This part of IEC 60793 provides a practical method for evaluating fibre performance in a defined environment. The purpose of this document is to determine the suitability of optical fibre (Types A1a to A1d and B1 and B4) to withstand the environmental condition of high humidity and high temperature which may occur in actual use, store and/or transport. The test is primarily intended to permit the observation of effects of high humidity at constant temperature over a given period.