Safety-lifecycle

As indicated, a poor specification was the root cause of 44% of the automation system problems, which is by far the largest single cause. In effect, needed functionality was missing or incorrect. How can a control system designer create an automatic protection fimction when that designer does not know that it is needed  

The study found that many problems also occurred during installation, commissioning, operations, and maintenance. Largest of these were attributed to changes after commissioning (21%)— an understandably vulnerable aspect of automation systems. 

In 2000 the US Environmental Protection Agency (ERA) and the Occupational Safety and Health Administration (OSHA) investigated recent accidents at chemical facilities and refineries (Ref. 8). When aU the incidents were compared to one another, some common themes identified were  

Inadequate hazard review or process hazards analysis - In almost every accident. Process Hazards Analysis (PHA) was found to be lacking. This relates to identifying the hazards and properly 

Specifying the SIS based on the risk reduction required to mitigate hazardous events. 

---

MIR based SLM Maturity Index on Reliability based Safety Lifecycle Management... 

Knegtering B., 2002. Safety Lifecycle Management in the process industry, PhD-thesis, Eindhoven University Press, Eindhoven. 

The safety lifecycle is a model for identifying the activities appropriate to safety-related systems... 

This International Standard has two concepts, which are fundamental to its application safety lifecycle and safety integrity levels. The safety lifecycle forms the central framework which links together most of the concepts in this International Standard. 

This International Standard sets out an approach for safety lifecycle activities to achieve these minimum standards. This approach has been adopted in order that a rational and consistent technical policy is used. The objective of this standard is to provide guidance on how to comply with lEC 61511-1 ANSI/ISA-84.00.01-2004 Parti (lEC 61511-1 Modi. 

At the earliest possible stage of the safety lifecycle, a unique plant identification should be given to each device. In some cases, earlier models/versions still in use may also be maintained and... 

The functional safety achieved in any process facility is dependent on a number of activities being carried out in a satisfactory manner. The purpose of adopting a systematic safety lifecycle approach towards a safety instrumented system is to ensure that all the activities necessary to achieve functional safety are carried out and that it can be demonstrated to others that they have been carried out in an appropriate order. lEC 61511-1 ANSI/ISA-84.00.01-2004 Parti (lEC 61511-1 Mod ) sets out a typical lifecycle in Figure 8 and Table 2. Requirements for each lifecycle phase are given in Clauses 8 through 16 of lEC 61511-1 ANSI/ISA-84.00.01-2004 Part 1 (lEC 61511-1 Mod). 

The standard recognizes that the specified activities might be structured in different ways, provided that all the requirements are complied with. This restructuring can be beneficial if it allows safety activities to be better integrated into normal project procedures. The purpose of Clause 6 of lEC 61511-1 ANSI/ISA-84.00.01-2004 Part 1 (lEC 61511-1 Mod) is to ensure that if a different safety lifecycle is used, the inputs and output of each phase of the lifecycle are defined and all essential requirements are incorporated. 

The key consideration is to define in advance the safety lifecycle of the SIS that is going to be used. Experience has shown that probiems are likely to occur, unless this activity is planned well in advance and agreements are reached with all persons, departments and organizations taking responsibility. At best, some work will be delayed or have to be redone at worst, safety can be compromised. 

Another important part of safety lifecycle planning is to identify the techniques that will be used during each phase. The identification of such techniques is important since it is often necessary to use a specific technique that requires persons or departments with unique skills and experiences. For instance, consequences in a particular application may be dependent on the maximum pressure developed after a failure event and the only way this can be determined is to develop a dynamic model of the process. The information requirements for dynamic modelling will then have an important impact on the design process. 

The purpose of verification is to ensure that the activities for each safety lifecycle phase, as determined by verification planning, have, in fact, been carried out and that the required outputs of the phase, whether they be in the form of documentation, hardware or software, have been produced and are suitable for their purpose. 

It is important that the results of verification are available so that it can be demonstrated that effective verification has taken place at all phases of the safety lifecycle. 

It may be necessary for the hazard and risk assessment to be repeated at different stages in the overall SIS safety lifecycle, as decisions are taken and available Information becomes more refined. 

The development of the SIS safety requirements specification is one of the more important activities of the whole safety lifecycle. It is through this specification that the user is able to define how he wants the Safety Instrumented Functions (SIF) to be designed and integrated into a SIS. 

A working definition of the Safely Lifea/cle is that it is an engineering process utilizing specific steps to ensure that Safety Instrumented Systems (SIS) are effective in their key mission of risk reduction as well as being cost effective over the life of the system. Activities associated with the Safety Lifecycle start when the conceptual design of facilities is complete and stop when the facilities are entirely decommissioned. Key activities associated with a Safety Lifecycle are outlined below. 

Safety Lifecycle analyses heavily involve probabilistic calculations to verify the integrity of the safety design. 

The Safety Lifecycle (SLC) is an engineering process that contains all the steps needed to achieve high levels of functional safety during conception, design, operation, and maintenance of instrumentation systems. Its objective is clear An automation system designed according to SLC requirements will predictably reduce risk in an industrial process. A simple version of the SLC is shown in Figure 1-3. 

The safety lifecycle from the lEC 61508 standard is shown in Figure 1-4. This drawing provides more details of the safety lifecycle, but die three distinct phases are stiU clearly present. The lEC 61508 safety lifecycle shows that most of the activities of the analysis phase constitute a logical... 

The lEC 61508 safety lifecycle prescribes that planning for all maintenance testing and maintenance activities must be accomplished in the realization phase. To a certain extent this work can proceed in parallel with safety instrumented system design. This lifecycle diagram also shows that operation and maintenance responsibilities focus on periodic testing and inspection as well as management of modifications, retrofits, and eventual decommissioning. 

The safety lifecycle from the ANS1/1SA84.00.01-2004 (lEC 61511 Mod) standard is shown in Figure 1-5. Although the drawing looks quite different from Figure 1-4, the fundamental requirements are much the same. Again, there are clear analysis, realization, and operation phases. 

The safety lifecycle from ANSl/lSA-84.00.01-2004 (lEC 61511 Mod) was created specifically for the process industries, and thus many requirements are tailored for process applications. Note that there is an emphasis on managing functional safety on the structure and planning of the safety lifecycle and on verification throughout the entire lifecycle. 

The lEC 61511 standard and the lEC 61508 standard emphasize good management of functional safety, which includes the application of a good plan and verification activities for each step of the safety lifecycle. These steps are shown as overtly drawn boxes on each side of the Figure 1-5 lifecycle diagram. 

Figure 1-6. Activities in Detail for the Analysis Phase of the Safety Lifecycle...

Figure 1-6 provides a detailed diagram of activities in the analysis phase of the safety lifecycle. When the conceptual process design is complete, detailed process safety information is available such as ... 

---