Investigation of the Potential Antimicrobial Efficacy of Seal-
ants Used in HVAC Systems
K.K. Foarde and D.W. VanOsdell,
Center for Engineering and Environmental Sciences, Research Triangle Institute, Research Triangle
Park, NC 27709, USA;
M.Y. Menetrez,
Air Pollution Prevention and Control Division, National Risk Management Research Laboratory, U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
ABSTRACT
Recent experiments confirm field experience that duct cleaning alone may not provide adequate protection
from regrowth of fungal contamination on fiberglass duct liner. Current recommendations for remediation of
fungally contaminated fiberglass duct materials specify complete removal of the materials. But removal of
contaminated materials can be extremely expensive. Therefore, a common practice in the duct cleaning in-
dustry is the post-cleaning use of antimicrobial surface coatings with the implication that they may contain or
limit regrowth.
Little information is available on the efficacy of these treatments. This paper describes a study to evaluate
whether three commercially available antimicrobial coatings, placed on a cleaned surface that 1 year previ-
ously had been actively growing microorganisms, would be able to prevent regrowth. The three coatings
contained different active antimicrobial compounds.
The study included field and laboratory assessments. The three treatments were evaluated in an uncon-
trolled field setting in an actual duct system. The laboratory study broadened the field study to include a
range of humidities under controlled conditions. Both static and dynamic chamber laboratory experiments
were performed. The results showed that two of the three antimicrobial coatings limited the regrowth of
fungal contamination, at least in the short term. The third did not. Before use in the field, testing of the effi-
cacy of antimicrobial coatings under realistic use conditions is recommended because antimicrobials have
different baseline activities and interact differently with the substrate that contains them and their local envi-
ronment.
INTRODUCTION
That microbial contamination in heating, ventilating, and air-conditioning (HVAC) systems, or on any build-
ing material, is not acceptable, and that the contamination should be removed and further growth prevented
are the conclusions of expert panels from three important organizations — Health Canada1, International So-
ciety of Indoor Air Quality and Climate2, and North Atlantic Treaty Organization (NATO)?. In some in-
stances, the proper use of antimicrobials may be appropriate, but this is generally discouraged because little
research has been conducted on the effectiveness of most products in HVAC systems and because of the
possible health hazards associated with their use.
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HVAC systems become dirty to various degrees after a period of use. Depending primarily on the amount
of dirt, the material, and the environmental conditions, the HVAC system may become an active growth site
for microbial organisms4. In these cases, it may be a source of biological contaminants (spores and micro-
biological debris) that cause health problems for some people5. Cleaning alone for the remediation of
microbiological growth on "porous" materials such as fiberglass duct liner (FGDL) has been shown to be
ineffective6. In fact, replacement of the material, not cleaning, is generally recommended6"9. In addition to
becoming microbially contaminated, FGDL may become frayed due to poor installation, damage, or dete-
rioration and release debris into the air stream. Because it is expensive, time-consuming, and disruptive to
normal building use, replacement of contaminated FGDL is sometimes not acceptable to building owners.
Encapsulants / sealants / coatings are used to seal the frayed material and are applied to FGDL systems
following cleaning to:
1) reduce fiber shedding from surface damage or degradation,
2) isolate remaining contaminants from the air stream, and/or
3) reduce microbia! growth or regrowth through the use of antimicrobials in the coatings.
Generally, these are polymer coatings that are applied as thick liquids or mastics using brushes or trowels or
by spraying, depending on the material properties. With regard to microbial growth, little field data regard-
ing the efficacy of the antimicrobials incorporated into coatings has been reported.
In an earlier study, a Cary, NC, EPA test house was found to have a biocontaminated FGDL supply
trunk10. The surface ofthe FGDL-lined portion of the supply-side trunk duct was found to be contaminated
primarily with a yeast and the fungus Cladosporium. PenicilHitm spp. was isolated from the duct surface
samples only at locations distant from the air handler. In contrast, bioaerosol samples collected from the
heating and air-conditioning (HAC) supply ducts with the HAC fan operating showed a predominance of
Pemcillium spp., not Cladosporium. Based on the organisms' moisture requirements for growth, we pos-
tulated that the yeast and Cladosporium were growing primarily in the high moisture portions ofthe trunk
duct (near the air handler), while the airborne Penicillium spp. originated in either the flexible feeder duct
downstream ofthe trunk ducts or was being recirculated in the duct system but originated somewhere else
inside the test house.
