This part of IEC 60721 classifies groups of microclimatic conditions, to which components (basic parts, assemblies, built-in units) may be subjected inside products, which are used under the climatic conditions as classified in IEC 60721-3-3 and IEC 60721-3-4. Characteristic parameters for the microclimates are high air temperature and high relative air humidity. Further parameters of the climatic classes e.g. low temperature can affect the components additionally, but have not been considered here. A limited number of microclimatic classes is specified taking into consideration typical limiting high air temperatures of components. The user of the standard should select the lowest class necessary for covering the intended use. NOTE Microclimate can mean, e.g., in meteorology or buildings a different thing than those discussed in this standard.