(46y) Control Systems Integrity Review - Selective Application of Controls Systems HAZOP (CHAZOP) Study

A Control Systems Hazard and Operability Study (CHAZOP) provides a means of systematically reviewing the design and operation of a control and safety system to identify potential hazards and/or operability problems.  It focuses on how a control or safety system may deviate from the design intent, and draws on the expertise of the team members and their past experience with the design and/or operations of similar facilities.

The CHAZOP technique stemmed from the evolution of control and protection system designs, from single-element analog devices a couple of decades ago, to the increased application of electronics, logic solvers with redundant processors and voting capabilities, and feedback loops to identify various sensor and end-device failures, including covert.  Although the control and protection systems were evolving, many of the HAZOP Study applications and Teams did not always involve participants that could properly weave these new control and protection system features into the HAZOP Study scenarios.  To address this gap, CHAZOP was developed to help ensure that the safety evaluation objectives of the HAZOP were achieved.

For high-quality HAZOP Studies that are supported by individuals with the correct "skill sets" and thoroughly address instrumentation issues (to the extent necessary for the conservative scenarios evaluated for the HAZOP Study), it can be argued that a complete CHAZOP isn't necessary.  CHAZOP can also be a significant effort that is difficult to justify to management, if a HAZOP Study has been performed.  However, there can still be value in reviewing some of the key characteristics associated with the Integrated Control and Safety Systems (ICSS) that are applied at modern process facilities.  With the HAZOP Study Team (and any necessary supplemental instrumentation specialists), there can often be value in a general review of network architecture, workstations, switching networks, key communications/power cable routing, data transfer strategies, human-machine interface issues, back-up strategies, and power sources/reliability.  This Control Systems Integrity Review can be implemented in a focused manner to review single failures and potential vulnerabilities.

The objective of this paper is to review appropriate applications of CHAZOP and to define a streamlined approach for Control Systems Integrity Reviews that can benefit many capital and instrumentation retrofit projects in process facilities.  Tips will be provided to maximize the effectiveness of the Team's efforts when performing the Control Systems Integrity Review.