IAQ Problems in Schools

IAQ Problems in Schools
Causes of
Indoor Air
Problems in
Summary of
Scientific Research
Revised Edition
Charlene W. Bayer, Ph.D., Principal
Research Scientist and Branch Head
Georgia Tech Research Institute
Atlanta, Ga.
Prepared by
SEMCO, Inc., Columbia, Mo.
Subcontract Number 86X-SV044V
Prepared for the
Energy Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831-6285
managed by
UT-Battelle LLC
for the
U.S. Department of Energy
under contract DE-AC05-00OR22725
Sidney A. Crow, Ph.D., Associate Vice
President for Research and
Sponsored Programs
Georgia State University
Atlanta, Ga.
John Fischer, Technology Consultant
Columbia, Mo.
May 2000
List of Illustrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Preface to Revised Edition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
School Facilities and Indoor Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
IAQ Investigations Conducted in School Facilities . . . . . . . . . . . . . . . . . . . . . . . 5
Factors Determining Growth of Microorganisms . . . . . . . . . . . . . . . . . . . . . . .
Growth of Fungi in HVAC Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Toxin Production by Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Production of Volatile Emissions by Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Humidity Control and the Impact on IAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Impact of High Space Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Impact of Low Space Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
VOCs and Other Chemical Compounds That Affect IAQ . . . . . . . . . . . . . . . . . . 31
Control of Indoor Environments with HVAC Systems . . . . . . . . . . . . . . . . . . . 37
Impact of IAQ on Productivity and Satisfaction
in the Learning Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Space humidity measured by Downing at three operating modes with and
without the dual-wheel total energy recovery systems . . . . . . . . . . . . . . . . . . . 9
Impacts of ASHRAE Standard 62-1989 on classroom humidity levels in three
Florida cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alternative technologies to meet ASHAE Standard 62-1989 in Florida
schools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ontario Ministry of Labor findings on relationships between extent of
complaints regarding IAQ and CO2 levels and ventilation rates . . . . . . . . . .
Maryland’s requirements for outdoor air ventilation rates in schools . . . . . .
Particulate matter levels in schools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cost vs benefit comparison for providing desirable IAQ in schools . . . . . . . .
Since this report was first published, a number of new articles reporting the results
of research on IAQ in schools have appeared in journals and conference proceedings.
Several of these articles deal with the impact of indoor airborne contaminants on
students’ health. As a result of this additional research, particularly the healthrelated papers, we decided to update and revise this literature review summary
report. The text of this revised report contains summaries of these recent IAQ
articles, with 50 new items added to the References. In addition, we have expanded
the discussion of carbon dioxide in response to concerns about this section in the
first version of the report.
American Society of Heating, Refrigerating and Air-Conditioning
cubic feet per minute
colony-forming unit
carbon monoxide
carbon dioxide
dual-wheel total energy recovery system
energy recovery ventilator
heating, ventilation, and air-conditioning
indoor air quality
microbial volatile organic compound
nitrogen dioxide
oxides of nitrogen
particulate matter of <10 )m diameter
particulate matter of <2.5 )m diameter
parts per million
relative humidity
sick building syndrome
single-wheel total energy recovery system
variable air volume
volatile organic compound
According to the U.S. government’s General Accounting Office, one in five
schools in the United States—representing 8.4 million students—has problems with
indoor air quality (IAQ) (GAO 1995, 1996). According to the same studies, 36% of
the schools surveyed listed HVAC systems as a “less-than-adequate building
feature.” The reports also suggested that there appears to be a correlation between
unsatisfactory IAQ and the proportion of a school’s students coming from lowincome households.
Fourteen states regulate one or more environmental factors related to IAQ in
schools (ELI 1996). These regulations and states include
pesticide application: Arizona, Louisiana, Michigan, Montana, Tennessee, and
urea-formaldehyde insulation: California and Connecticut;
ventilation standards in schools, public
buildings, or workplaces: California,
Connecticut, Maine, New Jersey, and
One in five U.S. schools have indoor air
quality (IAQ) problems, a real concern in
New Hampshire;
schools because
mandatory consideration of IAQ in
school energy conservation efforts:
• children are still developing physically
California and Maine;
and are more greatly affected by
state review or evaluation of school IAQ:
the number of children with asthma is
Florida, Maine, and New Hampshire;
up 49% since 1982;
state assistance to local health
• children up to the age of 10 have three
departments in adopting IAQ programs
times as many colds as adults;
in public buildings: Wisconsin;
• poor IAQ can lead to drowsiness,
headaches, and a lack of concentration.
mandatory school IAQ programs and
best practices requirements to improve
IAQ in new school buildings:
Most other states are less proactive and are therefore dependent upon national
building standards such as the Southern Building Code, industry standards such as
the American Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE) Standard 62-1989, and the professional judgment of architects,
consulting engineers, and state and local school facility managers. These decision
makers are faced with many priorities other than IAQ concerns, all of which
compete for what is often a limited budget.
Bascom (1997) states that “schools are facing two epidemics: an epidemic of
deteriorating facilities and an epidemic of asthma among children.” He notes that
while clinicians are trying to instruct schools regarding environmental control
measures for children with asthma, these clinicians have little information about
the conditions and practical means in schools. The schools are ill-equipped to receive
the recommendations, assess their reasonableness, and effect the recommendations
at a reasonable cost. Bascom calls for the development of task forces to assemble the
necessary expertise to solve these problems. He points to the need for a controlled
IAQ research study so that effective IAQ plans can be developed and implemented.
There are many reasons to consider IAQ a top priority in the school
environment. One is that children are still developing physically and are more likely
to suffer the consequences of indoor pollutants. Another is that the number of
children suffering from asthma is up 49% since 1982, according to the American
Lung Association (Sundell and Lindvall 1993). Asthma is the principal cause of
school absences, accounting for 20% of lost school days in elementary and high
schools (Richards 1986). Richards also notes that allergic disease (nasal allergy,
asthma, and other allergies) is the “number one” chronic childhood illness,
accounting for one-third of all chronic conditions occurring annually and affecting
20% of school children. Children from birth to age 10 have three times as many
colds as adults (Tyrrell 1965, p. 19). School facilities, by design, are densely
populated, making the task of maintaining an acceptable IAQ more difficult than in
many other types of facilities. Another consideration is that the sole purpose of a
school facility is to foster the learning process, which is impacted directly by the
quality of the indoor environment (HPAC 1990; Dozier 1992; Boone et al. 1997).
Finally, most individuals have experienced drowsiness, lack of concentration, or
headaches in a classroom or auditorium environment and understand the impact
these symptoms have on comprehension and motivation. {
In the modern urban setting, most individuals spend about 80% of their time
indoors and are therefore exposed to the indoor environment to a much greater
extent than to the outdoors (Lebowitz 1992). Concomitant with this increased
habitation in urban buildings, there have been numerous reports of adverse health
effects related to IAQ (“sick buildings”). Most of these buildings were built in the
last two decades and were constructed to be energy-efficient.
The quality of air in the indoor environment can be altered by a number of
factors: release of volatile compounds from furnishings, floor and wall coverings,
and other finishing materials or machinery;
inadequate ventilation; poor temperature
and humidity control; re-entrainment of
A study by Armstrong Laboratory, at
outdoor volatile organic compounds (VOCs);
Brooks Air Force Base, Texas, found
that the three most frequent causes of
and the contamination of the indoor
unacceptable indoor air quality (IAQ)
environment by microbes (particularly
are (1) inadequate design and/or
fungi). Armstrong Laboratory (1992) found
maintenance of the heating,
that the three most frequent causes of IAQ
ventilation, and air-conditioning
are (1) inadequate design and/or
(HVAC) system, (2) a shortage of fresh
air, and (3) lack of humidity control.
maintenance of the heating, ventilation, and
air-conditioning (HVAC) system, (2) a
shortage of fresh air, and (3) lack of
humidity control. A similar study by the National Institute for Occupational Safety
and Health (NIOSH 1989) recognized inadequate ventilation as the most frequent
source of IAQ problems in the work environment (52% of the time).
Poor IAQ due to microbial contamination can be the result of the complex
interactions of physical, chemical, and biological factors. Harmful fungal
populations, once established in the HVAC system or occupied space of a modern
building, may episodically produce or intensify what is known as sick building
syndrome (SBS) (Cummings and Withers 1998). Indeed, SBS caused by fungi may
be more enduring and recalcitrant to treatment than SBS from multiple chemical
exposures (Andrae 1988). An understanding of the microbial ecology of the indoor
environment is crucial to ultimately resolving many IAQ problems. The incidence of
SBS related to multiple chemical sensitivity versus bioaerosols (aerosolized
microbes), or the contribution of the microorganisms to the chemical sensitivities, is
not yet understood.
If the inhabitants of a building exhibit similar symptoms of a clearly defined
disease with a nature and time of onset that can be related to building occupancy,
the disease is generally referred to as “building-related illness.” Once the SBS has
been allowed to elevate to this level, buildings are typically evacuated and the costs
associated with disruption of the building occupants, identification of the source of
the problem, and eventual remediation can be significant.
Understanding the primary causes of IAQ problems and how controllable
factors—proper HVAC system design, allocation of adequate outdoor air, proper
filtration, effective humidity control, and routine maintenance—can avert the
problems may help all building owners, operators, and occupants to be more
productive (Arens and Baughman 1996). This report provides a comprehensive
summary of IAQ research that has been conducted in various types of facilities.
However, it focuses primarily on school facilities because, for numerous reasons that
will become evident, they are far more susceptible to developing IAQ problems than
most other types of facilities; and the occupants, children, are more significantly
affected than adults (EPA 1998). {
Daisey and Angell (1998) conducted a survey and critical review of the existing
published literature and reports on IAQ, ventilation, and building-related health
problems in schools. They found that the types of health symptoms reported in
schools are very similar to those defined as SBS, although this finding may be due,
at least in part, to the type of health symptom questionnaires used. Some of the
symptoms (e.g., wheezing) are indicative of asthma. In the studies in which
“complaint” and “noncomplaint” buildings were compared, complaint buildings
usually had a higher rate of health-related symptoms.1
Formaldehyde, total VOCs, CO2, and bioaerosols were the most commonly
measured pollutants in schools. Most of the formaldehyde measurements made in
the United States were in complaint schools but were still generally below
0.05 ppm. The measurements of the other pollutants were too limited to draw
conclusions as to the prevalence of indoor concentrations of concern, even in
problem schools. However, there was some evidence that microbiological pollutants
are of particular concern. The few scientific studies on causes of symptoms in
complaint schools indicate that exposure to molds and allergens in schools
contributes to asthma, SBS, and other respiratory symptoms. Other indoor
pollutants, such as VOCs and aldehydes, have been investigated to only a very
limited extent, although there are reasons to suspect that they may also contribute
to the prevalence of health-related symptoms in schools.
The major building-related problem identified was inadequate outdoor air
ventilation. Water damage to the building shells of schools, leading in turn to mold
contamination and growth, was the second most frequently reported buildingrelated problem. The root cause of many of the ventilation and water-damage
problems in the schools was inadequate and/or deferred maintenance of school
buildings and HVAC systems.
1. Complaint buildings are those for which an abnormal number of complaints are made
regarding the quality of the indoor air.
Daisey and Angell concluded that there is now considerable qualitative
information on health complaints, ventilation, and IAQ problems in complaint
schools. It is unknown what fraction of schools are experiencing IAQ and ventilation
problems and related health problems. There is also a lack of the scientifically
rigorous and quantitative information on
causal relationships between health
symptoms, exposure, and dose-response
Daisey and Angell found that the major
relationships that is needed to establish
building-related problems in “complaint”
schools were inadequate outdoor ventilation,
health standards for the protection of
children in schools. The effectiveness and followed by water damage to building shells
that set up conditions for mold
the costs and benefits of various remedial
contamination and growth.
actions undertaken to solve problems in
specific schools remain largely unknown.
The report recommended the following research:
Determine more quantitatively the degree to which IAQ problems in schools
increase asthma, SBS symptoms, and absentee rates of students.
