Mold - The Fungus Among Us


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Delwyn E. Kubeldis, CIH, CSP, ARM

American Geosciences Inc.


A.  Mold - What Is It, and Why the Nationwide Hysteria?


Mold, mildew, yeast, and mushrooms are all various names for fungi.  Fungi, the plural of Fungus, are a group of organisms that obtain nutrients by absorbing soluble substances and they obtain their carbon and energy source from organic means.  Molds are forms of fungi that are found everywhere - both indoors and outdoors all year round.  More than 100,000 species of mold exist naturally in the environment, and the various species of mold can be in any color, including white, orange, green, brown, or black. 


Molds grow throughout the natural and built environment, and can grow on almost every type of material, as long the appropriate conditions are present.  These conditions include sufficient oxygen, a nutrient source, sufficient moisture, appropriate temperature, and a safe place to grow (some references list a nutrient source, sufficient moisture, and appropriate temperature as the only conditions needed, recognizing that oxygen and a safe place to grow are ubiquitous).  Outdoors, these conditions are omnipresent, so molds readily grow on soil, foods, decaying/plant matter and other items. 


In the indoor environment, our offices, apartments, homes, schools, and other private and public buildings regularly provide all but one of these criteria – sufficient moisture.  Clearly there exist sufficient oxygen content and safe places to grow in the indoor environment.  Indoor nutrients are likewise plentiful as well and include wood, paper, dead skin, or other cellulose- or carbon-based material.  These sources exist in or on carpets, drywall, HVAC components, ceiling tiles, paint – almost any porous surface.  Note also that sometimes the mold will feed selectively, choosing to feed on the underlying material (e.g., wallpaper glue) versus the surface material, or vice versa.  While greater than 70° F is optimum for growth of most molds, some species can tolerate temperature extremes that range from 23° F to 140° F. 


The most critical condition necessary for indoor mold growth (which is fortunately typically absent) is sufficient moisture.  The role of moisture in prompting mold growth indoors is pivotal, and worthy of a separate discussion (see Molds and Moisture).


How does mold get into buildings?  Most molds reproduce through a life cycle in which spores are formed that disperses into the air in search of more food and moisture.  Live spores, therefore, act like seeds, forming new mold growths (colonies) when they find the right conditions.  Given the diversity and ever-present nature of mold in our environment, outdoor air always contains some level of airborne mold spores.  While some spores are visible (e.g., puffball), most mold spores are microscopic and invisible to the naked eye, ranging in size from 1 to 100 microns and many times between 2 and 20 microns.  It is not uncommon to find hundreds or even thousands of mold spores per cubic foot of outdoor air.  This small spore size means that they can infiltrate our environments with air and can be very difficult to detect and remove. 


Microbiologists use the terms viable and non-viable to describe the ability of spores to reproduce.  However, spores retain their adverse health characteristics regardless of their ability to reproduce.  That is, non-viable spores are still allergens, contain toxins and can potentially impact human health. 


The right combination of appropriate conditions can cause the spore to change from its inactive to active form in the life cycle of the mold.  This process is known as spore germination (see Figure 1 for life cycle of a mold).  Some fungal spores must come into contact with liquid to germinate.  Other spores require in excess of 70 percent relative humidity for germination while other spores can germinate at extremely low relative humidity.  Generally speaking, however, fungal growth occurs best in warm and wet environments.  Thus, the most effective way to prevent fungal growth is by keeping material dry. 



Figure 1

(Adapted from


1) Hyphal Growth

This stage consists of thread-like filaments called hyphae, which release enzymes for the degradation and absorption of specific substrates (e.g. components of wood, organic debris, or skin).

2) Spore Formation

Spore production is dependent on a number of environmental variables such as light, oxygen levels, temperature, and nutrient availability. Spores are produced on specialized hyphal cells.

3) Spores

Spores serve as the primary means for dispersal and survival. Mold spores can remain dormant for months or even years and are often able to withstand extremely adverse conditions.

4) Spore Germination

Spore germination also requires specific environmental and biological factors.  Nutrient availability and moisture levels are especially important; however, fungi in certain environments may require more specific cues.


