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Indoor Air Quality

Quick Tips #230

Indoor air quality (IAQ) refers to the quality of air in non-industrial environments, such as offices. Since the energy crisis of the mid-1970s, indoor air quality has become an increasingly important issue for building owners, managers and occupants. The recent increase in indoor air quality complaints can be attributed to a decrease in building ventilation and a higher level of indoor-generated pollutants.

Poor building ventilation is a result of more energy-efficient construction and the use of mechanical ventilation instead of natural ventilation (windows). The indoor pollutant level has increased because of synthetics in building materials and office furniture, the use of chemical cleaning products, and increased office-equipment use, all of which contribute to chemical and particulate contamination.

Mechanical ventilation equipment can also contribute to indoor-air contamination. In fact, it can be a source of dust, mold, bacteria and viruses. Improperly located air intake ducts will bring outside pollutants into the indoor environment.

Building occupants are an additional source of pollutant. Our metabolic processes are a source of many different volatile organic compounds, not to mention perfume, deodorant, hair spray and other grooming products that add contaminants to the indoor air.

Tobacco smoke is a controversial contaminant. OSHA's proposed indoor air quality standard requires that a designated area with separate ventilation be provided in workplaces where smoking is allowed.

Results of Poor Indoor Air Quality

Two types of illnesses can result from contaminated indoor air. Sick building syndrome, or SBS, is a physical reaction to multiple low-level contaminants. These contaminants could be chemical (formaldehyde), biological (mold) or physical (heat, humidity and lighting). Symptoms for SBS include headache, nausea, fatigue, eye irritation and respiratory irritation. These symptoms normally disappear when the afflicted individuals leave the building for a period of time, such as a weekend, but return when they re-enter it.

Building-related illness also is caused by contaminated indoor air. This differs from sick building syndrome in that it is a physical reaction to a single, identifiable contaminant found to be prevalent in the indoor environment. An example of building-related illness is Legionnaires' Disease.

Building managers need to treat indoor air quality complaints seriously and deal with them promptly. These situations often are difficult to diagnose and solve. Quick action will help prevent other occupants throughout the building from thinking they might have SBS when they're really experiencing some other form of stress, such as being overtired.

Mechanical Ventilation Systems

The purpose of mechanical ventilation systems is to bring in outside air and mix it with a percentage of return inside air, condition the air (heat, cool and humidify), and then distribute it to various areas of the building. The National Institute for Occupational Safety and Health (NIOSH) found that up to 52 percent of indoor air quality problems are a result of insufficient or ineffective ventilation.

Outside air is brought into buildings to dilute contaminants originating within the building. Insufficient outside air intake, from improper system design or mechanical malfunction, can lead to contaminant buildup inside the space. Contaminated outside air brought into the building from poorly located intakes will also contribute to contaminant load in the building.

Very few problems would exist if only outside air was used to replenish exhaust air. The drawback to this solution is cost. Because of the expense, newer ventilation equipment is computer controlled to provide the most cost-effective mix of inside and outside air. Proper maintenance of mechanical ventilation equipment keeps the system cost-effective and functioning as designed. It also prevents the system from becoming a source of contaminants.

The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) has specified limits on the amount of outside air that must be brought in and distributed to various parts of buildings. For example, office space requires 20 cu. ft. of outside air per minute per occupant; a designated smoking area requires 60 cu. ft. per minute per occupant.

Carbon dioxide, the gas that we all exhale, is a useful indicator of insufficient outside air intake and ventilation problems. OSHA's proposed indoor air quality standard requires that CO2 levels be maintained below 800 ppm and monitored on a quarterly basis. ASHRAE and NIOSH both specify 1000 ppm as an indicator of insufficient ventilation. The ambient outside CO2 concentration is about 300 ppm. Note: 800 ppm or 1000 ppm of carbon dioxide is not a hazardous concentration, but rather an indicator of potential ventilation problems. OSHA's permissible exposure limit for CO2 is 5000 ppm.

Air Monitoring

Indoor air quality problems are difficult to diagnose and solve because of the large number and many types of contaminants or building stressors that can cause problems. The cumulative effect of chemical, biological and physical stressors is often the most difficult to identify. An indoor air quality investigation begins with thorough research and investigation at the problem site to identify potential contaminants or stressors. No monitoring should be done until these items have been identified. The flowchart below shows just one possible approach to an indoor air quality investigation.

If air monitoring is necessary, comparative samples from non-problem areas of the building are a useful tool in determining what the possible contaminants are.

The following is a brief list of building stressors and contaminants and the types of equipment used to identify each one:


Contaminant/Stressor Monitoring Equipment
Air speed Anemometer
Lighting Light meter
Heat Thermometer
Noise Sound level meter
Humidity Hygrometer
Bacteria, virus, mold Andersen air sampler
Volatile organic compounds Photo ionization detector (PID), sampling pump and collection media, dosimeter badges and colorimetric tubes, specific colorimetric tubes
Dust and other particulates Collection media and sampling pumps
Carbon dioxide Colorimetric detector tubes , electronic monitor


Note: This is not intended to be a complete list of contaminants. ASHRAE 62-1989 lists common contaminant levels for these and other specific chemicals.

Standards and Regulations

ASHRAE 62-1989—Ventilation for acceptable indoor air quality. Specifies minimum ventilation rates and indoor air quality needed to avoid adverse health effects to human occupants.

ASHRAE 55-1981—Thermal environmental conditions for human occupancy. Specifies minimal indoor thermal parameters (air temperature, humidity and movement) needed to avoid adverse health effects to human occupants.

Occupational Safety & Health Standards 1910.19—Special Provisions for Air Contaminants—Indoor Air Quality. (Proposed Rule)

Commonly Asked Questions

QWhen is the final indoor air quality standard expected? AThis topic is extremely controversial, and there have been numerous comments on the initial proposed standard. It does not appear that a final rule can be completed in the near future. QDoes OSHA have specific limits set contaminants in non-industrial environments? AThe current permissible exposure limits are used for industrial and non-industrial environments.

American Society of Heating, Refrigeration and Air Condition Engineers Inc. (ASHRAE)
1791 Tullie Circle NE
Atlanta, GA 30329

EPA Indoor Air Quality Information Clearinghouse
P.O. Box 37133
Washington DC 20013-7113
Phone: 800-438-4318

NIOSH Guidance for Indoor Air Quality Investigations

National Institute for Occupational Safety & Health

Hazard Evaluation and Technical Assistance Branch
4676 Columbia Parkway, Cincinnati, OH 45226
Phone: 513-841-4374

NIOSH Information Line
Phone: 800-356-4674

(Rev. 12/2013)

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at

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Please Note:
The information contained in this publication is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This publication is not a substitute for review of the current applicable government regulations and standards specific to your location and business activity, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.

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