Skip to main content
NCBI home page
HHS Author Manuscripts logoLink to HHS Author Manuscripts
. Author manuscript; available in PMC: 2017 Mar 1.
Published in final edited form as: J Environ Health. 2016 Mar;78(7):8–44.

Formaldehyde levels in traditional and portable classrooms: A pilot investigation

Isabela C Ribeiro 1,#, Peter J Kowalski 2,#, David B Callahan 3,#, Gary P Noonan 2,#, Daphne B Moffett 3,#, David R Olson 3,#, Josephine Malilay 2,#
PMCID: PMC4876979  NIHMSID: NIHMS717252  PMID: 27197349

Abstract

This pilot study assessed formaldehyde levels in portable classrooms (PCs) and traditional classrooms (TCs) and explored factors influencing indoor air quality (e.g., carbon dioxide (CO2), temperature, and relative humidity). In a cross-sectional design, we evaluated formaldehyde levels in day and overnight indoor air samples from nine PCs renovated within three years previously and three TCs in a school district in metropolitan Atlanta, Georgia. Formaldehyde levels ranged from 0.0068 to 0.038 ppm. In both type of classrooms, overnight formaldehyde median levels (PCs = 0.018 ppm; TCs = 0.019 ppm) were higher than day formaldehyde median levels (PCs = 0.011 ppm; TCs = 0.016 ppm). CO2 levels measured 470–790 parts per million (ppm) at 7AM and 470–1800 ppm at 4PM. Afternoon medians were higher in TCs (1,400 ppm ) than in PCs (780 ppm). Consistent with previous studies, formaldehyde levels were similar among PCs and TCs. Reducing CO2 levels by improving ventilation is recommended for classrooms.

Keywords: Indoor Air Quality, Schools, Formaldehyde, Carbon Dioxide, Ventilation, Furnishings

BACKGROUND

During 1985-2008, public school enrollment increased from 39.4 million to 49.8 million in the United States (U.S.) (National Center for Educational Statistics (NCES), 2008), which led to overcrowding in some schools districts. A common response to overcrowding is to install temporary structures such as modular or portable buildings for use as classrooms. An estimated 33% (26,700 of 80,910) schools reported the use of portable classrooms in 2005. Over 350,000 portable classrooms are used throughout the U.S. (NCES, 2007).

Typical materials for building and furnishing portable classrooms, as well as new or modernized traditional school buildings, may off-gas formaldehyde, as well as other volatile organic compounds (VOCs), and result in exposures of public health concern (Hodgson, Shendell, Fisk, & Apte, 2004). Formaldehyde levels vary with type of construction materials, presence of pressed wood products, type of carpeting and flooring material, and efficiency of heating, ventilation and air conditioning (HVAC) systems. The release of formaldehyde from pressed wood products and other sources is known to decrease over time (Meyer, 1979). Studies consistently show that highest indoor formaldehyde concentration occur in new mobile homes and buildings, with values decreasing gradually over time (Sexton, Petreas & Liu, 1989; Norsted, Kozinetz & Annegers, 1985; Hanrahan, Dally, Anderson, Kanarek & Rankin, 1984). Additionally, formaldehyde emissions from indoors sources, such as plywood and particle board, increase with temperature and relative humidity, being highest in the summer months (Meyer, 1979).

Children have greater susceptibility to some environmental pollutants, including formaldehyde, than adults because they breathe higher volumes of air relative to their body weights and have actively growing tissues and organs (Faustman, Silbernagel, Fenske, Burbacher, & Ponce, 2000). Acute exposure to formaldehyde can result in irritation of the throat, nose, eyes, and skin (Agency for Toxic Substances and Disease Registry (ATSDR), 2010). Several observational studies have demonstrated associations between formaldehyde and asthma outcomes, such as increased bronchial responsiveness in children with asthma, emergency treatment for asthma, increased risk of IgE-mediated sensitization, and increased diagnoses of asthma (ATSDR, 2010). Indoor exposure to formaldehyde has also been associated with chronic respiratory symptoms and decreased pulmonary function among children (Krzyzanowski, Quackenboss, & Lebowitz, 1990). Nasal irritation, eye irritation, and increased risk of asthma and allergies have been observed at airborne formaldehyde levels at 0.01 – 0.5 ppm. Continuous exposure to formaldehyde also has led to increased IgE-mediated sensitization and symptoms at levels greater than 0.05 ppm, the World Health Organization's threshold, among primary schoolchildren (Wantke, Demmer, Tappler, Götz, Jarisch, 1996). Formaldehyde is also a human carcinogen (NTP, 2013).

