Molds are ubiquitous in nature, and mold spores are a common component of household and workplace dust. However, when spores are present in large quantities, they are a health hazard to humans, potentially causing allergic reactions and respiratory problems.
Some molds also produce mycotoxins that can pose serious health risks to humans and animals. The term “toxic mold” refers to molds that produce mycotoxins, such as Stachybotrys chartarum, not to all molds. Exposure to high levels of mycotoxins can lead to neurological problems and in some cases death. Prolonged exposure, e.g., daily workplace exposure, can be particularly harmful.
Symptoms of mold exposure
- Nasal and sinus congestion, runny nose
- Eye irritation, such as itchy, red, watery eyes
- Respiratory problems, such as wheezing and difficulty breathing, chest tightness
- Throat irritation
- Skin irritation, such as a rash
Causes & Growing Conditions
Molds are found everywhere inside and outside, and can grow on almost any substance when moisture is present. Molds reproduce by spores, which can be carried by air currents. When these spores land on a moist surface that is suitable for life, they begin to grow. Mold is normally found indoors at levels that do not affect most healthy individuals.
Because common building materials are capable of sustaining mold growth, and mold spores are ubiquitous, mold growth in an indoor environment is typically related to water or moisture indoors. Mold growth may also be caused by incomplete drying of flooring materials such as concrete. Flooding, leaky roofs, building maintenance problems, or indoor plumbing problems can lead to mold growth inside.
For significant mold growth to occur, there must be a source of water (which could be invisible humidity), a source of food, and a substrate capable of sustaining growth. Common building materials, such as plywood, drywall, furring strips, carpets, and carpet padding are food for molds. In carpet, invisible dust and cellulose are the food sources (see also dust mites). After a single incident of water damage occurs in a building, molds grow inside walls and then become dormant until a subsequent incident of high humidity; this illustrates how mold can appear to be a sudden problem, long after a previous flood or water incident that did not produce such a problem. The right conditions reactivate mold. Studies also show that mycotoxin levels are perceptibly higher in buildings that have once had a water incident (source: CMHC).
Although this home suffered only minor exterior damage from Hurricane Katrina, small leaks and inadequate air flow permitted this mold infestation.
Spores need three things to grow into mold:
- Nutrients: Cellulose is a common food for spores in an indoor environment. It is the part of the cell wall of green plants.
- Moisture: Moisture is required to begin the decaying process caused by the mold.
- Time: Mold growth begins between 24 hours and 10 days from the provision of the growing conditions. There is no known way to date mold.
Mold colonies can grow inside building structures. The main problem with the presence of mold in buildings is the inhalation of mycotoxins. Molds may produce an identifiable smell. Growth is fostered by moisture. After a flood or major leak, mycotoxin levels are higher in the building even after it has dried out (source: CMHC).
Food sources for molds in buildings include cellulose-based materials, such as wood, cardboard, and the paper facing on both sides of drywall, and all other kinds of organic matter, such as soap, fabrics, and dust containing skin cells. If a house has mold, the moisture may be from the basement or crawl space, a leaking roof, or a leak in plumbing pipes behind the walls. People residing in a house also contribute moisture through normal breathing and perspiration. Insufficient ventilation can further enable moisture build-up. Visible mold colonies may form where ventilation is poorest, and on perimeter walls, because they are coolest, thus closest to the dew point.
If there are mold problems in a house only during certain times of the year, then it is probably either too air-tight, or too drafty. Mold problems occur in airtight homes more frequently in the warmer months (when humidity reaches high levels inside the house, and moisture is trapped), and occur in drafty homes more frequently in the colder months (when warm air escapes from the living area into unconditioned space, and condenses). If a house is artificially humidified during the winter, this can create conditions favorable to mold. Moving air may prevent mold from growing since it has the same desiccating effect as lowering humidity. Molds grow best in warm temperatures, 77 to 86 degrees Fahrenheit, though some growth may occur anywhere between 32 and 95 degrees.
