Abstract: The present invention is a penetrator for passing blown optical fiber through a pressure-proof boundary. The penetrator comprises a cylinder for attachment substantially in line with an opening in the boundary. The cylinder has a proximal and a distal end cap, a cylinder wall, and a central passage or dip tube for optical fibers. The central passage has substantially the same cross-sectional area as the opening in the boundary. The dip tube is sealed to each end cap and has distal and proximal tee fittings for injecting sealing materials into the dip tube. The tee fittings are joined by a length of optical fiber duct therebetween. The invention permits the optical fiber duct circuit to be easily changed.