Few published studies have examined formaldehyde levels in occupied portable classrooms, mainly from California, United States (Hodgson et al., 2004; Shendell, Prill, Fisk, Apte, Blake, & Faulkner, 2004; Shendell, Winer, Weker, Colome, 2004a; California Air Resources Board (CARB), 2003). Public health concerns about formaldehyde exposure during travel trailer and mobile home use following the Gulf Coast hurricane Katrina in 2005 prompted this investigation (Centers for Disease Control and Prevention (CDC), 2008). Our primary objective was to describe formaldehyde levels in portable classrooms (PC) and traditional classrooms (TC) occupied by school-aged children, a potentially sensitive population. Secondary objectives were 1) to develop and field test a noninvasive, nonintrusive, and non-disruptive sampling protocol to measure levels of formaldehyde during school hours and overnight; and 2) to explore factors that may influence indoor air quality, such as use of HVAC systems, levels of CO2, temperature, and relative humidity. To our knowledge, this is the first study assessing levels of formaldehyde in school classrooms in the southeastern US, where hot temperatures and high humidity characterize spring and summer months.

METHODS

Participants

The metro Atlanta School District participating in this study has nine PC units that were renovated within 3 years of the investigation. Twelve classrooms were sampled as follows: School A = four PC (Quad units) and one TC; School B = one PC and one TC; and School C = four PCs (each as an individual portable unit) and one TC. Because Quad units have four classrooms per unit, one classroom per unit was randomly selected at School A. The school district was selected by convenience and data were collected in the last week of the district's school year, May 18-21, 2009.

Procedures

Investigators pre-tested a standardized nine-page questionnaire with the school district's Indoor Air Quality (IAQ) Coordinator, who then distributed it to facility managers and teachers for recording indoor environment and classroom exterior characteristics. Teachers from PCs and TCs responded to questions about the HVAC system, such as noise level and use during class hours, air quality, and environmental conditions in the classrooms.

Two simultaneous 9-hour school day and two overnight 15-hour samples of formaldehyde were collected in each classroom, using the 1994 National Institute for Occupational Safety and Health (NIOSH) Manual of Analytical Methods, Method 2016, with Supelco® S10 LpDNPH cartridges (St. Louis, Mo). Samplers were positioned in opposite corners of the PCs and TCs within 10 meters distance. Teachers were requested to open or close doors and windows as they might during typical classroom instruction hours. Samples were collected using SKC, Inc. (Eighty Four, PA) Model 210 personal sampling pumps. Samples were drawn at a low-flow rate between 0.05 and 0.1 liters per minute, and the pumps were placed at a height of 1.2 meters. Air sampling pumps were calibrated before and after use with a Bios Dry Cal® calibrator primary standard. For day sampling, pumps were started immediately prior to the beginning of the school day (i.e., the arrival of the students at 7 AM) and stopped after the end of the school day (around 4 PM). For overnight sampling, pumps were operated after the school day ended (4 PM) and stopped in the morning prior to the school day's start (7 AM). One outdoor and one field blank sample were collected on each sampling day (four days) in the field from all three schools. Field blanks are used as part of quality control procedures and no contamination was observed during handling. All sample tubes were stored in a freezer or in a cooler on ice at all times when not being used for sampling. At the end of each sampling day, sample cartridges were resealed using cartridge plugs, and placed in a re-sealable pouch. Samples were transported to a refrigerator and shipped to the designated analytical laboratory (Bureau Veritas, Novi, Michigan) in coolers via overnight express.

