Abstract: The invention provides a device for blocking the ingress of air on the surface of a moving member such as an optical fiber. The blocking of air is achieved by the establishment of a low pressure zone at the entry point of the fiber, the lower pressure zone being created by the injection of an inert gas in a direction opposite the direction of travel of the fiber. The invention is particularly useful in preventing the ingress of air into a UV curing apparatus for curing the ink on an optical fiber. There is also provided a method for reducing such ingress of air.