An outer wall of a component [any part, or system of parts functioning as a unit, including, but not limited to, piping, processing equipment, containers, control devices, impounding systems, lighting, security devices, fire control equipment, and communication equipment, whose integrity or reliability is necessary to maintain safety in controlling, processing, or containing a hazardous fluid]
served by an impounding system [includes an impounding space, including dikes and floors for conducting the flow of spilled hazardous liquids to an impounding space]may not [means is not permitted to or is not authorized to] be used as a
dike [the perimeter of an impounding space forming a barrier to prevent liquid from flowing in an unintended direction] unless the outer
wall is constructed of concrete.