Concurrent (day and overnight) measurements of indoor temperature and relative humidity were conducted in each classroom using HOBO® U23 dataloggers. CO2 was measured in each classroom at the start (7 AM) and at the end (4 PM) of the school day by use of TSI, Inc Q-TRACK™. Temperature, relative humidity, and outdoor CO2 were also measured in all three schools; CO2 levels were used as indicators of classroom ventilation.

Strict quality assurance/quality control (QA/QC) procedures were observed including the use of chain of custody forms (NIOSH, 1994). To ensure schools’ privacy and safeguard data, each PC or TC was assigned a unique identifier number linked to data recorded on paper interview and abstraction forms. Laboratory samples were analyzed using specific standard QA/QC procedures (NIOSH, 1994) for an American Industrial Hygiene Associated-accredited laboratory.

The primary outcome variable was the one entire school day concentration of formaldehyde measured in PCs and TCs. The average between the two formaldehyde samples from each classroom was used to calculate the overnight and day means and medians for over the four days of testing. Data on potential factors that might affect the formaldehyde levels were collected, including indoor temperature, indoor relative humidity, and CO2 concentration. Other classroom characteristics, such as window and/or air conditioning use, time spent in classroom, age of construction or renovation of the portable classroom, exterior temperature, and direction of prevailing wind during the sampling days, were also collected.

Data analysis

Data were analyzed using SAS version 9.1. Differences in means were tested for statistical significance using the unpaired Student t test. Statistically significant differences in proportions were determined using the chi-square test. Since samples are small and the distribution of concentrations is unknown, differences in means and proportions were also analyzed using non-parametric methods, with no change in findings or conclusions (data not shown). Results were considered statistically significant at p<0.05.

RESULTS

Three schools participated in this pilot study, two elementary—including pre-kindergarten aged children—and one high school. None of the studied classrooms were adjacent to a laboratory, an industrial building, an art shop, or other special purpose rooms. Building characteristics for portable and traditional classrooms for all three schools (A, B, and C) are shown in Table 1. Even though only PCs in school A were built three or less years prior to this pilot study, all PCs were considered new because PCs in schools B and C had been fully renovated (with completely new interior) within three years from the beginning of the study, and were acquired one year before the study. All TCs were built more than 3 years prior to the study and had not been renovated. With the exception of the TC in school C, no classrooms had interior items replaced in the last three years before this study, or since they were built new or renovated. Building construction materials such as roof, interior and exterior walls, were similar among same type of classroom, but differed between PCs and TCs. The composition of classroom furnishings was similar across all PC and TC units sampled. Tables and desks were mostly a combination of solid and pressed wood, plastic, and metal, while bookcases, cabinets, and chairs were made primarily of solid and pressed wood. Floors in all PCs and in one TC (school B) were entirely carpeted and two TCs had concrete flooring. Finally, all twelve classrooms featured windows on only one side of the classroom.

Table 1.

Building characteristics of portable and traditional classrooms among study schools A, B, and C

Characteristics School A Portable (n=4) Traditional (n=1) School B Portable (n=1) Traditional (n=1) School C Portable (n=4) Traditional (n=1)
Acquisition status New, ≤3 years before study Built ≥3 years before study New, renovated 1 year before study (originally built 15 years before study) Built ≥3 years before study New, renovated 1 year before study (originally built 10 years before study) Built ≥3 years before study
Replacement status --- No renovation --- No renovation --- Lighting, floor, and HVAC unit replaced in last 3 years
Roof composition Synthetic rubber Composite shingle or tar/gravel Synthetic rubber Composite shingle or tar/gravel Synthetic rubber Composite shingle or tar/gravel
Exterior walls composition Concrete-based, mixed wood/panel board, metal Masonry Concrete-based, mixed wood/panel board, metal Masonry Concrete-based, mixed wood/panel board, metal Masonry
Interior walls composition Vinyl-coated or gypsum dry wall Painted cinderblock Vinyl-coated or gypsum dry wall Painted cinderblock Vinyl-coated or gypsum dry wall Painted cinderblock
Floor composition Entirely carpeted Concrete Entirely carpeted Entirely carpeted Entirely carpeted Concrete
Open in a new tab

