Efficient and effective management of any incident depends, in the first instance, on a careful and detailed assessment of the event and its impact. During exercises or practice, there is often the presumption that full knowledge of the extent and impact of the disaster will be immediately available. The reality is that during a disaster, there will be initial chaos. Information will be incomplete at first. There is also limited capacity of those directly affected to be able to step outside of their immediate priorities of preservation of life to undertake a comprehensive analysis and evaluation of the situation. This is compounded by disruptions to communication systems and networks. Often bystanders can be critical of this initial confusion. In reality, this will always be so, particularly in major catastrophic incidents. For example, it may be difficult to distinguish an explosion as a terrorist act from an accident (e.g. gas explosion) until forensic examination has occurred.