ABSTRACT
Reason’s Model serves the accident investigator well in determining the causes of occurrences. The relation of human activity to the operational environment or preexisting conditions can be analysed, leading to the identification of safety defences that may not be adequate. However, in some cases, the terminology used to categorize human behaviour can be an impediment to an acceptable or complete analysis of an occurrence. For example, the term ‘unsafe act’ is used because the result of the act being described is known. Some have questioned the adjective ‘unsafe’ for behaviour that could be considered to be normal or expected. Yes, there are unsafe acts, but there are also positive safety acts that may limit the consequences of an occurrence. Whether unsafe or positive, the human act under study is a safety significant act. This chapter addresses the investigation of the influence of human behaviour during an occurrence by considering these safety significant acts.