Most, if not all, of the mold found indoors comes from outdoor sources.  Spores are already present on virtually all building materials at the time of construction.  Wood joists and studs, cement blocks and bricks, and other materials carry spores present from the manufacturing process, storage, transport, and during construction.  While a building is being erected, the open sides, walls, and doors permit additional infiltration of spores.  During occupancy, mold spores will enter buildings through air currents when windows or doors are opened, and introduced into the building when attached to new and used furnishings (carpets, furniture, etc.).  Building occupants and visitors can also introduce spores into building air via their clothes, shoes, hair, and articles. 


The building HVAC (Heating, Ventilation, and Air Conditioning) system may actively pull spores into the building if not equipped with adequate filtration.  Once inside, the HVAC system may serve as a suitable growth medium for mold or may spread mold spores throughout the building.  Sometimes operation of an inefficient or improperly balanced HVAC system will create a pressure differential that will “pull” outside, spore-laden air into the building.


Indoor Air Quality (IAQ) has gradually become an issue of concern since the mid-1970’s, when the energy crisis forced commercial and industrial building owners to control fuel costs by minimizing the influx of outside air and increasing the insulation of buildings.  Other factors influencing the rise of IAQ complaints include:


·          Operation and maintenance issues associated with older buildings due to competing resources (reduced budgets, decreased manpower, etc.).

·          Greater use of HVAC systems to control building climate.

·          Shifting of work population to indoor environment (of 131 million workers in U.S., 70 million work indoors in an estimated 4.5 million commercial buildings).

Recently, mold has developed as a specific IAQ problem as the public has become aware that exposure to mold may cause a variety of health effects and symptoms.  These ailments include eye/nose irritation, aggravation of asthma, respiratory ailments, headaches, and dermatitis.  Other health effects have been proposed for mold metabolites that are irritants or mycotoxins, and plausible mechanisms exist for health effects due to these mold metabolites.  However, the clinical relevance of these mycotoxins and irritants under realistic airborne exposure levels is not fully established.  Further, some or much of the supporting evidence for these other health effects is based on the following:  case studies rather than controlled studies; studies that have not yet been reproduced; or subjective symptoms (American Industrial Hygiene Association, 2003).


There are some trends that suggest increasing public activism in IAQ and mold issues, including:


·          Movement of U.S. economy from industry-based to service-based, resulting in more workers inside buildings and offices as opposed to working in factories and manufacturing facilities.  While manufacturing plants were not without their own host of health concerns, their occupants often considered an unhealthy work environment as “part of the job” and not always controllable.  Office workers, however, do not share that sentiment and are demanding healthier work areas.

·          The long term and continuing public interest in general environmental consciousness and health consciousness; for instance, there is widespread support for clean air, clean water, and uncontaminated food.  The public is concerned with outside air pollution and is growing in its recognition of the important role that indoor air contaminants can have on a person’s health.  Mold is the latest in the list of indoor air contaminants potentially affecting our health.

·          The increasing prevalence of childhood asthma, adult allergies, chronic fatigue syndrome, and the impact of our physical environment on stress, all continue to lead people to consider IAQ (and specifically mold) as a parameter for correction.

Mold is unique, however, as an IAQ issue because:


·          Hysteria surrounds mold largely due to uncertainty regarding potential and reported adverse health effects (e.g., over 8,000 “toxic mold” articles since 2000).

·          Claims have surfaced in virtually every region of the U.S.

·          1 of 5 Americans suffers from allergic disease – including a sensitivity to mold.

·          It is estimated that 70% of commercial and municipal buildings contain some water damage history.

·          Left unchecked, mold causes odors and can damage building materials, finishes, and furnishings.  If allowed to grow in HVAC systems, mold can spread throughout the building.

It is likely that litigation and insurance industry positions on mold coverage will shape the short-term future and drive the expansion of the mold industry. 


Concerns on the part of building owners and property management firms to consider mold-related liability and litigation (or the threat of possible litigation) have been fueled by some very public and extraordinary legal claims and awards (both residential and commercial):


·          A Texas jury ordered Farmers Insurance to pay $32M (later reduced to $4M) to a family whose house was infested with mold. 

