In the engineering of complex systems, sophisticated risk assessments are often made within safety engineering and reliability engineering when it concerns threats to life, environment, or machine functioning. The agriculture, nuclear, aerospace, oil, railroad, and military industries have a long history of dealing with risk assessment.Also, medical, hospital, social service, and food industries control risks and perform risk assessments on a continual basis. Methods for assessment of risk may differ between industries and whether it pertains to general financial decisions or environmental, ecological, or public health risk assessment.