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Danger lurking everywhere

There’s no single measure of IAQ; the factors influencing it are complex, and they depend on the design of the building and the way it is used, as well as specific pollutants. Effects of IAQ – such as unpleasant odours, stuffy or stale-feeling air, and physical symptoms – clearly indicate that there is a problem, but air quality can also be measured more objectively by collecting samples of air and of particles deposited on surfaces. Other techniques, such as computerised modelling of air

flow and calculation of the frequency with which the air inside a space is replaced, do not in themselves tell you whether or not IAQ is a problem but they can suggest whether it might be. But why does the problem arise at all – why can air quality be so much worse inside buildings than outside? Substances used in building materials, decoration and furnishing are a major factor; asbestos is the most famous, but others include formaldehyde (found in particle board, fabrics and furniture) as well as the volatile organic compounds (VOCs) that abound in paints, adhesives and polishes. Tiny particles can in themselves be an issue, for example when they become detached from insulation materials; some of the everyday paraphernalia of business contributes too, for example with VOCs from printers, and particles from paper. Tobacco smoke is another well-known factor, albeit one that

is increasingly under tight control in most jurisdictions, but it is not the only “combustion contaminant” that plays a role; furnaces and generators can also emit harmful by-products. Then there are the natural and biological factors. Radon, coming from the soil or rock on which a building sits, is a major IAQ issue in North America and Europe. Molds can develop on wet materials, and humidifiers can encourage them. Rodents and dust mites may also contribute to IAQ, as ironically can pesticides. Exacerbating all these root causes are factors in building

design and facilities management. As the EPA observes, “the tendency toward tighter building envelopes and reduced ventilation to save energy, and pressures to defer maintenance and other building services to reduce costs have fostered indoor air quality problems in many buildings”. Finally, air quality problems from outside can penetrate


ir is not a static thing. It moves around a building, and contaminants move with it as it

flows. The flow is affected by many factors in the building’s design, including doors and windows, air intakes, fans, flues, ducts, stairwells, and elevator shafts. Pressure is also key: like any other gas, air will naturally move from places where it is under high pressure to places where the pressure is lower. Temperature affects pressure, and so it too is a factor. The upshot of this is that air pollutants can be found a long distance from the source of the pollution. For example, they can easily travel up several floors via a stairwell, or along a lengthy corridor if there is a pressure differential between one end and the next. A local pollutant can become a building-wide one. Fortunately, this constant motion of air can be exploited to improve IAQ, too, and pressure differences are a powerful tool. Ventilation systems can create areas of

lower or higher pressure in different rooms or areas of the building, by adjusting the relative rates at which air is brought into and expelled from that particular space. Air, and the pollutants it carries, will

never flow from an area of low (or “negative”) pressure into one of higher (or “positive”) pressure – the flow will always be in the other direction. So, if the main sources of pollution are kept under negative pressure while other areas of the building that people use are under positive pressure, the tendency will be for clean air to flow into the polluted space rather than vice-versa. An obvious example of this is seen in smoking booths inside confined spaces, for example in airport departure lounges. Negative pressure within the booth means that air will flow into it, but not out into the rest of the lounge. Ultimately, of course, the air is then expelled from the building altogether.

indoors, including pollutants caused by vehicles or construction work. Given all this, it’s clear that completely avoiding the causes

of IAQ is almost impossible. Some – for example cleaning materials – can be removed relatively easily. But in cases where the fabric of the building or the geology of the site itself are concerned, that may be unrealistic, and building management strategies need to concentrate on reducing their effects. For example, a construction material might emit pollutants that degrade IAQ, but if the building is adequately ventilated they can be kept to acceptably low levels.

In search of a solution

There are three main approaches to addressing IAQ issues, which can all be used in combination. First, you can clean the air, using commercial air purifiers to

remove pollutants. This is something of a brute-force approach (it does not solve the problem of undesirable matter getting into the air in the first place) but it can be effective on a small scale, for example where one area of the building has especially high levels of pollutants from a local source. Implementing it throughout a large facility is, however,

unlikely to be practical. More realistically, you can control the pollutants at their source. As we’ve said, this is straightforward in some cases but impractical in others. However, a large number of apparently

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