Health Hazard Evaluation Report 2017-0030-3277 Page 1

Evaluation of Indoor Environmental Quality 

Concerns in an Elementary School

HHE Report No. 2017-0030-3277

May 2017

Shilpa Gowda, MD, MPH

Leonard Zwack, ScD

Gregory A. Burr, CIH

U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Page 2 Health Hazard Evaluation Report 2017-0030-3277

Contents

Highlights...............................................i

Abbreviations ..................................... iii

Introduction......................................... 1

Methods ............................................... 1

Results .................................................. 3

Discussion ............................................ 8

Conclusions........................................ 11

Recommendations............................. 11

Appendix A .........................................13

Appendix B......................................... 17

References.......................................... 21

Acknowledgements........................... 27

The employer is required to post a copy of this report for 30 days at or near the 

workplace(s) of affected employees. The employer must take steps to ensure 

that the posted report is not altered, defaced, or covered by other material.

The cover photo is a close-up image of sorbent tubes, which are used by the HHE 

Program to measure airborne exposures. This photo is an artistic representation that may 

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2017-0030-3277 Page i

We evaluated indoor 

environmental quality in an 

elementary school building. 

We saw no widespread mold 

or water damage. Carbon 

dioxide levels were high in 

some classrooms, meaning that 

the ventilation did not provide 

enough outdoor air throughout 

the school day. Some symptoms 

reported by employees 

have been associated with 

inadequate ventilation; 

these types of symptoms are 

also common in the general 

population. Cancer and other 

medical conditions reported by 

some employees are not related 

to exposures in the school. We 

recommended a comprehensive 

ventilation assessment.

Highlights of this Evaluation

The Health Hazard Evaluation Program received an employee request from an elementary 

school. Employees were concerned about a perceived high incidence of cancers and other 

medical conditions and a possible association with the school’s indoor environmental quality.

What We Did

● We looked for moisture, water damage, and mold.

● We measured carbon dioxide, temperature, and relative humidity and looked at the

ventilation systems in the building.

● We interviewed 89 employees. We asked about

their work, medical history, and work-related

health concerns.

● We participated in a town hall-style meeting at

the school at the end of our visit. We presented

our initial findings and answered questions.

What We Found 

● We found no widespread areas of current water

leaks or wet materials in the building.

● All of the classroom unit ventilators appeared in 

good condition. We saw no microbial

contamination in the units we checked.

● Carbon dioxide levels were high in some

classrooms. This means that the ventilation did

not provide enough outdoor air throughout the

work day.

● Temperatures in the classrooms and offices were 

within the recommended thermal comfort

guidelines, and relative humidity levels were

below 65%, and generally between 35% and 50%.

● We saw scented air fresheners in use in a few

interior locations, broken or disconnected exterior

roof drains, and debris in an exterior dry well. 

● Of the 89 employees interviewed, 22 reported symptoms that included headache and

upper respiratory symptoms. These nonspecific symptoms are commonly reported in

the general population and can occur in buildings with poor ventilation.
Page ii Health Hazard Evaluation Report 2017-0030-3277

What the Employer Can Do

● Hire a licensed professional mechanical engineer to assess the ventilation systems.

● Repair broken or disconnected roof drains, clean debris from the dry well, and 

discourage the use of air fresheners, scented candles, or potpourri.

● Encourage employees to report symptoms that they are concerned about to their 

healthcare providers. 

What Employees Can Do

● See an occupational medicine physician about health problems that you are concerned 

may be related to work.

● Tell building managers when the ventilation system is not working properly.

● Recognize that some symptoms may not have a medical diagnosis.

● Learn about things you can do to reduce your risk of cancers.
Health Hazard Evaluation Report 2017-0030-3277 Page iii

Abbreviations

ANSI/ASHRAE American National Standards Institute/ASHRAE 

CO2 Carbon dioxide 

HEPA High efficiency particulate air 

IEQ Indoor environmental quality 

NIOSH National Institute for Occupational Safety and Health

ppm Parts per million 

RH Relative humidity 
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Health Hazard Evaluation Report 2017-0030-3277 Page 1

Introduction

The Health Hazard Evaluation Program received a request from three employees at an 

elementary school. The employees perceived an excess of cancer, Parkinson disease, upper 

respiratory disorders, and allergies among school employees since the 1980s. Twelve 

female employees reportedly had been diagnosed with breast cancer during this time frame. 

The requestors were concerned about an association of these diagnoses with the indoor 

environmental quality (IEQ) in the building. 

In December 2016, we spoke by telephone with the requestors about their health concerns. 

We were able to determine that no excess of or unusual distribution of cancer existed among 

employees. We also were able to determine that no potential exposures in the school would 

cause the reported cancers. 

During a January 2017 site visit, we met with the school principal, other school managers, 

the teachers’ union representatives, and building maintenance personnel to discuss the 

request. We also conducted an environmental and health assessment. At the end of that 

visit, we met with about 40 school employees to present our findings and answer questions. 

Additionally, we sent letters summarizing our preliminary recommendations to employer and 

employee representatives in February 2017.

The school operated in a predominantly single-story masonry building, which was finished 

around 1955. Fifty elementary school employees, including faculty and staff, 30 district 

administrators; and 9 other district employees worked there at the time of our evaluation; 

400 students attended the school.

Methods

Our objectives for this evaluation were to: 

1. Identify if the building had a mold or other IEQ problem

2. Determine to what extent employees were reporting work-related health effects 

Prior Indoor Environmental Quality Consultant Reports

We reviewed two IEQ-related consultant reports for work done in 2015 and 2016. 