·          Entertainer Ed McMahon filed a $20 million lawsuit in April 2002 against his home insurance company and several contractors, which he claims had mishandled a repair on a broken plumbing pipe. 

·          A $14M verdict was rendered against the construction manager of the Martin County, Florida Courthouse.  The plaintiff alleged that leaks occurred in the new courthouse, causing mold infestation and resulting in illnesses of persons working in and conducting business in the courthouse.


In addition to these more sensational cases, there are scores of other mold-related lawsuits targeting property managers, building owners, construction managers, contractors, and others.  Additional claims are likely forthcoming, prompting the Association of Trial Lawyers of America to establish a new Toxic Mold Litigation Group to address personal injury and insurance claims related to mold growth.


B.  Molds and Moisture


1.  The Significance of “Water Activity Level” of Organic Materials


As with all living organisms, mold requires water in order to metabolize, grow, and reproduce.  The optimum amount of water, however, varies by the type of mold, and is also influenced by environmental factors (temperature, types of nutrients available, etc.).  Some mold can grow at relatively low moisture levels (e.g., mold growing on bread), while other molds require significant amounts of moisture for optimum growth. 


Moisture control, therefore, plays a critical role in both preventing and solving indoor mold problems.  What remains perplexing to many property managers is that mold growth often occurs even without noticeable water damage or that growth reappears even after the water damage has been repaired.  The basics behind this phenomenon can be summarized with these three important points:


1.       Molds differ in their specific requirements for water (see following discussion on “water activity level”).

2.       Water requirements may be met by ambient vapor or condensation.  Generally speaking, most molds will grow when the relative humidity of the air is 70% or greater. 

3.       Mold spores may remain viable even when dried.  Simply killing mold, either by removing the moisture or spraying with a substance such as bleach, does not eliminate the potential exposure.


For mold, the amount of water required is termed the water activity level (Aw); a measure of water in the substrate that an organism can use to support growth.  A value of unity (i.e., 1.0) indicates pure water whereas zero indicates the total absence of water molecules.  A high Aw (i.e. >0.8) indicates a 'moist' or 'wet' system and a low Aw (i.e. <0.7) generally indicates a 'dry' system.  Water activity reflects a combination of water-solute and water-surface interactions plus capillary forces.  For the types of mold compatible with indoor environments, few are considered capable of growing below Aw = 0.65.  Primary fungal colonizers, such as Penicillium, require a relatively low water activity constant (Aw <0.8).  Secondary colonizers, such as Cladosporium, require an Aw between 0.8-0.9.  Tertiary colonizers, such as Stachybotrys, require an Aw >0.9.  Thus the type of mold present can be indicative of the extent and duration of moisture damage. 


2.  Mold Problem Causes:  Water Disasters, Condensation and Capillary action


It's easy to understand how the surfaces of building materials (known as substrates) can be dampened, and molds begin to grow, by water disasters such as flooding, roof leaks, and plumbing leaks.  Dealing with water in liquid form is relatively straightforward.  There are other forces, however, which warrant consideration including hydrostatic pressures, capillary action, and differences in the partial pressures of water vapor.  In simplest terms, water will move from 'wet towards dry' in an attempt to reach equilibrium between these forces. 


All exterior surface treatments leak to some extent at joints, cracks, seams, etc., allowing moisture to enter the building undetected.  For example, rain falling on an exterior wall will move into the wall.  When the sun shines on the wall, it raises the vapor pressure and causes condensation behind the wall covering.  In addition, many materials are porous and will absorb moisture in an attempt to reach equilibrium with the source.  For example, concrete, brick, mortar, grout, drywall, and wood are porous and do allow water vapor to pass.  Often it is the moisture contained in these porous materials that allows mold to survive and grow. 


Other factors are more complex and more difficult to isolate as the cause of mold growth.  Very high room Relative Humidity (RH) can cause moisture in a substrate.  This, of course, can cause condensation to occur and resulting drips from the cold surfaces of ceiling diffusers, registers, improperly insulated cold ducts, and chilled water piping.


