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The fundamentals of functional safety in an industrial process environment

by | Oct 6, 2016 | Engineering Design & HSE

Have you ever wondered about the difference between “functional safety” and “safety”? In this post, we go back to basics to explain the fundamentals, how it differs and what constitutes a functionally safe system.

What is functional safety?

In broad terms, the word “safety” means freedom from unacceptable risk of physical injury, or of damage to the health of people. Ensuring personnel are adequately protected with suitable clothing against burns or chemical spillage, or are isolated from potentially hazardous environments by guards or other suitable barriers will, to a large extent, achieve a degree of protection for workers in an industrial process environment. Functional safety is concerned with the appropriate responses of instrumented process systems to hazardous or dangerous conditions that are likely to lead to injury and/or equipment damage – or injury and damage beyond the boundaries of the plant. Being functionally safe provides a proactive means of detecting the potential onset of a hazard or dangerous condition and subsequently preventing it from arising in the first place, rather than simply offering primary, passive protection after the event.

How relevant is functional safety to process plant operations?

Process plants – particularly those involving the handling and processing of hazardous materials – are subject to Control of Major Accident Hazards (COMAH) regulations. Under COMAH, the design, installation, operation and maintenance of a plant’s electrical, control and instrumentation systems must be inspected and considered functionally safe by a competent authority such as the Health & Safety Executive (HSE). These Safety Instrumented Systems (SIS), as they are termed, are the foundation of implementation.

How is a functionally safe system implemented?

The whole process begins with a full hazard and risk analysis, with a Safety Requirement Specification (SRS) being developed simultaneously as the risks are identified. The SRS is a benchmark for the SIS, determining the functionally safe system design and enabling its performance to be verified and any later modifications validated. The plant’s Safety Integrity Levels (SILs) – SIL being the relative level of risk-reduction – are subsequently established, and these will define the appropriate Safety Instrumented Functions (SIFs). The SIF arrangement of sensor, logic and control elements combine to maintain a system within an acceptable safety envelope, which is defined and managed within the SRS document.

What standards and guides exist to help with implementation?

The standards IEC 61511 and IEC 61508 cover the functional safety lifecycle from concept, through hazard analysis, implementation and operation to end-of-life decommissioning. IEC 61511 is targeted specifically at the design, operation and maintenance of SIS used in the process industry. IEC 61508 covers a broader range of safety-related systems, including emergency shutdown, fire and gas, machine devices and networks, and much more.

For those requiring more in-depth detail about implementation in process plant operations, we have published a comprehensive whitepaper, available for download below. GSE also offers a recorded webinar on functional safety and its implementation.



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