Building related illness

Introduction In many modern air-conditioned buildings the only point of entry of air into the building for ventilation is through the air-conditioning system. Of course, air is able to leak through small gaps and defects in the buildings structure both into (infiltration) and out of (exfiltration) the building. Exfiltration causes loss ofheat from the building. Since the early 1970s, the increasing cost of energy has lead to considerable efforts to reduce exfiltration and infiltration in buildingsinorder to conserve energy [I]. This has been termed 'tightening up' ofa building, and has involved the usage of many new building materials and techniques. Hence in a modern air-conditioned building, the windows in all rooms are sealed and cannot be opened. Air is ducted into and out ofthe working environment and various parameters of the air (e.g.. temperature, relative humidity) are controlled by a central air-conditioning plant. Modern systems enable some control of the environment within individual rooms. Another major source of energy consumption in buildings is that used to condition air used for ventilation of the building [2]. This involves heating in cool climates and cooling in warm. To reduce costs from this source, two measures have been taken: firstly, the percentages of return (conditioned) air from the building which are recirculated have been increased with only a small percentage 'top up" of fresh air and secondly, the total amount of air circulated per person has been reduced. Ventilation standards have been reduced in the years following the oil crisis and there has been a tendency to supply the minimum amount of air required by a particular standard rather than the recommended amount [1]. In the best air-conditioning systems, air is drawn into the air-conditioning plant through a series of filters which remove large airborne particles. The temperature ofthe air is adjusted by heater/cooler batteries and is then humidified at the selected temperature. The air temperature is further adjusted to approximately 20-22 C by more heater/cooler batteries and this adjusts the relative humidity ofthe air to a value which should be in the comfort zone of 4070°;, relative humidity [3]. Usually a figure of 40-5 5% relative humidity is chosen. The art is to control both the temperature of the air before humidification and the degree of humidification to achieve the required relative humidity. There are several methods of humidifying air. Dry steam injection is an expensive but relatively trouble free method in terms of associated medical problems (see on). Since with this method, the process of humidification adds heat to the air, there may be