Environmental Reporter
Home > Resources > Education > Environmental Reporter > Floods, Molds and Rats

Floods, Molds and Rats

Floods, Molds and Rats

By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board

A flood may be as small as a broken pipe in the bathroom, a failed water heater, or an overflowing toilet. On the other hand, it may be massive with thousands of gallons of ground water, rain, and sewage entering a space. The smaller floods, while annoying, can usually be controlled rapidly enough that problems with living "pests" do not occur. Obviously, if they aren't addressed immediately, problems do result, leading sometimes to expensive remediation.

In this report, we will talk about the large "disaster" floods and what you can do to minimize your risks.

First, such floods are usually not preventable, although building in a flood plain, or building a home that cannot withstand inevitable hurricanes is asking for trouble. Once the flood has occurred, getting rid of the water is often not under the control of those responsible for the environment. So, what can one do to minimize both the health risks and the damage?

If you have warning of the flood, you can prepare in advance. Of primary importance is to remove people of fragile health to a place of safety where they will have continued access to medical care. The very old and the infirmed are the first to succumb due primarily the inability to access medical care. They also are the most susceptible to diseases spread by flood waters (i.e. viruses, bacterial pathogens, etc.). The very young are also at risk. Sometimes older people resist leaving their homes. You can work with them to develop a plan to protect their belongings so they can leave with some confidence that they will return to their familiar surroundings. You also should remove pets to a place of safety. Many dogs and cats have been lost in recent flooding in the US. If you live in an area where flooding may occur without warning, be sure to have an emergency plan in place to deal with medical problems and the possibility of being trapped without power or drinking water for an extended period. The American Red Cross has good information on planning for all kinds of disasters.

For ground water floods you can remove fragile items to upper floors, or enclose them in plastic. Artwork can be removed from walls and stored in safety. The point is obvious. Try your best to prevent water from reaching things that you feel are irreplaceable. You can even be doing these things as the floodwaters rise. If possible, make sure there are no holes leading into your building from outside through which a rat can gain entry (mice are almost impossible to exclude). Rats run from floods, and may see your home as a safe refuge. Once there they may be difficult to remove, and rats do carry disease.

Once the water has entered a building, it is best to stay out. There will be rats as well as waterborne viruses and bacteria that could cause illness. There also may be chemicals in the water that could lead to toxicoses. During the standing water phase of a flood, bacteria will be the first to colonize wet material. Bacteria can grow under water, and they reproduce quickly so that significant contamination can be present within 24 hours. The fungi don't do so well under water, and tend to grow at the interface between wet and dry. After 48 hours, there will be a line of mold at this interface, and as water is drawn upward (by capillary action) into absorbent materials, this band will gradually widen. At the same time, the humidity in the flooded environment will rise, and materials that can absorb water from the air will become wet enough for fungal growth. Condensation may also occur. Interiors where water has stood for as long as a week are usually fungal gardens that are beautiful only to fanatical mycologists!

During this period it is important to remember that upper floors, especially in houses, may be dry but are often filled with clouds of fungal spores. It is not safe to occupy these environments even if you are not "allergic" to molds. Repeated exposure to very high levels of fungal spores can lead to hypersensitivity pneumonitis, a serious lung disease. If you must enter these environments, wear respiratory protection. An N95 mask will minimize exposure as long as it fits tightly against your face. Safety goggles may also be important from the fungal perspective.

It is a waste of time to try any kind of remediation unless you have a means for getting rid of the water. Once the water has receded, you are faced with mold, mud, bacterial slime, possibly enteric viruses (those that infect the stomach and intestines), as well as rats and mice. Cockroaches are also likely to invade the space as well as other arthropods. I would attack the rat problem first, before they have had a chance to actually colonize the space and start reproducing. There are commercially available rat poisons and traps, or you can call in a professional. Second, you need to get rid of the remaining moisture. This will require dehumidification, as well as removal of any absorbent materials that are to be discarded. Removing upholstered furniture, paper goods, carpeting, and any other soft materials, will help to accelerate drying and possibly prevent further damage to the structure. Rapid removal of wallboard that is to be discarded is important. Mud will also dry slowly and should be removed as quickly as possible. This all sounds drastic, but if structural wood remains wet for weeks, wood rotting fungi are likely to invade and the building will be lost. Once everything is dry, contamination will be in the form of dust that contains fungal spores, dried chemicals, dead bacteria, viruses, and other materials. Wearing good respiratory protection, the space should be thoroughly vacuumed with HEPA vacuums. Surfaces can be wiped with a damp cloth (with dehumidifiers still in place) and reconstruction can begin.

The most important part of these directions is SPEED. If you wait for the insurance company to come in and offer to pay for remediation, the problem will inevitably become worse, often to the point of total loss. If you really want to save your home, be proactive and do it yourself, then involve the insurance people.

I know these thoughts are simplistic. I have a basement that floods with groundwater every year, and I have designed the space to minimize problems. I have not been faced with the massive floods that have occurred this year in this country, and I know that reality is far worse than I can imagine. On the other hand, the steps I have outlined may at least help to minimize the overwhelming problems associated with severe flooding.


This article was originally published on August 2008.