IEC 61300-2-19:2012 details a procedure for determining the suitability of a fibre optic device to withstand the environmental condition of high humidity and high temperature which may occur in actual use, storage and/or transport. The test is primarily intended to permit the observation of effects of high humidity at constant temperature over a given period. This third edition cancels and replaces the second edition published in 2005. It constitutes a technical revision. The changes with respect to the previous edition are to reconsider the severities and details to be specified.Keywords: high humidity and temperature, environmental condition