Abstract: An electric cable support system is provided having means for supporting electric cables and an elongate metal duct housing said support means and divided transversely into separately formed parts that are detachably secured together, the internal surface of at least a part of the length of the elongate duct is lined with a continuous wall of thermal insulating material and/or absorbing material comprising a closed envelope, or at least two closed envelopes arranged adjacent one another, containing non-flammable evaporative cooling fluid. Preferably, the or each envelope is made of a flexible material which will melt at a temperature at or near the boiling point of the cooling fluid. In the event of an external fire, when the temperature of the duct wall is sufficient to melt the flexible material of an envelope, the cooling fluid will start to evaporate and cool the duct interior.