Capillary action (e.g., wicking) occurs when the surface of a liquid is in contact with a solid and the liquid is elevated or depressed, depending upon the relative attraction of the molecules of the liquid for each other or for those of the solid.  Water intrusion and damage continue to increase as long as free-water touches the solid surface (gypsum board, wood floors, furniture, etc.) due to the tendency of materials to draw in moisture through capillary action. 


Once all the required elements are satisfied, and a sufficient period of time has elapsed, mold growth will occur and will become more difficult to address as the time period lengthens.  Thus, it is critical to address moisture problems, particularly water disasters like floods and leaks, as soon as possible to prevent mold growth.  If corrective actions can be initiated quickly, usually within the first 24 to 48 hours following a disaster, mold growth will be minimized and effective remediation can occur.


C.  Mold Sampling


1.  Building Evaluation


A decision to evaluate a building for mold can be prompted by occupant complaints, evidence of water damage, real estate due diligence requirements, presence of visible mold, proactive building operation and maintenance, and others factors.  The approach used for conducting an evaluation will also vary widely depending upon the risk tolerance of parties involved (How much mold is too much?), the extent of perceived mold growth, the urgency of the event, the nature of the potential growth, the professional experience of the investigator(s), and other factors.


Currently there are no national or local standard methodologies for conducting mold assessments.  There are, however, several widely accepted guidance documents for conducting assessments that were developed by various public agencies in response to differing needs.  The two most recognized are the “Guidelines on Assessment and Remediation of Fungi in Indoor Environments” developed by the New York City Department of Health & Mental Hygiene, and the Environmental Protection Agency’s “Guidance for Mold Remediation in Schools and Commercial Buildings”.  These documents provide detailed guidance on issues and topics relative to the assessment process and should be reviewed by anyone interested in conducting a thorough evaluation of indoor mold. 


A number of practical elements should nonetheless be applied to any assessment, including:


·          Inspect building materials and spaces for visible mold.  Any occupant complaints or reported health problems should be noted as well as any musty or moldy odors.  Actively search areas with noticeable mold odors.  When mold is visible, testing is not recommended by either the New York City and EPA guidelines as part of the initial survey.

·          Focus on sources of water/moisture release into the building envelope.  Identify current signs of excess moisture and water damage or evidence of a history of water leaks, high humidity levels, and/or condensation.  Look for water stains and leaks, standing water and condensation problems.  Are there any watermarks or discoloration on carpets, walls, ceilings, furniture, or other building materials? 

·          Components of the building HVAC system should also be inspected.  A moisture meter is often very helpful in identifying wet or damp building materials.  If mold growth or moisture problems are discovered, the air pressure differentials between the area of growth and surrounding areas should be determined and potential air pathways from the source should be characterized to determine its impact on the building and its occupants.

·          Search behind and underneath materials (carpet and pad, wallpaper, vinyl flooring, sink cabinets), furniture, or stored items (especially things placed near outside walls or on cold floors).  Sometimes destructive techniques may be needed to inspect and clean enclosed spaces where mold and moisture are hidden; for example, opening up a wall cavity.


2.  Sampling Limitations, Strategy and Quality Control


Debate exists within the IAQ community regarding the value of collecting samples for mold assessment purposes.  This debate is based on both scientific and professional judgment principles.  For example, methods of sampling have been shown to underestimate the amount of mold colonies or numbers present, single samples have demonstrated a low predictive value for exposures over extended periods, and inter- and intra-sampling variability has been demonstrated to occur.  Recall also that sampling for mold is not specifically recommended as part of an initial mold evaluation survey.  Further, it is widely accepted that if visible mold is present then it should be remediated, regardless of what species are present and whether samples are taken. 


Nonetheless, many practicing IAQ professionals collect and rely on samples for information when conducting mold assessments, either prior to the mold remediation or immediately after as a form of “clearance” or “re-occupancy” testing.  Sampling may be considered a necessary part of a building evaluation when health concerns are an issue, litigation is involved, or the source(s) of contamination is unclear.  For example, sampling may be warranted when:


·          Mold is being removed and there is a question about how far the colonization extends.  In this instance, surface or bulk sampling in combination with moisture readings may be useful. 

