Risks may be divided into three tiers. In the lower band, the public readily accepts risks because benefits are felt to outweigh the disadvantages. In the upper band, risks are regarded as completely unacceptable and must be reduced even at very high cost or, if not possible, the activities must cease. The intermediate region is one in which decisions on risk reduction are made by trading off associated costs and benefits.

Traditionally, the field of risk management has three elements - identification of risks, risk assessment and implementaton of solutions and plans.

Risk assessment is defined as "The overall process of risk identification, quantification, evaluation, acceptance, aversion and management." Risk management is the managerial response based on the resolution of various policy issues such as acceptable risk. Risk management decisions are made by considering risk assessments within the context of political, social and economic realities. Such decisions are frequently controversial due to the difficulty in determining risks that are acceptable to the public.

Risk assessment includes risk determination and risk evaluation. Risk management includes risk assessment and risk control.

Risk determination involves the related processes of risk identification and risk estimation. Risk identification is the process of observation and recognition of new risk parameters or new relationships among existing risk parameters, or perception of a change in the magnitudes of existing risk parameters.

Risk, at the general level, involves two major elements: the occurrence probability of an adverse event and the consequences of the event. Risk estimation, consequent-ly, is an estimation process, starting from the occurrence probability and ending at the consequence values.

Risk evaluation is a complex process of developing acceptable levels of risk to individuals, groups, or the society as a whole. It involves the related processes of risk acceptance and risk aversion.

Risk acceptance implies that a risk taker is willing to accept some risks to obtain a gain or benefit, if the risk cannot possibly be avoided or controlled. The acceptance level is a reference level against which a risk is determined and then compared. If the determined risk level is below the acceptance level, the risk is deemed acceptable. If it is deemed unacceptable and avoidable, steps may be taken to control the risk or the activity should be ceased. The perception and the acceptance of risks vary with the nature of the risks and depend upon many underlying factors. The risk may involve a "dread" hazard or a common hazard, be encountered occupationally or non-occupationally, have immediate or delayed effects and may effect average or especially sensitive people or systems.

Risk aversion is the control action, taken to avoid or eliminate the risk, regulate or modify the activities to reduce the magnitude and/or frequency of adverse affects, reduce the vulnerability of exposed persons, property or in this case urban systems, develop and implement mitigation and recovery procedures, and institute loss-reimbursement and loss-distribution schemes.