A system comprises a track (26), a trolley (17), coupled to the track, a safety line (16) extending from the trolley to a harness, where at least a portion of the safety line is rigid, and a locking mechanism (31) on the trolley, allowing the trolley to move freely along the track in normal operation but automatically locking the trolley in the event of a fall. Preferably the safety line passes through a rigid tube (25) and is would onto a spring loaded reel (34) so that the line is extended and retracted as required, except in the case of a fall when it is automatically locked. When the track is vertical or inclined the rigid portion, or tube, maintains the trolley above the harness attachment point, thus minimising the fall distance (Figure 9). Further inventions include a safety harness, track assembly and folding guard rail.