Appendix 2A Process Plant Example of the Stepladder Model

APPENDIX 2A PROCESS PLANT EXAMPLE OF THE STEPLADDER MODEL 

Consider a process worker monitoring a control panel in a batch processing plant. The worker is executing a series of routine operations such as opening and closing valves and turning on agitators and heaters. 

Scan information sources (dials, chart recorders, etc.). If the pattern of indicators is very familiar, the worker will probably immediately branch to the Execute Actions box (via the thin arrow) and make the usual response to this situation (e.g., pressing the alarm accept button if the indications suggest a nonsignificant event). 

If the pattern does not fit into an immediately identifiable pattern, the process worker may then consciously apply more explicit if-then rules to link the various symptoms with likely causes. Three alternative outcomes are possible from this process. If the diagnosis and the required actions are very closely linked (because this situation arises frequently) then a branch to the Execute Actions box will occur. If the required action is less obvious, then the branch to the Select/Formulate Actions box will be likely, where specific action rules of the form if situation is X then do Y will be applied. A third possibility is that the operating team are unable or imwilling to respond immediately to the situation because they are uncertain about its implications for safety and/or production. They will then move to the Implications of plant state box. 

At this stage the implications of the situation will be explored, using the operating team s general fxmctional knowledge of the process. This explicit 

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