Grantee Research Project Results
Final Report: Longitudinal Studies of Indoor Air Quality in Office Buildings
EPA Grant Number: R825272Title: Longitudinal Studies of Indoor Air Quality in Office Buildings
Investigators: Batterman, Stuart A. , Franzblau, Alfred , Baker, Wayne
Institution: University of Michigan
EPA Project Officer: Chung, Serena
Project Period: July 1, 1997 through June 30, 2000 (Extended to June 30, 2002)
Project Amount: $430,000
RFA: Air Quality (1996) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics
Objective:
The overall objectives of the study were to identify and quantify effects of various indoor pollutants and potential mitigation strategies, and to improve protocols for building investigations. The study addressed relationships between indoor air quality (IAQ), occupant health and comfort, and mitigation strategies. The study was designed to relate direct measurements of IAQ to building-related illness (BRI) and sick building syndrome (SBS), in the hope of increasing the understanding of the relationships between occupant health, building system operation, and air quality.
The study used a series of controlled interventions in large, mechanically ventilated office buildings with simultaneous measurements of IAQ parameters and surveys of occupant health and perception. The experimental interventions included variations in fresh air exchange; ventilation rates; heating, ventilating, and air-conditioning (HVAC) scheduling/operation; humidity; nighttime purge; filtration; and cleaning. A psychosocial survey was used to account for job-related and personal cofactors that may affect reporting results of the IAQ and symptom survey. The blind, controlled, and repeated measures design of the study was intended to provide high discriminatory power, experimental controls, and carefully controlled interventions to minimize the effects of confounding factors. Statistical analyses of survey results in conjunction with various IAQ indicators were used to control for confounding and indicate the controlling factors.
Summary/Accomplishments (Outputs/Outcomes):
Building Selection
Building selection was a critical factor for this study, as it determines: (1) the study population; (2) the feasible interventions; and (3) current IAQ exposures. After site visits and detailed examination of a number of candidate buildings, we selected a six-story building (including an occupied basement) that was constructed in the early 1980s. The building dimensions are approximately 56 feet by 115 feet, and the total occupied area is approximately 40,000 square feet. Floors 2-5 contain mostly small office spaces, and open areas are targeted for study. Each floor accommodates 45-60 individuals, giving a total target population of about 240. This building is connected to two other buildings. The selected building is a non-problem building (see exceptions described below).
One of the major advantages of the selected building was the ability to manipulate the HVAC systems. The building utilizes five, nearly identical, variable air volume, air-handling units (AHU). A 14,000 cfm AHU services the basement and first floor. The remaining floors use a separate 9,000 cfm AHU located on the same floor. The air intake for the five AHUs is a common vertical louver on the building’s west side; the relief is a similar vertical louver located nearby. The reliefs are located above a loading dock, and the intakes are around a corner of the building from the loading dock along a busy street; there have been occasional complaints about an unpleasant odor. The HVAC systems use pleated prefilters and medium-efficiency bag filters. Carbon-impregnated prefilters have been used to control odors. The AHUs had sufficient room for installation of monitoring equipment and possibly additional filtration equipment upstream of the prefilters and bag filters. Beyond the filters and heating/cooling decks, direct steam humidification is provided, although not normally used. The mechanical rooms were clean and relatively spacious. Each system is equipped with direct digital control (DDC) systems linked to a central computer. The older, mechanical gauges remain in place and are functional. The DDC system monitors and/or controls temperatures, airflows, humidity, and damper positions.
The ground-level floor differs from other floors in that it has greater occupant traffic leading to elevators and stairs, and its doors allow largely uncontrolled entry of outside air, dust, etc. This floor was not examined. The similarity of building systems on most floors was advantageous to the study, as the HVAC systems on selected floors could be altered independently.
IAQ Monitoring
This project involved a variety of IAQ monitoring, including continuous, integrated, and grab-sampling. The integrated and grab-sampling approaches are standard. The continuous monitoring approaches are innovative, and three identical systems were developed to provide continuous monitoring of eight environmental parameters. Each system contained the following sensors:
· Temperature was continuously measured using a solid-state device (Omega HX93V).
