United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/088
September 1995
EPA Project Summary
Microbiological Screening of the
Indoor Air Quality in the Polk
County Administration Building
D. W. VanOsdell, K. E. Leese, and K. K. Foarde
Designing and operating a ventila-
tion system for increased outdoor air
rates, as required by ASHRAE Stan-
dard 62-1989, improves indoor air qual-
ity (IAQ) but is thought to extract a
penalty in energy costs and, potentially,
increased microbial contamination in a
hot humid climate. A two-part research
program into the impact of increased
outdoor air rates (per ASHRAE 62-1989)
on building microbial contamination
and the cost of providing that outdoor
air was initiated by the Research Tri-
angle Institute for the U.S. EPA. The
Polk County Administration Building
(PCAB), a large negatively pressur-
ized building, not known to be
biocontaminated, was selected for the
study. The microbiological screening
of the PCAB is the subject of this re-
port; the energy/cost analysis is the
subject of a separate report.
The microbiological screening in-
cluded bioaerosol, bulk material, con-
densate, surface, and building floor
dust samples taken at multiple loca-
tions. In general, the microbial results
were consistent with the PCAB's being
a non-problem building. However, the
study was too limited in both duration
and number of sample locations to
completely evaluate the building. The
results of a few samples indicated mi-
crobiological conditions that might war-
rant further investigation but were not
of themselves adequate to indicate a
building-wide problem.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
This research was an indoor microbio-
logical screening of the Polk County Ad-
ministration Building (PCAB) in Bartow,
FL. Its goal was to generate a baseline
measurement that could be used, in
conjuction with additional sampling that
has not been undertaken at this time, to
evaluate the impact of ventilation system
design and operation on the microbiologi-
cal aspects of indoor air quality (IAQ).
Indoor microbiological contamination can
be a significant cause of poor IAQ and is
known to be associated with building ven-
tilation systems. The impact of a building's
ventilation system on biocontamination is
complicated. On the positive side, build-
ing pressurization reduces the infiltration
of biocontaminants, while maintenance of
relatively dry indoor environmental condi-
tions prevents the growth of the microor-
ganism spores inside. Biocontaminants will
grow and amplify on building materials at
lower moisture levels than previously re-
ported, and the appropriate level of mois-
ture remains under investigation. Filtration
equipment in the ventilation systems can
similarly reduce the influx of environmen-
tal microorganisms. On the other hand,
improperly designed, maintained, or oper-
ated ventilation systems can contribute to
indoor biocontamination. In addition, the
increased outdoor air rates called for in
ASHRAE Standard 62-1989 are said to
both increase building energy requirements
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and lead to increased microbiological con-
tamination in hot and humid climates.
The PCAB was not thought to have a
microbiological (or any other) problem.
However, a neighboring building with some
characteristics similar to the PCAB was
known to have had a very significant mi-
crobial contamination problem. The PCAB
operated under negative pressure, which
had the potential to bring in outdoor mi-
croorganisms. Microbiological investiga-
tions are commonly conducted in problem
buildings, and the mere presence of mi-
croorganisms in a building does not in
itself indicate a problem. Microorganisms
are endemic in buildings, their concentra-
tions can vary widely over short periods of
time, and the "grab-sample" nature of
bioaerosol samplers makes the results of
a small number of short-term samples dif-
ficult to analyze. The indoor and outdoor
levels and types of organisms must be
interpreted in relation to those in nearby
buildings or control areas of the same
building. For these reasons, a screening
study such as this one is too limited in
both duration and number of sample loca-
tions to completely evaluate a building.
During this study, microbiological data
were collected from bulk, surface, and
bioaerosol samples, and the moisture con-
tent of some building materials was mea-
sured. Each of the measurements ap-
proaches the question of biocontamination
from a different perspective, thus address-
ing the problem of identifying the sources
of biocontamination.
The PCAB is a 5-story, 14,000 m2
(149,000 ft2) brick-faced building con-
structed in 1988. It has a permanent oc-
cupancy of approximately 300 county em-
ployees and elected officials, and also has
a transient population who come to the
building to conduct county business.
Bartow is in central Florida and has the
hot, humid climate typical of that area.
The heating, ventilating, and air-condi-
tioning (HVAC) system in the PCAB uti-
lizes variable air volume delivery of condi-
tioned air and a plenum return. The air is
conditioned in chilled water coils located
in variable air volume (VAV) air handling
units (AHUs), filtered with 5-cm (2-in.)
ASHRAE-30 filters, then reheated as re-
quired for delivery to the space. The air is
distributed to fan-powered VAV terminal
boxes. The relative humidity in the build-
ing is controlled to approximately 40%.
Each floor has multiple HVAC zones.
Procedure
The screening study included a building
walk-through, outdoor and indoor
bioaerosol sampling, bulk and surface
sampling, and occasional building mate-
rial moisture measurement. All sampling
was conducted in April 1994. Bulk samples
consisted of HVAC fiberglass ductliner,
condensate from drain pans, and com-
posite carpet dust. Surface samples in-
cluded swabs from inside selected AHUs
and the back side of ceiling tiles. This
study was HVAC-system driven, and the
test plan allowed some adjustment of test
sites and other aspects of the study based
on conditions in the building. All microbial
samples were shipped to RTI for analysis.
