Achieving integrated process and product safety arguments

Process-based certification standards such as IEC 61508 and DO-178B are often criticised for being highly prescriptive and impeding the adoption of new and novel methods and techniques. Rather than arguing safety based on compliance with a prescribed and fixed process, product-based certification standards require the submission of a well structured and reasoned safety case. Ideally, the safety case presents an argument that justifies the acceptability of safety based on product-specific and targeted evidence. However, the role of process assurance should not be underestimated even in product arguments. Lack of process assurance can undermine even the seemingly strongest product safety evidence. However, unlike the SIL-based process arguments, the process argument of the type we suggest are targeted and assured against specific safety case claims. In this way, a close association between product and process safety arguments can be carefully maintained. This paper shows how integrated process and product safety arguments can be achieved using the modular features of the Goal Structuring Notation (GSN).