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Mold Prevention Cleanup After Hurricanes and Major Floods
June 9, 2006

Extensive water damage after major hurricanes and floods increases the likelihood of mold contamination in buildings. This article provides information on how to limit exposure to mold and how to identify and prevent mold-related health effects. Also included are ways of assessing exposure, clean-up and prevention, personal protective equipment, and public health strategies and recommendations. The recommendations assume that, in the aftermath of major hurricanes or floods, buildings wet for >48 hours will generally support visible and extensive mold growth and should be remediated, and excessive exposure to mold-contaminated materials can cause adverse health effects in susceptible persons regardless of the type of mold or the extent of contamination.

For most people, undisturbed mold is not a substantial health hazard. Mold is a greater hazard for persons with conditions such as impaired host defenses or mold allergies. To prevent exposure that could result in adverse health effects from disturbed mold, you should 1) avoid areas where mold contamination is obvious; 2) use environmental controls; 3) use personal protective equipment; and 4) keep hands, skin, and clothing clean and free from mold-contaminated dust.

Clinical evaluation of suspected mold-related illness should follow conventional clinical guidelines. In addition, in the aftermath of extensive flooding, health-care providers should be watchful for unusual mold-related diseases. The development of a public health surveillance strategy among persons repopulating areas after extensive flooding is recommended to assess potential health effects and the effectiveness of prevention efforts. Such a surveillance program will help CDC and state and local public health officials refine the guidelines for exposure avoidance, personal protection, and clean-up and assist health departments to identify unrecognized hazards.

On August 29 and September 24, 2005, hurricanes Katrina and Rita, respectively, made landfall along the Gulf Coast. After both storms, levees were breached, leading to massive flooding in New Orleans and surrounding parishes.

The duration of flooding, the extent of flooding, and the number of structures flooded in New Orleans as a result of hurricanes Katrina and Rita in August and September 2005 made the likelihood of massive mold contamination a certainty. Many structures remained flooded for weeks after the hurricane and became saturated with water. An assessment of homes in New Orleans (Orleans Parish) and the surrounding parishes of St. Bernard, East Jefferson, and West Jefferson (excluding the 9th Ward) identified an estimated 46% (>100,000 homes) with some mold contamination; approximately 17% (40,000 homes) had heavy mold contamination (1).

Recent parallels to the kind of flooding observed in New Orleans as a result of hurricanes Katrina and Rita occurred in 1997 in Grand Forks, North Dakota, and in 1999 in North Carolina after Hurricane Floyd (2). The number of structures affected was much smaller in North Dakota than in New Orleans, and the population affected in North Carolina was much more dispersed than the population affected in New Orleans. In North Carolina, a reported increase in persons presenting with asthma symptoms was postulated to be caused by exposure to mold (2). In 2001, flooding and subsequent mold growth on the Turtle Mountain reservation in Belcourt, North Dakota was associated with self-reports of rhinitis, rash, headaches, and asthma exacerbation (3).

This document was initially prepared by CDC as a guide for public health officials and the general public in response to the massive flooding and the anticipated mold contamination of homes and other structures along the U.S. Gulf Coast associated with hurricanes Katrina and Rita (4).

This revised version is intended to more broadly address public health concerns related to limiting exposure to mold and identifying, preventing, and managing mold-related health effects following any natural disasters or other occurrences that results in flooding or major water intrusion. Published guidelines, established standards, and the peer-reviewed literature were reviewed to ensure the accuracy and consistency of the recommendations. In addition, the document was sent for stakeholder review and external peer review by experts in the areas of worker protection, general public health, medical, environmental and occupational epidemiology, allergy, industrial hygiene, mycology, and pulmonology.

Mold: A Definition
Molds, mushrooms, mildews, and yeasts are all classified as fungi, a kingdom of organisms distinct from plants and animals. Fungi differ from plants and animals in several respects. Unlike animals, fungi have cell walls. However, unlike plants, which also have cell walls, fungal cell walls are made mostly of chitin and glucan. Fungi cannot produce their own nutrients as plants do through photosynthesis. Fungi secrete enzymes that digest the material in which the fungi are imbedded and absorb the released nutrients. Multicellular fungi do not differentiate into different organs or functional components the way plants and animals do (5).

Approximately 100,000 species of fungi exists; fewer than 500 fungal species have been described as human pathogens that can cause infections (5). Visible growth of multicellular fungi consisting of branching filamentous structures (mycelia) are known popularly as molds (5) and are referred to by that term in this report.