Removing one of the three requirements for mold reduces or eliminates the new growth of mold. These three requirements are 1) Moisture, 2) Food source for the mold spores (dust, dander, etc.), and 3) Warmth (mold generally does not grow in cold environments).
HVAC systems can create all three requirements for significant mold growth. The A/C system creates a difference in temperature that allows/causes condensation to occur. The high rate of dusty air movement through an HVAC system may create ample sources of food for the mold. And finally, since the A/C system is not always running – the ability for warm conditions to exist on a regular basis allows for the final component for active mold growth.
Because the HVAC system circulates air contaminated with mold spores and sometimes toxins, it is vital to prevent any three of the environments required for mold growth. A) Highly effective return air filtration systems are available that eliminate up to 99.9% of dust accumulation (as compared to 5% elimination by typical HVAC air filters). These newer filtration systems usually require modification to existing HVAC systems to allow for the larger size of electrostatic 99.9% filters. However, thorough cleaning of the HVAC system is required before usage of high efficiency filtration systems will help. Once mold is established, the mold growth and dust accumulation must be removed. B) Insulation of supply air ducts helps to reduce or eliminate the condensation that ultimately creates the moisture required for mold growth. This insulation should be placed externally on the air ducts, because internal insulation provides a dust capture and breeding ground for mold.
The first step in an assessment is to determine if mold is present. This is done by visually examining the premises. If mold is growing and visible this helps determine the level of remediation that is necessary. If mold is actively growing and is visibly confirmed, sampling for specific species of mold is unnecessary.
These methods, considered non-intrusive, only detect visible and odor-causing molds. Sometimes more intrusive methods are needed to assess the level of mold contamination. This would include moving furniture, lifting and/or removing carpets, checking behind wallpaper or paneling, checking in ventilation duct work, opening and exposing wall cavities, etc.
Careful detailed visual inspection and recognition of moldy odors should be used to find problems needing correction. Efforts should focus on areas where there are signs of liquid moisture or water vapor (humidity) or where moisture problems are suspected. The investigation goals should be to locate indoor mold growth to determine how to correct the moisture problem and remove contamination safely and effectively.
In general the EPA does not recommend sampling unless an occupant of the space is symptomatic. When sampling is necessary it should be performed by a trained professional who has specific experience in designing mold-sampling protocols, sampling methods, and the interpretation of findings. Sampling should only be conducted to answer a pertinent question: examples “what is the spore concentration in the air”, or “is a particular species of fungi present in the building.” The following additional question should be asked before sampling: “what action can or should a person take upon obtaining data.”
The sampling and analysis should follow the recommendations of Occupational Safety and Health Administration (OSHA), National Institute for Occupational Safety and Health (NIOSH), Environmental Protection Agency (EPA), and the American Industrial Hygiene Association (AIHA). Most importantly, when a sample is taken the proper chain of custody should be adhered to. The AIHA offers lists of accredited laboratories that submit to required quarterly proficiency testing.
Three types of sampling include but are not limited to:
- Air sampling: the most common form of sampling to assess the level of mold. Sampling of the inside and outdoor air is conducted and the results to the level of mold spores inside the premises and outside are compared. Often, air sampling will provide positive identification of the existence of non-visible mold.
- Surface samples: sampling the amount of mold spores deposited on indoor surfaces (tape, and dust samples)
- Bulk samples: the removal of materials from the contaminated area to identify and determine the concentration of mold in the sample.
When sampling is conducted, all three types are recommended by the AIHA, as each sample method alone has specific limitations. For example, air samples will not provide proof of a hidden source of mold. Nor would a tape sample provide the level of contamination in the air.
Though it may not be recommended, air sampling following mold remediation is usually the best way to ascertain efficacy of remediation, when conducted by a qualified third party.
