Evaluate the Plant-Wide Safety of Your Interlock Systems

Interlocks serve as important safety devices in industrial settings, where they protect equipment from damage and employees from toxic and harmful releases from that equipment arising out of unsafe conditions. However, evaluation of the effect of the actions of interlock on other process systems is required. In some of the cases, we encountered initiation of interlocks in equipment caused severe damage to other equipment (due to change in composition) or initiation of interlock caused damage to the same equipment it was intended to protect (due to incorrect sequencing of interlocks). The information available with the cause and effect diagrams is limited to the vicinity of that particular interlock. It does not give any information about the relationship of the interlock, under study, with other process equipment or even with other interlocks (except for initiation). The relationship between safety interlocks and process system arises out of the behavior of the process system (e.g. change in composition) to the actions taken by the interlock. This paper proposes how a holistic view for these behavioral responses can be obtained by developing the IRM (Interlock Relationship Matrix). IRM is a single process document (excluding instrumentation and logic details) that provides information on the effects of all interlocks on each element of process system. Developing IRM is crucial in evaluating the interlock-process interference (behavioral responses) and is beneficial in managerial decision making to assess the likely damage to equipments and provide mitigation thereof.