|dc.description.abstract||Standards are used widely to provide guidance for the development of safety instrumented system.
However, safety systems, implemented in railways, aviation, nuclear, etc., also require the
development of a safety case to obtain the acceptance. At the same-time, it is important to know
that like hardware, software reliability of such systems also has direct relation to safety, where
safety is a condition of being safe from an unwanted situation. In other words, the state free
from risk is called safe, which eventually leads to safety of the humans, environment and assets.
Safety instrumented systems play a vital role to maintain the system safety and their reliable
operation and therefore they are important for the safe system operation. In order to ensure
system safety, many principles and methods have been proposed and extensive research has
been done and still going along. However, in software, it is not possible to measure the associated
hazards, therefore, current standards in the railways, aviation and nuclear sectors have
identified design and safety processes for different safety integrity levels (SILs) or development
assurance levels (DALs). The assumption is that the software development for the components
with higher SILs/DALs will be less prone to critical failures. Therefore, it is important to note
that for the safe system operation or overall system, safety is combined outcome of both system
hardware and the underlying software running on it. As earlier we mentioned that, significant
research has been carried out on the reliability assessment of such systems with regard to hardware
part, but little has been done with regard to software part.
The goal of this thesis is the provision of support during the software development of safety
related systems in terms of guidelines on the important aspects based on the IEC 61508, IEC
61511 standards that refer to the best practices in different sectors of the relevant area. In order
to achieve this goal, the best practices of the software development are evaluated by conducting
interviews in different industries and individuals based on their expertise in the area of safety
related systems and this evaluation is the main contribution of this thesis. Particularly, two different
manufacturers, one of them works at the product level and the other at the application
level (Integrator) have been interviewed to explore their best practices in the of software development.
Different measures and standardized techniques which are widely and most likely
adapted by different sectors have been investigated. Pros and cons of traditional and agile software development methods are illustrated.
It is recognized that the selection of appropriate techniques/ measures for the software development
decided according to the assigned safety integrity level. The software requirements
get stricter as the level of safety and integrity increases. Standards have ranked each technique/
measure as highly recommended (HR), recommended (R) and not recommended (NR)
based on the required SIL of the software system. The sole purpose of such ranking is to aware
one regarding the importance of certain techniques/measures. For example, if some technique/measure
has assigned HR ranking, it means that technique/measure is highly recommended for that particular
application and must be applied during the software development.
The thesis concludes with the discussion of trends, new methods and approaches of software
development of the safety critical system.||en