【71-75】Safety cntical systos are syste me in which failures may affect the environment ofthe esem ard cwse injury or desth to the people in that environment. The principal conce ofsntty specificetion is to fdentily requir ements that will minimize the probability that sueetem fhiur es will occur.Safely requirements are primarily protection requirements and arees oorcened with nomel system operation. They may specify that the system should be shu deymso that wafely is maintained. in deriving safety requirements. you. therefore，need to fin atacceptable balance between safety and functionality and avoid overprotection. There is auintin banking a very safe system if it does not operate in a cost-effective way.Saferyspecification is usually focused on the hazards that may arise in a given situation, and theevents that can lead to these hazards. The activities in the general risk -based icationprocess. map onto the safety specification process as follows.1.（71 ）.In safery specification,this is the hazard identification process that identifies hazards that may threaten thesystem.2（72）.This is a process of hazard assessment to decide which hazards are the mostdangerous and or the most likely to occur.These should be prioritized when deriving safetyregurements.3.（73）.This process is concerned with discovering the events that can lead to theaccurrence of a hazard. In safety specific ation，the process is known as hazardanalysis.4.（74）.This process is based on the outcome of（75）and leads to identification ofsafety requirements. These may be concer ned with ensuring that a hazard does not arise oriead to an accident or that if an accident does occur.the associated damage is minimized.
