embodiments of the invention provide a method of determining a storage lifetime of a wafer in a storage environment , the storage environment corresponding to an environment having a first value of temperature and a first value of relative humidity , the wafer having a pre - test value of a first contamination parameter , including the steps of : subjecting the wafer to a test environment for a test period , the test environment includes an environment having a second value of temperature and a second value of relative humidity ; subsequently , inspecting the wafer thereby to determine a post - test value of a second contamination parameter , wherein the second value of relative humidity is greater than 30 % and the second value of wafer temperature is greater than 30 ° c .