On average, 23 students occupied both PCs and TCs, with 83 percent typically changing rooms during the day, with the exception of two classrooms—one PC and one TC—where students stayed all day. The average time students spent inside the same classroom was 1.8 hours for PCs and 4.2 hours for TCs. Teachers typically spent six or more hours in the same classroom five days per week. Among the five classrooms with doors opening directly to the outdoors (all portable classrooms), teachers of three classrooms reported occasionally leaving the door open during the school day. Of twelve teachers, five reported occasionally opening the classroom windows for natural ventilation. Each of the twelve classrooms had functioning air conditioning units and a thermostat; only one traditional classroom teacher reported not being able to adjust the thermostat because it was locked. Two teachers reported turning off the air conditioning frequently, and two reported turning it off occasionally.

At the time the samplers were placed inside the classrooms (7 AM for day and 4 PM for overnight measures), none of the classrooms had open windows or exhaust vents and the AC was on only in two PCs and one TC at the beginning of the overnight sampling period, and in one PC at the beginning of the day sampling period. Four of 48 formaldehyde samples were void during the sampling period due to battery pump failure (three during the day and one overnight). Overall, across schools (A, B, and C), classroom types (portable, traditional), and sampled period (overnight, day), measured levels of formaldehyde ranged from 0.0068 ppm to 0.038 ppm with a median of 0.017 ppm. Figure 1 illustrates measured overnight and day formaldehyde levels in all twelve classrooms. No statistically significant differences were observed when comparing formaldehyde levels in TCs versus PCs for daytime (t(10) = −0.05, p value = 0.96) or overnight (t(10) = −0.43, p=0.68) periods (TCs shown in light gray box). School A consistently presented the highest concentrations of formaldehyde across sampled period and classroom type. School C presented the lowest levels among the PCs. The overall variability in formaldehyde concentrations in schools A and B was greater than in school C, respectively (SD =0.010, 0.010, and 0.0048 ppm).

Figure 1.

Figure 1

Open in a new tab

Average Indoor Air Formaldehyde Levels In Portable and Traditional Classrooms

Between-school variability, measured by comparing the average and median values and the ranges of measured values, was also substantially high. Median values, for both classroom types, in school A (0.031 ppm ) were over twice as high as in schools B and C (0.011 and 0.012 ppm, respectively), and means were 0.027, 0.016, and 0.013 ppm for schools A, B, and C, respectively. The day average concentration of formaldehyde (ppm) was higher in TCs (0.019) than in PCs (0.016); however, the highest value was found in a PC (0.034) (Table 2). Overnight mean formaldehyde levels were similar for PCs and TCs. Both overnight mean and median levels were higher than day levels across the two types of classrooms but these differences were not statistically significant (t(22)=1.24, p=0.23). Day–night differences among formaldehyde levels may be reflective of differences in classrooms’ night-time HVAC settings.

Table 2.

Day and overnight environmental measures distribution (mean, standard deviation (SD) and range) for portable and traditional classrooms

Portable (n = 9) Tradition (n = 3)
Day Mean Median SD Min Max Mean Median SD Min Max
Formaldehyde (PPM) 0.016 0.011 0.011 0.0068 0.034 0.019 0.016 0.009 0.012 0.029
CO2 (PPM) (1) 890 780 440 480 1800 1300 1400 216 1000 1400
Temperature (C) 21.4 1.4 19.5 23.4 22.3 1 21.3 23.3
RH (%) 48 10.6 37.7 69.7 47.3 10.3 38.8 58.8
Overnight Mean Median SD Min Max Mean Median SD Min Max
Formaldehyde (PPM) 0.022 0.018 0.011 0.0073 0.038 0.022 0.019 0.014 0.01 0.038
CO2 (PPM) (2) 560 580 72 470 680 610 540 166 480 790
Temperature (C) 25.3 1.9 22.2 27.4 25.1 1.4 24.1 23.3
RH (%) 43.6 5.2 37.3 53.9 38.2 3.2 35.8 58.8
Open in a new tab

