Abstract: This invention relates to structural devices which include intumescent material for the purpose of inhibiting the flow of heated air, smoke, and other products of extraordinary heat conditions, as in the case of a fire, from flowing therethrough. In one embodiment, useful as a tray for supporting insulated electrical conductors, a structure with double floor members spaced apart from each other, has convection holes in both of the floor members. The holes in one of the members are out of alignment with the holes in the other, and the top surface of the lower floor member has intumescent material positioned thereon.