Safety Criticality Model

In summary, process models play an important role (1) in understanding why accidents occur and why humans provide inadequate control over safety-critical systems and (2) in designing safer systems. 

Bukowski, J. V., "Modeling and Analyzing the Effects of Periodic Inspection on the Performance of Safety-Critical Systems," IEEE Transactions of Reliability, Vol. 50, No. 3, NY New York, IEEE, September 2001. 

The reUabUity and safety analysis needs for complex safety critical systems development are not in contradiction with the current techniques used in SE. The effort consists in detailing new kinds of requirements and integrating the new type of analysis techniques and tools to the common SDE. Nevertheless, it imposes on the project management to define when the diverse phases of reliability and safety studies must be conducted. Indeed, it is impossible to quantify and to assess the dysfunctional behaviour of a system, only with a traditional functional model employed in classic SE. The study of the system must go through multiple phases, from the risks and failure mode identification... 

With the expected growth of puhhc transport volmnes within the next years, the simulation of pedestrian flows to design new and assess existing pedestrian walking facilities becomes of increasing importance. To get meaningful simulation results, accurate pedestrian flow models are required. These models include the appropriate description of the pedestrian behaviour in normal as well as safety-critical conditions (e.g. evacuations). Furthermore, planners and engineers require tools, which allow for fast and reliable simulations of real-world problems. 

A key concept of the lEC 61508 as mentioned before is the implementation of a safety lifecycle that includes hardware and software development life cycles for the safety functions. The AOP 52 recommends the usage of a lifecycle during development of hardware and software. One can say that there is a basic correspondence between the key concept of using process models for the development of safety critical systems. 

SysML modelling of safety critical multi-technological systems... 

We further specify which systems we model. Safety critical systems are systems that lead to hazardous events in case of failure (SommerviUe 2007 Wdliamson 1997). Embedded systems (Wolf 2002) and embedded software (Baier and Katoen 2008) can be foimd in the safety critical domain (Metzner 2006). As examples of safety critical systems airplanes, vehicles, power plants and chemical plants are mentioned in (Borcsok 2006 Borscok 2004). 

As mentioned in section 2.2 the use of the include and extend relationships is subjective. We decided to use the include relationship between the use cases laimch and detonation. The include relationship, shown in Figure 5, is meant as following. The detonation always has to include the launch use case. In fact this is one of the safety critical aspects of modelling this kind of systems. The system is designed so that the detonation shall not be possible before launch. 

The biggest advantage of using SysML for modelling safety critical multi-technological systems is unification. It is not necessary to learn new model languages for each diagram that is used. 

The described platform is applied to a model which describes part of a safety critical system currently under research. Figure 5 shows the architecture of a two out of three SIL4 voting system used in a safety critical application. Apart from the inclusion of three processors, Filters and the elements of FIK are added to enable the fault injection. 

VII.13. It would be helpful to include a table that identifies all different material regions in the criticality safety calculational models. This table should list the following, as appropriate, for each region the material, the density of the material, the constituents of the material, the weight per cent and atom density of each constituent, the region mass represented by the model, and the actual mass of the region (consistent with the contents and packaging description discussed in paras VII.3-VII.6). 

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