Test Locations
A walk-through of the entire building to
note any visible potential microbial prob-
lems was the first step of the screening
study. Study locations were chosen to be
in both the interior and exterior HVAC
zones and would have been chosen to
coincide with a potential problem area had
one been observed. Each indoor
bioaerosol sample was paired with an out-
door sample near the outdoor air intake
for the HVAC unit serving the indoor site.
The majority of the screening samples
were collected in two rooms on the first
floor, two rooms on the fourth floor, and at
one location on the fifth floor.
Sampling and Inspection
The HVAC systems serving the test
zones were inspected for visible problems
(standing water, plugged condensate
drains, duct leaks, etc.), and samples were
obtained when appropriate.
Cleanliness near the air sampling re-
gions was evaluated qualitatively by in-
spection and noted on the data sheet by
location.
Building material moisture content was
evaluated when appropriate using a con-
ductivity meter internally calibrated and
set on the concrete and plaster scale. The
readings are relative, and the instrument
was used to help identify any moist loca-
tions that might be microbial reservoirs or
have the potential to become microbial
sources.
Biocontaminant Sampling
All bioaerosol sampling was conducted
in temporarily vacated offices or after work
hours to avoid disturbing the PCAB occu-
pants. Indoor and outdoor air samples
were obtained with Mattson-Garvin slit-to-
agar samplers operated for 30 minutes
indoors and 5 minutes outdoors. Tests
were conducted at nine sites, and at each
site duplicate samples were collected se-
quentially with each of two fungal media
and one bacterial media, for a total of 54
Mattson-Garvin runs. At a single test site,
the total period during which sampling was
conducted was about 90 minutes indoors
and 45 minutes outdoors.
Swab surface and bulk material sam-
ples were collected at appropriate loca-
tions to assess microbial flora within the
PCAB. Three microbiological media were
employed during the analysis to cover as
broad a range of microorganisms as pos-
sible.
Results and Discussion
Air Samples
Table 1 summarizes the mean levels of
colony forming units (CFU)/m3 for the xe-
rophilic (low water requirement) fungi and
the bacteria at each of the nine sites
sampled. The results of the analyses on
the general fungal media are not shown
but supported those for the xerophilic me-
dia. Each entry is the mean of sequential
duplicate measurements. A comparison of
the outdoor and indoor mean levels shows
that for all the pairs there were less or-
ganisms isolated indoors than out. This
result is consistent with that found in a
non-problem building. However, the mean
values given in Table 1 do not show that
for Rooms 170 and 413 there were con-
siderable differences between the results
for the two sequential duplicates. In both
rooms, one of the two replicates was sev-
eral times higher than the other, and that
result was observed on both media col-
lected at the same time. Thus the el-
evated values are not experimental error,
but true measurements of a short-term
elevated level. This difference between
sequential duplicate sampling runs in the
same room suggested that comparisons
should be made between the runs based
on the identification of the organisms.
Cladosporium spp. predominated in all
the outdoor samples taken at the PCAB,
with over 50% of the total CFUs identified
as belonging to that genus. The second
most commonly isolated mold in the out-
door air was Penicillium with less than
25% of the total colonies. It is generally
expected that the numbers and distribu-
tion of indoor airborne fungi in mechani-
cally ventilated non-problem buildings will
reflect those found in the outdoors, but at
lower levels. In most of the indoor sam-
pling locations in the PCAB, Cladosporium
was the predominant genus followed by
Penicillium. The duplicate samples for
Rooms 170 and 413 were noticeably dif-
ferent in that there was a change in the
distribution of the predominant fungi. In
Room 170 there was an increase in the
Penicillium isolated from 7 to 28%. In
Room 413, the numbers were 14 and
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Table 1. Mean Total Airborne Fungi and Bacteria in CFU/m3
Location
Room
Xerophilic Fungi
Bacteria
1st floor NE
1st floor NE
1st floor SW
1st floor SW
4th floor NE'
4th floor NE
4th floor SW
4th floor SW
5th floor NE
5th floor NE
Outdoor Air
Room 170
Outdoor Air
Room 138A
Outdoor Air
Room 413
Outdoor Air
Room 440
Outdoor Air
Indoors
1100
610
580
110
530
210
830
80
530
30
520
330
1900
270
250
80
440
190
250
30
* The outdoor air sample collected on the 5th floor NE was paired with both the 5th floor indoor sample and the sample
collected in Room 413 because it was near both the 4th and 5th floor outdoor air intakes.
67%. By itself, the 28% Penicillium spp.
isolated from Room 170 might not be ex-
cessive. However, there was also a 10-
fold increase in total counts between the
duplicates, suggesting that an indoor
source might be present. In the same
samples, the airborne concentrations of
Aspergillis spp. also increased. For Room
413, while the counts on the second repli-
cate increased, the total level was only
332 CFU/m3 and, therefore, not exces-
sively high. However, that 67% of those
were Penicillium suggests again that an
indoor source might be present. Although
airborne fungal measurements are grab
samples and subject to considerable vari-
ability, in both of these rooms the increase
in Penicillium was detected by two differ-
ent samplers on two different media at the
same time. The combined evidence indi-
cates that potential source reservoirs of
Penicillium spp. may be contaminating the
rooms.
