Indoor Air Quality FAQ's

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Indoor Air Quality (IAQ) FAQ's


1. What is indoor air quality?

Understanding indoor air quality first requires a basic knowledge of ventilation. Ventilation is a combination of processes which results in the supply and removal of air from inside a building. These processes typically include:

  • Bringing in outdoor air
  • Conditioning and mixing the outdoor air with some portion of indoor air
  • Distributing this mixed air throughout the building, and
  • Exhausting some portion of the indoor air outside

The goal of a ventilation systems is to maintain a healthy, safe, and comfortable environment with contaminants, humidity, fresh-air, and temperature in an optimal range.

2. How does indoor air quality deteriorate?

If one or more of these ventilation processes is inadequate, due to poor building design, inappropriate occupant activities, or improper maintenance or operation, the quality of indoor air may deteriorate. When that happens, occupants may suffer from Sick Building Syndrome (SBS) or Building Related Illness (BRI).


3. What is SBS and BRI?

Sick Building Syndrome refers to those situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be widespread throughout the building.

Symptoms include:

  • headache
  • eye, nose, or throat irritation
  • dry cough
  • dry or itchy skin
  • dizziness and nausea
  • difficulty in concentrating
  • fatigue
  • sensitivity to odors

With SBS, the cause of the symptoms is not known. Most of the complainants report relief soon after leaving the building. In contrast, the term Building Related Illness (BRI) is used when symptoms of diagnosable illness are identified and can be attributed directly to airborne building contaminants.


Symptoms include:

  • cough
  • chest tightness
  • fever and chills
  • muscle aches

The symptoms can be clinically defined and have clearly identifiable causes. Complainants may require prolonged recovery times after leaving the building. It is important to note that complaints may result from other causes. These may include an illness contracted outside the building, acute sensitivity (e.g., allergies), job related stress or dissatisfaction, and other psychosocial factors. Nevertheless, studies show that symptoms may be caused or exacerbated by indoor air quality problems.

4. How common are indoor air quality-related problems?

A committee of the World Health Organization estimates that as many as 30 percent of new or remodeled buildings may have unusually high rates of sick building complaints. While this is often temporary, some buildings have long-term problems which linger, even after corrective action. The National Institute for Occupational Safety and Health (NIOSH) reports that poor ventilation is an important contributing factor in many sick building cases.

5. Why be concerned with indoor air quality-related problems?

It is generally agreed that poor indoor air can adversely affect employee health and productivity. These costs to industry have been estimated to be in the "tens of billions of dollars per year" (Report to Congress on Indoor Air Quality, 1989). Improvements in the indoor air environment may substantially increase employee morale and productivity. Therefore, it is important to include indoor air quality controls in operation, maintenance, and energy conservation strategies.

6. What causes indoor air quality-related problems?

The following have been cited as causes of or contributing factors to Sick Building

  • Syndrome:
  • Inadequate ventilation
  • Periods of operation
  • Maintenance
  • Chemical contaminants from indoor sources
  • Chemical contaminants from outdoor sources
  • Biological contaminants

Inadequate ventilation: In the early and mid 1900's, building ventilation standards called for approximately 15 cubic feet per minute (cfm) of outside air for each building occupant, primarily to dilute and remove body odors. As a result of the 1973 oil embargo, however, national energy conservation measures called for a reduction in the amount of outdoor air provided for ventilation to 5 cfm per occupant. In many cases these reduced outdoor air ventilation rates were found to be inadequate to maintain the health and comfort of building occupants.

Inadequate ventilation, which may also occur if heating, ventilating, and air conditioning (HVAC) systems do not effectively distribute air to people in the building, is thought to be an important factor in SBS. In an effort to achieve acceptable IAQ while minimizing energy consumption, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recently revised its ventilation standard to provide a minimum of 15 cfm of outdoor air per person (20 cfm/person in office spaces). Up to 60 cfm/person may be required in some spaces (such as smoking lounges) depending on the activities that normally occur in that space (see ASHRAE Standard 62-1989).