·          Visible mold is present and there is a need to have the mold identified.  Sampling for airborne mold spores would be useful also in indicating whether the mix of indoor molds is typical of outdoor molds present in the same environment.  Mold testing, however, is rarely useful for trying to answer questions about health implications based on specific types of mold. 

·          If mold is suspected, but not detectable by visual observation after an inspection, then sampling may reveal evidence of mold amplification or indoor mold reservoirs.  In such cases, a combination of air (outdoor and indoor air samples) and bulk (material) samples may help determine the extent of contamination and where cleaning is needed. 


Any sampling conducted should be performed by a professional experienced with mold issues, sampling protocol, and current guidelines on data interpretation.  If samples are collected, regardless of the purpose, there should be a clear question that the sample results should help to answer.  Often it is useful to establish a hypothesis prior to sampling based on the visual inspection and information provided by occupants.  Sampling without a specific purpose greatly increases the chances of generating useless data


There are different approaches to mold sampling and different types of sampling available depending upon the desired outcome of the sampling.  Note that laboratories vary in experience and proficiency; and using an American Industrial Hygiene Association (AIHA) Environmental Microbiology Laboratory Accreditation Program (EMLAP) accredited lab is highly recommended.


Sampling Methods and Limitations


In general, the following quantitative methods of mold assessment are most useful as part of a broader qualitative approach, indicating the relative change in building conditions and NOT as an absolute pass/fail criteria.  Substantial quantitative report issues other than accuracy include wide variation among labs in counting and skill levels, and more interestingly, the lack of and virtual impossibility of establishment of valid quantitative standards for mold exposure.


Air Samples


Many IAQ professionals use various sampling methods as their initial screening tool because, depending upon the method, the results of direct analysis can report both viable spores (those able to reproduce under the right conditions) and nonviable spores.  In addition to quantifying spore populations or concentrations in the air that can cause allergic reactions but might not necessarily grow because they are nonviable, direct analysis allows one to identify hyphal fragments and provides information on the source of the spores, an interior source or not.


Viable bioaerosol sampling involves the collection of air samples using a single-stage air sampler operating at a flow rate of 28.3 liters of air/minute.  The collected air is deposited on growth media (such as inhibitory mold agar [IMA] plates, 2% malt extract agar [MEA] or tryptic soy agar [TSA] plates) and cultured.  Airborne Spore Trap sampling involves the collection of air samples using filter cassettes (e.g., “Air-O-Cell”) with a collection flow rate of 15 liters of air/minute.  The Air-O-Cell cassette is analyzed and the results reported as a concentration of spores per cubic meter of air.  Culturing involves the collection of particles that are then applied to one or more petri dishes of culture media for incubation and subsequent examination of the growth product.  Culturing is useful for more detailed genera speciation (identifying the various kinds of mold species) once a single or dominant sample is collected whose importance is known. 


Swab Samples


Swab (i.e., wipe) samples for mold are collected with sterile swabs (e.g., Fisherbrand Transport Swabs) by wiping an area of approximately one (1) square inch.  At the laboratory, the swab samples are placed in a measured amount of sterile deionized water, allowed to stand at room temperature for 30 minutes, vortexed vigorously, and dilutions streaked on to IMA plates.  The IMA plates are incubated at 27° C for eight days and the fungal colonies counted. 


Bulk Samples


Bulk samples for mold are collected using sterile gloves and sterile collection containers (bottles, bags, vessels, etc.).  At the laboratory a portion of each bulk sample is weighed on an analytical balance.  The weighed materials are placed in a measured amount of sterile deionized water, allowed to stand at room temperature for 30 minutes, vortexed vigorously, and dilutions streaked to IMA plates.  The IMA plates are incubated at 27° C for eight days and the fungal colonies counted.


