Methodologies for Separate CHAZOP and COOP Studies

摘要

Hazard and operability (HAZOP) studies are used extensively throughout the process industries as a formal means of analysing the safety of plant design. The methodology is well established and in the public domain. Most modern plants are controlled by some form of computer control system to which computer hazard and operability (CHAZOP) studies relate. These are essentially an extension to HAZOP with an emphasis on control system hardware. However, review of the safety aspects of the design of application software is somewhat ad-hoc, with a variety of in-company approaches and methodologies. This paper, therefore, argues the case for a more systematic approach. Two separate methodologies are advocated: CHAZOP and control and operability (COOP) studies. The role of CHAZOP is to focus on the safety related issues of the control system's hardware design and its system software. COOP focuses on the application software. An understanding of the difference in emphasis of the methodologies is fundamental. In HAZOP the emphasis is on plant and/or process issues, in CHAZOP it is on the control system's I/O and communications channels, and in COOP it is on the functionality of the control system. The paper outlines current practice with regard to HAZOP studies. This provides a basis for presenting CHAZOP and COOP as extensions to HAZOP. Methodologies for both CHAZOP and COOP are proposed with guidewords suggested for each. The guidewords are different from the standard set used for HAZOP and are more appropriate for use with control systems.