Identify the specific agents that cause health effects and determine exposureand dose-response relationships for those pollutants that are the most
significantly related to health symptoms.
Determine whether learning can be significantly increased through improved
Determine the cost-effectiveness of various remediation measures undertaken to
solve problems in complaint schools through intervention studies in which
changes in health symptoms and test scores are measured before and after
Determine the costs of deferred building maintenance with respect to health and
learning in students.
Determine the viability of using CO2 detectors and other types of sensors to
routinely control ventilation and to provide an indication of inadequate
Develop improved sampling and analysis methods for bioaerosols.
Develop low-cost samplers for measuring 6-hour exposures to other key indoor
pollutants, such as aldehydes, that may be contributing to the kinds of
symptoms observed in problem schools.
The U.S. Environmental Protection Agency (EPA 1998) is formulating a major
study of IAQ in school buildings to provide baseline IAQ data. The study is to be
similar to the BASE study (Womble et al. 1993) on office buildings, following a
similar protocol. Six basic activities have been proposed:
school selection representing both public and private schools;
physical characterization of the buildings in terms of location, physical
structure, ventilation, occupant density, occupant activities, and potential indoor
pollutant sources associated with special use areas;
definition of building study areas and random selection of four study areas for
more extensive evaluation;
monitoring for one week in the study areas to generate data on HVAC operation,
environmental problems, and comfort factors using standard procedures and
good quality assurance/quality control practices;
administration of an occupant questionnaire to all adult occupants; and
development of a publicly accessible database of study results.
Parameters proposed for monitoring include
temperature, relative humidity, sound level, and illuminance;
air pollutants [CO2, CO, inhalable particles (PM2.5 and PM10), VOCs,
formaldehyde, bioaerosols, radon];
HVAC supply measurements (airflow rate, air temperature, air relative
percentage and rate of outdoor air intake;
exhaust fan and supply diffuser airflow rates; and
supply diffuser parameters (temperature, relative humidity, and CO2).
The protocol is currently in a draft form and is not to be cited or quoted specifically.
Henckel and Angell (1999) reported on the results of 169 investigative reports of
IAQ in Minnesota schools. Data were collected on health and environmental
complaints, pollutant concentrations, and building-related factors. Health
complaints, particularly upper respiratory and central nervous system problems,
occurred at a frequency similar to that of environmental complaints. The majority of
environmental complaints were about odors, too little air movement, and
temperature variation. Carbon dioxide levels were elevated in 66% of the schools in
which measurements were taken. Microbiological contamination was the primary
concern in 33% of the investigations. The most commonly cited building factor
associated with IAQ complaints was insufficient outdoor air supply; moisture
problems were ranked second, and poor air distribution was ranked third. Henckel
and Angell concluded that a significant number of IAQ problems could be avoided by
addressing ventilation and moisture problems.
Downing and Bayer (1993) investigated the relationship between ventilation
rate and IAQ in classrooms. Samples were collected and analyzed for VOCs,
formaldehyde, CO2, temperature, and humidity. Downing and Bayer confirmed in
this study that 15 cfm per student of outdoor air was required to maintain CO2
concentrations at levels below 1000 ppm. The recommendation was made that
classrooms, both new and existing, be provided with at least 15 cfm per student of
outdoor air on a continuous basis during school hours. It was found that VOC
concentrations exceeded 1000 )g/m3 when only 5 cfm per student was provided,
even on a continuous basis. Tucker (1986) indicated that this level of VOCs is an
indication of potential IAQ problems.
Downing and Bayer also measured space humidity as a function of the operating
mode of packaged rooftop equipment compared with humidity levels maintained
with a system utilizing a dual-wheel total energy recovery system (DWERS) (see
Fig. 1). Humidity measurements collected over time for a school that had
experienced serious microbial and IAQ problems showed that even with only 5 cfm
per student being provided on a continuous basis, the space relative humidity
exceeded 80% for an extended period of time and averaged well over 70% during the
investigation. When the fan was cycled with the cooling coil, the average space
humidity dropped somewhat to approximately 70%, but it still exceeded 80% during
the evening hours. With the DWERS maintaining the humidity content of the
continuously supplied outdoor air, the space relative humidity averaged 53% and
remained below 58% throughout the investigation.
Downing and Bayer reported that
In a school studied by Downing and Bayer,
before the school was retrofitted with a
there was visible mold on building surfaces
DWERS, there was visible mold growth
before retrofit. With a DWERS installed,
on building surfaces, carpeting, and
average relative humidity dropped from 80%
to 53%.
books. The IAQ complaints and
illnesses included respiratory and
allergy problems, headaches, and
lethargy. The HVAC system modification, which provided increased outdoor air
quantities on a continuous basis while controlling space humidity, eliminated both
the mold and the IAQ complaints by the teachers and students. This finding was
confirmed through follow-up interviews by Downing and Bayer with a number of
the teachers who had complained the most about the building’s IAQ prior to the
HVAC system retrofit.
Bayer, Crow, and Noble (1995) reported on case studies conducted in five school
systems in Georgia. In each of these schools, the students and teachers were
experiencing rashes and respiratory illnesses. In each of the schools, microbial
amplification was identified, and Cladosporium sp. was the most prevalent fungi
found. Although atopic dermatitis has been reported to be relatively rare, one cause
may be contact with molds such as Alternaria, Cladosporium, and Aspergillus in
atopic individuals (Flannigan and Morey 1996). Bayer, Crow, and Noble also
Fig. 1. Space humidity measured by Downing at three operating modes
with and without the dual-wheel total energy recovery systems, showing
lack of humidity control with conventional packaged HVAC units.
confirmed, via comparison of field results with laboratory studies, that many of the
detected VOCs were microbial in origin.
Bayer (unpublished results) investigated IAQ problems in a southern school that
had had to conduct an emergency evacuation because of strong odors and visible
microbial growth. The school had to be abandoned within a few weeks after
completion of a massive renovation that included new rooftop HVAC units, new
carpeting, furnishings, painting, and so on. The carpet was covered with visible
microbial growth and had a strong cinnamon odor in the most contaminated areas.
Investigation revealed that water was condensing under the carpet on the concrete
slab as a result of the poor humidity control within the building. Using
environmental chamber technology to simulate ongoing conditions in the school,
Bayer found that the carpet adhesive would reactivate to a wet state whenever it
was exposed to humidities greater than 75% for a period of several hours. The
adhesive would reset to a hardened state when the humidity was lowered below
75% for several hours. When the adhesive was wet, strong solvent-type odors were
emitted. The biocide present in the adhesive was designed to prevent microbial
growth only in the sealed container before use; it was not able to prevent microbial
growth in this cycling wet-dry-wet state. Without biocide protection, the carpet
adhesive was an excellent nutrient base for microbial growth. The result was
excessive amounts of microbial growth. The volatile emissions from the microbes
were very strong: total VOC levels in the school exceeded 23,000 )g/m3. The hexane
levels exceeded 13,000 )g/m3.
Although schools are prime candidates for fungal colonization, few studies have
systematically examined the mycoflora of school buildings. Crow et al. (1993, 1994);
Crow, Ahearn, and Noble (1995); Bayer and Crow (1992); Bayer, Crow, and Noble
(1995); and Downing and Bayer (1993) have examined a number of buildings,
including primary and secondary schools and university buildings. Samples
represent a single collection of airborne viable samples from sites of amplification
where fungal colonies were growing on surfaces within the building.
Crow et al. (1994) reported on two schools in a series of ten buildings sampled
for airborne fungi. Both schools had both complaint and control sites. The first
school had humidities of 58–61% during the test period. The viable fungal counts
were 140–1615 cfu/m3. Populations were dominated by species of Cladosporium and
Penicillium. The second school had relative humidities of approximately 60–63%
during the test period. This school had experienced obvious humidity control
problems, indicated by sagging ceiling tiles and evidence of water condensation; and
it yielded extremely high fungi numbers (735–5180 cfu/m3) found on a variety of
media. The dominant species were again Cladosporium and Penicillium.
In a second paper Crow, Ahearn, and Noble (1995) discussed three additional
schools. The viable counts of airborne fungi were lower (35–1280 cfu/m3) than those
described for the previous schools. Dominant species were Cladosporium and
Penicillium. At three additional schools sampled (unpublished data), airborne
counts were in similar ranges and were generally dominated by Cladosporium and
Penicillium. Clearly, variations in seasonal occurrence of outdoor fungi can confuse
the interpretation of indoor air counts. Critical seasonal studies coupled with
sophisticated data on humidity and the nature of volatiles will help clarify the
meaning of airborne viable counts. Understanding of the basic physiological
phenomena in microbes and the influence of environmental parameters on variation
in basic processes, such as the formation of conidia and volatiles and their
subsequent release, will clarify the etiology of SBS.
Wurtz et al. (1999) investigated airborne microflora in four schools in Denmark.
Thirty percent of the samples taken in this study contained bacteria concentrations
of more than 5.0 × 103 cfu/m3, which may indicate crowding or poor ventilation.
These researchers found that significant parameters for predicting airborne
bacterial concentrations were air exchange rate and the area (in cubic meters) per
person. Area per person also appeared to be associated with airborne fungal
Bartlett, Kennedy, and Brauer (1998, 1999a,b) recently conducted one of the few
statistically significant IAQ investigations of schools. These researchers
investigated IAQ in terms of microbial contamination (focusing on mesophilic and
thermophilic fungi and bacteria), occupancy load and patterns, CO2, total particles,
temperature, humidity, and air change rates in 39 schools in British Columbia, a
coastal and temperate climate zone. The 39 noncomplaint schools were randomized
into three identifiable sampling periods—winter, spring, and fall. Two sampling
cycles were required to investigate all of the schools, with three rooms sampled in
each school. Bartlett, Kennedy, and Brauer found that the outdoor concentration of
mesophilic fungi was statistically different from the indoor concentration and that
the variable with the highest predictive value for indoor mesophilic fungi was
outdoor temperature (using multiple linear regression equations, r2 = 0.61). There
was a seasonal correlation with concentrations of the fungi, and the winter indoor
and outdoor counts were lower than either the spring or fall counts. Twenty-eight
percent of the classrooms studied had culturable fungal concentrations greater than
500 cfu/m3. The xerophilic fungi (those able to grow with reduced biologically
available water) were present in greater concentrations in the fall. Xerophilic fungi
are potential colonizers of building materials and potential allergens. Some
xerophilic genera are suspected of being contributors to fungal allergic responses.
The apparent failure, found by Bartlett, Kennedy, and Brauer, of school
ventilation systems to filter out fungi originating from the outside could allow for
increased fungal exposure to susceptible individuals. Seventy-one percent of the
classrooms failed to meet the ASHRAE 62-1989 ventilation standard. Forty-five
percent of the classrooms had average CO2 concentrations greater than 1000 ppm.
Using multiple linear regression equations, these authors found that the highest
predictive value for bacterial
concentration was indoor CO2
In Canadian schools studied by Bartlett,
concentration (r2 = 0.586), and concluded
Kennedy, and Brauer, 71% of the
that high commensal bacterial counts
classrooms failed to meet the ASHRAE
were related to inadequate ventilation of
ventilation standard, and 45% of the
classrooms had average CO2
the occupied spaces. The air exchange
concentrations above the ASHRAE
rates were lower in winter, when the
maximum limit of 1000 ppm.
HVAC systems were set at the minimum
outside air supply level by the school
facilities managers to reduce energy usage
or avoid dumping cold air on the space occupants. The mean relative humidity level
during the winter season was 36.9%. Bartlett, Kennedy, and Brauer concluded that
the combination of the lower relative humidity and the inefficient ventilation,
particularly in the winter season, may contribute to the spread of airborne
infectious diseases that are common in classroom settings.
In a 1998 paper, Lytton stated: “It is often taken for granted that schools are
incubators of disease. . . . Most of us probably grew up assuming that schools are
places where illnesses spread from child to child and from children to staff” (Lytton
1998). Unfortunately, in most schools this is true, but with better control and
understanding of school indoor environments this is not an inevitable situation.