This paper describes the results of a project using the contaminated FGDL from the test house to evaluate
microbial growth in the presence of coatings on a contaminated residential duct system and on contaminated
FGDL in a laboratory test. The objective was to determine whether three different commercially available
antimicrobial coatings, placed on a cleaned surface that 1 year previously had been actively growing micro-
organisms, could prevent regrowth over a period of 1 to 2 years. The study included both in-situ field ex-
periments and laboratory experiments. The field study was representative of an HAC system located in a
residential crawl space in the southeastern U.S. The laboratory research supplemented the field work by
providing microbial growth evaluations ofthe same materials at a range of constant relative humidity (RH)
conditions at a fixed temperature. The FGDL was cleaned and coated by members ofthe National Air
Duct Cleaners Association (NADCA) using three different coatings they selected as being commonly used
in the industry.
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METHODS AND MATERIALS
Field Study
The field study component of the project was conducted in three phases: first, a precleaning evaluation or
test house characterization was performed to establish the microbial background in the test house. Second,
the duct was prepared for long-term monitoring by modification, cleaning, and coating, as well as both pre-
and post-cleaning sampling. Finally, the third phase of the field work consisted of routine operation of the
test house for 18 months with constant monitoring of the test house environment and periodic microbiologi-
cal sampling of the duct system
Test House Characterization
A full characterization of the test house was required to locate all microbial reservoirs that might confound
the experiment and either eliminate them or adjust the experiment to minimize their impact. The entire
house, attic, and crawlspace were inspected to identify any areas that appeared to be microbially contami-
nated. These were noted for additional sampling effort. The HAC and duct system was inspected to look
for changes since the HAC cleaning 1 year previously.
The investigation included a visual inspection for moisture and moisture meter measurements of the carpet
surface and subflooring in all interior rooms, the attic, and joists and foundation walls in the crawlspace. The
moisture assessment was done by visual inspection and by taking measurements with a conductive moisture
meter. Building material moisture content was evaluated using a conductivity meter internally calibrated and
set on the "concrete and plaster" scale (Delmhorst DB-8, Delrnhorst Instrument Co., Towaco, NJ). As an
indicator of microbial growth, the measurement is relative and the instrument has been shown to be a useful
tool to identify any moist locations that might be microbial reservoirs or have the potential to become micro-
bial sources''. The meter was calibrated before the initial use. The short-pronged electrodes of the mois-
ture meter were then carefully inserted approximately 1/4-in. into the material to be tested. The "READ"
button was depressed and the moisture level read off the "plaster/concrete" scale. Duplicate readings were
taken at all locations.
Carpet dusts, H VAC insulation dusts, direct plate swabs, and air samples were taken for bacterial and fun-
gal analyses. Carpet dusts were collected with a High Volume Small Surface Sampler (ITVS3) in areas of
the living room, family room, master bedroom, front bedroom, and hallway. The HVS3 is a commercial
vacuum cleaner modified to collect particle-size fractionated samples12. For collection of microbial samples,
the HVS3 is operated per the manufacturer's recommendations with the addition of decontamination be-
tween samples, sterilization of the collection bottles, and use of a particulate collection bag13. Samples (10
cm2 each) were taken of the supply ducts at the east and west ends of the system, of the return duct liner,
and of the return air filter by a template/vacuurn/membrane filter method described previously14. The tared
membrane filter was weighed to d etermine the mass of dust collected. After weighing, the filter sample was
eluted into a sterile buffer solution, plated, incubated, and the colonies counted. The results were presented
in colony forming units (CPUs) per square centimeter and per gram of dust. Sterile swabs were used to
obtain surface samples from small areas of non-porous surfaces. A template was used to-obtain semi-
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quantitative samples. Sterile swabs were dampened with sterile water and wiped across the surface being
sampled. The used swabs were then transferred to sterile tubes, sealed, and placed in resealable plastic
bags. Bulk material samples were collected from the carpet and floor from areas that were or visibly had
been wet, areas with visible or otherwise apparent mold growth, and areas with restricted ventilation.
An air conditioner drain pan condensate liquid bulk sample was obtained by pipetting directly into sterile
containers, which were then sealed and placed in resealable bags. Similarly, solid bulk samples of fiberglass
duct liner were collected and placed directly in resealable bags. All microbial surface and bulk samples
were eluted into sterile buffer with Tween 80 and plated onto Tryp icase Soy Agar (TSA) and Sabourauds
Dextrose Agar (SDA). The samples plated onto SDA were evaluated for fungal growth and the TSA
plates for bacterial growth.
