Safety Argumentation for Machinery Assembly Control Software

Assemblies of machinery commonly require control systems whose functionality is based on application software. In Europe, such software requires high safety integrity levels in accordance with the Machinery Directive (MD). However, identifying the essential regulatory requirements for the safety approval is not an easy task. To facilitate this job, this paper presents a process for Safety Argumentation for Machinery Assembly Control Software (SAMACS). We are inspired by patterns provided in the Goal Structuring Notation (GSN) and the use of contracts in safety argumentation. SAMACS contribution is aligning those methods with the MD by adopting EN ISO 13849. In particular, we define safety goals based on expected software contribution to control system safety and the standard guidance. Software safety goals are detailed into software safety requirements and expressed further as contracts, which shall be verified with prescribed techniques. We apply SAMACS to a case study from a European mining company and discuss the findings. This work aims at helping practitioners compose the safety case argumentation necessary to support machinery integration approval in Europe.