· Relative humidity was continuously measured using a capacitive, solid-state device (Omega HX93V).
· Carbon dioxide was continuously measured using a nondispersive, infrared detector (Vaisala GMW21).
· Illuminance was measured continuously using a solid-state photodetector (Extech Instruments 401021 Light Adaptor). The interface circuitry caused the output signal to track other, higher-output sensors. Therefore, illuminance data were suspect and not used in analyses.
· Sound pressure level was measured continuously using a microphone with appropriate frequency response and damping (Radio Shack Analog Sound Level Meter, 33-2050).
· Total volatile organic compounds (TVOCs) were continuously measured using a photoionization detector (RAE Systems ModuRAE, PDM-10A). Speciated volatile organic compounds (VOCs) also were monitored with collection, using a sorbent tube and laboratory analysis by gas chromatography/mass spectrometry (GC/MS). The photoionization detector was found to be highly temperature-dependent, resulting in significant and frequent loss of calibration during thermal cycling. Therefore, TVOC data collected from the photoionization detector were suspect and not used in analyses.
· Motion was measured continuously using a differential infrared sensor (Radio Shack Passive Infrared Motion Sensor, 49-208). This technology commonly is used in intruder alert systems. The sensor indicates activity near the monitoring location and is configured to provide sensitivity in a wide aperture and at an adjustable distance. The instantaneous response obtained from the sensor was integrated and dampened using a low-pass filter, making the final output signal proportional to the amount of activity within the sensing region. This approach did not strictly quantify the number of individuals near the monitoring location, but it did indicate activity near the monitoring site that may affect monitoring results. This method is innovative in the context of IAQ investigations.
Each sensor was interfaced to a data acquisition system consisting of an 8-channel 12-bit analog-to-digital card (Computer Boards PCM-DAS08), a laptop personal computer (PC) (Hitachi Vision Book Plus 4140X), and software (Labtech Notebook Pro, version 10.0). The sensors, interface circuitry, PC, and related equipment were housed inside an enclosure designed to accommodate requirements for component cooling, power, airflow, and security. The enclosure occupied about 2 cubic feet.
Calibration methods were developed for most of the sensors, and standard protocols were developed for laboratory and field maintenance and calibration.
The data acquisition hardware and software were configured to record at 1 Hertz, and write data to log files after calculating 1-minute and 1-hour averages. Log files were created at the beginning, and closed at the end, of each day to minimize data loss in case of a catastrophic event, such as a power failure. The log files consist of nine tab-delineated columns of numbers, each column corresponding to the block-averages of the analog voltage output of each sensor, plus a time column recording the time of day each set of entries is written to the file. This numerical information was imported into an Excel spreadsheet application, where it was converted to relevant values (e.g., parts per million) using information obtained during the calibration procedures. The converted values were then trended as scatter plots, with time as the ordinate, and the converted value(s) as the abscissa. The trends then were displayed using identical time scales to facilitate comparison of variables. In addition to trending, this data format readily lent itself to statistical analysis, using functions bundled into Excel and other statistical analysis applications (e.g., Systat, version 10.0).
Particulate concentration was measured using conventional low-flow filter samples from which concentrations are quantified gravimetrically. Speciated VOCs were measured using integrated sampling and GC/MS analysis based on the U.S. Environmental Protection Agency Compendium Method Toxic Organic-17, and detailed in Batterman and Peng (2000).
Bioaerosol samples were taken each Wednesday morning from June 7–August 16, 2000, shortly after sampling for speciated VOCs and particulate matter (PM2.5) had begun. To estimate sampling precision, sequential duplicate samples were collected on the 5th floor of the study building each week with each agar type. Field blanks of each agar type were taken every week on the 5th and 2nd floors and transported, incubated, and counted, along with the sample agars. In total, 21 samples were taken per week.
To characterize indoor nonvitreous fiber concentrations and to measure the effects, if any, of HVAC cleaning interventions, a pilot study measuring fiber concentrations was conducted from June to mid-August 2000. Fiber data were collected following procedures in the National Institute for Occupational Safety and Health (NIOSH) Method 7400, "Asbestos and Other Fibers by Phase Contrast Microscopy (PCM)."