Surface and Bulk Samples
A number of different surface and bulk
samples were collected: condensate from
drain pans, swabs of ceiling tiles and
AHUs, bulk samples of fiberglass ductliner,
and composite carpet dust. None of these
samples showed any remarkable levels or
distribution of bacteria or fungi.
The other bulk samples, fiberglass
ductliner samples from the 4th floor AHU
and swab samples from the 1st floor south-
west AHU and the 4th floor northeast AHU,
yielded potentially significant numbers of
Penicillium'm practically pure culture. Swab
samples of a small patch of white myce-
lial-like material were taken in AHU2 lo-
cated on the 1st floor (southwest) and
AHU9 located on the 4th floor (northeast).
Analysis showed they were a pure growth
of Penicillium. Isolation of Penicillium spe-
cies from both the AHU swabs and the
fiberglass ductliner suggests that possible
source reservoirs may have been identi-
fied. Although speciation of the Penicil-
lium was not performed, isolation of the
colonies in some of the AHUs is consis-
tent with the evidence of potential con-
tamination suggested by the air sampling,
though it does not confirm the identifica-
tion of a source reservoir.
Moisture and Cleanliness
Moisture meter readings were taken at
a variety of locations within the building.
Only one potential water stain was identi-
fied during inspection of the building. No
readings suggested moisture problems.
Cleanliness was also determined visually.
Overall, the impression of the building was
that of a clean, well-maintained facility.
Conclusions and
Recommendations
The overall impression of the PCAB
was of a clean, well-maintained, low oc-
cupancy (relative to the HVAC flows) struc-
ture. The combined results of the air, bulk,
and surface sampling did not indicate a
clear biocontaminant problem in the build-
ing. On the other hand, the sampling pe-
riod was short and samples were taken in
only a few locations. The elevated air-
borne levels for one of two sequential
airborne fungi samples in each of two
different rooms (confirmed by the second
fungal media), coupled with the isolation
of essentially pure Penicillium in some of
the AHUs, give some cause for concern.
Considering that the building is located in
a hot, humid climate, that biological con-
tamination problems have occurred in ad-
jacent county buildings (and some occu-
pants have been exposed and may have
been sensitized to fungal contamination),
further investigation for potential source
reservoirs might be prudent.
The PCAB is negatively pressurized and
appears to have restricted outdoor air in-
takes. Infiltration air is unfiltered and un-
conditioned, and the potential exists for
transport of biocontaminants in the infil-
trating air, condensation of water vapor in
infiltration paths, and consequent building
contamination. On the other hand, the
PCAB is operated at a low relative humid-
ity that tends to prevent microbial growth,
though it is presumably expensive to op-
erate. This combination of characteristics
presents a number of research opportuni-
ties:
1)The results of this screening study
are not conclusive to either identify
the PCAB as a biocontaminated prob-
lem building or clearly show that
biocontamination is not an issue in
the PCAB. The study was not de-
signed to accomplish that task. The
results do show that fungi (Penicil-
lium spp.) may have become estab-
lished in some AHUs and are either
established in some parts of the ven-
tilation system downstream of the fil-
ters or at least occasionally trans-
ported through the filters to some
rooms at levels above those found in
most PCAB indoor locations and
roughly equivalent to outdoor levels.
The building may be in transition from
non-problem to problem, and as such
presents an unusual opportunity to
study some important questions, such
as: a) How extensive is the HVAC
system contamination? b) What con-
ditions led to that contamination? c)
Is PCAB becoming a problem build-
ing and is the contamination getting
worse? and d) Can conditions be
modified to prevent a serious con-
tamination problem from developing?
2)The PCAB could be modified physi-
cally to operate at a controlled posi-
tive pressure to ensure that air enter-
ing the building is conditioned. Both
short- and long-term studies of the
microbial ecology in the building would
provide valuable information concern-
ing the impact of building pressuriza-
tion in a hot and humid climate.
3) In combination with pressurization, a
reduced-energy operating mode could
be designed for the PCAB to, poten-
tially, provide both reduced costs and
reduced microbial contamination po-
tential.
4) In addition to building pressurization,
the impact of building ventilation rates
on microbial contamination and gen-
eral indoor air quality could be stud-
ied by modifying the outdoor air in-
takes to allow increased outdoor air
delivery. Such operation should be
optimized for energy efficiency con-
sistent with prevention of conditions
conducive to microbial growth in the
building.
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D. I/I/ VanOsdell, K. E. Lease, andK. K. Foarde are with Research Triangle Institute,
Research Triangle Park, NC 27709-2194.
Russell N. Kulp is the EPA Project Officer (see below).
The complete report, entitled "Microbiological Screening of the Indoor Air Quality in
the Polk County Administration Building," (Order No. PB95-243085; Cost:
$17.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-95/088
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