Some ventilation system design flaws include:


Intermittent air flow:
Designs that specify HVAC system operation at reduced or interrupted flow during certain portions of the day in response to thermal conditioning needs (as in many variable air volume installations) may cause elevated indoor contaminant levels and impair contaminant removal. Minimum ventilation rates should be defined by air cleanliness and distribution, as well as temperature and humidity.

Distribution of air:
Failure to maintain proper temperature, humidity, and air movement in a building can lead occupants to block supply registers if they emit air that is uncomfortably hot or cold; this disrupts air flow patterns. Placement of partitions or other barriers within a space can also impair air movement. In addition, locating air supply and return registers too close together can result in an uneven distribution of fresh air and insufficient removal of airborne contaminants. Precautions must be taken to maintain comfortable thermal conditions, and proper placement of supply and return registers, and furnishings.


Building supply and exhaust locations:
Air supply vents that are installed too close to building exhaust vents re-entrain contaminated exhaust air into the building, increasing indoor pollution. Placement of supply vents near outdoor sources of pollution, such as loading docks, parking and heavy traffic areas, chimneys, and trash depots, provides a pathway for contaminants into the building's ventilation system. The location of all air supply vents must be carefully considered.


Proportion of outdoor air:
To dilute and eventually remove indoor contaminants, HVAC systems must bring in adequate amounts of outdoor air. However, because it is costly to heat cold winter air and to cool hot summer air, some building engineers reduce or eliminate the amount of outdoor air brought into the system during hot and cold spells; this allows contaminated air to accumulate inside, causing pollutant concentrations to increase. Therefore, a continuous supply of fresh air must be provided.


Periods of Operation: An HVAC system that begins to operate after building occupants have arrived,or shuts off before the end of the work day can cause an increase in building and occupant-generated pollutant levels.

Similarly, if the system is off during periods of non-occupancy (e.g. at night and on weekends) building-generated pollutants may accumulate. Therefore, the ventilation system should be turned on several hours prior to occupancy, and shut down only after occupants have left.

Maintenance: HVAC systems must be properly maintained to promote indoor air quality. If this is not done, ventilation systems can become a source of contamination or become clogged and reduce or eliminate air flow. Humidification and dehumidification systems must be kept clean to prevent the growth of harmful bacteria and fungi. Failure to properly treat the water in cooling towers to prevent growth of organisms, such as Legionnella, may introduce such organisms into the HVAC supply ducts and cause serious health problems. Accumulations of water anywhere in the system may foster harmful biological growth that can be distributed throughout the building.

Chemical contaminants from indoor sources: Most indoor air pollution comes from sources inside the building. For example, adhesives, carpeting, upholstery, manufactured wood products, copy machines, pesticides, and cleaning agents may emit volatile organic compounds (VOCs), including formaldehyde. Environmental tobacco smoke contributes high levels of VOCs, other toxic compounds, and breathable particulate matter.


Research shows that some VOCs can cause chronic and acute health effects at high concentrations, and some are known carcinogens. Low to moderate levels of multiple VOCs may also produce acute reactions. Combustion products such as carbon monoxide, nitrogen dioxide, as well as respirable particles, can come from unvented kerosene and gas space heaters, woodstoves, fireplaces and gas stoves.

Chemical contaminants from outdoor sources: The outdoor air that enters a building can be a source of indoor air pollution. For example, pollutants from motor vehicle exhausts; plumbing vents, and building exhausts (e.g., bathrooms and kitchens) can enter the building through poorly located air intake vents, windows, and other openings. In addition, combustion products can enter a building from a nearby garage.

