Two independent Quick Isolation Shutdown Systems (QISS) are installed at the BASF/FINA Port Arthur Steam Cracker. One is for the steam cracker, the other is for the Pygas hydrogenation/aromatics recovery section. These systems are intended to mitigate potential hazard caused by a major loss of containment by limiting the amount of hydrocarbon released from an individual process system. The installation of such a system is based on BASF internal safety practices. This paper will provide an overview of the experiences with this system at Port Arthur.

This system is not intended as a safety instrumented system (SIS), but as a hydrocarbon loss prevention measure. As such QISS is a non-fail safe system. The QISS system employs a two out of three (2oo3) architecture to insure greater reliability. During a loss of power or system failure the QISS will not trigger automatically.

The system closes or opens approximately 200 valves throughout the plant. Most valves are changed immediately, some (less than 10%) are changed after a time delay. The QISS blocks all hydrocarbon import and exports, trips all major energy sources, and isolates all major hydrocarbon inventories. The QISS system does not automatically de-inventory or depressurize process equipment. De-inventory or depressurization requires independent operator action. Activation of the QISS may cause the ESD system to respond by taking additional actions as unsafe conditions arise.