A method of operating a sterilization system having a vacuum chamber for sterilizing instruments, the chamber connected to a reservoir of sterilant by a valve in a closed state, is disclosed. The method may include taking a baseline humidity measurement while the pressure within the chamber is a first pressure, lowering the pressure within the chamber to a conditioning pressure, maintaining the conditioning pressure for a dwell time, increasing the pressure within the chamber, acquiring a second humidity measurement from within the chamber, and comparing the baseline humidity measurement to the second humidity measurement.