Biological contaminants: Bacteria, molds, pollen, and viruses are types of biological contaminants. These contaminants may breed in stagnant water that has accumulated in ducts, humidifiers and drain pans, or where water has collected on ceiling tiles, carpeting, or insulation. Sometimes insects or bird droppings can be a source of biological contaminants. Physical symptoms related to biological contamination include cough, chest tightness, fever, chills, muscle aches, and allergic responses such as mucous membrane irritation and upper respiratory congestion. One indoor bacterium, Legionella, has caused both Legionnaire's Disease and Pontiac Fever.

These elements may act in combination, and may supplement other complaints such as inadequate temperature, humidity, or lighting. Even after a building investigation, however, the specific causes of the complaints may remain unknown.

7. Do radon and asbestos contribute to indoor air quality-related problems?

SBS and BRI are associated with acute or immediate health problems; radon and asbestos cause long-term diseases which occur years after exposure, and are therefore not considered to be among the causes of sick buildings. This is not to say that the latter are not serious health risks; both should be included in any comprehensive evaluation of a building's IAQ.

8. How do ventilation standards and building codes help protect against indoor air quality related problems?

After achieving industry consensus in 1989, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) published its "Standard 62-1989: Ventilation for Acceptable Indoor Air Quality." This is a voluntary standard for "minimum ventilation rates and indoor air quality that will be acceptable to human occupants and are intended to avoid adverse health effects." This standard applies to all types of facilities, including dry cleaners, laundries, hotels, dormitories, retail stores, sports and amusement facilities, and teaching, convalescent and correctional facilities. The specified rates at which outdoor air must be supplied to each room within the facility range from 15 to 60 cfm/person, depending on the activities that normally occur in that room.


Standard 62-1989 is a voluntary standard, which means that it becomes enforceable only after a state or locality adopts the standard in its building code. Furthermore, most current building codes pertaining to ventilation are standards only for the way buildings in a particular jurisdiction must be designed; they are not enforceable standards for the way the buildings are operated. A few states, through recently promulgated regulations, pending legislation, labor agreements and other mechanisms, are working to apply existing design codes and standards to building operations.

9. How do I locate the cause of indoor air quality problems?

The first step is a building investigation. The goal of a building investigation is to identify and solve indoor air quality complaints in a way that prevents them from recurring and which avoids the creation of other problems. To achieve this goal, it is necessary for the investigator(s) to discover whether a complaint is actually related to indoor air quality, identify the cause of the complaint, and determine the most appropriate corrective actions.

An indoor air quality investigation procedure is best characterized as a cycle of information gathering, hypothesis formation, and hypothesis testing. It generally begins with a walkthrough inspection of the problem area to provide information about the four basic factors that influence indoor air quality:

  1. the occupants
  2. the HVAC system
  3. possible pollutant pathways
  4. possible contaminant sources.

Preparation for a walkthrough should include:

  • documenting easily obtainable information about the history of the building and of the complaints identifying known HVAC zones and complaint areas
  • notifying occupants of the upcoming investigation
  • identifying key individuals needed for information and access

The walkthrough itself entails visual inspection of critical building areas and consultation with occupants and staff. The initial walkthrough should allow the investigator to develop some possible explanations for the complaint. At this point, the investigator may have sufficient information to formulate a hypothesis, test the hypothesis, and see if the problem is solved. If it is, steps should be taken to ensure that it does not recur. However, if insufficient information is obtained from the walkthrough to construct a hypothesis, or if initial tests fail to reveal the problem, the investigator should move on to collect additional information to allow formulation of additional hypotheses. The process of formulating hypotheses, testing them, and evaluating them continues until the problem is solved.

10. Is air sampling the easiest way to identify indoor air quality problems?

Although air sampling for contaminants might seem to be the logical response to occupant complaints, it seldom provides information about possible causes. While certain basic measurements, e.g., temperature, relative humidity, CO2, and air movement, can provide a useful "snapshot" of current building conditions, sampling for specific pollutant concentrations is often not required to solve the problem and can even be misleading. Contaminant concentration levels rarely exceed existing standards and guidelines even when occupants continue to report health complaints. Air sampling should not be undertaken until considerable information on the factors listed above has been collected, and any sampling strategy should be based on a comprehensive understanding of how the building operates and the nature of the complaints.