Disease and allergenic agents are airborne particles that are spread among building
occupants. These particles are droplet nuclei (ranging in size from 1 to 5 )m) and
fungal spores (ranging in size from 1 to 5 )m)—particles that can be removed from
air by commercially available filters (Wheeler 1993).
Green (1985) reduced airborne bacteria levels in school classrooms by filtering
recirculated air. He reported that in the studied school, respiratory infection
accounted for 60% of all absenteeism prior to reduction of the airborne bacteria
levels through filtration. Wheeler (1993) applied the Wells-Riley equation to predict
the performance of alternative air-conditioning systems, dilution ventilation rates,
and filter efficiencies for calculation of risk of infection in an elementary school
classroom. Wheeler’s modeling technique can be applied to calculate the filtration
efficiencies and HVAC system performance needed to reduce the risk of infections
among school children, teachers, and staff.
Mouilleseaux, Squinazi, and Festy (1993) conducted a microbial characterization
of the indoor air in the classrooms in ten primary and nursery schools in Paris. The
average aerobic bacteria count was 3000 cfu/m3. They found that 32.7% of the
analyzed samples contained Staphylococcus aureus (a germ indicative of human
mucous/cutaneous contamination), 6.2% contained enterobacteria (a marker of
faecal/hydrotelluric air contamination), and 50.6% contained thermotolerant
Streptococcus (a marker of faecal/hydrotelluric air contamination). The average
fungal counts were 100 cfu/m3, and yeasts were 20 cfu/m3. The fungal flora were
Airborne microbial contamination in naturally and mechanically ventilated
buildings was studied by Maroni et al. (1993). These buildings included ten schools
and seven office buildings. Maroni et al. did not find major differences in detected
fungi between naturally and mechanically ventilated buildings. However, in the
mechanically ventilated buildings, they did find a significant correlation between
microorganisms and the relative humidity in wintertime, a negative correlation
between bacteria and particulate matter in summertime, and a positive correlation
between bacteria and temperature in summertime. They also found a weak
correlation between total VOCs and fungi in the schools.
Rand (1999) inspected 631 schools in the Canadian Atlantic provinces for mold
contamination. He found that species type and amounts vary widely depending on
the school construction type, school age, and composition and water activity of the
amplifying substrate material. The most common contamination sites, in
descending order of occurrence, are classrooms and administration sites, especially
in peripheral wall cavities and ceiling plenums; libraries; gymnasiums; basements
and crawl spaces; ventilation systems; janitor and mechanical rooms; and portable
classrooms. The most commonly contaminated substrates in schools are drywall,
ceiling tiles, structural wood, insulation, carpets, and concrete wall surfaces that
have been exposed to chronic water infiltration, condensation, and/or wicking
problems. Mold species composition in normal and moisture-damaged schools vary
greatly. Species commonly encountered in moisture-damaged schools are
Acremonium spp., Aspergillus fumigatus, Aspergillus niger, Aspergillus ustus,
Aspergillus versicolor, Chaetomium spp., Paecilomyces variotii, Penicillium
brevicompactum, Penicillium aurantiogriseum complex, Penicillium variablile,
Phoma spp., Stachybotrys chartarum, Trichoderma harzianum, and Tichoderma
viride. In schools not damaged by moisture, the mold species assemblage should be
similar to that encountered in the surrounding outdoor environment. An
understanding of the school building design is required to identify and remediate
amplification sites. Rand found a positive correlation between health complaints
and the presence of certain toxigenic molds (Penicillium aurantiogriseum and
Trichoderma harzianum) in the studied schools.
The sensitization of 622 school
children to molds and respiratory
In one study of more than 600 school children,
symptoms was investigated by
although skin tests showed low sensitivity to
Taskinen et al. (1999). Two
common molds and allergens, reactivity to
elementary schools were targeted for molds appeared to be associated with asthma or
this research—one with a
asthma-like symptoms.
documented moisture problem (the
index school) and one without a
moisture problem (the control school). The geometric mean of total viable fungi
concentration was 21 cfu/m3 in the index school and 4 cfu/m3 in the control school. In
the index school, the primary species isolated from the indoor air and/or building
materials were Aspergillus fumigatus, Aspergillus versicolor, Actinomycetes,
Eurotium, Exophiala, Fusarium, Phialophora, Rhodotorula, Stachybotrys,
Trichoderma, and Wallemia. Low indoor air concentrations of Aspergillus
fumigatus, Actinomycetes, Eurotium, and Wallemia were found in the control school.
Taskinen and associates distributed a questionnaire to children ranging in ages
between 7 and 13; in addition, the children received skin prick tests for 13 molds
and 11 common allergens. The researchers found that although skin test positivity
was rare in the children (only 2% had strong positive tests), reactivity to molds
appeared to be associated with asthma or asthma-like symptoms. Respiratory
infections seemed to be associated with mold exposure. Asthma and asthma-like
symptoms were common in the children from the index school.
Thorstensen et al. (1990) studied ten schools in Greater Copenhagen to quantify
pollutant sources in the schools and to relate students’ complaints and symptoms to
physical, chemical, biological, and sensory measurements. The IAQ in the schools
was investigated under three conditions: (1) while the schools were unoccupied and
the mechanical ventilation system was not operating (if the school was mechanically
ventilated; six of the ten schools were mechanically ventilated); (2) while the schools
were unoccupied and the mechanical ventilation system (if available) was operating;
and (3) while the schools were normally occupied and ventilated. A panel of
students trained in making sensory measurements by the “olf” method (Fanger
1988) determined the quality of the air. Ventilation rate, CO2, airborne bacteria and
microfungi, airborne dust, accumulated floor dust, immunogenic components in floor
dust, total volatile organic compounds, temperature, and relative humidity were
measured. Thorstensen et al. found considerable variation between the schools,
especially in prevalence of students’ symptoms, physical and sensory
measurements, and pollutant loads. They found a significant correlation between
the panel’s decipol judgment of air quality and the prevalence of symptoms. On
average the ventilation rate was only 2.3 L/s per olf in the six mechanically
ventilated schools, approximately three times lower than the recommended 7 L/s
per olf level (Fanger 1988). In the mechanically ventilated schools, the pollutant
source determinations indicated that 40% were a result of the ventilation system,
40% were from the occupants, and 20% were from other sources.
Smedje, Norback, and Edling (1997) studied the perceptions of school occupants
of the IAQ in their schools. Data on subjective air quality, domestic exposures, and
health aspects were gathered via questionnaires sent to all school employees in 38
schools (1410 people in all) in Sweden. Exposure data were gathered by classroom
monitoring of temperature, relative humidity, rate of air exchange, CO2, CO, NO2,
formaldehyde, other VOCs, respirable dust, molds, bacteria, settled dust, and mite
allergens. The questionnaires indicated that 53% of the school occupants perceived
the IAQ in their school as bad or very bad. The younger staff were more dissatisfied
than older personnel. Also, those from homes with no tobacco smoking were less
tolerant of the school indoor environment. Dissatisfaction also was increased among
those dissatisfied with their psychosocial work climate. In older school buildings
and buildings with displacement ventilation, there was less dissatisfaction with the
Smedje, Norback, and Edling demonstrated that the subjective perceptions of air
quality were related significantly to exposure to microorganisms, VOCs, and dust,
as well as to personal factors such as age, atopic disposition, and perceived work
social climate. Respondents with allergies or an atopic disposition were more
negative about school IAQ. Significant correlations were found between subjective
air quality and exposure to settled and airborne dust, mold and bacteria, and total
volatile organic compounds. Even at low concentrations, these pollutants affected
perceived IAQ.
Smedje, Norback, and Edling did not find a significant relationship between the
complaints and the rate of air exchange or the CO2 concentration. The CO2 levels
ranged from 375 to 2800 ppm. The air quality was perceived to be worse at higher
exposure levels of airborne contaminants, such as VOCs (which ranged between
3 and 580 )g/m3), molds (ranging between 7 and 360 + 103/m3 for total molds),
bacteria (ranging between 8 and 290 + 103/m3 for total bacteria), NO2 (ranging
between 1 and 11 )g/m3), CO (ranging between <0.1 and 0.9 )g/m3), and respirable
dust (ranging between 6 and 60 )g/m3). Therefore, they concluded that exposure to
indoor pollutants affects the perception of IAQ, even at the low pollutant
concentrations normally found indoors. The relative humidity in these schools
ranged between 16% and 75%, with a mean of 38%.
Norback (1995) reported on an investigation of subjective IAQ in14 Swedish
schools. He found a relationship between perception of poor IAQ and high room
temperature, fleecy wall materials, and VOCs, particularly xylene, limonene, and
butanols. Wall-to-wall carpets and fleecy materials had a significant influence on
the subjective perception of poor IAQ. These related both to a higher perceived
indoor air temperature and higher concentrations of dust and VOCs. Among
Norback’s study participants, perceptions of air dryness were related to atopy, work
stress, poor climate, high room temperature, low air humidity, and high VOC
concentrations (indoor/outdoor ratios ranged between 1.5 and 32). A perception of
dusty air was related to work stress, teaching responsibilities, and exposure to 2ethyl-1-hexanol [a microbial VOC (MVOC)].
Walinder et al. (1997) studied the potential for exposure to increased levels of
indoor air pollutants in schools to increase swelling of the nasal mucosa. The degree
of mucosal swelling was estimated indirectly via the decongestive effect of
xylometazolin, measured with acoustic rhinometry. The study was conducted in 39
Swedish schools and included both children and adult staff. Walinder et al. found
that the indoor concentrations of VOCs, respirable dust, bacteria, molds, and
MVOCs were highest (2–8 times higher) in the school that had the lowest
ventilation rate and was naturally ventilated. They concluded that inadequate
outdoor air supply in schools may lead to increased levels of indoor air pollutants,
resulting in subclinical swelling of the nasal mucosa.
The relationship of asthma to the indoor environment and the occurrence of
asthma among school employees was studied by Smedje et al. (1996). Data were
gathered among Swedish school employees (1410 subjects) via questionnaire. Data
on exposure were collected by monitoring temperature, relative humidity, rate of air
exchange, CO2, NO2, formaldehyde, VOCs, MVOCs, respirable dust, molds, bacteria,
allergens, and endotoxins in dust. The MVOCs identified were 3-methylfuran,
3-methyl-1-butanol, 2-methyl-2-butanol, 2-pentanol, 2-heptanone, 3-octanone,
3-octanol, 1-octen-3-ol, 2-octen-1-ol, 2-methylisoborneol, geosmin, and 2-isopropyl3-methoxypyrazine. No significant correlation was found between asthma and air
exchange rate, type of ventilation system, visible dampness, amount of fabrics or
open shelves in the classroom, room temperature, relative humidity, CO2, respirable
dust, viable or total bacteria, viable molds, total MVOCs, formaldehyde, total VOCs,
NO2, cat or dog allergens, or endotoxins. Significance was more common among
atopic individuals, those who had recently painted in their homes, and those who
felt work was stressful.
Asthma was found to be more common among subjects working in schools with
higher concentrations of total molds and four MVOCs: 3-methylfuran, 2-heptanone,
1-octen-3-ol, or 2-methylisoborneol. The concentrations found of these MVOCs were
very low. Smedje et al. concluded that the relationship to asthma may be principally
that the occurrence of MVOCs in indoor air is an indicator of active microorganism
growth compared with measurements of airborne microorganisms. MVOCs also
have the advantage of providing data about microbial growth inside sealed surfaces.
The authors emphasized that these
Asthma was found to be more common among
results stress the importance of
building, controlling, maintaining, and subjects working in schools with higher
concentrations of total molds and four
cleaning schools so that exposure to
microbial growth is limited.