Footnotes

(1) CO2 measured at 4:00 PM

(2) CO2 measured at 7:00 AM

RH = relative humidity

Temperature and relative humidity (RH) exhibited small variations, compared to formaldehyde and CO2 concentrations. Seven classrooms (3 traditional and 4 portable) had at least one of the measured indoor CO2 concentrations above 1,000 ppm. Outdoor CO2 concentrations were 380 ppm, 420 and 420 ppm at schools A, B, and C, respectively. Table 2 summarizes descriptive statistics (mean, median, SD, range) of day and overnight environmental measures. CO2 AM and PM concentrations were significantly different (t(22)=3.36, p=0.003). However, the overall difference in CO2 concentrations between PCs and TCs (including day and night measurements) were not statistically significant (t(22)=−1.28, p=0.21) (Figure 2). CO2 day concentrations did not differ between PCs and TCs (t(10)=−0.75, p=0.47), nor did overnight concentrations between PCs and TCs (t(10)=−1.46, p=0.18) (Figure 2). Temperature and RH median values were similar between PCs and TCs (Table 2). Indoor temperatures were higher overnight than during the day, and this finding was very similar among PCs and TCs. Measured indoor RH was higher during the day than overnight, and again, RH was fairly similar across the two types of classrooms.

Figure 2.

Figure 2

Open in a new tab

Average Indoor Carbon Dioxide Levels in Portable and Traditional Classrooms

DISCUSSION

Formaldehyde levels in PCs measured during this investigation were similar to those measured in TCs and those found in portable trailers in California (CARB, 2003), and below levels observed to result in eye and nasal irritation, and increased risk of asthma (ATSDR, 2010). The mean formaldehyde levels measured in a comprehensive study of air quality in portable classrooms conducted by the California Air Resources Board were 0.015 ppm for PCs (n=135) and 0.012 ppm for TCs (n=64); indoor CO2 and humidity showed positive associations with formaldehyde levels (CARB, 2003). The measured levels of formaldehyde in air were below the American Conference of Governmental Industrial Hygienists’ (ACGIH®) Threshold Limit Value (TLV®) for formaldehyde of 0.3 ppm as a ceiling concentration not to exceed during the work day (ACGIH, 2001).

In this pilot study, teachers from PCs complained more about indoor noise, specifically noise produced by the HVAC system, than teachers from TCs and a few teachers reported having to turn the air conditioning off because of its excessive noise, a finding similar to that observed in the CARB study (CARB, 2003) (data not shown). Because HVAC systems tend to reduce indoor volatile organic compounds, including formaldehyde, among other chemical and microbiological potential sources of respiratory illness, it is important that these systems are well designed and functioning adequately. HVAC systems are often used to mechanically ventilate classrooms, although these systems may provide less ventilation than intended as a result of design and installation problems, poor maintenance, and infrequent operation during occupancy (Shendell, Winer, Weker, & Colome, 2004b).

Because measuring the actual ventilation rate requires specialized skill and equipment, the indoor concentration of CO2 has been used as a surrogate for the ventilation rate per occupant, including in schools (Lee & Chang, 1999); Shaughnessy, Haverinen-Shaughnessy, Nevalainen, Moschandreas, 2006; Shendell, et al., 2004). The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) developed consensus standards and a guideline for HVAC systems. The ANSI/ASHRAE 62.1-2007: “Ventilation for Acceptable Indoor Air Quality” recommends that indoor CO2 concentrations be no greater than 700 ppm above outdoor CO2 concentrations in order to satisfy comfort needs of the majority of occupants (ASHRAE, 2009). This standard corresponds to indoor levels less than 1080 ppm since outdoor CO2 concentrations usually range between 380 to 410 ppm. NIOSH, 2008, states that “Elevated CO2 concentrations suggest that other indoor contaminants may also be increased.” The Occupational Safety & Health Administration's (OSHA) permissible exposure limit for indoor CO2 is 5000 ppm (OSHA).