Molds are ubiquitous in nature and grow almost anywhere indoors or outdoors. The overall diversity of fungi is considerable. For example, the genus Aspergillus has at least 185 known species (6). Molds spread and reproduce by making spores, which are small and lightweight, able to travel through air, capable of resisting dry, adverse environmental conditions, and capable of surviving a long time. The filamentous parts of mold (hyphae) form a network called mycelium, which is observed when a mold is growing on a nutrient source.

Although these mycelia are usually firmly attached to whatever the mold is growing on, they can break off, and persons can be exposed to fungal fragments. Some micro-organisms, including molds, also produce characteristic volatile organic compounds (VOCs) or microbial VOCs (mVOCs). Molds also contain substances known as beta glucans; mVOCs and beta glucans might be useful as markers of exposure to molds (7).

Some molds are capable of producing toxins (sometimes called mycotoxins) under specific environmental conditions, such as competition from other organisms or changes in the moisture or available nutrient supply. Molds capable of producing toxins are popularly known as toxigenic molds; however, use of this term is discouraged because even molds known to produce toxins can grow without producing them (6). Many fungi are capable of toxin production, and different fungi can produce the same toxin (6).

Factors That Produce Mold Growth
Although molds can be found almost anywhere, they need moisture and nutrients to grow. The exact specifications for optimal mold growth vary by the species of mold. However, mold grows best in damp, warm environments. The availability of nutrients in indoor environments rarely limits mold growth because wood, wallboard, wallpaper, upholstery, and dust can be nutrient sources. Similarly, the temperature of indoor environments, above freezing and below the temperature for denaturing proteins, can support mold growth, even if the actual temperature is not optimal (8).

The primary factor that limits the growth of mold indoors is lack of moisture. Substantial indoor mold growth is virtually synonymous with the presence of moisture inside the building envelope. This intrusion of moisture might be from rainwater leaking through faulty gutters or a roof in disrepair, from a foundation leak, from condensation at an interface (e.g., windows or pipes), or between a cold and a warm environment. Water also can come from leaks in the plumbing or sewage system inside the structure. Studies of mold growth on building materials, such as plywood, have found that mold grows on materials that remain wet for 48--72 hours (8). Flooding, particularly when floodwaters remain for days or weeks, provides an almost optimal opportunity for mold growth.

How Persons Are Exposed to Mold
Mold exposure can produce disease in several ways. Inhalation is usually presumed to be the most important mechanism of exposure to viable (live) or nonviable (dead) fungi, fungal fragments or components, and other dampness-related microbial agents in indoor environments. The majority of fungal spores have aerodynamic diameters of 2--10 ┬Ám, which are in the size range that allow particles to be deposited in the upper and lower respiratory tract (5). Inhalation exposure to a fungal spore requires that the spore be initially aerosolized at the site of growth. Aerosolization can happen in many ways, ranging from disturbance of contaminated materials by human activity to dispersal of fungi from contaminated surfaces in heating, ventilating, and air-conditioning (HVAC) systems. Fungal spores also can be transported indoors from outdoors. Overall, the process of fungal-spore aerosolization and related issues (e.g., transport, deposition, resuspension, and tracking of fungi to other areas) are poorly understood.

Persons can be exposed to mold through skin contact, inhalation, or ingestion. Because of the ubiquity of mold in the environment, some level of exposure is inevitable. Persons can be exposed to mold through contact with airborne spores or through contact with mycelial fragments. Exposure to high airborne concentrations of mold spores could occur when persons come into contact with a large mass of mold, such as might occur in a building that has been flooded for a long time. Exposure to mycelia fragments could occur when a person encounters a nutrient source for mold that has become disrupted, such as would occur during removal of mold-contaminated building material. Skin contact or exposure by inhalation to either spores or mycelial fragments also could occur in a dusty environment, if the components of dust include these fungal elements.

For the majority of adverse health outcomes related to mold exposure, a higher level of exposure to living molds or a higher concentration of allergens on spores and mycelia results in a greater likelihood of illness. However, no standardized method exists to measure the magnitude of exposure to molds. In addition, data are limited about the relation between the level of exposure to mold and how that causes adverse health effects and how this relation is affected by the interaction between molds and other microorganisms and chemicals in the environment. For this reason, it is not possible to sample an environment, measure the mold level in that sample, and make a determination as to whether the level is low enough to be safe or high enough to be associated with adverse health effects.

