The effects of indoor air quality on performance and productivity

The main justification for ventilation has historically been to create a healthy indoor environment. Ventilation removes air pollutants originating inside the building, including bio-effluents. The outdoor air supply rate that has been found by experience to provide subjectively acceptable indoor air quality and to prevent the accumulation of moisture in the building is generally sufficient to maintain the concentration of pollutants at healthily low levels. Until 5 years ago this would have been the justification for current ventilation practices, but in 1999 the first of a series of experiments was published, revealing new mechanisms by which raised levels of indoor air pollution may reduce productivity, either in addition to or instead of having negative effects on comfort and health. It was shown in realistic experimental exposures lasting up to 5 h that the performance of simulated office work could be significantly increased by removing common indoor sources of air pollution, such as floor-coverings, used supply air filters and personal computers, or by keeping them in place and increasing the rate at which clean outdoor air was supplied from 3 to 10 to 30 l s(-1) per person. These short-term effects were demonstrated repeatedly even at pollutant levels that had no measurable effects on the perception of air quality by the occupants themselves, although there were effects on subclinical SBS symptoms such as headache. Temperature and noise distraction have since been studied in directly comparable exposures. The prediction arising from these experiments, that the performance of real office work over time would be significantly and substantially affected by the changes in indoor environmental quality that take place in the course of normal building operation, have recently been validated in 8-week field intervention experiments carried out in call-centers in northern Europe and the Tropics. These findings have far-reaching implications for the efficient use of energy in buildings.

It has now been shown beyond reasonable doubt that poor indoor air quality in buildings can decrease productivity in addition to causing visitors to express dissatisfaction. The size of the effect on most aspects of office work performance appears to be as high as 6-9%, the higher value being obtained in field validation studies. It is usually more energy-efficient to eliminate sources of pollution than to increase outdoor air supply rates. The experiments summarized in this article have documented and quantified relationships that can be used in making cost-benefit analyses of either solution for a given building. The high cost of labor per unit floor area ensures that payback times will usually be as low as 2 years.