A fall arrest block has a drum (40) on which a lifeline is wound and from which the line can be drawn off or drawn back on, as the work man moves towards and away from the block. One end of the lifeline is permanently secured to the drum, and the drum has sockets (50) for securing ends of more than one different type of lifeline. The block also has a brake (24) in the form of a sealed unit which can be removed and replaced with a fresh unit, when servicing of the brake is required.