A housing for protecting monitoring equipment employed to maintain watch over dusty environments. The housing comprises a cylindrical jacket (1) that accommodates the equipment. The front of the jacket is closed except for one or more apertures (12) and extends into the environment being monitored. The housing is provided with a connection (10) for a coolant or flush in the form of air. One or more outlets (15 & 17) communicate with the inside of the housing in the vicinity of the aperture and are oriented such that the air emerging from the outlets forms a cushion between the aperture and the environment being monitored.