A method of inhibiting combustion within a vacuum pump is provided. The method steps include monitoring and composition of a fluid within the pump and supplying purge gas to the pump to inhibit the onset of a combustion of the fluid. There is also provided a pumping arrangement comprising a vacuum pump (1) together with means (8) for supplying purge gas to the pump. Sensor means (21a, 21b, 21c) are provided for outputting a signal indicative of the onset of a combustion condition within the pump. Control means (22) receive the signal and, in turn, actuate the supply means (9) dependant on the signal received.