ABSTRACT
In a modern well-designed process plant, it is difficult to cause a major accident from the control room. Hazard and operability studies and safety integrity level reviews will have ensured that there is monitoring of all critical process parameters and alarms, trips and interlocks which will stop a plant or prevent hazardous events before they become serious. There are in principle possibilities to bypass trips and interlocks and to adjust trip set points beyond the safe levels. In a modern plant, these values are generally specified quite clearly, though, in the manual of permitted operations and in the standard operating procedures. In a well-designed modern distributed control system (DCS), overrides are possible only by means of a special key or password, and the fact of the override is reported automatically to plant management. Changes are subject to safety analysis through the management of change procedure.