The first step in solving an indoor mold problem is stopping the source of moisture. Next is to remove the mold growth. Common remedies for small occurrences of mold include:
- Wall insulation/Dry Wall
- Non-porous building materials
- Household cleansers
There are many ways to prevent mold growth; see heating, ventilating, improved insulation and air conditioning, and dry fog. New technology allows some mold remediation companies to fill a room with a dry fog that kills mold and stops its growth. This fog uses a chemical that is EPA approved and does not harm or damage the physical well being of persons or animals. There are also cleaning companies that specialize in fabric restoration – a process by which mold and mold spores are removed from clothing to eliminate odor and prevent further mold growth and damage to the garments.
Improper methods for cleaning mold include exposure to high heat, dry air, sunlight (particularly UV light), ozone, and application of fungicides. These methods may render the mold non-viable, however, the mold and its by-products can still elicit negative health effects. As noted in following sections, the only proper way to clean mold is to use detergent solutions that physically remove mold. Many commercially available detergents marketed for mold clean-up also include an anti-fungal agent.
Significant mold growth may require professional mold remediation to remove the affected building materials and eradicate the source of excess moisture. In extreme cases of mold growth in buildings, it may be more cost-effective to condemn the building rather than clean the mold to safe levels.
The goal of remediation is to remove or clean contaminated materials in a way that prevents the emission of fungi and dust contaminated with fungi from leaving a work area and entering an occupied or non-abatement area, while protecting the health of workers performing the abatement.
Cleanup and Removal Methods
The purpose of the clean-up process is to eliminate the mold and fungal growth and to remove contaminated materials. As a general rule, simply killing the mold with a biocide is not enough. The mold must be removed since the chemicals and proteins, which cause a reaction in humans, are still present even in dead mold.
Evaluating Mold Exposures
Before beginning mold remediation you should make sure you assess the area infected with mold to ensure safety, you clean up the entire moldy area, and properly approach the mold.
- Assess the area infected with mold, checking for any hidden mold
- Fix moisture problems before you remove and clean up the moldy area to prevent future mold growth issues
- If the area of mold is large you should get a remediation manager to properly dispose of the mold
- Be sure to identify the source of water or moisture that caused the mold growth to begin with
- Check all air ducts, ventilation systems and air handling units so that the mold problems do not persist in the indoor environment
- Consult a qualified professional if you have any problems or if you are not confident that you can properly remove all mold or sources of mold growth
These steps should always be done by a trained professional.
- First, make sure to remove any object near the insulation system that may have been contaminated from floodwater. Properly dispose of the contaminated materials according to your local, State, and Federal regulations. (The insulation you might removed may be contaminated with asbestos. Always make sure to call a trained professional to avoid serious injury or death)
- Make sure to remove the contaminated HVAC filter media to ensure your HVAC system is not bringing in contaminated air. Make sure to dispose of it reading the same regulations listed above.
- Remove any debris and insulation; clean all components of the HVAC system to ensure nothing becomes contaminated and/or more contaminated from floodwater. Use a HEPA-filtered vacuum, cleaner to make sure you get rid of all the debris, dirt, and microorganisms. Pay special attention to the drain pans, filter areas, curves, and air ducts since debris often collects in these places.
- Disinfect all components of the HVAC system after turning off the HVAC system. To clean use 1 cup of normal household chlorine bleach mixed with a gallon of water, do not mix this with cleaning products containing ammonia.
- Be sure to use fans to create filtration by blowing the contaminated air outdoors, to protect the health of the workers.
- After cleaning all components with bleach rinse with clean water to eliminate the potent bleach smells.
- Important: You must remove and properly discard the HVAC components that are contaminated with floodwater to prevent the growth of mold if it cannot be cleaned, and replace them with new components.
- After the HVAC has been properly cleaned and disinfected, replace the insulation in the HVAC system with an external, smooth-surfaced insulation to prevent future floodwater contamination.
- To ensure safety have you HVAC system tested by a qualified professional before you begin using your HVAC system again.
Once again these further steps should be done by a trained professional, a Master Certified Professional if available.