For the blood system and perhaps other aspects of the Canadian healthcare system, Krever highlighted two key elements -the institution of precautionary measures and the creation of a governance system emphasising safety (see [32] ). Risk assessment became based on scientific tests and evidence and the management system highly coupled and structured to protect human health. The Canadian blood system is currently seen as a high reliability organisation, emphasising safety and responsiveness to problems [33] . In fact, these elements were introduced so the Canadian blood system could respond to threats in a timely and effective way. This was the case for threats from infectious agents with product recall or donor deferral being rapidly instituted for variant Creutzfeldt-Jacob disease (See [33, 34] ), West Nile virus (see [35] ) and SARS. It is also the case for 'organisational threats' in which practice errors over labelling, documentation, or other deviations from procedures are dealt with through product withdrawal. For such threats, it may be said that the Krever report is one dimension in the increasing use of quality assurance for among other things patient safety in health care. But we know from other settings that challenges occur and 'accidents' (often resulting from operator error or technical malfunction) are normal in complex systems [36] . It seems therefore worth discovering if in this highly coupled, apparently well-managed system, all experts agree about the nature of arising hazards.