A fluid leak detection system for detecting fluid leaks in an industrial assembly, said industrial assembly including a pipe or conduit for receiving a flow of fluid therealong which is not provided as a free-surface flow, and characterized by , an acoustic emitter operable to emit and propagate an output emitted acoustic signal along at least part of said conduit, said output emitted acoustic signal including one or more preselected baseline frequency components in a frequency range selected above a background noise frequency of the industrial assembly, an acoustic sensor for receiving and sensing the output emitted acoustic signal at a location along said conduit spaced from said acoustic emitter, the acoustic sensor operable to output data signals representative of the sensed output emitted acoustic signal, a processor electronically communicating with said acoustic sensor, the processor including programme instructions operable to, detect the occurrence of one or more frequency components of the sensed output emitted acoustic signal which can be associated with preselected target frequencies indicating specific process information, compare whether one or more of the at least one baseline frequency components of the sensed output emitted acoustic signal deviates from a respective preselected target frequency by a threshold amount; and on identifying the at least one compared baseline frequency component as deviating from the preselected target frequency by the threshold amount, outputting at least one of a signal indicative of a potential fluid leak, and a control signal to effect a pre-selected safety protocol. said industrial assembly including a pipe or conduit for receiving a flow of fluid therealong which is not provided as a free-surface flow, and characterized by , an acoustic emitter operable to emit and propagate an output emitted acoustic signal along at least part of said conduit, said output emitted acoustic signal including one or more preselected baseline frequency components in a frequency range selected above a background noise frequency of the industrial assembly, an acoustic sensor for receiving and sensing the output emitted acoustic signal at a location along said conduit spaced from said acoustic emitter, the acoustic sensor operable to output data signals representative of the sensed output emitted acoustic signal, a processor electronically communicating with said acoustic sensor, the processor including programme instructions operable to, detect the occurrence of one or more frequency components of the sensed output emitted acoustic signal which can be associated with preselected target frequencies indicating specific process information, compare whether one or more of the at least one baseline frequency components of the sensed output emitted acoustic signal deviates from a respective preselected target frequency by a threshold amount; and on identifying the at least one compared baseline frequency component as deviating from the preselected target frequency by the threshold amount, outputting at least one of a signal indicative of a potential fluid leak, and a control signal to effect a pre-selected safety protocol. detect the occurrence of one or more frequency components of the sensed output emitted acoustic signal which can be associated with preselected target frequencies indicating specific process information, compare whether one or more of the at least one baseline frequency components of the sensed output emitted acoustic signal deviates from a respective preselected target frequency by a threshold amount; and on identifying the at least one compared baseline frequency component as deviating from the preselected target frequency by the threshold amount, outputting at least one of a signal indicative of a potential fluid leak, and a control signal to effect a pre-selected safety protocol. <EOS>