Abstract: To detect escape or spillage of a cold liquid, for example liquefied natural gas, a narrow, robust, flexible, resilient, plastics tube, placed where the escaped or spilled cold liquid can contact it, is filled with carbon dioxide gas from a gas supply via a non-return valve and a pressure regulator which ensures that the maximum pressure in the tube is at a desired value which is preferably greater than the pressure of the ambient atmosphere surrounding the tube. A gas pressure drop detector is provided to observe a pressure drop in tube. Should escaped liquefied natural gas contact the tube the latter is so cooled that the carbon dioxide gas inside de-sublimates to a solid of greatly reduced volume causing a marked drop in pressure in the tube. This is observed by the pressure drop detector which initiates a warning or some safety action. A gas flow restrictor ensures the gas supply cannot rapidly re-charge the tube before the pressure drop detector has responded to the pressure drop.