Risk Perception

'Risk' is a complex concept to the general public who may interpret it as something involves probability, consequence, and something implying monetary or other loss. Risk perception involves people's beliefs, attitudes, judgements, feelings, social or cultural values, etc. The factors affecting risk perception include (Melcher, 1993; Royal Society, 1992):

• the likely consequences should an accident occur,

• the uncertainty in that consequence estimate,

• the perceived possibilities of obviating the consequences or reducing the probability of the consequences occurring, or both,

• familiarity with the 'risk',

• level of knowledge and understanding of the 'risk' or consequences or both, and

• the interplay between political, social and personal influences in forming perceptions.

'Acceptable' risk does not mean that it is 'tolerable'. For a risk to be acceptable, it means that for the purposes of life or work, one is prepared to take it well as it is. On the other hand, to tolerate a risk means that one does not regard it as negligible or something one might ignore, but rather as something one needs to keep under review and reduce still further if and as one can (HSE, 1992; Royal Society, 1992).

The most fundamental approach to the setting of tolerable risk levels is based on the HSE's (1992) development of the ALARP (As Low As Reasonably Practicable) principle for nuclear power stations. In this approach there is an upper limit of risk above which it cannot be tolerated and it must be refused in any circumstance, and there is a lower limit below which risk is of no practical interest. Between the two limits is the region that risk must be reduced to a level 'as low as reasonably practicable' (ALARP). The legal interpretation of ALARP is well established in English case law in that the "sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble)" is not grossly disproportionate to the benefit obtained. Figure 1 illustrates the levels of risk and the ALARP principle.

A pilot study has been carried out to investigate the public perception and tolerability of landslide risk in Hong Kong (The University of Hong Kong, 1998). It is found that the general public have greater tolerability of risk from their own perspective than from the societal point of view. In addition, the study has achieved the objective well in experimenting various surveying methods in collecting data on risk perception and Willingness to Pay.

At present, interim risk guidelines are available for natural terrain landslide and boulder fall hazards (ERM-Hong Kong, 1998). They are based on the existing guidelines on land use planning in the vicinity of Potentially Hazardous Installations (PHIs). The recommended interim societal risk criteria for landslides and boulder falls from natural terrain are shown in Figure 2.