Dru Sahai, M.Sc(A), Project Coordinator, CSAO
Construction Safety Association of Ontario
More and more construction firms are involved in removing toxic moulds from contaminated buildings. As a result, there's an increasing demand for information on toxic moulds. This article explains
Information also covers the obligations of employers and others under Ontario's Occupational Health and Safety Act.
What are moulds?
Where are moulds found?
Construction workers can be potentially exposed to toxic spores when working on buildings with some sort of water damage from flooding, plumbing leaks, or leaks in the structure itself.
Why are moulds of concern?
Stachybotrys has gained special attention recently because it has been discovered in portable classrooms with ongoing moisture problems. It appears as small black patches and grows well on water-soaked cellulose material such as wallpaper, ceiling tiles, drywall, and insulation containing paper.
In addition to Stachybotrys, construction personnel working in water-damaged buildings may be exposed to other types of toxic moulds such as Fusarium, Aspergillus, and Penicillium.
What health effects can
Owners of buildings that may be mould-contaminated should conduct, at their own expense, an assessment to determine whether or not the buildings are indeed contaminated. The assessment should include building inspection and analysis of bulk samples.
Mould on visible surfaces may be just the tip of the iceberg. Since they thrive in dark, moist environments, moulds may be hidden from view. Thorough inspections of water-damaged areas must therefore be conducted. This involves looking into wall cavities, behind drywall, under carpets, and above ceiling tiles.
Not all moulds are toxic. The type of mould identified and the extent of the contamination will determine the precautions to be taken.
Bulk sampling and laboratory analysis are used to document the type of mould growing on surfaces. The procedure involves scraping surface material into a sealable plastic bag and sending it by overnight delivery to an accredited laboratory.
An accredited laboratory is one that participates in the American Industrial Hygiene Association's Environmental Microbiology Proficiency Analytical Testing Program. The chosen laboratory should have a competent mycologist (a person that studies moulds) who can analyze the sample and determine whether the mould is likely to pose a health risk.
Based on the presence of visible mould, evidence of water damage, and symptoms that are consistent with allergic or toxic response to mould, it may be justified to skip bulk sampling and go straight to remediation (removal).
The person taking
bulk samples or performing inspections must be suitably protected for
Level 1 work (see table below) and must be careful not to unduly disturb
How can moulds be safely
The extent of contamination governs what remediation measures need to be taken in order to prevent the spread of toxic moulds.
Note: The cause of moisture problems should be corrected before any mould remediation takes place.
A follow-up inspection should be conducted 3-6 months after remediation to ensure that the mould has not returned.
Health Canada and the New York City Department of Health have both produced documents on the assessment, remediation, and management of fungal contamination. The table below summarizes their recommendations with minor updates to reflect current best practices. The Canada Mortgage and Housing Corporation is developing comprehensive cleanup procedures for toxic mould. The document is still in draft form and not yet publicly available.
Obligations under the Act
Employers have a duty to instruct workers in the safe removal and handling of mould-contaminated material. Workers in turn have the duty to follow these instructions. Building owners must ensure that trade contractors follow proper remediation procedures.
The following table is intended only as a summary of remediation procedures and is not intended, nor should it be used, as a guideline for mould removal. For that purpose, refer to
Levels of remediation based on the extent of toxic mould contamination