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. Thereby, upon exposure of the lower floor member to the heat of a fire for example, the intumescent material will expand, causing either or both the holes and the passageways that are described by the space between the holes of one floor member and those of the other floor member, to become blocked, thereby preventing the passage of heat, smoke and flame therethrough, to localize the fire, and deter consequent damage to the cables being held in the tray.
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