Abstract: The support (10) is securely clampable to a raised profile (12) of the roof decking (14) without piercing the decking and supports a safety barrier (34). Alternatively the support (10) may support a display sign or formwork locator. The support (10) comprises a clamp (24) and a support element (25) over which an upright support post (26) carrying the barrier (34) is telescopically received. The clamp (24) comprises a pair of clamping jaws (36 and 38) which are pivoted to each other and have respective feet (56) at their ends remote from the pivotal connection (44). The feet engage the deck (14) and particularly have respective projecting flanges (66) which cooperate with opposed undercuts on the raised profile (12) when the clamp (24) is tightened by a screw threaded arrangement (50, 52) remote from the pivotal connection (44). A brace (68) is provided with a clamp (84) similar to the clamp (24 ).