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Proper Use Of Chemicals Important In Flood Cleanup

Sanitizing is one step of cleaning up after a flood. Flood cleanup experts often recommend people use a water and chlorine bleach solution to destroy bacteria. However, biocides such as bleach aren’t effective in all instances.

For example, bleach and other biocides destroy living organisms such as mould, but they do not prevent future mould growth. Also, dead mould still may cause an allergic reaction in some people, so killing the mould is not enough; it must be removed.

Encapsulating or painting over mould does not eliminate the health hazard, either, according to Ken Hellevang, North Dakota State University Extension Service agricultural engineer and flooding expert. People can react to the microbial volatile organic chemicals that mould produces. Most sealers will not encapsulate these chemicals because they do not prevent gas exchange.

“Because killing the mould with bleach or other biocides does not eliminate the health hazard, there is little benefit to applying bleach or other biocides after the area has been cleaned and the mould removed,” Hellevang says.

When selecting a product to prevent future mould growth, make sure it is labelled as being effective on the type of mould of concern and for the surface you are treating. Some products listed as limiting mould growth are effective only on mould or fungi that cause wood decay but are not effective at limiting general mould growth on wood. Make sure the product you select specifically states on the label that it is effective for limiting all types of mould growth that may be a health hazard, such as aspergillus or penicillium.

The best way to limit future mould growth is to dry wood or other surfaces rapidly, Hellevang says.

Flood cleanup experts recommend using bleach or other biocides because flood waters and the sediment left behind may contain sewage and other contaminants, including pathogens that are harmful to people. However, organic material makes biocides ineffective, so clean meticulously prior to applying a biocide. After cleaning thoroughly, use a biocide such as chlorine bleach to destroy any remaining bacteria on hard surfaces such as concrete and nonporous materials such as glass.

Bleach and other biocides are effective at disinfecting, or destroying all organisms, on hard and non-porous surfaces. However, bleach and other biocides are not disinfectants on porous materials such as wood. Water and the contaminants in it soak into the porous materials. Bleach and other biocides destroy organisms on or near the surface of porous materials but do not destroy all the organisms, which, by definition, is sanitizing, Hellevang says.

Make sure you only use biocides approved as a sanitizer or disinfectant for the specific material you are treating, and follow the instructions on the biocide’s label for concentration, contact time and safety guidelines.

If you hire contractors to do the cleanup work, verify that they are using only registered products according to the label and they have appropriate training, licensing and certification to use the biocide.

Bacteria and pathogens need organic material and moisture to live, so thorough cleaning and rapid drying is the best approach for cleaning studs and other structural lumber in a building. You do not need to apply a biocide after cleaning and drying to create a healthy environment. “If you choose to use disinfectants or biocides, always ventilate the area and exhaust the air to the outdoors,” Hellevang advises. “Never mix chlorine bleach solutions with other cleaning solutions or detergents that contain ammonia because toxic fumes could be produced.”

For more information on using bleach safely, see details on NDSU’s flood website at



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