Lundin (1999a) investigated how allergic and nonallergic students perceive their
indoor school environment by administering a questionnaire to the students in five
high schools in Sweden asking questions about allergies (asthma, hay fever, and
eczema), subjective symptoms, annoyance reactions, and the perception of the
environment (IAQ, noise, and cleanliness). Fifty-five percent of the students
reported having some form of allergy. The findings indicated that allergic students
experience discomfort earlier and are more critical about the environment,
particularly about the specific factors that affect their health. Allergic students
often were bothered by dust and dirt, stuffy or stale air, and passive smoke
exposure. All of the students in schools perceived to have a “bad environment” were
dissatisfied with the air quality, while all students in a perceived “good
environment” were more satisfied with the air quality and cleanliness of the schools.
In general the allergic students, as a group, were more critical of these factors.
School surveys outlined by Andersson (1998) revealed that high school teachers
and students tend to report different symptom patterns in the same environment.
The students reported a higher prevalence of general symptoms, particularly
concentration difficulties, than the teachers, irrespective of the IAQ. Students rarely
reported a high prevalence of mucous membrane irritation, even in environments
with severe dust and moisture problems. Landrus and Axcel (1990) found similar
results. Usually, parents of younger
children (those in elementary schools Studies of students’ and teachers’ perceptions of
and day care) tended to blame the
air quality in “bad” environments were
school’s IAQ for their children’s
inconclusive, but allergic students were more
aware of and critical of factors contributing to
symptoms. These reporting
poor IAQ, and teachers who had worked in a
discrepancies may confound data
correlating IAQ and perceived health repaired water-damaged school were more
sensitive to histamine than those who had not,
even after four years.
Teachers who had worked in a
repaired water-damaged school demonstrated increased sensitivity to histamine
when compared to teachers in a control school (Rudblad et al. 1999). These teachers
had worked in the water-damaged school for more than five years before
remediation was done. Prior to remediation in 1995, the teachers were tested for
nasal histamine sensitivity by rhinostereometry; the follow-up study indicated that
the sensitivity, although diminished, has continued even four years after
remediation. The researchers concluded that remaining in an indoor environment
with moisture problems for long periods of time is associated with an increased risk
for developing nasal hypersensitivity. {
In buildings, the conditions for microbial growth vary from structures where
water is scarce or seldom available to those where water is constantly present.
Systems containing water, such as standing water in cooling coil drain pans or
condensed water on cold surfaces (i.e., slab floors, inner walls, or ductwork), favor
the growth of bacteria, algae, protozoa, and certain fungi. Consistently high
numbers of bacteria in office buildings (excluding food service areas) have been
associated mostly with standing water. Most fungi, however, prefer the surfaces of
moist materials instead of liquid water (Nevalainen 1993). Buildings that have
suffered water damage from leakage or flooding often experience fungal “blooms”
that may degrade air quality (Morey 1992). The inside surfaces of outside walls or
any surfaces that are temperature clines (wide and/or rapid fluctuations) and foci of
condensation may support microbial growth (Flannigan 1992).
In the past few years, fungi have been increasingly linked to SBS (Miller 1992;
Samson et al. 1994). The sources and sites of amplification of fungi in indoor
environments are highly variable; as a result, establishing a direct link between the
presence of fungi and SBS is often
problematic. In individual residences, in
Fungi have been increasingly linked to
older buildings with water damage and
SBS in recent years. A number of
decay, and in situations following chronic
construction materials support their
or catastrophic water damage, the harmful
growth, particularly if those materials
effects of fungi are more obvious
are wet and dirty.
(Batterman and Burge 1996; Samson et al.
1994, p. 695).
Typical construction materials that can support the growth of fungi include
wood, cellulose, hemicellulose, and wallpaper; some organic insulation materials;
glues, paints, and mortars that contain carbohydrates or proteins; and textiles,
especially natural fibers. Materials that are not easily degraded by fungi—such as
mineral wool, metal, polyvinyl chloride and other synthetic polymers, and bricks,
tiles, and other such mineral products—still may be extensively colonized by fungi
(Ahearn et al. 1995, 1996). In such cases, the fungi do not use the metal or concrete
for their growth but, rather, use the water and organic debris on the surface,
including organics absorbed from the air (Nevalainen 1993; Ahearn et al. 1996).
Fungi that have been isolated commonly from indoor environments include species
of Aspergillus, Penicillium, Cladosporium, Alternaria and Aureobasidium species
(Bisett 1987; Nelson et al. 1988; Ahearn et al. 1991; Mishra et al. 1992; Ahearn et
al. 1992a; and Nevalainen 1993). These fungi usually are recovered from sources
such as wood rot in domestic interiors, wall coverings, house dust, pets, and
houseplants (Mishra et al. 1992; Ahearn et al. 1992b).
Growth of Fungi in HVAC Systems
HVAC systems have been associated with increased airborne densities of fungi
of various genera, particularly Cladosporium and Penicillium (Hirsch, Hirsch, and
Kalbfleisch 1978; Mishra et al. 1992). Ahearn et al. (1991) reported the colonization
of painted metal surfaces of HVAC systems by Cladosporium sp. in a study in which
airborne conidia appeared in low densities. The fungi were present not in the form
of dormant conidia originating from outside air, but as reproducing fungal colonies
tightly adhered to the metal surfaces. In Belgium, studies of air-conditioned
buildings suggested that the HVAC system was the source of Penicillium sp. in the
indoor air (Heinemann, Beguin, and Nolard 1994).
Many species of fungi have been isolated from various types of fiberglass used in
HVAC systems, particularly when the fiberglass was laden with soil and moisture
(Morey 1992; Morey 1993; Bjurman 1993). Ahearn et al. (1992a, 1996) reported the
colonization of relatively new fiberglass duct insulation in well-maintained HVAC
systems. The facings of the duct insulation were densely colonized with a few
species of xerophilic fungi (Talaromyces sp. and Eurotium herbariorum) or
Penicillium sp. and Cladosporium sp. Colonization appeared related to the use of
adsorbed organics and the availability of moisture. Price et al. (1994) and Ezeonu et
al. (1994), in laboratory challenge studies, demonstrated that certain types of new
fiberglass insulation were readily colonized by certain species of fungi (e.g.,
Aspergillus versicolor) with resistance to formaldehyde residues as a probable
selection factor.
Armstrong Laboratory (1992) reports that its studies showed complaints of
musty odors and allergic or asthmatic reactions were confined to microbiologically
contaminated buildings. The causes of bioaerosol contamination were (1) poorly
maintained HVAC systems; (2) high space relative humidities; (3) water-soaked
materials, such as ceiling tiles, walls, and carpets; and (4) sick occupants
transmitting viruses in the highly recirculated air systems. The most common
health complaint from bioaerosol contamination was allergic reactions leading to
hypersensitivity pheumonitis, allergic rhinitis, and allergic asthma. Most often,
these symptoms were caused by mold spores or bacteria that had accumulated in
the ventilation systems. For microbiological contamination to occur, three conditions
must be met: (1) the organism must be able to enter the ventilation system,
(2) there must be an amplification site promoting growth to problem levels, and
(3) dissemination must occur. The Armstrong report states that the normal indoor
mold levels average 60 cfu/m3, and normal bacteria levels average 80–100 cfu/m3. It
recommends that indoor mold concentrations in excess of 200 cfu/m3 be considered
to signify unacceptable contamination.
Toxin Production by Fungi
Mycotoxins are secondary metabolites that are produced by strains of some
species of fungi under restrictive environmental conditions, usually during the
stationary growth phase. Although the vast majority of mycotoxin studies have
involved foods, some intoxications [e.g., “atypical farmers lung,” studied by
Emanuel, Wenzel, and Lawton (1975)] appear to involve inhalation of mycotoxincontaining dust and/or spores (Jarvis 1990).
Some fungi commonly found indoors—for example Aspergillus versicolor, A.
parasiticus, A. flavus, Penicillium spp., Fusarium spp., Trichoderma spp. and
Stachybotrys (atra) chartarum—may produce a variety of toxins that might become
airborne (Smith and Hacking 1983; Bisett 1987; Sorenson et al. 1987; Jarvis 1990;
Borgesson, Stollman, and Schnurer 1992; Mattheis 1992; Johanning, Morey, and
Goldberg 1993). Stachybotrys chartarum is the etiologic agent of stachybotryotoxicosis and has been found to produce a potent cytotoxin, satratoxin H (Bisett
1987; Johanning, Morey, and Goldberg 1993). This toxin is a member of the
tricothecene mycotoxin group and is the most active of these mycotoxins
(Johanning, Morey, and Goldberg 1993). Trichothecenes produced by Stachybotrys
chartarum and Trichoderma spp. are potent inhibitors of protein synthesis. Toxic
effects include dermatitis, respiratory irritation and distress, cardiovascular effects
including lowered blood pressure, and immunosuppressive effects (Bisett 1987;
Johanning, Morey, and Goldberg 1993). The intestinal tract is also an important
target organ, and acute poisoning may lead to severe nausea and diarrhea
(Johanning, Morey, and Goldberg 1993). Some of these symptoms were reported for
inhabitants of a building found to be significantly contaminated by Stachybotrys
chartarum (Croft, Jarvis, and Yatawara 1986). Sorenson et al. (1987) later
confirmed the presence of trichothecene toxins within the conidia of Stachybotrys
A review of two buildings reported by Morey (1992) showed that several
occupants in one building had developed asthma or allergic respiratory illness that
appeared to be building-related. Air and surface sampling in the building revealed
high concentrations of Aspergillus versicolor (>20,000 colony-forming units/m3) in
the air, as well as A. versicolor and Stachybotrys chartarum on some contaminated
walls. Because conidia of these species potentially contain sterigmatocystin,
prolonged exposure to and inhalation of high numbers may present a health hazard
(Bisett 1987; Jarvis 1990; Morey 1992; Johanning, Morey, and Goldberg 1993). Our
experiences with buildings colonized by both these species have shown them to have
an anecdotal association with abnormally high incidences of malaise and
absenteeism among occupants. Where toxigenic fungi such as Aspergillus flavus or
Stachybotrys (atra) chartarum are concerned, toxicoses as well as allergenic
responses require consideration. The conditions for toxin production appear to be
restricted in most cases, and the presence of a potentially toxigenic fungus does not
necessarily indicate the presence of the toxin as well.
Production of Volatile Emissions by Fungi
A number of fungi are known to produce volatile metabolites on natural
substrates. Borgesson, Stollman, and Schnurer (1992) studied the growth of six
fungi— Aspergillus candidus, A. flavus, A. versicolor, Penicillium brevicompactum,
P. glabrum, and P. roqueforti—on oat and wheat meals. They found that all species
produced a variety of volatile metabolites and that all species produced 3-methylfuran regardless of substrate. Aliphatic alcohols, ketones, and terpenes appear to be
the predominant volatiles produced by fungi; as many as 50 volatile compounds
have been identified from Aspergillus clavatus alone (Bisett 1987; Borgesson,
Stollman, and Schnurer 1990; Bjurman and Kristensson 1992a; Bayer and Crow
1993). Some of the more commonly identified VOCs of fungi include geosmin,
3-octanone, 2-octen-1-ol, 3-methyl-1-butanol and 3-methylfuran (Bisett 1987;
Borgesson, Stollman, and Schnurer 1992; Mattheis 1992; Bjurman and Kristensson
1992b; Zeringue, Bhatnagar, and Cleveland 1993). The types of volatiles produced
are greatly influenced by the type of medium or substrate on which the fungus is
growing (Bjurman and Kristensson 1992; Bjurman 1993; Nikulin et al. 1993).
Fungi and actinomycetes have been shown to produce a range of VOCs,
including many compounds such as acetone, ethanol, and isopropanol, more
commonly associated with solvents and
cleaning materials (Bayer and Crow 1993).
Fungi and actinomycetes produce a
Bayer and Crow demonstrated that a range
range of VOCs, including many
of fungi isolated from indoor environments
compounds commonly associated with
are capable of producing and emitting these
solvents and cleaning materials.
compounds into the atmosphere when grown
on complex media. At least 26 different
volatile compounds were found to be produced by the fungi in this study, including
known carcinogens such as benzene.
