The present invention relates to the degassing of polymer powder, and in particular provides an interlock for use in a process for degassing of a polymer powder in a degassing vessel, which interlock comprises: a. measuring the temperature of the vapour phase resulting from a liquid-vapour separation, which vapour phase is used as a purge gas in a degassing vessel, b. comparing said measured temperature to a threshold value, and b. in the event that the measured temperature is above the threshold value then the use of the vapour as purge gas is stopped or reduced.