Risk assessment: Establishing practical thresholds for acceptable and tolerable risks

Abstract

Risk levels or ‘thresholds’ presents a standard for determining lower and upper thresholds above and below which risks are either negligible and unacceptable respectively. Between these two thresholds there is a region where risks are tolerated. Nevertheless as people do not necessarily share the same risk perceptions the acceptability thresholds will vary for different sources of hazard and different cultural and social conditions. In disaster related studies, and particularly for phenomena such as mass movements, there are surprisingly few cases where household culture on risk management and risk acceptability thresholds are analysed. The locality of Tresenda (Sondrio Province, Italy) is considered to be one of the most exposed to significant potential losses due to Debris flows in the area. By making use of people-centred approaches such as surveys and with semi-structured interviews the attitude of households towards risk, and their perception of the maximum damage – in economic terms, they can both manage and tolerate was researched. The case study helped to expose a culture of risk denial and optimistic bias where people tend to reject own risk and hope that dreadful things will never happen to them but rather to ‘the others’. The poor risk avoidance culture found, evidences how, despite a widespread knowledge of the risk, people’s awareness and concern not necessarily lead to actions such as avoiding or shifting the risk. In terms of damage they would be able to deal with low to moderate levels leaving a great percentage of residual risk either uncovered or to be undertaken by the state. In small isolated towns, factors such as the greying’ phenomenon where found to decrease the manageability of risk by natural hazards such as debris flows.