This part of IEC 61300, when required by the relevant specification, evaluates the ability of the materials used for passive fibre optic devices to withstand the action of fungi and bacteria and soil microorganisms likely to be encountered during usage. The type and extent of material deterioration may be determined by visual examination and/or changes in mass or any other physical property. Since mould growth conditions include high relative humidity, the test is applicable to passive optic devices under humid operating conditions according to IEC 61753-1, in storage and/or transport.