Indoor Air Concerns

A formal IAQ management plan, specific to the building, is an excellent tool to help prevent problems and to effectively solve problems that do arise.

ACCORDING to the Environmental Protection Agency, Americans spend an average of 90 percent of their time indoors.1 Approximately 50 percent of that time is spent in the work environment. Experts estimate that nearly 30 percent of office buildings nationwide experience some form of indoor air quality (IAQ) problems. Employers, building managers, and building owners are faced with complaints, worker's compensation claims, and even lawsuits. This article describes some of the factors that affect IAQ and provides some guidance on IAQ management.

IAQ complaints in office environments seem to be on the rise and can be difficult to resolve. Factors affecting IAQ can range from physical (temperature and humidity) to chemical (carbon monoxide, volatile organic compounds, etc.), to biological (molds and other allergens), to occupant perceptions and susceptibilities. Effects associated with most of these factors typically occur during or shortly after exposure and are usually reversible, although some chemicals found in buildings (e.g., formaldehyde) are carcinogens. In addition, asbestos and radon, while are not typically regarded as IAQ issues, may cause health effects that have long latency periods and are not reversible. Asbestos and radon are elements that should be included in an IAQ management plan.

Maintenance of good indoor air quality includes 1) introduction of ventilation air that is appropriately distributed, 2) removal of airborne contaminants, and 3) maintenance of thermal comfort. Implementation of an IAQ management program can help improve occupant health, comfort, and productivity by preventing IAQ problems and solving them when they occur.

General IAQ Indicators
General IAQ indicators include carbon dioxide (CO2), temperature, and humidity. CO2 is a colorless, odorless gas that, in the indoor environment, is generated mainly by human respiration. The amount of CO2 generated depends upon the level of activity, i.e., more CO2 will be generated as activity levels increase. According to the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 62.1-2004, Ventilation for Acceptable Indoor Air Quality, the indoor to outdoor differential concentration should not be greater than about 700 parts per million (ppm) of CO2. If CO2 levels rise above the 700 ppm differential, occupants may perceive the air to be "stale" and containing objectionable body odors. CO2 concentrations in acceptable outdoor air typically range from 300 to 500 ppm.2

Indoor air temperature and relative humidity are physical conditions important to the perception of comfort. ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy, identifies six primary factors that affect comfort: metabolic rate (affected by the activity being performed), clothing insulation, air temperature, radiant temperature, air speed, and humidity.3

Chemical Compounds
Chemicals from a variety of sources may contribute to IAQ complaints and may be organic or inorganic. Furniture, carpeting, paint, office equipment and supplies, cleaning products, fragrances in personal care products, pesticides, etc., may emit volatile organic compounds (VOCs). Formaldehyde may be released from fabrics, particle board, plywood, and furniture. Concentrations of such chemicals are typically present in very low concentrations but may affect people who are sensitive to them.

Inorganic chemicals include carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2), all products of combustion. In the indoor office environment, malfunctioning furnaces, flue pipe leakage, and vehicle exhaust gas infiltration are typical sources of combustion products. Concentrations of combustion products vary with use patterns and between rooms inside a building. Outdoor conditions also may affect concentrations.4

CO is a colorless, odorless gas that interferes with the blood's ability to transport oxygen. Effects of exposure to CO are often mistaken for flu symptoms and may include fatigue, headache, and nausea and vomiting. NO2 and SO2 are primarily irritants and may affect the eyes, nose, throat, and respiratory tract.5

Organic and inorganic chemicals may react with each other in the indoor environment.6 For example, VOCs emitted from new carpet may react with ozone (O3) at low levels typically found indoors to produce various aldehydes, including formaldehyde.7

Bioaerosols are airborne particulates that are biological in origin. Bioaerosols may be living or originate from living organisms and include microorganisms (alive or dead), fragments, toxins, and particulate waste products from living organisms. Biological organisms also may produce VOCs. Many bioaerosols or other substances produced by organisms are capable of producing health effects, such as infection, sensitivity, irritation, or inflammation.8

Molds are common bioaerosols and also produce an assortment of VOCs. Molds are microscopic fungi. Fungi live on plant or animal matter and represent a large proportion of the total biomass on earth. More than 100,000 known species of fungi have been identified, but there may be many more. Fungi are important agents of human disease, but they are equally important as sources of food, antibiotics, and drugs used to treat cancer.

Good growth conditions for mold include oxygen, temperature (40-100 degrees F), food (anything organic), and water. Water is usually the limiting factor.9 When sufficient water is present, molds begin to grow exponentially with 24 to 48 hours. If the source of water can be removed within that time period, mold is usually not an issue. Different molds require different amounts of water; for some molds, high relative humidity may be sufficient to support growth. For this reason, EPA recommends that relative humidity levels be maintained below 60 percent.10

Molds are ubiquitous in the outdoor environment, which is the most common source of airborne mold spores and fragments in the indoor environment. Molds enter buildings through doors and windows, on people's clothing and shoes, and through the heating, ventilating, and air conditioning (HVAC) system. When conditions are right (i.e., sufficient water is present), mold spores may germinate indoors and grow.

We may be exposed to molds through ingestion; contact with moldy surfaces; or inhalation of spores, fungal fragments, and/or VOCs. We know that ingestion of certain fungi or fungal toxins can cause serious illness and even death. Contact with moldy surfaces may result in dermatitis. However, in the indoor environment, inhalation is the most common route of exposure to molds.

Various health effects have been attributed to mold exposure, including allergies, asthma, infection, and toxic effects.11 Allergies are probably the most common responses to molds and may range from mild, transitory responses to severe, chronic illnesses, depending upon an individual's sensitivity. Allergic rhinitis or sinusitis is a common response and is similar to hay fever or a common cold but typically lasts longer. Some molds are opportunistic human pathogens, which means they can cause infections in people who are already sick.

