Failure risk analysis in the collective water supply systems in crisis situations

Risk is a basic category to estimate water supply system safety. The first step in risk assessment is to identify the threats and their possible consequences. One of methods for risk assessment is the method using the socalled risk graphs. It relies on the preliminary analysis of such risk factors as: the frequency of threat occurrence – F, the duration of the risk exposure – E, the size of the possible consequences – C and a degree of protection – O, that is inversely proportional to the mentioned measures of risk. The route along the branches of the risk graph should be started from the determination of the initiating/peak event which is the undesirable event (e.g. secondary water contamination in water-pipe network). The expanded risk graph presented in the work differs from the standard (commonly used) graph because it takes into consideration all combinations of the particular risk factors.