11. How do I resolve indoor air quality problems?

Solutions to Sick Building Syndrome usually include combinations of the following:


Pollutant source removal or modification: This is an effective approach to resolving an IAQ problem when sources are known and control is feasible. Examples include routine maintenance of HVAC systems, e.g., periodic cleaning or replacement of filters; replacement of water-stained ceiling tiles and carpeting; institution of smoking restrictions; venting contaminant source emissions to the outdoors; storage and use of paints, adhesives, solvents, and pesticides in well ventilated areas, and use of these pollutant sources during periods of non-occupancy; and allowing time for building materials in new or remodeled areas to off-gas pollutants before occupancy. Several of these options may be exercised at one time.

Increasing ventilation rates and air distribution: This often can be a cost effective means of reducing indoor pollutant levels. HVAC systems should be designed, at a minimum, to meet ventilation standards in local building codes. However, many systems are not operated or maintained to ensure that these design ventilation rates are provided. In many buildings, IAQ can be improved by operating the HVAC system to at least its design standard, and to ASHRAE Standard 62-1989 if possible. When there are strong pollutant sources, local exhaust ventilation may be appropriate to exhaust contaminated air directly from the building. Local exhaust ventilation is particularly recommended to remove pollutants that accumulate in specific areas such as rest rooms, copy rooms, and printing facilities. (For a more detailed discussion of ventilation, read Indoor Air Facts No. 3R, Ventilation and Air Quality in Office Buildings.)

Air cleaning: Air cleaners may be an important part of an HVAC system, but cannot adequately remove all of the pollutants typically found in indoor air. Air cleaners should only be considered as an adjunct to source control and ventilation. Air cleaners that have a high filter efficiency and are designed to handle large amounts of air are the best choice for use in office buildings.

Air cleaners include the simple furnace filter, the electronic air cleaner,and the ion generator. Mechanical filters, either flat or pleated, are generally effective at removing particles. Flat filters collect large particles and pleated filters such as the high-efficiency particulate air (HEPA) filters collect the smaller, respirable particles. Electronic air cleaners and ion generators use an electronic charge to remove airborne particles. These devices may also produce ozone, a lung irritant. All air cleaners require periodic cleaning and filter replacement to function properly.

In addition to removing particles, some air cleaners may remove gaseous pollutants. This is possible only if the air cleaner contains special material, such as activated charcoal, to facilitate removal of harmful gases. Although some of the devices which are designed to remove gaseous pollutants may be effective in removing specific pollutants from indoor air, none are expected to adequately remove all of the gaseous pollutants typically present in indoor air. Information is limited on the useful lifetime of these systems. They can be expensive and require frequent replacement of the filter media.

Education and communication: These are important elements in both remedial and preventive indoor air quality management programs. When building occupants, management, and maintenance personnel fully communicate and understand the causes and consequences of IAQ problems, they can work more effectively together to prevent problems from occurring, or to solve them if they do.

HVAC system operation and maintenance: Operate the ventilation system in a manner consistent with its design. Perform maintenance and inspections on a regular basis, as prescribed by the manufacturer.

Record keeping: Maintain records of all HVAC system problems, as well as routine maintenance and inspection activities. Document the nature of complaints concerning the indoor air environment, as well as steps taken to remedy each complaint. These records may be useful in solving future problems.

Occupant activities: Eliminate practices which may restrict air movement (e.g., furniture placement relative to air vents).

Building maintenance activities: Increase ventilation rates during periods of increased pollution, e.g., during painting, renovation, and pesticides use;schedule use of pollutant sources to minimize the impact on indoor air quality.

Ventilation standards and codes: Keep abreast of revisions to ventilation standards and building codes affected by those standards.

Energy conservation: Re-examine energy conservation practices with regard to indoor air quality considerations, employee health, and productivity costs.