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Indoor Air Quality (IAQ)

Overview of the Building Assessment Survey and Evaluation Study

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What is the BASE Study?

The Building Assessment Survey and Evaluation (BASE) study was conducted over a five-year period from 1994-1998, to characterize determinants of indoor air quality (IAQ) and occupant perceptions in representative public and commercial office buildings across the U.S. This study provides normative IAQ data and baseline symptom rates in typical office buildings and establishes standardized testing protocols. The data collected as part of this study

  • allow examination of relationships of symptoms and building characteristics
  • allow for the development of hypotheses to investigate sick building syndrome
  • provide a stronger scientific basis for policy makers to develop guidance on building design, construction, operation and maintenance.

The BASE study used a standardized protocol to collect extensive indoor air quality data from one hundred randomly selected public and commercial office buildings in thirty-seven cities in twenty-five States. The data collected provide normative IAQ data and baseline symptom rates in typical office buildings and includes general information regarding:

  • the building itself
  • indoor pollutant concentrations
  • basic occupant statistics
  • occupant health symptoms and perceptions of indoor air quality
  • the design, maintenance and operation of building HVAC systems

Buildings included in the sample were randomly selected from cities with populations greater than one hundred thousand within ten climatic regions in either winter or summer. Buildings with highly publicized indoor environmental quality problems were excluded.

Information from the one hundred buildings studied as part of BASE including several publications describing the study and summarizing preliminary results are available on this website. In addition, the raw data from this study is available to researchers and others interested in IAQ and office buildings.

This study was conducted by the BASE Workgroup of EPA's Office of Radiation and Indoor Air.

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What Were the Goals and Objectives of the Study?

The primary goal of the study was to address a significant data gap that existed regarding baseline IAQ and occupant perceptions in large public and commercial office buildings. One of the major objectives of the BASE program included providing a database and summary information of IAQ-related parameters in office spaces for the research, building professional and policy-making communities to help further the understanding of indoor air quality and the role of environmental factors in occupant perceptions of IAQ and health symptoms.

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Why Did EPA Conduct This Study?

Early IAQ research in office buildings in the United States focused on evaluating buildings whose occupants had significant complaints about IAQ. Since IAQ baseline information from typical buildings was sparse, no reference existed with which to compare the “problem” buildings. Therefore, the EPA designed the BASE study as a cross-sectional study of office buildings without regard to IAQ complaints.

The study encompasses three major areas of investigation:

  • comfort and environmental measurements
  • building and heating, ventilation and air conditioning (HVAC) characterization
  • an occupant questionnaire

What Type of Data Were Collected?

  • General information was collected regarding the building itself, such as the age, construction features, use, furnishings, renovations, local pollutant sources and general maintenance.
  • The HVAC systems were characterized regarding maintenance, design features, and the amount and quality of fresh air being introduced into the building and, more specifically, the study space (the specific indoor occupied area studied within the building).
  • Environmental measurements including comfort parameters such as light, sound, temperature and relative humidity as well as pollutant concentrations such as particulate matter, volatile organic compounds (VOCs), biological contaminants and radon were collected at three or more sites within the indoor study space and at one outdoor site for each building.
  • Basic occupant demography, health symptoms and perceptions of indoor air quality were collected from occupants within the study space in each building using a questionnaire.

A representative listing of core parameters collected are listed below:

Building and HVAC Characteristics
Environmental Monitoring Building Checklist HVAC Checklist Occupant Survey
  • Particles (PM10, PM2.5)
  • VOCs
  • Formaldehyde
  • Bioaerosols (air, visible growth)
  • Radon
  • Temperature
  • Relative Humidity
  • Carbon Dioxide
  • Sound
  • Light
  • Carbon Monoxide
  • Use
  • Occupancy
  • Geographical Location
  • Ventilation (equipment, operation schedule)
  • Construction
  • Outdoor Sources
  • Smoking Policy
  • Water Damage
  • Fire Damage
  • Renovation
  • Pest Control
  • Cleaning Practices
  • Type Specifications (air handler, exhaust fans)
  • Filtration
  • Air Cleaning Systems
  • Air Washers
  • Humidification Systems
  • Maintenance Schedule
  • Inspection Schedule
  • Supply Air Flow Rate
  • Percent Outdoor Air
  • Outdoor Air Intake Rate
  • Supply Air (temperature, relative humidity)
  • Exhaust Fan Rates
  • Local Ventilation Performance
  • Natural Ventilation
  • Measurements (if needed)
  • Workplace Physical Information
  • Health and Well-being
  • Workplace Environmental Conditions
  • Job Characteristics
  • Occupant Demographics

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Ten Climate Regions of the BASE Target Cities

Building design and operation is influenced by climatic considerations, therefore various climatic regions were represented in the study. The BASE Regional Map is the ten BASE study climatic regions.

See the table below for descriptions of the letter designations for each climatic region

Map of the united states demonstrating Climate Regions

Ten Climate Regions of the BASE Target Cities

  Summer Design Conditions a
Dew Point < 53 °F Dew Point ≥ 53 °F
Temp. < 94 °F
Temp.≥ 94°F
Temp. < 94 °F
Temp.≥ 94 °F
Cool ≤ 10 °F Climate Region
Climate Region
Climate Region
Climate Region
Mod. 11 °F - 32 °F Climate Region
Climate Region
Climate Region
D or I
Climate Region
Hot > 32 °F Climate Region
Climate Region
Climate Region
G or J
Climate Region
G or H

°F = Degrees Fahrenheit
a = 2.5% dry-bulb design temperature
b = 97.5% dry-bulb design temperature

Reference: American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., Chapter 26, Table 1 Climatic Conditions for the United States, in: "1989 ASHRAE Handbook Fundamental."

Please forward all comments and questions concerning BASE and this map to the BASE Workgroup (

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How Can I Obtain the BASE Raw Dataset?

To obtain the BASE data on CD, please read, fill out and sign the Notification Prior to Use Data Form. Mail or fax the completed form to EPA using the information below. Please review your form before you submit it as incomplete forms will delay processing.

Please forward all comments and questions concerning the BASE study to the BASE Workgroup (

US EPA/Indoor Environments Division
BASE Workgroup
1200 Pennsylvania Avenue, N.W.
Mail Code 6609J
Washington, DC 20460
FAX: (202) 343-2393

The data have undergone documented quality assurance procedures and all reasonable efforts have been made to ensure the validity of the data. However, it is expected that anomalies may be discovered as further analysis is made. EPA plans to maintain a list of all requesters of these data in order to track how data are being used and may provide updates and information on anomalies identified.

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