Indoor and outdoor bioaerosol samples were collected using Mattson-Garvin slit-to-agar samplers. The
Mattson-Garvin sampler draws air at 28.3 L/mirt through a 0.15 mm slit allowing a broad range of airborne
particles to be impacted on the surface of a 150 mm rotating agar plate. The sampler was decontaminated
with 70% ethanol before the initial sampling and each time the test location was changed. Both fungal and
bacterial samples were collected using TSA and SDA. All samples were taken in duplicate sequentially.
Cleaning the Duct Systeim and Applying the Encapsulants/Sealants
Following published NADCA procedures, modified as required for the test house, NADCA personnel
cleaned the test house ductwork and inspected all components8. NADCA or EPA completed any repairs
required to bring the HAC system to full working condition.
NADCA personnel applied each test coating to the duct test zones as diagramed in Figure 1. The coatings
were applied in the order shown in F'gure I:11,1, III, then I, III, II, on the left trunk of the supply duct; and
III, II, I, on the right trunk of the supply duct to ensure that the antimicrobial order would not bias the result.
A single coating was applied to all designated locations in the duct at one time, the coating equipment was
cleaned, and then the next coating was applied. Each coating was applied following the manufacturer's di-
rections for usage as a duct coating, including surface preparation, rate of application, application method,
and drying time. Each coating was applied to overlap the test zone boundaries by about 1 in. to prevent
uncoated areas between test zones. The areas to which the coatings were not being applied were protected
during application to prevent overspray.
FGDL samples from the test house duct were obtained for the laboratory portion of the experiment. The
laboratory experiment sections were removed carefully to prevent damage and new FGDL was used to re-
place those sections. The removed laboratory experiment sections were stored in the test house or test
house garage between removal and cleaning and coating. NADCA personnel cleaned the duct sections
using techniques deemed comparable in efficiency to those used in the test house duct. Chamber duct
pieces were coated at the test house as described above and allowed to dry at the test house prior to being
moved to the laboratory.
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FGDL sections removed and
replaced with new FGDL
(used for chamber tests.)
N
0 ^
N d"
.M O
"8 rs
n f-
O T3
O
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Figure 2. Artist's rendition of DMTC.
Dynamic Chamber
Experiments were conducted in the Dynamic
Microbial Test Chamber (DMTC)14. The
DMTC is a room-sized test facility designed
and constructed to conduct studies on the
conditions and factors that influence biocon-
taminant emissions and dissemination. The
chamber, a cube with inside dimensions of
2.44 m, was constructed with stainless steel
walls and floor and an acrylic drop-in ceiling,
Temperature (18 - 32°C) and RH (55 to
95%) control are provided through an air
handler unit (AHU) with an air circulation
rate of 1.4 to 4.8 nrVmin.
The chamber was adapted to contain eight
miniducts16. Figure 2 is an artist's rendition
of the DMTC containing the miniduct appa-
ratus. The blower forces the cond itioned DMTC air into a High Efficiency Particulate Air (HEPA) filter,
from which the air for the eight miniducts is obtained. The channel design was chosen for the miniducts to
limit the total amount of air required for a single test, allowing multiple tests to be run simultaneously, and
simulate flow cond itions in an H VAC duct. For this test, the air velocity over the surface of the duct mate-
rial was maintained at 250 cm/s (500 fi/min), which is a reasonable duct velocity and has been used in other
miniduct experiments14. The dynamic chamber conditions were controlled to 23.5 °C and 95% RH. This
provided approximately 94% RH to the FGDL samples in the miniducts because the blower warms the air
slightly. The four test conditions (three coated and one uncoated), soiled and unsoiled, made up the eight
miniduct samples in the dynamic chamber.
Static Chambers
The static chamber tests were performed following ASTM 6329-98, Standard Guide for Developing
Methodology for Evaluating the Ability of Indoor Materials to Support Microbial Growth Using
Static Environmental Chambers^. The use of this method enabled us to generate a quantitative end point
for growth in a well-controlled environment with improved repeatability and comparability between tests.
This method was developed for evaluating fungal growth (as measured by sporulation) on indoor materials
as part of a comprehensive research program to apply indoor air quality engineering to bbcontamination of
buildings17'18.