In this pilot investigation, elevated (>1,080 ppm) levels of CO2 were observed, particularly in TCs, in concurrence with the findings of Shendell, et al. (2004) of lower ventilation rates in TCs than in PCs. Although the levels of CO2 concentrations observed in this pilot study do not represent a health threat, this finding is noteworthy because lower rates of ventilation, as indicated by higher CO2 concentrations, are known to be associated with increased respiratory illness (Fisk, 2000). In addition, high CO2 concentrations have been associated with relative increases in students’ school absence (Mendell, Eliseeva, Davies, Spears, Lobscheid, Fisk, & Apte, 2013; Shendell et al., 2004b) and lower performance (Haverinen-Shaughnessy, Nevalainen, Moschandreas, & Shaughnessy, 2010; Mendell & Heath, 2005). It might be noted that OSHA standards for exposure concentrations do not apply to children, who may be at greater risk to adverse effects from exposure to CO2.

These results demonstrated the feasibility of conducting indoor air quality investigations in the school environment with minimal disruption on school days – the goal of the investigation. This pilot investigation has a number of limitations. First, the field team was allowed limited, fixed time on the schools’ grounds and inside classrooms, a restriction reducing the ability to complete a comprehensive walk-through survey in classrooms. Because the data collection occurred in the last week of the school year, conditions may not have been representative of the whole year pattern, and such factors (e.g., attendance) could have affected the magnitude of measured indoor CO2 concentrations. A 100 percent questionnaire response rate was attributed to a small sample size and the ability of the school system's IAQ Coordinator to follow up with facility managers and teachers. This questionnaire may be useful for conducting similar school air quality investigations, particularly for study designs involving larger sample sizes.

Because this pilot study was carried in only one school district, interpretation of results was limited to these parameters as well as a relatively small number of classrooms sampled and different configurations of classrooms in each school. Further, sampling newly manufactured portable classrooms which might be expected to off-gas more formaldehyde than older ones was not possible. Lastly, airborne particulate levels in PCs were not measured although classrooms often were located adjacent to particulate sources such as parking lots and roadways.

Conclusion

Consistent with previous findings, the levels of formaldehyde measured in PCs were similar to levels observed in TCs. Elevated levels of CO2 were found in both PCs and TCs, indicating inadequate ventilation. On the basis of this work, we believe that a well-designed study of portable and traditional classrooms would be an appropriate effort that should not only examine formaldehyde levels and ventilation in portable classrooms, including CO2 levels, but also address other potential factors affecting indoor environments in PCs and TCs. Upon acquisition or renovation of PCs, a school district is encouraged to access resources, such as the Environmental Protection Agency's Indoor Air Quality Tools for Schools Reference Guide and Design Tools for Schools (EPA, 2009, 2010).

Acknowledgments

The authors would like to thank Drs. Susan Lance and John Horan from the Georgia Division of Public Health, and David Williams and Richard Whatley from the participating school district for providing invaluable support for this activity. The assistance of the district's IAQ coordinator greatly facilitated the gathering of questionnaire data. We also appreciate the schoolteachers for responding to the questionnaires. We also thank Dr. Michael McGeehin (NCEH) for generating the project idea, Dr. Paul Garbe (NCEH), Susan Moore and Dr. Susan Metcalf (ATSDR) for providing technical input on data collection planning and implementation, Dr. Anne Sowell (ATSDR) for providing technical feedback, Karl Feldman (NIOSH) for supporting our equipment needs, and ATSDR's field sampling team: LT Chris Fletcher, Jane Zhu and Rachel Worley. This project was funded by National Center for Environmental Health (NCEH) and Agency for Toxic Substances and Disease Registry (ATSDR).