Persons affected by major hurricanes or floods probably will have exposure to a wide variety of hazardous substances distributed by or contained within the floodwater. This report does not provide a comprehensive discussion of all such potential hazards; such situations will of necessity require case by case evaluation and assessment. Guidance has been provided by CDC for such issues in a number of documents, including NIOSH Hazard Based Interim Guidelines: Protective Equipment for Workers in Hurricane Flood Response (9) and the CDC guidance: Protect Yourself From Chemicals Released During a Natural Disaster (10).

Clean-up and Prevention
The most effective way to eliminate mold growth is to remove it from materials that can be cleaned and to discard materials that cannot be cleaned or are physically damaged beyond use (9,18,19,26--30). Persons with respiratory conditions, allergies, asthma, or weakened immune systems should avoid mold cleanup if possible or seek the advice of their doctor and determine what type of personal protective equipment is appropriate. Appropriate PPE (e.g., tight-fitting NIOSH-approved N-95 respirator, gloves to limit contact of mold and cleaning solutions with skin, and goggles) (13,26--30) should be used when performing clean-up or other activities in mold-contaminated homes or buildings after a flood.


Removing mold problems requires a series of actions (6,9,16). The order of these actions is sometimes important (6), but might vary on a case-by-case basis. Typically, the following actions are taken regardless of whether a problem is small and simple or large and complex:
  • Take emergency action to stop water intrusion, if needed.
  • Determine the extent of water damage and mold contamination.
  • Plan and implement remediation activities.
    --- If needed, establish containment and protection for workers and occupants.
    --- Eliminate or limit water or moisture sources.
    --- Decontaminate or remove damaged materials, as appropriate.
    --- Dry any wet materials, if possible.
    --- Evaluate whether space has been successfully remediated.
    --- Reassemble the space to prevent or limit possibility of recurrence by controlling sources of moisture.
For small, simple problems, the entire list of tasks can be done by one person. Large, complex problems might require many persons from different professions and trades. For circumstances that fall between those extremes, some combination of occupant action and professional intervention will be appropriate. In general, no single discipline brings together all the required knowledge for successful assessment and remediation.

Returning to Mold-Contaminated Homes or Buildings After a Flood
When persons return to homes or buildings after a flood, they should take the following steps (6,9,16,26--30):
  • 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 >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.

Removing and Cleaning Up Mold in a Building
For cleaning mold covering <10 square feet in an area flooded by clean water, detergent and water might be adequate (9,16). However after hurricanes and major floods, flood water is likely to be contaminated and, in this setting, mold can be removed with a bleach solution of 1 cup chlorine bleach per 1 gallon of water (26--30). Never mix bleach or bleach-containing products with ammonia or ammonia-containing products. If water damage is substantial or mold growth covers >10 square feet, consult the EPA guide, Mold Remediation in Schools and Commercial Buildings (15).

Some companies specialize in water damage restoration and can assess the issues involved in cleaning up homes after a flood. Two professional trade groups that might be able to help locate such an expert are the Association of Specialists in Cleaning and Restoration (http://www.ascr.org) and the Institute of Inspection, Cleaning, and Restoration Certification (http://www.iicrc.org).

Contractors used for remediation should have experience in cleaning mold. Check references and ask the contractor to follow the recommendations in the guidelines of the American Conference of Governmental Industrial Hygienists (ACGIH) or other guidelines from professional organizations or state agencies. Contact your state health department's website for information about state licensing requirements for contractors in your state. Examples of websites from states that have recently dealt with natural disasters include http://www.tdh.state.tx.us/beh/mold (Texas) and http://www.lslbc.louisiana.gov (Louisiana).

Cleaning Clothes, Textiles, or Stuffed Animals
Ensure that laundry is washed in safe water. Use only water that is properly disinfected or that the authorities have stated is safe. Take the appropriate steps to make sure that use of gas or electric appliances is safe.
Before using a washing machine that was in a flooded building, run the machine through one full cycle before washing clothes. Use hot water and a disinfectant or sanitizer. Take clothes and linens outdoors and shake off any dried mud or dirt before washing them. Hose off muddy items to remove all dirt before putting them in the washer.

If the items are only wet, they can be laundered normally. Check the labels on clothes and linens and wash them in detergent and warm water if possible, or take them to a professional cleaner. Adding chlorine bleach to the wash cycle will remove most mildew and will sanitize the clothing. However, bleach might fade some fabrics and damage other fabrics. If the label reads "dry clean only," shake out loose dirt and take the item to a professional cleaner.

