Functional safety refers to “Safety Instrumented Systems” that implement “Safety Instrumented Functions” (SIFs) as part of a company’s overall risk management strategy. A Safety Instrumented Function is designed to respond to a specific hazardous event. It implements an action that will achieve or maintain a safe state for the equipment under control.
Functional safety must always be seen within the wider context of company risk management. It cannot be seen in isolation; it makes no sense without that broader basis. Functional safety is just one element in a range of risk treatments.
A Safety Instrumented System is composed of a combination of
⦁ Sensors
⦁ A logic solver
⦁ Final elements such as actuators and valves
The functional safety standards provide a very specific quality management system to implement one part of an overall risk management strategy.
Functional Safety Management Planning
The appropriate standards are required to manage functional safety in the process industries. A company that chooses to use Safety Instrumented Functions in managing risk needs to demonstrate that it has taken reasonable steps to comply with these standards. There should be a deliberate process to plan how the standards will be applied. Without a plan compliance will be ad-hoc and difficult to demonstrate.
The need for Functional Safety Management Planning (FSMP) applies to all the parties involved in engineering and operating a functional safety system.
Objectives:
The objectives in planning are to:
⦁ Define the Lifecycle Model, i.e., which parts within the overall lifecycle are relevant
⦁ Define responsibilities
⦁ Specify management and technical activities
⦁ Establish the documentation framework
⦁ Facilitate and demonstrate compliance to the standards
⦁ Plan the verification, validation, and assessment activities
⦁ Provide a “live” planning document that can be maintained throughout the lifecycle
⦁ Obtain acceptance of the plan from the risk owners
Levels of Planning
It may be useful to have several levels of functional safety management planning:
⦁ An overall company-wide plan
⦁ A plan for an individual operating facility
⦁ A project plan for a specific project
⦁ The system vendors may have plans covering only their scope
Document / Lifecycle Plan
The document/lifecycle plan identifies which stages of the lifecycle apply for the scope of work being planned:
⦁ Conceptual design & requirements development
⦁ System design & engineering
⦁ Testing
⦁ Installation & commissioning
⦁ Operations, maintenance & ongoing modifications
Requirements
The Safety Requirements Specification (SRS) is a collation of many elements:
⦁ Control & Safeguarding Philosophy
⦁ SIS Architecture Specification
⦁ HAZOP Reports
⦁ SIL Determination Report
⦁ Cause & Effect Charts
⦁ Functional Specifications
⦁ SIF Narratives
⦁ Ranges, Alarm and Trip Settings Schedule
⦁ Overrides