Toxic effects may result from exposure to mycotoxins, VOCs, or glucans (components of fungal cell walls).8 Molds may produce mycotoxins to help them compete against other molds and microorganisms in their environment. Not all molds produce mycotoxins. Molds that are capable of producing mycotoxins only produce them under specific environmental conditions and may produce different mycotoxins depending upon substrate, pH, temperature, and presence of other microorganisms or other environmental conditions. Mycotoxins are not volatile and accumulate in the substrate, fungal spores, and fragments. Health effects depend upon the type of mycotoxin and the nature of the exposure. At the present, much more is known about the effects of ingesting mycotoxins than about inhaling them.

VOCs produced by molds are the source of the odors often associated with molds. Some of these VOCs have low odor thresholds, and many people find them offensive. One of the most common VOCs produced by molds is geosmin, which has an earthy odor. The odor threshold for geosmin ranges from 150 to 200 nanograms per cubic meter of air.9 Exposure to VOCs may account for nonspecific symptoms, but the role of VOCs in clinically evident illness has not been studied.11

Glucans are major components of fungal cell walls and have irritant effects. However, glucans may be useful in fighting some bacterial infections and also have anti-tumor activity. Again, the role of glucans in causing indoor-related health effects has not been studied.8

Other Bioaerosols
Other bioaerosols found in buildings include bacteria, viruses, pollen, protozoa, algae, and arthropod (e.g., dust mites) fecal pellets and body parts.5 Many of these bioaerosols originate outdoors and are brought in through HVAC systems, doors, and windows. Some cause serious disease (such as Legionella, which is responsible for Legionnaires' disease). Others are allergens, such as pollen and arthropod fecal pellets and body parts.

Asbestos-containing materials (ACM) are common in older buildings and may even be found in newer buildings. Intact and undisturbed ACM does not pose a health risk, but it should be identified so it can be properly managed. Custodial and maintenance workers typically have the greatest risk of exposure to asbestos in buildings and should know where ACM is located and how to avoid disturbances. In addition, EPA's 40 CFR 61, Subpart M, National Emission Standards for Hazardous Air Pollutants, prohibits the release of asbestos fibers to the atmosphere during renovation or demolition activities. The asbestos NESHAP requires that potentially regulated asbestos-containing building materials be identified, classified, and quantified prior to renovation or demolition activities.

Radon is a naturally occurring radioactive gas. It is produced by the decay of radium and is present in nearly all soil and rock. Radon migrates through soil and groundwater and can enter buildings through cracks and other penetrations in the foundation. EPA has developed guidance documents for measuring and controlling radon in residences, schools, and large buildings. The documents are available at this Web site:

IAQ Management
Obviously, there are many facets to indoor air quality. A formal IAQ management plan, specific to the building, is an excellent tool to help prevent IAQ problems and to effectively solve problems that do arise.

The management plan may include a baseline or IAQ profile for the building. The IAQ profile is a description of the building's structure, function, and occupancy and how they may affect IAQ. Construction and operating documents are a good place to start; try to determine what changes have been made in the building over time and how those changes might affect IAQ. A walkthrough inspection will help in understanding occupant activities and building functions and identifying any IAQ problem indicators. The profile may include testing of various kinds, for example, measurements of airflow, temperature, humidity, CO2, and/or pressure differentials.

Other elements of the management plan include appointment of an IAQ manager, staff responsibilities, facility and maintenance operating procedures, training, and mechanisms of communication with building occupants.


  1. Healthy Buildings, Healthy People: A Vision for the 21st Century. United States Environmental Protection Agency, Indoor Environments Division, Office of Air and Radiation; EPA-402-K-01-003, October 2001.
  2. Ventilation for Acceptable Indoor Air Quality; ANSI/ASHRAE Standard 62.1-2004. American Society of Heating, Ventilating, and Air-Conditioning Engineers, Atlanta, Georgia, 2004.
  3. Thermal Conditions for Human Occupancy; ANSI/ASHRAE Standard 55-2004. American Society of Heating, Ventilating, and Air-Conditioning Engineers, Atlanta, Georgia, 2004.
  4. Indoor Air Quality: Position Paper. American Society of Heating, Ventilating, and Air-Conditioning Engineers, Atlanta, Georgia, 2000.
  5. Indoor Air Pollution. An Introduction for Health Professionals. American Lung Association, Environmental Protection Agency, Consumer Product Safety Commission, and American Medical Association; EPA 402-R-94-007, 1994.
  6. Indoor Environmental Quality. National Institute of Building Sciences, Washington, D.C., 2005
  7. 4-Phenylcyclohexane, Review of Toxicological Literature. National Toxicology Program, July 2002.
  8. Macher, J. (Ed.), Bioaerosols: Assessment and Control. American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 1999.
  9. Hung, L, J.D. Miller, and H.K. Dillon (Eds.), Field Guide for the Determination of Biological Contaminants in Environmental Samples. American Industrial Hygiene Association, Fairfax, VA, 2005.
  10. IAQ Building Education and Assessment Tool (I-BEAM). United States Environmental Protection Agency, Indoor Environments Division, Office of Air and Radiation; EPA-402-C-01-001, September 2001.
  11. Damp Indoor Spaces and Health. Institute of Medicine, Washington, D.C., 2004.

IAQ and Mold Resources
There is a wealth of information about IAQ available, much of it on the Internet.

Indoor air quality in general:

For more information about molds:

This article appeared in the July 2006 issue of Occupational Health & Safety.

This article originally appeared in the July 2006 issue of Occupational Health & Safety.

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