The findings and conclusions in this presentation are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention. Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

Footnotes

Human Subjects Approval Statement: This pilot investigation was completed as a CDC Epi-AID to the State of Georgia and met all the CDC Human Subjects requirements.

REFERENCES

  1. Agency for Toxic Substances and Disease Registry (ATSDR) Addendum to Toxicological Profile for Formaldehyde, Health Effects. Author; 2010. Retrieved from http://www.atsdr.cdc.gov/ToxProfiles/formaldehyde_addendum.pdf. [PubMed] [Google Scholar]
  2. American Conference of Governmental Industrial Hygienists (ACGIH) TLVs® and BEIs® Based on the Documentation of Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices. Formaldehyde. American Conference of Governmental Industrial Hygienists, Inc.; Cincinnati, OH.: 2014. [Google Scholar]
  3. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Ventilation for Acceptable Indoor Air Quality. Author; 2009. [Google Scholar]
  4. California Air Resources Board (CARB) California Portable Classrooms Study. Author; 2003. Retrieved from http://www.arb.ca.gov/research/indoor/pcs/pcs-fr/pcs-fr.htm. [Google Scholar]
  5. Centers for Disease Control and Prevention (CDC) Final Report on Formaldehyde Levels in FEMA-Supplied Travel Trailers, Park Models, and Mobile Homes. Author; 2008. Retrieved from http://www.cdc.gov/nceh/ehhe/trailerstudy/pdfs/FEMAFinalReport.pdf. [Google Scholar]
  6. Environmental Protection Agency (EPA) Indoor Air Quality Tools for Schools Reference Guide (EPA 402/K-07/008) Author; 2009. Retrieved from http://www.epa.gov/iaq/schools/tfs/refguide_toc.html. [Google Scholar]
  7. Environmental Protection Agency (EPA) Indoor Air Quality Design Tools for Schools. Environmental Protection Agency. Author; 2010. Retrieved from http://www.epa.gov/iaq/schooldesign/ [Google Scholar]
  8. Faustman EM, Silbernagel SM, Fenske RA, Burbacher TM, Ponce RA. Mechanisms underlying children’s susceptibility to environmental toxicants. Environ Health Perspect. 2000;108(suppl 1):13–21. doi: 10.1289/ehp.00108s113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Fisk WJ. Health and productivity gains from better indoor environments and their relationship with building energy efficiency. Ann Rev. Energy Environ. 2000;25:537–566. [Google Scholar]
  10. Hanrahan LP, Dally KA, Anderson HA, Kanarek MS, Rankin J. Formaldehyde vapor in mobile homes: a cross sectional survey of concentrations and irritant effects. Am J Public Health. 1984;74(9):1026. doi: 10.2105/ajph.74.9.1026. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Haverinen-Shaughnessy U, Nevalainen A, Moschandreas DJ, Shaughnessy RJ. Association between substandard classroom ventilation rates and students’ academic achievement. Indoor Air. 2010;21:121–131. doi: 10.1111/j.1600-0668.2010.00686.x. [DOI] [PubMed] [Google Scholar]
  12. Hodgson AT, Shendell DG, Fisk WJ, Apte MG. Comparison of predicted and derived measures of volatile organic compounds inside four new relocatable classrooms. Indoor Air. 2004;14(suppl 8):135–144. doi: 10.1111/j.1600-0668.2004.00315.x. [DOI] [PubMed] [Google Scholar]
  13. Krzyzanowski M, Quackenboss JJ, Lebowitz MD. Chronic respiratory effects of indoor formaldehyde exposure. Environ Res. 1990;52:117–125. doi: 10.1016/s0013-9351(05)80247-6. [DOI] [PubMed] [Google Scholar]
  14. Lee SC, Chang M. Indoor air quality investigations at five classrooms. Indoor Air. 1999;9:134–138. doi: 10.1111/j.1600-0668.1999.t01-2-00008.x. [DOI] [PubMed] [Google Scholar]