IAQ measurements continued through the interventions. Bioaerosol and fiber measurements were discontinued after August 15, 2000, as levels were very low. Integrated samples of PM2.5 and VOCs (for GC-MS analysis) continued though June 6, 2001. The three continuous monitoring arrays discontinued operation around the same time. Building performance data (including temperatures in the supply, return, and mixed air plenums; supply and return airflow; the mixed air damper position; and outside temperature and relative humidity) were collected through this period. These samples, constituting a large amount of data, were carefully analyzed, trended (plotted), and checked for quality assurance/quality control.
In a complementary research project, a multipoint monitoring system was installed in the building. Samples were taken at two to four sites on each floor of the building, and at several heights outdoors. A total of 21 measurement sites were monitored for ammonia, CO2, NO, NO2, NOx, O3, and TVOC. Installation was performed during the week of March 14-17, 2000, in the evening, to avoid interferences with building occupants. This system has the advantage of characterizing the spatial and temporal variability of IAQ levels throughout the building, and several additional pollutants were monitored beyond the scope. Several time periods of data were selected from the 2000-2001 overall time period for intensive analysis, including validation of the sampler arrays. [On June 15-16, 2000, we discovered and repaired anomalies in the sampling sequence. This was repaired in September 2000, and all sites were validated using a CO2 scrubber. Also at this time, the system controller (computer) was replaced, and the ammonia sensor was removed. As levels fell below detection limits, a 3rd floor, outside-air sampling point was added. In October, we added O3 and NOx sensors.
Occupant Survey
Several questionnaires were administered to building occupants to gather information regarding: (1) demographics; (2) medical history; (3) symptoms and perceptions, such as odors and irritants; and (4) psychosocial factors, such as perceived stress. The initial questionnaire administered to occupants was fairly lengthy (18 pages), but comprehensive, innovative, and the product of an extensive review of the literature. The followup survey, administered during each intervention, was short (3 pages) and focused on symptoms and perceptions.
Both questionnaires underwent extensive revision and many iterations. The questionnaires were evaluated in pilot tests using a small group (11 individuals) who were individually interviewed following the survey administration. The pilot study identified potential problems related to the length, wording, confidentiality, ease of completion, and other features.
Presentations were made to staff in the buildings, and letters were sent to recruit subjects for the study. Contacts were made on each floor and in each group to discuss procedures. Some difficulties were encountered in several groups because managers were reluctant to participate, and additional time was needed to inform managers of the goals and procedures of the research. Ultimately, most managers were cooperative. Institutional Review Board procedures were followed in each phase, including recruiting and obtaining consent.
In December 1999, the initial survey was administered to 40 of the approximately 85 eligible subjects recruited in the building. Subsequently, a total of six waves of followup surveys were administered to the subjects (including eight new occupants of the study floors who agreed to participate in October 2000), until the closing of the field portion of the study in June 2001. Institutional Review Board procedures were followed in each phase, including recruiting and consenting.
Building Interventions
Mechanical drawings, key plans, and other technical information for the case study building were obtained. Trending of the HVAC system operation was completed, and computer files of hourly averages of all measured and controlled variables were generated weekly. An energy report for the building was developed. This information was used to define the "envelope" for potential building interventions, including changes in ventilation, outside air, pressurization, humidity, and filtration. The interventions were mandated to meet minimum air requirements and to not impose excessive energy costs.
Several filtration companies were contacted and willing to donate materials and services to this project. We investigated the feasibility of installing gas-phase filtration systems upstream from the existing particulate filters to remove oxidants, sulfur, and VOCs. We also investigated the feasibility of retrofitting the existing, direct-steam injection system with a secondary steam system to avoid problems associated with anticorrosive steam agents (such as amines). Ultimately, we were unable to implement either intervention for a variety of reasons (see below).
