Control Systems HAZOP (CHAZOP)


Control System HAZOP (CHAZOP)

Understanding Control Systems HAZOP (CHAZOP)

In today’s operational climate, it’s vital to get the most out of your existing equipment. Avoiding needless downtime is more essential than ever. Using Control Systems HAZOP (CHAZOP), the risks and impact of control systems failures can readily be assessed, yielding an action plan for preventing losses and accidents caused by control system upsets.

CHAZOP also gives important input to a RAMS (Reliability – Availability – Maintainability Study), giving you a pathway towards optimal use of maintenance resources and helping you increase uptime and throughput.

The team at xSeriCon is exceptionally experienced in leading CHAZOP studies in the process and energy sectors. Contact us to find out about our cost-effective CHAZOP and RAMS solutions.

What is CHAZOP?

To understand the weaknesses of a control system and its potential for failure, a number of steps may be required. Each of these steps can be termed CHAZOP, although the term CHAZOP is most commonly applied to the second step:

  • Calculate a predicted failure rate for the control system, using FMEA/FMEDA.
  • Perform a workshop study to assess the risks and impact of a control system failure on the process, using a What-If/Checklist style approach.
  • Perform software criticality analysis on the application software implemented in the control system.
  • Perform human factors analysis to find opportunities to optimize the interaction efficiency between operators and the control system.
  • Perform cyber security assessment to understand the vulnerability of the control system to attack.
  • All these results can then feed into RAMS, giving you a complete picture of plant availability.

What does a CHAZOP study entail?

A CHAZOP workshop study is a deep dive into the detailed workings of the control equipment, looking for any potential points of failure, especially single-point failure. Aspects to be considered include power supplies, hardware failure, software bugs, human factors, maintainability, non-normal operating conditions, and diagnostics, among others. In each case, the team asks the questions:

  • What can go wrong?
  • If it goes wrong, what is the potential impact on the process? (This often requires input from a previous HAZOP study.)
  • What protective measures are in place to avoid or mitigate the consequences?
  • What further action or study is required?

The CHAZOP report shows all the cases considered, and lists prioritized actions for improvement or further study.

Case Study: Gas Metering Plant

In a recent CHAZOP study performed by the xSeriCon team, a client desired to perform a study to find vulnerabilities in the control system of a gas metering plant. The study was commissioned following a trip incident caused by a hardware maintainability problem, which led to shutdown of a gas-fired power station nearby.

The study found a number of unexpected issues for further investigation, including:

  • Trip of a specific circuit breaker in a third-party facility some distance away could cause loss of supply from the metering station.
  • Fault behaviour of the diagnostics in the on-site UPS was unknown, and could potentially lead to a spurious shutdown.
  • The impact of loss of utility supply (instrument air and hydraulic pressure) to a critical control valve was not well understood and, again, could lead to a shutdown.