Biomedical Engineering Reference
In-Depth Information
Finally, safety considerations that may apply during decommissioning should also
be taken into account. Thus an assessment of the impact of the decommissioning
should be made on both the components and the process of the system. This pro-
cess will use hazard and risk assessment approaches to determine the level of
safety-related work. The safety related work must be satisfied during the decom-
missioning activity of the critical system.
2.5 Traditional Safety Analysis Techniques
Safety provides protection from hazard to human life, the environment or property.
There are not such a magical thing that can guarantee for absolute safety. However,
a system can be enough safe that can accept any risk related to the life, environ-
ment or property. The risk can be measured through probability and the complex
calculations of a system, while a system can be failed due to use of any harmful
substances in the process. However, software is not a harmful substance. Software
can be used to control the system behaviour using a set of processes. Moreover,
the software can contribute to safety, e.g. through control over hazardous physical
processes [ 72 ]. Software hazard and safety analysis refer to the process of assess-
ing and to make contribution to design a safety software. According to [ 81 ], four
safety-relevant elements of a system development process are defined as follows:
1. Identifying hazards and associated safety requirements.
2. Designing the system to meet its safety requirements.
3. Analysing the system to show that it meets its safety requirements.
4. Demonstrating the safety of the system by producing a safety case.
2.5.1 Hazard Analysis
Software development life-cycle and engineering techniques are used to design and
develop a system to meet all the functional requirements. These techniques place a
little effort to examine failure cases of a system. However, a highly critical system
like aviation, medical or automotive needs to consider all possible failure scenarios
to avoid from any hazard. Different kinds of techniques may be employed for safety
assessment from hazard analysis. When a system has many components, then take
a modular approach for analysing a system using System Hazard Analysis (SHA)
and Subsystem Hazard Analysis (SSHA). The SHA discovers all associated hazards
of a system, while the SSHA discovers how an operation of a particular component
affects on the whole system.
The SHA and SSHA analyses are performed by several techniques, which are
provided by the standard authorities. Traditional safety analysis techniques such
as Hazard and Operability study (HAZOP) [ 92 ], Functional Hazard Assessment
(FHA) [ 109 ], Fault Tree Analysis (FTA) [ 73 ], and Failure Mode Effects Analysis
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