Interventions accomplished included the following: (1) removal of fibrous insulation and painting of the interior surface with an antimicrobial paint from HVAC units on floors 2 and 4 (June 18–July 17, 2000, respectively); (2) removal of fibrous insulation and painting for HVAC units on floors 3 and 5 (June 19, 2000); (3) building pressurization (March 2001); (4) informational (psychosocial) intervention (April 25, 2001); and (5) changeover from heating to cooling systems (each fall and spring). We also attempted to implement a humidification intervention in February 2001, but the was vetoed by management. The pressurization intervention included installation of pressure sensors on each floor, coupled to the DDC system. Tests wherein return fans and bathroom exhaust fans were shut completely and supply fans were turned on fully on each floor provided less than 0.01" H2O pressure, a change approximately equal to the normal fluctuations caused by wind or doors opening. Shutting down floors above and below the test floor somewhat increased the differential. Overall, the pressure differential could not be maintained in a feasible manner. During these tests, we discovered a malfunctioning vortex fan damper on floor 5, which was subsequently corrected.
Study Results
This research investigated several innovative methods for measuring environmental parameters. Cart-mounted measurement systems automatically recorded responses from multiple sensors into computer-based, data acquisition systems each second, providing very detailed trend data over extended periods (days-to-weeks) without the need for a technician. A prototype, multi-point system measuring CO2 and TVOC at several points on each of the six floors provided detailed spatial information. Both systems generate enormous quantities of data and provide the ability to characterize both the spatial and temporal fluctuations of several indoor parameters with great accuracy. The second system, a prototype multi-point sampling system, showed significant potential for characterizing the spatial dimension of several key comfort parameters.
Several sensor types did not function adequately under field conditions. In particular, the photoionization detectors did not have the sensitivity nor the temperature stability necessary to measure the low levels of VOCs encountered. Also, the signal-to-noise ratio was too low for the light meter to provide reliable data. Therefore, data from these systems were excluded. Other measurement types on the sensor arrays performed well.
The temporal data captured by the measurement systems allow analysis of both short- and long-term trends that can be used to identify emission sources and operational issues affecting air quality. For example, trend data indicated brief periods during which conference rooms in the case study building were overcrowded and/or inadequately ventilated. In a separate study in a dental clinic, trend data, obtained using the same sensor array, identified high, short-term exposures to PM, a potential concern, given that such material may be pathogenic (Godwin, et al., 2003). Trend data also permit much more detailed characterization of IAQ and comfort factors for epidemiologic uses, potentially reducing exposure misclassification.
Air quality was measured over a 17-month period at three locations in the case study building. Concentrations of carbon dioxide, VOCs, fibers, bioaerosols, and PM under 2.5 µm were comparable to, or lower than, concentrations measured in similar U.S. buildings. Indoor concentrations were lower than published standards and recommendations. Comfort parameters (temperature and humidity) measured in the study building were within recommended guidelines, except for relative humidity in the heating season. Significant cross-floor differences were found for comfort parameters in some seasons. Because each floor had different workgroups, floor plans, workstation configurations, etc., variations in the results may have reflected personal preferences in thermostat settings, the locations of the measurement systems, as well as HVAC system functioning.
Among study participants, the frequency of symptoms ranged from 1.1 percent to 50 percent and generally were comparable to those reported in other U.S. surveys. The most common symptoms were found in upper respiratory, eye, and musculoskeletal categories. Using the SBS case definition, which required that the symptoms occur only in the workplace, the relative frequency was 0.5 percent to 31.7 percent, with the most common symptoms being described as "tired or strained eyes" (31.7 percent), "pain or numbness in shoulder or neck" (21.1 percent), and "eye irritation" (17.9 percent). As in other studies, women reported more symptoms than did men. These figures are slightly lower than, but generally comparable to, those reported in other surveys of large office buildings. Frequencies of negative environmental perceptions reported by participants ranged from 1 percent to 41 percent, with the most common complaints being "too dry" (41 percent), "too hot" (36 percent), "too cold" (35 percent), and "too little air movement" (35 percent). These frequencies also are comparable to those reported in other U.S. surveys.