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Static chambers (32 x 39 x 51 cm), modified acrylic-walled desiccators, were placed in a temperature-
controlled, Class 10,000 eleanroom. Each static chamber was equipped with shelving, a bottom tray con-
taining a saturated salt solution, and a hygrometer. Saturated salt solutions are used to maintain known
equilibrium relative humidities (ERHs) within each chamber19.
Selection of Test Organisms and Inoculation
Aspergittus versicolor was selected as the test organism for these studies. A. versicolor was selected be-
cause its growth on fiberglass materials is well documented20, and because it is a toxigenic fungus. The A.
versicolor was isolated from contaminated duct liner. The organisms were prepared for inoculation as pre-
viously described'4.
Artificial Soiling of Duct Materials
The materials were artificially soiled first, and then inoculated in an aerosol deposition chamber, as de-
scribed previously14. Sieved (250 /urn) autoclaved duct dust obtained from a local duct cleaner was used to
soil the samples. The targeted amount of dust for deposition was approximately 100 mg dust /100 cm2.
This level has been considered moderately soiled in previous experiments and was selected to relate these
data to previous experimental results. In previous experiments following this protocol where no coatings
were used, the samples were lightly autoclaved to increase dust adhesion and simplify later handling. Be-
cause the effect of autoclaving on the coatings was unknown, the test pieces were not autoclaved.
Coatings Tested
All three of the coatings were designed for use on HVAC system components and/or interior surfaces of
lined and unlined duct systems. Coating I was a polyacrylate copolymer containing zinc oxide and borates.
Coating II was an acrylic coating containing decabromodiphenyl oxide and antimony trioxide. Coating III
was an acrylic primer containing a phosphated quaternary amine complex.
Experimental Procedure
For the dynamic chamber experiments, after artificial soiling and inoculation, the 30.5 x 91.4 cm (1 x 3 ft)
pieces of test material were placed in the miniducts. Surface samples were collected at day 0 and again at
monthly intervals for 3 months. Surface samples were obtained by the vacuum method described above
and analyzed in duplicate each time from each duct material. The plates were incubated at room tempera-
ture. CPUs were counted shortly after visible growth was first noted and again as moderate growth became
apparent.
Static chamber experiments were conducted by placing small square blocks (2.5 to 3.8 cm squares) of the
test material, inoculated with a test organism, in the constant humidity chambers maintained at 70,85,90,
and 94% RH. To quantitate microbial growth, triplicate samples were removed from the chambers sus-
pended in sterile phosphate buffered saline containing Tween 80 and agitated for at least 5 minutes. All
necessary dilutions were made in the same buffer. Aliquots of the suspension were plated on SDA and al-
lowed to grow at room temperature. CPUs were then counted and calculated per sample and per area of
sample. As with the dynamic chamber experiments, samples were analyzed at day 0 and again at monthly
-------
intervals for 3 months.
RESULTS AND DISCUSSION
Field Study
Figure 3 shows the mean quantities of fiingi isolated from the FGDL surface for each of the dates sampled
prior to coating. The bars labeled 5/27/96 are the results of the initial study in which the FGDL was identi-
fied as contaminated with fungi. The bar representing the samples collected during the test house characterir
zation is dated 2/17/97. And results from the final pre- and post- clean samples immediately before the
coating application are dated 3/3/97 and 3/6/97, respectively.
As can be seen from the results, small changes were measured with the cleaning presumably through the
removal of surface debris. Prior to coating, there were approximately 1,000 CPUs/10 cm2 on the surface
of the FGDL. The test house chararacterization found no other confounding sources of contamination.
Bacteria levels for all sample dates were similar prior to coating.
l.E+04
l.E+03 -
l.E+00
-£-
-^
Initial Preclean Initial Post- Characterization Study Preclean Study Post-clean
5/27/96 clean 5/27/96 2/17/97 3/3/97 3/6/97
Figure 3. Fungal levels collected from surface of FGDL before coating,
Figure 4 shows the quarterly sampling results for all 18 months of the field study. The first set of data points
(3/3/97) is the post-cleaning measurements taken from each of the FGDL locations prior to coating. The
second set of data points (3/6/97) shows the results immediately after the coating was applied. An un-
treated control sample was collected at the same time. As can be seen from the figure, coating the samples
significantly reduced the numbers of fungi we were able to collect from the surface of the FGDL. The re-
sults for all three coatings were similar.
