A protection device for an Optical Emission Spectrometer (OES) and a method of protecting a detector to which purge gas is supplied, in an OES, are disclosed. The protection device comprises a timer, which measures a parameter, such as a humidity value, indicative of a shut down time period following cessation of application of purge gas to the detector. The protection device comprises a processor, which determines a start-up time period, based on the parameter, during which purge gas is supplied to the detector prior to cooling of the detector. The processor may selectively trigger commencing or maintaining application of purge gas to the detector or cooling of the detector in dependence on the parameter.