Indoor Environmental Technologies (IET)

Mold, Mold Growth and Buildings


Concern about mold exposures in buildings continues to be a significant issue. The bottom line is that mold has been around for eons and is not going away.  It will grow whenever and wherever buildings get wet and materials suitable for mold growth are present.  The following paragraphs are meant to shed light on mold issues related to microbiology, health and safety, moisture control, and remediation practices necessary to properly deal with areas of mold growth. 

What is Mold?

Molds are members of the biological kingdom Fungi, which is distinguished, along with bacteria, from the other kingdoms, by the way it grows and derives nutrients (through absorption rather than ingestion).  There are over 100,000 identified species of molds and it is likely another 100,000 have yet to be discovered.  Of these, only a relative handful have been studied for their benefits and health risks.

Mold requires moisture to grow.  In the presence of sufficient moisture, molds secrete enzymes. These enzymes break down the nutrient source (commonly cellulose for the molds that most frequently grow in buildings), allowing it to serve as food, which supports continued growth. The key to controlling mold growth is to control the moisture. 

Mold spores range from ~1 micron to over 100 microns in size. Most molds associated with water-damaged buildings have spores that range from 2 to 10 microns in size. 

Several species of concern (a term used to describe molds associated with health risks), are also associated with water- damaged buildings. Stachybotrys chartarum is probably the best known mold, as it has a great press agent,  having been dubbed “killer mold” or “black mold” in numerous TV and newspaper articles, which in the public perception tends to make it public enemy #1.  Interestingly, though, a number of other mold species may be equally hazardous, and there are hundreds of molds that are “black” in color.  In fact, the color of many molds varies with food source and other factors.  As far as Stachybotrys being a “killer mold,” while there have been some cases where Stachybotrys or other molds have been suspected as the primary cause of death in a healthy individual, these instances are very rare. 

Several other groups of molds related to water-damaged buildings include species of the Penicillium, Aspergillus, Chaetomium, Trichoderma, and Cladosporium genera, to name a few.  Many of these molds may, when conditions are appropriate, produce chemicals called mycotoxins during their growth cycle. Mycotoxins may be capable of cauing adverse health effects at very low concentrations.  Not all molds produce mycotoxins and of those that do, they may only produce them some of the time, usually as a result of competition with other molds for a food source or when stressed out by other environmental factors.  The application of biocides may actually increase the production of mycotoxins as it could be considered a stressor. 

That musty odor you notice when you enter a moldy building is actually gasses produced by active mold growth.  Microbial volatile organic compounds (MVOC’s) are a byproduct of mold digesting its food and are the cause of these malodors.  There are continuing studies related to MVOC’s, many of which are known irritants.  Exposure to MVOC’s from molds has been reported to cause symptoms such as headaches, nasal irritation, dizziness, fatigue, and nausea (taken from EPA Mold Remediation in Schools and Buildings). Research on MVOC’s is still in the early stages. Time will tell how these metabolites impact occupant health. 

Health and Safety

When moisture problems occur and mold growth results, building occupants may start reporting odors or a variety of health problems.  Symptoms associated with mold exposure can include breathing difficulties, headaches, allergic reactions, skin rashes, and aggravated asthma symptoms, among many others.  The safety of building occupants and also of workers performing the mold repairs (remediation) must always be taken into consideration.  The possible consequences of exposure to molds may be greater for certain individuals than for others, just as bee stings pose much greater risks for persons with a history of allergic reactions to bee stings than to those who just suffer a minor irritation.  The possibility of different levels of sensitivity must always be considered when evaluating potential health risks. 

All molds have the potential to cause health effects.  Through the production of allergens, irritants, and perhaps toxins, molds can affect the wellbeing of building occupants and remediation workers. The reactions of the individuals exposed to mold and the severity of the symptoms may vary based on the types and concentrations of molds present, the duration of the exposure and the sensitivity and age of the individual(s) exposed. 

There are certain groups that are commonly considered to be higher-risk populations for mold exposure.  Persons with compromised immune systems, the elderly, young children, people with respiratory sensitivities and those with chronic exposure may all beat greater risk for developing symptoms than healthy adults or those with limited exposure. 

Exposure to mold can include the following types of reactions:

Allergic reactions to mold are common and can be set off by breathing spores or by skin contact with mold when the person has an increased level of sensitivity.  Reactions can be immediate or delayed. They may include fever, sneezing, runny nose, and/or burning eyes.  In extreme cases, life-threatening reactions such as anaphylactic shock have been reported. Repeated or even a single exposure to a sufficiently high concentration of mold may cause a previously non-sensitive individual to become sensitive.  The more prolonged the exposure, the greater the risk of developing allergic sensitivity.  Mold spores and spore and cell fragments may be capable of producing allergic reactions whether the molds are dead or alive (viable).

Asthma attacks have been known to be triggered by mold exposure. The irritants produced by molds may also worsen asthma in non-allergic (non-sensitized) people.

A chronic disease that resembles pneumonia called Hypersensitivity Pneumonitis may develop during either a short, acute exposure or as a result of chronic exposure to low or moderate levels of mold. 

Persons with compromised immune systems may fall prey to Opportunistic Infections as a result of their body’s inability to protect itself against common mold exposures. Because of their compromised immune system, they are much more susceptible to these types of mold infections.  Aspergillus fumigatus and Trichoderma, among many others, have been identified as species of molds that can cause opportunistic infections in immune-compromised adults and children.  It should be noted that massive and/or extended exposures are more likely to lead to infection, perhaps even in healthy indivisuals.

It must be noted that molds are found in the outside air almost all the time.  Most people do not have extreme reactions to exposures to mold in the outside air.  This leads some to erroneously assume that mold exposures in buildings should be of no greater concern than those outside.

