Functional Safety

Functional Safety Assessment (FSA):
FSA is the process of performing independent reviews and audits at predefined stages of the Safety Life-cycle. FSA is the activity of ensuring the quality of execution is adequate and as per the requirements of international standards such as IEC 61508 and IEC 61511.

The purpose of Functional Safety Assessments (FSAs) is twofold: to ensure that all the activities and documentation for the particular Safety Lifecycle (SLC) phase have been completed as per requirements; to help prevent systematic failures from being introduced.

Compliance:
Defines compliance with the standard as: “to conform to this standard it shall be demonstrated that all the relevant requirements have been satisfied to the required criteria specified (for example safety integrity level) and therefore, for each clause or sub-clause, all the objectives have been met.”

FSA is a way of monitoring the effectiveness of risk management strategies that rely on automated safety systems (i.e. functional safety)

FSAs may be conducted at the following time:

• After the hazard and risk assessment has been carried out, the required protection layers have been identified and the Safety Requirement Specification (SRS) has been developed;
• After the Safety Instrumented System (SIS) has been designed;
• After the installation, pre-commissioning and final validation of the SIS has been completed and operation and maintenance procedures have been developed;
• After gaining experience in operation and maintenance;
• After modification and prior to decommissioning of a SIS.

Functional Safety Audit :
An FS Audit provides a systematic and independent examination of the particular safety lifecycle 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.

Industry good practice is encapsulated in the IEC 61511 standard [1]. Its clause 5.2.6.2.1 notes: “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.

Safety Requirement Specification (SRS) :
The Safety Requirements Specification (SRS) is a core document, which is used as the main reference to be followed by designers, installers, and operators of a Safety Instrumented Function (SIF). The SRS details all the crucial functional and integrity requirements for each of the SIFs. Prior to commissioning, the SIF is normally validated against the SRS to ensure that all the stated requirements are met.

The IEC 61511 Standard requires the user to create a Safety Requirements Specification (SRS) for a Safety Instrumented System (SIS) that incorporates all the analysis done during the Risk Assessment, HAZOP/PHA and LOPA reviews. 

SIL Determination :
Safety Instrumented Functions (SIF’s) are important elements within many industries for the protection and mitigation of risks. Therefore, it is important to identify the protection requirements of each SIF in respect to its function. The requirement is often described in terms of Safety Integrity Level (SIL). A SIL can be one of four levels, each within a target band known as the Probability of Failure on Demand (PFD), where SIL1 is considered the lowest and SIL4 is considered the highest.

SIL Verification – It’s a process of calculating the average probability of failure on demand (or the probability of failure per hour) and architectural constraints for a safety function design to see if it meets the required SIL. 

SIL Validation :
SIL (Safety Integrity Level) Validation (SIL-V) is carried out to establish a “fit for purpose“ design of instrumented safety measures that are capable of mitigating hazards with respect to safety, environmental consequences, and economic loss.

SIL Validation is carried out with the intent to allocate safety functions to protection layers, determine the associated safety integrity level for each safety instrumented function, and allocate safety functions to protection layers. It is carried out prior to the operation phase of the IEC 61511 safety lifecycle to put forth a plan for routine actions such as proof testing, maintenance override conditions, documentation of system demand and failure rates consistent with the Safety Integrity Level (SIL), verification calculations, audit and test documentation, and diagnostic and repair procedures.

Reliability, Availability & Maintainability Study (RAMS) :
RAM study is well-designed and properly implemented asset optimization program that can significantly lower project costs. The results from a RAM modeling will identify possible causes of production losses and can examine possible system alternatives. The RAM study is, thus, a tool for decision-making, with additional insights for costs-versus-benefits analysis