Abstract: Arrival of a pressure wave front is detected at a plurality of monitoring stations spaced along a protected section of a fluid-carrying pipeline. Arrival times obtained at the monitoring stations are qualified as to whether they correspond to a pressure transient event (critical event) which originated in the protected section. If so, the location, amplitude and time of occurrence of the critical event are determined. An uncertainty zone is derived at the extremes of the protected section having a length dependent on the precision of a time standard to which the monitoring stations are referenced and on the exactness of fluid velocity in the pipeline. An operator is so informed if the location of the critical event is determined to fall in the uncertainty zone. It is also possible to determine whether wave fronts correspond to an event occurring outside the protected section. Information from the resulting pass-through wave is used to update needed parameters useful for the critical event determinations.