Spurious Activation of Safety Instrumented Systems

Spurious activation of the SISs may result in full or partial shutdown of an ongoing process. In the published literature, spurious activation is known under many different names. Some examples of such names are spurious trip, spurious initiation, premature closure, spurious operation (SO), false trip, spurious activation, and spurious stop [14-17]. In the oil and gas industrial sector, it is very important to reduce or eliminate the occurrence of spurious activations because of the following factors [14]  

A premature closure of a hydraulically operated, spring loaded, failsafe close safety valve because of leakage in the hydraulic circuit. 

A high-level alarm from a level transmitter without the level of liquid having exceeded its upper limit because of the failure to distinguish the foam from the real level of the liquid in the separator. 

A false signal about high level from a level transmitter because of an internal malfunction of the transmitter. 

A spurious trip is activation of one or more SIS elements or components such that the SIS performs an SIF without the existence of a stated process demand. Two examples of the spurious trip are presented in Reference 14. Finally, a spurious shutdown is a complete or partial process shutdown without the existence of a stated process demand. 

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What are the main types of spurious activation of safety instrumented systems ... 

Lundteigen, M.A., Rausand, M., Spurious activation of safety instrumented systems in the oil and gas industry Basic concepts and formulas. Reliability Engineering and System Safety, 93,2008,1208-1217. 

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