Safety cases definition

The widening use of safety cases stimulated consideration of what should constitute a safety case. This was particularly important in areas where there were no regulations that prescribed what should be addressed in a safety case. Definitions vary in detail, but an influential definition which is consistent with general usage comes from the military domain (MoD 2007). A safety case is ... 

This definition is widely accepted within the safety critical systems community. Safety case can be considered as a special case of the trust case where focus is on a specific trust objective, i.e., safety, and highly demanding requirements are needed to be met by the base supporting the case. 

Thus, it is clear that the safety surveillance process is an iterative one. It looks at multiple data sources, whether screening large regulatory databases, looking at company databases or looking at manufacturing Lot related AEs for patential problems. The surveillance process screens the data using both the intraproduct and the interproduct methods. The object is to identify topics for further review to develop case definition, to compile a case series and then to characterize that case series. 

The safety case provides a structured argument, supported by a body of evidence, that provides a compelling, comprehensible and valid case that a system is acceptably safe for a given application in a given context [6]. Let s break that definition down into its component parts. 

The Safety Case provides a justification that the considered system or equipment is safe to be used or deployed in a specific operational environment. One example of a definition is taken from the British Defence Standard JSP 430 ... 

In this section, we show how the GSN patterns extension can be used to capture variation in the product-line safety case. A product-line safety case comprises reusable argument structures and evidence used as the basis for the definition of the safety case for each product derived from the product-line assets. Some of these argument structures and evidence are shared between all product safety cases, and therefore are core, while others differ from one product safety case to another, and therefore are variable. Generally, there are two types of product-line safety case variation intrinsic and extrinsic variation. 

Industrial Avionics Working Group (lAWG) Modular Software Safety Case Process — Part A Process Definition (October 2007), http / /www. assconline. co. uk/... 

EAST-ADL supports determination and modeling of FSRs by safety cases. The derivation of FSRs is not supported [16]. In EAST-ADL-2.0, the relation between an item and its containing elements or systems is depicted by a composition between the class item definition, which is interpreted as a collection of entities defining the item that the safety case is valid for (i.e. a "system"), and the abstract class ADLEntity [18]. More precise statements about specializations of ADLEntity are not provided. 

The data imply that the railway industry was generally perceived as a risky workplace, albeit not unequivocally so. In response to the question Is the railway a risky industry to work in , directors and departmental safety officers definitely regarded the industry as risky. Indeed two safety officers wished that they could convey this to the staff with greater clarity. The need for this is revealed by the responses from the rest of the sample. While a majority (55 per cent) did regard the railways as risky and were prepared to use strong language to emphasize how risky they considered it to be, a minority (14 per cent) were prepared to reply that the industry was not at all risky and the rest (31 per cent) either claimed that the risks varied or qualified their responses. In the case of these qualified responses, the need to adhere to the rules or to train staff was heavily emphasized ... 

It can be seen that, although the above definitions have a lot in common, there is not a single, agreed-upon definition as to what constimtes a Safety Case. Heiler (2005) states ... 

The case of German Rail has important implications for the deregulation debate since it has autonomous responsibility for safety. The definition of safety standards and testing for compliance has been the above department s responsibility for decades, and this never gave rise to discussion. What has changed since 1990 is that commercialisation has reached German Rail. Since the government decided to convert the state-owned company into a privately owned joint-stock company, commercial forces have acted on the company in the same way as on all other commercially operated enterprises. 

Vaccine safety is a global issue. Collaborative approaches are fundamental to improve precision of the identification of clusters or signals of vaccine safety issues. Europe has looked into a system to enhance the accurate detection of rare AEFI by looking beyond individual coxmtry boundaries. The Vaccine Adverse Events Surveillance and Com-mxmication consortium was set up to establish a European Safety Datalink. They have proposed a shared protocol, with standard case definitions and methods of analysis. 

In the generalised system description, described eariier, information, energy, and action, are three general categories of inputs and outputs of the system. Also, a special class of inputs and outputs of the system related to the environment was identified. In the case of the safety case derivation process system , elements of a generalised system definition can be characterised as follows ... 

System Definition A safety case can only exist within a context of the system for which the safety case is being writtem This part relates to bullet point 4. Context above ... 

System Definition This section provides context for the safety case (point 4 above) ... 

Definition 3 (Safety Case Argument Structure). A safety case argument structure is a 3-tuple where N is a set of nodes fx (where X e t, d, m, s ) gives... 

Building a safety case is an increasingly common practice in many safety critical domains [7]. A safety case comprises both safety evidence and a safety argument that explains that evidence. The safety evidence is collected throughout the development and operational phases, for example from analysis, test, inspection, and in-service monitoring activities. The safety argument shows how this evidence demonstrates that the system satisfies the applicable operational definition of acceptably safe to operate in its intended operating context. 

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