SIL Studies

Functional safety acts as added layer of protection to basic process control systems (BPCS). Functional safety loops or safety systems are independent of the basic process control systems which are tasked with safe operation of any process.  In scenario where there is a BPCS failure, functional safety loops or safety system acts as a safe guard and take process to the safe state preventing any untoward incident.

Implementation of functional safety can save business from loss of human life, infrastructure, environmental damages as well as reputational losses. This can be achieved by carrying out various SIL studies as per safety life-cycle requirements of IEC 61511 and IEC 61508 series standards.

Use of any SIL certified components in a safety function does necessarily qualify whole safety function to achieve required performance criteria. The process industry standard on functional safety IEC 61511 describes various activities involved in designing, commissioning, operating and maintaining a Safety Instrumented System (SIS) to establish and claim certain SIL. IEC 61511 suggests to follow the complete safety life-cycle approach for management of functional safety in process industries.

TUV India has pool of safety experts who can perform SIL Studies with safety life-cycle approach as mentioned in IEC 61511 and provide below services.

It must be emphasized that any risk assessment technique, including LOPA, cannot yield the exact requirements for a SIS. These assessments establish a required risk reduction and a preferred method to achieve it. When it is decided that a required safety function will be allocated to a safety instrumented system, LOPA aids in setting the ‘target SIL’. The next important step is to develop a SRS which translates the SIF identified by the SIL assessment to an engineering design specification.

When the end user simply procures and installs individual elements, functional safety cannot be achieved. This aspect of functional safety is often overlooked by end users. Validation has to be carried out after completion of installation and commissioning of the SIS. This also involves the Factory Acceptance Test (FAT) and also a strict crosscheck against the SRS.

The Functional Safety Assessment (FSA) is an investigation to determine if the safety function under study achieves the required level of functional safety to support a decision to either progress to the next phase of the safety life-cycle or remain in the same phase until all necessary measures are in place.

Conducting an FSA (Stage 3 & 4) is a mandatory requirement under IEC 61511 prior to introduction of hazards and after substantial operation & maintenance experience is achieved, in order to confirm that functional safety has been achieved with regards to the necessary risk reduction for the system under study. 

However, it is encouraged to conduct all 5 stages of the FSA so as to comply with the safety life-cycle (SLC).

An FS Audit provides a systematic and independent examination of the particular safety life-cycle phase activities under review. It determines whether the “procedures” specific to the functional safety requirements comply with the planned arrangements, are implemented effectively, and are suitable to achieve the specified objectives.

The purpose of the audit is to review information documents and records to determine whether the Functional Safety Management System (FSMS) is in place, up to date, and being followed. Where gaps are identified, recommendations for improvements are made.