The scientific study of risk, the potential realization of undesirable consequences from hazards arising from a possible event, the assessment of the acceptability of the risks, and the management of unacceptable risks. For example, the probability of contracting lung cancer (unwanted consequence) is a risk caused by carcinogens (hazards) contained in second-hand tobacco smoke (event). The risk is estimated using scientific methods and then the acceptability of that risk is assessed by public health officials. Risk management is the term for the systematic analysis and control of risk, such as prohibiting smoking in public places. Risks are caused by exposure to hazards. Sudden hazards are referred to as acute (for example, a flash flood caused by heavy rains); prolonged hazards are referred to as chronic (for example, carcinogens in second-hand tobacco smoke and polluted air).