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I
o
l.OE+5
l.OE+4
l.OE+3
O l.OE+2
l.OE+1
l.OE+0
coil
replaced
H Untreated
• Coating I
• Coating II
D Coating ID
3/3/97 3/6/97 6/9/97 9/9/9712/11/973/31/986/30/98 9/30/98
Date
Figure 4. Levels of fungi collected from the FGDL surfaces in the test house duct for 18 months.
Between the 6/9/97 and 9/9/97 samplings, the downflow coil in the HAC started to cause excessive
amounts of water to enter the duct due to blowby and was replaced. The fungal levels on the untreated
sample decreased almost 2 logs between those dates. With the exception of coating II, for the rest of the
study, the levels remained fairly constant except for the slight increases expected with the normal accumula-
tion of dirt over time. Coating II increased suddenly between the 6/30/98 and 9/30/98 samplings. These
results suggested an increase due to more than the natural accumulation of dirt, but no one organism was
isolated and examination did not demonstrate active growth conclusively. On 12/11/97, 3/31/98, and
6/30/98, four samples were collected where the counts were below the detection limit (BDL) of 4 CFUs/10
cm2.
Laboratory Study
Figures 5 and 6 show the results of the dynamic chamber experiments for the FGDL samples removed from
the test house. The X-axis shows the month of the study during which the samples were collected. The Y--
axis shows the amount of growth for each month minus the inoculum level measured on day 0. Growth, as
measured by sporulation, was defined for this study as an increase in culturable organisms of at least 10-fold
(1 logic).
As can be seen from Figure 5, the numbers of A. versicolor collected from the surface of the untreated
samples increased over 3 logs (1,000 fold) by the first month and maintained similar levels through the 3-!4
months of the study. Little increase was seen in the levels of A versicolor isolated from the Coating I and
III FGDL samples for the 3-Vz months of the study. However, increases near those of the untreated sam-
-------
s.oo rf
0 1 2 3.5
Month
Figure 5. Growth of A. versicolor on the surface of untreated and coated FGDL maintained at 94% RH.
pies were seen for Coating II. The results suggested that both Coatings I and III were able to limit the
growth of A. versicolor for at least 3 months, while Coating II did not.
5.00
4.00
"Z 8 3.00
,' § 2.00
" h1
"§ f1: 1.00
"Untreated Soiled
•Coating I Soiled
D Coating II Soiled
13Coating III Soiled
0
1
3.5
Month
Figure 6. Growth of A. versicolor on the surface of untreated and coated moderately soiled FGDL
maintained at 94% RH.
10
-------
The results for the moderately soiled FGDL pieces are found in Figure 6. The pieces were all artificially
soiled with duct dust to a level of 100 mg/100 cm2. In previous experiments, we have considered this mod-
erately soiled6'14. Both the untreated and Coating II samples were able to support the growth of A. versi-
color at levels similar to those seen in Figure 4 for the samples not artificially soiled. The results of the artifi-
cial soiling on the samples treated with Coatings I and III were very interesting. In both cases, there was a
slight increase in CPUs in month 1, but the levels had decreased by month 3.
In a recently completed study of antimicrobial treated air filters, we observed a masking of the antimicrobial
treatment by dust-loading of the filters21. The dust provided a physical barrier between the antimicrobial
and the organism. However, only folly dust- loaded filters were evaluated. Partially dust- loaded filters were
not included. Of interest has been the impact of partial dust loading on antimicrobial efficacy. The results
shown in Figure 5 suggest that antimicrobials can remain effective with partial dust loading. In other words,
the dust is not fully masking the antimicrobial. After a slight increase in CPUs in the first month, the CPUs
isolated from the surface of the moderately soiled FGDL treated with Coating I or III decreased in months
2 and 3. This result suggests that some antimicrobials may be effective, at least in the short-term before
soiling masks the active antimicrobial, in continuing to suppress fungal growth under favorable environmental
conditions.
Table 1 shows the results from the dynamic chamber testing compared to the static chamber testing. The
static chamber testing was performed to extend the number of humidities to which the materials were ex-
posed. Dynamic chamber experiments were performed at 94% RH. The static chamber experiments were
performed at 70, 85, 90, and 94% RH. As can be seen from Table 1, there is good agreement between
Table 1. Change in Log IQ CFU/cnr of A.versiciolor during the 3-month study.
