Hurricane Irene caused flooding in at least a dozen states. All that water closed roads, battered beaches and seeped into basements. That means more work ahead for homeowners. To prevent mold from growing and spreading after a flood, you have to act fast—within 24 to 48 hours. Here's what the Centers for Disease Control recommends:

• Clean up and dry out the building quickly. Open doors and windows and use fans or dehumidifiers to dry out the building.
• Remove all porous items that have been wet for more than 48 hours and that cannot be thoroughly cleaned and dried. These items can remain a source of mold growth and should be removed from the home or building.
• Porous, noncleanable items include carpeting and carpet padding, upholstery, wallpaper, drywall, ceiling tiles, insulation material, some clothing, leather, paper, some wood and wood products, and food. Removal and cleaning are important because even dead mold can cause allergic reactions.
• Clean wet items and surfaces with detergent and water to prevent mold growth.
• Temporarily store damaged or discarded items outside the home or building until insurance claims can be processed.

In recent years, there has been some conflicting advice over whether or not homeowners should use chlorine to clean up mold outbreaks. The Environmental Protection Agency recommends using just water and detergent to attack mold but doesn't rule out the use of bleach or other biocides for larger problems.

The Occupational Safety and Health Administration recommends using a mixture of ½ cup of bleach mixed into a gallon of water for mold that's caused by floodwaters. Never mix bleach or bleach-containing products with ammonia or ammonia-containing products. "Because floodwaters are likely to be contaminated with human and animal waste, OSHA recommends the use of bleach, but only in situations where there is a light covering of mold, and only after the area is cleaned with soap and water," says OSHA spokesman Richard DeAngelis.

To keep mold from moving as fast as Irene, dry out your basement or damp area as soon as possible. If you think a serious mold problem is developing, consult a professional mold remediation service. You should also consult an expert if people who live in your home have health issues or are immune suppressed.

If the floodwaters have affected your heating and air conditioning you'll need help from a qualified professional, says the CDC. All surfaces of an HVAC system and all its components that were submerged during a flood are potential reservoirs for dirt, debris, and microorganisms, including bacteria and mold. In addition, moisture can collect in areas of HVAC system components that were not submerged (e.g., air supply ducts above the water line), and this also can lead to the growth of microorganisms. That's why all components of the HVAC system should be thoroughly inspected, cleaned of dirt and debris, and disinfected by a professional.