A kind of [[defense in depth]] philosophy ## Reason model This model is also used inversely by James Reason (1990), identifying four levels of human failure. 1. Unsafe acts 2. preconditions for unsafe acts: this level involves conditions such as mental fatigue, poor communication, etc 3. unsafe supervision: these preconditions can be traced back to instances of unsafe supervision 4. organisation influences will have a significant hand in creating areas of unsafe supervision ### Critique - this model may only be useful with hindsight: there is little real-world application of the theory - consequently we don't necessarily know what the holes are - not sure about this