Consistency, control design, human factors

Whatever method is used, there should be a clear design philosophy for the basic process control system (BPCS) employed at a facility that is consistent throughout each process and throughout the facility. Consistency in application will avoid human factor errors by operators. The philosophy should cover measurements, displays, alarms, control loops, protective systems, interlocks, special valves (e.g., PSV,... 

Until recently, the standard software development methodologies consisted of a requirement phase, a functional and detail design phase and a verification phase, but without a separately identifiable effort devoted to safety considerations. Several factors, in recent years, have changed this view forcing a focused and specific effort on safety aspects throughout the development process. One important aspect is the use of safety critical systems which are controlled by software and where it is vital to be able to ascertain that this type of software does not contain an error that will result in human injury or loss of life. 

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