IEC 60721-2-3:2013 presents a selection of different values of air pressure appearing in nature. It is intended to be used as part of the background material when selecting appropriate severities of air pressure for product applications, which products are liable to be exposed during storage, transportation and use. This second edition cancels and replaces the first edition, published in 1987, and constitutes a technical revision. The main changes with regard to the previous edition are as follows: - removal of figures for decreasing cooling efficiency for altitude; - simplification of Table 1; - additional formula for calculating air pressure from altitude.