A proactive, standards-based approach that addresses a plant’s process safety throughout its life cycle can help reduce both risk and costs.
By Pete Skipp, process safety manager, Rockwell Automation
A standards-based approach to process safety, one that actively addresses risks across a plant’s lifespan, can lead to safer chemical processes, fewer safety functions and lower operating costs. The problem, however, is that too few companies take this approach, opening themselves up to greater risk of a catastrophic incident as a result.
The U.S. Chemical Safety Board (CSB) pointed to this problem in a video that examined process safety in the 10 years following the major refinery explosion in Texas City. The video cited multiple instances in which risks went unaddressed in chemical operations, sometimes resulting in fatal incidents. According to one CSB official, every incident his organization investigated in the 10 years after the Gulf incident was preventable. “There has not been one investigation we’ve done that we found the incidents were unavoidable,” he says.
Today, as many chemical companies look to replace decades-old safety-related technologies, they have an opportunity to put an end to this trend by rethinking their approach to process safety.
Why Is Process Safety Falling Short?
One problem many chemical companies face is they simply don’t have dedicated resources for process safety. As a result, they are unable spend sufficient time to help meet requirements for specifying, designing and implementing a safety instrumented system (SIS), as well as helping to maintain it properly throughout its life including functional safety assessments and periodic audits.
In some cases, companies will specify a certified programmable logic controller (PLC) with a specific safety integrity level (SIL) because it meets their expected highest level of protection. The result, however, is that they don’t apply the same rigor to the field devices, such as sensors and final elements, or to other layers of protection necessary for effective process safety.
Another issue is companies will strive for compliance when they deploy a SIS but not its functional safety management aspects throughout its lifespan. For example, they don’t proof-test the system’s safety instrumented functions (SIFs) to make sure they maintain the target SIL.
Independent reports such as the U.K. government’s Health and Safety Executive (HSE) report on control system failures helps illustrate where failures are causing or contributing to industrial accidents.
The report found that 44% of failures were caused by an inadequate specification, due to either a poor hazard analysis or an insufficient assessment of the impact of control system failure modes on the specification. Meanwhile, 15% of failures were caused by inadequate operation and maintenance and 20% were caused by changes after commissioning.
Since 2003, there has been an international standard (IEC61511) based on a life-cycle approach to process safety. This standard addresses these known issues and largely was written by end users for end users.
The Definitive Standard
A methodical and standards-based approach can help companies understand their process safety risks better and then implement the right level of protection. This approach also can help companies design maintenance and support into SIFs to reduce the risk of safety integrity performance degrading over time.
The functional safety standard IEC 61511 should be the foundation for a standards-based life cycle approach to process safety. It defines the requirements that must be met, not only in designing and implementing a SIS, but also in maintaining it for the system’s entire operating life.
Applying this standard requires more upfront work because of its analysis phase and management aspects. Managing the safety loops throughout a system’s life cycle also creates more work, but the payoff from this added effort is significant: the likelihood of fewer safety risks, a right-sized SIS and increased process uptime.
Moving Through the Life Cycle
A life cycle-based safety approach has three main phases of execution: analysis, realization and operation. When moving through these phases, it’s important to remember every task must be verified by someone independent from those who performed the task.
- Analysis: The purpose of the analysis phase is to understand how much risk exists within the process, and then define where and how that risk can be mitigated. Processes such as the hazard and operability (HAZOP) study identify the risk and generate the safety requirements specification (SRS) and techniques, such as inherently safer designs, alternate layers of protection, alarm management and SIS implementation to mitigate the risk.
- Realization: During this phase, a functional design specification can be developed from the SRS. This document describes how the safety functions defined in the SRS are implemented using the selected SIS technology, thus meeting the SRS.
In the design and engineering portion of this phase, technology is selected to help implement the required behaviors. There’s no requirement that the technology be certified by groups such as TÜV Rheinland and exida, but choosing such solutions can help users meet the required integrity with less documentation. The SIS then can be installed and validated in a documented manner to confirm it meets the requirements outlined in the SRS.
- Operation: Organizations must make sure the identified and implemented risk-reduction measures are maintained throughout a plant or process’s lifespan. This even includes identifying how hazards will be managed during decommissioning.
Safety integrity performance will degrade over time, which is why regular proof tests are critical. Also, any changes to a SIS can impact safety. Clause 17 of IEC 61511 provides guidance for SIS modifications.
The many chemical companies seeking to replace their decades-old SIS have a choice. They can continue with the status quo or grandfathering, which assumes what has been providing protection for the past 20+ years will continue to do so, or they can take a more proactive, standards-based approach that addresses their plant’s process safety needs across its entire life cycle.
The latter can reduce the potential for a catastrophic safety incident, help verify operations teams are living up to corporate leadership’s expectations for safety, and create overall safer and more productive chemical operations.
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