Strom et al. (1994) investigated the production of MVOCs as a means to detect
the occurrence of fungi and bacteria within building constructions. A significant
increase in the concentration of MVOCs was observed in houses with microbial odor
problems, compared with unaffected houses and outdoor air samples. Microbial
analysis of damaged building materials from houses with odor problems showed
highly significant differences from the corresponding material collected from
unaffected houses. Additionally, it was found that MVOCs diffuse through plastic
sheeting used as water vapor barriers. Therefore, these barriers do not prevent the
diffusion of the MVOCs and permit contamination of the indoor air with microbial
Strom et al. identified the representative MVOC compounds that indicate
microbial activity to be 3-methylfuran, 2-methyl-1-propanol, 1-butanol, 3-methyl-1butanol, 3-methyl-2-butanol, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone, 3octanol, 1-octen-3-ol, 2-octen-1-ol, 2-methylisoborneol, geosmin, and 2-isopropyl-3methoxypyrazine. The primary odor-causing compounds are probably geosmin, 2methylisoborneol, and 2-isopropyl-3-methoxypyrazine. These three compounds have
an “earthy” odor. A mushroom-like odor is produced by 1-octen-3-ol and 2-octen-1-ol.
These are thought to be the source of the “musty” odor.
Ezeonu et al. (1994) demonstrated the production of 2-ethyl hexanol,
cyclohexane, and benzene by a mixed fungal population colonizing fiberglass
insulation. Aspergillus versicolor and Chaetomium globosum have both been shown
to produce geosmin, a VOC with a distinct “earthy” odor (Bjurman and Kristensson
1992a,b). Geosmin has also been associated with Streptomyces sp. isolated along
with a number of fungal species from an odor-producing HVAC system (Crow 1993).
Moisture requirements for volatile production by fungi also may be different from
those for growth (Moss 1991; Bjurman and Kristensson 1992a; Nikulin et al. 1993).
The possibility exists that VOCs produced by fungi at one location in a structure
could influence the growth of other fungi at remote sites through dissemination of
these compounds by mechanical ventilation systems. This influence could indirectly
contribute to further degradation of air quality as a result of increased airborne
loading of conidia, sclerotia, or hyphal fragments.
Horner, Morey, and Worthan (1997) performed sampling in an extensively
water-damaged school. The students and teachers were complaining of musty odors
and allergic responses. Cladosporium cladosporidoides dominated all of the outdoor
air samples and was collected in 99% of the indoor air samples. The total
concentrations of the culturable molds were lower indoors than outdoors when the
ventilation system was operating, indicating that airborne exposure to the fungi
indoors was similar to the outdoor exposure. However, dust sampling of the carpet,
air supply louvers, and duct liner surfaces indicated microbial amplification.
MVOCs were also measured, and 2-octen-1-ol was detectable at most of the
sampling locations. MVOCs were not detectable in the noncomplaint or outside
Joki et al. (1993) found that the respiratory symptoms of people living in moldy
houses may be caused by MVOCs. These researchers studied the effects of MVOCs
from Penicillium, Trichoderma viridae and two actinomycete strains, along with
those from Klebsiella pneumoniae lipopolysaccharide on tracheal tissue in vitro.
Trichoderma viridae, Penicillium, and the actinomycete strains showed a tendency
towards ciliostimulation. The effect was similar to the ciliostimulatory effect
brought about by respiratory infections. Joki et al. concluded that the MVOCs could
adversely affect the mucociliary defense in respiratory airways. {
Impact of High Space Humidity
As discussed previously, moisture is a key factor in the growth and amplification
of mold, fungi and other microbes. As a result, problems with these organisms can
be severe in air-conditioned buildings located in humid environments, especially the
southern United States and tropical climes. The accumulation of moisture on or in
the envelope of buildings in these climates is strongly influenced by indoor
temperature and outdoor humidity. Mold growth typically occurs on internal
surfaces of the external walls or floors, since these surfaces are cooled by the airconditioning system to below or near the dew point temperature of humid air
infiltrating into the building envelope (Flannigan and Morey 1996). Moisture enters
the building because of (1) leakage of rain into the wall cavities, (2) movement of
humid air into the interior because of poor building construction, (3) water vapor
diffusion from the humid exterior to the dry interior, and, perhaps most common,
(4) entry through the conventional HVAC system when the supply air fan is
operated while the cooling coil is cycled off.
Overcooling of indoor spaces results in moisture and mold problems in buildings
in climates where the outdoor dew point temperature is at or above about 25(C
(77(F). The problems can become
severe when the internal surface
temperatures drop a few degrees below
Moisture is a key factor in the germination
25(C and the likelihood increases that
of mold, fungi, and other microbes; and
the surface relative humidity will
therefore, problems with these organisms
can be severe in air-conditioned buildings in
exceed 65% (Flannigan and Morey
humid climates because of overcooling of
1996). Ironically, when building
indoor spaces.
occupants feel clammy because of high
space humidity, the typical response is
to lower the space thermostat setting.
The result is that the space cools further, most often increasing the space relative
humidity along with the likelihood of condensation of moisture on supply air ducts,
floors, and other building surfaces.
Moisture problems can also be a function of the occupancy load (Merrill and
TenWolde 1989). High occupant densities, such as those in schools, generally result
in a relatively high degree of moisture release into room air. When there is a
combination of high occupant densities (such as in schools), poor ventilation, and
cold external walls, often moisture, dirt accumulation, and mold growth occurs in
walls and on building surfaces. These can be controlled by proper ventilation with
preconditioned (dehumidified air at room neutral temperature) outdoor air
(Lstiburek 1994).
Fischer (1996) concluded that improved
humidity control, reduced coil condensate,
In eight schools studied by Fischer,
improved humidity control, reduced
and the low (60%) relative humidity
coil condensate, and the low relative
maintained in the supply air ductwork by a
humidity maintained by a DWERS
DWERS helps to avoid microbial problems
helped avoid microbial problems and
and illness in humid climates. Fischer based
his conclusions on a survey of eight schools
investigated. The schools were specifically
chosen because each had experienced serious IAQ problems, had subsequently been
retrofitted with desiccant-based total energy recovery systems, and had since
operated with these systems for at least 2 years. His survey revealed that in each of
the schools, the modifications resulted in a complete and lasting resolution of the
IAQ problems.
Davanagere et al. (1997) evaluated the impact of ASHRAE Standard 62-1989 on
the sensible and latent cooling loads in Florida’s hot and humid climate. ASHRAE
Standard 62-1989 (ASHRAE 1989) raised the minimum outdoor air requirements
for ventilating school classrooms by a factor of 3 over the previous ASHRAE
Standard 62-1981. Davanagere and associates performed an annual building energy
simulation for a protypical school in three Florida cities—Miami, Orlando, and
Jacksonville—analyzing the performance of a conventional HVAC system and
several alternate technologies. The simulation results indicated that the
conventional HVAC system will have problems maintaining relative humidity levels
at or below 60% in Florida schools at the specified ASHRAE ventilation rate of 7.5
L/s (15 cfm/person). The chiller size, energy usage, electrical peak demand, and
operating costs were predicted to significantly increase. The hours above 60%
relative humidity are outlined in Table 1.
The alternate technologies considered in the Davanagere et al. study are shown
in Table 2; those that were predicted to maintain indoor humidity levels below 60%
relative humidity for most of the occupied hours are indicated by a check mark.
Gas-fired desiccant systems will use the least amount of electrical energy of the
pretreatment alternate technologies, but natural gas is required to regenerate the
Table 1. Impacts of ASHRAE Standard 62-1989 on classroom humidity levels
in three Florida cities (Davanagere et al. 1997)
Total hoursb above 60% RH at
Std. 62-1981 ventilation rate
Std. 62-1989 ventilation rate
Std. 62-1981 ventilation rate
Std. 62-1989 ventilation rate
Occupied hoursc above 60% RH at
RH = relative humidity
Standard 62-1981 ventilation rate = 5 cfm (2.5 L/s) per person
Standard 62-1989 ventilation rate = 15 cfm (7.5 L/s) per person.
Total hours = occupied + unoccupied hours.
Total number of occupied hours = 1512 per year.
desiccant wheel. Operating costs should be reduced when thermal energy storage
systems are used. Davanagere et al. concluded that a conventional HVAC system
will not be able to maintain the proper indoor humidity levels and that
pretreatment of the outdoor air with these alternate technologies will provide better
humidity control in the occupied areas.
Baughman and Arens (1996) summarize numerous health-related effects
associated with high and low indoor relative humidity, including mycotoxins and
VOCs produced by fungi. Bayer, Crow, and Noble (1995) investigated schools with
complaints of rashes and respiratory illnesses. The investigation focused on
microbial growth, which was identified in all cases. It concluded that many of the
airborne VOCs appeared to be microbial in origin. Bayer and Downing (1992)
reported on three schools using packaged HVAC equipment that were investigated
and found to have serious humidity problems, even with only small percentages of
intermittent outdoor air supplied to the occupied space.
The Armstrong Laboratory (1992) study cited microbial contamination in nearly
50% of the buildings investigated. Its authors stated that, based on their findings,
carpet, curtains, furniture, and so on can absorb enough moisture at space
humidities greater than 65% to promote microbial growth. At relative humidities
greater than 70%, according to the report, VOCs are emitted at greater rates than
at below 60%. The Armstrong report recommends that buildings be operated to
maintain the space relative humidity between 40 and 60%. This study agrees well
with ASHRAE Standard 621989, which recommends that
space relative humidity be
maintained at between 30 and
Table 2. Alternative technologies to meet
ASHAE Standard 62-1989 in Florida schools
(Davanagere et al. 1997)
Demand-control ventilation
Technologies to pretreat outdoor air
Impact of Low Space
Enthalpy recovery wheels
Gas-fired desiccant systems
100% outdoor air DX units
Although too much airborne
Heat-pipe-assisted cooling coils
moisture (humidity above 70%
relative humidity) can
Chilled-water coils
exacerbate the symptoms of
Chilled-water coils combined with partial
people with asthma and
thermal energy storage
allergies, air that is too dry
(below 30% relative humidity)
Chilled-water coils combined with full
thermal energy storage
can cause eye, nose, and throat
irritation; discomfort for
Baseline systems
contact lens wearers;
Thermal partial energy storage system
nosebleeds; and static electric
shocks (Quinlan et al. 1989).
Thermal full energy storage system
The Armstrong Laboratory
Cold air distribution systems
(1992) report states that relative humidities of less than
Partial thermal energy storage
40% cause physiological effects
Full thermal energy storage
leading to environmental
Liquid refrigerant overfeed system.
discomfort and dissatisfaction.
The symptoms include dry and
sore nose and throat, bleeding
nose, sinus and tracheal irritation, dry scratchy eyes, inability to wear contact
lenses, and dry, itchy, flaky skin. Low relative humidities contribute to an increase
in respiratory illness by weakening the defense provided by the mucous membranes.
This report recommends that relative humidity be controlled between 40 and 60%,
and that humidity control devices be installed in the HVAC systems because
“natural” humidification does not maintain the relative humidity of a building at
40–60% throughout the entire year.
A study conducted by Arundel et al. (1986) concluded that influenza virus
cultivated in human cells survived at the highest rate when exposed to low relative
humidities (20%), survived at a minimum rate at between 40% and 60% RH, and
increased again after exposure to high humidity (70–80%). A plot of the morbidity
from colds and low indoor humidity has been shown by Hope-Simpson (1958) to
have a “high correlation.”
Three different researchers studied the relationship between humidification and
absenteeism (Sale 1972; Ritzel 1996; Green 1974, 1985). Sale and Ritzel studied
controlled populations of kindergartens to determine the relationship between
respiratory illness and space relative humidity. Both studies found that in schools
where the humidity was increased with humidifiers, the absenteeism was 40–50%
lower than in unhumidified schools. They reported a decrease in colds, sneezing,
sore throats, and fever experienced by the children in spaces humidified in winter.
Sale included approximately 500 kindergarten children in the study, investigating
the impact of humidification in the home in conjunction with humidification in the
school. The students were divided into four groups (the rate of absenteeism is in
parentheses): humidification at home and at school (1.3%), humidification at school
only (3.9%), humidification at home only (5.1%), and no humidification (7.1%).
