Occupational Hygiene

Indoor Air facts – Ventilation and Air Quality in offices

IntroductionDelta OHM Indoor Air Quality Machine

Millions of South Africans work in buildings with mechanical heating, ventilation and air conditioning (HVAC) systems; these systems are designed to provide air at comfortable temperature and humidity levels, full of harmful concentrations of air pollutants. While heating and air – conditioning are relatively straightforward operations, the more complex processes involved in ventilation are the most important in determining the quality of our indoor air.

While many of us tend to think of ventilation as either air movement within a building or the introduction of outdoor air, ventilation is actually a combination of processes which in the supply and removal of air from inside a building. These processes typically include bringing in outdoor air, conditioning and relaxing the outdoor air with some portion of indoor air, distributing this mixed air throughout the building, and exhausting some portions of the indoor air outside. The quality of indoor air may deteriorate when one or more of these processes is inadequate. For example, Carbon dioxide (CO2) (a gas that is produced when people breathe), may accumulate in building spaces if sufficient amounts of outdoor air are not brought into and distributed throughout the building. Carbon dioxide is a surrogate for indoor pollutants that may cause occupants getting drowsy, headaches, or function at lower activity levels. There are many potential sources of indoor air pollution, which may singly, or in combination, produce other adverse health effects. However, the proper design, operation and maintenance of the ventilation system is essential in providing indoor air that is free of harmful concentrations of pollutants.


Indoor air pollution is caused by an accumulation of contaminants that come primarily from inside the building, although some originate outdoors. These pollutants may be generated by a specific, limited source or several sources over a wide area, and may be generated periodically or continuously. Common sources of indoor air pollution include tobacco smoke, biological organisms, building materials and furnishing, cleaning agents, copier machines, pesticides, dust mites, etc.


Harmful pollutants from a variety of sources can contribute to building – related illnesses, which have clearly identifiable causes, such as Legionnaire’s disease. Heating Ventilation, Air Conditioning (HVAC) systems that are improperly operated or maintained can contribute to sick building syndrome (SBS); and has physical symptoms without clearly identifiable causes. Some of these symptoms include dry mucous membranes and eye, nose, and throat irritation. These disorders lead to increased employee sick days and reduced work efficiency.


  • Volatile Organic Compounds (VOC’s) EG: Glues, Cleaning Agents, etc.
  • Nicotine
  • Carbon Monoxide (CO)
  • Carbon Dioxide (CO²)
  • Air Exchange Rate
  • Nitrogen Dioxide (NO²)
  • Formaldehyde (CH²O) – Slow emissions from press-wood furniture, etc.
  • Benzo(a)prene and other Polynuclear Aromatic Hydrocarbons (PAH)
  • Acids, Gases and Aerosols Nitrous oxides (NOx, ammonia and NH³)
  • Particulate Matter
  • Pesticides

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