A concertina smoke or fire barrier comprising a curtain having a plurality of concertina-fold curtain webs and a plurality of concertina flanges. The flanges extend from a stitching joint between each adjacent pair of curtain webs. There is a normally closed door opening in the curtain, the door opening being provided by a slit extending through several of curtain webs and their flanges. Cuts in the flanges adjacent to the slit allow flange portions between the slit and the cuts to be stitched against their webs. A strip of curtain web material is stitched to the curtain webs on one side of the slit for covering it when the door opening is closed. Hook and loop fastening tape is located on both sides of the slit, one piece of the tape being stitched to the strip and another complementary piece being stitched to the curtain webs to the other side of the slit.