The acceptance criteria for safety cases (i.e. the acceptable means of demonstrating safety rather than the acceptable level of safety) are poorly defined in many of the sectors reviewed in the study (e.g. automotive), and they also vary significantly between domains. The lack of clearly defined and understood acceptance criteria (e.g. to help assess whether a safety case is ‘‘compelling” as required by UK Ministry of Defence (2007) can challenge already stretched and understaffed regulatory authorities, which will also struggle to build assessment expertise due to differences between the acceptance criteria, safety arguments and items of evidence submitted for each safety case (Leveson, 2011). The lack of adequate funding of the regulatory authority is a key concern and threat to the successful adoption of the safety
case approach. Steinzor even argues that the US petrochemical industry should not adopt the UK safety case regime because the American regulator was not adequately resourced (Steinzor, 2011).