Functional safety engineering involves identifying specific hazardous failures which lead to serious consequences (e.g., death) and then establishing maximum tolerable frequency targets for each mode of failure. Equipment whose failure contributes to each of these hazards is identified and usually referred to as “safety-related.”
Functional safety is related to the process and the Basic Process Control System (BPCS) which depends on the correct functioning of the SIS and other protection layers. A high level of functional safety means that a safety instrumented system (SIS) will work correctly and with a high probability of success.
Functional safety includes industrial process control systems, process shutdown systems, rail signalling equipment, automotive controls, medical treatment equipment, etc. In other words, any equipment (with or without software) whose failure can contribute to a hazard is likely to be safety-related.
A Safety Function is thus defined as a function, of a piece of equipment, which maintains it in a safe state, or brings it to a safe state, in respect of some particular hazard.
Functional safety refers to a part of the overall safety that depends on a system or equipment operating correctly in response to its inputs, including the safe management of likely operator errors, hardware failures, and environmental changes. It involves the detection of potentially dangerous conditions, the activation of protective or corrective devices or mechanisms to prevent hazardous events, and the mitigation of their consequences.
Functional safety is critical in many industries, including automotive, aerospace, industrial automation, and medical devices. Key standards governing functional safety include:
- IEC 61508: General standard applicable to various industries.
- ISO 26262: For automotive safety.
- IEC 62061: Safety of machinery.
- ISO 13849: Safety of machinery and control systems.
- IEC 60601: Medical electrical equipment.
- IEC 61511: is a simplified form of IEC 61508 catering for the more consistent equipment architectures found in the process industries.
These standards outline the requirements for ensuring that systems function correctly and safely, especially in the presence of faults.
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Functional Safety in the Process Industry
In the process industry, functional safety is a crucial aspect of ensuring the safe operation of systems that handle hazardous materials and processes. The primary objective is to prevent accidents that could result in harm to people, the environment, or property. Functional safety in this context involves the design, implementation, and management of safety-related systems that can detect hazardous conditions and take appropriate actions to mitigate risks.
Key Aspects of Functional Safety in the Process Industry
1. Hazard and Risk Assessment
- Identifying potential hazards and assessing the associated risks.
- Determining the necessary safety functions to mitigate these risks.
2. Safety Instrumented Systems (SIS)
- Designing and implementing SIS that can perform specific safety functions when dangerous conditions are detected.
- Components of SIS typically include sensors, logic solvers (e.g., programmable logic controllers), and actuators.
3. Safety Integrity Levels (SIL)
Defining the required SIL for each safety function, which indicates the level of risk reduction provided by the function. SIL levels range from SIL 1 (lowest level of risk reduction) to SIL 4 (highest level of risk reduction).
- SIL 4: the highest target and most onerous to achieve, requiring state-of-the-art techniques (usually avoided).
- SIL 3: less onerous than SIL 4 but still requiring the use of sophisticated design techniques.
- SIL 2: requiring good design and operating practice to a level such as would be found in an ISO 9001 management system.
- SIL 1: the minimum level but still implying good design practice. <SIL 1: referred to (in IEC 61508 and other documents) as “not-safety related” in terms of compliance
Adhering to international standards such as IEC 61511, which is specifically tailored for the process industry and is based on IEC 61508. Complying with local regulations and industry-specific guidelines.
4. Lifecycle Approach
Implementing a comprehensive safety lifecycle approach, from initial risk assessment and design through to operation, maintenance, and decommissioning. Regularly reviewing and updating safety systems to address changes in processes or operating conditions.
5. Functional Safety Management
Establishing a functional safety management system to oversee all aspects of functional safety activities. Ensuring that personnel are adequately trained and competent in functional safety practices.
Key Standards
- IEC 61511: This standard provides guidelines for the implementation of safety instrumented systems in the process industry. It covers the entire safety lifecycle and emphasizes the importance of a systematic approach to safety.
- IEC 61508: While IEC 61511 is derived from IEC 61508, the latter is a more generic standard applicable to all industries. It provides a framework for the design and management of electrical, electronic, and programmable electronic safety-related systems.
Example Applications
- Chemical Plants: Implementing SIS to detect leaks, overpressure, or temperature excursions and initiating shutdown procedures or activating alarms.
- Oil and Gas: Using SIS to manage the risks associated with drilling operations, pipeline transportation, and refining processes.
- Pharmaceuticals: Ensuring safe operation of processes involving hazardous chemicals or reactions.
By following these practices and standards, the process industry aims to minimize the risk of accidents and ensure the safe operation of its systems, thereby protecting people, the environment, and assets.
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