It is noteworthy that the greatest frequency of symptoms and negative perceptions occurred during the heating season, in part because of very low relative humidity levels. In contrast, much of the current IAQ activity and remediation actions are associated with mold growth resulting from excessive humidity, as well as water leaks, clogged drains, etc. It is suspected that the seasonal patterns found in the case study building also are found in other offices in cold climates, because humidification during heating is quite rare. Therefore, this research suggests that increased attention be paid to occupant health and comfort during periods of low humidity to potentially reduce occupant complaints.
The HVAC cleaning intervention did not alter measured air pollutant concentrations significantly, but it did appear to affect a few symptoms and environmental perceptions. After controlling for sex, age, perceived stress, time effects, and selected IAQ parameters (such as temperature and relative humidity) in the multivariate models, the only participant outcomes changed by the intervention were "sinus irritation" and perceptions of odor. Although removing fibrous insulation and cleaning the HVAC system did not produce dramatic results in this study, such actions may be helpful in rectifying problems in a building or a contaminated HVAC unit. In a nonproblem building, these efforts may help to avoid future problems. The fact that measured building levels were not significantly altered may be a result of low levels of contaminants in the building, levels changing in places other than those monitored, or temporal changes correlated with the interventions such as seasonal changes.
The informational document intervention was designed to test the hypothesis that providing relevant information to occupants regarding IAQ would affect their perceptions of the indoor environment and possibly their health symptoms. No effects consistent with this hypothesis were found. The negative findings, however, should not be interpreted to mean that informing occupants of building conditions may not be helpful in reducing occupant complaints. Psychological factors appear to be important contributors to SBS; therefore, further research using larger sample sizes and better controls is needed.
The operational mode of the HVAC system (heating, cooling, economizer) appeared to affect several symptoms and perceptions. "Dry or itchy skin" and "tobacco smoke odors" decreased with higher ventilation rates during economizer modes. These findings generally are consistent with previous studies, which show that some symptoms and perceptions become less frequent during periods of relatively high ventilation, as compared to air-conditioned periods.
Because this study used data collected over an 18-month period, many changes occurred in the building and workplace other than the HVAC system operation, including, renovation, painting, floor plan alterations, workload changes, outdoor pollutants, pollen, and humidity. Such changes are normal and unavoidable and therefore, do not represent unusual conditions; however, they might affect participants’ responses. Most building and workplace factors will be confined to a (often small) section of the workplace and thus should not greatly affect results. Nevertheless, the possibility of such changes should be considered in planning and conducting building studies.
Reference:
National Institute for Occupational Safety and Health. Method No. 7400: asbestos and other fibers by PCM., accessed January 3, 1994.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 10 publications | 3 publications in selected types | All 3 journal articles |
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Batterman S, Metts T, Kalliokoski P, Barnett E. Low-flow active and passive sampling of VOCs using thermal desorption tubes: theory and application at an offset printing facility. Journal of Environmental Monitoring 2002;4(3):361-370. |
R825272 (2000) R825272 (Final) |
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Godwin CC, Batterman SA, Sahni SP, Peng CY. Indoor environment quality in dental clinics: Potential concerns from particulate matter. American Journal of Dentistry 2003;16(4):260-266. |
R825272 (Final) |
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Peng CY, Batterman S. Performance evaluation of a sorbent tube sampling method using short path thermal desorption for volatile organic compounds. Journal of Environmental Monitoring 2000;2(4):313-324. |
R825272 (Final) |
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Supplemental Keywords:
indoor air, exposure, health effects, human health, sensitive populations, volatile organic compound, VOC, survey, social science, epidemiology, monitoring, midwest., Health, Scientific Discipline, Air, Epidemiology, Risk Assessments, indoor air, Atmospheric Sciences, Environmental Engineering, building related illness, fresh air exchange, hvac, office buildings, surveys, occupant health, filtration, ventilation rates, ambient air, workplace, human exposure, mitigation strategies, sick building syndrome, furnaces, indoor air quality, air qualityRelevant Websites:
http://www.sph.umich.edu/faculty/stuartb.html Exit
http://www.cdc.gov/niosh/nmam/nmammenu.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.