Chemical process plants are complex integrated systems which often operate under limiting conditions. The raw materials used are flammable, toxic, corrosive, and explosive. Process system safety and reliability analysis is a systematic, rigorous decision-making approach to improve system reliability and subsequently to control the risk. Risk is calculated by determining both the likelihood and severity of system failure. There may be several types of system failure, each of which may result in a spectrum of consequences. Component models are a set of logic/mathematical expressions describing the behavior of the component under both fault and working conditions. In contrast to component modeling, structure modeling decomposes the system into a set of functional subsystems. These subsystems are the control loops. Physically, the control loop consists of two main parts: control instrument and process. Control loop failure occurs when controlled variable deviations occur. The various ways in which control loop failure can occur are identified by analyzing the disturbances.