I work at a chemical plant where flammable vapors are present. Static discharges are not our friend, so we bond everything to buillding steel. I've been asked to prove that our earth ground is viable. My problem is that the plant utilized concrete encased rebar to establish the ground. Cables were attached using cadwelds and bolted to the columns. I can't get to these cables in most cases and when I can the results with my clamp on are 0 ohms. I've got an instrument that uses the fall of potential method, but I have no place to drive my stakes, everything is concrete. Is there another method for confirming my ground?