Use of the indoor air quality guidelines in protecting public health

ing group from 2006 (5). Nevertheless, it is important to emphasize the need to consider the health risks of all pollutants for which guidelines are available in activities to improve indoor air quality. This, to some extent, is addressing the health hazard of combined exposure. Furthermore, situations where following the guideline for one pollutant adversely affects other aspects of indoor air quality should be avoided. When strategies to protect public health are under consideration, the air quality guidelines on selected substances need to be placed in the perspective of total chemical exposure. The interaction of humans and the biosphere is complex. Individuals can be exposed briefly or throughout their lifetimes to chemicals in air, water and food; exposures may be environmental or occupational. In addition, individuals vary widely in their response to exposure to chemicals; each person has a pre-existing status (defined by, for example, age, sex, pregnancy, pulmonary disease, cardiovascular disease, genetic make-up) and a lifestyle, in which such factors as exercise and nutrition play key roles. All these different elements may influence a person’s susceptibility to chemicals.

Use of the indoor air quality guidelines in protecting public health

The primary aim of these guidelines is to provide a uniform basis for the protection of public health from adverse effects of indoor exposure to air pollution, and to eliminate or reduce to a minimum exposure to those pollutants that are known or are likely to be hazardous. The guidelines are targeted at the public health professionals involved in preventing health risks of environmental exposures, as well as the specialists and authorities involved in the design and use of buildings, indoor materials and products. The guidelines are based on the scientific knowledge available at the time of their development. They have the character of recommendations, and it is not intended or advocated that they be adopted as standards. Nevertheless, countries may wish to transform the recommended guidelines into legally enforceable standards. In the process of moving from a “guideline” or a “guideline value” to a “standard”, a number of factors beyond the exposure–response relationship need to be taken into account. These factors include current concentrations of pollutants and exposure levels of a population, the specific mixture of air pollutants and the specific social, economic and cultural conditions encountered. In addition, the standard-setting procedure may be influenced by the likelihood of implementing the standard. Broader discussion of these considerations has been presented in an earlier edition of the WHO air quality guidelines (2). Establishing legally binding concentration-based standards of indoor air quality requires, inter alia, determination of the methods for enforcement of the regulation, including compliance testing. This poses difficulties for the use of standards as a means of reducing the effects on health of indoor exposure to air pollutants. Routine monitoring in people’s homes is unlikely to be widespread,

and the application of measures to enforce standards is often not feasible or, at least, difficult. The concentrations of pollutants in both indoor and outdoor air can be reduced by controlling the primary factor that determines their presence in the air: their sources. In the outdoor environment, this is all that can be done because the secondary factors that control concentrations – dispersion and dilution – are not generally under control as they depend largely on meteorological conditions. In the indoor environment, dispersion (to and from the outdoor environment) can be influenced by controlling the ventilation of the indoor space. This provides an additional means of changing indoor concentrations of pollutants. It also creates a difficulty: a source that might be entirely acceptable as regards output of pollutants in a well-ventilated space might be unacceptable in a poorly ventilated space. Of course, significant indoor sources should not be allowed to release pollutants into the indoor space: conducting pollutants to the outside space by flues and chimneys is clearly desirable. It should be noted, however, that indoor sources can make a substantial contribution to outdoor concentrations, especially in places where there are large, widespread sources of indoor pollution. This should be avoided by control of emission from indoor sources. Thus, acceptable indoor air quality can be achieved through source control and pollutant dispersion, and in particular through: application of low-emission materials and products; proper selection of the devices and fuels used for combustion indoors; the venting of products to the outdoor air; and ventilation control.

In many countries, these means of control are encapsulated in product standards and building standards or regulations. In practice, both sets of standards are derived from calculations or experiments and are implemented without routine monitoring of pollutant levels indoors. Surveys of indoor concentrations of pollutants act as a means of checking that the standards are appropriate or, more often, that they are being appropriately applied. Here there is another difference between the approaches taken indoors and outdoors: monitoring outdoor concentrations of air pollutants is standard practice in many countries but routine monitoring of indoor concentrations hardly exists. The development of product and building standards requires targets for acceptable indoor concentrations of air pollutants: here guidelines can play an important role. This is not very different from the approach adopted outdoors. Even in periods of high outdoor concentrations of air pollution, reduction of emissions is seldom more than an ad hoc solution, although reducing vehicle usage or industrial emissions at such times has been tried in a number of cities. Much more important than this are calculations based on inventories of sources and atmospheric dispersion modelling that form the basis of “product standards” as