A seal obstructs the migration of particulates and precipitation into a pipe fusion chamber through its pipe stick entry and pipeline exit passages. Sheets of cloth serially overlap the anticipated center axis of a pipe stick/pipeline which will pass through the machine. The outer edge of each sheet is pleated and fixed to a frame contiguous with the perimeter of the passage and the inner edge of each sheet is gathered on an elastic band. When a face of a pipe stick/pipeline pushes the sheets away from the frame, the pleats and bands cooperate to allow the inner edges of the sheets to slide over the face and hug substantially the entire outer circumference of the pipe stick/pipeline.