Instrumented protective system

References Guidelines for Safe and Reliable Instrumented Protective Systems, American Institute of Chemical Engineers, New York, 2007 ISA TR84.00.04, Guidelines for the Implementation of ANSI/ISA 84.00.01-2004 (IEC 61511), Instrumentation, Systems, and Automation Society, N.C., 2005 ANSI/ISA 84.00.01-2004, Functional Safety Safety Instrumented Systems for the Process Industry Sector, Instrumentation, Systems, and Automation Society, N.C., 2004 IEC 61511, Functional Safety Safety Instrumented Systems for the Process Industry Sector, International Electrotechnical Commission, Geneva, Switzerland, 2003. 

It is important that personnel understand how to achieve safe operation, but not at the exclusion of other important considerations, such as reliability, operability, and maintainability. The chemical industry has also found significant benefit to plant productivity and operability when SIS work processes are used to design and manage other instrumented protective systems (IPS), such as those mitigating potential economic and business losses. The CCPS book (2007) Guidelines for Safe and Reliable Instrumented Protective Systems discusses the activities and quality control measures necessary to achieve safe and reliable operation throughout the IPS lifecycle. 

Guidance can be found in the CCPS book (2007) Guidelines for Safe and Reliable Instrumented Protective Systems related to the development of the process requirements specification. 

If it is not possible to be confident that the relief system will operate without blockage, then, consideration should be given to installing further measures to prevent runaway occurring and/ or the use of alternative measures to mitigate its effects (see Annex 1). Unfortunately, the same mechanisms by which a relief system may be expected to block may also cause blockage of pressure or temperature measurement points within an instrumented protective system, so care should be taken, in such cases. 

Safety systems such as relief valves, instrumented protective systems, and restriction orifices that protect the plant from loss of containment as a result of exceeding design conditions... 

First, the importance of learning lessons from past process safety incidents is highlighted in Section 3.2. The subsequent section presents preliminary hazard review procedure, risk matrix, what-if method, plot plan and layout review, pressure relief system review and fire safety design aspects. Section 3.4 presents PHA techniques and procedures hazards and operability analysis (HAZOP), failure modes and effects analysis (FMEA), instrumented protective system (IPS) design, fault trees, event trees, layer of protection analysis (LOPA) and finally SIS life eyele. The importanee of revision of PSI is highlighted in Seetion 3.5. 

The first two layers are described in section 3.1 and 3.2. Apart fi om these control layers the plant is protected against excursions outside the operating boimdaries by an Alarm Management system and an Instrumented Protective System (IPS). The Alarm Management system warns the operators to take manual action in case the plant moves outside the allowed operating window. The IPS system is fully independent fi om the control and alarm system and can automatically shut down (parts ol) the plant in a safe manner. 

This 2nd edition of ISA-TR84.00.04-1 amends and updates some guidance, but predominantly expands guidance related to user approval (Annex L), setpoint determination (Annex Q), and performance metrics (Annex R). Additional guidance on applying SIS as well as instrumented protective systems can be found in CCPS Guidelines for Safe and Reliable Instrumented Protective Systems, published in 2007. 

CCPS/AIChE Guidelines for Safe and Reliable Instrumented Protective Systems, Wiley-Interscience, New York, 2007, ISBN 978-0-471-97940-1... 

In LOPA studies, the normal convention is that the need for SIS is determined when all other protection layers have been considered. If an existing SIS complies with BS EN 61511 then a reliability performance consistent with the SIL-rating of the SIS and its design and operation can be claimed. If any instrumented protection does not comply with BS EN 61511 then a risk reduction factor of no greater than 10 can be claimed for it. However, experience has shown that it is unlikely that an instrumented protection system that does not comply with BS EN 61511 would have a reliability assessment associated with it, and therefore an assessment would have to be made to determine the performance level that could be claimed. 

On this tank, the LAFIFI includes a trip function to terminate the transfer. For a well-designed and maintained safety instrumented protective system, a response time of two minutes between activation and complete cessation of flow into the tank is claimed. This includes the time needed to take urgent action in case the trip action is not successful - in this case to immediately close another remotely operated valve, readily accessible in the control room (the system having been designed for this emergency closure). 

Center for Chemical Process Safety, Guidelines for safe and reliable instrumented protective systems, WUey-Interscience, 2007. 

J. Reason, Managing the risks of organizational accidents, Ashgate, 1997 N. Storey, Safety-critical computer systems, Prentice Hall, 1996 Guidelines for safe and reliable instrumented protective systems. Centre for Chanical Protective Safety, Wiley-Interscience, 2007... 

In the process industry it is normal to undertake a HAZOP to identify potential hazards that may require mitigation (e.g., instrumented protection systems) in order to reduce risk to persons, environment, or plant. 

ABB, Industrial IT System SOOxA, http //www.abb.com (2009). AIChE Center for Chemical Process Safety, Guidelines for Safe and Reliable Instrumented Protective Systems, AIChE, NY, 2007. AIChE Center for Chemical Process Safety, Guidelines for Safe Automation of Chemical Processes, AIChE, NY, 1993. 

Identical content with API 41C 4th edition. Revised version being developed incorporating instrument protection systems to be implemented according to lEC 61508. 

Functional safety systems (instrumented protective systems) and alarms... 

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