Risk assessment of health hazards introduced by chemicals is based on two basic elements: (i) exposure assessment and (ii) hazard identification. Risk characterisation is performed by comparing the exposure level with the NOAEL to establish the margin of exposure. If this margin is too narrow, then a concern is assumed which requires additional analyses, e.g. by refining data, or by performing additional studies. Assessment of risks by inhalation normally takes into consideration the concentrations in air that lead to toxic effects which can be compared by concentrations revealed from model assessments of measurements of concentrations of substances in room air. The key issues for exposure assessment can be separated into three parts: (i) the characterisation of the exposure scenario, (ii) the derivation of an adequate exposure model and (iii) the selection of model parameters, i.e. the determinants of the exposure. Particularly, complex evaluations need high efforts to retrieve and provide information and data. Therefore, exposure analysis should follow a tiered approach, starting with simple assumptions for exposure scenarios and models, as well as default parameters. The refinement aims at narrowing the assessment closely to reality. Therefore, due to different regulations, this approach avoids unnecessary investigations of data. The consideration of variability and uncertainty is getting more and more important in exposure evaluations, and some concepts have been recently published. The main objective of an uncertainty analysis (UA) in exposure assessment is to identify the sources of uncertainty thus providing support for decision makers which parameter is, e.g. the most critical one in an exposure scenario. An UA gives the assessor the opportunity to re-evaluate the scenario, model approaches and parameters of the analysis, and to consider their influence in the overall analysis by means of a tiered approach.