Optical fiber cable with tampering detecting means

Abstract From the Canadian patent

An optical fiber cable with optical fibers surrounded by a first gas blocking layer which is surrounded by a second gas blocking layer spaced from the first layer so as to provide longitudinal gas flow channels between the first and second layers. The channels are filled with a gas under a pressure above atmospheric pressure so that when the second layer is punctured, there is a gas flow and/or gas pressure drop indicating such puncturing and hence, if caused by tampering the, fact of tampering. Also, devices for indicating the gas flow and/or pressure drop and alarms and/or signal transmission terminating apparatus responsive to such devices.