Risk Management / Functional Safety: A Practical Approach For End Users and System Integrators
- Valentino Vande Capelle (HIMA Middle East) | Michel Houtermans (Risknowlogy)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- March 2007
- Document Type
- Journal Paper
- 1 - 8
- 2007. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 6.1.4 HSSE standards, regulations and codes, 5.1.2 Faults and Fracture Characterisation, 6.3.7 Safety Risk Management, 7.2.1 Risk, Uncertainty and Risk Assessment
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The objective of this paper is to demonstrate, through a practical example, how an end user should deal with functional safety while designing a safety-instrumented function and implementing it in a safety-instrumented system. The paper starts with explaining the problems that exist inherently in safety systems. After understanding these problems, the paper takes the reader from the verbal description of a safety function through the design of the architecture, the process for the selection of safety components, and the role of reliability analysis. After reading this paper, the end user understands the practical process for implementing the design of safety-instrumented systems without going into detail of the requirements of the standard.
Every day, end users around the world are struggling with the design, implementation, operation, maintenance, and repair of safety-instrumented systems. The required functionality and safety integrity of safety-instrumented systems is in practice determined through a process-hazard analysis. This task is typically performed by the end users as they are the experts on their own production processes and understand the hazards of their processes best. The result of such a process-hazard analysis is among others a verbal description of each required safety function needed to protect the process. These safety functions are allocated to one or more safety systems, which can be of different kinds of technology. Those safety systems that are based on electronic or programmable electronic technology need as a minimum to comply with the functional safety standards IEC 61508 and/or 61511.
The end user is typically not involved in the actual design of the safety system. Normally this is outsourced to a system integrator. The system integrator determines the design of the safety system architecture and selects the safety components based on the specification of the end users. No matter who designs the safety system according to the safety function requirements, in the end it is the end user who is responsible for the safety integrity of the safety system. This means that the end user needs assurance that the chosen safety architecture and the selected safety components meet the requirements of the applicable standards, and should be able to defend his or her decision to any third party performing the functional safety assessment.
In reality, end users and system integrators are not experts in hardware and software design of programmable electronic systems. They know how to run and automate chemical or oil and gas plants, but most likely they are not experts on how the operating system of a logic solver works, or whether the communication ASIC of the transmitter is capable of fault-free safe communication. Even if they are experts, the suppliers of the safety components will not give them sufficient information about the internals of the devices to assure them of the safety integrity of these devices. Yet they are responsible for the overall design and thus need to assure themselves that functional safety is achieved. But how can this be accomplished in practice?
The objective of this paper is to demonstrate, through a practical example, how an end user and/or system integrator should deal with functional safety while designing a safety-instrumented function and implementing it in a safety-instrumented system. The paper starts with explaining the problems that exist inherently in safety systems. After understanding these problems, the paper takes the reader from the verbal description of a safety function through the design of the architecture, the process for the selection of safety components, and the role of reliability analysis. After reading this paper, the end user understands the practical process for implementing the design of safety-instrumented systems without going into detail of the requirements of the standard.
Why Safety Systems Fail
The hardware of a safety-instrumented system can consist of sensors, logic solvers, actuators, and peripheral devices. With a programmable logic solver there is also application software that needs to be designed. An end user in the process industry uses as basis for the design and selection of the safety devices the IEC 61511 standard. This standard outlines requirements for the hardware and software, and refers to the IEC 61508 standard if the requirements of the IEC 61511 cannot be not met. This means that even if the IEC 61511 standard is used as a basis, some of the hardware and software needs to comply with IEC 61508.
As with any piece of equipment, safety equipment can fail. One of the main objectives of the IEC 61508 standard is to design a "safe?? safety system. A "safe?? safety system means a system that is designed in a way that it can either tolerate internal failures and still execute the safety function or, if it cannot carry out the safety function, it at least can notify an operator through an alarm. If we want to design a safe safety system, we should first understand how safety systems can fail. According to IEC 61508, equipment can fail because of three types of failures:
- Random hardware failures.
- Common-cause failures.
- Systematic failures.
|File Size||947 KB||Number of Pages||8|
Börcsök, J. 2004. Electronic SafetySystems, Hardware Concepts, Models, and Calculations. Heidelberg, Germany:Huethig Verlag.
Houtermans M.J.M. and Velten-Philipp, W.2005. The Effect of Diagnostics and Periodic Proof Testing on Safety-RelatedSystems. Paper presented at the TUV SafetySymposium, Cleveland, Ohio,June 14-15.
IEC. 1999. Functional safety ofelectrical, electronic, programmable electronic safety-related systems, IEC61508. Geneva: IEC.
IEC. 2003. Functional safety—safetyinstrumented systems for the process industry, IEC 61511. Geneva:IEC.
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