Building Walk-through Survey

We toured the entire building, including classrooms, multipurpose areas, library (referred to 

as the IMC), art room, gymnasium, and administrative offices for the school and the school 

district administration, which is also housed in the building. We also examined areas in the 

school not readily accessible to teachers and students, such as a basement storage area, the 

roof, and storage areas used by the school district staff. 
Page 2 Health Hazard Evaluation Report 2017-0030-3277

We visually assessed the school for potential mold contamination. We also used the following 

instruments to check for the presence of hidden moisture or water damage:

● A FLIR TG165 imaging infrared thermometer. We used this direct-reading device to 

identify potential moist or water-damaged areas in surfaces such as walls, floors, and 

ceilings. It uses infrared thermal imaging technology to react to temperature differences 

to identify dry and wet materials, even materials that are not readily visible, such as 

behind drywall or above a suspended ceiling.

● A TRAMEX Moisture Encounter Plus nondestructive moisture meter. This handheld direct-reading device can measure the interior wall moisture levels. We used 

the moisture meter to confirm if suspected moist areas identified by the infrared 

thermometer were actually moist.

We measured carbon dioxide (CO2), temperature, and relative humidity (RH) in classrooms 

and multipurpose areas over 2 school days with calibrated TSI Q-TrakTM Indoor Air Quality 

monitors. We selected classrooms on the basis of their location and type of ventilation 

(either unit ventilator or forced-air). We compared indoor and outdoor CO2 concentrations 

to determine if indoor occupied spaces were adequately ventilated [ANSI/ASHRAE 2013]. 

Carbon dioxide is a normal constituent of exhaled breath and can be used as an indicator 

of whether enough outdoor air is being introduced into an occupied space to maintain body 

odors to an acceptable level. Indoor CO2 concentrations no greater than 700 parts per million 

(ppm) above outdoor CO2 concentrations will satisfy a substantial majority (about 80%) of 

visitors [ANSI/ASHRAE 2016].

We measured temperature and RH because these characteristics can affect how employees 

perceive their indoor environment. We compared the temperature and RH levels to American 

National Standards Institute/ASHRAE (ANSI/ASHRAE) thermal comfort guidelines [ANSI/

ASHRAE 2013]. The ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions 

for Human Occupancy, specifies conditions in which 80% or more of the occupants would 

be expected to find the environment thermally comfortable [ANSI/ASHRAE 2013]. Several 

factors affect thermal comfort including air movement, operative temperature, relative 

humidity, clothing levels, and an individual’s work activities. A thermal comfort tool 

developed by the Center for the Built Environment allows comparison to the ANSI/ASHRAE 

criteria and is available at http://comfort.cbe.berkeley.edu/. The ASHRAE (ANSI/ASHRAE) 

thermal comfort guidelines recommend RH be maintained below 65%, and the U.S. 

Environmental Protection Agency recommends that RH be maintained below 60% (ideally 

30%‒50%) to prevent mold growth. Very low RH levels may contribute to dry and irritated 

mucous membranes of the eyes and airways [Wolkoff and Kjaergaard 2007]. 

We visually inspected the exterior and interior of two randomly selected unit ventilators. We 

checked if these unit ventilators were operational, the type and condition of the air filters, 

whether the outdoor air damper was in the opened or closed position, and if furniture or 

school supplies interfered with the flow of room air through the ventilator. We also randomly 

checked one rooftop air handler.
Health Hazard Evaluation Report 2017-0030-3277 Page 3

Employee Interviews and Medical Record Review

We interviewed all available employees in the building about perceived work-related medical 

conditions or symptoms. We took a medical history to identify unrecognized occupational 

illness. Medical records were requested if an employee reported symptoms or an illness we 

thought might be related to work in the school. We did not request medical records for health 

problems we determined were not related to the school, such as cancers.

Results

Prior Indoor Environmental Quality Consultant Reports

Initial and follow-up evaluations were performed by a consultant hired by the school district. 

Summary results are provided in Table 1. The consultant followed typical investigative 

techniques and used appropriate monitoring equipment.

Table 1. Recent IEQ assessments of the school

Report date Summary

10/30/15 Initial evaluation conducted on October 14, 2015, in response to an apparent 

increase in work-related health concerns by school staff. Monitoring was performed 

for volatile organic compounds, temperature, RH, and CO2. All volatile organic 

compound levels were far below applicable occupational exposure limits, and only 

heptane was measured in the ppm range. Temperatures and RH were within 

ANSI/ASHRAE comfort guidelines, but CO2 concentrations up to 3,300 ppm were 

measured in some classrooms, indicating that insufficient outdoor air was being 

provided by the classroom ventilation systems during peak occupancy.

3/25/16 Follow-up evaluations conducted on January 15, 2016, and March 17, 2016, 

focused on temperature, RH, and CO2. On both days the temperature and RH were 

within ANSI/ASHRAE comfort guidelines. The CO2 concentrations on January 15, 

2016, ranged up to about 3,800 ppm, similar to those measured in October 2015. 

In response, the school replaced the CO2 sensors in all of the classroom unit 

ventilators. CO2 concentrations on March 17, 2016, after the sensors were 

replaced, were lower than on January 15, 2016, ranging up to about 1,400 ppm.

Walk-through Survey 

We found no areas of active moisture intrusion in any classroom on the basis of our visual 

assessment and use of an infrared camera and a moisture meter. We did see isolated waterstained ceiling tiles in the auditorium, gym, and classroom 21, but none of these stained 

surfaces were wet at the time of our visit. We also observed water-staining on the rear wall of 

the auditorium, behind the curtain. This area was not wet either (Appendix A, Figure A1). 

We saw scented air fresheners in use in a few locations. These can be a potential source of 

irritation, odor, and allergy to some employees (Appendix A, Figure A2). We saw chipped 

and cracked floor tiles in the lunch room. Considering the age of the building, these tiles 

could contain asbestos (Appendix A, Figure A3). However, these damaged tiles did not 

appear friable (easily crumbled), so there is little risk of exposure to asbestos-containing 
Page 4 Health Hazard Evaluation Report 2017-0030-3277

material. We saw rolled faced insulation installed above suspended ceiling tiles in classroom 

22. The insulation appeared old and was dusty (Appendix A, Figure A4). Aside from energy 

conservation, we were uncertain what the purpose of this insulation was because we did not 

see any rolled faced insulation in the plenum space above another classroom. Finally, we saw 

dusty ceiling fans in multiple classrooms (Appendix A, Figure A5).