Tape Samples


Tape sampling is a recommended method, combined with visual inspection, for mold investigations per various mold sources.  A tape lift sample involves using a small section of clean, transparent tape placed directly over a surface suspected to be contaminated with mold.  The tape is then peeled up and applied to a pre-cleaned microscopic slide.  The laboratory prepares the tape for microscopic examination, and the presence of mold is noted.  This method permits rapid identification of genera (family name) and very often species (individual member name).  Tape samples can also be cultured if additional speciation is needed.  Since tapes collect the hyphae (tube-like projections on basic structural units of mold) and conidiophores (specialized hyphae) portions of mold, they provide more data than either an air or vacuum sample.  Tape samples are often the preferred method of collecting surface samples in buildings.  A properly collected sample is likely to contain fungal bodies, conidiophores, and hyphae, the latter two of which are important aids for speciation.


Vacuum Samples


Vacuum sampling utilizes a collection canister that is connected to an air or vacuum pump to draw particles onto a filter or into a special collection container.  The lab clears the filter onto a microscope slide, washes the filter onto a microscope slide or uses another method to transfer particles for examination by microscope for preparation by culture. 


3.  Interpretation of Results


Currently there are no strict numerical guidelines that are appropriate for assessing whether the level of contamination in an area is acceptable or not.  Typically, the method for interpreting microbiological results is to compare the kinds and levels of organisms detected in different environments.  Usual comparisons are indoor air versus outdoor air and known complaint versus suspected non-complaint areas.  A careful consideration of the distribution and types of mold present is also very useful in interpreting results.


It is recommended that in buildings without mold problems the qualitative diversity of airborne mold indoors and outdoors should be relatively similar.  Conversely, the dominating presence of one or two kinds of mold in the indoor air and the absence of the same kind in the outdoor atmosphere may indicate a mold problem and/or degraded air quality.  Also, the consistent presence of certain molds such as Stachybotrys chartarum, Aspergillus versicolor, or various Penicillium species over and beyond background concentrations may indicate a potential atypical exposure and the occurrence of a moisture problem that should be addressed.  Generally indoor mold types should be similar and levels should be no greater than outdoors and non-complaint areas.  Analytical results from bulk material or dust samples may also be compared to results of similar samples collected from reasonable comparison areas (AIHA, 2003).


4.  Governmental/Quantitative Guidelines


There are currently no federal, state, or local laws that designate safe versus unsafe levels of indoor mold.  Interpretation of the results and observations of a mold evaluation will generally vary for every assessment as a function of the circumstances of the mold problem, the qualitative and quantitative results and the professional judgment of the evaluator. 


OSHA offers no direct guidance to the public regarding recommendations for indicators of indoor contamination.  In their Technical Manual for compliance officers, however, OSHA states, “The identification of predominant taxa, or at least fungi, is recommended in addition to determining the number of colony-forming units/m3 of air (cfu/m3).  Contamination indicators: 1,000 viable colony-forming units in a cubic meter of air, 1,000,000 fungi per gram of dust or material, and 100,000 bacteria or fungi per milliliter of stagnant water or slime.  Levels in excess of the above do not necessarily imply that the conditions are unsafe or hazardous. The type and concentrations of the airborne microorganisms will determine the hazard to employees” (OSHA, 2003).


According to the AIHA, health hazards of exposure to environmental molds relate to four broad categories of chemical/ biological attributes of molds and their metabolites.  These materials may be: 1) irritants, 2) allergens, 3) toxins, and rarely 4) pathogens.  Different mold species may be more or less hazardous with respect to any or all of these categories.  However, the risks from exposure to a particular mold species may vary depending on a number of factors.  This uncertainty is complicated further by the almost complete lack of information on specific human responses to well-defined exposures to mold contaminants.  In combination, these knowledge gaps have made it impossible to set simple exposure standards to molds and mold-related contaminants (AIHA, 2003).


