A safety sensing system includes an apparatus for use in a doorway having a powered door slidable for closure of the doorway. The apparatus includes radiation transmitters and/or receivers for providing a curtain of detection beams across the doorway, and is formed as a composite structure that includes: a fixative member connectable by securing means to a side of the doorway at a door frame, the fixative member including a first portion of a mating connection means; and, a housing containing a plurality of the transmitters and/or receivers along its length, and including a second portion of the mating connection means for attaching the sealed housing to the fixative member. The mating connection means allows the housing to be removed and replaced while the fixative member remains in situ.