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Learn When to Use Bleach and Other Chemicals for Flood Cleanup

NDSU’s flood expert provides advice on using biocides for 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 mold, but they do not prevent future mold growth. Also, dead mold still may cause an allergic reaction in some people, so killing the mold is not enough; it must be removed.

Encapsulating or painting over mold 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 mold produces. Most sealers will not encapsulate these chemicals because they do not prevent gas exchange.

“Because killing the mold 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 mold removed,” Hellevang says.

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

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

Flood cleanup experts recommend using bleach or other biocides because floodwaters 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 nonporous 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. People applying any pesticide (including disinfectants, biocides and sanitizers) for hire in North Dakota need to be certified as a commercial applicator or work under the direct supervision of a certified applicator. Specifically, people applying these products in or around homes and structures need to be certified commercially in the Home and Industrial category.

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 http://www.ag.ndsu.edu/flood/home/chlorine-bleach-safety.

NDSU Agriculture Communication - Aug. 1, 2011

Source:Ken Hellevang, (701) 231-7243, kenneth.hellevang@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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