Process safety interlocks

Implementation of process interlocks within process control systems is perfectly acceptable. Furthermore, it is also permissible (and probably advisable) that responsible operations personnel be authorized to bypass or ignore a process. Safety interlocks must be implemented within the separate safety interlock system. Bypassing or ignoring safety interlocks by operations personnel is simply not permitted. When this is necessary for ac tions such as verifying that the interlock continues to be func tional, such situations must be infrequent and incorporated into the design of the interlock. 

When a gas and vapor detection system is used either for fire protection or for personnel exposure protection, the system should be managed, inspected and tested on a scheduled basis, and maintained similar to any other major element of the fire protection system or any process safety interlock or safety instrumented system. 

Mechanical Integrity Program for Process Safety Interlocks and Alarms... 

Alarms, process safety interlocks, and safety instrumented systems can be modified easily by aging or tampering and such critical safeguards are just too vital to neglect. Each organization must develop an effective way to ensure that process safety systems will properly function when the process demands protection. 

Whereas numerous safety relief valves share many similarities, process safety interlocks are each individually tailored to the unique requirements of the process. The final parts of this chapter will discuss the critical process shutdown systems and the process safety alarms management systems used by three different major chemical plants. 

Protective Process Safety Interlocks at a DuPont Plant... 

Barclay, D. A., Protecting Process Safety Interlocks, Chemical Engineering Progress, Feb. 1988, pp. 20—24. 

Process safety interlocks can be used to prevent ttnd/or mitigate tin upset condition. Salety interlocks consist of outputs from process control systems, such as programmable logic controllers or distributed control systems, which trigger tut action designed to compensate I ot an upset condition and thus avoid an accident even in the e em of human or computer error. An example of a salety interlock would be the introduction of full cooling if the temperature of a reaction exceeded a safe level. 

Mechanical integrity program for process safety interlocks and alarms... 

Protective process safety interlocks at a DuPont plant... 

Barclay DA. Protecting process safety interlocks. Chem Eng Prog 1988 Feb 20-4. 

A matrix drawing showing the functional process safety interlocks between inputs and outputs of a safety system (see also FLD ). 

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