Further, the lack of meaningful threshold limit values (a/k/a TLVs) for most indoor air quality contaminants is a major obstacle to establishing regulatory standards for individual exposure to airborne contaminants.  The same is certainly true for molds.  Until microbiological methods for demonstrating mold concentrations in the environment are standardized and reproducible, epidemiological studies necessary to determine dose-response can only suggest association, not cause and effect, with respect to mold exposures and health effects. (AIHA, 2003)


Some scientists and IAQ consultants have assembled a large body of anecdotal information that relates fungal counts from direct analysis samples to building occupant complaints and symptoms.  These data have prompted some experts to adopt 2,000 counts of mold spores per cubic meter of air (c/m3) as a maximum for a clean building.  In addition to the total count, these quasi-industry standards set limits for species known to generate more-significant allergic reactions (e.g., Penicillium and Aspergillus at less than 1,000 c/m3 each) as well as species that have toxigenic properties (e.g., Stachybotrys or Fusarium) that are not acceptable in indoor air at any level. 


D.  Remediating Moldy Environments


Regardless of the nature and extent of mold contamination present, the first and most important step in solving a mold problem is to identify and correct the moisture source(s) that allowed the growth in the first place. 


Once the apparent source of water intrusion has been identified and addressed, the remediation of mold present in the building can begin.  In any remediation, goals should be established that include:


1.       Protection of occupants and remediation workers from microbial contamination.

2.       Containment of the area of concern.

3.       Proper packaging and removal of porous, visibly contaminated material.

4.       Removal of mold and water-damaged porous and non-porous surfaces.

5.       Thorough cleaning of remaining semi-porous and non-porous surfaces.

6.       Thorough damp wiping and HEPA vacuuming of the affected area(s).

7.       Provision of limited post-remediation sampling to assure a reduction in microbials of concern.

8.       Approval of affected space for reoccupation.


Both the New York City and Environmental Protection Agency guidelines provide direction on remediation of mold.  The New York City guidelines outline general abatement strategies based on the square footage of the moldy area.  The levels are defined as follows:


·          Level I: Small Isolated Areas (10 square feet or less)-e.g., ceiling tiles, small areas on walls.

·          Level II: Mid-Sized Isolated Areas (10 to 30 square feet)-e.g., individual wallboard panels.

·          Level III: Large Isolated Areas (30 to 100 square feet)-e.g., several wallboard panels.

·          Level IV: Extensive Contamination (greater than 100 contiguous square feet in an area).

·          Level V: Remediation of HVAC Systems.

E.  Proactive Risk Management and Transfer of Risk


Risk management for mold is predicated on recognizing and evaluating the level of risk associated with each particular building and set of circumstances.  Over the last two to three years, over 10,000 mold insurance claims have been filed and estimates of new claims anticipate an increase of three to five times that volume.  The average mold insurance claim now costs between $10,000 and $30,000 to handle. 


In addition to the insurance ramifications, mold exposure is one of the fastest growing areas of toxic tort and construction litigation in the country.  Despite conflicting and incomplete scientific data, juries are handing down verdicts against developers, commercial property owners, real estate investors, and contractors (roofers, HVAC companies, etc.).  Claims are being filed for negligence, breach of contract, failure to maintain, and others.  Given the weight of these recent trends and events, it is likely that mold issues will continue to develop and expand.  There are, however, some proactive risk management steps that affected parties can take to potentially avoid or control mold issues and claims.  Some specific methods for minimizing mold growth include:


Facility Executives

(Adapted from Today’s Facility Manager)


1.       Train staff to be on guard for signs of uncorrected moisture—stained ceiling tiles, staining on or around supply diffusers, water near air handling units and HVAC systems, stained carpeting and water stains under or near windows.

2.       Develop a water damage response plan and standard operating procedure for the prevention and mitigation of moisture and other potential indoor air quality concerns.

3.       Inspect all HVAC and air-handling units on a fixed schedule to ensure condensate pans are not overflowing and no condensate is released into drop ceiling tile, insulation or other building surfaces.

4.       Inspect HVAC ductwork periodically for signs of moisture, damage or mold growth.

5.       Dry all water spills and leaks immediately and thoroughly. With major leaks (such as a water line break), retain a qualified and competent drying contractor immediately.

