For more information on basic design principles for interlock systems, However, it must be remembered that interlocks are not a replacement for good process or mechanical or piping system design, installation, inspection or maintenance. Process containment is the key issue.
No safety interlock can protect against premature rupture or failure of process equipment or the piping system under normal process conditions. No safety interlock can prevent harmful process upsets or catastrophic damage, but only serve to reduce the risk of such occurrences to an acceptable level.
Thus, the design of inherently safe systems should always be the first consideration; designing protective system systems, particularly interlock systems, should then be considered.
The provisions of alarms and interlock systems do not make humans irrelevant. The operator’s task under normal conditions is mainly to ensure that the process plant is operating in an economical and safe condition.
However, when an upset occurs, there will be a greater degree of interaction between the operator and the instrumentation and control system. At that time, the operator must be prepared to analyze the situation and decide whether or not action is required.
Therefore, even when there are automatic trips through interlocks, the operator must be informed as to the status of the plant and the effects that may result when the interlocks are activated.