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IAQ FREQUENTLY ASKED
QUESTIONS
The following questions have been
developed to help inform and guide you when making decisions regarding
microbial contamination in ventilation systems.
What are Bioaerosols?
Bioaerosols are airborne particles of biological origin. A contaminated HVAC
system can act as a source of bioaerosols by providing a hospitable
environment for the growth of fungi and bacteria, and then distributing
biologically contaminated air within occupied spaces. Fungi includes molds,
mildew and yeast.
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What is mold and where does it come from?
Mold is a type of fungus. It grows on surfaces in masses of branching threads
which resemble dense cobwebs. The fertile threads, those which produce spores,
often stand up from the surface into the air to release their spores. Spores
are carried by air currents or by adhering to insects or animals. Active mold
can be any color, depending on the species and the substrate upon which it is
growing. Mildew is another type of fungus, similar in structure to mold, but
distinct as one species of fungus is distinct from another. The terms
"mildew" and "mold" are not interchangeable; they are most
often used in the common names of various fungi. Fungi is a kingdom of
organisms, with a single division, Mycota. The fungi have traditionally been
classified with plants but are not considered a distinct group of organisms.
Unlike plants, which produce their own food, fungi absorb nutrients from dead
or living organic matter. Fungi also lack photosynthetic pigments. There are
over 100,000 known living species of fungus, some of which are beneficial to
mankind. Mycologists estimate that there may be as many as 200,000 more
unidentified species of fungus. Yeasts, molds, mildews, rusts, and mushrooms
are types of fungus.
The spores of fungi that become mold or mildew are always present in the
air and on objects. When the temperature and moisture in the environment are
suitable for germination, the fungus spore bursts and grows into a thread-like
filament called a hyphae. Using the object it is growing on as a food source,
the hyphae form a mass, called a mycelium, and within a short time begin to
produce spores. At maturity, spore sacs burst and release spores, which
eventually land on other material and begin the reproductive cycle again.
In HVAC systems, optimum conditions for mold and mildew development exist
when temperature is above 70°Fahrenheit and relative humidity is above 70%.
However, some common molds can grow at temperatures as low as 50° Fahrenheit
and in relative humidities as low as 45%. It is also possible for molds to
begin growing in conditions of high relative humidity and temperature and then
continue growing in environments with significantly lower relative humidity
and temperature.
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What does mold need to grow?
- A food source such as dirt, debris, or organic materials such as paper,
wood, man-made fibers.
- A source of moisture, with relative humidity over 60%, typically
available for over 24 hours.
- A surface to grow on out of direct sunlight.
Once microorganisms enter the HVAC system by being pulled in with the
"make up air", they can be transported quickly throughout the
building. They settle on receptive surfaces, and quickly begin to reproduce.
Some types can multiply from one organism to more than one billion in just 18
hours. A good growth source for a particular organism can quickly result in
outbreaks in every part of a building.
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Are there toxic effects from molds?
Although many indoor molds are benign, there are certain types of molds that
can produce toxins called mycotoxins. These mycotoxins are organic by-products
of mold metabolism that the mold uses to inhibit or prevent the growth of
other organisms. Mycotoxins are found in both living and dead mold spores.
Some are lipid soluble, which means they are readily absorbed by certain
biological systems such as the respiratory system, digestive system and skin.
Molds that produce mycotoxins include Stachybotrys chartarum, Aspergillus
fumigatus, Trichoderma horzianum, Fusarium moniliforme, and Penicillium.
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How much mold can make me sick?
It depends. For some people, a relatively small number of mold spores can
cause health problems. For other people, it may take many more. The basic rule
is, if you can see or smell it, take steps to eliminate the excess moisture,
and to clean up and remove the mold.
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What symptoms are common?
Allergic reactions may be the most common health problem of mold exposure.
Typical symptoms reported (alone or in combination) include:
 | Respiratory problems, such as wheezing, and difficulty in breathing
| Nasal and sinus congestion
| Eyes-burning, watery, reddened, blurry vision, light sensitivity
| Dry, hacking cough
| Sore throat
| Nose and throat irritation
| Shortness of breath
| Skin irritation
| Central nervous system problems (constant headaches, memory problems,
and mood changes)
| Aches and pains
| Possible fever |
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Who is at greater risk when exposed to mold?
