Risk of Mold Growth Outbreak after Flooding

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Mold growth outbreak in homes and commercial building after flooding is inevitable.

Although the flooded buildings could have been dried, some moisture can remain in drywall, wood furniture, cloth, carpet, and other household items and surfaces and could lead to mold growth. Exposure to mold can cause health problems such as hay-fever-like reactions (such as stuffy nose, red, watery or itchy eyes, sneezing) and asthma attacks.

It is important to completely dry water-damaged areas and items within 24-48 hours to prevent mold growth. Buildings wet for more than 48 hours will generally contain visible and extensive mold growth. Generally after mold is established it does not require as much moisture for growth as it needed for spore germination.

How Mold Growth Develops After Flooding

Calgary Curling FloodedMold growth develops from spores. Old mycelium could also be reactivated and produce new mold growth when water becomes available.

Once the spores get into contact with water/moisture, they absorb the water, swell and develop new layers of material.

This process is then followed by germination of spores which involve production of a germ-tube (a root-like structure).

Spore germination takes place regardless of where the spores are. The spores could be on concrete, drywall, in water, in air, on fibreglass or any surface. Spore germination can take as few hours as 12 or less from the time the spores absorbed moisture. The germ-tube elongates and then branch in all directions forming circular colonies of mold.

For mold to continue growing after spore germination, it needs a food source, suitable temperature and moisture. Where these conditions are present, molds can colonize the surfaces. Houses offer an ample food supply in form of drywall, paper, wood, and dust on surfaces of inorganic material such as concrete, insulation, glass, plastics and metal surfaces. Since water is a critical requirement for mold growth, complete colonization can be arrested if the wet surfaces are dried within 48 hours.

What is a Pre-Existing Mold Condition?

Flooded Kensington Homes, Calgary June 2013

Many times, after flooding, roof or plumbing leaks mold investigators are asked by their clients to determine whether the mold was “pre-existing” prior to moisture damage.

Whereas this may be a valid question there is no simple method for determining pre-existing mold contamination. And given that mold is present virtually everywhere, what then do we mean by pre-existing mold?

If by pre-existing mold we mean “pre-existing mold growth” that occurred before moisture damage, then it would be difficult to separate “pre-existing mold growth” from the mold growth that developed due to current flooding. However, if areas that were not flooded were found to have mold growth, then it would be logical to conclude that there was pre-existing mold growth prior to the current water damage.

How to deal with mold growth in buildings after flooding

The most practical and reliable tools for detecting mold growth are visual observation and the sense of smell.

However, it’s important to know that mold at the very early stages of growth may not be visible neither odorous. The fact is that mold growth is inevitable after flooding if the building is not dried within 48 hours. After the 48 hours mold growth may not require a lot of moisture to continue growing and this means that drying alone is not enough. Below are the mold guidelines that one could follow if mold growth occurs after flooding.

1. Mould Guidelines by the Canadian Construction Association

2. Mould Abatement by the Environmental Abatement Council of Ontario (EACO)

3. Guidelines on Assessment and Remediation of Fungi in Indoor Environments by the New York City Department Of Health.

Post Flood, Sewage Release and Contamination Investigations

Mold growth and bacteria contamination of residential and commercial buildings following flooding or escape of sewage events can create a host of problems including risk to human health. Therefore, sewage contamination inspection is recommended to safeguard the health and well being of occupants.

Testing for sewage contamination after flooding involves testing for sewage indicator organisms. The most commonly tested sewage indicator organisms include the E. coli and Enterococci. Both of these bacteria are associated with feaces since they are typically found in high numbers in the lower intestinal tracks of mammals, including humans. The risks associated with sewage spills include exposure to infectious microorganisms and endotoxins produced by gram negative bacteria.

Often emergency or post flooding mold and bacteria sampling and analysis are required to assess risks and determine the efficacy of clean up operations. Samples for analysis should be sent to an accredited laboratory for analysis.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at www.drjacksonkungu.com.
Dr Jackson Kung'u

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