The building’s membrane-style flat roof had been replaced within the past 2 years and 

appeared in excellent condition, with little standing water and no debris that could potentially 

clog roof drains. While walking around the perimeter of the building, we saw broken and 

disconnected roof drains along the exterior wall of classrooms 40 to 45 (Appendix A, Figure 

A6). We also saw leaves and other debris in a shallow storm water well near the exterior wall 

of classroom 32 (Appendix A, Figure A7). We were informed that the roof drains had been 

damaged by the local utility company the prior year. 

Two of the three vacuums used by the school’s custodial staff were not equipped with 

high-efficiency particulate air (HEPA) filters. The remaining vacuum, a backpack-style 

unit manufactured by Proteam, could use HEPA filters (according to the manufacturer’s 

website), but a school custodian indicated that this vacuum was seldom used (no reason 

provided). Products from a list of green certified cleaning products were used throughout the 

school district. The school had no written program, but we were told the pest management 

plan included monthly checks of the building and that baits and traps were preferred over 

pesticide spraying, which was reportedly done only when necessary.

Ventilation 

In most classrooms a unit ventilator was located on the exterior wall beneath an operable 

window, a design not uncommon in older schools. A unit ventilator, also called a fan coil 

unit, is a simple ventilation system. In this instance hot water from a natural gas-fired boiler 

or chilled water from a cooling tower was piped to each unit ventilator. A fan inside each 

unit ventilator circulated classroom room air across the hot or chilled water lines to provide 

heating or cooling, depending on the season. Each unit ventilator also had an outdoor air 

intake in the exterior wall that could allow outdoor air to be mixed with recirculated room 

air. In two classrooms, the unit ventilator was located in the ceiling because of grade and the 

building’s roof line. Each unit ventilator was centrally controlled by the maintenance office. 

Each unit ventilator had a direct-reading CO2 sensor (replaced in 2016) installed inside the 

unit ventilator cabinet that controlled the position of the unit’s outdoor air damper (Appendix 

A, Figure A8). When the CO2 level in a classroom exceeded 1,000 ppm the outdoor air 

damper on the unit ventilator would begin to open to provide more dilution air. Sensor data 

was remotely tracked and recorded by the maintenance staff.

A few interior classrooms, as well as all of the administrative offices, the library, gymnasium, 

and the auditorium had a forced-air, variable air volume ventilation system, with heating and 

cooling provided by rooftop package ventilation units. According to the maintenance staff, all 

of the forced-air and unit ventilators had been replaced in 2010.
Health Hazard Evaluation Report 2017-0030-3277 Page 5

The interiors of two unit ventilators and one rooftop ventilation unit that we randomly 

checked were clean and had no visible evidence of microbial contamination. The air filters in 

these units were also the correct size, properly installed, and appeared in excellent condition 

(Appendix A, Figure A9). All of the ventilation systems in the school used medium efficiency 

reporting value 8 air filters, an air filter type often used in nonindustrial work places such 

as offices and schools. The air filters in the rooftop air handlers were replaced twice per 

year, while those in the unit ventilators were replaced three times per year. We saw two unit 

ventilators that had teaching supplies and furniture partially blocking air intakes and/or air 

exhausts (Appendix A, Figure A9). We also saw one ceiling-mounted diffuser in the district 

office that was blocked by what appeared to be a pink blanket (Appendix A, Figure A10).

Carbon Dioxide, Temperature, and Relative Humidity

Table 2 summarizes the CO2 concentrations and temperature and RH levels we measured 

in classrooms and other school areas over 2 days. Seven of the eight classrooms with unit 

ventilators that we tested (rooms 3, 9, 11, 20, 35, 42, and 45) had maximum carbon dioxide 

concentrations that exceeded the ambient outdoor air concentration (approximately 400 

ppm) by at least 700 ppm, and Figure 1 shows the CO2 concentrations in classroom 35. This 

suggests that classroom ventilation systems were not always providing sufficient outdoor 

air to maintain acceptable ventilation throughout the school day [ANSI/ASHRAE 2016]. 

In comparison, only two of the six classrooms or offices with forced-air ventilation that we 

tested had CO2 concentrations above recommended levels (Table 2 and Figure 2). This topic 

is discussed more in the following section. 

On the days of our evaluation, the average lower RH was 40% and average upper RH was 

49% in the classrooms and offices that we evaluated. Using these RH averages, and assuming 

an operative temperature range of 68°F to 78°F (Table 2), a metabolic rate for the occupants 

of 1.2 (equivalent to standing, relaxed), and occupants wearing typical winter clothing, the 

classrooms and offices were within the recommended thermal comfort guidelines [ANSI/

ASHRAE 2013]. On both days of our evaluation, the RH levels were below 65% [ANSI/

ASHRAE 2013], and on January 18, were within 30%‒50% as recommended by the U.S. 

Environmental Protection Agency [EPA 2012].
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Table 2. Carbon dioxide, temperature, and relative humidity measurements in the building

Location* Room 

ventilation type

Carbon dioxide 

(ppm)

Temperature 

(°F)

Relative 

humidity (%)

January 17, 2017

Arts studio Forced air 60–180 68–74 53–67

Curriculum office Forced air 290†–500 65–75 42–53

Room 5 Unit ventilator 540–900 70–74 44–51

Room 9 Unit ventilator 780–2,200‡ 66–74 47–51

Room 35 Unit ventilator 900–3,200‡ 68–74 42–52

Room 42 Unit ventilator 820–1,800‡ 68–74 42–51

Room 45 Unit ventilator 850–2,220‡ 70–78 37–53

January 18, 2017

Counselor office Forced air 640–1300 68–72 34–48

Curriculum coaches Forced air 370†–540 70–72 40–44

Room 3 Unit ventilator 550–1,600‡ 68–74 35–45

Room 11 Unit ventilator 960–2,400‡ 62–73 34–46

Room 20 Unit ventilator 1,200–2,500‡ 69–72 40–48

Room 41 Forced air 660–990 71–73 31–36

Room 38 Forced air 550–1,100 70–73 33–36

Outdoor 430 63 63

*The sampling period was 8:00 a.m. to 4:00 p.m. each day.

