IEC 61300-2-46:2019 is available as IEC 61300-2-46:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61300-2-46:2019 describes a test to determine the suitability of a fibre optic device to withstand the environmental condition of high humidity and change of temperature which can occur in actual use, storage and/or transport. The test is primarily intended to determine the suitability of fibre optic components under conditions of high humidity – combined with cyclic temperature changes and, in general, producing condensation on the surface of the device under test (DUT). Absorption of moisture can result in swelling that would destroy functional utility, cause loss of physical strength, and cause changes in other important mechanical properties. Degradation of optical properties can also occur. Although not necessarily intended as a simulated tropical test, this test can, nevertheless, be useful in determining moisture absorption of insulating or covering materials. This second edition cancels and replaces the first edition published in 2006. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) complete revision to harmonize with IEC 60068-2-30; b) addition of detail description Clause 4, General description; c) addition of detail description Clause 5, Apparatus; d) addition of detail description Clause 6, Procedure. Keywords: suitability of fibre optic devices to withstand the environmental condition