Green (1974) compared the absenteeism in 18 schools, with a total of
approximately 4800 students, for 11 years. Some of the schools were humidified to
greater than 25% and others were not humidified. There was a statistically lower
rate of absenteeism in the humidified schools. He concluded that a possible reason
for the reduction in absenteeism may have been a reduction in disease
Fischer (1996) concluded that the free humidification provided by total energy
recovery systems can maintain the space relative humidity above 30% during all but
the most extreme winter time conditions, and can thereby reduce the incidence of
respiratory illness and absenteeism in classrooms located in colder climates. {
Downing and Bayer (1993) investigated the relationship between ventilation rate
and IAQ in classrooms. Their investigation was conducted in a 2-year-old school in
Georgia that had experienced serious IAQ problems and SBS. Samples were
collected and analyzed for VOCs, formaldehyde, CO2, temperature, and humidity.
Downing confirmed in this study that 15 cfm of outdoor air per student, provided
continuously, was required to maintain CO2 concentrations at levels below 1000
ppm. The recommendation is made that classrooms, both new and existing, be
provided with at least 15 cfm per student of outdoor air on a continuous basis
during school hours. It was found that VOC concentrations exceeded 1000 )g/m3
when only 5 cfm per student was provided, even on a continuous basis, and that the
occupants were dissatisfied with the air quality at these conditions. Tucker (1986)
indicated that this level of VOCs is an indication of potential IAQ problems.
Hydrocarbon levels measured in the classroom were found to be nine times higher
than those measured outdoors when the outdoor air quantities were cycled with the
cooling coil. Indoor hydrocarbon levels were reduced to approximately the outdoor
concentration levels when 15 cfm of outdoor air per student was provided on a
continuous basis and humidity was controlled.
The school investigated by this
study used 3-ton rooftop-packaged
In a Georgia school, when the HVAC system
systems operating at a maximum of
was modified to include a DWERS that
provided a continuous outdoor air supply of
5 cfm per student. The relative
15 cfm per student and controlled the space
humidity exceeded 70% for extended
relative humidity at between 50 and 55%, all
time periods (see Fig. 1), resulting in
complaints related to IAQ — respiratory and
microbial amplification. With the
allergy problems, headaches, and lethargy —
original HVAC system in operation,
there was visible mold growth on
building surfaces, ceiling tiles, and
books. The IAQ complaints and illnesses included respiratory and allergy problems,
headaches, and lethargy. When the HVAC system was modified to include a
DWERS that provided a continuous outdoor air supply of 15 cfm per student and
controlled the space relative humidity at between 50 and 55%, all complaints
regarding IAQ stopped. They have not returned after approximately 5 years of
As discussed previously, Bayer and Crow (1993); Bjurman and Kristensson
(1992b); Borgesson, Stollman, and Schnurer (1992); Nikulin et al. (1993); Strom et
al. (1994); and others documented the emission of a wide range of VOCs and
mycotoxins associated with microbial activity in buildings. These emissions have
been documented in both dry climates (i.e., Sweden) and humid climates. As shown
in the Downing and Bayer (1993) investigation, the measurement of specific VOCs
can serve as an effective marker for identifying microbial activity. According to this
investigation, continuous ventilation may have served to purge the high levels of
VOCs resulting from microbial activity, as well as limit the possibility that VOCs
produced by fungi at one location would enhance the growth of other fungi at other
sites throughout the facility.
ASHRAE Standard 62-1989 (ASHRAE 1989) recommends that indoor CO2 levels
not exceed 1000 ppm for satisfactory occupant comfort. Experimental studies have
demonstrated that outdoor air ventilation of approximately 7.5 L/s will control
human body odor so that about 80% of unadapted people will find the odor level
acceptable. That same level of body odor acceptability occurs at a CO2 concentration
approximately 650 ppm above the outdoor concentration (ASTM 1998; Cain et al.
1983). Bakke (1999) states that “the scientific basis for the CO2-criterion of 1000
ppm is on studies of acceptability of air quality for persons entering the room—that
is, perceptions in non-adapted persons. There is not sufficient or conclusive evidence
for effects on health or productivity when controlled for temperature, humidity and
other pollutants.” He concludes that although the ventilation criterion has been
insufficiently studied, the prevailing ventilation requirements are founded on
experience and include a proper margin of safety.
A number of researchers have used CO2 levels to assess IAQ and calculate
ventilation rates, but incorrect assumptions and misinterpretation of data can lead
to erroneous conclusions about the adequacy of ventilation air and health impacts
(ASTM 1998; Bearg, Turner, and Brennan 1993; Persily 1997; Mudarri 1997;
Persily and Dols 1990). Indoor CO2 concentrations generally are dependent on
occupancy (which may change significantly during the day); changes in occupant
activity levels; and the performance, limitations, and characteristics of the
ventilation system. In addition, measurement of CO2 levels are affected by the
limitations and accuracy of sampling methods and instrumentation, and sampling
locations, frequency, and times.
Inadequate and inefficient ventilation of occupied zones has been associated with
higher CO2 levels and increased frequency of IAQ complaints by many researchers
(Casey et al. 1995; Godish et al. 1986; Rajhans 1983; Salisbury 1986; Skov et al.
1987; Turiel et al. 1983; Wallingford
and Carpenter 1986). Most
Inadequate and inefficient ventilation of
researchers cite the use of the
occupied zones has been associated with
ASHRAE guideline limit of 1000 ppm
higher CO2 levels and increased frequency of
for CO2 (ASHRAE 1989) as a surrogate
IAQ complaints by many researchers.
for a lack of fresh air supply in
occupied spaces. The Ontario Ministry
of Labor (Rajhans 1989) linked CO2 levels and the frequency of occupant complaints
(Table 3) and also set a guideline of 1000 ppm CO2 as an indicator of insufficient
fresh air supply.
The Maryland Public Schools Indoor Air Quality guideline (Maryland State
Department of Education 1987) lists acceptable outdoor air ventilation rates for
different types of spaces in schools to achieve an acceptable level of IAQ by
controlling CO2 levels to 1000 ppm or less (Table 4).
A study by Quinlan et al. (1989) notes that when the indoor CO2 level reaches
1000 ppm, “it is likely that some of the occupants will begin to complain.” These
complaints “are not directly related to CO2, but to an inadequate supply of fresh air
and the resulting increase of various contaminants inside the building. At higher
levels of CO2 a greater number of people will feel uncomfortable.” This study advises
that the CO2 level be maintained at a level below 800 ppm.
Table 3. Ontario Ministry of Labor findings on relationships between
extent of complaints regarding IAQ and CO2 levels and ventilation
rates (Rajhans 1989)
Extent of complaint
CO2 level
Ventilation rate/person
Occasional complaints, esp. with
rise in air temperature
More prevalent complaints
Insufficient makeup air; more
general complaints
Table 4. Maryland’s requirements for outdoor air ventilation rates in
schools (Maryland State Department of Education 1987)
Type of space
Training shop
Music room
Smoking lounge
Conference room
Reception area
Locker room
(playing floor)
Swimming pool
Spectator area
Public restroom
Est. max.
(people/1000 ft2)
Ventilation rate
Special contaminant control systems may be required for processes or functions.
Supplementary tobacco smoke removal equipment may be required.
Higher values may be required for humidity control.
Value given is cfm per water closet or urinal.
Makeup air for hood exhaust may require more ventilation air. The sum of outdoor air
and transfer air of acceptable quality from adjacent spaces should provide an exhaust rate
of not less than 1.5 cfm/ft2.
The Armstrong Laboratory (1992)
report concludes that CO2 concentration is a useful indicator of
inadequate makeup air and that
concentrations above 600 ppm are
the cause of some specific IAQ
irritations, for which these
researchers have excellent
A group of researchers from Armstrong
Laboratory found that CO2 concentrations in
excess of 600 ppm cause significant
physiological effects, such as fatigue,
drowsiness, lack of concentration, and
sensations of breathing difficulty.
correlations. They found that 15–33% of the population will have symptoms from
CO2 exposure at 600–800 ppm, approximately 33–50% will have symptoms at
800–1000 ppm, and virtually 100% will show symptoms at greater than or equal to
1500 ppm. Armstrong Laboratory’s observations indicate that CO2 concentrations
exceeding 600 ppm may result in physiological complaints: fatigue, drowsiness,
difficulty concentrating, and difficulty breathing. The Armstrong researchers
developed a satisfaction model based on data from medical interviews and
questionnaires in 18 buildings. Based on this model and an 80% satisfaction rate,
they calculated that the CO2 levels should not exceed 600 ppm, and that when the
CO2 concentration was 1000 ppm a 42% satisfaction rate was predicted. Based on
this model, the report recommends that CO2 concentrations not exceed 600 ppm, a
level that can be achieved with a minimum of 40 cfm per person.
Bakke and Levy (1990) investigated the IAQ in six kindergartens during the
winter in Norway. They found a correlation between the highest CO2 levels and
highest relative humidity and the most frequent complaints of “dry air” and eye
irritation (which is usually associated with dry air). The complaints of dry air were
most frequent at the kindergartens with the lowest ventilation rate and the highest
relative humidity. Bakke and Levy conclude that high CO2 levels and high relative
humidity may indicate that a building has a ventilation rate that is too low.
Seppanen, Fisk, and Mendell (1999) reviewed available literature for the
association of ventilation rates and CO2 concentrations with health or perception
outcomes. were not able to determine a clear threshold value for CO2 levels below
which further reductions in concentration were not associated with further
decreases in SBS symptoms. However, 7 of 16 studies suggested that the risk of
SBS symptoms continued to decrease with decreasing CO2 concentrations below 800
Correlations between pupils’ health and performance and CO2 concentrations in
classrooms were determined by Myhrvold, Olsen, and Lauridsen (1996). These
researchers conducted physical measurements of CO2 and other indoor air
parameters, distributed questionnaires, and administered a Swedish Performance
Evaluation (SPES) test to students in eight schools in Sweden. During the sampling
days of this study, they found the following CO2 exposure levels among the students:
% of students
CO2 level
0–999 ppm
1000–1499 ppm
1500–4000 ppm
These researchers divided the reported health symptoms into two categories:
(1) headache, dizziness, heavy-headedness, tiredness, concentration difficulties, and
unpleasant odor; and (2) throat irritation, nose irritation, runny nose, coughing fits,
short-windedness, runny eyes, and irritations of the upper airway. The SPES test
was administered to students between the ages of 11 and 20 to measure
performance. Since age proved to be a confounder, only the results from pupils 15
years old or older were used in the statistical data interpretations. Strong
correlations were found between CO2 and the first category of health symptoms,
particularly when the CO2 levels were 1500 ppm or greater. Weaker correlations
were found between CO2 levels and the second category of health symptoms.
Myhrvold, Olsen, and Lauridsen also showed a correlation between CO2
concentrations and poor performance but were not able to show statistically
significant differences between the three CO2 concentration groups.
Ligman et al. (1999) reported on PM10 and PM2.5 data collected in U.S. elementary
and secondary schools. The overall results are presented in Table 5. In general, the
airborne particulate matter levels were higher in schools than in office buildings
and were in higher concentrations in the schools than in the ambient outdoor air.