Exposure to mold is not healthy for anyone inside buildings. It is important
to quickly identify and correct any moisture sources before health problems
develop. The following individuals appear to be at higher risk for adverse
health effects of molds:
| Infants and children
| Elderly
| Immune compromised patients (people with HIV infection, cancer
chemotherapy, liver disease, etc.)
| Pregnant women
| Individuals with existing respiratory conditions, such as allergies,
multiple chemical sensitivity, and asthma. |
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People with these special concerns should consult a physician if they are
having health problems.
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Can cleaning up mold be hazardous to my health?
Yes. Exposure to mold can occur during the cleaning stage. Mold counts are
typically 10 to 1000 times higher than background levels during the cleaning
of mold damaged materials. The use of respiratory protection (P100 disposable
respirator), gloves, and eye protection is recommended. For remediation of
HVAC systems or large areas see "Guidelines on Assessment and Remediation
of Fungi in Indoor Environments" on this
web page.
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What is Sick Building Syndrome (SBS)?
The term sick building syndrome (SBS) is used to describe situations in which
building occupants experience acute health and comfort effects that appear to
be linked to time spent in a building but no specific illness or cause can be
identified. Symptoms include headaches, cough, sore throats, eye irritation,
fatigue, fever and nausea. These symptoms usually disappear shortly after
leaving the building.
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What is Building Related Illness (BRI)?
Building related illness (BRI) is defined as the clinical manifestation of
occupant exposure to excessive airborne pollutants in a building. The symptoms
can be similar to SBS, but they can be clinically defined and their causes
clearly identified. Legionnaire's disease is one type of BRI. Occupants
suffering from one of these afflictions must be away from the building for a
prolonged period of time to realize significant improvement. Microorganisms,
especially fungi, are implicated as primary and contributory factors.
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What are the signs/features of potential
amplification sites for fungi?
| Musty odors. It should be noted that when fungal sites dry, odors may
disappear. This does not, however, mean that the health threat has been
eliminated, or that remediation should be ignored. The fungi are in a
dormant state, and growth is likely to recur with the introduction of
moisture.
| The existence of discolored surface accumulations (in general: green,
black, white, and/or pink).
| Standing water; especially water that is slimy, turbid, or sludgy. |
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If someone suspects fungal problems within an HVAC
system, what should be the first step toward confirming or denying their
suspicions?
A visual inspection for fungi, as well as potential areas for growth, should
be the first step. Such areas would include condensate pans, ductwork, cooling
coils, humidification systems, and other areas that have the potential to
contain dust and excessive moisture.
It is also important to check for fungal growth on interior and exterior
building surfaces, including furnishings and ceiling plenums.
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If microbiological activity (i.e.
visible growth) is observed in a ventilation system, should testing be
performed?
Not necessarily. It may not be as important to know what spores or fungi are
in the system as it is to remove the potential hazard. Testing may be needed
if there is a diagnosed illness and a need to identify the source of the
disease agent.
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What are examples of potential fungal growth
locations in a ventilation system?
Potential areas for fungal growth are often referred to as amplification
sites. Typical examples in an HVAC system would include filters, cooling
coils, blowers, condensate pans, water damaged porous liners, dirty, wet
ductwork, humidifiers, as well as registers and diffusers where condensation
has occurred.
Internal insulation materials with a rough porous surface will trap
particles and particulates from the air stream which are often hydroscopic.
The accumulated dust then absorbs moisture from the air, allowing fungal
spores to germinate and grow. The cooling season is when fungi and bacteria
can proliferate due to condensation from cooling coil and water in the drain
pans.
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Can non-porous materials be effectively treated for
biological contamination?
Yes, in most cases. It is critical to first perform Source Removal cleaning
procedures to remove accumulated debris and contaminants. This should be
followed by the application of a disinfectant registered by the EPA for use in
HVAC systems such as Foster 40-80.
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Can porous materials be treated for biological
contamination?
Currently there is no set protocol for remediating porous material
contaminated with microbiological organisms. As a result, each situation must
be addressed on a case by case basis. Disinfectants would not be effective
below the contacted surface of materials. Often, the most viable solution is
removal of the contaminated porous materials. The U.S. EPA, NAJMA, and the
American Conference of Governmental Industrial Hygienists (ACGIH) recommend
that water damaged porous material be discarded rather than treated with
antimicrobial products.
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What equipment and materials must one have to properly
remediate fungal contamination within HVAC systems?