†Although calibrated prior to use, this CO2 monitor appeared to measure unusually low levels, 

thus CO2 levels may be underestimated.

‡Maximum carbon dioxide concentrations exceeded ambient outdoor air concentrations by at least 

700 ppm.
Health Hazard Evaluation Report 2017-0030-3277 Page 7

Figure 1. Range of CO2 concentrations in classroom 35 on January 17, 2017.

Figure 2. Range of CO2 concentrations in classroom 38 on January 18, 2017.
Page 8 Health Hazard Evaluation Report 2017-0030-3277

Employee Interviews and Medical Record Review

We interviewed all 89 employees present at the school during our visit, including teachers, 

district administrators, custodial, maintenance, office, supervisory, and cafeteria staff. Of 

these, 70 (79.5%) were female. The length of employment ranged from less than 1 year to 

26 years with a median of 7 years. Seven employees had worked less than 1 year.

Of the 89 interviewed employees, 67 reported no symptoms that they related to work, while 

22 employees did report symptoms or medical conditions that they felt were or might be related 

to work. The most common reported symptoms thought to be related to the building were 

sinus problems (n = 6), headache (n = 3), nose irritation (n = 3), and throat irritation (n = 3). 

Symptoms or conditions reported by fewer than five people included frequent upper respiratory 

infections, worsening of allergies, cough, sneezing, nausea, post-nasal drip, and fatigue.

Fifteen employees reported ever being diagnosed with asthma. Ten of these employees were 

diagnosed with asthma prior to working at the school. Of those 10, nine reported that their 

asthma symptoms were the same on days at work as days off work. One was not sure if the 

asthma symptoms were the same on days at work and days off work. Five employees reported 

being diagnosed with asthma after beginning work at the school. Two of these five reported 

that their asthma symptoms were the same on days at work as on days off work, one was 

unsure, and one reported that symptoms were a little worse on days at work. One of these five 

employees reported that overall, their asthma had worsened since beginning work at the school. 

Medical records were requested for one employee who reported seeing a physician for asthma 

that she thought might be worsened by conditions in the school. We found that the records did 

not support a relationship between this employee’s work and asthma.

Four employees reported having miscarriages, two had Parkinson disease, one had Alzheimer 

disease, and one had a history of pancreatitis. Additionally, 12 employees had been diagnosed 

with breast cancer, five with skin cancer, two with ovarian cancer, and one with uterine 

cancer over the last 2 decades. 

Discussion

One of the most common deficiencies we have found over many years of health hazard 

evaluations in nonindustrial indoor environments like this school is the improper operation 

and maintenance of ventilation systems, resulting in inadequate ventilation rates. An analysis 

of the published scientific literature showed that nonspecific symptoms such as headache, 

fatigue, and mucous membrane irritation increase as ventilation rates decrease [Fisk et al. 

2009]. Employees reported all of these symptoms in our interviews, although the percentage 

of employees reporting such symptoms was low. Studies in schools and office buildings have 

found decreased illness absence with increased ventilation rates [Mendell et al. 2013; Milton 

et al. 2000; Shendell et al. 2004]. Thus, improving heating, ventilation, and air-conditioning 

operation and maintenance and increasing ventilation rates can improve symptoms without 

ever identifying any specific cause-effect relationships. We believe similar benefits would 

occur if the ventilation rates are improved at this school. 
Health Hazard Evaluation Report 2017-0030-3277 Page 9

The unit ventilators in the school were centrally controlled, and each had a direct-reading 

CO2 sensor that opened the unit’s outdoor air damper with increasing CO2 concentrations 

(Appendix A, Figure A8). These unit ventilator design elements can help maintain 

temperature and RH within recommended comfort guidelines and ensure that sufficient 

outdoor air is introduced into the occupied spaces. Therefore, we were surprised to find CO2

concentrations greater than 1,000 ppm above outdoor levels in all but one of the classrooms 

with a unit ventilator that we monitored.

We discussed our findings with the maintenance staff and compared our CO2 measurements 

with those obtained from a unit ventilator’s direct-reading sensor. We selected classroom 35 

because this room had among the highest CO2 concentrations that we measured (up to about 

3,300 ppm). The trends in our CO2 measurements throughout the school day were similar to 

those downloaded from the unit ventilator sensor. However, the maintenance staff discovered 

that the computer ventilation controls had been overwritten to prevent the CO2 sensors from 

fully opening the outdoor air dampers in the unit ventilators. This reprogramming had been 

done the prior week in response to a period of unusually cold weather to avoid freezing the 

water pipes in the unit ventilator and damaging the system. Temporarily restricting how 

much an outdoor air intake may open during weather extremes is not uncommon. In this 

instance, the maintenance staff had forgotten to remove the programming change, and the 

unit ventilator control system did not alert the user that the outdoor air damper restriction was 

still in place.

We saw damaged exterior roof drains with ponding water near the school’s foundation, and 

a shallow storm water well with debris. Because these were also near outdoor air intakes for 

classrooms (Appendix A, Figures A6 and A7), the standing water and organic matter could be 

potential sources of microbial contamination and odors that could affect the IEQ of the school. 

