This document deals with the classification of low corrosivity of indoor atmospheres. The aim of this document is to characterise indoor atmospheric environments of low corrosivity that can affect metals and metallic coatings during storage, transport, installation or operational use, to set a consistent way of indoor corrosivity classification, and to prescribe procedures for derivation and estimation of indoor corrosivity categories. This document specifies technical metals, whose corrosion attack after a defined exposure period is used for determination of corrosivity categories of indoor atmospheres of low corrosivity. This document defines corrosivity categories of indoor atmospheres according to corrosion attack on standard specimens. This document indicates important parameters of indoor atmospheres that can serve as a basis for an estimation of indoor corrosivity. Selection of a method for determination of corrosion attack, description of standard specimens, its exposure conditions and evaluation are the subject of ISO 11844-2. Measurement of environmental parameters affecting indoor corrosivity is the subject of ISO 11844-3.