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Concern about indoor air quality (IAQ) and the study of air quality issues is a fairly recent phenomenon. Some of the earliest documented studies occurred in Scandinavia in the mid-1960s and were focused primarily on thermal comfort issues. For the first decade or so, IAQ studies primarily involved comparing indoor air to outdoor air. The level of outdoor pollution was a chief concern and the goal was to ensure that indoor air was of better quality than the outdoor air subjected to pollutants.

Investigating IAQ

A typical IAQ investigation requires several steps:

• Planning –

* Gather background information about the building and its systems.

* Interview affected people – understand the complaints and symptoms and check for patterns as to where and when they occur.

* Set objectives.

* Determine the strategy to be employed.

• Gathering data – make necessary measurements throughout the building, possibly including temperature, humidity, CO2, CO, particles, VOCs, chemicals and bioaerosols.

• Analyzing the data – check for acceptable measurements to eliminate certain areas or suspected problems, as well as anomalies that directs to areas requiring additional focus (remember, there can be multiple problems).

• Reporting findings – all results indicating a need for corrective action should be reported.

• Offering assistance – prepare an IAQ management plan that includes setting policies and conducting routine measurements to ensure good air quality is maintained.

To help steer an investigation, the affected occupants should be asked questions related to symptoms, origin of symptoms, the time of occurrence of symptoms, the nature and place of occurrence and change in one’s activities, etc. Criteria for determining indoor air quality can be separated into two basic categories – comfort and health. The difference, of course, is the way in which humans are affected, and some criteria may influence both comfort and health.

Common measurable characteristics of comfort include temperature, humidity, air velocity (draft), ventilation, vibration and noise. Factors much harder to quantify yet able to impact perceived individual comfort include light glare, odours, physical space layout, proximity to other areas, clothing, activity, and ergonomics. Even emotional or psychological stress in the workplace or at home can contribute to a person’s feeling of comfort. When making a measurement, allow sufficient time for the instrument to capture a “stable” reading. If you move from a hot area to a cold area and quickly take a temperature measurement, for example, the accuracy of the reading could be subject to question.


Temperature is one of the basic IAQ measurements that has a direct impact on perceived comfort and, in turn, concentration and productivity. According to ASHRAE Standard 55, the recommended temperature ranges perceived as “comfortable” are 73 to 79°F (22.8 to 26.1°C) in the summer and 68 to 74.5°F (20.0 to 23.6°C) in the winter. Measurements should be taken periodically at many areas of the building to be sure that air is distributed evenly and temperatures are consistent. TSI offers a number of instruments that measure temperature. These include IAQ monitors, thermohygrometers and multi-parameter ventilation meters.


Too little humidity in a space may create static build-up and people will sense that their skin feels dry. Too much humidity and people will think it feels “sticky.” According to ASHRAE Standard 55, indoor humidity levels should be maintained between 30 to 65% for optimum comfort.

Humidity can be measured in several ways. Typically, references such as relative humidity, wet bulb, dry bulb, humidity ratio and absolute humidity are used. Whichever method is chosen, measurements should be taken periodically and spread throughout the building to ensure that air is distributed evenly and humidity levels are consistent and within goals. Several portable instruments that measure humidity include IAQ monitors, thermohygrometers and multi-parameter ventilation meters. ASHRAE Standard 55 links temperature and humidity together to provide a measure of thermal comfort. The objective should be to set the appropriate temperature and humidity levels so as to maximize occupant comfort while controlling energy consumption.

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