The difference is that mold exposures inside are generally both quantitatively and qualitatively different. 

The indoor environment is quite different from those outside. Thus certain molds have a competitive advantage, with molds that are often rare outside often dominant inside.  Unfortunately, many of the types of molds that often grow inside buildings are “species of concern,” molds that have been associated with health effects in humans.

When mold spores grow and are released into the air outside, they disperse.  Exposures for people in the vicinity are limited.  But when molds grow inside buildings, their released spores and other particles tend to be trapped and thus are able to build up to concentrations rarely if ever seen outside. 

For example, in Florida total mold spore concentrations outside are often in the range of 500 to 5000 per cubic meter of air, m3.  Although outside concentrations may often go much higher, 50,000/m3 or more, such concentrations tend to be transient. By contrast, concentrations in moldy buildings may sometimes be as high as 500,000/m3 or even considerably higher.  To make matters worse, these concentrations do not disperse and may remain at such high levels for long periods, exposing occupants to doses (exposure x duration) that would never be found outside.

Mold Growth in Buildings

When mold has been identified within a building, certain steps must be taken to isolate the contaminated materials and to make proper repairs.  Appropriate Engineering Controls must be considered to control the mold and prevent the spores and dust from spreading during remediation. 

Containment is used to isolate the areas of contamination, usually behind plastic sheeting.  The goal of establishing an effective containment strategy is to control the spread of spores during repairs and to protect uncontaminated areas as well as remediation workers and building occupants that may still be present during the repairs.  It is necessary to design these containment systems to allow for an entry/exit area where workers can remove their protective clothing without risking cross contamination outside the work zones.  This area is called a clean room.  Usually, workers put on their Personal Protective Equipment (PPE) prior to entering the clean room.  They then perform their work shift, exit through the clean room taking off their PPE and then enter the unaffected portion of the building.  This is a very specific process requiring advanced training.  Untrained persons should not perform mold remediation, as this may result in a significant release of spores into the unaffected areas of the building and extensive cross-contamination. 

Further adding to the engineering controls is the use of HEPA filtered negative air machines, more correctly called Air Filtration Devices (AFD’s).  A HEPA AFD is used to create negative air pressure within the work zone, thus attracting mold spores and construction dust towards the filter.  This device, working in conjunction with the containment plastic, creates an effective engineering control that minimizes the spread of mold and dust from the work zone to adjacent uncontaminated areas, while filtering out a large portion of the spores released during remediation.  The HEPA filter, when functioning properly, will remove essentially all mold spores from the exhaust air stream. 

The use of controlled demolition is recommended to avoid unnecessarily disturbing microbially-contaminated building materials during removal.  The use of hammers, sawzalls, and other coarse demolition methods can all significantly increase mold spore levels within the containment. This may overload the filtering capacity of the respirators designed to protect the workers.  Tools such as utility knives, drywall saws and vacuum-attached circular saws have all proven effective as remediation tools. 

The capture zone of a negative air machine is from one to three feet in front of the intake of the filter.  Locating the filter close to the work zone ensures that much of the dust created during removal of contaminated materials will be captured.  The farther away the filter is from the work zone, the more dust will be released into the air. When implemented properly, controlled demolition and engineering controls can reduce the airborne concentrations of mold and dust tremendously.

A final line of defense for the remediation worker is the use of personal protective equipment (PPE).  This involves the use of respirators and protective clothing to prevent inhalation and dermal exposure to spores during remediation.  It is very important to understand that not everybody is able to wear a respirator.  A medical evaluation and fit testing are required to ensure that all persons using these types of PPE are medically fit and have the lung capacity to handle the resistance created by the respirator filters.

There are different types of respirators for different applications.  Depending on the conditions observed, the appropriate type of respirator is chosen.  It is usually recommended that a full-face respirator be used when involved in remediation projects that require the removal of contaminated materials greater than 10 square feet.  Those wearing respirators must get the proper training and fit testing to ensure proper protection. 

Protective clothing, usually consisting of a Tyvek-type material, is used to protect the skin and clothing of the workers.  This type of material is sufficient to prevent the penetration of spores through the suit.  The suit usually consists of a hood and boots incorporated into a jumpsuit-type garment.  This suit, in conjunction with rubber gloves taped to the wrists and a full-face respirator, will protect workers against exposure. 

During hot summer months, these suits will add significantly to the heat load of the worker. Often, frequent breaks are required to ensure worker safety against heat stress.  These and other health-related safety issues are discussed in much greater detail in classes offered for certification in microbial remediation. 

A basic knowledge of microbiology, health and safety issues, engineering controls and remediation skills is needed to complete an effective remediation project. The skills and disciplines necessary to perform these types of tasks can be developed while working under a qualified microbial remediation technician, or learned at certification courses taught throughout the country. 

These various types of disciplines are referenced in current published industry standards listed below.  Should you have any questions regarding these subjects, please feel free to contact our office.


ACGIH Bioaerosols Assessment and Control

IICRC Standard and Reference Guide for Professional Water Damage Restoration S500

IICRC Standard and Reference Guide for Professional Mold Remediation S520

EPA  Mold Remediation in Schools and Commercial Buildings

About Indoor Environmental Technologies

Since 1992 and with over 7,000 building surveys performed, Indoor Environmental Technologies (IET) continues to lead the industry in investigating indoor environmental issues which includes mold inspections and indoor air quality testing. Our mission remains the same - to inspect, detect and correct indoor environmental challenges within a building through applied science - to protect the health and well being of residential or commercial occupants and the value of the property. IET provides inspections for residential and commercial clients in the entire Tampa Bay area, Florida and have at times traveled throughout the United States and Carribbean.

Feel free to contact us today:866-446-7717

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