Table 5. Particulate matter levels in schools (Ligman et al. 1999)
Type of
Location (state)
Sample results
(geometric mean,
PM10 indoor
PM2.5 indoor
PM10 outdoor
PM2.5 outdoor
PM10 indoor
PM2.5 indoor
PM10 outdoor
PM2.5 outdoor
Meyer et al. (1999) conducted an epidemiological study that suggested an
association between building-related symptoms and dust with a high inflammatory
potential. Seventy-five schools in Copenhagen, Denmark, were included in a crosssectional epidemiological study. The building-related symptoms analyzed were eye
irritation, nasal irritation, nasal congestion, throat irritation, flushing or irritated
facial skin, headache, fatigue, and lack of concentration. Symptom frequencies were
grouped in two categories: (1) “never/seldom” plus “now and then,” and (2) “several
times a week” plus “daily.” The inflammatory potential of dust collected from floors,
surfaces, and exhaust ducts was tested in an in vitro bioassay with human lung
epithelial cells. For all eight building-related symptoms, the researcher saw a
significant increase in symptom prevalence with increasing exposure index. {
The quantity of air in a modern building is highly dependent upon the operation
of its HVAC system. HVAC systems are designed to mix a given amount of outdoor
air with some amount of recirculated air, condition this mixture, and distribute it to
the occupied space (Morey 1988). The amount of recirculated air in the mixture
varies from system to system and building type to building type. In the U.S. service
sector (commercial, institutional, and government buildings), the estimated energy
consumed for ventilation is about one-fourth of the total service-sector building
energy use (Orme 1998). Climate has a significant impact on the amount of energy
consumed to condition ventilation air. In the hot and humid climate of Miami,
removal of moisture from ventilation air consumes 86% of the energy usage in
buildings (Seppanen, Fisk, and Mendell 1999). Therefore, energy-efficient
technologies that provide optimum indoor air environments are critically needed.
Large buildings typically use chilled water systems with large central air
handling systems that, if sized correctly, are capable of conditioning the outdoor air
quantities recommended by ASHRAE Standard 62-1989. A conventional variableair-volume (VAV) system distributes approximately 1.5 cfm/ft2 of 56(F air, of which
typically 20% is outdoor air and 80% is recirculated air. However, it has been shown
that even if 15 cfm per person of outdoor air is provided to the central air handling
system, it is possible to have poor air circulation within individual zones. The lack
of circulation causes contaminant buildup either continuously or intermittently at
low-flow (part-load conditions) within a typical VAV system (Meckler 1992). For this
reason, ASHRAE recommends increasing the outdoor air quantity delivered to the
VAV system beyond 15–20 cfm per person (the Z factor) to ensure adequate outdoor
air to all zones (Brady 1996).
Seppanen, Fisk, and Mendell (1999) reviewed literature and determined that a
significant association has been reported between lower ventilation rates (below the
normally encountered range of 2.5–30 L/s per person) and increased health effects
and worsened air quality perception. Of 31 studies of buildings with ventilation
rates below 10 L/s per person, 27 reported a significant worsening of health or
perceived IAQ. Mendell (1993), in a review of six ventilation and air quality studies,
reported a consistent association between higher SBS symptom prevalence and
outdoor air ventilation rates below 10 L/s per person. In a study in Swedish schools,
Walinder et al. (1998) measured nasal patency and biomarkers for allergic reactions
associated with ventilation rate (ranging from 1.1 to 9 L/s per person). This study
did not find a significant association, which suggested a pollutant source in the
schools buildings, such as emissions from building materials or microbial emissions
from moisture-damaged structures.
Seppanen, Fisk, and Mendell (1999), using on a calculated relative risk of 1.1
determined by Jaakkola and Miettinen (1995), estimated that a 5 L/s per person
increase in ventilation rate in U.S. office buildings would reduce the proportion of
occupants with frequent upper respiratory symptoms from 25% to 16%. Similarly,
they calculated that a 5 L/s person decrease in ventilation rate would increase the
proportion of occupants with frequent upper respiratory symptoms from 25% to
40%. Their predictions suggest that increasing the ventilation rate in schools may
have a significant impact on chronic and acute upper respiratory symptoms in
children, so long as the humidity is controlled within acceptable levels.
In large buildings, an HVAC system may serve to transport microorganisms from
the locus of contamination (e.g., a humidifier or moist insulation) to the vicinity of
sensitive occupants (Morey 1988, 1992; West and Henson 1989; Turner et al. 1993,
1996a; Price et al. 1995; Batterman and Burge 1996). For this and other reasons
discussed previously, both outdoor air ventilation and humidity control are essential
issues in the relationship between HVAC systems and IAQ.
Innovative designs have been employed in large buildings to ensure adequate
humidity control and outdoor air delivery with traditional VAV systems. For
example, a cold air distribution system can be applied so that all of the air
processed by the VAV air handling system is outdoor air (Meckler 1992). Bayer and
Downing (1991) investigated a 30-story
building that successfully used a total energy
The use of innovative HVAC
recovery preconditioning unit to provide a
designs in large buildings can
constant supply of outdoor air to each VAV
ensure adequate humidity control
system on a floor-by-floor basis. This system
and outdoor air delivery with
ensured that approximately 20 cfm of outdoor
traditional VAV systems.
air per person was delivered even as the return
air percentage varied between 80 and 20% at
the VAV air handling system. Various contaminants measured— including VOCs,
CO2, formaldehyde, and others— confirmed the effectiveness of this design
The vast majority of facilities constructed each year in the United States are
considered small buildings (i.e., three stories or less). These facilities—which
include small offices, schools, restaurants, municipal buildings, and nursing
homes—typically use packaged HVAC equipment because of its low cost, compact
size, and ease of installation and maintenance. Unfortunately, packaged equipment
is far more limiting with respect to outdoor air delivery and humidity control
capability than are the large chilled water systems used in large buildings.
Packaged systems have been designed to provide only a modest percentage of
outdoor air on an intermittent basis in order to minimize cost. When they are
operated with continuous outdoor air or an increased percentage of outdoor air,
comfort and humidity control is often lost (Downing and Bayer 1993; Henderson and
Rengarajan 1996).
As a result, small facilities often are not designed and/or operated in accordance
with ASHRAE 62-1989. Besides the inability of packaged equipment to
accommodate increased outdoor air ventilation rates and maintain space comfort,
reasons include the perception that there is a significant first-cost premium,
potentially high operating costs, and a general ignorance of IAQ on the part of many
building owners and installation contractors. Many small buildings are constructed
on a design/build basis, with the installing contractor (not a consulting engineering
firm) completing the mechanical design with the primary objective of minimizing
the HVAC system installation cost.
Until recently, few economical options have been available to design engineers
and contractors that combine effectively with conventional packaged HVAC
equipment and enable it to perform as required while accommodating the
recommendations made by ASHRAE 62-1989 (i.e., increased outdoor air provided on
a continuous basis to the occupied space). As a result of these and other factors,
many small buildings have been designed with an inadequate supply of outdoor air
being provided on an intermittent basis. Two of the most common design schemes
are the following:
• Using rooftop packaged equipment that provides approximately 10–15% outdoor
air. In very cold or hot/humid climates, the fans in these units are typically cycled
with the heating source (burner) or cooling source (coil), to avoid dumping of cold
air during the heating mode and poor humidity control during the cooling mode.
• Using rooftop packaged equipment or split systems with little or no outdoor air
being provided to the space by the HVAC equipment. Infiltration through door
and building leaks is assumed to deliver “adequate” outdoor air.
As the research summarized in this paper indicates, compromising either the
continuous supply of outdoor air or proper humidity control can result in serious
IAQ problems, especially in school facilities. During the air-conditioning season, the
intermittent use of ventilation causes extreme variation in indoor contaminant
concentrations and space relative humidity, which may result in absorption of water
into porous materials (West and Henson 1989; Morey and Williams 1991). The
availability of both water and nutrients controls microbial growth in porous
insulation. Water condensation alone is not a problem as such, but if the
temperature is sufficient and organic material is present, viable fungal spores will
have an opportunity to germinate and proliferate (Morey and Williams 1991).
Fischer (1996) concluded that desiccant-based recovery systems can be easily and
cost-effectively integrated with conventional packaged HVAC equipment to provide
the increased outdoor air quantities and humidity control recommended by
ASHRAE 62-1989 and shown to be critical by the research summarized in this
paper. In his investigation, Fischer
summarizes first-cost information provided
by the design engineers for seven different
Desiccant-based energy recovery
systems, dehumidification, and cooling
school projects which demonstrates that
systems and various other overcooling
the ASHRAE 62-1989 recommendations
with reheat approaches can dehumidify
can be accommodated with a cost-effective
the outdoor air stream provided to the
occupied space or to the intake of the
mechanical design. In each project, the
conventional HVAC equipment. Thus,
benefits of improved IAQ were found to far
downsized packaged equipment linked
outweigh any incremental investment by
with a preconditioning system can be
cost-effective means of accommodating
the engineers, owners, and occupants
the ventilation and humidity control
required to incorporate the required
needs recommended by ASHRAE.
desiccant-based preconditioning
Investigations by Bayer and Downing (1991), Coad (1995), and Downing and
Bayer (1993) all support the need to improve the performance of packaged HVAC
equipment through preconditioning the outdoor air supplied to a building so that
the latent load (humidity) is decoupled from the sensible (temperature) load that is
effectively handled by the packaged HVAC equipment. The sensible load can then
be easily managed, usually with smaller-capacity packaged equipment, using simple
thermostat controls and on a room-by-room basis if desired. Such an arrangement
provides improved comfort and energy efficiency and is probably the most costeffective way of accommodating the ASHRAE 62-1989 guidelines.
Numerous articles and manufacturer case histories are available to demonstrate
how technologies such as desiccant-based energy recovery, dehumidification, and
cooling systems and various other overcooling with reheat approaches have been
applied successfully to dehumidify the outdoor air stream provided directly to the
occupied space or to the intake of the conventional HVAC equipment (HPAC 1996a,
1997; Gatley 1993; Turner et al. 1996b). These approaches have shown that
downsized packaged equipment linked with a preconditioning system can be costeffective to install and operate and can accommodate the ventilation and humidity
control needs recommended by ASHRAE. In addition, several desiccant system
design approaches have been shown to deliver air through the ductwork that is well
below saturated conditions, operate with dry cooling coils, remove contaminants
from the outdoor air and kill bacteria, all of which are beneficial to improving indoor
An alternative approach was used by one engineering firm in a south Florida high
school (HPAC 1996b). The school board requested that the outside air flow rate be
lessened to 5 cfm per person so that the operating costs and humidity control needs
would be reduced. The problem with this approach, as was recognized by the
engineering firm, was that lessening the amount of fresh ventilation air probably
would lead to costly maintenance and operations problems, and to occupant health
and comfort problems. The engineering firm chose to use increased filtration, rather
than innovative ventilation technology, applying the Indoor Air Quality Procedure
in ASHRAE Standard 62-1989. Eighty-five percent efficiency particle filters and
80% carbon-absorbing gaseous removal filters were installed. The suppliers of the
filters were required to provide written documentation that the filtration devices
would provide the equivalent IAQ that would be achievable with increased
quantities of outside air, documenting compliance with ASHRAE 62-1989. The
report does not present longitudinal air testing data in the school to prove the
maintenance of adequate indoor air quality in the school.
Wheeler and Abend (1991) examined the occupancy and operational characteristics of typical Maryland public schools. They then constructed a model to assess
alternate HVAC design strategies and concepts that would minimize the adverse
energy consequences of the ventilation requirements in ASHRAE Standard 62-1989.
At maximum occupancy, this standard recommends an outdoor air ventilation rate
of 0.75 cfm per ft3 of floor space. Wheeler and Abend list the environmental
contaminants of interest in a classroom setting to be odorous bioeffluents,
microorganisms, and VOCs. The major HVAC system objectives in a classroom are
low initial and operating costs; thermal comfort; humidity control; pathogen
removal; and odor dilution. These authors propose using a conventional variable air
volume (VAV) system with fan-powered, series arrangement terminals. The air
supply to the room would be constant, and recirculated air would be filtered.
