Is deterministic design risk free? how design options differ between deterministic & risk based processes

Abstract

Australian Standards are adopting quantitative risk assessment as the means for establishing design targets for earthing systems. This practice is novel to Australia but there are clear indications that the practice will be adopted in Europe and the USA within the next decade. This emergence does not alleviate the apprehension designers have in adopting the new practice, as the old practice of comparing calculated hazards with a fixed limit is somehow reassuring. This paper explores what differences exist between the 'deterministic' design practices outlined in standards such as IEEE Std 80 and EG-1 and 'risk methods' outlined in standards such as EG-0 and AS/NZS2067. Deterministic design using empirically derived safety limits can falsely imply risk elimination with a binary assessment of safety. Risk based design acknowledges is that risk is only ever reduced, not eliminated. Furthermore, this paper proposes that risk based design is a more flexible and transparent platform, upon which to base earthing designs and that reliance on empirical methods can be a threat to sound decision making and a due diligence defence.