At least two of the three vacuums used by the custodial staff were not equipped with HEPA 

filters. Using vacuums with properly installed HEPA filters will reduce the chance that captured 

particles could be resuspended back into the room. We saw loose pieces of fiberglass apparently 

from old roll-faced fiberglass insulation installed in the plenum above classroom 22 (Appendix 

A, Figure A4). Any maintenance activities performed in this plenum space could potentially 

disturb the fiberglass insulation, thus releasing dust and fiberglass into the classroom below. 

Roll-faced fiberglass insulation was not present in the plenum in another classroom.

The employees’ reported headache, sinus problems, worsening of allergies, eye irritation, 

frequent upper respiratory infections, fatigue, throat irritation, and cough. These are 

common symptoms that we have frequently found in people working in buildings with 

poor ventilation. They can also be found frequently in the general population and can have 

non-occupational causes. Of the general population, 86%–95% have one or more common 

symptoms during any given 2- to 4-week period, and the average adult reports a minimum of 

one symptom every 4–6 days [Barsky and Borus 1995]. Table 3 lists the general population 

prevalences of many of the symptoms reported by employees in this school. In addition, the 

average adult has two to three upper respiratory infections per year [Benninger et al. 2003]. 

According to the National Health Interview Survey, 12% of U.S. adults reported physiciandiagnosed sinusitis in 2012, and women were more likely to be diagnosed with sinusitis 

(15% compared to 9% in men) [Centers for Disease Control and Prevention 2014]. 
Page 10 Health Hazard Evaluation Report 2017-0030-3277

Table 3. General population prevalence of symptoms similar to those reported by employees

Clustered random 

sample of households 

in Australia

General medical 

practices in the 

United Kingdom

Representative sample 

of general population of 

New Zealand

Participants n = 3,016* n = 2,474† n = 1,000‡

Time frame 14 days 14 days 7 days

Number of 

symptoms asked 

about

12 25 46

Percent reporting at 

least one symptom

80 > 75 89

Number of 

symptoms reported, 

mean (range)

Not reported 3.6 (0–22) 5 (0–36)

Symptoms similar to 

those reported in 

this building (%)

Stuffy nose (46)

Headache (33)

Unusually tired (30)

Cough (26)

Dry, itchy, or 

irritated eyes (25)

Dry or sore throat (22)

Skin rash (12)

Tired/run down (41)

Headache (39)

Sore throat (19)

Cough (18)

Fatigue (36)

Headache (35)

Congested or 

runny nose (34)

Cough (28)

*Reference: Heyworth and McCaul 2001

†Reference: McAteer et al. 2011

‡Reference: Petrie et al. 2014

The U.S. Environmental Protection Agency conducted a systematic survey of 100 randomly 

selected office buildings without known IEQ complaints in the United States to develop 

baseline data about U.S. office buildings [Brightman et al. 2008]. The National Institute 

for Occupational Safety and Health (NIOSH) conducted a similar study of 80 buildings 

with IEQ complaints [Malkin et al. 1996]. Occupants in both studies reported work-related 

symptoms. The rank order of symptoms was the same, but rates were significantly higher 

in the buildings with IEQ complaints. The most common work-related symptoms reported 

in both studies were dry, itching, or irritated eyes; unusual tiredness or fatigue; headache; 

tension or irritability; pain in back, neck, and shoulders; stuffy or runny nose, or sinus 

congestion; sneezing; sore or dry throat; and difficulty remembering things or concentrating. 

Of the employees in the randomly selected buildings, 45% reported at least one work-related 

symptom [Brightman et al. 2008; Malkin et al. 1996]. These common symptoms in the 

general population and in buildings are also among the most common symptoms reported by 

employees in this school. 

Exposures that could be related to new-onset or worsening asthma include fragrances, dust 

mites, dander from rodents, and excrement of rodents and other pests such as cockroaches. 

Some allergens can be carried in on employees and visitors. The most common of these 

are cat and dog allergens, which can be an unrecognized source of allergic upper and lower 

respiratory and skin symptoms. 
Health Hazard Evaluation Report 2017-0030-3277 Page 11

Several employees reported having medical conditions that we determined were unrelated to 

the school’s conditions or exposures in the school based upon current scientific knowledge. 

These included cancer, Parkinson disease, Alzheimer disease, pancreatitis, and miscarriages. 

The number and types of medical conditions are not unusual, and general IEQ problems are not 

known to be linked to the types of medical conditions reported. Appendix B provides a more 

detailed discussion of cancer and how we determine if cancer is related to a common exposure.

Conclusions

We saw no evidence of a current mold problem in the school, and the ventilation systems 

and roof were well maintained and in good condition. However, most of the classrooms 

with unit ventilators that we monitored had inadequate ventilation during at least part of the 

school day. Inadequate ventilation means that insufficient outdoor air was being brought 

into the classroom. This situation occurred after the computer ventilation controls were 

changed in response to unusually cold weather prior to this evaluation, but were not reset. 

Many of the symptoms employees reported, such as sinus problems, eye and throat irritation, 

and headaches, have been associated with dampness or inadequate ventilation but are also 

common in the general population. We found no evidence that other reported health problems 

were related to the school. 

Recommendations

On the basis of our findings, we recommend the actions listed below to create a more 

healthful workplace. We recommend the school use a labor-management health and safety 

committee or working group to discuss our recommendations and develop an action plan. 

Our recommendations are based on the hierarchy of controls approach. This approach groups 

actions by their likely effectiveness in reducing or removing hazards. In most cases, the 

preferred approach is to eliminate hazardous materials or processes and install engineering 

controls to reduce exposure or shield employees.

Engineering Controls

Engineering controls reduce employees’ exposures by removing the hazard from the process or by 

placing a barrier between the hazard and the employee. Engineering controls protect employees 

effectively without placing primary responsibility of implementation on the employee. 

