TERMINOLOGY

Acceptable Risk: A risk for which, for the purposes of life or work, society is prepared to accept as it is with no regard to its management. Society does not generally consider expenditure in further reducing such risk justifiable (IUGS Working Group on Landslides, 1997).

ALARP (as low as reasonably practicable): The risk is regarded as tolerable only if risk reduction is impracticable or if the cost is grossly disproportionate to the improvement gained. This involves determining (HSE, 1992):

1. whether a given risk is so great or the outcome so unacceptable that it must be refused altogether; or

2. whether the risk is, or has been made, so small that no further precaution is necessary; or

3. if a risk falls between these two states, that it has been reduced to the lowest level practicable, bearing in mind the benefits flowing from its acceptance and taking into account the costs of any further reduction. The injunction laid down in safety law is that any risk must be reduced so far as reasonably practicable, or to a level which is 'as low as reasonably practicable'.

Element at Risk: Meaning the population, buildings and engineering works, economic activities, public services utilities and infrastructure in the area potentially affected by landslides (IUGS Working Group on Landslides, 1997).

Event Tree Analysis (ETA): A technique, which can be either qualitative or quantitative, used to identify the possible outcomes and, if required, their probabilities, given the occurrence of an initiating event (CSA, 1991).

Fault Tree Analysis (FTA): A technique, which can be either qualitative or quantitative, by which conditions and factors that can contribute to a specified undesired event (called the top event) are deductively identified, organized in a logical manner and represented pictorially (BSI, 1996).

F-N Curve: A plot showing, for a specified hazard, the frequency of all events causing a stated degree of harm to N or more people (Jones, 1992).

Hazard: A physical situation with the potential for causing an undesirable consequence. Descriptions of landslide hazard, particularly for zoning purpose, should include the characteristics of the landslides, which may include the volumes or areas of the landslides and the probability of their occurrence. There may also be value in describing the velocities, and differential velocities of the landslide. Alternatively, the hazard is the probability a particular landslide occurs within a given time (IUGS Working Group on Landslides, 1997).

Hazard Identification: The recognition that a hazard exists and the definition of its characteristics (CSA, 1991).

Individual Risk: The risk of fatality and/or injury to any identifiable individual who lives within the zone exposed to landslide, or who follows a particular pattern of life that might subject him or her to consequences of the landslide (IUGS Working Group on Landslides, 1997).

Probability: The likelihood of a specific outcome, measured by the ratio of specific outcomes to the total number of possible outcomes. Probability is expressed as a number between 0 and 1, with 0 indicating an impossible outcome, and 1 indicating that an outcome is certain (IUGS Working Group on Landslides, 1997).

Risk: A measure of the probability and severity of an adverse effect to health, property, or the environment. It is often estimated by the product of probability and consequences. However, a more general interpretation of risk involves probability and consequences in a nonproduct form. This presentation is sometimes useful in that a spectrum of consequences with each magnitude having its own probability of occurrence is outlined (also see F-N curve) (CSA, 1991; IUGS Working Group on Landslides, 1997).

Risk Analysis: The use of available information to estimate the risk to individuals or populations, property or the environment, from hazards. Risk analyses generally contain the following steps: scope definition, hazard identification, and risk estimation. (CSA, 1991; IUGS Working Group on Landslides, 1997).

Risk Assessment: The process of risk analysis and risk evaluation (CSA, 1991; IUGS Working Group on Landslides, 1997).

Risk Control: The process of decision-making for managing risk, and the implementation, enforcement, and re-evaluation of its effectiveness from time to time, using the results of risk assessment as one input (CSA, 1991).

Risk Criteria: A qualitative and quantitative statement of the acceptable standard of risk with which the assessed risk needs to be compared (Royal Society, 1992)

Risk Estimation: The process used to produce a measure of the level of health, property, or environmental risks being analysed. Risk estimation contains the following steps: frequency analysis, consequence analysis and their integration (CSA, 1991; IUGS Working Group on Landslides, 1997).

Risk Evaluation: The stage at which values and judgements enter the decision process, explicitly or implicitly, by including consideration of the importance of the estimated risks and the associated social, environmental, and economic consequences, in order to identify a range of alternatives for managing the risks (CSA, 1991; IUGS Working Group on Landslides, 1997).

Risk Management: The complete process of risk assessment and risk control (CSA, 1991; IUGS Working Group on Landslides, 1997).

Societal Risk: The risk of multiple injuries or deaths to society as a whole: one where society would have to carry the burden of a landslide accident causing a number of deaths, injuries, financial, environmental, and other losses (IUGS Working Group on Landslides, 1997).

System: A bounded, physical entity that achieves in its environment a defined objective through interaction of its part. This definition implies that (a) the system is identifiable, (b) the system is made up of interacting parts or subsystems, (c) all the parts must be identifiable, and (d) the boundary of the system can be identified (CSA, 1991).

Tolerable Risk: A risk that society is willing to live with so as to secure certain net benefits in the confidence that it is being properly controlled, kept under review and further reduced as and when possible (IUGS Working Group on Landslides, 1997).

Top Event: The selected outcome whose possible causes are analyzed in a fault tree (Jones, 1992).

Vulnerability: The degree of loss to a given element or set of elements within the area affected by the landslide(s). It is expressed on a scale of 0 (no loss) to 1 (total loss). For property, the loss will be the value of the property; for persons, it will be the probability that a particular life (the element at risk) will be lost, given the person is affected by the landslide (IUGS Working Group on Landslides, 1997).

Reference

BSI (1996). Risk Management - Part 3: Guide to Risk Analysis of Technological Systems (BS 8444: Part 3: 1996, IEC 300-3-9: 1995). British Standards Institution, London, UK, 32p.

CSA (1991). Risk Analysis Requirements and Guidelines. Toronto, Canada, CAN/CSA-Q634-91. Canadian Standards Association, 42p.

HSE (1992). The Tolerability of Risk from Nuclear Power Stations. Health and Safety Executive, London, 61p.

International Union of Geological Sciences (IUGS) Working Group on Landslides, Committee on Risk Assessment (1997). Quantitative risk assessment for slopes and landslides - The state of the art. Proceedings of the Landslide Risk Workshop, IUGS Working Group on Landslides, Honolulu, pp 3-12.

Jones, D. (1992). Nomenclature for Hazard and Risk Assessment in the Process Industries. Institution of Chemical Engineers, 49p.

Royal Society (1992). Risk: Analysis, Perception and Management. Report of the Royal Society Study Group, London, 201p.