Risk mitigation within industrial installations: criticalities in overpressure protection systems design

One of the main causes of severe accidents in industrial installations is represented by the accidental and uncontrolled increase of the operating pressure within some process equipment or piping. When this happens without a timely and effective intervention of the control system, the possible catastrophic release of large amounts of dangerous materials is possible, with subsequent possible large scale accidents like fires, explosions or toxic cloud dispersion. In order to avoid this kind of events, different prevention and/or protection measures are generally adopted: accurate process design, testing and maintenance, adequate instrumentation and control, and, as a last barrier, proper emergency systems, in particular an emergency relief system. Emergency relief systems are widely adopted since long in all branches of industrial applications and even in common home devices, and they usually act safely and reliably. However some lack of understanding and a number of uncertainties are still present both in their sizing criteria and management procedures. These issues should be properly addressed in order to reach a higher level of trust and to avoid the occurrence of accidents which, even if already characterized by low values of frequency of occurrence, might give rise to very severe consequences, either for the exposed population and the environment. The above mentioned uncertainties and lack of understanding actually relate to a range of issues. After a general overview of them, some of the most important causes of possible errors, and hence sources of possible accidents, will be addressed, with specific reference to emergency scenarios identification and relieving fluid characterization. It is expected that a more thorough knowledge of the involved phenomena will allow a more proper sizing, selection and installation of these very important safety systems