1. Hire a licensed professional mechanical engineer to do a comprehensive assessment of 

the school’s ventilation systems. This assessment should include checking the calibration 

and operation of the CO2 sensors controlling the outdoor air intakes of classroom unit 

ventilators. The mechanical engineer should have experience in the design of heating, 

ventilating, and air-conditioning systems for buildings that include multi-use areas such 

as classrooms, dining and kitchen areas, gymnasiums, and offices, and be familiar with 

buildings ventilated by both forced-air and unit ventilator-type systems. 

2. Remove the rolled faced insulation in the plenum space above classrooms because it 

could contribute to dustiness in the classroom. The insulation should be removed when 
Page 12 Health Hazard Evaluation Report 2017-0030-3277

the classroom is not in use. Employees removing the insulation should minimize direct 

skin contact with the potentially irritating insulation material by wearing gloves and 

long-sleeve shirts. After removal clean the surfaces in the classroom with a HEPAfiltered vacuum to remove any residual insulation that may have fallen.

3. Repair the cut roof drains to ensure that water does not accumulate around the foundation 

of the school or near outdoor air intakes. Keep storm water wells clean of debris.

Administrative Controls

The term administrative controls refers to employer-dictated work practices and policies 

to reduce or prevent hazardous exposures. Their effectiveness depends on employer 

commitment and employee acceptance. Regular monitoring and reinforcement are necessary 

to ensure that policies and procedures are followed consistently.

1. Stop any additional environmental sampling for chemical and biological agents to 

identify a cause for nonspecific symptoms among employees.

2. Establish a fragrance-free workplace policy. Ensure that it addresses perfumes and 

other scented personal care products, air fresheners, and potpourri. 

3. Use vacuums equipped with HEPA filters when cleaning the school.

4. Clean the ceiling fans regularly.

5. Move objects so that they do not block airflow around unit ventilators or supply air ducts.

6. Minimize the use of carpet and upholstered furniture. Porous materials are more difficult 

to clean than smooth, nonporous surfaces and can harbor microbes and dust mites.

7. Ask employees to report signs of moisture intrusion to the maintenance staff. Establish 

a system for responding to requests and notifying the requestor what is being done and 

when the work is complete.

8. Encourage employees with health concerns to seek evaluation and care from their 

regular healthcare provider. It may be useful to provide the physician with a copy of 

this report. If an employee is determined to have an illness related to an occupational 

exposure, the healthcare provider and the appropriate management personnel should 

work to eliminate that exposure and assess the need for environmental evaluation. 

If symptoms persist despite best efforts to address the workplace exposures, an 

occupational medicine physician may need to recommend work accommodations 

for the employee. Occupational medicine physicians can be found through a variety 

of sources, including the Association of Occupational and Environmental Clinics, at 

http://www.aoec.org/, and the American College of Occupational and Environmental 

Medicine, at http://www.acoem.org/. Additionally, in such circumstances, evaluation 

of other employees who may also be potentially affected may be appropriate.
Health Hazard Evaluation Report 2017-0030-3277 Page 13

Appendix A: Figures

Figure A2. Electrically-heated scented candle warmer in classroom. Photo by NIOSH.

Figure A1. Old water stains on auditorium wall. Photo by NIOSH.

Figure A3. Chipped and cracked 9 inch by 9 inch floor tiles in school lunchroom. Photo by NIOSH.
Page 14 Health Hazard Evaluation Report 2017-0030-3277

Figure A4. Dusty roll-faced insulation in plenum above classroom. Photo by NIOSH.

Figure A5. Dusty ceiling fan blades in classroom. Photo by NIOSH.

Figure A6. Broken and disconnected exterior roof drain outside classroom. Photo by NIOSH.
Health Hazard Evaluation Report 2017-0030-3277 Page 15

Figure A7. Debris in shallow dry well near outdoor air intake for classroom. Photo by NIOSH.

Figure A8. Interior of a typical classroom unit ventilator. Photo by NIOSH.
Page 16 Health Hazard Evaluation Report 2017-0030-3277

Figure A10. A blocked ceiling mounted diffuser in an office. Photo by NIOSH.

Figure A9. Storage cabinet (on floor) and teaching supplies (on top) blocking air intakes on a 

classroom unit ventilator. Photo by NIOSH.
Health Hazard Evaluation Report 2017-0030-3277 Page 17

Appendix B: Cancer and Cancer Clusters

Cancer is a group of different diseases that share the same feature of uncontrolled growth 

and spread of abnormal cells. Each different type of cancer may have its own set of causes. 

Cancer is common in the United States. In the United States, one in two men and one in three 

women will develop cancer over the course of their lifetimes [American Cancer Society 

2016a]. This does not include basal or squamous cell skin cancers, which are very common 

(more than 3 million diagnosed annually), or any in-situ carcinomas other than bladder. If 

these were included, rates would be even higher. One of every four deaths in the United 

States is from cancer [American Cancer Society 2016a]. Among adults, cancer occurs more 

frequently with increasing age. Cancer cases may appear to occur with alarming frequency 

even when the number of cases is not more than would be expected in the general population 

because cancer is common, the population is aging, and more people are surviving cancer. 

This perception is especially common among a small group of people who have something in 

common with the cases, such as working in the same building as in this school. 

Many factors play a role in the development of cancer. The importance of these factors varies 

for different types of cancer. Most cancers are caused by a combination of several factors. 

Some of the factors include (1) personal characteristics such as age, sex, and race; 

(2) family history of cancer; (3) diet; (4) personal habits such as cigarette smoking and 

alcohol consumption; (5) the presence of certain medical conditions; (6) exposure to 

cancer-causing agents in the environment; and (7) exposure to cancer-causing agents in the 

workplace. In many cases, these factors may act together or in sequence to cause cancer. 

Although some causes of various types of cancer are known, we do not know everything 

about the causes of cancer. One important point to note is that the absence of a risk factor 

does not mean there is no risk for developing cancer. For example, employees often say to us 

that they got breast cancer despite having no family history of breast cancer, so it must be due 

to their work. In fact, while having a first-degree relative with breast cancer increases one’s 

risk of developing breast cancer, most people who get breast cancer do not have a family 

history of it. 

