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What is IAQ

Indoor Air Quality (IAQ) Explained

1. Introduction

Since most of us spend most of our time indoors, indoor air quality is paramount to our health and comfort. In the last decade, increasing scientific evidence has show the air within buildings can be more seriously polluted than the outdoor air.

Research show that the more people spend time indoor the concentration of contaminants may build up in an enclosed space, the risks to health may be greater due to exposure to air pollution indoors than outdoors.

IAQ Definition

Indoor air quality (IAQ) is a result of complex relationship between the contaminant sources in a building and the ventilation rate which can affects the health and well-being of occupants. Some of the main factors affecting IAQ in buildings includes:

a) Emission from indoor contamination source
b) Thermal Acceptability
c) Maintenance of normal concentrations of respiratory gases; and
d) Dilution and removal of contaminants to levels below health or odour discomfort thresholds.

Emissions from contamination source in a building are the primary determinants of IAQ. They include building materials, consumer products, cleaners, furnishing, combustion appliance and processes, biological growth, building occupants, etc. The physiological reaction to air coupled with the wide range of human susceptibility to indoor air contaminant, have lead to acute building sicknesses such as sick building syndrome (SBS), building-related illness (BRI) and multiple chemical sensitivity.

Indoor Air pollutions and their source

Formaldehyde, is one of the most important indoor air contaminants, it is highly reactive and soluble. It is irritable to moist body surfaces. It has been identified as a “carcinogen” and linked particularly to nasal cancer. Mobile homes have been found to have higher concentration of formaldehyde because of the extensive use of particleboards and plywood in construction, tight sealing, and increased use of recalculated air.

Another significant source of indoor air is radon gas, it is a decay product of radium-226, it’s odourless, colourless radioactive gas and it is a chemical inert. Most people who get exposed to radon is because or the radioactive elements contained in the bedrock and soils. Exposure to high concentration of radon has serious health effects.

Soil is the main source of indoor radon. It enters the building through crawl spaces, hollow concrete block walls and crack concrete slabs. The main health effect due to exposure to radon is the increased possibility of cancer of internal organs such as lung cancer.

Particles penetrating into the lungs may cause various health problems. Asbestos, used for insulation and fireproofing mostly in old buildings is a significant IAQ problem. Asbestos contaminants occur when the fibres become friable and released into indoor air. Asbestos is carcinogen and has been linked to stomach and lung cancers. Fiberglas and Rockwool are also insulation materials that can cause indoor air quality problems.

We are all exposed to microorganisms everyday. These include viruses, bacteria, and fungal spores to pollen grains and dust mites. These sometimes cause sneezing and wheezing and others may cause severe diseases. Also, a contaminated heating, ventilating and air-conditioning (HVAC) system can distribute millions of microorganisms.

Microorganisms indoors are of great concern to us, because they can cause diseases. Some microorganisms can cause allergic reactions, irritation and weaken immunity so that the body can become susceptible to other diseases. High humidity and condensation also increase the number of airborne fungal spores and bacterial growth.

Carbon monoxide (CO), Sulfur dioxide (SO2), Nitrogen Dioxide (NO2) and carbon dioxide (CO2) are among some of the major byproducts of combustion of indoor air contaminant. CO is an odourless, tasteless and colorless gas. It combines with haemoglobin in the blood to form carboxyhemoglobin (COHb) which interferes with the ability of blood to carry oxygen to the blood tissue. High level exposure of CO may cause dizziness, headaches, nausea, vomiting, coma, and even death.

SO2 is produced during the combustion of sulfur-containing material. It is soluble is water and absorbs easily by the mucous membranes of the respiratory system. Exposure to SO2 primarily affects the respiratory system.

NO2 is a dark brown gas, exposure will result in sever irritation to eyes and other membranes of the body, and damage to the lungs.

CO2 is relatively nontoxic and considered to be excellent surrogate for odour and indirect measure of the adequacy of mixing outside and recirculated air.

VOCs are used in the formulation of almost all materials and products such as construction material, furnishing, fuels, consumer products and pesticides. Indoor VOC levels are often much higher than outside concentrations outside. They are lipid soluble compound and often absorbed through the lungs.

How indoor air pollution affect you

The effect of IAQ can be categorised as;

● Chronic health effects
● Acute health effects
● Comfort

It is likely contaminants in indoor environment can increase the risk of illness and affect work productivity. Health effects linked with chronic low-level exposure to common indoor air pollutants still remain unexplored. The effects could be divided into six categories:

Respiratory cancer,
Chronic obstructive pulmonary disease,
Infectious disease and microbial toxins,
Immunologic disorders,
Irritation phenomena, and

Health effects from indoor air pollutants may very from person to person and can be immediate or years later. Effects may be experienced shortly after a single exposure or several. Symptoms includes respiratory conditions, watering eyes, Itching eyes, nose, and throat, Sneezing, conjunctivitis, allergic Reactions, asthma, Humidifier Fever, Influenza, Infectious diseases, headaches, Breathing difficulties, Skin irritation, allergic reactions, aggravation of asthma symptoms, lung cancer, respiratory irritation, bronchitis, pneumonia in children, emphysema, lung cancer, fatigue and Heart Disease. Some of these health effects are usually short-term and treatable. The most effective treatment in most cases is eliminating the source of the exposure.

Other health effects which includes respiratory conditions, Heart Disease and cancer, can be fatal. It is important to note that some minor indoor air quality problems can go unnoticed, however even such low exposure can affect the productivity and morale of the occupants. In a work environment this may manifest in the form of lost in concentration and increased absenteeism leading to financial losses. IAQ issues can have several economic impacts at both individual and organisational level.

Sick building syndrome (SBS)

Sick building Syndrome (SBS) is often associated with buildings in which a majority of occupants experience a variety of health and comfort problems for which no specific cause can be identified. Health related complaints from occupants often include irritation of eyes, nose, throat and upper respiratory.

  1. Fiberglass Insulation
  2. Poor ventilation
  3. Lack of Circulation
  4. Limited fresh Air
  5. Smoke
  6. Paint Fumes
  7. Dustmites
  8. Carpet Outgassing
  9. Pet Dander
  10. Toxic Cleaning chemicals
  11. Fabric Outgassing
  12. Natural Gas & CO2
  13. Building Materials
  14. Bacteria in toilet.
  15. Mold
  16. Toxic Paint
  17. Carbon Monoxide (CO)
  18. Oil & Gas Fumes

Diagnosis of SBS is mainly based upon the exclusion of other disease and is determined essentially by perception. The common symptoms associated with SBS include.

  • Fatigue,
  • headache,
  • eye, nose or throat irritation,
  • skin irritation,
  • dry cough,
  • irritability,
  • difficulty concentrating,
  • nausea,
  • dizziness
  • hypersensitivity to odours.
  • Headaches Dry skin
  • Rashes Nausea
  • Nasal congestion

Additional information

Health and Safety Executive
(1G) Redgrave Court
Merton Road
L20 7HS
Phone: 0845 345 0055

National Institute for Occupational Safety and Health
US Department of Health and Human Services
4676 Columbia Parkway (Mail Drop R2)
Cincinnati, Ohio 45226


Meckler, M. (Ed), indoor Air Quality Design Guidebook, Ch. 4: Major Combustion Byproducts, by Larry C. Holcomb and Elia M. Serling, The Fairmont Press, Inc./Prentice Hall, 1991.

Improving Indoor Air Quality Through Design, Operation and Maintenance
by Milton Meckler (Author)


Information in this website is intended for information purposes only and is not to be used as a substitute for consultation with a medical practitioner.

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