"Establishing target and intervention guidance values for indoor air in dwellings and publicly accessible buildings: The Flemish approach".

Indoor air quality has been recognized by the Flemish authorities as an important policy field in view of protection of public health. In 2018, the revised Flemish Indoor Air Decree (Belgisch Staatsblad, 2018), entered into force in Flanders and is applicable for dwellings and publicly accessible buildings (PAB). The Decree is based on three pillars, 1) creating awareness on the importance of good indoor air quality for health, 2) a service for indoor air dwelling examination in case of health complaints that are likely provoked by bad indoor air, and 3) target and intervention guidance values for chemical, physical and biotic factors in the indoor environment. The target guidance values are set up as a measurable concentration of a chemical, physical or biotic factor in the indoor environment corresponding to a quality level which should be achieved as much as possible. For chemical factors, this level corresponds to a concentration where negative impact on health of the occupants due to the indoor environment is not expected. An intervention guidance value is a measurable concentration of a chemical, physical or biotic factor in the indoor environment requiring a remediation action because the concentrations might provoke a health risk for the occupants of the indoor environment. Target and intervention guidance values for indoor air in Flanders have been established for 23 substances, mainly Volatile Organic Compounds (VOCs), NO, PM and asbestos. The indoor air target and intervention guidance values for these substances are based on chronic exposure since they are designed to be health protective for prolonged use of the indoor environments by the occupants, including vulnerable populations. Both a threshold-based approach, and specific for carcinogenic substances, a non-threshold-based approach is included. In this paper, we provide an overview of the methods for establishing the indoor air target and intervention guidance values for substances in the Flemish Indoor Air Decree along with the resulting values.