The American Cancer Society estimates that about 171,000 cancer deaths in 2015 were 

caused by tobacco use alone [American Cancer Society 2016a]. This is one third of all cancer 

deaths. It is well known that tobacco use increases the risk of cancer of the lung, mouth, nasal 

cavities, larynx, pharynx, esophagus, stomach, colorectum, liver, pancreas, kidney, bladder, 

uterine cervix, and ovary (mucinous), and myeloid leukemia [American Cancer Society 

2016a]. There is limited evidence that tobacco smoking causes female breast cancer. 

Another one quarter to one third of cancer deaths are due to poor nutrition, physical 

inactivity, overweight, and obesity [American Cancer Society 2016a]. Being overweight 

or obese is clearly associated with increased risk for developing cancer of the breast 

(in postmenopausal women), colon and rectum, endometrium, kidney, pancreas, and 

adenocarcinoma of the esophagus. Obesity increases the risk of gallbladder cancer and 

possibly cancers of the liver, cervix, and ovary; multiple myeloma; non-Hodgkin lymphoma; 

and aggressive forms of prostate cancer [American Cancer Society 2016a].
Page 18 Health Hazard Evaluation Report 2017-0030-3277

Alcohol consumption is another modifiable personal risk factor that increases risk of cancer, 

in addition to the almost two thirds of cancer due to smoking, poor nutrition, physical 

inactivity, overweight, and obesity. Alcohol causes cancers of the mouth, pharynx, larynx, 

esophagus, liver, colorectum, and breast [American Cancer Society 2016a]. Even a few 

drinks weekly increase the risk of breast cancer. 

Breast Cancer

Breast cancer is the most common cancer in women in the United States. Approximately 

250,000 cases of invasive breast cancer will be diagnosed in women in the United States in 

2016, not including 61,000 cases of carcinoma in situ [American Cancer Society 2016b]. 

One in eight women in the United States will develop breast cancer in her lifetime [American 

Cancer Society 2016b]. Well-established breast cancer risk factors include family history 

of breast cancer, biopsy-confirmed atypical hyperplasia, early menarche (first menstrual 

period), late menopause, not having children or having the first child after age 30, overweight 

or obesity (especially after menopause), never breastfeeding a child, low physical activity 

levels, and higher levels of education and socioeconomic status [American Cancer Society 

2016b; Weiderpass et al. 2011]. 

The International Agency for Research on Cancer has classified alcoholic beverages of all 

types, in utero exposure to diethylstilbestrol, estrogen-progesterone oral contraceptives and 

hormone replacement therapy, and exposure to x-rays and gamma rays (types of ionizing 

radiation) as “carcinogenic to humans” with regard to breast cancer [International Agency 

for Research on Cancer 2017]. The risk from ionizing radiation is highest if exposure 

occurs during childhood and is negligible if exposure occurs after age 40 [Ronckers 2004]. 

The International Agency for Research on Cancer classifies digoxin, estrogen hormone 

replacement therapy, ethylene oxide, polychlorinated biphenyls, smoking, and shift work as 

“probably carcinogenic to humans [International Agency for Research on Cancer 2017].” 

While scientific studies have found an association between certain substances or occupations 

and breast cancer, the results are conflicting or unconfirmed. Some studies have found 

increased risk of breast cancer among nurses, librarians, laboratory technicians, telephone 

operators, glass manufacturing workers, textile workers, meat wrappers and cutters, printers, 

security personnel, scientific researchers, and hairdressers/cosmetologists, among others 

[Coogan et al. 1996; Gardner et al. 2002; Labrèche et al. 2010; Morton 1995; Peplonska et al. 

1998, 2010; Shaham et al. 2006; Teitelbaum et al. 2003; Zheng et al. 2002]. 

Several studies have found teachers and other professional and managerial employees to 

have an increased risk for developing breast cancer [Bernstein et al. 2002; King et al. 1994; 

MacArthur et al. 2007; Pollán and Gustavsson 1999; Rubin et al. 1993; Snedeker 2006], but 

others have not [Calle et al. 1998; Coogan et al. 1996; Petralia et al. 1998]. No causative 

workplace exposures have been identified for these occupations, and it is postulated that the 

possible increase in risk is a result of nonoccupational risk factors such as parity (number 

of times a woman has given birth), maternal age at first birth, contraceptive use, diet, and 

physical activity [MacArthur et al. 2007; Snedeker 2006; Threlfall et al. 1985]. Women 

with higher educational status are also more likely to have mammograms, thus increasing 
Health Hazard Evaluation Report 2017-0030-3277 Page 19

detection of breast cancer. Several studies have found that about one quarter to one third of 

invasive breast cancers detected by mammograms were overdiagnosed, i.e., would not have 

progressed or caused harm [Jørgensen and Gøtzsche 2009; Miller et al. 2014; Zahl et al. 2008].

Cancer Clusters 

Cancers often appear to occur in clusters, which scientists define as a greater than expected 

number of cancer cases that occurs within a group of people in a geographic area over a 

defined period of time [Centers for Disease Control and Prevention 2012]. A cluster also 

occurs when the cancers are found among employees of a different age group or sex than is 

usual. A statistically significant excess of cancer cases may have a common cause but can 

occur without a clear cause and can occur by chance [Aldrich and Sinks 2002; Thun and 

Sinks 2004]. In many workplaces the number of cases is small. This makes detecting whether 

the cases have a common cause difficult, especially when no apparent cancer-causing 

exposures are present. It is common for the borders of the “cluster” to be drawn around 

where the cases of cancer are located, instead of defining the population and geographic 

area first. This often leads to “clusters” that are not real. This is referred to as the “Texas 

sharpshooter effect” because the Texas sharpshooter shoots at the barn and then draws his 

bull’s eye around the bullet hole.