The equipment falls under three categories:
| Equipment needed to remove and eliminate the fungi, such as brushes,
scrapers, HEPA vacuums, and biocidal chemicals.
| Equipment employed to protect the surrounding area during the
remediation process, such as negative air machines, and critical and
non-critical barriers.
| Equipment used to protect workers such as respirators and protective
clothing. |
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Will cleaning the "make up" air
entering the HVAC system with air filters prevent SBS or BRI?
All building HVAC systems are designed with air filtration but this has
certain limitations. Most air filters do not effectively capture small
particles, and are inadequate for fine particles of dirt and microorganisms.
Dust particles still accumulate in the HVAC air ducts, and when combined with
poor maintenance practices, mold growth can be amplified. High performance air
filters capture the smaller, respirable particles, but are relatively
expensive to install and operate, and require more frequent replacement.
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What methods have been used for remediation of HVAC
systems?
| Gaseous ozone or chlorine dioxide sprayed into the airducts:
These gases are highly toxic, and contamination of occupied spaces may
pose a health threat. Their use is not recommended. Furthermore, the
effectiveness of these treatments is unproven.
| High efficiency air cleaners and filters:
 | Electronic air cleaners and ion generators use an electronic charge
to remove airborne particles. These devices may also produce ozone, a
lung irritant and health risk agent.
| Activated charcoal filtering systems can remove some gaseous
pollutants, but cannot be expected to adequately remove all of the
gaseous pollutants typically present in indoor air.
| High efficiency filters can remove fine particles, but are expensive
to operate and maintain. They need frequent replacement, and are not
effective below 1 micron. Particles with the greatest concern are .1
to 1.5 microns, which are respirable. |
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Air cleaning is an important part of an HVAC system, but is not a
substitute for source control. All air cleaners must be properly sized and
maintained to be effective.
| Ultra Violet Light:
UV light can disinfect when at a wavelength of about 254 nanometers.
However, it takes a certain amount of contact time and energy level to be
effective so it's only beneficial for hard surfaces that are close by and
directly in front of the bulb. The light travels in a straight line, so
any surface not facing the bulb will not be disinfected. The intensity of
the UV light decreases with the square of the distance from its source, so
the energy output decreases extremely fast with distance from the bulb,
and so does its effectiveness in disinfecting those more distant surfaces.
UV light bulbs also deteriorate with time, producing less concentration
output, so need to be replaced often. Any dirt or moisture on the bulb
surface also decreases the effective light output concentration. Since air
travels through an air duct at least at 800 feet per minute, there is
insufficient exposure time passing by a bank of bulbs to effectively
disinfect the intake air.
| Biocides sprayed into the air duct:
EPA registered disinfectants labeled for use in HVAC systems can be used
effectively to disinfect when used according to directions. They should
only be used on pre-cleaned non-porous surfaces to be effective, with the
surface kept wet for at least 10 minutes. Simply atomizing/fogging them
into the operating duct system is not recommended. The majority of the
disinfectant will be carried through the system and out into the room
space. Sufficient depositation can not be accomplished by atomization to
be of any real benefit. A disinfectant provides only a one-time kill,
being effective only while wet. Once the surface again accumulates dirt,
new spores entering the system with make-up air can start to grow on the
contaminated surface. Repeat applications would be required to maintain
the system free of growth. Sanitizers are less effective as they will
reduce, but not necessarily eliminate microbial contaminants.
| IAQ Coatings:
Coatings applied directly over cleaned duct liner can improve the air
quality by preventing air erosion of the duct liner and thus keep the air
free of airborne fiberglass fibers. The coating also seals off the
surface, providing a smoother surface which does not hold dirt. This helps
keep the surface clean and free of nutrients, and therefore minimizes mold
growth. IAQ coatings like Foster 40-10, 40-11, and 40-23 sealer also
contain fungicides which will resist mold, and protect them from fungal
growth. Fungal growth may still occur wherever dirt and debris have
accumulated over the surface.
| Fungicidal Protective Coatings:
The best solution for maintaining surfaces free of fungal growth is to use
an EPA registered fungicidal coating for all use sites allowed by the EPA.
Foster 40-20 and 40-30 are EPA registered fungicidal coatings that can be
used in HVAC systems as well as on walls and ceilings. These coatings will
kill fungi and odor producing bacteria which come in contact with its
surface. They will also act as other IAQ coatings in sealing off the
surface to prevent dirt accumulation and eroded fiber release. These
coatings provide long lasting protection when used along with good HVAC
system maintenance. |
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Copyright © 2000
H.B. Fuller Company.
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