TREATMENT
Not Soiled
Not Treated
Coating I
Coating 11
Coating III
Artificially Soiled
Not Treated
Coating I
Coating II
Coating III
STATIC CHAMBER
70% RH
BDL*
BDL
<1.0
<1.0
85% RH
1.4
BDL
1.9
BDL
90% RH
4.4
BDL
3.4
BDL
94% RH
4.4
<1.0
4.3
BDL
BDL
<1.0
BDL
-------
the results of the 94% static chamber testing and the 94% dynamic chamber testing. One concern with
static chamber testing has been how closely the static conditions mimic the real world conditions without the
airflow. These results demonstrate that similar results are measured with both methods.
CONCLUSIONS
Three commonly used HVAC antimicrobial coatings were evaluated by a combination of field and labora-
tory experiments. The field study provided an uncontrolled field setting. The laboratory study broadened
the field study to include a range of humidities under controlled conditions. Laboratory chamber experi-
ments were performed under both static and dynamic conditions. The field testing was inconclusive as the
study conditions were changed with the replacement of the coil. The results of the laboratory study showed
that two of the three antimicrobial coatings limited the regrowth of fungal contamination, at least in the short
term. The third did not. Before use in the field, testing of the efficacy of antimicrobial coatings under realis-
tic use conditions is recommended because antimicrobials have different baseline activities and interact dif-
ferently with the substrate that contains them and their local environment.
ACKNOWLEDGEMENTS
The authors greatly appreciate the technical assistance of Eric A. Meyers, Tricia D. Webber, and Kaemi A.
Matthews of Research Triangle Institute in collecting the data. We would also like to thank Roy Fortmann
and Sam Brubaker of ARCADIS Geraghty and Miller, Inc. for their assistance at the test house. A special
thanks to NADCA members, Tim Hebert, Robert Krell. and Charles Cochrane, for their invaluable assis-
tance.
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the National Bureau of Standards —A. Physics and Chemistry. 1977; 81A(1): 89-96.
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brous Air Filters (ASHRAE Research Project-909). ASHRAE Transactions. In Press.
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N RMRL- RTF- P- 530
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA/600/A-00/066
2,
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Investigation of the Potential Antimicrobial Efficacy
of Sealants Used in HVAC Systems
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
K.K.Foarde and D. W. VanOsdell (RTI), and
M. Y. Menetrez (EPA)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Research Triangle Institute
Air Pollution Prevention and Control Division
P, O. Box 12194
Research Triangle Park, North Carolina 27709
11. CONTRACT/GRANT NO.
CR822642-01-6
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVEREC
Published paper; 4/99-4/00
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES AppCD project officer is Marc Y. Menetrez, Mail Drop 54, 919/
541-7981. For presentation at Engineering Solutions to IAQ Problems, Raleigh, NC,
7/17-19/00.
i6. ABSTRACT
paper gives results of an investigation of the potential antimicrobial
efficacy of sealants used in heating, ventilation, and air-conditioning systems. Re-
cent experiments confirm field experience that duct cleaning alone may not provide
adequate protection from regrowth of fungal contamination in fiberglass duct liner.
Current recommendations for remediation of fungally contaminated fiberglass duct
materials specify complete removal of the materials. But removal of contaminated
materials can be extremely expensive. Therefore, a common practice in the duct
cleaning industry is the post- cleaning use of antimicrobial surface coatings with the
implication that they may contain or limit regrowth. The paper describes a study to
evaluate whether three commercially available coatings, placed on a cleaned sur-
face that 1 year previously had been actively growing microorganisms, would be able
to prevent regrowth. The three coatings contained different active antimicrobial
compounds. Test results showed that two of the three antimicrobial coatings limited
the regrowth of fungal contamination, at least in the short term. The third did not.
Before use in the field, testing of the efficacy of antimicrobial coatings 'under real-
istic use conditions is recommended because -antimicrobials have different baseline
activities and interact differently with the substrate that contains them.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTlFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Fungi
Sealers
Air Conditioning
Fungicides
Ducts
Glass Fibers
Fungus Resistant
Coatings
Pollution Control
Stationary Sources
Antimicrobials
Fiberglass
13 B HE, 11B
06 C
11A 11C
13A
06F
13K
18. DISTRIBUTION STATEMENT
Release to Public
19, SECURITY CLASS (ThisReportJ
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 222O-1 (9-73)
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