Page "Alarm management" Paragraph 2

Alarms were added to alert the operator to a condition that was about to exceed a design limit, or had already exceeded a design limit.

Additionally, Emergency Shut Down ( ESD ) systems were employed to halt a process that was in danger of exceeding either safety, environmental or monetarily acceptable process limits.

Alarm were indicated to the operator by annunciator horns, and lights of different colors.

( For instance, green lights meant OK, Yellow meant not OK, and Red meant BAD.

) Panel boards were usually laid out in a manner that replicated the process flow in the plant.

So instrumentation indicating operating units with the plant was grouped together for recognition sake and ease of problem solution.

It was a simple matter to look at the entire panel board, and discern whether any section of the plant was running poorly.

This was due to both the design of the instruments and the implementation of the alarms associated with the instruments.

Instrumentation companies put a lot of effort into the design and individual layout of the instruments they manufactured.

To do this they employed behavioral psychology practices which revealed how much information a human being could collect in a quick glance.

More complex plants had more complex panel boards, and therefore often more human operators or controllers.