  15. Mendell MJ, Eliseeva EA, Davies MM, Spears M, Lobscheid A, Fisk WJ, Apte MG. Association of classroom ventilation with reduced illness absence: a prospective study in California elementary schools. Indoor Air. 2013;23(6):515–28. doi: 10.1111/ina.12042. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Mendell MJ, Heath GA. Do indoor pollutants and thermal conditions in school influence student performance? A critical review of the literature. Indoor Air. 2005;15:27–52. doi: 10.1111/j.1600-0668.2004.00320.x. [DOI] [PubMed] [Google Scholar]
  17. Meyer B. Urea-Formaldehyde Resins. Addison-Wesley Publishing Co. 1979 [Google Scholar]
  18. National Center for Education Statistics (NCES) Public School Principals Report on their School Facilities: Fall 2005. Author; 2007. Retrieved from http://nces.ed.gov/pubs2007/2007007.pdf. [Google Scholar]
  19. National Center for Education Statistics (NCES) Digest of Education Statistics National Center for Education Statistics. Author; 2008. Retrieved from http://nces.ed.gov/programs/digest/d08/index.asp. [Google Scholar]
  20. National Institute for Occupational Safety and Health (NIOSH) Manual of Analytical Methods (NMAM®) 4th ed. Author; 1994. [May 25, 2013]. Publication 94-113. Retrieved from http://www.cdc.gov/niosh/nmam/pdfs/2016.pdf. [Google Scholar]
  21. National Institute for Occupational Safety and Health (NIOSH) Safety and Health Topic: Indoor Environmental Quality: Building Ventilation. Author; 2008. Retrieved from http://www.cdc.gov/niosh/topics/indoorenv/BuildingVentilation.html. [Google Scholar]
  22. National Toxicology Program (NTP) Thirteenth Report on Carcinogens. National Institute of Environmental Health Sciences. Research Triangle NC; 2014. [Google Scholar]
  23. Norsted SW, Kozinetz CA, Annegers JF. Formaldehyde complaint investigations in mobile homes by the Texas Department of Health. Environ Res. 1985;37(1):93–100. doi: 10.1016/0013-9351(85)90052-0. [DOI] [PubMed] [Google Scholar]
  24. Occupational Safety and Health Administration 29 CFR 1910.1000 Air Contaminants. 2006 Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9992.
  25. Sexton K, Petreas M, Liu KS. Formaldehyde exposures inside mobile homes. Environ Sci Technol. 1989;23(8):985–988. [Google Scholar]
  26. Shaughnessy RJ, Haverinen-Shaughnessy U, Nevalainen A, Moschandreas DA. A preliminary study on the association between ventilation rates in classrooms and student performance. Indoor Air. 2006;6(6):465–468. doi: 10.1111/j.1600-0668.2006.00440.x. [DOI] [PubMed] [Google Scholar]
  27. Shendell DG, Prill R, Fisk WJ, Apte MG, Blake D, Faulkner D. Associations between classroom CO2 concentrations and student attendance in Washington and Idaho. Indoor Air. 2004;14:333–341. doi: 10.1111/j.1600-0668.2004.00251.x. [DOI] [PubMed] [Google Scholar]
  28. Shendell DG, Winer AM, Weker R, Colome SD. Air concentrations of VOCs in portable and traditional classrooms: Results of a pilot study in Los Angeles County. J Expo Anal Environ Epidemiol. 2004a;14:44–59. doi: 10.1038/sj.jea.7500297. [DOI] [PubMed] [Google Scholar]
  29. Shendell DG, Winer AM, Weker R, Colome SD. Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County. Indoor Air. 2004b;14:154–158. doi: 10.1111/j.1600-0668.2004.00235.x. [DOI] [PubMed] [Google Scholar]
  30. Wantke F, Demmer CM, Tappler P, Götz M, Janisch R. Exposure to gaseous formaldehyde induces IgE-mediated sensitization to formaldehyde in school-children. Clinical and Experimental Allergy. 1996;26:276–280. [PubMed] [Google Scholar]

RESOURCES