Consult a remediation professional for advice on whether heavily mold-contaminated items made of leather, suede, or a similar material are salvageable or should be discarded. Do not burn or bury textiles that cannot be cleaned. Put them into properly sealed plastic bags and dispose of them as you would normal household garbage in your area.

Salvaging Household Items
When assessing or remediating mold contamination to a house, homeowners or clean-up personnel might decide to repair or clean household items (e.g., housewares or kitchen items) damaged or contaminated by flood waters. As with clothing and other textiles, make sure the water being used is safe. Use only water that is properly disinfected or that the authorities have stated is safe.

Nonporous items (e.g., dishes, pots, glass items, and hard plastic items) can be salvaged. However, because floodwaters are contaminated, nonporous items should be washed by hand in a disinfectant and then air-dried. Do not use a dish towel. Porous items (e.g., cloth, some wood and wood products, and soft plastic) must be discarded because they probably absorbed whatever contaminants were in the floodwaters.
Before using the dishwasher, clean and disinfect it. Then use a hot setting to wash your pots, pans, dishes, and utensils. Do not use the energy-saving setting. Throw away canned foods that are bulging, opened, or damaged. Food containers with screw-caps, snap-lids, crimped caps (soda pop bottles), twist caps, flip tops, snap-open, and home-canned foods should be discarded if they have come into contact with floodwater because they cannot be disinfected. If intact cans have come in contact with floodwater or storm water, remove the labels, wash the cans, and dip them in a solution of 1 cup of bleach in 5 gallons of water. Relabel the cans with a marker.

Cleaning a Heating, Ventilating, and Air Conditioning System

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. Therefore, all flood water-contaminated and moisture-laden components of the HVAC system should be thoroughly inspected, cleaned of dirt and debris, and disinfected by a qualified professional. CDC has prepared recommendations for professionals to help ensure that floodwater-contaminated HVAC system components are properly cleaned and remediated (21). If HVAC systems are not properly cleaned and disinfected to prevent the dissemination of mold and other debris throughout a building, bioaerosols of mold and other microorganisms might exists and can cause a variety of adverse health effects to the building's occupants. Ensure that the HVAC system is shut down before any remedial activities.

Types of Personal Protective Equipment

Skin and Eye Protection

Gloves keep the hands clean and free from contact with mold (9,29). Gloves also protect hands from potentially irritating cleaning solutions (29,32,33). Long gloves that extend to the middle of the forearm are recommended. The glove material should be selected on the basis of the type of substance or chemical being handled. When using a biocide (e.g., chlorine bleach) or a strong cleaning solution, gloves made from natural rubber, neoprene, nitrile, polyurethane, or PVC are needed. When using a mild detergent or plain water, ordinary household rubber gloves can be used. Latex or nonlatex medical examination gloves should be used if hands are likely to be in contact with infectious materials. Persons with natural rubber latex allergy should not use natural rubber latex gloves and should consult the NIOSH Alert on latex gloves for further information (34).
To protect eyes, properly fitted goggles or a full face-piece respirator are needed. Goggles must be designed to prevent the entry of dust and small particles. Safety glasses or goggles with open vent holes are not appropriate in mold remediation. CDC has published guidelines on this topic (35).

Protective Clothing
When conducting building inspections and remediation work, workers or homeowners might encounter hazardous biologic agents and chemical and physical hazards. Consequently, appropriate personal protective clothing, either reusable or disposable, is recommended to minimize cross-contamination between work areas and clean areas, to prevent the transfer and spread of mold and other contaminants to street clothing, and to eliminate skin contact with mold or chemicals (9,32). In hot environments, precautions to prevent dehydration and heat stress when wearing protective clothing (e.g., drink plenty of water) are needed.

Disposable PPE should be discarded after it is used. Such equipment should be placed into impermeable bags and usually can be discarded as ordinary construction waste. Protective equipment for biocide applicators (e.g., goggles or face shield, aprons or other protective clothing, gloves, and respiratory protection) must be selected on the basis of the product manufacturer's warnings and recommendations. In addition, the manufacturer's recommended precautions should be followed. Reusable protective clothing, including respiratory equipment (36,37), should be cleaned according to manufacturers' recommendations for PPE exposed to mold and other potentially hazardous chemicals (e.g., bleach and biocides).

Respiratory Protection
Inhalation is the primary exposure route of concern related to mold for workers, homeowners, and building occupants (6,9,17,18). When administrative and engineering controls are not adequate to eliminate airborne exposure to mold (or dust containing mold), respirators provide additional protection from inhalation of airborne mold, contaminated dust, and other particulates that are released during dust-generating processes (e.g., remediation work or debris removal) (6,9,17).

