Safety instrumented system perspective

Fire and Gas Systems From Safety Instrumented System Perspective... 

It is interesting to note the heading of the chapter It is named like this to indicate that safety instrumented functions (SIFs—in plural) constitute a safety instrumented system (SIS). From the discussions in previous chapters, readers have come across varieties of definitions of accidents, hazards, and risks from different perspectives. Also there were a few things common such as the accidents are not always negative, and there are always aim to avoid accidents so that there is not loss to the system, personnel, and environment. At the back of the mind, we always try to develop and incorporate some things to reduce risks and to maintain work safety. Therefore, safety work involves some activities, measures, and techniques, which can contribute or help to reductions in losses in different forms, and human injury or fatality. There are quite a good number of elements involved in work safety these include, but are not limited to the following ... 

Reactor A process hazards analysis identifies a hazard associated with a reactor dump valve. If the dump valve opens when the reactor is not depressurized, downstream equipment is overpressured. An SIF is implemented to prevent the reactor dump valve from opening when the pressure is high, using a solenoid-operated valve that controls the instrument air supply to the dump valve actuator. To support batch operation, the SIF energizes the solenoid-operated valve for each batch when the reactor pressure is low. However, from a safety perspective, the SIF prevents a hazardous event only when the control system fails and tries to open the control valve when the reactor is under pressure. This failure is estimated to be approximately 1 in 10 years. The SIF is operating in demand mode with regard to the hazard. 

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