Extension and Ag Research News


Use Caution When Cleaning Flooded Buildings

Thorough cleaning and disinfecting are keys to recovering after a flood.

Using personal protective equipment is critical for anyone cleaning a building after a flood.

Floodwaters and the sediment left behind when the water recedes contain sewage and other contaminants, including pathogens that are harmful to people, according to Ken Hellevang, a North Dakota State University Extension Service agricultural engineer and flood expert.

Mold, which will be extensive in flooded buildings, also is a health hazard. Scientific evidence links mold in damp buildings to asthma symptoms in those with the chronic disorder; coughing, wheezing and upper respiratory symptoms in otherwise healthy individuals; and lower respiratory illness in children.

Hellevang recommends using personal protective equipment including a proper fitting N-95, N-100 or HEPA-rated respirator/mask; rubber gloves; eye protection; and a protective suit.

Using a biocide or other method to kill mold does not eliminate the health hazard. Instead, mold must be removed from the building.

Here is how to handle mold on various materials:

  • Remove porous materials such as drywall and carpet with mold growth.
  • Use normal cleaning methods to get rid of mold on nonporous materials. A biocide such as chlorine bleach is not necessary.
  • Remove mold from semiporous materials such as structural wood by scrubbing or more aggressive methods such as sanding.

All porous materials, including carpet and drywall (gypsum board), that were exposed to overland floodwaters must be discarded. They cannot be cleaned adequately. Open walls to remove contaminated materials and facilitate cleaning and drying.

Remove the floor covering if contaminated water has seeped under it, even if the covering is not absorbent material, Hellevang says. The subfloor needs to cleaned, dried and sealed prior to installing a new floor covering.

Fabric such as clothing may be cleaned if it can be laundered thoroughly and sanitized using an approved product such as chlorine bleach.

After removing porous materials, thoroughly clean the remaining structural materials. Rinse with water to remove large quantities of mud and dirt that remain. Next, clean nonporous materials such as metal and glass and semiporous materials such as concrete and structural wood using nonphosphate detergents and normal cleaning procedures. Phosphate may leave a residue on which mold will grow.

Do not mix products. For example, ammonia and chlorine bleach when combined produce a very toxic gas.

After a thorough cleaning, use a biocide or disinfectant such as chlorine bleach to destroy any remaining bacteria on hard surfaces such as concrete and nonporous materials such as glass. Organic material makes biocides ineffective, so clean meticulously prior to applying a biocide.

Only use biocides that are approved for the specific material and application, labeled as a disinfectant and registered with the Environmental Protection Agency (they have an EPA registration number, abbreviated as EPA Reg. No., on the product label). Follow the instructions on the biocide’s label for concentration, contact time and safety guidelines.

More information on approved biocides/pesticides is available on the North Dakota Department of Agriculture website at http://www.agdepartment.com/. Click on Pesticide, then pesticide registration program, and then pesticide registration data base, followed by pesticide registration search.

If you have other people doing the cleanup work, verify that they are using registered products according to the label and they have appropriate training, licensing and certification to use the biocide/disinfectant.

Biocides and disinfectants generally are not approved for porous structural materials such as wood because the biocide may not reach the contaminant absorbed into the wood. 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, Hellevang says.

Some antifungal products have limited benefit because they are effective only on molds that cause wood decay and will not prevent all mold growth.

No reconstruction should occur until the moisture content of the wood is less than 15 percent or the below the moisture content specified by the floor covering manufacturer. Other materials need to have dried to a low enough moisture content to prevent mold growth. Rebuilding before the wood is dry leads to mold growth and health problems in the future.

For more information on flood recovery, visit NDSU’s flood website at http://www.ag.ndsu.edu/flood.

NDSU Agriculture Communication - July 15, 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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