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Environmental and Workplace Health

Mould, Dampness and Humidity


Since moisture promotes mould growth, dampness is one of the most common causes of poor indoor air in homes, classrooms and public spaces. Controlling the level of moisture is one of the best and easiest ways to improve indoor air and protect your health.

Mould is the common word for any Fungus that grows on food or damp building materials. It often looks like a stain and comes in a variety of colours. In some cases, however, mould may not be visible but may have a musty odour. If it is allowed to grow, mould can contribute to poor indoor air quality.

In order to reproduce, moulds release "spores" into the air and these spores are small enough that people can actually breathe them in. Mould spores are always present outdoors. So, when mould grows indoors, the number of mould spores and fragments is usually higher indoors than it is outdoors. High concentrations of airborne mould spores can have a number of adverse health effects.

This section provides detailed information about mould and the effects it can have on your health. It also offers tips for how you can remove mould, prevent future growth and improve the quality of your indoor air.

Health Canada helps protect Canadians from the effects of mould by conducting research and by providing information about healthy indoor air.

A publication entitled Indoor Air Quality in Office Buildings: A Technical Guide, published by Health Canada in 1995, did provide some advice on how to interpret mould air testing done in large office buildings. It included some numerical limits for spore counts (in CFU / m3) that are often misinterpreted as Health Canada guidelines. The numbers provided are typical values found in sampling done in federal government buildings by the author, using a specific sampling method. They are meant to help guide investigations in office buildings, where mould is suspected but was not located by a visual inspection. They do not represent a "safe level" of mould, are not applicable to homes, and in no way represents an official Health Canada guideline or recommendation.

The document has been removed from the Health Canada Indoor Air website. Health Canada considers that this publication requires updating but that this task does not fall within the current mandate of the Indoor Air program. The guide was originally published when Health Canada was responsible for responding to requests for air quality investigations in federal buildings. This activity is now carried out by Public Works and Government Services Canada.

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