infants who developed idiopathic pulmonary hemorrhaging." Journal of occupational and environmental medicine 46, no. 6 (2004): 596-601.
  • Yike, Iwona, Anne M. Distler, Assem G. Ziady, and Dorr G. Dearborn. "Mycotoxin adducts on human serum albumin: biomarkers of exposure to Stachybotrys chartarum." Environmental health perspectives (2006): 1221-1226.

Guidelines on Assessment and Remediation of Fungi in Indoor Environments. New York City Department of Health. April 2000.

Facts About Mold. New York City Department of Health. February 2001.

Health Canada: Fungal Contamination in Public buildings

Fighting Mold. Canada Mortgage and Housing Corporation. 1999

After the Flood. Canada Mortgage and Housing Corporation.

Moulds: Controlling Exposure is Essential. Construction Safety Association of Ontario.

Remember that while complying with occupational health and safety laws, you are also required to comply with applicable environmental laws.

Please photocopy Ministry of Labour Alerts, distribute them widely and post them where people will see them.


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