The requirement process, shown in Figure 8.11 may be extended to incorporate an explicit safety analysis activity whose results are used to modify (where necessary) suggested system requirements. The safety analysis process is based on requirements information drawn from the requirement elicitation and documentation process. A set of abstract safety requirements serves as a reference model for identifying initial safety considerations or concerns relating to each requirement source or viewpoint. An operator using the guillotine, for example, has obvious safety concerns relating to the operation of the paper guillotine. The output from the safety analysis process is a set of suggestions and improvement that are fed back into the main requirement process.