6.       Wet ceiling tiles, drywall, spray-on insulation and fiberboard ductwork are usually difficult to dry and are often disposed of after a major water leak. Carpeting can sometimes be saved—but only if it is dried quickly, usually in 24-48 hours.



(Adapted from


1.       Use quality building products, especially when dealing with siding, shingles, windows and pipes.

2.       Carefully install roofs and windows, ensuring they are properly flashed.

3.       Ensure that lumber and drywall are dry during installation.

4.       Add insulation around cold surfaces to reduce the possibility of condensation.

5.       Ensure that rainwater drains away from the building through downspouts and proper landscaping.

6.       Provide ample and properly sized venting fans.

7.       Position hot air registers so they don’t force air onto exterior walls, creating condensation.

8.       Avoid using vinyl wallpapers in high-moisture areas, as they can create a de facto vapor barrier, trapping moisture in the wall.


(Adapted from the National Association of Realtors)


1.       Follow existing requirements of state law relating to latent defects and disclosure, including any particular requirements and standards of care set forth by state licensing authorities.

2.       Identify publications of the state or local departments of health or other appropriate agencies that explain the mold issue.  Provide these public education booklets as a service to clients and customers.

3.       If a visual inspection reveals conditions indicative of a mold problem (water stains, musty odors, leaky roofs or windows, plumbing leaks, sink/sewer overflows, visible mold growth), licensees should not speculate on the presence or likely development of mold.  Instead, they should advise buyers—in writing—to contact a qualified expert to inspect the property, determine the nature of the problems and learn about remediation options.

4.       Encourage sellers to disclose any actual knowledge they may have of mold problems on their properties, subject to any state disclosure requirements.

 Each approach to avoiding mold issues and liabilities will vary depending upon your exposures, facility issues, and available resources.  Clearly the best ways to avoid liability exposure from mold claims are: 1) to maintain buildings in a clean, dry condition, and 2) have adequate insurance coverage to handle all water-damage and mold-related claims in the event of catastrophic damage beyond the normal scope of building maintenance.


Many building owners are learning the benefits of being proactive with regards to mold and IAQ issues.  One way to avoid mold-related IAQ complaints and problems is to engage experts to test and inspect the building on a routine basis.  An industrial hygienist or professional engineer with experience in IAQ issues can be engaged to effectively anticipate, recognize, evaluate, and control problems. 


Another popular approach is to develop a Mold Prevention Program (MPP) for a facility.  The objective of the MPP is to foster a proactive view of mold prevention by educating facility personnel about the issue of mold and the actions all personnel can take to prevent mold growth in the facility.  These programs are similar to an asbestos Operations & Maintenance program, and are often developed with the assistance of outside professional resources.





Entin, Jeffrey, 2003.Sick Buildings: Common Causes And Sensible Solutions,” Today’s Facility Manager, Tinton Falls, New Jersey.


Kendrick, Lee, 2001. “Mitigating Mold,” Engineered Systems Magazine.


Layman, Herbert, and Rindy, John, 2003. Various guidance documents and laboratory report attachments. U.S. Micro-Solutions, Inc., Greensburg, Pennsylvania.


Microbial Diagnostics, Inc., 2003. “Molds and Moisture”. Minnesota.


Microbial Diagnostics, Inc., 2003. “An Introduction to Fungi”. Minnesota.


Montz, Edward W. Jr., 2003. “Avoiding Mold Related IAQ Liability” Engineered Systems Magazine.


Williams, Del, 2002. “Toxic Mold Remediation”. Risk Management Magazine.


Web Resources

American Industrial Hygiene Association

Mold Resources


Centers for Disease Control and Prevention

Mold, General


Environmental Protection Agency, United States

Mold Resources, Mold Remediation in Schools and Commercial Buildings


Housing Zone – Reed Business Information


National Association of Realtors "Field Guide to Mold and Health Issues"


Occupational Health and Safety Administration

OSHA Technical Manual


Occupational Health and Safety Administration

Molds and Fungi


University of Minnesota

Indoor Air Quality


New York City Department of Health

Guidelines on Assessment and Remediation of Fungi in Indoor Environments


Environmental Risk Resources Association

Mold Insurance Resources