United States National Risk Management

Environmental Protection Research Laboratory

Agency Cincinnati, OH 45268

E AP Project Summary

Research and Development EPA/600/SR-95/088 September 1995

Designing and operating a ventilation system for increased outdoor air

rates, as required by ASHRAE Standard 62-1989, improves indoor air quality (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 Triangle Institute for the U.S. EPA. The

Polk County Administration Building

(PCAB), a large negatively pressurized building, not known to be

biocontaminated, was selected for the

study. The microbiological screening

of the PCAB is the subject of this report; the energy/cost analysis is the

subject of a separate report.

The microbiological screening included bioaerosol, bulk material, condensate, surface, and building floor

dust samples taken at multiple locations. 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 microbiological conditions that might warrant further investigation but were not

of themselves adequate to indicate a

building-wide problem.

This Project Summary was developed

by the National Risk Management Research Laboratory’s Air Pollution Prevention and Control Division, Research

Microbiological Screening of the

Indoor Air Quality in the Polk

County Administration Building

D. W. VanOsdell, K. E. Leese, and K. K. Foarde

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 microbiological screening of the Polk County Administration 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 microbiological 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 ventilation systems. The impact of a building’s

ventilation system on biocontamination is

complicated. On the positive side, building pressurization reduces the infiltration

of biocontaminants, while maintenance of

relatively dry indoor environmental conditions prevents the growth of the microorganism spores inside. Biocontaminants will

grow and amplify on building materials at

lower moisture levels than previously reported, and the appropriate level of moisture remains under investigation. Filtration

equipment in the ventilation systems can

similarly reduce the influx of environmental microorganisms. On the other hand,

improperly designed, maintained, or operated 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 contamination 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 microbial contamination problem. The PCAB

operated under negative pressure, which

had the potential to bring in outdoor microorganisms. Microbiological investigations are commonly conducted in problem

buildings, and the mere presence of microorganisms in a building does not in

itself indicate a problem. Microorganisms

are endemic in buildings, their concentrations 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 difficult 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 locations to completely evaluate a building.

During this study, microbiological data

were collected from bulk, surface, and

bioaerosol samples, and the moisture content of some building materials was measured. Each of the measurements approaches the question of biocontamination

from a different perspective, thus addressing the problem of identifying the sources

of biocontamination.

The PCAB is a 5-story, 14,000 m2

(149,000 ft2) brick-faced building constructed in 1988. It has a permanent occupancy of approximately 300 county employees 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-conditioning (HVAC) system in the PCAB utilizes variable air volume delivery of conditioned 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 required for delivery to the space. The air is

distributed to fan-powered VAV terminal

boxes. The relative humidity in the building 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 material moisture measurement. All sampling

was conducted in April 1994. Bulk samples

consisted of HVAC fiberglass ductliner,

condensate from drain pans, and composite carpet dust. Surface samples included 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 problems 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 outdoor 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 regions was evaluated qualitatively by inspection and noted on the data sheet by

location.

Building material moisture content was

evaluated when appropriate using a conductivity 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 locations 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 occupants. Indoor and outdoor air samples

were obtained with Mattson-Garvin slit-toagar samplers operated for 30 minutes

indoors and 5 minutes outdoors. Tests

were conducted at nine sites, and at each

site duplicate samples were collected sequentially 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 samples were collected at appropriate locations to assess microbial flora within the

PCAB. Three microbiological media were

employed during the analysis to cover as

broad a range of microorganisms as possible.

Results and Discussion

Air Samples

Table 1 summarizes the mean levels of

colony forming units (CFU)/m3 for the xerophilic (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 media. 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 organisms 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 considerable differences between the results

for the two sequential duplicates. In both

rooms, one of the two replicates was several times higher than the other, and that

result was observed on both media collected at the same time. Thus the elevated 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 outdoor air was Penicillium with less than

25% of the total colonies. It is generally

expected that the numbers and distribution of indoor airborne fungi in mechanically ventilated non-problem buildings will

reflect those found in the outdoors, but at

lower levels. In most of the indoor sampling locations in the PCAB, Cladosporium

was the predominant genus followed by

Penicillium. The duplicate samples for

Rooms 170 and 413 were noticeably different 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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67%. By itself, the 28% Penicillium spp.

isolated from Room 170 might not be excessive. 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 replicate increased, the total level was only

332 CFU/m3

 and, therefore, not excessively 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 variability, in both of these rooms the increase

in Penicillium was detected by two different samplers on two different media at the

same time. The combined evidence indicates 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 southwest AHU and the 4th floor northeast AHU,

yielded potentially significant numbers of

Penicillium in practically pure culture. Swab

samples of a small patch of white mycelial-like material were taken in AHU2 located 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 species from both the AHU swabs and the

fiberglass ductliner suggests that possible

source reservoirs may have been identified. Although speciation of the Penicillium was not performed, isolation of the

colonies in some of the AHUs is consistent with the evidence of potential contamination suggested by the air sampling,

though it does not confirm the identification 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 identified 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 occupancy (relative to the HVAC flows) structure. The combined results of the air, bulk,

and surface sampling did not indicate a

clear biocontaminant problem in the building. On the other hand, the sampling period was short and samples were taken in

only a few locations. The elevated airborne 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 contamination problems have occurred in adjacent county buildings (and some occupants 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 intakes. Infiltration air is unfiltered and unconditioned, and the potential exists for

transport of biocontaminants in the infiltrating air, condensation of water vapor in

infiltration paths, and consequent building

contamination. On the other hand, the

PCAB is operated at a low relative humidity that tends to prevent microbial growth,

though it is presumably expensive to operate. This combination of characteristics

presents a number of research opportunities:

1)The results of this screening study

are not conclusive to either identify

the PCAB as a biocontaminated problem building or clearly show that

biocontamination is not an issue in

the PCAB. The study was not designed to accomplish that task. The

results do show that fungi (Penicillium spp.) may have become established in some AHUs and are either

established in some parts of the ventilation system downstream of the filters or at least occasionally transported 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 conditions led to that contamination? c)

Is PCAB becoming a problem building and is the contamination getting

worse? and d) Can conditions be

modified to prevent a serious contamination problem from developing?

2)The PCAB could be modified physically to operate at a controlled positive pressure to ensure that air entering the building is conditioned. Both

short- and long-term studies of the

microbial ecology in the building would

provide valuable information concerning the impact of building pressurization in a hot and humid climate.

3)In combination with pressurization, a

reduced-energy operating mode could

be designed for the PCAB to, potentially, provide both reduced costs and

reduced microbial contamination potential.

4)In addition to building pressurization,

the impact of building ventilation rates

on microbial contamination and general indoor air quality could be studied by modifying the outdoor air intakes to allow increased outdoor air

delivery. Such operation should be

optimized for energy efficiency consistent with prevention of conditions

conducive to microbial growth in the

building.

Table 1. Mean Total Airborne Fungi and Bacteria in CFU/m3

Location Room Xerophilic Fungi Bacteria

1st floor NE Outdoor Air 1100 520

1st floor NE Room 170 610 330

1st floor SW Outdoor Air 580 1900

1st floor SW Room 138A 110 270

4th floor NE* Outdoor Air 530 250

4th floor NE Room 413 210 80

4th floor SW Outdoor Air 830 440

4th floor SW Room 440 80 190

5th floor NE Outdoor Air 530 250

5th floor NE Indoors 30 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.
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D. W. VanOsdell, K. E. Leese, and K. 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

EPA/600/SR-95/088

Official Business

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