When cancer in a workplace is described, learning whether the type of cancer is a primary 

cancer or a metastasis (spread of the primary cancer into other organs) is important. Only 

primary cancers are used to investigate a cancer cluster. To assess whether the cancers among 

employees could be related to occupational exposures, we consider the number of cancer 

cases, the types of cancer, the likelihood of exposures to potential cancer-causing agents, and 

the timing of the diagnosis of cancer in relation to the exposure. These issues are discussed 

below in a series of questions that relate to this request. 

Do employees at this school have more cancer than those who do not 

work at this school?

No. Because cancer is a common disease, it may be found among people at any workplace. 

When several cases of cancer occur in a workplace, they may be part of a true cluster when 

the number is greater than we expect compared to other groups of people similar in age, 

sex, and race. Disease or tumor rates, however, are highly variable in small populations and 

rarely match the overall rate for a larger area, such as the state. Therefore, for any given 

time period, some populations have rates above the overall rate, and others have rates below 

the overall rate. Even when a higher rate occurs, it may be consistent with the expected 

random variability. In addition, calculations like this make many assumptions that may not 

be appropriate for every workplace. Comparing rates without adjusting for age, sex, or other 

population characteristics assumes that such characteristics are the same in the workplace 

as in the larger population, which may not be true. However, general information on cancer 

rates is useful for providing perspective on the cancers in your population. The occurrence of 

20 cases of cancer among employees at this school over more than 30 years is not excessive. 

It is likely that many more current and former employees have been diagnosed with cancer 

than those who were reported to us, but the numbers and types of the reported cancers do not 
Page 20 Health Hazard Evaluation Report 2017-0030-3277

suggest a need for further case finding. As employees age, more cases of cancer (of many 

types) will appear. 

Do employees in this school have an unusual distribution of types of 

cancer? 

No. Cancer clusters thought to be related to a workplace exposure usually consist of the 

same types of cancer. When several cases of the same type of cancer occur and that type 

is not common in the general population, it is more likely that an occupational exposure 

is involved. When the cluster consists of multiple types of cancer, without one type 

predominating, then an occupational cause of the cluster is less likely. The 10 most common 

cancers in women are (in order): breast; lung and bronchus; colon and rectum; uterine 

corpus; thyroid; non-Hodgkin lymphoma; melanoma of the skin; kidney and renal pelvis; 

pancreas; and ovary. The 10 most common cancers in men are (in order): prostate; lung and 

bronchus; colon and rectum; urinary bladder; melanoma of the skin; kidney and renal pelvis; 

non-Hodgkin lymphoma; oral cavity and pharynx; leukemia; and pancreas. Several female 

employees in this school, where 66% of employees are female, have been diagnosed with 

breast cancer, the most common cancer among women in the United States. Three other of 

the most common types of cancer were also diagnosed among employees.

Is exposure to a specific chemical or physical agent known or suspected 

of causing cancer or other health effects occurring at this school? 

No. The relationship between some agents and certain cancers has been well established. 

For other agents and cancers, there is a suspicion of a link, but the evidence is not definitive. 

When a known or suspected cancer-causing agent is present and the types of cancer occurring 

have been linked with these exposures in other settings, we are more likely to make the 

connection between cancer and a workplace exposure. 

Office buildings rarely have hazardous exposures relevant to cancer. Asbestos can be a 

concern in older buildings, but it is known to cause lung cancer and mesothelioma, neither 

of which were reported among employees. Suspected asbestos-containing floor tiles were 

present in this school, but because the tiles were not friable (easily crumbled), asbestos would 

not be released into the air and create a hazard for employees. Radon can be of concern in 

basement or lower floors of some buildings, but radon causes lung cancer, not other types of 

cancer. Radon monitoring is performed in the school building every 2 years, and levels have 

been acceptable. 

Has enough time passed since exposure began? 

Latency is the time between first exposure to a cancer-causing agent and clinical recognition 

of the disease. Latency periods vary by cancer type but usually are a minimum of 10–12 

years [Rugo 2004]. 

This question is not relevant when considering the reported cancers at this school because 

there is not an excess of cancer among employees, the distribution of cancers is not unusual, 

and no exposures were associated with the cancers diagnosed.
Health Hazard Evaluation Report 2017-0030-3277 Page 21

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Health Hazard Evaluation Report 2017-0030-3277 Page 25

Keywords: North American Industry Classification System 611110 (Elementary and 

Secondary Schools), Ohio, IEQ, ventilation, school, cancer, carbon dioxide, temperature, 

relative humidity
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Health Hazard Evaluation Report 2017-0030-3277 Page 27

The Health Hazard Evaluation Program investigates possible health hazards in the workplace

under the authority of the Occupational Safety and Health Act of 1970 (29 U.S.C. § 669(a)

(6)). The Health Hazard Evaluation Program also provides, upon request, technical assistance

to federal, state, and local agencies to investigate occupational health hazards and to prevent

occupational disease or injury. Regulations guiding the Program can be found in Title 42, Code

of Federal Regulations, Part 85; Requests for Health Hazard Evaluations (42 CFR Part 85).

Disclaimer

The recommendations in this report are made on the basis of the findings at the workplace

evaluated and may not be applicable to other workplaces.

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Acknowledgments

Desktop Publisher: Shawna Watts 

Editor: Ellen Galloway 

Logistics: Donnie Booher, Kevin Moore

Medical Field Assistance: Elena Page, Sophia Chiu, Martha Montgomery

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have also received a copy. This report is not copyrighted and may be freely reproduced. 

Recommended citation for this report:

NIOSH [2017]. Evaluation of indoor environmental quality concerns in an elementary 

school. By Gowda S, Zwack L, Burr GA. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, Health Hazard Evaluation Report 2017-0030-3277, 

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