Respirators provide varying levels of protection. Selecting a respirator to minimize exposure to molds should be based on a qualitative assessment because quantitative data on mold-contaminated environments are not informative (38--41). All decisions about respirator selection should be made with knowledge of the relative protective capabilities and the advantages and disadvantages of different respirators. Further discussion of respirator selection is available (38--41).

Standard surgical or dust masks are intended for use only as barriers against large particles and do not provide protection against many airborne particles (38). Respirators used to protect persons from airborne contaminants (including mold and mold spores) must be certified by CDC's NIOSH. In addition, as specified by the OSHA respiratory protection standard (37), workers whose employers require them to use respirators must be properly trained, have medical clearance, and be properly fit-tested before they use the respirator. If a worker must use respirators, the worker's employer must develop and implement a written respiratory protection program with worksite-specific procedures and elements. Additional information on respiratory protection is available from OSHA (37,42,43).

PPE Guidelines for Workers in Mold-Contaminated Areas
Exposure to some level of airborne mold is inevitable because molds are found indoors and outdoors (6,17). However, demolishing or cleaning heavily mold-contaminated materials outdoors can lead to excessive exposure to mold. The level of exposure to mold outdoors is primarily based on the amount of mold-contaminated material, the amount of mold in the material, and the type of work being performed. The need for PPE (including respiratory, skin, and eye protection) for outdoor workers requires ongoing professional assessment that considers the potential for exposure to mold and the potential for exposure to other hazardous substances that might be in the outdoor work area.

Guidelines summarized below are based on guidelines from OSHA (37,42,43), EPA (13), and the New York City Department of Health and Mental Hygiene (18). These guidelines recommend particular respirators on the basis of the size of the area of mold contamination. However, the size criteria are based on general professional judgment and practicality because data are limited related to the extent of contamination to the frequency or severity of health effects.

When determining the potential for airborne exposure to mold and the need for PPE, the size of the area is not the only criterion to be considered. The activities being performed in relation to the mold-contaminated materials are at least as important. Therefore, ongoing professional judgment always must play a part in decisions concerning PPE. For example, any remediation or other work that disturbs mold and causes mold spores to become airborne increases the degree of respiratory exposure. Actions that tend to disperse mold include breaking apart moldy porous materials such as wallboard; destructive invasive procedures to examine or remediate mold growth in a wall cavity; removal of contaminated wallpaper by stripping or peeling; and using fans to dry items or ventilate areas. In addition, health status and other characteristics of the persons potentially exposed to mold also might need to be considered (Table 1).

Category I Protection

Respiratory protection (e.g., N-95 disposable respirator). Respirators must be used in accordance with the OSHA respiratory protection standard (9,37).

Gloves and eye protection. (Safety goggles, safety glasses)
For use while cleaning the following:
  • Small isolated areas (<10 square feet) of heating, ventilation, and HVAC systems (includes pipes, ducts, and vents).
  • Isolated areas (<100 square feet) of building materials (e.g., ceiling tiles, small areas on walls, and individual or multiple wallboard panels).
Category II Protection
Respiratory protection with full face-piece respirators, with N100, R100, P100 (or for powered air purifying respirators, HEPA) particulate filters. Respirators must be used in accordance with the OSHA respiratory protection standard (13).

Disposable protective clothing covering entire body including both head and shoes.

For use while cleaning the following:
  • Large contaminated areas (>10 square feet) of HVAC systems.
  • Extensively contaminated (>100 contiguous square feet) building materials.
  • Any size area where substantial dust is generated during cleaning or debris removal (e.g., when abrasives must be used to clean contaminated surfaces or plaster walls are being demolished).
  • Areas where the visible concentration of mold is heavy (blanket coverage rather than patchy).

These guidelines should be followed according to professional judgment. For example, more protective respirators might be required if toxic contaminants such as asbestos or lead are encountered during cleanup. All workers dealing with large areas of contamination should be properly trained to handle hazardous materials.

PPE Guidelines for the Public (Nonworkers) in Residences and Nonoccupational Settings

Clean-up, Debris Removal, or Similar Activities
The activities (and possible exposure to mold) of persons re-entering their homes or working outside might be similar to those of workers. Preventing the creation of dust and limiting exposure to dust are the best ways to minimize exposure to mold (1,9,18). For example, using wet mops or vacuums with HEPA filters instead of dry sweeping dust and debris will decrease the amount of dust in the air (1,9,18).

If building occupants, residents, or anyone must be around mold-contamin.

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