The primary goal of a safety system is to reduce operational risks and improve the overall process safety of a plant over its entire lifecycle.

In the event of a deviation or failure of the safety system, Safety Instrumented Systems (SIS) are there to ensure that a plant is taken into a safe state, limiting the negative consequences to people, equipment and the environment. It is important that organizations in the process industry are able to react quickly under variable conditions and have the capabilities to continuously monitor and evaluate safety system performance.

Why should you monitor the performance of a safety system? What are the advantages?

We identified our top 5 reasons to monitor safety system performance. The monitoring will help you maintain the safety integrity of a plant during operations.

1. The integrity of a SIS will degrade over time

It is widely recognized that the integrity of an SIS degrades during operation. SIS solutions are regulated by two international standards, the IEC 61508 Edition 2 (2010) and IEC 61511 Edition 2 (2016). A key component of IEC 61511 Edition 2 (2016) is clause 16, which requires that the mandatory SIL of each SIF be upheld during operation and maintenance. In addition, the SIS should be operated and maintained such that functional safety is also maintained.

The implications of IEC 61511 Edition 2 (2016) clause 16 on SIS operators and managers are that they must perform and conduct regular maintenance and proof testing of their SIS. Additionally, they must also maintain adequate documentation of process data, proof test records and inspection procedures to prove compliance to IEC61508 and IEC61511 requirements.

2. Safety design information needs to validated with actual operational data

During the HAZOP/LOPA, the likelihood of failure of an initiating event is usually based on the Centre of Chemical Process Safety (CCPS) data. This assumption needs to be re-validated periodically (e.g. every 5 years as per OSHA) with actual operational data as recommended in IEC 61511 Edition 2 (2016) to identify the gaps in safety performance and address them.

IEC 61511 Edition 2 (2016) requires existing SISs designed and constructed in accordance with code, standards, or practices prior to this current issue, the user shall determine that the equipment is designed, maintained, inspected, tested and operating in a safe manner.

Example: IEC 61511 Edition 2 Clause 16.2.9:

Discrepancies between expected behaviour and actual behaviour of the SIS shall be analysed and, where necessary, modifications made such that the required safety is maintained.

3. Business requires a means to optimize their OPEX

Industrial processes, regardless of the complexity and size of safety systems and equipment, require an ongoing assessment of their performance. Traditionally this a labour-intensive process, consuming valuable time and resources to manually document, record, and process raw safety data, which may lead to errors and inaccuracies during the assessment. Hence, plant owners must re-evaluate their approach to the collection, measurement, and analysis of safety data, to optimize safety performance and costs throughout the plant lifecycle.

4. Mounting pressure to adhere to safety standards

Within a production environment, maintaining compliance to required standards and processes is not an optional requirement, it must be adhered to, to protect the integrity of the safety system.

Perhaps one of the biggest threats to safety system equipment and functionality is the incorrect assumption, incorrect operation, non-rigorous maintenance and uncontrolled modifications, supplemented by the difficulty in maintaining synchronicity between related applications. These operational challenges are referenced within many of the safety standards and regulations including IEC 61508 and IEC 61511, Control of Major Accident Hazards (COMAH), American Petroleum Institute (API), Serveso III and Occupational Safety and Health Administration (OSHA).

5. Ensure the plant remains at a safe level when safety equipment is unavailable

During operations, it is important for organizations to manage process risks and maintain safe operations throughout the safety life cycle. Safety functions shall be made available at all times. However, there are certain instances when bypasses or overrides might be applied to certain pieces of equipment or sensors. This bypassing of safety function shall be carried out after the risk assessment has been completed and appropriate compensating measures are in place. Therefore, safety systems are essentially bypassed by plant personnel under calculated and intensely watched conditions, with associated risk assessment. Evidence of risk assessment for all bypasses are required for audits by technical authorities and insurance as it shows that organization are proficient in operations and maintenance requirements.

Comprehensive safety system performance monitoring

We offer a comprehensive safety performance monitoring solution to automatically collect, organize and present all safety-related data from a safety instrumented system (SIS). It enables measuring conveniently the safety system performance to help ensure that risks are reduced and safe operation can be assured.

Talk to your local Yokogawa representative to find out how our software solutions can help manage and oversee the operational safety performance of the plant. We are happy to help. Move a step ahead towards a safety culture of “What gets measured gets managed.”