Integrating the quantitative and qualitative aspects of safety assessment

We present an approach to the integration of the quantitative and qualitative aspects of safety assessment to facilitate the certification of complex systems using a quantitative criteria. The approach is based on documenting all of all of the relevant safety factors in a system safety case and then transitioning all of the qualitative factors to conservative quantitative factors or to conditions in conditional probabilities. We illustrate the technique using a hypothetical UAS system.