Wheeler and Abend also consider displacement ventilation from floor to ceiling to be
a promising alternative approach. When the model was used to compare these
alternative technologies with the commonly used unit ventilators that are
ventilation-only systems, the finding was that the alternative technologies were
Energy recovery ventilators (ERVs) were installed in two classrooms in two
schools in Nevada (a hot, arid climate) to increase the ventilation rates
(Shaughnessy et al. 1998). The ventilation rates of outdoor air prior to installation
of the ERVs were only 1.4–4.4 cfm per occupant. The ERVs boosted the outdoor air
ventilation rates in the classrooms to approximately 21 cfm per occupant. The CO2
levels prior to installation of the ERV were consistently above 1000 ppm and
occasionally exceeded 5000 ppm. In the classrooms, average CO2 concentrations
were reduced to below 1000 ppm with the ERVs operating. Concentrations of total
VOCs averaged less with the ERVs operating, but were highly dependent on source
and activity. Shaughnessy et al. found no correlations between the operation of the
ERVs and bioaerosol levels and airborne particle concentrations. In the hot, arid
climate, bioaerosol concentrations were very low both indoors and outdoors, and
differences between the ventilation conditions were impossible to distinguish. A
total energy balance on each of the ERV systems indicated a negative energy usage
impact, probably as a result of to the climate. {
Even though IAQ is perceived to be important for the learning ability of students
(Daisey and Angell 1998), there have been few good scientific, statistically sound
studies of school IAQ and its impact on the learning ability of students. Romm
(1994) and Romm and Browning (1994) have documented that buildings and offices
designed or renovated to reduce energy use and indoor pollution boosted worker
efficiency by increasing output, decreasing errors, and improving attendance. Romm
looked for a similar result in schools but found that there are virtually no environmentally sustainable schools and few studies on the productivity consequences of
energy-saving measures in educational facilities. Lundin (1999b) found covariance
among students’ atopic sensitivities, IAQ, the physical environment, and the study
environment. He suggests that the combination of a bad physical environment and a
bady study situation may be a determining factor in symptom frequencies.
McLoughlin et al. (1983) conducted a series of studies to clarify the relationship
between allergies and school performance and behavior. Although he was not able to
demonstrate a direct link between allergy and allergy treatment and academic
performance, he was able to show that there was a relationship between respiratory
problems and listening and attention. He found that eustachian tube disfunctions
were related significantly to academic performance and behavior. There are also
studies linking specific environmental conditions, such as light, noise, or room color,
to student performance (Lytton 1997).
Subjective perception of impaired mental performance due to poor IAQ was
reported by 21% of 627 Swedish secondary school pupils answering a postal
questionnaire (Smedje, Norback, and Edling 1996). The subjective data was paired
with exposure measurements in 28 classrooms. Reports of impaired performance
were more common in schools with lower air exchange rates, higher relative
humidities, and higher concentrations of respirable dust, formaldehyde, VOCs, and
total bacteria or molds. A relationship was demonstrated between subjective reports
of impaired mental performance, measured indoor air pollutants, and low air
exchange rate.
In a study of elementary schools in a Canadian school district, Landrus and Axcel
(1990) found that children with allergies were disproportionately in the belowaverage category of academic achievement. They found that for a group of 366
children identified by their teachers as having asthma, allergies, or environmental
sensitivity, there was a significant association between clay, odorous markers,
wallpaper paste, and sand or water centers and a higher frequency of symptoms. In
this same study, 540 children not identified by their teachers as having asthma,
allergies, or environmental sensitivity nevertheless had significant symptom
associations with inks, clay, and odorous markers. While the frequency of symptom
occurrence was linked to exposure to these materials, no causal relationships were
These studies provide anecdotal evidence that healthful and well-lit schools may
result in higher academic achievement. However, the complexity of measuring
academic performance and understanding how it is achieved challenges claims of
direct causal links.
Three different researchers studied the relationship between humidification and
absenteeism (Sale 1972; Ritzel 1996; Green 1974, 1985). Sale and Ritzel studied
controlled populations of kindergarteners to determine the relationship between
respiratory illness and space relative humidity. In both studies, in the schools
where the humidity was increased with humidifiers, absenteeism was 40–50% lower
than in unhumidified schools. The schools reported a decrease in colds, sneezing,
sore throats, and fever experienced by the children in spaces humidified in winter.
Sale included approximately 500 kindergarten children in the study, investigating
the impact of humidification in the home in conjunction with humidification in the
school. The students were divided into four groups (the rate of absenteeism for each
group is given in parentheses): humidification at home and at school (1.3%),
humidification at school only (3.9%), humidification at home only (5.1%), and no
humidification (7.1%).
Green compared the absenteeism in 18 schools, a total of about 4800 students, for
11 years. Part of the schools were humidified to greater than 25%, and others were
not humidified. There was a statistically lower rate of absenteeism in the
humidified schools. He concluded that a possible reason for the reduction in
absenteeism may have been a reduction in disease transmission.
Fischer (1996) compared the actual cost premium associated with accommodating
ASHRAE Standard 62-1989 recommendations in school facilities with the costs for
the same facility designed to provide only 5 cfm per student of outdoor air without
controlling the indoor relative humidity to between 60 and 30%. This investigation
concluded that cost premiums associated with compliance with ASHRAE 62-1989
recommendations ranged from $62 to $205 per student, and averaged $95 and $142
for the single-wheel total energy recovery system (TERS) and the dual-wheel
desiccant-based total energy recovery system (DWERS) approaches, respectively
(Table 6). Fischer concluded that the cost savings and cost avoidance associated
with the benefits likely to be recognized from providing a desirable IAQ in the
school environment would justify this additional expenditure.
Fischer also surveyed school operators to quantify legitimate cost savings and
cost avoidance numbers (see Table 6) to support the conclusion that the payback
period associated with providing a desirable IAQ may be very short. He reported
that many of the benefits listed would be recognized year after year, whereas the
cost associated with providing the desired IAQ is a one-time expense if energy
recovery is used to offset the added energy requirements. The projected benefits—
which included reductions in absenteeism, substitute teachers, and health care
costs—quickly exceed the initial expense associated with the improved indoor
Hardin, in personal communication, estimates the cost to the state of Washington
for poor humidity control in schools in billions of dollars for structural damage
alone. Schools are not the only structures with billions of dollars with structural
damage due to poor humidity control in Washington State. Hardin also estimates
that there are billions of dollars of damage to multifamily housing.
The U.S. Environmental Protection Agency in partnership with NAESCO (a trade
association representing energy service companies) has demonstrated the
integration of IAQ improvements and energy efficiency upgrades to schools using
“performance contracts” (Redding and Harrison 1999). Using this approach schools
can finance capital upgrades, which improve IAQ by upgrading schools HVAC
systems to meet the ventilation recommendations of ASHRAE Standard 62-1989,
through contracts that are repaid from the utility and maintenance savings realized
as a result of new equipment, systems, and controls. Redding and Harrison
estimate, based on a five-school demonstration project, that the energy savings will
average 407,200 kWh per school and that costs will average $535,300 per school.
Table 6. Cost vs benefit comparison for providing desirable IAQ in schools
Added costs for desirable IAQ
Case 1: Hot, humid climate
DWERS approach: $142/student
Case 2: Moderately humid/cold
TERS approach: $95/student
DWERS = dual-wheel desiccantbased total energy recovery system
TERS = single-wheel total energy
recovery system
Assumes the use of the dualwheel, total energy recovery
preconditioner directly to and from
each occupied area, decoupling the
outdoor air load from space load,
which is handled by a typically 2ton conventional HVAC.
Added cost reflects increase in
overall mechanical cost of either
the DWERS or TERS approach
providing 15 cfm/person of outdoor
air (as compared with only
5 cfm/person with a conventional
HVAC) and continuously
controlling space relative humidity.
Assumes the use of a single-wheel
energy recovery preconditioner
ducted to space or to the return air
side of a conventional HVAC unit.
Benefits from maintaining desirable IAQ
• Improved effectiveness
of the learning process
Impacts on comprehension, alertness,
drowsiness, allergies,
respiratory illness
• Reduced absenteeism
Funding increase based on
reduced absenteeism
Significant $/ student
Savings due to fewer
substitute teachers
Health care savings,
reduced doctor visits
• Avoided property
Carpet replacement in a
typical school
Ceiling tile replacement in
a typical school
Partial book replacement
• Reduced maintenance
Doubled time between
filter changes
• Avoided remediation
Avoided duct cleaning,
facility IAQ investigation,
legal expenses
Significant $/ student
There are few reported estimates of the magnitude of productivity gains in
schools from improved IAQ, but there are a few estimates on the productivity gains
in the total building stock in the United States (Fisk and Rosenfeld 1997). Based on
these data, Fisk and Rosenfeld estimate that the United States can achieve
potential annual savings and productivity gains of $6–$19 billion from reduced
respiratory disease, $1–$4 billion from reduced allergies and asthma, $10–$20
billion from reduced SBS symptoms, and $12–$125 billion from direct improvements
in worker performance that are unrelated to health. They calculate that the
potential financial benefits of improving U.S. indoor environments exceed costs by a
factor of 18 to 47. These estimates justify changes in building code components
pertinent to indoor air, such as prescribed minimum ventilation rates and minimum
air filtration system efficiencies; in school, company, and institutional policies
related to building and school design; in operation and maintenance practices; and
in staff selection and training. {
This investigation makes clear that more research is justified to investigate the
specific causes of IAQ problems within schools and to quantify the specific benefits
that are recognized from providing a desirable indoor air environment. Given that
the General Accounting Office concluded that one in five schools has IAQ problems,
and given that thousands of schools are slated for construction or renovation within
the next 5 years, the need to identify simple, effective, energy-efficient ways of
resolving these IAQ problems is both obvious and significant.
Fortunately, as shown by this investigation, much credible research has already
been conducted. Based on these scientific data, it can be concluded that most IAQ
problems can be avoided (or resolved) by providing an adequate amount of outdoor
air on a continuous basis, controlling space relative humidity so that it seldom
exceeds approximately 60% or drops below approximately 30%, and using a level of
outdoor air filtration efficiency necessary to prohibit most mold spores and fungi
from entering the HVAC system.
The research conducted to date
confirms that both proper outdoor
air ventilation and humidity control
are necessary. Too often in practice,
one is obtained at the expense of the
other. Packaged systems that
provide the outdoor air volume only
when the coil is energized improve
humidity control but allow indoor
contaminants to build to
unacceptable levels. The same
equipment can be operated with the
supply fan running continuously
and with an outdoor air damper
adjusted to provide the required
One in five schools has IAQ problems, and
thousands of schools will be built in the next
5 years. How can we resolve these problems in
existing schools and prevent them in new ones?
Most IAQ problems can be avoided or resolved
providing an adequate amount of outdoor
air on a continuous basis,
controlling space relative humidity so that
it seldom exceeds approximately 60% or
drops below approximately 30%, and
using a level of outdoor air filtration
efficiency necessary to prohibit most mold
spores and fungi from entering the HVAC
quantity of outdoor air, but humidity control is lost, especially at part-load
conditions. Fortunately, proven and cost-effective system solutions exist that allow
satisfaction of both the continuous ventilation and the humidity control objectives
while they provide a central location for effective outdoor air filtration, which can be
easily accessed for routine maintenance.
In summary, the research identified as part of this investigation provides the
basis for the formation of a simple hypothesis: Most IAQ problems in school
facilities can be avoided by (1) providing adequate outdoor air ventilation on a
continuous basis (15 cfm per student), (2) controlling the space relative humidity
between 30 and 60% and (3) providing effective particulate filtration of the outdoor
It is recommended that a research project be initiated to analyze a statistically
significant number of existing school facilities, comparing those constructed with
conventional HVAC system approaches that do not provide simultaneous,
continuous ventilation and humidity control, with schools designed to include
systems that meet the ventilation, humidity control, and filtration criteria in the
previous paragraph. If our stated hypothesis is correct, the analysis we recommend
should show very acceptable IAQ at the schools designed and operated to conform to
ASHRAE Standard 62-1989 recommendations, and very few IAQ complaints by the
occupants. Conversely, the schools that do not conform to the ASHRAE IAQ
standard should show much higher levels of indoor air contamination and microbial
activity and a much higher level of dissatisfaction with regard to IAQ among the
If the recommended research is completed, and assuming the stated hypothesis is
confirmed, valuable direction would be provided to school officials, architects, and
consulting engineers responsible for schools scheduled for construction or
renovation in the future, as well as those faced with resolving the many IAQ
problems that currently exist in school facilities. {
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