A system of gravel modules to be used atop a room or other enclosure in which there is a threat of explosion. Each module has a rigid metal box frame, which contains a two layers of gravel. The lower gravel layer is screen gravel, and a layer of graded gravel is above the screen gravel. The box frame has a lower and an upper criss-cross pattern of bridge cable. A stack of wire mesh and other supporting material is laid over the lower bridge cable to support the screen gravel, and more wire mesh is laid over the screen gravel to support the graded gravel. The depths and grades of gravel are selected according to the type potential explosion, in terms of explosive fragment sizes and the nature of any expanding gases.
Thomas Z. Moore; Walter M. Gray