Safety instrumentation systems other issues

The lEC 61508 standard (lEC 1998) is currently under revision and discussion by the community. Among other issues the methods for calculating the probability of failure on demand (PFD) of safety instrumented systems (SIS) are being revised. This paper reviews the existing methods and provides some indications for practitioners on which method can/should be used under which conditions. The authors would like to point to two papers with a similar theme, namely (Rouvroye 1999) and (Rouvroye 2002). The focus of these papers is on comparing different analysis techniques. 

These are instrument system loops that are necessary to avoid a failure which could result in nonreportable environmental releases, equipment or production losses, or reduced economic life, plus all other systems and alarms that assist operations that require prooftesting. These alarms and shutdown systems include refrigeration units that have less impact or safety or environmental issues than the Class 2 units, important pump shutdown alarms, low pressure utility alarms (well water, cooling tower water, natural gas, instrument air, nitrogen), and numerous low-pressure lubrication alarms. 

Implementation workspaces enable students to build or develop small, medium, and large systems including, for example, mechanical or electronic software components, or new chemical processes. Typical equipment includes hand tools and instruments, measurement and manufacturing equipment, and computers for integration of software. The range of smdent projects calls for a great deal of flexibility. Safety and accessibility are other critical issues. 

Non-routine procedure such as equipment clean-outs and preparation of equipment for maintenance Auxiliary equipment operations inciuding as examples LEV and Ventilation Systems, Heat/Cool Skids, Water (Soft, RO, WFI, Tower, etc.) Systems, Instrument and Process Air Systems, Waste Treatment Systems, Cooling (Glycol Refrigeration) Systems, Steam Generation, and others Safety and operational issues Change control procedures ... 

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