Abstract: This invention relates to a safety line system for use by a person working at a height above the ground. In particular the invention relates to a support post for a safety line system. A support post assembly for supporting a fall safety line comprises a base; a support post to which a fall safety line is connectable, the support post having a longitudinal axis; cooperating curved bearing surfaces disposed between the base and the support post; and a detent assembly for preventing relative movement of the bearing surfaces below a threshold force, application of a force to the support post by the fall safety line above the threshold force causing the support post to pivot with respect to the base such that the bearing surfaces slide with respect to each other and friction between the bearing surfaces dissipates energy.